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Built-up radially battened columns (RBCs), comprising several identical circular steel tubes interconnected by multiple radial-shaped battens, represent an innovative column design that combines aesthetic appeal with exceptional load-bearing capacity. This makes them well-suited for architectural applications in large public buildings such as stations and airports. The axial compressive strength design methods for the built-up RBC have been extensively explored in the authors' prior studies. However, in real-world engineering applications, built-up RBCs may experience simultaneous axial compression and varying directional bending moments, particularly when considering potential eccentric compression or wind and earthquake loads in public buildings. Currently, strength design methods for this loading condition are still lacking. To address this deficiency, this paper primarily delves into the failure mechanism and strength design methods for built-up RBCs experiencing combined axial compression and arbitrary directional bending moments. Initially, the sectional strength of the built-up RBC is investigated by using a shell finite element model (FEM) for the built-up RBC. It is revealed that the compression-bending sectional strength of the built-up RBC exhibits significant differences with varying bending directions and tube numbers. Moreover, in some bending directions, the M - N sectional strength curve of the built-up RBC exhibits convexity. By integrating theoretically derived equations grounded in the principles of materials mechanics with FEM numerical calculations, concise and practical design equations are proposed for accurately predicting the sectional strength of the built-up RBC under combined axial compression and arbitrary directional bending moments. Subsequently, The buckling strength of the built-up RBC is studied using the FEM, considering initial geometrical imperfections consistent with first-order flexural buckling and accounting for geometric nonlinearity. It is noted that the bending direction of the built-up RBC may deviate during loading. Besides, the M - N buckling strength curve of the built-up RBC is not as convex as its M - N sectional strength curve. Based on calculations from numerous examples, practical design equations for predicting the buckling strength for the built-up RBC under axial compression and any directional bending moments are introduced. The key findings of this paper contribute to the compression-bending strength design of RBCs, enriching RBC design theory and promoting the widespread application of built-up RBCs in actual engineering projects. [Display omitted] • The M - N strength of RBCs varies with different bending directions and tube numbers. • The M - N sectional strength curve of the built-up RBC is convex. • The built-up RBC's bending direction may deviate during loading. • The M - N buckling strength curve of RBCs is less convex compared to its M - N sectional strength. • The M - N strength of RBCs can be predicted by a quadratic function. [ABSTRACT FROM AUTHOR]

Rammed earth is a traditional construction technique that has recently gained attention because of its benefits from an ecological perspective. The conservation of the existing valuable cultural heritage sites and the quality control of new constructions built with this material require the development and application of practical inspection techniques. This paper explores the application of sonic tests and sonic tomography as practical tools for monitoring the state of conservation of existing structures and the identification of heterogeneities or damaged areas. Two groups of 6 rammed earth specimens were manufactured and tested. The manufacturing process of each group allowed the application of compression loads and the identification of the Sonic Wave Propagation Velocities along directions parallel and perpendicular to the compaction forces during manufacturing. The SWPV were identified for the different paths between 9 measuring points located at two opposite sides of the specimens, leading to up to 6 different planes for each specimen. The SWPV are identified by identifying the Time-of-Flight of the elastic wave between each pair of excitation and receiver points. A discretized coloured map of the SWPV distribution for each plane defined by the measurement points array is obtained by the application of an algorithm already developed by the authors to obtain tomographic images for other materials and applications. The SWPV are identified after 2 different increasing values of a uniform compressive load is applied to each specimen. The results show that the analysis of the SWPV and tomographic images is sensitive to heterogeneities, such as compaction gradients from the manufacturing process, and also to the accumulated damage in the solid. The paper demonstrates that the proposed technique can be potentially used for a qualitative inspection of the state of conservation of specific rammed earth constructions. • Sonic wave propagation velocities (SWPV) are identified for different directions. • SWPV maps are obtained following a transmission tomography approach. • Estimated values of SWPV at 3 horizontal and 3 vertical planes are analysed. • SWPV are sensitive to progressive damage and compaction gradients. • No material anisotropy is found according to SWPV values. [ABSTRACT FROM AUTHOR]

• A novel composite column for being applied in island engineering, named seawater-sea sand coral aggregate concrete (SSCAC)-filled prefabricated ultra-high performance concrete (UHPC) tube (SFCT), is presented in the paper. • Total 36 relatively large-scale columns are tested in axial compression and a special strength model is proposed for SFCT columns. • Compared with existing SSCAC confined by fiber reinforced polymer (FRP) tube or hoops, the compressive behavior of SFCT column is effectively improved, especially important is increased the axial stiffness. To reduce construction costs, seawater, sea sand, and dead coral are often used in concrete buildings on distant islands. Such seawater-sea sand coral aggregate concrete (SSCAC) typically has insufficient mechanical properties and high chloride ion content. In this paper, a novel composite column, named SSCAC-filled ultra-high performance concrete (UHPC) tube (SFCT), is proposed and studied. The SFCT column combines a prefabricated fiber reinforced polymer (FRP) hoop reinforced thin-walled UHPC tube with the infill SSCAC. A total of 36 relative large-scale columns were conducted for axial compression tests. The SFCT columns showed a multi-crack failure mode on the surface of the tube without obvious peeling-off of the UHPC cover in the whole loading process. The test results reveal that the UHPC tube in the composite system effectively takes on the additional load released by the inner SSCAC during compacting due to the porous nature and low strength of coral aggregates. Therefore, the compressive behavior of the pre-peak stage of SFCT column is effectively improved compared with existing SSCAC confined by FRP tube or hoops, especially important is increased the axial stiffness. The proposed composite system effectively combines the ultra-high compressive performance of UHPC and the lateral confining effect from FRP hoops. A model was also proposed for predicting the axial load carrying capacity of SFCT columns. The analysis results indicate that selecting relatively thinner UHPC tube in SFCT composite system and using relatively flexible and low-cost basalt FRP (BFRP) and glass FRP (GFRP) hoops instead of carbon FRP (CFRP) hoops as the lateral confining component are economical and could be reasonable measures for manufacturing the composite columns. [ABSTRACT FROM AUTHOR]

• This paper presents a study on reinforced SHS T-joints. • The study was completed using nine full-scale tests and a parametric study. • It was found that the behaviour of the two different reinforcing types is similar. • The study found that the current design method may be unconservative. • This paper presents a new design equation. This paper presents outcomes of experimental and numerical studies completed on unreinforced, collar plate reinforced and doubler plate reinforced Square Hollow Section (SHS) T-joints subjected to axial compressive loading on the brace member. A total of nine full-scale SHS T-joint specimens were fabricated and tested, in which six specimens were reinforced with collar plate and doubler plate. Non-linear finite element (FE) models were developed using finite element code, ABAQUS. Test data was used to validate these FE models. Subsequently, validated FE models were used to conduct an extensive parametric study to investigate the effect of various geometrical parameters of main members and reinforcement plates on the ultimate capacity of reinforced SHS T-joints. The parametric study found that use of both collar and doubler plate reinforcements significantly increase the ultimate capacity of SHS T-joints. Thickness of the reinforcing plate has a positive effect if the thickness of the reinforcing plate is limited to twice the thickness of the chord member. This study, however, found that the capacity of a reinforced SHS T-joint is not dependent on the type of reinforcing plate. The study concludes that the maximum capacity that can be achieved from a reinforced joint is about double the capacity of a similar unreinforced joint. It was found that the Eurocode EN 1993-1-8 overestimates the capacity of reinforced SHS T-joints. Therefore, a new design method for predicting the ultimate capacity of the collar plate and doubler plate reinforced SHS T-joints was developed and this new design method is presented in this paper. [ABSTRACT FROM AUTHOR]

This paper focuses on the development of much-needed numerical and experimental models for understanding the mechanical behaviour, section capacity and energy absorption of the innovative fabricated columns consisting of corrugated mild-steel plates. The corrugated square columns proposed in this paper are fabricated by welding four corrugated plates which are originally produced from 3 mm thick flat mild steel plates. The experiments consist of applying a compressive axial force to the columns to determine load–displacement curves of the fabricated sections. The effects of geometric parameters such as inclination angle and corrugation height are also investigated experimentally by considering three different types of corrugated columns. Moreover, a finite element model in which the effects of material and geometric nonlinearities as well as residual stresses are taken into account is developed using ABAQUS. The experimental results are also compared with those given by the finite element (FE) model whilst a good agreement is achieved. A cost analysis is also conducted in which the cost of the innovative columns proposed in this research is compared to those of conventional welded columns currently available in the civil engineering market. [ABSTRACT FROM AUTHOR]

• The compressive behaviour of GFRP-confined GRAC was investigated for the first time. • The effects of the GFRP confinement ratio, RA content and GRAC size were examined. • Compressive strength and ultimate strain models for GFRP-confined GRAC were proposed. • A unified stress–strain model was developed for GFRP-confined geopolymeric concrete with or without RA. Substituting geopolymeric recycled aggregate concrete (GRAC) for normal concrete (NC) to fill glass fibre-reinforced polymer (GFRP) tubes and produce green high-performance compression members is a promising construction technology. Although extensive research has been conducted on the performance of GFRP tubes filled with NC in the past decade, gaps in knowledge make it difficult to predict the mechanical behaviour of this new composite member. This paper presents an experimental and analytical study on the progressive failure of GFRP-confined GRAC under compressive loads. A comprehensive investigation was conducted on the effects of the confinement ratio, recycled aggregate (RA) content, and tube size on the compressive behaviour of GFRP-confined GRAC. The test results were compared with those from available studies on confined NC specimens with or without RA. This paper found that GFRP tube confinement had an advantage in alleviating the negative impact of RA on GRAC. The RA replacement ratio and cylindric dimension had no influence on the linear relationship between the confinement ratio and strength enhancement ratio. Predictive models considering the effect of RA content and GRAC size were proposed for the compressive strength and ultimate strain of GFRP-confined GRAC. Finally, a recalibrated stress–strain model was developed to describe the compressive behaviour of GFRP-confined geopolymeric concrete. [ABSTRACT FROM AUTHOR]

This paper presents a new and accurate finite element contact-modeling approach, to predict the axial compressive behaviour of bare cold-formed steel (CFS) lipped-channel sections (studs) set in tracks under concentric, static axial compressive loading. Detailed finite element analysis (FEA) models of the stud-track assemblies are developed using the ABAQUS software. The new modeling approach is validated against test results and captures stud-to-track gap and contact normal behaviour, which significantly influences studs' axial compressive performance. Hard contact (HC) has been used widely in literature for its simplicity, although it overestimates axial structural stiffness. Two softened pressure-overclosure relationships, with linear (LSC) and piecewise linear (PLSC) functions, were investigated for the first time in axially loaded bare CFS studs. PLSC best-replicated studs' axial-compressive behaviour, post-peak response, and failure mechanism under track boundary conditions. PLSC slightly overestimated the axial stiffness by 1 %, underestimating axial shortening and ultimate capacity by 3 % and 6 %, respectively. HC significantly overestimated the axial stiffness by a factor of 3, with a 5 % overestimation of ultimate capacity. LSC failed to predict the accurate failure mechanism for studs having gauge thicknesses less than 3 mm. PLSC scale factors were established and were found to be closely correlated with studs' non-dimensional slenderness (λ), following bilinear relationships. New predictive equations were developed to determine the PLSC scale factors for λ ranging between 0.49 and 1.2 to enable designers to use accurately calibrated models to capture bare studs' complex axial compressive behaviour in the elastic and inelastic range. • Axial compressive contact modeling of bare cold-formed steel studs set in track. • Studied two softened pressure overclosure relations: Linear (LSC) and Piecewise linear (PLSC). • Compared softened contact results with hard contact (HC) and forty-two test data. • PLSC captured the most accurate peak load, axial stiffness, and failure mechanism. • Proposed novel bilinear equations to determine accurate PLSC scale factors. [ABSTRACT FROM AUTHOR]

A discussion on the paper by Leeanansaksiri et al. (2018) is presented. In the paper, strengthening of the masonry infill walls using ferrocement reinforced with standard expanded steel plates (EMS) was investigated experimentally. A bare frame without infill wall, a frame with a plain (unstrengthened) infill wall and a frame with a strengthened infill wall were tested under reversed cyclic lateral loading. The type of EMS to be used for strengthening was decided based on compressive strength tests on plain (unstrengthened) and strengthened masonry prisms and monotonic diagonal loading tests on wall panels. The results of the prism and panel tests were also used to determine the parameters of the analytical hysteric models, which closely estimated the experimental results of the frame tests. While the paper reached important conclusions related to the proposed strengthening technique, the authors of this discussion felt obliged to present their significant findings on the issues, raised in the paper for further research to increase the efficiency of the proposed technique. Furthermore, this discussion summarizes the findings of the authors on the strategies to investigate the efficiency of an infill wall strengthening technique. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on the mechanical behaviors of engineered cementitious composite (ECC)-encased concrete filled steel tube (CFST) columns under axial loading. Six specimens, including four ECC-encased CFST columns and two concrete-encased CFST columns were tested. According to the test results, ECC-encased CFST columns showed both higher loading carrying capacity and more ductile behavior. The influence of longitudinal reinforcement ratio, stirrup ratio and the thickness of steel tube were discussed in this paper. Furthermore, a new method to calculate the carrying capacity of ECC-encased CFST columns was proposed and verified with experimental results. [ABSTRACT FROM AUTHOR]

Efficacious monitoring the mechanical stress of engineering structures or components holds the key to understanding the occurrence of structural damage in Structural Health Monitoring (SHM) domains. This paper investigated the monitoring of the load-induced structural tension/compression stress and damage using smart Piezoelectric lead Zirconate Titanate (PZT) transducers mounted to specific locus on structures. Structural tension/compression stress was theoretically incorporated into mechanical impedance to formulate a novel one-dimensional PZT-structure dynamic interaction model. Proof-of-concept experimentation was conducted using a reinforced concrete (RC) beam subjected to a four-point bending test till failure, in which tension and compression stress were simultaneously produced at the bottom/top edge of the beam and captured by two mounted PZT transducers. Load-induced structural tension/compression stress and stress-induced damage were qualitatively evaluated through analyzing the characters of electromechanical admittance (EMA) signatures and comparing to that of the non-stressed PZT transducer. Quantification assessment of stress and damage using statistical root mean square deviation index were also presented. Test results indicated that the peak variation and frequency shift of EMA signatures responding to tension and compression stress were converse in nature, and their gradual changes provided cogent evidences for predicting the development of stress and damage. Results of this paper can be potentially to help monitor structural stress and discriminate from damages in real-life SHM applications. [ABSTRACT FROM AUTHOR]

This paper investigates the buckling behaviour and load-carrying capacity of G550 high-strength cold-formed steel multi-limb built-up section columns under axial compression. Each built-up section consists of multiple lipped and unlipped channel sections connected by self-tapping screws. The C3U1 section is formed by three C-sections (i.e. lipped channel section) and one U-section (i.e. unlipped channel section), while the C2U2 section is formed by two C-sections and two U-sections. The experimental programme involved tensile coupon tests, measurements of initial geometrical imperfection, and column tests on ten C3U1 and ten C2U2 multi-limb built-up section columns. The numerical modelling programme was then performed, with the nonlinear finite element models created and validated against the experimental results. The applicability of the codified Effective Width Method and Direct Strength Method for predicting the strengths of G550 high-strength cold-formed steel multi-limb built-up section columns, as specified in the American Specification and Australian Standard, was then evaluated. The evaluation results showed that the codified Effective Width Method led to rather conservative and less accurate failure load predictions for G550 high-strength cold-formed steel multi-limb built-up section columns, while the codified Direct Strength Method provided accurate and consistent failure load predictions and thus applicable to the design of G550 high-strength cold-formed steel multi-limb built-up section columns. Concerning the lack of design guidelines specifically for multi-limb built-up sections, a modified Direct Strength Method was thus proposed as an alternative design method and shown to provide accurate failure load predictions. • The structural performance of G550 high-strength CFS multi-limb built-up section columns was investigated. • 20 axial compression tests on G550 high-strength CFS multi-limb built-up section columns were conducted. • FE models were developed and validated against test results and then used for future analysis. • Codified design methods were evaluated for their applicability to G550 high strength CFS multi-limb built-up section columns. • A modified DSM was proposed as an alternative design method and shown to provide accurate failure load predictions. [ABSTRACT FROM AUTHOR]

This paper aims to explore the enhancement effect of spiral stirrup on concrete-filled cold-formed steel built-up box (CF-CFB) columns. Herein, four specimens were designed and fabricated to explore the impact of the spiral stirrup and riveted form on the axial compression performance of CF-CFB columns. Then, the finite element model of spiral stirrup-reinforced concrete-filled cold-formed steel built-up box (RCF-CFB) stub columns was established, and a systemic parametric investigation was conducted to explore the impact of geometric and material parameters on the compression performance of RCF-CFB stub columns. Afterwards, the analysis included an assessment of contact stress and stress distribution was conducted to uncover the confining effect. The analysis results revealed that the failure mode of the RCF-CFB column was tube buckling and concrete crush, accompanied by the spliced tube separating at the buckling area. The built-in reinforcement could significantly improve the performance of the built-up column, while riveted forms of spliced steel tubes had little effect. Furthermore, the axial bearing capacity of the RCF-CFB column would increase with the enhancement in steel yield strength, concrete strength, tube thickness, and longitudinal bar diameter. Finally, a calculating method to predict the axial bearing capacity of the RCF-CFB column was proposed, and the applicability of the method was demonstrated by comparison with experimental and FE data. • Compression tests were carried out on the performance of the concrete-filled cold-formed steel built-up box columns. • An analysis model of concrete-filled cold-formed steel built-up box stub columns was established and validated. • A practical method for predicting the axial compression load capacity was proposed. [ABSTRACT FROM AUTHOR]

The grouted connection (GC) of the offshore wind turbine (OWT) jacket foundation mainly bears axial loads, the wind and wave load in the working environment make the structure prone to fatigue problems. The construction environment of the OWT foundation is relatively harsh, so there will be vertical and horizontal errors during the construction process. In this paper, the fatigue test of 9 specimens were designed to analyze the influence of vertical and horizontal errors, water ingression and other factors on the axial fatigue performance of the GC section. The static ultimate bearing capacity test was carried out to determine the load ranges of the fatigue test. Results of fatigue tests indicate that the fatigue performance of the GC considerably degenerates with the load eccentricity, especially at the end sections of the inner and outer tubes. Water ingression has a significant negative influence on the fatigue performance of the GC section. The presence of water contributes to the propagation and development of cracks in the grout layer. Load range, vertical and horizontal errors and grout material have negligible effect on the fatigue performance of the structure. • Fatigue test of grouted connections under axial loading with constructional errors. • Effects of load range, load eccentricity, water ingression, constructional errors and grout material were investigated. • The water ingression speed is measured during the test to assess the grout damage. • The fatigue performance of the grouted connection significantly deteriorates with increasing load eccentricity. • Water presence promotes crack propagation and development of the grout layer. [ABSTRACT FROM AUTHOR]

The stability properties of double-layer H-section aluminum alloy members were studied under eccentric compression loads in this paper. Firstly, six double-layer members were designed and tested under a set of eccentric compression loads with different eccentric distances; as a contrast, six single-layer members were also tested under the same loading conditions; based on the test results, it was compared that the ultimate bearing capacity and buckling modes of the single-layer and double-layer members with different load eccentricity ratios. The experimental results indicated that the stability properties of double-layer H-section aluminum alloy members were better than corresponding single-layer members, but the ultimate strengths of double-layer members were less than the twice of that of single-layer members. A numerical simulating method for single-layer and double-layer H-section aluminum alloy members was established and validated against the experimental results. • Double-layer H-section aluminum alloy members can reinforce the weak region in single-layer reticulated structures. • The failure mode of double-layer H-section aluminum alloy members is classical flexural buckling under centric compression. • The failure mode of double-layer H-section aluminum alloy members is flexural-torsional buckling under eccentric compression. • The mechanical properties of double-layer H-section aluminum alloy members are better than that of single-layer members. • Chinese code GB 50429-2007 is applicable to double-layer H-section aluminum alloy members under eccentric compression. [ABSTRACT FROM AUTHOR]

Testing of small-scale physical models of masonry structures can be useful both to study Soil Structure Interaction problems and to provide large enough datasets to statistically validate the global level assumptions of masonry numerical models. This paper proposes the use of a sand-based Binder Jet 3D printer to manufacture 1:10 scaled physical models of masonry walls, that can be used within a centrifuge. As such printers can only print one material, mortar is emulated by controlling the micro-geometry of the printed material at the position of the joints (i.e., by printing joints). Walls were printed and tested in compression and cyclic shear under fixed-fixed conditions and constant compressive load. Different notch geometries were tried. The tested specimens were found to behave similarly in compression and shear to full scale masonry walls. A numerical model using a concrete damage plasticity model was built in Abaqus. It captured the cyclic response of the masonry walls with a reasonable accuracy. Therefore, such small-scale models can be used to expand centrifuge modeling in structural engineering. • Novel approach for the physical modelling of masonry walls. • Scale 1:10, models to be used in the centrifuge. • Models were manufactured via 3D printers. • Compressive and shear tests showed that they behave similarly to true masonry. [ABSTRACT FROM AUTHOR]

This paper reports the results of an experimental campaign carried out on prestressed concrete beams (PCB), equipped both with bonded and unbonded strands, with the aim to employ Operation Modal Analysis (OMA) techniques to detect early warning signs (i.e., variation of natural frequencies and/or relevant mode shapes) associated to the onset of structural damages. With respect to similar past experimental studies, the main novelties presented hereafter concern the application of OMA to the following situations: (1) a PCB equipped with bonded strands and affected by a "almost pure" shear-cracks pattern; (2) a PCB equipped with unbonded strands and affected by an almost negligible (i.e., reversible) flexural damage. Among the outcomes of this study, it was found that, especially in the second case, the assessment of variations in the PCB natural fundamental frequencies, is not always an effective index of damage. On the contrary, a qualitative comparison between the undamaged and damaged identified mode shapes can be helpful even for the spatial location of the damage. Eventually, despite the diverging opinions in the reference literature, it is found that OMA technique is not a suitable tool to assess the potential influence of variations of the precompression load on the PCB fundamental frequencies, unless this variation is so high to cause cracking. • Operation Modal Analysis (OMA) applied to prestressed concrete beams (PCBs). • Beam-1 equipped with bonded strands and affected by almost pure shear-cracks. • Beam-2 equipped with unbonded strands and affected by negligible (i.e., reversible) flexural cracks. • Surprisingly, variations in the PCB natural fundamental frequencies are not always an effective index of damage. • On the contrary, a qualitative comparison between the undamaged and damaged identified mode shapes can be helpful even for the spatial location of the damage. • OMA technique is not a suitable tool to verify the potential influence of variations of the actual strands' tensile load on PCB fundamental frequencies. [ABSTRACT FROM AUTHOR]

The Ayrton-Perry (or Perry-Robertson) formula based stability resistance model (APF) is very popular in steel structural design standards. Although the original version of the model is more than 100 years old, it is still frequently used and continuously researched due to its simplicity and adaptability. The original and most widely accepted version of the APF is valid only for the flexural buckling of compression members yielding the basic formulation of the column buckling curves of several structural design codes. Recently there were more successful attempts for the extension of the APF type resistance model for other buckling modes such as torsional buckling or lateral-torsional buckling. The paper continues this research by deriving a complete closed-form universal APF type solution for steel beam-column stability problems. Rigorous mathematical solution is given for the so-called “fundamental case” which is defined by a simply supported prismatic beam-column with arbitrary cross-section subjected to uniform compression and biaxial bending. The exact interpretation and the universal form of the member slenderness, imperfection and reduction factors are presented for all possible buckling cases. The results of the paper can widen significantly the field of applicability of APF based design methods providing a theoretically consistent physical model for the beam-column stability problems. [ABSTRACT FROM AUTHOR]

• Multi-objective design optimization using meta -modelling by FEM-RSM. • A New meta -heuristic of optimization (Lichtenberg Algorithm) was applied. • Five responses of a sandwich tube with auxetic core were analyzed. • A statistical analysis was performed. • The Poisson's ratio was reduced in more than 56% • All the responses have been improved. In this paper, the multi-objective optimization of a sandwich composite tube with an auxetic reentrant core was done. Five different responses of the model were considered: mass; critical buckling load; natural frequency; Poisson's ratio; and failure load under compression effort. The Response Surface Methodology was applied, and a new meta -heuristic of optimization called the Multi-objective Lichtenberg Algorithm was used to find the optimized configuration of the structure. In addition, a parametric analysis was performed to verify how each of the design factors influenced each of the responses. It was found that the unit cell height is the most significant factor for failure load, natural frequency, and mass. On the other hand, unit cell height has no significance for Poisson's ratio. Furthermore, it was also verified that the Poisson's ratio has no correlation with any of the other responses studied (failure load, critical buckling load, mass, and natural frequency). Finally, it was possible to improve (reduce) the Poisson's ratio by more than 56% in the optimization of the modal performance and improve the mass, the Poisson's ratio, the failure load, and the critical buckling load in the static performance. Thus, this paper shows something unprecedented in the literature to date when evaluating the multi-objective design optimization of a tubular sandwich structure with an auxetic core. [ABSTRACT FROM AUTHOR]

This paper proposes a new type of buckling-restrained braces (BRBs), namely shuttle-shaped buckling-restrained braces (SS-BRBs). The proposed SS-BRB is composed of a circular steel tube as the inner core, and a shuttle-shaped thin-walled steel tube as the external restraining member. The space between them is filled by a steel-plate isolation system. The shuttle-shaped restraining member of the SS-BRB significantly improves load-carrying efficiency and saves material in its strength design. Moreover, the SS-BRB is more aesthetically appealing and can be utilized as an exposed BRB in long-span or spatial structures. In terms of the concept of restraining ratio of a BRB, no design method of an SS-BRB is available currently because it concerns the solution of the elastic buckling load of an SS-BRB. Therefore, the elastic buckling load of a pin-ended SS-BRB is initially studied by adopting the equilibrium method and is further verified through finite element (FE) method. The lateral displacement function of an SS-BRB, and the longitudinal stress at the extreme fiber of the external restraining member are derived by considering an initial geometric imperfection that is consistent with the first order overall buckling shape of the SS-BRB. A correction factor considering shear deformation has been incorporated for a more accurate prediction. The lower limit of the restraining ratio for a load-bearing type of SS-BRBs is further obtained based on yielding of the extreme fiber of the restraining member. Furthermore, the proposed formula has incorporated a strain hardening factor for the SS-BRB that experiences strain hardening of the core after its initial yielding. The proposed formulas have been validated through FE numerical analysis. The findings in this paper provide fundamentals to develop the design method for an energy-dissipation type of SS-BRBs. [ABSTRACT FROM AUTHOR]

This paper presents the experimental and analytical results of 32 circular-section and 16 square-section concrete columns confined by CFRP sheets under axial compression. The main parameters were: the preload ratio, the concrete strength and the number of CFRP piles. The failure modes, mechanical behaviors, and reasons of the descending of the peak stress and strain of the confined concrete in columns were analyzed. The experiment results indicated that the effectiveness of CFRP confinements were influenced by the preload ratio observably. Both the ultimate stress and strain decreased with the increasing of the preload ratio, and the increasing of CFRP piles will magnify the negative effect. Combined with the previous literatures, this paper concluded formulas about the second stiffness, lateral expansion coefficient, peak stress and strain of the concrete columns confined by CFRP under a certain preload ratio. Furthermore, based on these concluded formulas, a new design-oriented stress-strain model for the circular and square concrete column confined by CFRP sheets under preload was purposed respectively. [ABSTRACT FROM AUTHOR]

The paper provides the systematic derivation of a new analytical approach to tensile membrane action of lightly-reinforced thin concrete slabs at large deflections. The basic motivation for the work comes from the recent use of tensile membrane action as an enhancement, in the fire condition, of the capacity of the thin concrete slabs which are normally made composite with downstand steel beams, at temperatures which have substantially degraded the contribution of these steel beams. The method accepts as a premise that such slabs form a pattern of localized yield lines as an initial small-deflection failure mechanism, and that these yield lines retain their positions as subsequent deflection occurs. As the slab deflects, maintaining the correct kinematics of the articulation and displacement of the system of slab facets, interacting across the yield lines, is extremely important to the horizontal equilibrium of the slab. In this process it becomes necessary to re-think the basic assumption of traditional yield-line theory that any local cross-section of unit width along a yield line equilibrates the force of its concrete compression block with the yielded steel’s tension force, producing constant plastic moment capacities for the mesh in either direction along any yield line. In the approach set out in this paper only overall equilibrium of the system of facets needs to be maintained. As in normal rigid-plastic analysis, concrete acts only when compressed, and then at its compressive strength, and steel acts at its tensile yield strength whilst it remains intact. However, steel in either direction can fracture when the local crack-width causes its local strain to exceed its fracture ductility. When the rebar crossing the diagonal yield lines begins to fracture this generally indicates that the slab’s capacity is about to reduce with further deflection. The paper does not attempt to address how a rebar’s free length across a discrete crack is generated, or the limiting crack widths implied, but this is shown in a range of examples to be a major issue if tensile membrane action is to be used in practice to enhance the capacity of slabs, for example in hazard loading situations. It is important that principles be established in future to quantify this aspect of rebar ductility. [ABSTRACT FROM AUTHOR]

Angles exhibit a complex structural behaviour, responsible for the fact that, in the current North American Specification for Cold-Formed Steel Structures, short-to-intermediate equal-leg angle columns are (i) not yet pre-qualified for the Direct Strength Method (DSM) design and (ii) excluded from the application of the LFRD resistance factor ϕ = 0 . 85, valid for all other cold-formed steel compression members. Recently, the specific behavioural features exhibited by the above angle columns were incorporated into the proposal of a novel DSM-based design approach, for both fixed-ended and pin-ended columns, and it was shown that this added rationality goes along with quite accurate and reliable failure load predictions. However, the investigation leading to this design proposal also unveiled that there are no available experimental failure loads of slender pin-ended columns with intermediate-to-high slenderness values, which implied that the design procedure was validated for such columns exclusively on the basis of numerical failure loads. The research work reported in this paper provides a contribution towards filling this gap, since it mainly consists of an experimental study, carried out at the Federal University of Rio de Janeiro, on the behaviour and collapse of short-to-intermediate slender pin-ended cold-formed steel equal-leg angle columns. After addressing the selection of the columns to be tested, the experimental set-up and test procedure are described in detail and the results obtained are presented and discussed. Such results involve (i) initial imperfection measurements, (ii) equilibrium paths relating the applied load to key column displacements, (iii) deformed configurations (including the collapse mode) and (iv) failure loads. Next, those same experimental results are used to validate a shell finite model previously developed by the authors, which is subsequently employed to obtain additional numerical failure load data concerning the pin-ended angle columns under scrutiny. Then, attention is turned to assessing the merits of the novel design approach. The comparison between the experimental and numerical values obtained in this work and their estimates provided by the design equations shows a very good correlation, perfectly in line with that observed in the recent studies available in the literature − this means that the validation and calibration of the above design approach may be deemed (successfully) completed. Finally, the paper closes with the presentation and assessment of small alterations to the existing design expressions, aimed at improving their accuracy and rationality, thus paving the way towards codification in the near future. [ABSTRACT FROM AUTHOR]

An experimental investigation into the structural performance of compressed high strength steel (HSS) square and rectangular hollow sections is described in this paper. Both hot-rolled and cold-formed HSS sections were examined. In total six S460NH and five S690QH hot-rolled section sizes and three S500MC, two S700MC and four S960QC cold-formed section sizes were tested. The experimental programme comprised tensile coupon tests on flat and corner material, measurements of geometric imperfections, full cross-section tensile tests and stub column tests. The results of the experiments presented in this paper have been combined with other available test data on high strength steel sections, and used to assess the existing design guidelines for high strength steels given in Eurocode 3. The focus has been on the material ductility requirements, the Class 3 slenderness limit for internal elements in compression and the effective width formula for Class 4 internal elements in compression.Reliability assessments of the Class 3 slenderness limit (both the current value of 42 and a proposed value of 38) and the effective width formula for Class 4 internal elements in compression were carried out. The analysis indicated that, based on the assembled test data considered in this study, and the assumptions made regarding the statistical distributions of material and geometric properties, a partial safety factor greater than unity is required for HSS. Similar findings have also recently been presented for ordinary strength steels. [ABSTRACT FROM AUTHOR]

• A novel composite structure of CFCST-PST column was proposed. • A series of axial compression experiments on CFCST columns were conducted. • The 3D refined FEM model was established, and parametric analysis was carried out. • The confinement mechanism of multi-cell steel tubular column was investigated. • Formulas to predict the ultimate axial strength of CFCST-PST were proposed. This paper proposed a novel composite structure of concrete-filled corrugated steel tubular column with polygonal steel tubes (CFCST-PST), which consisted of concrete and multi-cell steel tubular column, including polygonal steel tubes and corrugated steel plates. This new column enables the confinement of multi-cell steel tubular column to the core concrete in addition to preventing local buckling of the tubes. To investigate the axial compression mechanical properties of the column and the capabilities of polygonal steel tubes, a concrete-filled corrugated steel tubular column with square steel tubes (CFCST-ST) was designed and fabricated as a comparative specimen. Axial compression experiments and finite element studies (FEM) were carried out on both CFCST-PST and CFCST-ST specimens. Through the previous research, it was found that CFCST-ST has better ductility and higher bearing capacity, while the corrugated plate with higher lateral stiffness, so that concrete is well restrained. In this paper, research had revealed that CFCST-PST effectively expands the strongly confined area of core concrete, as compared to CFCST-ST. A detailed discussion of the strain development of the corrugated plates was presented in order to demonstrate the confinement effect. Finally, the method of confining stress homogenization was used to establish formulas for calculating the axial compression load capacity of CFCST-PST for engineering purposes. [ABSTRACT FROM AUTHOR]

The paper presents drift-based fragility functions for nonductile reinforced concrete (RC) columns having light transverse reinforcement steel ratio which predominantly fail in shear. These fragilities were developed for four key damage states (i.e., light cracking, severe cracking, shear failure, and loss of axial load carrying capacity) associated with their structural performance observed in laboratory tests and repairability. For this purpose, experimental results of 71 column specimens tested under cyclic lateral loading were collected from 22 research programs; particularly, drift ratios associated to the column specimens tested to reach axial collapse. It is shown that the shear span-to-depth ratio and level of axial load ratio have influence on the drift-based fragilities associated to the damage states considered in this investigation. Additionally, several sources of epistemic uncertainty due to specimen-to-specimen, finite-sample, column shear span-to-depth aspect ratio, and level of axial compression load were quantified from the experimental database. The introduced drift-based fragilities are a very useful tool to assess the expected damage of existing buildings, such as school buildings that might exhibit the short captive column effect. • New fragility functions for key damage states of RC columns failing in shear. • Fragilities for shear-critical RC columns are different than those for non-ductile RC columns. • Inclusion of epistemic uncertainties influence fragilities of shear-critical RC columns. • Uncertainties due to finite-sample, axial load ratio and span-to-length ratio. [ABSTRACT FROM AUTHOR]

Implementing section curvilinearization (SC) by curving flat sides into curved sides before fiber-reinforced polymer (FRP) jacketing has been proposed to enhance the FRP confinement effectiveness of FRP-confined rectangular concrete columns. In this paper, ultra-high performance engineered cementitious composite (UHP-ECC) is proposed as the added concrete for SC, with an aim to enhance both bending and axial strengths of concrete columns given that the UHP-ECC can contribute to resisting tensile stresses for columns. Thirteen large-scale FRP-confined square reinforced concrete (RC) columns with SC using UHP-ECC were tested under eccentric compression loading to explore their eccentric compressive behavior. The test parameters included the rise-to-span ratio, the FRP thickness, the eccentricity and the surface roughness of the old concrete. The test results show that FRP confinement with SC using UHP-ECC can substantially enhance the peak axial load and the bending moment than those without SC, while the ultimate lateral displacement is marginally increased. An increase in the rise-to-span ratio leads to an increase in the peak axial load. • UHP-ECC is proposed as the added concrete for section curvilinearization before FRP strengthening. • Thirteen large-scale FRP-confined square RC columns with SC using UHP-ECC were tested under eccentric compression. • FRP confinement with SC using UHP-ECC can substantially enhance the peak axial load and the bending moment than those without SC. • The ultimate lateral displacement of the strengthened columns is marginally increased. • An increase in the rise-to-span ratio leads to an increase in the peak axial load. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) columns play a crucial role in the overall performance of modern RC frame buildings under blast loading. The RC columns under blast loads might experience various irreversible consequences such as concrete cracks, crushing and spalling, changing the status of both modal properties and load-carrying capacity. In this paper, the blast-induced damage assessment of the RC columns involving the measurement of modal parameters was introduced and validated. Firstly, a modal-based method for blast-induced damage assessment of RC columns was proposed, in which the damage is characterized as the reduction of axial bearing capacity and further expressed as the explicit function of the vibration frequencies and the mass-normalized displacement mode shapes. Then, the finite-element analysis program LS-DYNA was employed to establish the numerical model of RC columns under axial compression loads and lateral blast loads. The residual load-bearing capacities and modal properties of the RC columns were illustrated. By using the numerical results collected in the present study, the validity of the proposed damage assessment method was discussed and proved numerically. Further, field explosion tests and experimental modal tests were conducted, and the results showed that the modal-based damage assessment method exhibited remarkable agreement with the blast damage determined by residual bearing capacities. Based on the numerical and experimental results, the proposed modal-based damage assessment method is applicable for the non-destructive evaluation of blast-induced damage of RC columns. • A modal-based mothed is proposed for post-blast damage assessment of RC column. • Blast-induced damage of RC column leads to decreasing of vibration frequencies. • Change of mode shapes cannot be ignored in blast damage assessment of RC column. • The proposed modal-based mothed is validated numerically and experimentally. [ABSTRACT FROM AUTHOR]

• Results from 62 tests on the bearing strength of concrete blocks are presented. • Influence of several parameters is studied, including bar and fibre reinforcement. • Modern measurement techniques gave valuable insight into the structural behaviour. • Bearing capacity of reinforced blocks is higher than predicted by current standards. • The proposed stress fields enable the design of more efficient structures. This paper presents the results of a comprehensive experimental campaign investigating the structural behaviour of concrete blocks subjected to partial area loading. A total of 62 concrete blocks were loaded up to failure by applying a compressive load over a limited area. The campaign focused on plane cases of partial area loading, i.e. the load was applied over the (almost) entire block length and thus dispersed mainly in one direction. The test parameters included (i) the specimen geometry; (ii) the size of the loaded area; (iii) the concrete strength; (iv) the conventional reinforcement ratio, layout, and detailing; and (v) the steel fibre content. Modern measuring techniques were applied to gain insight into the crack development, the reinforcement activation, and the contact pressure distribution over the loaded area. The test results, together with experimental data found in the literature, substantiate the fundamental mechanical behaviour identified in previous theoretical studies by the authors. It is shown that the Dual-Wedge and Dual-Cone stress fields presented in the companion paper can accurately reproduce the influence of the investigated test parameters. Moreover, the bearing capacity predictions by these stress fields correlate significantly better with the experimental data than existing design rules implemented in current design codes. [ABSTRACT FROM AUTHOR]

A cable-struts structure consists of tension-only cables and compression-only struts. The structural rigidity comes from the pre-stress. To determine the feasible pre-stress for the cable-struts structure efficiently and accurately, the paper first defines the three states for the cable-struts structure based on the loads applied, develops the fuzzy relationship between the internal force and the pre-stress under different states, and studies various essential conditions for the feasible pre-stress. Second, the paper gives a Newton iteration method to update the pre-stress and a simple method for updating the geometry based on the geometrical difference under different states and subsequently develops a process to find the feasible pre-stress, combining the pre-stress updating method with the geometry updating method. Last, the paper selects three types of cable-struts structures as illustrative examples, a traditional Geiger dome, a new form of Geiger dome and a Kiewitt dome with multiple self-stress modes, and successively calculates their feasible pre-stress using the proposed method. The results indicate that the proposed method is able to search for the feasible pre-stress for cable-struts structures efficiently and accurately; it can calculate not only the pre-stress without loads but also the pre-stress considering loads, and it can change the geometry for the feasible pre-stress. Meanwhile, the method is successful in obtaining the feasible pre-stress for the Kiewitt dome with multiple self-stress modes without the optimal process. [ABSTRACT FROM AUTHOR]

This paper presents research on a conventional but practical retrofitting method for masonry walls along with the numerical modelling of it under in-plane lateral shear–compression loading. The latter is capable of predicting the experimental collapse load and overall behaviour quite accurately. The retrofitting approach is based on building a wall parallel to an existing single-leaf wall and bonding the two leaves together using a mortar (collar) joint, merging the two individual panels into a unified double-leaf wall. Experiments on this retrofitting approach for both undamaged and damaged masonry walls have been introduced in the present paper. The tests revealed that the pre-damage application can increase the strength by 50% while the post-damage one can restore the initial strength. A micro-scale numerical model has been devised by considering the bricks as rigid elements and the mortar joint as a nonlinear failure surface. The model was implemented in the commercial Finite Element (FE) software MIDAS FEA and the numerical results were verified against the available experimental data. [ABSTRACT FROM AUTHOR]

Columns are considered to be critical members of moment-resisting structural systems. In seismically active regions, it is important to improve the ductile deformation capacity and energy dissipation capacity of columns so that the entire structure can endure severe ground motion and dissipate a considerable amount of seismic energy. Against this background, this paper presents the idea of a new transverse reinforcement configuration (TRC) for improved seismic performance of rectangular (including square) reinforced concrete (RC) columns. The novel features of the new TRC compared to conventional TRCs using rectangular hoops and cross ties mainly include the use of additional small circular spirals near the column ends (i.e., potential plastic hinge regions). Such a simple change can significantly enhance the performance of RC columns without complicating their construction. In this paper, the rationale for the new TRC together with its expected advantages is first explained. A series of axial compression tests on RC columns with the new TRC are then presented to demonstrate some of the expected advantages. The test results confirmed that the concrete is very effectively confined by the new TRC, leading to significant enhancements in both the load capacity and ductility of RC columns. [ABSTRACT FROM AUTHOR]

Current design rules for the member capacities of cold-formed steel columns are based on the same non-dimensional strength curve for both fixed and pinned-ended columns at ambient temperature. This research has investigated the accuracy of using current ambient temperature design rules in Australia/New Zealand (AS/NZS 4600), American (AISI S100) and European (Eurocode 3 Part 1.3) standards in determining the flexural–torsional buckling capacities of cold-formed steel columns at uniform elevated temperatures using appropriately reduced mechanical properties. It was found that these design rules accurately predicted the member capacities of pin ended lipped channel columns undergoing flexural torsional buckling at elevated temperatures. However, for fixed ended columns with warping fixity undergoing flexural–torsional buckling, the current design rules significantly underestimated the column capacities as they disregard the beneficial effect of warping fixity. This paper has therefore recommended the use of improved design rules developed for ambient temperature conditions to predict the axial compression capacities of fixed ended columns subject to flexural–torsional buckling at elevated temperatures within AS/NZS 4600 and AISI S100 design provisions. The accuracy of the proposed fire design rules was verified using finite element analysis and test results of cold-formed lipped channel columns at elevated temperatures except for low strength steel columns with intermediate slenderness whose behaviour was influenced by the increased nonlinearity in the stress–strain curves at elevated temperatures. Further research is required to include these effects within AS/NZS 4600 and AISI S100 design rules. However, Eurocode 3 Part 1.3 design rules can be used for this purpose by using suitable buckling curves as recommended in this paper. [ABSTRACT FROM AUTHOR]

• An isolator based on a rolling grout-filled tennis ball is studied in depth. • The compressive strength is found to be sufficient for the intended application and of small dispersion. The rubber layer manages to increase it compare to a plain grout sphere by almost 100% • The lateral behavior is bilinear with a coefficient of friction of roughly 5% (depending on the compressive force). There is no significant deterioration under multiple cycles. • To understand the rolling behavior and the nature of rolling friction, a FE model was built and validated. • The FE model was used to show that a thicker rubber layer would slightly increase the coefficient of friction. This paper describes the behavior of a low-cost seismic isolator comprising a grout-filled tennis ball rolling on concrete plates. The isolator could be used for isolating lightweight structures. Initially, the axial response of the system was characterized. Subsequently, full-scale isolators were tested in combined compression and lateral cyclic loading. Parameters of investigation were the testing velocity (frequency), the bearing load, the degradation due to consecutive loading, the bearing temperature, the specimen-to-specimen variability, and the engagement of the displacement restrainer. Finally, a three-dimensional finite element model was developed to model in detail the response of the isolator and to explore the influence of the rubber thickness. This is the first study to characterize the above effects and to propose a finite element model of these isolators. Results showed that the lateral cyclic response of the isolators is bilinear and can be approximated by rigid-body equations, whereas the values of the rolling friction coefficient and the yield displacement are suitable for seismic isolation applications. The specimen-to-specimen variability was minimal. Unlike sliding isolation systems, an increased bearing compressive load leads to a higher rolling friction coefficient. Analytical equations are offered to describe this effect. The rolling friction coefficient does not depend on velocity (frequency) or temperature, and the isolators did not deteriorate under consecutive loading. The proposed displacement restrainer effectively limits the motion of the isolator. The developed finite element model accurately captures the experimental response. It was used to study the influence of the thickness of the rubber layer on the lateral response, to conclude that it is minimal, for rubber layers ranging from 3.4 to 7 mm. [ABSTRACT FROM AUTHOR]

• The SRC columns were tested under combined compression-bending-shear-torsion cyclic load. • The effects of stud on the torsional properties of SRC columns were analyzed. • A certain number of structural studs need to be added for SRC columns with torque under the bending design conditions. • A calculation method of torsional bearing capacity of SRC columns under combined action was proposed. This paper presents the seismic behavior of steel reinforced concrete (SRC) column with welded studs. Nine SRC columns, varying in stud position, stud spacing, stud length and stud layout, were tested under combined compression-bending-shear-torsion cyclic load. All specimens were subjected to bending-torsion failure with the characteristics of concrete crushing and X-shaped cracks. The fullness of hysteretic curves of bending moment and torsion moment showed that the torsional energy dissipation of the SRC columns was poor. The arrangement of studs at the flange could improve the seismic behavior of SRC columns, and decreasing the stud spacing and increasing the stud length could play an enhanced effect, but the effect of setting the studs at the web was not significant. For SRC columns subjected to torsion moment, a certain number of structural studs need to be added to enhance their torsional properties under the condition that the studs can resist bending moment. In addition, the strain distribution illustrated that the web of encased steel played a great role in resisting torsion, so the torsional bearing capacity of SRC columns was mainly controlled by the strength of the web. Based on the unified strength equation established in this paper, a calculation method of torsional bearing capacity of SRC columns, subjected to combined action of compression-bending-hear-torsion, was proposed. [ABSTRACT FROM AUTHOR]

This paper focused on a new type of double-skin composite wall in which concrete-filled steel tubes are used as boundary elements, and steel-bar space trusses are used to stabilize the faceplates. The new composite wall is architecturally attractive and has some perceived advantages in strength and construction. However, limited knowledge exists regarding its behavior under the combined cyclic in-plane lateral load and axial compression. This paper reports the test results of five experimental specimens subjected to the intended combined loading. Among the tested specimens, four developed the preferred flexure-dominated limit state, while one developed the undesired shear-dominated limit state. The specimens with the flexure-dominated limit states exhibited ductile behavior up to the drift of 0.036 rad with minor strength degradations. It was found that local buckles in the faceplates of the composite wall did not compromise wall lateral resistance. The effect of using supplementary steel headed studs to stabilize faceplates is also addressed in the paper. Aside from the experimental work, a simplified model was established to compute the wall plastic moment and lateral resistance of the wall with the flexure-dominated limit state. Predictions from the model were found to agree well with the test results, suggesting the model can be used for future design and analysis of the composite wall. [ABSTRACT FROM AUTHOR]

• A novel shape optimization approach for strained gridshells is proposed. • All sensitivities to perform gradient-based optimization are derived analytically. • The construction of a 6 m by 6 m timber gridshell prototype is discussed. Strained gridshells are reticulated shell structures that are erected from a flat grid of initially straight laths. The structural efficiency of a gridshell is determined by its shape, which is traditionally designed using form-finding techniques. However, these techniques are primarily used to generate structures in pure tension or compression for a single load case only. In cases where classic form-finding techniques are not applicable, such as for cantilevering gridshells or simply supported gridshells, numerical optimization can be used to find a suitable shape. In this paper, an optimization procedure is proposed that optimizes the shape of a strained gridshell for a given grid. The forces applied to erect the gridshell are chosen as the design variables. These erection forces are optimized to minimize the so-called end-compliance, which is defined as the inner product of the external loads and the resulting displacements. The method of moving asymptotes is adopted to solve the optimization problem and implicit dynamic relaxation is used to solve the nonlinear equilibrium equations. Geometric nonlinearity is taken into account by using co-rotational beam elements to model the gridshell laths. To validate the proposed approach, a 6 × 6 m2 prototype was built. The results show that this approach allows the structure to be optimized considering multiple load cases, while accounting for practical building constraints, and potential designer constraints. [ABSTRACT FROM AUTHOR]

Highlights • Applied the Hencky bar-chain model (HBM) for frame buckling analysis considering different configurations. • Used easy-to-code stiffness matrices with patterns to simplify the expression of HBM formulations. • Demonstrated the advantage of localized model modification of HBM in considering a local damage/stiffening. Abstract This paper presents the development of the Hencky bar-chain model (HBM) for the buckling analysis of non-symmetric portal frames under vertical compressive axial loads on the columns. Generic stiffness and geometric matrices are derived for the frame buckling analysis. Based on these matrices, a simple computer code is developed to determine the buckling loads. Illustrative frame buckling problems are solved to demonstrate the ease and simplicity of the HBM for analysis of different and complex design conditions imposed on the frames. The advantages of consistent formulation, localized model modifications, and convenience in obtaining the buckling modes are further noted for the HBM. [ABSTRACT FROM AUTHOR]

Highlights • A stiffener on the compression diagonal increases the postbuckling shear strength. • The most important role of a stiffener is providing lateral restraint. • At ambient temperature, the axial force in the stiffener is negligibly small. • At 700 °C, the axial force in the stiffener is up to 35% of the shear strength. Abstract There are a growing number of bridge fire events and the National Fire Protection Association (NFPA) requires that critical structural elements of the bridge be protected from elevated temperatures due to fire. However, no guidance is given on how to protect these critical elements, nor how to identify them. Further, slender steel web plates have been shown to be vulnerable to shear buckling in fire events and recent research that indicates that the load path of shear forces in thin web plates is not well understood. The overall objective of this paper is to examine the effectiveness of stiffeners for enhancing the shear capacity of slender plates at ambient and elevated temperatures. Specifically, evaluations are made regarding the effectiveness of stiffeners for increasing the shear buckling capacity through various stiffener orientations, providing lateral restraint, and providing a load path for shear forces. In particular, the elastic shear buckling load, V cr , and the ultimate shear postbuckling load, V u , of the steel plate are examined. Finite element analyses, which have been validated with experimental data, are used as a basis for the study. The temperatures studied range from ambient to 1100 °C. This study provides some important insights on the behavior of plates under shear loads. For example, results indicate that the stiffener's role is not that of a load path for the shear forces, but one of lateral restraint, regardless of its geometric orientation. Further, it is shown that for lower temperatures a stiffener oriented along the compression diagonal (opposite to a tension field) provides the most improvement in postbuckling strength. [ABSTRACT FROM AUTHOR]

Highlights • A softened damage-plasticity model with compression-softening is used for concrete. • A stress-slip model is developed for precast concrete to reflect bond-slip effect. • A pre-post concrete interface layer is developed in the finite element model. • 3D numerical examples of cyclic tests of connections were performed and validated. Abstract In this paper, a finite element modelling approach is developed for the analysis of the cyclic behavior of precast beam-to-column connections. In particular, the modelling takes into account the compression-softening of concrete, the bond-slip effect in the critical regions and the representation of the post-cast concrete interface. A newly developed softened damage-plasticity model, which can reproduce the typical cyclic behavior of reinforced concrete, is adopted for concrete. Meanwhile, to reflect the significant bond-slip effect between concrete and reinforcement bars, the M-P stress-strain model is modified to account for the slippage by assuming the bar strain is the sum of the bar deformation and the slip, while the anchorage slip is theoretically derived and validated through benchmarking the pull-out tests. Additionally, a concrete layer between the precast concrete and the cast-in-situ concrete is incorporated to reflect the features of the interface. The proposed numerical modelling approach is validated through simulation of both interior and exterior precast beam-to-column connection tests. The validated models are subsequently employed to investigate the influences of key factors such as the compression-softening and the bond-slip effect on the analysis of the cyclic behavior of the precast beam-to-column connections. Results demonstrate that the proposed model is capable of reproducing the typical behavior of precast beam-to-column connections and can serve as an effective tool for the seismic performance analysis and investigation of design parameters of precast connections. [ABSTRACT FROM AUTHOR]

Highlights • Review of European standardized approaches. • Geometrical and design recommendations for three Step Joint typologies. • Mechanical behaviour of Step Joints under monotonic compression in the rafter. • Design equations of Step Joints against shear crack and crushing. • Reliability of design models still under discussion. Abstract When assessing timber roof structures on-site for any restoration project, engineers can be faced with elements that, over time, were poorly preserved, especially damaged joints in contact with moist masonry walls. Before dealing with any intervention technique, the mechanical behaviour of such carpentry connections must be properly understood. Therefore, it has to be determined how the joints fail, which parameters (i.e. geometrical configurations and mechanical properties of the joint) influence the appearance conditions of failure modes, and the way how the internal forces are distributed within the connection. Therefore, the present paper aims at overviewing three different typologies of Step Joints (SJ) which can often be encountered within traditional timber carpentries between the rafter and the tie beam: the Single Step Joint, the Double Step Joint, and the Single Step Joint with Tenon-Mortise. Regarding each SJ typology, some design rules and geometrical recommendations can be gathered from European Standards and from authors of works on the subject, but no design equation is conventionally defined. Hence, new design models have been determined through the Analytical Campaign for the investigated Step Joints according to their geometrical parameters and to both failure modes: the shear crack in the tie beam and the crushing at the front-notch surface. In order to check the reliability of new design models and the emergence conditions of both failure modes, future experiments and numerical analysis on the three SJ typologies are going to be performed. [ABSTRACT FROM AUTHOR]

In progressive collapse analysis, event-independent column loss is commonly used as a design scenario. Yet this scenario does not account for the fire-induced thermal forces that develop in case of a fire. The thermal forces may cause detrimental load redistributions in the structure, notably during the cooling phase. However, as the response of entire structures during the full course of fires until burnout has received little attention, these effects are not well established. The objective of this paper is to analyze the mechanisms of load redistribution in a structural system comprising a column subjected to localized fire, with a focus on the effects of the cooling phase. Numerical simulations by nonlinear finite element method are used, after validation against experimental data. The observed mechanisms result in tension building up in the fire-exposed column and overloading the adjacent columns in compression. Consequently, the damaged vertical member redistributes a force that is larger than the force initially carried. This can lead to failure of vertical members not directly affected by the fire and trigger a progressive collapse. These mechanisms are parametrically studied on a simple system composed of a column and a linear spring. Major parameters influencing the residual tensile force in the fire-exposed column are the maximum reached temperature and the relative stiffness of the remainder of the structure. The analysis of a twenty-story steel frame building under localized fire attacking one ground level perimeter column confirms the development of these mechanisms in a real design. The results have important implications as they question the validity of an event-independent design scenario for capturing the influence of column failure due to fire loading. [ABSTRACT FROM AUTHOR]

• An optimization strategy was conducted to obtain a final set of ANN model. • The developed ANN model exhibited superior performance than current codes and empirical equations. • An explicit equation based on Artificial Neural Networks were derived for practical application. In this paper an Artificial Neural Network (ANN) model is developed for the prediction of the ultimate compressive load of rectangular Concrete Filled Steel Tube (CFST) columns, taking into account load eccentricity. To this end, an experimental database of CFST specimens from the literature has been compiled, totaling 1224 individual tests, both under concentric and under eccentric loading. Except for eccentricity, other parameters taken into consideration include the cross section width, height and thickness, the steel yield limit, the concrete strength and the column length. Both short and long specimens were evaluated. The architecture of the proposed ANN model was optimally selected, according to predefined performance metrics. The developed model was then compared against available design codes. It was found that its accuracy was significantly improved while maintaining a stable numerical behavior. The explicit equation that describes mathematically the ANN is offered in the paper, for easier implementation and evaluation purposes. [ABSTRACT FROM AUTHOR]

• A comparison is performed between two modelling approaches, the homogenisation approach (macro-modelling) and the micro-modelling approach. • Both modelling approaches provide a reliable prediction of masonry response at the ambient and high temperatures. • These modelling approaches can be used in combination. Refractory masonry with dry joints is widely employed as a protective lining in industrial applications requiring high-temperature treatments. The thermal and mechanical behaviour of alumina spinel refractory masonry is investigated for a wide range of mechanical loading conditions at ambient and high temperature up to 1500 °C within the framework of the ATHOR project. This paper discusses the different numerical analysis approaches for the simulation of the experimental results. Micro and macro modelling approaches show good agreement with the large scale uniaxial and biaxial compression tests for loading and unloading at the ambient temperature. Simulations carried out for large scale uniaxial and biaxial creep tests as well as biaxial relaxation tests at 1500 °C show good agreement. The numerical results indicate the ability of these modelling approaches to represent the complex thermomechanical behaviour of the refractory masonry. Both methods demonstrate an orthotropic and highly nonlinear behaviour of the refractory masonry as observed in the experimental campaign. The numerical outcome, validated with experimental results demonstrate compatibility between micro and macro modelling approach that can be employed to evaluate local and global behaviour of large industrial installations. [ABSTRACT FROM AUTHOR]

• A re-entrant chiral deformation mechanism of honeycomb is studied. • This auxetic honeycomb has enhanced orthotropic anisotropy. • The Poisson's ratio of this honeycomb can reach −10 or even smaller. • This honeycomb can be used for the design of auxetic tubular stent. In this paper, we proposed a honeycomb structure with enhanced anisotropy in the orthogonal direction with a re-entrant chiral hybrid deformation mechanism. The analytical formulas for the equivalent Poisson's ratio and normalized Young's modulus were derived based on the theory of the Timoshenko beam under small static deformations and verified by experiments and finite element simulations. Parametric analysis demonstrated the extreme anisotropy of this structure in the orthogonal direction, achieving a Poisson's ratio −10 or lower in one direction, while remaining nearly zero in the other direction. This property allowed the structure to be designed into a tubular stent that remained stable along its axial length when subjected to a compressive load in the radial direction. However, the stent underwent significant contraction in the radial direction when a compressive load was applied along the axial direction. This stent is expected to have biomedical applications to solve problems associated with cardiovascular obstruction, esophageal obstruction, and airway stenosis. [ABSTRACT FROM AUTHOR]

• Buckling behavior of hybrid composites tubes. • Modal behavior or hybrid composites tubes before and after failure. • Analysis of variance of the structural responses in composites tubes with ply drop-off. • The results revealed that the hybrid structure with drop-offs is an appropriate option that offers the best cost-benefit. A comparative study of the static and dynamic behavior of a new type of tubular structure with drop-offs used in lower limb prostheses is presented in this paper. Composite structures that present mass reduction, low cost, and excellent performance are a great challenge for many researchers. In order to overcome these difficulties, numerical and experimental methods are performed, generating results regarding natural frequencies, damping loss factors, and maximum compression load for five different setups for tubes with drop-offs. For the manufacture of the structures, three types of fabrics are considered: carbon, glass, and a carbon/aramid hybrid fabric. Beyond the three types of tubes, two more setups are created considering hybridization, with the inner ply manufactured with glass fabric, the outer ply of the first setup manufactured with carbon fabric, and the outer ply of the second setup manufactured with carbon/aramid hybrid fabric. The structural hybridization and insertion of drop-offs provide a reduction in the cost of material. Firstly, an optimization strategy using the Lichtenberg algorithm is executed, aiming at the basic material properties in relation to elasticity modulus, strain modulus, Poisson ratio, and density. Then, it is possible to perform numerical modal analysis using the Finite Element Method in Ansys® software with the aim of obtaining the first natural frequencies for each setup. Modal experimental tests before and after failure obtained in the compression test are performed to measure the first natural frequency and damping loss factor for each setup, providing a comparison between the dynamic behavior of the undamaged and damaged structures, and, posteriorly, the numerical and experimental modal results before failure are compared. The compression test is performed to measure the maximum compression load supported by each structure. The results revealed that the hybrid structure with drop-offs is an appropriate option that offers the best cost-benefit for pylon tubes. [ABSTRACT FROM AUTHOR]

• Cellular filled composite crash boxes can be successfully fabricated by using carbon fibre reinforced polymer (CFRP) prepreg fabrics. • Empty cylinder (EC) type composite crash box provides better specific energy absorption ability than empty square (ES) and hexagon (EH) counterparts. • Hexagonal and square cellular fillers increase significantly crush strength and energy absorption performance of the composite crash boxes. • Finite elements method (FEM) presents an effective solution in modelling crushing response of the composite crash boxes. • The cellular filled composite crash boxes exhibit deformation behaviour in the form of opening outward during crushing. Composite structures have been used in the automotive and aircraft industries because of their superior properties such as specific energy absorption ability, lightweight and crashworthiness. This paper aims to determine energy absorbing and deformation behaviours of composite crash boxes designed in different geometries by an innovative approach. The hand-layup vacuum bagging method was utilized to produce the composite crash boxes, which were developed with three different outer wall geometries (square, hexagon, and cylinder), and cellular filled square and hexagonal interiors. Carbon fibre reinforced polymer (CFRP) material was used in fabrication of the crash boxes. Experimental and numerical studies were conducted to investigate the energy absorbing and deformation behaviours under static compression load of the composite crash boxes. A commercial finite elements (FE) software (Ls-Dyna) was used for the numerical model. The study's findings revealed that cellular-filled composite crash boxes perform significantly better in terms of energy absorption performance. It was observed that filling an empty square type composite crash box with hexagonal cells increased the box's specific energy absorption capacity by around 140%. [ABSTRACT FROM AUTHOR]

• Experimental testing of corrosion damage low-strength concrete columns under compressive loading. • Influence of corrosion damage on inelastic buckling of stocky low-strength concrete columns. • Impact of corrosion on confined low-strength concrete behaviour under cyclic loading. • Influence of cross sectional shape on failure modes of corroded column under cyclic loading. New codes have recently introduced seismic detailing for new structures. However, there are still older reinforced concrete (RC) structures without proper ductile detailing for earthquake resistance in seismic-prone areas. These structures are further impacted by the corrosion of their embedded reinforcing bars, which further reduces the strength and ductility under axial cyclic loading. This paper summarises the results of an experimental investigation performed on low-strength short RC columns, with different confinement configurations, subject to varying degrees of corrosion to investigate their structural responses to axial cyclic loading. The experiment was conducted on 30 short RC columns (square and circular) with three levels of confinement and steel reinforcement corrosion loss ranging from 0% to ∼ 30% subjected to cyclic compressive loading. The test results show that corrosion and inadequate confinements have a significant negative impact on the structural responses of corroded columns. [ABSTRACT FROM AUTHOR]

• Numerical investigation was conducted for CFHSS fully chord supported T-joints. • A total of 285 finite element analyses was carried out in the parametric study. • Chord face, chord sidewall and combination of these two failure modes were observed. • Static joint strengths were compared with the predictions of EC3 and CIDECT. • New design rules were proposed for CFHSS fully chord supported T-joints. A numerical investigation focusing on the design of fully chord supported cold-formed high strength steel (CFHSS) tubular T-joints is presented in this paper. The nominal yield strengths of the tubular members were 900 and 960 MPa. Square, rectangular and circular hollow sections (SHS, RHS and CHS) were used as the brace members, while SHS and RHS were used as the chord members. The tests conducted by Pandey and Young (2019) [1] were used to calibrate finite element (FE) models developed in this numerical investigation. The developed FE models were capable of replicating the test results, including joint resistances, load-deformation histories and failure modes. In order to determine the compression resistance, axial compression loads were applied through the brace members by fully supporting the chord members along their lengths. These calibrated FE models were then subsequently used for the parametric study, which comprised of a total of 189 FE analyses on T-joints with SHS and RHS braces and 96 FE analyses on T-joints with CHS braces. The nominal resistances calculated from the EC3 (2005) [2] and CIDECT (2009) [3] were used to compare the compression resistances obtained from both the tests [1] and the parametric study. In order to check the applicability of the design rules of tubular T-joints, the nominal resistances from these specifications (EC3 (2005) [2] and CIDECT (2009) [3]) were obtained with and without incorporating the recommended reduction (or material) factors. Through the comparison of 307 joints, including 22 tests (Pandey and Young (2019) [1]) and 285 FE analyses, it has been demonstrated that the existing design rules of T-joints given in the EC3 (2005) [2], CIDECT (2009) [3] cannot be directly used for fully chord supported tubular T-joints of S900 and S960 steel grades with validity ranges of governing parameters exceeding the limits specified in these specifications (EC3 (2005) [2], CIDECT (2009) [3]). Hence, new semi-empirical design rules are proposed in this paper for the observed failure modes, including chord face failure, chord side wall failure and their combined failure modes. Reliability analyses were also performed to check the reliability levels of both the existing and proposed design rules. [ABSTRACT FROM AUTHOR]

This paper aims at contributing to a better understanding of the physical-mechanical behaviour of partially loaded areas in reinforced concrete. Following a review of the current state of the art on this topic, which includes a description of the mechanical behaviour and existing predictive models, a remarkable knowledge gap in this standard problem is revealed. A new stress field solution for reinforced concrete blocks under strip loading is developed herein which is based on the lower-bound theorem of limit analysis and adopts a modified Coulomb failure criterion for concrete. Contrary to existing empirical design rules, the new mechanical model consistently accounts for the behaviour of concrete under multiaxial compression as well as the favourable effect of transverse reinforcement. While a comparison of the ultimate loads predicted using the new stress field solution shows a good correlation with the available test data, further experiments are required particularly for the validation of the predicted higher resistances of heavily confined areas as compared to existing design rules. [ABSTRACT FROM AUTHOR]

Application of fibre reinforced polymer (FRP) composites has steadily gained popularity in rehabilitation of steelwork over the last decade or so. This popularity is based on the inherent advantages of FRP and the considerable amount of research conducted on the response of FRP strengthened steelwork members under static loads. However, over the course of their service life, steel structures can be subjected to impact loads induced by a variety of sources. This necessitates the requirement for a comprehensive study that can shed light on the behaviour of FRP strengthened steelwork under various loading rates. This paper discusses the experimental results of carbon fibre reinforced polymer (CFRP) strengthened square hollow sections (SHS) under different loading rates. The experiments comprised a series of SHS columns tested under two loading rates: quasi-static (0.05 mm/s) and impact (4.43 m/s). Some of these columns were strengthened with different CFRP configurations comprising fibres oriented in the longitudinal direction, transverse direction and in both directions. The effect of co-existing axial compression applied prior and during the application of the transverse load (impact or quasi-static) was also examined. The axial load was introduced in the experimental program to simulate the normal service load that exists on columns in multi-storey frame buildings. Generally, it was found that the effectiveness of CFRP strengthening was increased at a higher loading rate to different degrees depending on the CFRP configuration. [ABSTRACT FROM AUTHOR]