Search

In order to promote the use of new sustainable steel fibers (SF) reinforced coal gangue aggregates (CGA) concrete, impact tests were performed in this paper. The impact resistance of steel fiber-reinforced coal gangue concrete was investigated using a self-developed drop-weight facility. The test variables were the CGA replacement rate (0 %, 50 %, and 100 %), the SF volume content (0 %, 0.75 %, and 1.5 %), and the drop height of the drop-weight (0.5 m and 1.0 m). Using 15 kg of hard steel as a drop-weight, the drop-weight impact test was performed on steel fiber-reinforced coal gangue concrete beams with a span of 300 mm; the damage pattern, impact reaction force-time, displacement-time relationships, and energy absorbed by steel fiber-reinforced coal gangue concrete beams were studied. The test shows that, compared with natural aggregate, CGA reduces concrete's static mechanical properties and impact resistance, and adding SF improves the static mechanical properties and impact resistance of coal gangue concrete. As the CGA replacement rate increased from 0 % to 50 % and 100 %, the reaction force of impact of the specimens decreased by 2.54 %− 6.06 % and 3.69 %− 12.33 %. The SF volume content was increased from 0 % to 0.75 % and 1.5 %, and the reaction force of impact of the specimens was increased by 23.05 %− 32.34 % and 72.27 %− 81.84 %, respectively. The impact resistance of steel fiber-reinforced concrete beams under impact loading was investigated numerically using a nonlinear explicit finite element model in LS-DYNA. The Finite Element results were validated with experimental results. Based on the validated finite element model, a parametric study was carried out to investigate the effects of coal gangue replacement rate, steel fiber volume content, and drop height of the drop weight on the behavior of the beams. This study might provide a basis for the future engineering project applications of steel fiber-reinforced coal gangue concrete under impact conditions. • New sustainable coal steel fibers reinforced gangue aggregates (CGA) concrete was investigated. • Impact resistance of this new type of concrete was studied. • Numerical modelling was made to this new type of structure. • Parametric analysis of SFCGC beams was carried out [ABSTRACT FROM AUTHOR]

Highlights • Beam finite element with eccentric, variable neutral axis. • Non-linear materials and material softening considered. • Computationally efficient finite element formulation. • Case studies considering large deflections and material nonlinearity considered. • Applicable to composite beams, bridge decks and other similar structures. Abstract This paper presents a beam finite element and analysis methodology for structures with neutral axes (NA) that are eccentric to the positions about which they are modelled, and that change position during the process of an analysis. This NA shift occurs due to non-linear material behaviour (softening, cracking, etc.). The proposed formulation is based upon a modified corotational approach. It has been developed specifically for structures subjected to severe fires, although it is also applicable to the non-linear analysis of structures such as wind towers and bridge decks where the position of the neutral axis in a beam section changes due to material nonlinearity. The analysis formulation results in lower computational effort relative to contemporary analysis methods employing shell or volume elements, while providing comparable results. Four case studies that include material nonlinearity, large deflections and geometric nonlinearity are included to validate the proposed formulation, and results are compared to shell element models analysed using Abaqus. The contributions of this paper are: (a) the application of standard Euler beam theory in a novel manner to allow for adjusted position of neutral axes in beams, (b) the presentation of simple case studies that can be used for validating finite element methods, but which incorporate material, geometric and cross-sectional non-linearity, and (c) illustrating the influence of cross-sectional discontinuity and how it may influence results when using beam elements. [ABSTRACT FROM AUTHOR]

Applications of concrete-filled square (or circular) stainless-steel tubes keep increasing in cold-region coastal engineering structures. However, their behaviours under low-temperature bending have not been fully investigated, which brings obstacles to their engineering applications. To address this issue, this paper investigated flexural behaviours of concrete-filled square/circular stainless-steel tubular beams (CFSSSTBs/CFCSSTBs) at low temperatures through eight four-point bending tests. The main studied parameters were low temperatures (20∼−60 ℃) and cross-section type (circular or square shape). Test results showed that both CFSSSTBs and CFCSSTBs exhibited flexural failure and exhibited excellent ductility under low-temperature bending benefiting from the excellent ductility of stainless steel; bending resistances of CFSSSTBs and CFCSSTBs were improved by 5% and 22%, respectively. This study also developed finite element models (FEMs) for simulations on flexural behaviours of CFSSSTBs/CFCSSTBs at low temperatures. The FEMs considered both low-temperature material and geometric nonlinearities. Validations against eight tests proved the capacities of FEM simulations on low-temperature flexural behaviours of CFSSSTBs/CFCSSTBs. Finally, the code equations in Eurocode 4 and AISC 360 were used to predict the stiffness and ultimate bending resistances of CFSSSTBs/CFCSSTBs. Validations showed that the code equations underestimated the bending resistances of CFSSSTBs/CFCSSTBs. This study provided fundamental information on the flexural bending mechanism of CFSSSTBs/CFCSSTBs) at low temperatures. • Low-temperature flexural behaviors of concrete-filled stainless-steel tubular beams (CFSSTBs) are reported. • Low temperatures improve stiffness and bending resistances of CFSSTBs. • Bending resistances of circular CFSSTBs are more improved than square ones as T decreases. • Code equations conservatively predict low-temperature bending resistances of CFSSTBs. [ABSTRACT FROM AUTHOR]

A numerical investigation on cold-formed high strength steel (HSS) tubular beams is presented in this paper. The nominal 0.2% proof stresses of the HSS sections ranged from 700 MPa to 1100 MPa. In the complementary study [1], experimental investigation on the beam specimens have been performed. In the present study, numerical modelling methodology for beams was first validated and parametric study on the cold-formed HSS tubular beams was conducted. A total of 423 numerical data was obtained to investigate the structural performance of HSS tubular beams. The experimental and numerical results were then compared with the codified design guidelines from ANSI/AISC 360-10 [2], EN 1993-1-1 [3], AS 4100 [4] and AISI S100 [5] in addition to the predictions from Direct Strength Method (DSM) for square hollow sections (SHS), rectangular hollow sections (RHS) and circular hollow sections (CHS). The codified slenderness limits for sections subjected to bending were examined. Improvements on the design guidelines are proposed in this paper. [ABSTRACT FROM AUTHOR]

This paper concerns the short-term behaviour of innovative steel-timber composite (STC) floors comprising of cross-laminated timber panels connected to steel girders by various mechanical fasteners and/or glue. The results of four-point bending tests performed on full-scale STC beams are reported and the structural behaviour (the load-deflection response, short-term stiffness, peak load capacity, and failure modes) of the proposed STC system is studied. In addition, extensive non-linear 1D and 2D finite element (FE) analyses of STC beams are carried out and the numerical results are verified against the test results. It is shown that 1D and 2D FE models are adequate in capturing the structural response of the STC beams. Using the FE and experimental results, the composite efficiency of STC beams that can significantly influence their structural behaviour beams is determined and reported in the paper. [ABSTRACT FROM AUTHOR]

This paper investigates the mechanical behaviour of lap steel-timber composite connections using a 3-D continuum-based finite element (FE) model. In the FE models developed, the non-linear behaviour and failure of the timber is captured by a stress-based failure criterion formulated in the framework of continuum-damage mechanics. Yielding of the steel plates and fasteners ( i.e. coach screws and bolts) is captured by an elastic-hardening plastic constitutive law. These FE models are validated by experimental (push-out) tests conducted on laminated veneer lumber (LVL)-steel and cross-laminated timber (CLT)-steel composite lap connections. It is shown that the FE models developed in the paper can replicate adequately the load-slip response and failure mode of the hybrid steel-timber composite connections tested. The validated FE model is used to undertake a parametric study that elucidates the influence of the yield strength and the length of the fasteners and the post-tensioning force in the bolts on the stiffness, load carrying capacity and load-slip behaviour of hybrid steel-timber composite connections. [ABSTRACT FROM AUTHOR]

This paper presents the application of a thick-shell nonlinear finite element analysis procedure to estimate the punching shear resisting performance of reinforced concrete slab-column connections under variable connection shear stress conditions. In the analyses performed, varied connection shear stress conditions stem from slabs being supported by columns with different cross-section aspect ratios, being subjected to different distributions of gravity loading, being constructed with different planar reinforcement ratios in orthogonal directions, as well as the application of unbalanced bending moments. Forty-eight isolated slab-column connection specimens presented in the literature were modelled and analyzed using a thick-shell finite analysis procedure. All numerical results were developed using a predefined set of material models and analysis parameters, a consistent meshing procedure, and are shown to provide meaningful agreement with experimental data without the need for case-specific model calibration or the adoption of specialised failure criteria. The results show that thick-shell modelling methods can be suitable for estimating the punching shear response of slabs subjected to non-uniform shear stress development in connection regions, and can provide similar levels of precision to that obtained for the analysis of idealised slab-column connections typically used for design procedure and model development. • Low-cost shell FEA for punching shear assessment of reinforced concrete flat plates. • Analysis of 45 non-idealised connection specimens representative of real-world construction. • Good agreement between FEA simulations and reported results without model calibration. • Result accuracy comparable to that obtained for more typical idealised connection specimens. [ABSTRACT FROM AUTHOR]

This paper studied the axial compression behavior of the steel tube reinforced concrete (STRC) column, which consisted of inner CFST and outer RC components. Ten specimens, including seven STRC columns, two RC columns, and one CFST column were tested. The test parameters included the CFST area ratio (inner CFST to the whole section), longitudinal rebar ratio and stirrup space. The test results showed that the compressive behavior of STRC column with a CFST area ratio of 0.04 was close to that of the RC column, and the compressive behavior of the STRC column with a CFST area ratio of 0.13 was between that of the RC column and CFST column. The finite element (FE) models were developed and verified by test results to investigate the effects of longitudinal rebar ratio and stirrup space on the axial compression behavior of STRC column with various CFST area ratios. The load distribution between inner CFST and outer RC components was analyzed. The FE results showed that the effects of the longitudinal rebar ratio on the ultimate load of STRC column were related to the CFST area ratio. The accuracy and applicability of the five methods suggested by codes for predicting the ultimate load of STRC column were discussed based on the test and FE results. • The compression test of steel tube reinforced concrete (STRC) column with low CFST area ratio was firstly carried out. • The influences of both CFST area ratio and longitudinal rebar ratio on ultimate strength of STRC column were discussed. • The refined finite element model of STRC column for parameter analysis is established. • The five methods of codes for ultimate strength of STRC column was calculated and discussed. [ABSTRACT FROM AUTHOR]

Metamaterial structures that exhibit negative stiffness (MSNS) behavior have shown the potential to be used as energy dissipation systems in different applications. Negative stiffness honeycomb structures consist of multiple pre-buckled beams that snapping through from one pre-buckled mode to another buckled mode, when subjected to transverse loads, displaying negative stiffness, and dissipating a significant portion of the input energy. This paper presents finite element models (FEMs) developed to investigate the performance of negative stiffness pre-buckled beams and honeycombs. The FEMs were validated using experimental results of single pre-buckled beams and honeycomb structures. The experimental testing of the pre-buckled beams was presented in the current study while the results of the honeycomb were available in the literature. The FEMs have the ability to capture the transition of the elements from one mode of buckling to another mode as well as the force thresholds, energy dissipation values, and residual displacements. The FEMs were extended to investigate the effect of different parameters such as boundary condition, apex height-to-beam thickness ratio, and constraining the second mode of buckling on the behavior of negative stiffness honeycombs. • Metamaterial structures that exhibit negative stiffness (MSNS) have potential for use in energy dissipation systems. • Finite element models (FEMs) are presented to study the performance of MSNS beams and honeycombs. • FEMs are validated using experimental results from single pre-buckled beams and honeycomb structures. • FEMs can accurately predict transitions between different modes of buckling, force thresholds, and energy dissipation. [ABSTRACT FROM AUTHOR]

The mechanical response of a wire strand is inherently complex because the helical wires undergo evolving stress and contact conditions as the strand is loaded. Further complications are added to the strand behavior if one or more of the wires break due to strand degradation over time. Although a detailed investigation on strand behavior is critically important for predicting the capacity of a broken strand as well as developing new monitoring approaches for wire break detection, there is little study available in the literature on wire breakage in a stressed strand. This paper provides an extensive investigation on stressing and post-breakage dynamic behavior of a prestressing strand. A finite element model is generally useful to study the global strand response, along with many localized phenomena that have strong influence on its performance, but are difficult to capture either experimentally or through closed-form analytical models. Investigations on certain behaviors, such as wire breaks, however, require a relatively large or even a full-scale model to adequately develop contact and frictional conditions. Moreover, such a sizeable model can account for any deviation points and may avoid edge effects. Consequently, several finite element parameters, such as the load ramp profile and duration, effects of damping and interwire friction, become critical for an accurate and efficient model. This paper first presents the use of a parametrized model to study strand behavior and evaluates the effects of these modeling parameters on strand response; load distribution and redistribution among the wires at the onset of interwire motion are also considered. The model is then used to simulate wire breakage in a prestressing strand, so that various aspects of post-breakage response can be examined. Numerical results show that a linear load ramp or stressing too quickly may lead to an inaccurate axial tension developed in the strand, whereas the inclusion of nominal mass-based damping has been found effective in achieving a quasi-static solution at a reasonable computational cost. In addition, the wire break simulation results indicate that breakage of an outer wire results in greater prestress loss than breakage of the center wire, which might have important implications for non-destructive wire breakage detection. [ABSTRACT FROM AUTHOR]

Abstract: This study is the first of two companions papers that present a finite element (FE) model of timber-frame structures. It introduces a versatile hysteretic constitutive law developed for various joints with steel fasteners commonly used in timber structures (nails, screws, staples, bracket-type 3D connectors, punched plates). Relative to previous models available in the literature, the proposed model improves numerical robustness and represents a step forward by taking into account the damage of joints with metal fasteners. More than 300 experimental tests are carried out on joints and used to calibrate the constitutive law for nails and bracket-type 3D connectors. An average calibration method is presented to take into account the experimental variability. 14 experimental tests are performed on different configurations of shear walls and are used to validate the proposed FE model. Both monotonic and reversed cyclic loadings are used in these quasi-static tests. The FE model predictions are in good agreement with the experimental results. The second paper will present dynamic experiments and numerical predictions of the tests, as well as the development and validation of a computationally efficient simplified modelling of timber-frame structures based on a simplified finite element model for shear walls. [Copyright &y& Elsevier]

Highlights • A finite element study of the out-of-plane behaviour of masonry infilled RC frames. • A 3D non-linear finite element model was developed. • Experimental results of four infilled RC frames were used in model validation. • Effect of several geometric parameters on infill strength was described in detail. Abstract The paper presents results of a finite element (FE) study of several critical geometric parameters on the out-of-plane behaviour of concrete masonry infills bounded by reinforced concrete (RC) frames. The development of FE model adopted a three-dimensional simplified micro-modeling technique considering detailed geometry and behaviour characteristics of concrete and masonry units through Concrete Damaged Plasticity (CDP) method. The surface-based cohesive interaction was incorporated to capture the behaviour and failure mechanisms of mortar joints. A concurrent experimental study was also conducted on four infilled RC frames and the results were used to validate the FE model. The model was shown to be capable of simulating accurately the out-of-plane behaviour and strength as well as capturing the cracking pattern and failure modes of infilled RC frames for different geometric and loading situations. The parameters considered in the FE study included infill aspect ratio, infill slenderness ratio, bounding frame stiffness, frame-to-infill interfacial gap, infill opening size and aspect ratio, and web thickness of masonry blocks. The numerical results showed that the out-of-plane behaviour of infilled RC frames was dependent on these parameters and the correlation between each parameter and its effect on the infill strength was described as appropriate. [ABSTRACT FROM AUTHOR]

Highlights • Nonlinear finite element model of built-up section were developed and verified. • A proposed design approach is presented using direct strength method (DSM) • The proposed approach is evaluated by comparing with the current existing method and FEA data. • A parametric study showing the influence of D1/B ratio on the stability and strength of the built-up columns. Abstract This paper, based on new proposed approaches, is a numerical investigation of the behavior of thin-walled cold-formed steel built-up columns under a uniform compression. Two types of cross sections have been studied, built-up closed and open sections formed by two channels connected by battens plates. First, a nonlinear finite element model has been developed and the results obtained show a good agreement against experimental results, such as the ultimate strength, the type of deformed shapes at failure and the lateral displacement. Second, a new proposed approach based on the DSM approach where the local, distortional or global buckling has been obtained numerically, using finite element method software, the thickness at the contact area in the web is taken as 1.0 times the thickness of the plate "t", instead of 1.5 or 2.0 times "t". In this case, the compound section is acting as one rigidly connected section. Comparisons with experimental data give a satisfactory degree of accuracy in the proposed design method (DSM-t) and the results are more conservative than those found by the DSM-1.5 and DSM-2. The results, for either closed or open sections, are also slightly conservative for columns failing in global modes than in local ones, if compared with the AISI and EC3 specifications. Some parameters, such as the spacing channels-web length ratio (B1/D) influence the stability and strength of the built-up columns. [ABSTRACT FROM AUTHOR]

Abstract: The direct design method recommended by ACI is commonly used for the design of flat slabs. Since the flexural stiffness of the waffle slab varies along the span, it is expected that the distribution of moments is different from that of flat slabs. Current design procedures do not provide recommendations specific of waffle slabs. Designers smear the contribution of the ribs and use the design guidelines for flat slabs to design ribbed slabs. In addition, the effect of openings on the response of waffle slabs is not fully explored. Therefore, modified moment coefficients are needed for waffle slabs. In this paper, numerical simulations using ANSYS are used to study the response of waffle slabs with and without openings. The main objectives of this paper are: (1) to obtain the design coefficients for the column and the field strips of the internal panel of a waffle slab and (2) to study the effect of openings and stiffening ribs on the design coefficients. Ninety Linear and non-linear analysis models using ANSYS were performed in the study to evaluate the response of various waffle slabs under uniform loading. The main parameters evaluated are the column size, the solid portion size, the opening size and its location, and the effect of stiffener ribs around the opening. The non-linear finite element model was verified using existing experimental results for two waffle slabs. The moment coefficients developed in this paper were used to modify the existing ACI flat-slab coefficients to be used for waffle slabs. [Copyright &y& Elsevier]

Abstract: This paper presents a methodological approach for finite element simulation of pretensioned concrete members. The three-dimensional analysis presented in this paper involves a rectangular [150 mm (6 in.) tall × 150 mm (6 in.) wide × 2440 mm (96 in.) long] concrete member hosting one 15-mm (0.6 in.) diameter 7-wire low-relaxation Grade 1860 MPa (270 ksi) prestressing strand. The finite element models are divided into two general classifications: (i) concentrically pretensioned, and (ii) eccentrically pretensioned. The finite element models are analyzed based on elastoplastic material behaviors as well as mesh sensitivity. Two approaches are examined for finite element modeling of the pretensioned concrete specimens: (i) the extrusion technique utilizing friction-based contact simulations, and (ii) the embedment technique simulating equivalent responses while being a computationally less expensive solution. A comparative analysis is presented to measure the validity as well as accuracy of the findings by the finite element techniques against the commonly used closed-form solutions based on elastic beam theory. The validity of the finite element approach is further verified by comparative analysis of the analytical data against the experimental findings. The paper concludes that the embedment technique provides an accurate and numerically efficient alternative in comparison with the extrusion method for the simulation of the pretensioned concrete members. While the extrusion technique provides more detailed information corresponding to the regions located immediately around the prestressing strands, including the interface overstresses and bond slippage, the embedment technique appears to have the ability to simulate the overall response of the concrete members with comparable accuracy. [Copyright &y& Elsevier]

Abstract: The effect of structural boundary conditions and explosive spalling on performance of concrete elements in fire is still an area of interest within the research community. This paper presents the results of experimental research executed on 30 high strength concrete columns. The parametric study investigated the high strength concrete columns under five loading levels (0.2, 0.3, 0.4, 0.5 and 0.6) subjected to two heating rates, with special attention directed towards explosive spalling. The second part of the paper represents a three-dimensional finite element (FE) model of the reinforced concrete columns, taking into account exposure to high temperatures. The effects of tension softening are included in the model and are based on the Hordjik, Cornelissen and Rienhardt curve. The concrete columns were modelled taking into account the embedded reinforcement and crack formation and propagation using the smeared cracks model, which allowed a nonlinear transient structural analysis to be conducted. The comparison of the results of the FE analysis and the tests performed showed a reasonable agreement and a divergence in some cases due to concrete spalling. An assessment of stresses generated in the high strength concrete columns under fire using the FE model is also presented in the paper. The evaluation shows that mechanical and thermal tensile stresses could reach up to 8.69 MPa, which is high enough to cause concrete spalling. [Copyright &y& Elsevier]

Abstract: The establishment of a baseline is essential for long-term structural health monitoring and performance evaluation. Usually, field testing data and finite element (FE) model are two critical tools used to develop the baseline. In this paper, the establishment of the baseline field database for a curved post-tensioned concrete bridge with expansion bearings is first introduced to include the effect of varying temperature conditions on the field testing data. This database uses data collected from a full year and is based on an undamaged status. The development of a baseline FE model for the bridge is then discussed. Model updating for the FE model are detailed in this paper which includes calibration of material properties, utilization of spring bearing elements, and replacement of Mindlin plate elements (MP4) on box–girder by recently developed cracked Mindlin plate elements (MP4C) to represent the bridge service conditions. A good agreement in modal results has been observed between the baseline FE model and the baseline field data. The proposed structural health baseline can be used for near real-time damage detection, development of monitoring techniques, and condition assessment. Finally, as an application of the baseline, this FE model is used for an earthquake simulation with a selected ground motion on the bridge. The seismic analysis demonstrates the beneficial effect of the guided expansion bearings on the bridge deck in the longitudinal direction. [Copyright &y& Elsevier]

Abstract: This paper presents experimental and numerical investigations of pre-stressed concrete filled circular steel tube columns by means of expansive (PCFT) under eccentric loading. Conventional concrete filled steel tube (CFT) specimens are also tested in this paper just for comparison purposes. Based on the steel follow-up strengthening and concrete bounding surface constitutive relationships, this paper writes a nonlinear finite element program for calculating complete load mid-height deflection curves of eccentrically loaded PCFT/CFT columns. A good agreement is obtained between the calculated and test results. The results indicate that the eccentrically loaded PCFT columns generally have higher load carrying capacities than the CFT ones when other parameters are kept the same. But by increasing the load eccentricity ratio, the difference of load carrying capacity between them decreases. Other factors such as pre-stress, load eccentricity ratio, and steel ratio, etc. are also investigated. [Copyright &y& Elsevier]

Abstract: In this paper, the nonlinear finite element model developed and verified in the companion paper [Son J, Fam A. Finite element modeling of hollow and concrete-filled fiber composite tubes: Part 1 — model development and verification in flexure. Engineering Structures 2008;30(10):2656–66] has been used to study fiber-reinforced polymer (FRP) tubular poles partially filled with concrete in flexure. Partial filling is proposed as a low-cost alternative to using thicker-walled tubes, to enhance flexural strength and stability. The partial concrete fill length is optimized in cantilever-type mono-poles for tubes with different diameter-to-thickness () ratios and different laminate structures. It was found that this optimum length is reduced in any one of the following conditions: as ratio becomes smaller, when fiber angles relative to the longitudinal axis in angle-ply tubes increases, when longitudinal fiber fraction in cross-ply tubes reduces, and when a laterally distributed load is applied instead of a point load at the tip. Simple expressions were established to calculate moment capacities of hollow and concrete-filled FRP tubes. They were then incorporated into a simple design approach developed to predict the optimum concrete fill length, on the basis of that failure occurs in the concrete-filled and hollow parts simultaneously. A procedure to account for tapered poles is also presented. [Copyright &y& Elsevier]

Abstract: The “Nuki” joint is a common timber connection in Japan, not only for historic buildings, but also for modern domestic houses. Its racking performance is dependent upon a number of factors, such as dimensions of the column and the beam, material properties of the joint members, and wedge configurations, etc. Among them, the wedge configuration, which leads to various tightnesses in the joints, may be the most influential factor on the structural behaviour during the service life. Various tightnesses introduced by wedges with different over-sizes introduce different initial stress states and stiffnesses to the joint, which have significant effects on the racking resistance of the joint. In this paper, 3D non-linear finite element models were developed to simulate racking resistance of joints tightened by different over-sized wedges. The models incorporate contact algorithms capable of modelling small slide and finite slide in different contact areas, especially large local indentations on the beam. Orthotropic elasticity was used to simulate the beam and the column in tension, whilst elasto-plasticity was used to simulate interactions in the contact zones where high contact stresses were expected. Contact stresses on both the beam and the column, also strains on the column, were studied. Finite element simulations of racking resistance of the joints with various initial conditions were compared with the corresponding experimental results. Reasonable correlation was obtained. Research on the initial stress states of “Nuki” joints was presented in Part 1 of this paper. [Copyright &y& Elsevier]

Abstract: Initial conditions introduced by different wedges in a traditional Japanese “Nuki” joint affect its stiffness and load carrying capacity significantly. Due to the complicated nature of the problem, no proper measurements have been undertaken historically, nor has there been theoretical modeling of the initial stress state in the joint. This leads to a lack of full understanding in the critical regions where high contact stresses are generated by locking wedges into various engaged positions. There is a need to undertake quantitative studies in those regions in order to make better designs and assist renovation of this type of the joint. In the work described in this paper, a series of experiments has been undertaken to investigate initial strain (and hence stress) states of the “Nuki” joint induced by the use of wedges with a typical angle but various tightnesses. A large number of strain gauges were used to obtain strain distributions in critical areas of the “Nuki” beam element. In Part 1 of the paper, 3-D nonlinear finite element models were developed to simulate the wedge insertion processes and the initial strain (stress) states. Numerical simulations were compared with the corresponding experimental results yielding reasonably good correlation. Racking resistance of the “Nuki” joint will be presented in Part 2. [Copyright &y& Elsevier]

Abstract: The combined effect of beam-to-column joint semi-rigidity and partial interaction in steel–concrete composite beams is considered in the present paper in order to quantify the relative importance of these two phenomena both affecting the global behavior of composite frames. A finite element model formulated by the authors in a previous paper is able explicitly to simulate partial interaction in composite beams and is extended herein with the aim also of analyzing framed structures, even those with semi-rigid beam-to-column joints otherwise called Partially-Restrained frames (PR-frames in the following). Final applications are devoted to point out the relative importance of partial interaction effect with respect to the well-recognized role played by joint semi-rigidity. Assessment of code provisions and alternative proposals are finally exposed for taking account of the effect of the former phenomenon on structural behavior. [Copyright &y& Elsevier]

This paper presents a procedure for the evaluation of the seismic damage in steel moment frame buildings. The rotational capacities, of typical connections of a building in the Los Angeles area, which suffered extensive damage during the Northridge earthquake, were determined using stress triaxiality as an indicator for fracture. The rotational demands of the same connections were obtained from a three-dimensional finite element analysis of the building model. Comparisons of the rotational demands at several locations in the building to the rotational capacities determined by the stress triaxiality analysis showed that fracture of steel moment connections of the building are governed by the triaxiality of stresses. Based on a number of moment connections analyzed, the paper suggests a moment capacity equation for the pre-Northridge welded steel moment connections taking into account the fracture incidence due to stress triaxiality effect. The moment capacity of such connections as dictated by stress triaxiality compared favorably to FEMA-350 requirements. [Copyright &y& Elsevier]

Whereas many publications report on alkali aggregate reaction (AAR) expansion or test analyses, very few address the more pressing issue of its impact on structures. Furthermore, given the uncertainties associated with characterization of the material, probabilistic based approach are not known to have been reported in the literature. This paper addresses these limitations through an analysis of a reinforced shear wall. A two-prone approach is followed: first a sensitivity analysis is performed to narrow the number of random variables (RVs) to the most relevant ones. Then, an uncertainty quantification is performed through Latin Hypercube Sampling with and without AAR expansion. Then the capacity curves (including the summarized ones to 16, 50 and 84% fractiles) are developed. Probability of non-exceedance of a specific capacity (i.e., limit state) is shown though the so-called fragility curves. It is found that in some cases AAR increases the shear capacity, while in others it decreased it. It highly depends on the initial combination of the RVs. [ABSTRACT FROM AUTHOR]

This paper presents a finite element analysis to determine the influence of geometrical properties of adhesive joints on the vibrational response of a metallic beam doubly supported on adhesive joints. This research is based on a previous experimental analysis in which it was concluded that larger experiments or numerical simulations are necessary in order to separate and investigate the influence of length, thickness and material of the adhesive joint. The finite element model is previously validated using experimental results for the transient response, mode shapes and transmissibility functions. Then, for the study, the model of the beam is seismically excited and the influence of joint thickness, overlapping length and adhesive properties on the beam motion is analyzed using the root mean square value of twenty-one transmissibility functions obtained from across the length of the beam. The study analyses resonance frequencies, peak amplitudes, and modal loss factors. [ABSTRACT FROM AUTHOR]

• Investigation of long-term effects on displacement and cracking of RC flat slabs. • Finite element modelling and analytical prediction of long-term displacements and cracking of RC flat slabs. • Validation of the numerical and analytical approaches with experimental tests. • Calculation of a simplified multiplicative coefficient to obtain long-term deflections. The Serviceability Limit States (SLS) of reinforced concrete structures, where cracking and deflection limits are verified in the design process, are directly related to time-dependent properties of concrete. In this study, the effects of creep and shrinkage of concrete, implemented in a Finite Element Model for Non-Linear Analysis, are in-deeply investigated for reinforced concrete flat slabs at SLS and used as basis for the development of an analytical framework. In particular, the paper focuses on: (i) the description of the FE model, (ii) the comparison between the numerical and experimental results of some reinforced concrete (RC) flat slab tests from literature characterized by different mechanical properties, span-to-depth ratios, boundary conditions and loading histories and (iii) the development of an analytical framework for the evaluation of long term-term deflections and crack openings in hogging regions of flat slabs near columns. Based on the findings, useful insights for the evaluation of the long term-term deflections and crack opening in the context of Serviceability Limit States are provided for practical purposes. [ABSTRACT FROM AUTHOR]

Finite element analysis was first used to replicate the inelastic cyclic test response of previously tested concrete filled steel sandwich panel (CFSSP) walls, to determine the material and contact models best able to capture the wall’s initial stiffness, the ultimate wall strength at each cycle, the web plate and HSS local buckling, and the pinching in the hysteresis loops. Results obtained show good agreement with all those aspects of response, while providing insights, guidance, and a validated model that will be of benefit in future studies of CFSSP-Walls. In a second part of this paper, the calibrated finite element model is used to provide insights and generate knowledge on some important aspects of wall behavior that is valuable for the design of CFSSP-Walls. Designers of CFSSP-Walls are typically provided little prescriptive guidance by design specifications and must instead rely, to a large extent, on findings from the recent research literature to ascertain that designs will perform as intended. For this new structural system, such insights into structural behavior are severely lacking. The findings here provide such insights on the distribution of wall-to-footing forces, shear force demands in critical tie bars, cumulative plastic strain value at failure due to low-cycle fatigue, the effect of hoop and shear stresses on uniaxial steel plate yielding, and the effect of interface friction on the force flow within boundary elements. These allow research to verify the adequacy of many of the assumptions used to determine the wall’s plastic moment, which is typically considered to be the flexural strength of CFSSP-Walls. [ABSTRACT FROM AUTHOR]

This paper detailed the development of a numerical model for simulating the nonlinear behaviour of the concrete masonry infilled RC frames subjected to in-plane lateral loading. The ABAQUS finite element software was used in the modeling. Nonlinear behaviour as well as cracking and crushing of concrete and masonry blocks were simulated using the Concrete Damaged Plasticity (CDP) model. The cohesive element method combined with hyperbolic Drucker-Prager and shear and tensile failure criteria were used to capture the possible failure mechanisms in mortar joints. Concurrent with the finite element modeling, an experimental study was also conducted and results of masonry infilled RC frame specimens incorporating infill openings and interfacial gaps were used to validate the model. The validation showed that the model can accurately simulate the behaviour and predict the strength of masonry infilled RC frames. A sensitivity study was subsequently conducted where the influence of mortar joint failure surface parameters, mortar dilatancy, and fracture energy on the lateral behaviour of infilled RC frames was investigated. Results showed that the in-plane behaviour of infilled RC frames was significantly affected by the input parameters of mortar failure surface and dilatancy and less affected by those of mortar fracture energy. [ABSTRACT FROM AUTHOR]

This paper is concerned with the shear capacity of keyed joints reinforced with overlapping U-bar loops in the transverse direction. The layout of the loop reinforcement affects the capacity and failure mode, and currently it is not accounted for by standards or previous theoretical work. A multiscale approach to the issue is proposed: An equilibrium element for finite element limit analysis representing keyed joints is coupled with a suitable submodel, which handles the complex stress states within the joint. The submodel is based on several modified stringer models, which makes it possible to account for local mechanisms in the core of the joint. The element and submodel are validated by comparison to a detailed model based on finite element limit analysis and experimental data. The joint element and submodel lead to a small optimisation problem compared to the detailed model and the computational time is reduced by several magnitudes. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and numerical study of semi-supported steel plate shear walls which are connected to frame beams and a pair of secondary columns. As the infill plates are not connected to the frame primary columns, the large stresses due to tension field, causing the formation of plastic hinges in the primary columns, are avoided. In order to intensively investigate the structural mechanism of this new type of shear walls, eight specimens were tested under reversed cyclic lateral load. The effects of four perforation diameters as well as two slenderness ratios of infill plates on the seismic behavior of SSSWs were studied experimentally and numerically. All the specimens exhibited satisfactory cyclic inelastic and energy dissipation, thereby indicating an alternative to traditional steel shear walls. Based on the test results, the strength, stiffness, ductility factor and energy absorption characteristics of the specimens were substantially reduced in specimens with openings. Maximum strength reduction, stiffness loss and ductility deterioration in the perforated specimens were 42%, 61%, and 33%, respectively. Deteriorating pinched hysteresis was observed due to the occurrence of cyclic out-of-plane buckling and tension field action. In addition to the test program, complex elastoplastic FE models of the eight specimens were developed to investigate in detail the cyclic behavior of semi-supported steel plate shear walls. Excellent agreement was observed between the experimental and numerical results. [ABSTRACT FROM AUTHOR]

Conical vessels are used around the globe for liquid storage in water tanks. These vessels can be made of steel, reinforced concrete, or composite; i.e. concrete and steel. Composite vessels consist of an external steel shell attached to an internal reinforced concrete wall through steel studs. Previous studies available in the literature focused on studying steel or reinforced concrete vessels. To the best of the author’s knowledge, this paper presents the first comprehensive study conducted on liquid-filled composite tanks. A Finite Element Model for Composite tanks (CFEM), which accounts for both the geometric and material nonlinearities, is developed. The material nonlinearity is considered by including nonlinear models for both steel and concrete. The developed CFEM also considers nonlinear behaviour of studs by including the nonlinear load-slip and load-peel curves obtained from test results reported in the literature. In the CFEM, both the concrete and steel walls are modelled using 13-node subparametric shell elements, while the connecting studs between the two walls are modelled using 26-node contact elements using a smearing approach. Validation of the CFEM is conducted by modelling two composite slabs from the literature and comparing the results with their counterparts obtained from the conducted experiments. The CFEM is used to evaluate the deflections, stresses, and internal forces in the concrete and steel walls as well as steel studs. An Equivalent Section Method (ESM) for the analysis of composite tanks, which is based on using an equivalent single wall, is introduced. Deflections, stresses, and internal forces in the steel and concrete walls predicted using this simplified approach are compared to those predicted by the detailed finite element model. [ABSTRACT FROM AUTHOR]

The Basilica of Collemaggio in L’Aquila is one of the outstanding architectural heritage in Abruzzo Region. The church, built in the late XIII century, has experienced many earthquakes during its life, some of which caused damages to the masonry structures, requiring continuous interventions and renovations. The last strong earthquake (April 6th, 2009) caused the collapse of the transept structures and significant damages in the apses area. Since 2009, several research groups have focused their attention on the Basilica, both from architectural and structural point of view. Particularly, recent studies have pointed out the historical value of nave columns, which seem to be XIII century authentic elements. Despite the magnitude of the last earthquake, the columns have proved limited resistance against seismic loads, resulting in a widespread damage, but without reaching the collapse. The aim of the present paper is to understand their structural behavior under horizontal actions. An overall finite element model of the church has been developed to perform eigenvalue and response spectrum analyses of the Basilica. Afterwards, a representative nave column has been studied considering both geometrical and mechanical non-linearity. In order to obtain a reliable evaluation of its structural behavior, two different models have been developed: an analytical model and a solid-brick finite element one. The performed analyses have allowed the evaluation of the stresses redistribution inside the columns after cracking. The results, provided in terms of force–displacement curve and stress contours, have permitted to identify some possible explanations about the columns seismic response. [ABSTRACT FROM AUTHOR]

Eduardo Torroja was one of the most innovative structural engineers of the 20th century. His legacy can be seen in the form of some of his remaining works and the memory of others that have now disappeared. Torroja’s structures have attracted a lot of attention in recent years, thanks in part to the publication of studies on some of his projects, such as, for example, the Frontón Recoletos, the Zarzuela Racecourse and the San Nicolás Church. However, up to now very little attention has been paid to his other legacy, consisting of designs that were never actually built. Some of the most important of these designs include the roof of the Tachira Club in Caracas, Venezuela, and the roof of the CASA factory in Seville, Spain. This paper studies in detail the CASA factory roof, which is a little known structure designed by Torroja in 1938. The roof covers a space measuring 230 m × 81.4 m in plan with a series of vaulted shells supported by parabolic arches. The study starts with a finite element analysis of the roof subjected to its self-weight, which helps to better understand the roof’s general structural behaviour. Then the roof reinforcement is obtained considering both the loads and materials used by Torroja and the loads and materials suggested by current building codes. The comparison of the results of both procedures leads to some interesting conclusions, and clearly shows the technical problems of building today the innovative designs that Torroja successfully built in his time. Finally, the roof is also analysed from the perspective of Structural Art, which is important in the development of the discipline of structural criticism, and demonstrates the inspirational power of the best works of structural engineering. [ABSTRACT FROM AUTHOR]

Post-tensioned (PT) steel frames, in which beams are connected to columns through high-strength PT strands, have been successfully developed in the past decade as a novel earthquake-resistant structural system. Compared to conventional steel moment frames, a PT steel frame demonstrates superior seismic performance, notably the minimum damages in main structural components and the self-centering capability under a design basis earthquake. Despite the abundant research on the seismic behavior of PT steel frames, there is an apparent lack of study on their load-redistribution behavior upon the notional removal of critical load-bearing columns, a commonly used threat-independent local structural damage scenario that potentially triggers the progressive collapse of the column-removed frame. This paper presents a first-of-its-kind numerical investigation on the unique structural behavior of PT steel connections and frames in redistributing the unbalanced gravity loads due to column removal. High-fidelity finite element structural models are constructed and validated using the available experimental data in the literature. The capacity of PT steel frames subjected to a gradually increasing vertical displacement along the removed column line is systematically studied. It is found that, besides the resistance of energy-dissipating elements, beam arching action and strand catenary action are the major sources of structural capacity of a PT steel frame against progressive collapse. The corresponding failure modes are identified and the design implications are suggested. [ABSTRACT FROM AUTHOR]

Elevated conical tanks are widely used as water reservoirs in various locations around the globe. The vessel of a conical tank can consist of a truncated cone solely or a truncated cone with a top cylindrical part. Current codes of practice do not provide any provisions or guidelines for designing reinforced concrete conical tanks under hydrostatic loading. Available provisions are limited only to cylindrical and rectangular tanks. In this paper, a nonlinear Finite Element Model (FEM), based on shell element discretization, is used to analyze hydrostatically loaded reinforced concrete conical tanks. A common simplified approach used in the design of conical tanks involves replacing the conical vessels with equivalent cylinders. The adequacy of this simplified method is assessed in this study through comparison with the detailed finite element results. The FEM is then used to develop a set of charts which can be used to determine the adequate thickness as well as straining actions that develop in a liquid filled reinforced concrete conical tank. The use of this set of charts in designing reinforced concrete conical tanks is illustrated through worked examples. [ABSTRACT FROM AUTHOR]

The tubed-reinforced-concrete (TRC) column is a relatively new kind of confined reinforced-concrete (RC) columns, where the outer encasing thin-walled steel tube is discontinued at the beam–column joint and thus the axial load is transferred to the RC core only. In this paper, the behavior of slender circular TRC columns under eccentric compression loads was studied. A total of sixteen specimens considering the following primary system parameters were tested: two slenderness ratios (24, 40), two load eccentricities (25 mm, 50 mm), two diameter-to-thickness ratios of the steel tube (133, 160), and two continuity conditions for the steel tube (continuous, discontinuous at mid-height). The test results indicate that the slender circular TRC specimens exhibit fairly ductile behavior and the discontinuity of the steel tube at mid-height has a small effect (≈5% on average) on the bearing capacity. A finite element (FE) model was developed to simulate the behavior of circular TRC columns under eccentric compression loads. The predicted load versus mid-span lateral displacement curves are generally in good agreements with the measured ones. To identify the influence of the key parameters on the second order effects of circular TRC columns, an extensive parametric study was carried out using the FE model. Lastly, a regression formula is suggested to estimate the moment magnification factor and simplified design equations for slender circular TRC columns under eccentric compression loads are proposed based on the section capacity analysis. [ABSTRACT FROM AUTHOR]

Fiber-based section analysis methods are widely used to model and predict the fundamental axial force-bending moment-curvature ( P - M - ϕ ) behavior and the strength interaction ( P - M ) of concrete-filled steel tube (CFT) members. The accuracy of these predictions is governed by the uniaxial effective stress-strain relationships assumed for the steel tube and concrete infill of the CFT section. Prior research has developed these effective stress-strain relationships for compact CFT members. This paper presents the development and verification of effective stress-strain relationships for the steel tube and concrete infill of noncompact and slender CFT members. These relationships are developed using results from comprehensive 3D finite element analyses of CFT members with a wide range of geometric and material parameters. The 3D finite element models, which were developed and benchmarked previously by the authors, accounted explicitly for the effects of steel yielding and tube local buckling, concrete cracking and compression inelasticity, and the transverse interaction leading to steel hoop stresses and concrete confinement. As a result, the developed effective stress-strain relationships also accounted (implicitly) for these complexities (yielding, local buckling, confinement, etc.) of behavior. These effective stress-strain relationships are implemented in a nonlinear fiber analysis (NFA) macro model, and used to predict the behavior of noncompact and slender CFT members in the experimental database. The conservatism of the predictions using the effective stress-strain relationships is evaluated. [ABSTRACT FROM AUTHOR]

Bi-concave cable truss systems are not only aesthetically appealing but they also offer elegant solutions for spanning large spans required in modern buildings such as convention centres, sport arenas and bridges. These structures, however, are notoriously difficult to model correctly using non-numerical based methods. The existing analytical methods are limited to uniformly distributed loads on half or the entire span, and do not include the stays in the calculations. This paper details a novel analytical method that not only covers wide spectra of loads, including both uniformly distributed and concentrated loads on any part of the span, but also includes the stays in the calculations. The mathematical formulation was based on the fundamental assumption that the hangers form a continuous and inextensible diaphragm. The main two nonlinear equations describing the cable thrusts, unknowns of the problem, were calculated using an orthogonal displacement equation based on the boundary conditions of the cable ends at the anchorages. The predicted results are compared to finite element analysis, and good agreement was found across all the load configurations. The presented method was found to be very efficient and reliable. [ABSTRACT FROM AUTHOR]

In this paper, the forced nonlinear dynamic behavior of thin-walled beams with open cross section under external dynamic loads is analyzed by means of a high order implicit algorithm. This algorithm is developed using a 3 D nonlinear model that takes into account the large torsion without any assumption on the torsion angle amplitude neither in the constitutive law nor in the derivation for governing dynamic equations. This algorithm is built by employing the following four steps: 1 – the space and time discretization procedures, 2 – a change of variable, 3 – a homotopy transformation, 4 – techniques used in the Asymptotic Numerical Method (ANM) (Cochelin et al., 2007; Mottaqui et al., 2010) [1,2]. The originality of this work reside in the fact that we use, for the first time, this algorithm for nonlinear analysis of thin-walled beams with open cross section under an arbitrary load. The space and time discretizations are performed respectively by the finite elements method and by the classical implicit Newmark scheme. The performance of the high order implicit algorithm is tested on four examples of nonlinear dynamic: a mono-symmetrical beam with a T cross section under external dynamic load, a mono-symmetrical beam with U cross-section under external dynamic load, a bi-symmetrical clamped-free beam IPE 300 under harmonic loads and a bi-symmetrical simply supported beam with cruciform section under harmonic loads. A comparison of the obtained results with those computed by the Abaqus industrial code is given. This comparison confirms the robustness, accuracy and efficiency of this high order implicit algorithm. [ABSTRACT FROM AUTHOR]

This paper presents a numerical investigation into the buckling behaviour of cold-formed steel zed purlins when subjected to transverse distributed uplift loading. The study uses both linear and non-linear finite element methods (ABAQUS shell Finite Element analyses) to investigate the pre-buckling, buckling and post-buckling behaviour of zed-section purlins in purlin-sheeting systems. The numerical modelling strategy is carefully validated using the results of available experimental data. Influences of boundary conditions and restraints from sheeting on web shear buckling, local, distortional and lateral-torsional buckling behaviour, and the buckling interactions of the purlins are discussed. Furthermore, the strengths and failure modes of the purlins obtained from numerical results are compared with the design strengths predicted using the direct strength method (DSM) specified in the ‘North American Specification’ (AISI S100). The comparisons show that the ultimate strengths of buckling interactions are generally underestimated. Hence, the DSM is modified to cover the partially restrained zed-sections in purlin-sheeting systems. [ABSTRACT FROM AUTHOR]

• Trucks traveling in the same lane can generate the most unfavorable stress reversal. • The maximum stress range of details in OSD may be underestimated by more than 40%. • A high-efficient loading scheme is proposed to obtain accurate maximum stress range. • The fatigue life of OSD may be overestimated by 95% if stress reversals are ignored. • The LWCD shows a better anti-fatigue performance when subjected to stress reversals. The effect of stress reversals, generated by vehicles passing the bridge deck in sequence from different transverse locations, has been underestimated or even ignored in the fatigue life evaluation of orthotropic steel decks (OSDs), which may result in an overestimated fatigue life of the whole bridge. In this paper, four distribution patterns of vehicle transverse locations were considered and the effect of stress reversals on the fatigue evaluation of a conventional OSD (COSD) and a lightweight composite deck (LWCD) was investigated from infinite-life and finite-life perspectives based on finite element analysis. The results show that the maximum stress range could be underestimated by over 40% if the most unfavorable stress reversal is underestimated. A convenient and efficient vehicle loading scheme was proposed to determine the accurate maximum stress range for the infinite fatigue life evaluation of OSDs. Besides, the stress reversals are found to have a significant effect on the finite fatigue life evaluation of both the COSD and the LWCD, and the fatigue life of COSDs could be overestimated by 95% if the stress reversals are ignored. Nevertheless, the effect of stress reversals on the finite fatigue life evaluation of the LWCD is much less than that of the COSD, which indicates a better anti-fatigue performance of the LWCD over the COSD. In addition, the stress reversals induced by overloaded trucks have a significant effect on the fatigue performance of OSDs. The results from the study can provide some references for the fatigue design and evaluation of OSD systems. [ABSTRACT FROM AUTHOR]

• Beech and Corsican Pine short chain supply hardwood was used to realize glulam beams. • Bending and shear test were performed. • Hybrid Beech-Corsican Pine glulam beams show high flexural mechanical performances. • Hypotheses have been formulated to extend the validity of the formulations of EN 14,080 also to homogeneous hardwood products. • Finite Elements analyses were carried out to compare C24 Spuce glulam beams with tested beams. This paper describes the results of an experimental investigation on novel homogeneous and hybrid beech-Corsican pine glue-laminated timber (glulam) beams made of short supply chain timber boards and melamine-based adhesive. The aim is to carry out the mechanical characterization of these glulam beams both in the homogeneous and in the hybrid configuration by four-point bending tests with different span to depth ratios of the specimens in order to differentiate bending and shear tests. The experimental results were fitted analytically as well as by means of Finite Element (FE) numerical simulations. Moreover, the stiffness of these novel beams is further evaluated, with respect to a comparison with a commercial product made of GL24h glulam. The experimental and numerical analysis point out the goodness of hardwood for the manufacturing of glulam beams, even in hybrid configuration in which the inner layers are made of low graded timber boards, with a great opportunity to optimize the raw material. [ABSTRACT FROM AUTHOR]

Fibre-reinforced polymer (FRP) offers an effective and convenient means to strengthen existing RC columns. However, classical mechanics could not have an accurate prediction of the lateral strain due to axial load, hence an assessment on the overall confinement effects of the FRP. The finite element (FE) method, on the other hand, can give a full picture of the stress and the strain developed at a typical cross-section from linear elastic to ultimate failure loads. In this paper, a finite element model for the nonlinear analysis of FRP-confined concrete columns is presented, in which concrete elements are formulated based on advanced constitutive models recently developed, and it is verified against specimens with rectangular sections from existing experimental studies. As a result, the non-uniform and anisotropic confinement effects within rectangular sections of different shapes are determined, and their significance on the overall behaviour of axially loaded concrete columns could be assessed. [ABSTRACT FROM AUTHOR]

This paper focuses on development of a simple frame finite element model for nonlinear analysis of timber–concrete composite (TCC) beams under long-term loads. The element formulation within the context of the force interpolation and modified fibre element is derived in which the partial interaction between the layers can be captured by discrete nonlinear springs at ends of the element. Further, a finite difference scheme is also developed to analyse variation of diffusion within the timber section with respect to relative humidity changes. Different long-term effects of timber, concrete and connection are taken into account and their formulations within the total secant approach and efficient step-by-step analysis are derived. The implementation of the proposed model in a 1D FE model is discussed and the long-term behaviour of TCC components and beams is verified with available test results from literature. [ABSTRACT FROM AUTHOR]

The influence of steel strain in bond–slip relationship has been the subject of recent literature, especially steel strain after yielding. This paper presents a new bond element for finite element packages which performs the bond–slip relationship, including steel strain effect. The developed element consists of an orthotropic four-node plane stress element whose constitutive material laws were changed. In order to verify the accuracy of this element several 2D numerical results were compared with experimental data. The results obtained with this element showed the need for its use to achieve good results and the relevance of steel strain effect on bond–slip relationship, especially in tension elements. [ABSTRACT FROM AUTHOR]

Understanding the behavior of steel frames under fire loading is critical since many recent events have demonstrated the vulnerability of steel frames to such hazard. Extensive numerical and experimental studies have been performed to investigate the behavior of various types of individual steel structural members, connections, and frames under fire conditions. However, the response of steel moment resisting frames with Reduced Beam Section (RBS) connection has not been previously studied under fire conditions. In this paper, a set of numerical models are developed and analyzed to assess the performance of low-, medium-, and high-rise moment resisting frames with RBS connection under single bay fire exposure. Global system response and local behavior of the heated beams, columns, and RBS connections are considered. The analyses demonstrate that global stability of the steel frames is not affected by single bay fire exposure. However, large axial force and deflection in the beams, yielding in the RBS connections, and buckling in the columns are observed at elevated temperatures. The results of the analyses can aid engineers in understanding the local and global response of steel moment resisting frames with RBS connection under fire loading. [ABSTRACT FROM AUTHOR]

This paper investigates the robustness of a parameter estimation procedure for nonlinear Finite Element (FE) model updating. Through this procedure, polynomial Response Surface (RS) models are constructed to approximate the response of a nonlinear FE model at every time step of the analysis. Subsequently, the optimization problem of model updating is solved iteratively in time which results in histograms of the updating parameters. With the assumption of White Gaussian measurement noise, it is shown that this parameter estimation technique has low sensitivity to the standard deviation of the measurement noise. In order to validate this, a parametric sensitivity study is performed through numerical simulations of nonlinear systems with single and multiple degrees of freedom. The results show the least sensitivity to measurement noise level, selected time window for model updating, and location of the true model parameters in RS regression domain, when vibration frequency of the system is outside the frequency bandwidth of the load. Further application of this method is also presented through a case study of a steel frame with bilinear material model under seismic loading. The results indicate the robustness of this parameter estimation technique for different cases of input excitation, measurement noise level, and true model parameters. [ABSTRACT FROM AUTHOR]

Abstract: A new self-centering steel post-tensioned connection has been proposed by the authors. The connection uses high-strength steel post-tensioned bars to provide self-centering behavior and steel energy dissipation elements that consist of cylindrical pins with hourglass shape to provide enhanced deformation capacity. Large-scale experimental tests showed that the connection has robust self-centering behavior by eliminating residual drifts and beam damage for drifts lower or equal to 6%. This paper presents finite element models which can be used to reliably assess the design and behavior of the connection. A simplified connection model was first developed using simple mechanics. This model can predict the connection stiffness and strength with reasonable accuracy, and enables the preliminary design of self-centering steel moment-resisting frames using the proposed connection. A detailed nonlinear finite element model was also developed. This model was calibrated against experimental results and found capable to trace the nonlinear cyclic behavior of the connection and capture all possible local failure modes. The calibrated finite element model was used to conduct a series of simulations to study the effect of different parameters on the connection behavior. The parameters studied include the adopted design procedure, beam reinforcing detailing, and the beam and column section sizes. [Copyright &y& Elsevier]

Abstract: This paper gives a detailed presentation of a generic three-dimensional discrete-finite-element model that has been constructed for reinforced-concrete frames with masonry infill using ANSYS. Appropriate experimental data available from the literature are utilised to verify the model. The reasons behind some of previously observed damage to infill-frames are given. A simple method is proposed to overcome convergence issues which are related to the Newton–Raphson algorithm. It is shown that the model can be employed to predict the behaviour of the infill-frame over a wide range of drift, and to interpret its response at various stages of in-plane or out-of-plane loading. [Copyright &y& Elsevier]

Abstract: Fatigue-crack formation in the web-gap region of multi-girder steel bridges has been a common occurrence due to differential deflections between girders resulting in diaphragm forces that subject the web-gap to out-of-plane distortion. However, bridge design specifications do not directly deal with distortion induced stresses. The objective of this paper is to examine the behavior of web-gap distortion of a skewed multi-girder steel bridge through field testing and finite element studies. The field test involved measurements of strains for eight load cases by using strain gages placed in the web-gap region and in the cross bracing adjacent to the web-gap. The results of the field test were used as a basis for the verification of developed finite element models. Critical spots in the web-gap were examined utilizing the finite element analysis. Retrofit methods that include the provision of a connection plate between the stiffener and the girder top flange, loosening of the bolts connecting the cross-bracing to the stiffener, and supplementing a stiffener plate opposite to the original stiffener side were investigated. The results indicated that the connection plate addition and loosening of bolts alternatives were effective in reducing induced strains and stresses in the web-gap region. The finite element study on the impact of web-gap height variation indicated an inverse relationship between web-gap height and induced strains and stresses with the shortest web-gap height resulting in the highest strains due to increased bending by diaphragm forces in the web. Influence surfaces for strains, diaphragm force and relative out-of-plane displacement provide insight into the behavior of web-gap distortion, and can be used to provide quick estimate of the effect of truck load positioning. Expressions developed that relate vertical stresses and relative out-of-plane displacements combined with measurements of out-of-plane displacements by transducers can be utilized for prediction of induced stresses at other critical web-gap regions of the bridge and at critical locations in the web gaps of similar bridges. [Copyright &y& Elsevier]