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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]

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]

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 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]