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This paper introduces a topology optimization approach based on the virtual element method (VEM), incorporating uncertainties. The objective of this optimization process is to design an optimal material layout for problems governed by linear elasticity equations to minimize the volume while satisfying probabilistic compliance constraints. The VEM is used to solve the boundary value problem in reliability-based topology optimization (RBTO). In the comparison between the VEM and the standard finite element method (FEM), a key difference emerges in the absence of explicitly defined shape functions tied to discrete degrees of freedom in VEM. Unlike FEM, VEM directly constructs the discrete bilinear form and load linear form without the need for computing shape function derivatives within the elements. This flexibility accommodates meshes with intricate geometries and arbitrarily shaped elements. The paper discusses the computational efficiency of VEM RBTO and explores the geometric impact of tessellations on converged topologies, demonstrating reduced susceptibility to checkerboard patterns compared to conventional quadrilateral elements. Additionally, the single-loop approach is examined, showcasing comparable accuracy to the first-order/second-order reliability methods (FORM/SORM) of RBTO using VEM. Numerical results for several problems that demonstrate the feasibility of the proposed method are presented. [ABSTRACT FROM AUTHOR]

Past research efforts have developed several self-centering beam-to-column connections for minimizing structural damage in steel moment frames after severe earthquakes. However, less focus has been on low-damage column base connections. Severe damage at the base of columns in conventional steel structures with moment frames is likely during an intense earthquake, rendering the building nonresilient. This paper evaluates the application of a recently developed viscoplastic damper in low-damage column base connections. The proposed viscoplastic damper is a rubber-steel core damper (RSCD), which consists of a high-damping rubber layer and several ductile steel bolts. The proposed column base connections prevent damage and inelastic deformations in the steel column and its base plate by allowing a rocking mechanism at the base of the column and limiting damage to easily replaceable steel bolts in the dampers. The paper discusses the design and behavior of the column base connections equipped with RSCDs. Continuum finite element models of RSCD dampers were developed and validated using experimental results. The rocking response was validated using experimental results for rocking columns with a silt damper. A total of 21 finite element models of rocking columns with RSCD were used to numerically examine the column response to combined axial loading and cyclic lateral loading. The influence of different parameters on the cyclic response of the proposed column base connections was also evaluated. These parameters are steel bolt diameter-to-length ratio (d/h), rubber thickness, column axial compressive load, number of bolts, and steel material type. The results confirmed the effectiveness of the proposed column base connection for minimizing damage to the steel column and its base plate. An optimal d/h ratio of 0.4 was found for the design of RSCDs. In addition, analytical formulas are presented to evaluate the yield and ultimate strength of the proposed column base connection, and the comparison with FEM results indicates that the presented mechanism has sufficient accuracy. [ABSTRACT FROM AUTHOR]

When designing steel members with nonsymmetric cross sections, it is essential to consider twisting effects when performing stability checks via second-order analysis according to the ANSI/AISC 360-22. Existing line-element formulations for nonsymmetric sections are mostly derived based on thin-walled assumptions, leading to an overestimation of member strength due to the inaccurate prediction of member behavior, especially when the cross sections have moderate wall thickness. This paper proposes an efficient line-element method for second-order analysis of steel members with nonsymmetric thick-walled sections considering the warping degree of freedom (DOF) and the twisting effects along with the transverse shear deformations. Additionally, a two-dimensional (2D) finite-element cross section analysis method employing the constant strain triangle (CST) element is developed to calculate the section properties for arbitrary cross sections, including the Wagner and the shear coefficients. The proposed method is implemented in the educational structural analysis software MASTAN2 and verified through two sets of examples. [ABSTRACT FROM AUTHOR]

Much of the current code provisions for designing slab-column connections against punching shear are based on empirically derived formulations based on tests of partial scale isolated slab-column specimens. Although many experiments have been conducted on shear reinforced concrete flat slabs supported on columns, due to cost or time constraints, there are still many parameters that have not been adequately studied in the laboratory. These tests can be supplemented by analytical results of properly calibrated nonlinear finite element analysis (NLFEA) to enhance the existing experimental database and formulate rational design recommendations for future codes. This paper presents a rational approach for calibrating an NLFEA model in ABAQUS using interior and edge slab-column connection specimens. The calibration includes a study to determine how to effectively model the shear reinforcement and shear reinforced area. This further includes a detailed analysis of the modeling of the shear reinforcing elements to ensure appropriate rotational capability of the shear reinforced region of the slab without significantly reducing the predicted capacity of the model. The calibrated models show good agreement with test data based on load-deflection, moment-curvature, and bolt strain behavior. [ABSTRACT FROM AUTHOR]

Pretensioned spun high-strength concrete piles usually use the traditional helical grooved steel bars as the main reinforcement, leading to insufficient ductility. Replacing prestressing steel bars with steel strands can effectively overcome the problem. To further enhance the overall seismic performance of the piles, pretensioned centrifugal spun concrete piles with combined use of pretensioned steel strands and nonprestressing deformed steel bars (PSRC piles) have been developed. This paper presents experimental and numerical investigations into the seismic performances of PSRC piles. Three full-scale PSRC pile specimens have been tested under lateral cyclic loading with different axial compressive forces, and the results are analyzed in detail and discussed. The influence of incorporating the deformed steel bars on the cyclic behavior of piles is examined with a comparison to the previous test results of the counterpart piles with only steel strands. A detailed finite element model of the PSRC pile specimens is developed and verified against the test results. Parametric analyses are then carried out using the validated model. The results show that the incorporation of nonprestressing deformed steel bars markedly improves the cracking behavior of the piles with much-diffused crack distributions. The combined use of steel strands and deformed bars also results in better deformation capacity as well as higher load-bearing capacity. By adjusting the concrete wall thickness and selecting a desirable ratio of prestressing steel strands and nonprestressing deformed bars, sufficient deformation and load-bearing capacities can be ensured with the piles. [ABSTRACT FROM AUTHOR]

This paper introduces a computational simulation scheme to describe the intrusion of corrosion-inducing chloride ions in prestressed bridge girders. This phenomenon impacts the durability of bridges in coastal zones or regions where deicing salts are used. The computational study is focused on two girders decommissioned from separate bridges in Virginia after 34 and 49 years of service. A time-dependent, nonlinear finite element scheme, accounting for coupled heat, moisture, and chloride transport, is formulated and used in the analyses. The model parameters are calibrated using data from material tests in the literature. Subsequently, two-dimensional analyses are conducted to determine the evolution of chloride in the girder cross-sections. Contrary to earlier studies using finite element analysis, which have been focused on laboratory specimens, the work presented herein is focused on reproducing the evolution of chloride ingress of actual bridge members, considering the local climate conditions through the use of temperature and relative humidity measurements from weather stations in the vicinity of the bridges. The simulations are found capable of capturing the actual chloride content at various depths from the surface, measured through titration tests. Further analyses indicate that using the simplified, design-oriented equations in the fib code may underestimate the chloride content during the lifespan of a bridge. A similar underestimation is observed if the impact of advective chloride transport is neglected in the finite element models. [ABSTRACT FROM AUTHOR]

Aeroelastic instability and buffeting are two wind-induced phenomena for long-span bridges. In the traditional method, aeroelastic instability and buffeting are analyzed separately. If geometric and aerodynamic nonlinearity are required, aeroelastic instability is normally calculated based on finite-element methods, and buffeting is carried out based on linearization of structural and aerodynamic nonlinearity. Then, the standard frequency-domain methods are utilized on the eigenvalue decomposition. However, for ultralong-span bridges, aerostatic deformation, aeroelasticity, and buffeting are strongly coupled. During buffeting, the bridge deck pitching will change both structural stiffness and aerodynamic loads; therefore, the nonlinearity should be included in the long-span bridge buffeting analysis. This paper establishes a reduced-order modeling procedure to simulate the wind-induced buffeting vibration for long-span bridges including the nonlinear aeroelasticity and buffeting force. First, the mode-based vibration formulas are derived to consider both structural and aerodynamic nonlinearity through polynomial expansion. Next, the numerically simulated turbulence is imported into the vibration governing equation, and the structural response can be calculated using the time-domain integration method. [ABSTRACT FROM AUTHOR]

Fire hazards are generally considered to be one of the major disasters that cause damage to grid structures, and when exposed to fire, their mechanical properties will directly affect whether the structure is safe. In this paper, the failure mode, strain analysis, load-displacement curve, initial axial stiffness, bearing capacity, and ductility of the joint are analyzed by the tensile testing of stiffened welded hollow spherical joints exposed to fire. The results show that the failure of the joint exposed to fire is a pull-out failure. With increasing temperature, the initial axial stiffness and bearing capacity of the joints gradually decrease. The ductility of joints exposed to fire shows an increasing trend with increasing temperature. The finite element model is verified based on the experimental results. Through parametric analysis, the calculation method for measuring the bearing capacity and initial axial stiffness of tensile-stiffened welded hollow spherical joints exposed to fire are proposed. [ABSTRACT FROM AUTHOR]

Composite plate shear walls/concrete-filled (C-PSW/CFs), also known as SpeedCore systems, are a relatively new structural member in American codes and standards. Prior research has focused primarily on C-PSW/CF walls with either flange/closure plates or filled composite members as boundary elements. Walls without boundary elements have also been studied, but they are no longer permitted by the American Institute of Steel Construction (AISC 341-22). The reason is that composite walls without boundary elements do not provide adequate ductility for seismic design. This paper presents the results of experimental and numerical studies conducted to evaluate the cyclic lateral load behavior of C-PSW/CFs using hot-rolled structural steel members as boundary elements. The steel web plates of the C-PSW/CF specimens were connected to each other using threaded tie bars with double nut connections. Composite interaction between the steel and concrete infill was achieved using the tie bars and additional shear studs welded to the boundary elements. The composite walls were embedded and anchored to reinforced concrete foundation blocks using welded deformed bar anchors. The experimental investigations focused on the cyclic lateral load-drift responses including test observations and limit states, moment-rotation response of the plastic hinge and the section moment-curvature relationship, overall lateral stiffness, strength, and displacement ductility. The experimental results show that the specimens exceeded their nominal flexural capacities calculated using the plastic stress distribution method or fiber-based section modeling using measured material properties. The specimens had plastic hinge rotation capacity greater than 0.028 rad. and displacement ductility ratio greater than 5.2. Detailed 3D nonlinear inelastic finite element models and simpler fiber-based macro models of the tested specimens were developed and benchmarked using experimental results. The detailed 3D finite element models can reasonably simulate the global and local behavior of the specimens, and are recommended for conducting further parametric studies of composite wall design details. Simpler fiber-based macro models can efficiently simulate the cyclic lateral load behavior of the specimens, and are recommended for modeling C-PSW/CFs while simulating the behavior of multi-story building structures. [ABSTRACT FROM AUTHOR]

This paper summarizes the results of a numerical simulation and subsequent variability analysis of the lateral load-resisting behavior of unbraced and chevron-braced glulam portal frames. Longitudinal tension/compression strengths of each glulam member were determined based on wood-size effect theory. The finite-element method (FEM) and an experimental study were carried out to determine the nonlinear mechanical behavior of glulam braces and bolted glulam beam-to-column connections. OpenSees "Pinching4" hysteresis models were adopted to model the mechanical behavior of both glulam braces and bolted beam-to-column connections. An FEM model of the glulam frames was developed to predict the lateral load-resisting hysteretic response of such frames. The stochastic finite-element method was used to calculate the frame capacity considering random distributions of connection and brace capacity. The FEM model presented can represent the nonlinear and hysteretic pinching behavior of an unbraced glulam frame whose behavior is dominated by splitting in the connection regions. Similarly, the strength softening and stiffness degradation of a chevron-braced glulam frame was also captured. Response surface method analysis was used to regress braced frame capacity from 200 analyses to a single set of capacity variables. The approach described in this paper demonstrates promise for optimizing the industrial-scale production of glulam portal frame structures. [ABSTRACT FROM AUTHOR]

Experimental data is imperative to characterize the behavior of materials used in structural analysis models. The aim of this data paper is to establish a database of material-scale uniaxial experiments, primarily conducted at EPFL, to assist with simulating the monotonic and cyclic behavior of structural steel materials and components. The proposed database consists of stress-strain data from test specimens subjected to tensile straining or to one of nine cyclic load protocols consistent with earthquake loading. The database includes 353 experiments on test specimens fabricated from 11 steel materials from around the world and an iron-based shape memory alloy; the database will evolve as additional tests are conducted. A downsampling method is developed that ensures a difference in strain energy of less than 0.5% between the original and downsampled data while reducing the number of datapoints by 89 times, on average. Results for S355 steels, constituting 57% of the database, are quantitatively validated by comparing the average measured initial yield stress and elastic modulus with prior work. The initial yield stress for S355 steels is found to be between 305 and 430 MPa and the elastic modulus between 190 and 230 GPa; these results are consistent with prior values. Finally, examples illustrate how the database can be used to calibrate constitutive models used in nonlinear finite element analysis. [ABSTRACT FROM AUTHOR]

This paper is an attempt to investigate the structural behavior of concrete-filled cold-formed steel stub columns with semi-oval cross sections via experimental and numerical studies. The test campaign included thirteen stub columns tests on four semi-oval sections infilled with both normal and high strength concrete. The details of test campaign and key observations are described and discussed. Validated against the test data obtained from this study, finite element model was developed to emulate the compressive behavior observed from tests and then used to derive more numerical data via parametric analyses. It is worth noting that the current codified design provisions for concrete-filled steel tubular columns do not explicitly include the semi-oval sections investigated herein. The acquired results from the test campaign and numerical analyses were employed to evaluate the applicability of the American Specifications (ANSI/AISC 360 and ACI318) as well as the European Code (EN1994-1-1). The evaluation results indicate that the aforementioned design rules are generally conservative for compressive strength predictions, among which the predictions by the European Code are the most accurate. Design method considering strength enhancement and confinement effect was proposed with improved accuracy. It is suggested to use the proposed design method for the compressive design of concrete-filled cold-formed steel semi-oval stub columns. [ABSTRACT FROM AUTHOR]

In this paper, the shaking table tests and finite element analyses were conducted on the traditional thermal power plant main building and the thermal power plant main building with BRBs, respectively. The differences in torsional resistance between the two structural systems were studied, and the suppression effect on the displacement field distortion of the plane consisting of crane and tracks through adding BRBs in the thermal power plant main building was discussed. The study shows that after adopting a buckling-restrained brace in a thermal power plant main building, the damage and torsional response of the structure under an earthquake can be reduced, the occurrence of inelastic torsion can be effectively blocked, and the translation-torsion coupling effect can be reduced. At the same time, it can reduce the distortion amplitude of the displacement field of the plane consisting of crane and tracks and play a key role in improving the reliability of roof truss, crane, coal bucket, and low-ductility connectors, and it also facilitates the realization of performance-based seismic design. [ABSTRACT FROM AUTHOR]

In this paper, three one-third scale reinforced concrete (RC) beam-column-slab structure specimen tests were conducted to investigate the collapse mechanisms under a loss of the corner column, including a frame with slab (S-COR), a frame with slab and secondary beams (SS-COR), and a frame without slab (NS-COR). The slab and secondary beam's contributions were investigated by comparing the SS-COR and NS-COR, SS-COR, and S-COR specimens. The results show that the RC slab significantly enhanced the load resistance. Only a slight increase in peak resistance capacity of the SS-COR specimen was observed, while the ductility improved obviously due to the existence of secondary beams. The failure mode of the SS-COR frame is different from that of the S-COR frame: No concrete failure line occurs on the slab bottom, and the cracks develop entirely on the slab top. Moreover, based on the test results, finite element models (FE) were updated by adapting the OpenSeespy, which shows a good fit between the test curves and simulation results. Finally, 1,000 samples considering the uncertainty parameters were generated using Monte Carlo sampling to better understand the effect of uncertainty on the structure response. Data-driven models based on machine learning were used to predict the peak resistance capacity of the RC structures with slab and secondary beams. [ABSTRACT FROM AUTHOR]

This paper presents the derivation and validation of a mechanics-based finite element for the analysis of shear-critical slender reinforced concrete beams and columns. The element can capture the load-deformation behavior associated with axial loads, bending moments, and shear in uncracked or cracked reinforced concrete using only a small number of degrees of freedom and easily measurable input parameters: the gross cross-section dimensions and steel and concrete material stress/strain curves. The element is specifically derived to represent the full reinforced concrete cross section (i.e., one element is required over the depth of a member) and consists of four nodes, with two translational degrees of freedom (DOFs) per node. This formulation facilitates modeling the interface regions between walls or joint regions, beams, or columns and lowers the numerical complexity and number of decisions that the user must make. The element shows improvements to results from design codes when validated against experimental results for 782 beams without shear reinforcement and 167 beams with shear reinforcement taken from the literature. By reducing the number of degrees of freedom, the element will allow relatively rapid two-dimensional (2D) nonlinear analyses of full reinforced concrete buildings. [ABSTRACT FROM AUTHOR]

The use of prequalified welded unreinforced flange-welded web (WUF-W) beam-to-column connections in capacity-designed steel moment-resisting frames necessitates the removal of the weld backing bar at the bottom beam flange-to-column flange groove welded portion. Weld root back gouging and fillet weld reinforcement is also necessary to minimize the fracture potential at this location. This paper revisits the current detailing of WUF-W connections in order to propose simplifications in their fabrication process by intentionally keeping a customized beveled backing bar in place without impairing the connection's ductility under seismic loading. The analysis relies on traditional fracture mechanics applied in three-dimensional continuum finite element models. The modeling approach is validated with welded unreinforced flange-bolted web (WUF-B) pre-Northridge connection tests. The results suggest that field-welded connections with the proposed beveled backing bar reach lateral drift demands of at least 4%–6% rads even when flange groove welds feature a low-toughness E70T-4 weld electrode, which was typical in pre-Northridge WUF-B connections. Fillet weld reinforced backing bars provide inferior connection ductility compared to the proposed beveled backing bar. The simulation results from a series of prequalified WUF-W connections that respect the current seismic design and fabrication requirements, indicate that when the beveled backing bar configuration is intentionally left in place after completing the complete joint penetration groove welds, WUF-W connections can sustain lateral drift demands of at least 6% rads prior to fracture regardless of the panel zone strength, the steel beam depth, and the flange thickness of the respective beam and column. Limitations as well as suggestions for future work are also discussed. [ABSTRACT FROM AUTHOR]

The net section fracture behavior and resistance of S690 high-strength steel angle-to-plate connections were investigated in this paper, underpinned by testing and numerical modeling. The experiments were conducted on 23 S690 high-strength steel angle-to-plate connections, with each comprising an equal- or unequal-leg press-braked angle section member bolted to gusset plates by one leg. The test procedures and setup and the key observed results were fully presented and analyzed. The experimental program was supplemented by a numerical modeling program with which finite element models were first developed and validated against the experimental responses and afterward adopted to perform parametric studies to produce additional numerical data. Based on the test and numerical data, the codified design rules for S690 high-strength steel angle-to-plate connections with net section fracture were evaluated. The results of the evaluation revealed that (1) the American specification leads to consistent but unsafe failure load predictions, (2) the European code yields conservative and scattered failure load predictions, and (3) the Australian standard results in scattered, though accurate on average, predictions of failure load, and many of the predicted failure loads are unsafe. Finally, a new design method was proposed and shown to offer substantially improved failure load predictions for S690 high-strength steel angle-to-plate connections over the design codes. [ABSTRACT FROM AUTHOR]

Heavy glulam timber framed structures are facing a growing inadequacy in resisting lateral actions from earthquakes and winds due to the increasing building heights. This paper presents the experimental and numerical analysis results on the hysteretic behavior of newly developed carbon fiber reinforced polymer (CFRP) confined timber-steel buckling-restrained bracings and the lateral performance of bolted glulam timber frames with such bracings. Ten timber-steel bracings and four frames with different bracing provisions were tested via reversed cyclic lateral loading. A finite-element method based model was developed, verified, and used for parametric studies. The bracing test results indicated that the design requirements for ordinary buckling restrained bracings on the confinement ratio and the transverse bulging force are adequate for the proposed timber-steel bracings. A confinement ratio no less than 4.6 is suggested. Compared to an otherwise similar bare frame, two frames with the proposed bracings were found to be 132% and 176% higher in the peak loads, more than 10 times higher in the elastic stiffness, 40% and 43% higher in ductility ratio, and on average 106% higher in the equivalent viscous damping ratio. The two frames also exhibited higher stiffness and energy dissipation than a frame braced by timber bracings, which are prone to buckling failure. Parametric studies indicated that the secant stiffness and the damping ratio of the frames at small drift can be substantially affected by the bolt slippage of the bracing-frame connections. The increased lateral stiffness ratio will lead to increase in the peak load and stiffness, but the equivalent viscous damping ratio remains nearly constant for lateral stiffness ratios larger than 2.5. The frame stiffness and peak load increase with increased rotational stiffness of the beam-column connections while the equivalent viscous damping ratio decreases. [ABSTRACT FROM AUTHOR]

A novel welded demountable shear connector for sustainable steel-concrete composite structures is proposed. The proposed connector consists of a grout-filled steel tube bolted to a compatible partially threaded stud, which is welded on a steel section. This connector allows for an easy deconstruction at the end of the service life of a building, promoting the reuse of both the concrete slabs and the steel sections. This paper presents the experimental evaluation of the structural behavior of the proposed connector using a horizontal pushout test arrangement. The effects of various parameters, including the tube thickness, the presence of grout infill, and the concrete slab compressive strength, were assessed. A nonlinear finite element model was also calibrated against the experimental results, and the validated numerical model was used to extend the validity of the experimental results and to perform further parametric studies. The experimental and numerical results show that the tested connectors have similar stiffness, but higher shear resistance and slip capacity compared with traditional welded shear studs and can be classified as ductile according to Eurocode 4. [ABSTRACT FROM AUTHOR]

Timber floors are prone to exhibit vibration levels, which can cause discomfort to the occupants. In the last 20 years , ambient vibration tests have become very popular due to the many advantages they have over traditional forced vibration tests when dealing with civil engineering structures. Furthermore, sensitivity analyses and black-box" optimization algorithms can support the development of refined finite-element models that accurately predict the structures' responses based on the experimental modal parameters. However, applications of these methods and techniques to timber structures are scarce compared with traditional materials. This paper presents and discusses the findings of an experimental testing campaign on a lightweight timber floor. At first, each component of the assembly was tested separately under different boundary conditions. Then, the authors evaluated the behavior of the whole floor assembly. In a second step, the authors carried out a covariance-based sensitivity analysis of finite element (FE) models representative of the tested structures by varying the different members' mechanical properties. The results of the sensitivity analysis highlighted the most influential parameters and supported the comparison among diverse FE models. As expected, the longitudinal modulus of elasticity is the most critical parameter, although the results are very dependent on the boundary conditions. Then automatic modal updating algorithms tuned the numerical model to test results. As a concluding remark, the experimental and numerical results were compared with the outcomes of a simplified analytical approach for the floor's first natural frequency estimate based on current European standards. [ABSTRACT FROM AUTHOR]

In this paper, an innovative low-yield-point corrugated steel plate damper (LCSPD) was proposed, which consisted of two corrugated webs as the shear component and two outer corrugated plates as the bending component. Four LCSPDs were studied by varying the corrugation directions and arrangement forms. The lateral strength, energy dissipation, ductility, hysteretic behavior, and equivalent viscous damping coefficient of the LCSPDs were estimated by quasi-static tests. A finite element analysis was carried out based on the variables of web thickness and aspect ratio, and the validity of the finite element analysis was confirmed by comparing the results of the model with the experimental results. Comparing the horizontal low-yield-point corrugated steel plate dampers (LCSPD_H) with the vertical low-yield-point corrugated steel plate dampers (LCSPD_V), Damper specimen LCSPD_H exhibited better energy dissipation and ductility. Finally, a simplified formula was proposed to estimate the shear-carrying capacity of the LCSPDs, and the calculated results agreed well with the experimental results. [ABSTRACT FROM AUTHOR]

In this paper, the punching shear behavior of interior slab-rectangular column connections without shear reinforcement under static concentric loading is studied using a three-dimensional, nonlinear, finite element model (FEM) in ABAQUS version 6.12 based on the concrete damaged plasticity model. The FEM was calibrated based on seven experimental tests selected from literature. The predicted shear capacities were compared to punching and one-way shear predictions according to published standards and the critical shear crack theory (CSCT). The finite element analysis results show that the impact of column rectangularity on punching shear capacity is not only dependent on the column aspect ratio but becomes more severe as the ratio of the minimum column dimension to the effective depth of the slab increases. This behavior was found to be implicitly accounted for in some published European standards and the CSCT. [ABSTRACT FROM AUTHOR]

This paper presents a density-based topology optimization framework for designing energy-dissipating plastic structures. In order to mitigate the material damage during the plastic energy dissipation process, the total material volume in a design is minimized while subjected to a minimum plastic work constraint and a maximum damage constraint. The Gurson–Tvergaard–Needleman (GTN) model with shear damage modifications is adopted to simulate the physics of ductile-damage mechanisms under various stress states. Path-dependent design sensitivities are analytically derived using the adjoint method within the framework of nonlinear finite element analysis. The effectiveness of the proposed framework is demonstrated by a series of numerical examples that shows the proposed framework can successfully limit damage in optimized plastic designs under the prescribed threshold by reconfiguring structural topologies. More notably, compared to the designs obtained with the von Mises plasticity model, damage constrained plastic designs with the GTN model have overall better ductility, higher load carrying capacity, and higher plastic work dissipation before failure initiation. [ABSTRACT FROM AUTHOR]

The use of integral mechanical attachments (IMAs) in spatial free-form timber plate structures has been revitalized by the production of engineered boards and recent developments in digital fabrication and computer-aided design. Despite the widespread interest in utilizing such structural systems, there have been very few efforts to develop modeling strategies that can be used by practitioners. Detailed finite-element (FE) models are typically computationally expensive and require advanced expertise. Accordingly, this paper introduces a simplified yet robust macroscopic modeling technique for spatial free-form timber plate structures with IMAs. This approach employs only beam and spring elements to simulate the structural behavior. The macromodel was introduced and the associated mechanical properties were computed. FE models constructed using shell elements and the results from recent experiments performed on a full-scale prototype were used to verify the proposed macromodel. The results showed that the response of the macromodel was closely in line with that of the experiments and FE models. Despite its simplicity, the macromodel is robust and can simulate the behavior of integrally attached timber plates. It was also demonstrated that the computational time for the macromodel is significantly less than the FE simulation. [ABSTRACT FROM AUTHOR]

This paper introduces an innovative structural system consisting of four-sided hyperbolic-paraboloid (hypar) roof umbrellas as hard countermeasures against nearshore hazards. The umbrellas line the coast and remain upright during normal operation, providing shade and shelter along the waterfront while not limiting access to the shore. A hinge at the hypar-column interface permits tilting to form a physical barrier against surge-induced coastal inundation. Analytical equations based on idealized boundary conditions are formulated in the hydrostatic regime. The equations provide insight into optimal geometric parameters and are used to validate a decoupled numerical scheme constituting smoothed particle hydrodynamics (SPH) and the finite element method (FEM). All numerical reactions concur with the analytical solutions for water inundation matching the total deployed height. A proof-of-concept study was employed to successfully illustrate the applicability of deployable hypar umbrellas as coastal armor from a structural engineering perspective. This work ultimately demonstrates the feasibility of decoupled SPH-FEM methods in modeling fluid-structure interaction involving hypar forms, while establishing a foundation for their analysis and design for coastal hazard adaptation. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive parametric study on the ultimate strength of perforated cold-formed steel columns using the finite element (FE) package ABAQUS. FE models were developed for columns predisposed to local (L), distortional (D), and global (G) buckling failures. The parametric study involved five cross-section types (i.e., C, stiffened C, Z, rack, and hat sections), five widths of holes, four lengths of holes, four different sizes of hole spacings, three material properties, two magnitudes and various directions of geometric imperfections, and three buckling modes (i.e., L, D, and G) and all of the possible interactions between them (i.e., LD, LG, DG, and LDG). Ultimate strengths, as well as failure modes, were obtained from the analyses and are plotted against the current codified direct strength method (DSM) in AS/NZS 4600. Significant discrepancies between the numerical results and the DSM-predicted strengths were observed due to the influence of holes, the interaction of buckling modes, and occasionally the inherent limitations of the DSM itself. The effects of column length, material properties, and centroid shift due to perforation are also discussed. A data pool including 146,207 column-ultimate strengths were obtained, most of which were used to formulate new design equations for perforated thin-walled columns based on the direct strength method, as presented in a companion paper. [ABSTRACT FROM AUTHOR]

Strengthening of deteriorating structural members by fiber-reinforced polymers (FRPs) is an increasingly common and validated technique; however, concerns over means to evaluate the long-term durability of these retrofits exist. This paper explores a novel approach to overcome this concern through the use of a novel self-sensing composite material. Specifically, the objective of this paper is to provide a proof of concept for an integrated strengthening and sensing methodology for structural steel members achieved via infusing more-traditional composites with carbon nanotubes (CNTs). To assess the strengthening and sensing capabilities of the CNT-based composite, a set of unidirectional tensile tests were conducted. The experimental results show stiffness increases and strain reductions due to the application of the CNT-based sensing composites that were in close agreement with both analytical and finite-element models. The sensing aspect was also validated by a corresponding linear change in resistance of the CNT-based sensor with increasing load up to the point at which debonding of the adhesive layer occurred. The nanotube sensing layer is able to capture the strain in the member as well as the onset and extension of interfacial debonding. [ABSTRACT FROM AUTHOR]

The lateral torsional buckling (LTB) equations in some current standards are based on unified equations that are a fit to a large body of experimental test data. However, these curves tend to overestimate the capacities from finite-element (FE) simulations based on typical idealized end conditions, residual stresses, and geometric imperfections. Uniform moment tests conducted on various types of cross sections have led to proposed modifications of the current specification for LTB equations. This paper investigates and recommends, by means of FE test simulations, the use of the modified equations with additional improvements for moment gradient cases. The emphasis of the studies is on rolled I-section members. Specifically, the paper demonstrates an inelastic Cb effect that can be particularly significant for beams in which the maximum moment occurs within the unbraced length rather than at a braced point. A new way of applying the LTB modification factor, Cb, in the inelastic LTB region for these cases is recommended for ordinary application of current standard resistance equations. Also, it is shown that this effect can also be captured seamlessly via an explicit inelastic buckling analysis using stiffness-reduction factors (SRFs) derived from the design resistance curves. [ABSTRACT FROM AUTHOR]

A concrete strength-sensitive finite element (FE) model applicable to concrete subjected to various confining pressure levels and conditions is presented. This paper focuses primarily on the failure surface and flow rule of concrete in multiaxial compression, which were experimentally observed to vary with the unconfined concrete strength and level of confining pressure. To this end, a large experimental database, which consists of more than 1,700 results of concrete specimens tested under biaxial and triaxial compression, was assembled through an extensive review of the literature. This database was augmented with another test database of concrete in uniaxial compression that consists of more than 4,000 test results. Based on the test database results, it was observed that the tangential slope of the failure surface reduces with an increase in the unconfined concrete strength and confining pressure. The concrete dilation angle considered in the flow rule was observed to be nonlinear throughout loading history. To incorporate the observed changes in the failure surface and flow rule of concrete subjected to uniaxial, biaxial and triaxial compression, an extension of Lubliner's concrete-damage plasticity model was proposed and presented in this paper. Comparisons with experimental test results show that the predictions of the extended model are in good agreement with the test results of both normal-strength concrete (NSC) and high-strength concrete (HSC). [ABSTRACT FROM AUTHOR]

Development in ultra-high-performance fiber-reinforced concrete (UHPFRC) structural applications that has taken place over the last two decades has generated innovative concepts that could significantly impact the concrete construction practice. The transition from conventional concrete with brittle behavior to strain-hardening behavior in direct tension allows consideration of the design of innovative structural components and offers development of newtechniques for rehabilitation. Building on experimental results of internally instrumented reinforcing bars, this paper investigates the impact of tensile characteristics of UHPFRC on the performance of lap splice connections using a refined three-dimensional (3D) finite-element (FE) model at rib scale and a 3D concrete constitutive model implemented in a computer program. The results show that the model reproduces with accuracy the experimental behavior of lap splice connections in UHPFRC in terms of maximum strength, splitting failure mode, crack pattern, steel stress distribution along the splice, and eventual loss of bond. Using the validated 3D nonlinear finite-element model, the influence of splice length and UHPFRC cover thickness are highlighted in a parametric study of corner and interior lap splices. The paper illustrates the methodology that can be adopted along with experimental results to develop guidelines for designing lap splice connection in UHPFRC. [ABSTRACT FROM AUTHOR]

This paper presents the development of a lumped-parameter model of multistory framed shear buildings supporting rigid blocks with the possibility to slide. After favorably comparing with results from finite-element analyses and shake table tests, the model was used to assess design provisions in regard to the treatment of live load as seismic weight. It was found that using the minimum live load percentage in current design standards may lead to unconservative drift estimates for buildings supporting heavy and nearly permanent live load objects and structures that are (1) designed for higher R values, (2) located in regions of low-to-moderate seismic risk, or (3) base isolated. Results from a parametric study led to a design expression that allows determining the portion of the expected live load that is effective as seismic weight on the structure as a function of the object/floor interface's friction coefficient and the maximum floor acceleration of the building alone. The adequacy of the design expression was confirmed through three-dimensional finite-element analyses of two- and four-story buildings supporting live load objects that could slide. [ABSTRACT FROM AUTHOR]

This paper presents the experimental investigation on the compressive behavior of cold-formed high-strength steel tubular stub columns. In this paper, the nominal 0.2% proof stress of the high-strength steel was 700, 900, and 1,100 MPa. A total of 25 stub column tests on circular, rectangular, and square hollow structural sections were conducted. Geometric imperfections and load-deformation histories were reported and assessed. The experimental results were compared against the design values calculated from the Australian, European, and North American codes, and the corresponding compactness criteria were assessed. A finite-element model, which incorporated the varying material properties, was described, and the influence of geometric and material imperfections was also evaluated. The finite-element results successfully captured the experimental observations and can be adopted for future parametric studies. [ABSTRACT FROM AUTHOR]

In-plane shear capacity formulation of reinforced masonry is commonly conceived as the sum of the capacities of three parameters, viz, the masonry, the reinforcement, and the precompression. The term "masonry" incorporates the aspect ratio of the wall without any regard to the aspect ratio of the panels inscribed (and hence confined) by the vertical and the horizontal reinforced grout cores. This paper proposes design expressions in which the aspect ratio of such panels is explicitly included. For this purpose, the grouted confining cores are regarded as a grid of confining elements within which the panels are positioned. These confined masonry panels are then considered as building blocks for multi-bay, multi-storied confined masonry shear walls and analyzed using an experimentally validated macroscopic finite-element model. Results of the analyzes of 161 confined masonry walls containing panels of height to length ratio less than 1.0 have been regressed toformulate design expressions. These expressions have been first validated using independent test data sets and then compared with the existing equations in some selected international design standards. The concept of including the unreinforced masonry panel aspect ratio as an additional term in the design expression for partially grouted/confined masonry shear walls is recommended based on the conclusions from this paper. [ABSTRACT FROM AUTHOR]

This paper presents a three-dimensional inclined parabolic cable element for static analysis of cable structures. After a catenary cable element is briefly reviewed, the three dimensional parabolic cable considered in this paper is presented. The derivation of the stiffness matrix for the element is described by equating the total differentiations of the cable length and its elastic elongation, and defining the stiffness as the ratio of the infinitesimal force increment to the infinitesimal length increment. The static equilibrium equation for a two-node cable element and the procedure for nonlinear structural analysis using the Newton-Raphson iterative method are presented as well. The proposed element can consider an inclined cable without the need for a transformation, and has explicit and simple stiffness formulas compared with those of a catenary element. To validate the proposed parabolic cable element, four example models subjected to static loadings are analyzed using the proposed element, and the displacements are compared with those obtained by previous researchers and finite element analysis software. The verification proves that the proposed parabolic cable element offers highly accurate static responses for cable structures. [ABSTRACT FROM AUTHOR]

This paper is the second part of a two-part report describing the behavior of headed stud-SFRCC (steel-fiber-reinforced cementitious composite) shear connection. The first paper presented an experimental study of headed stud-SFRCC shear connections, whereas this paper focuses on the strength evaluation of those shear connections. This paper first presents a finite-element model of the connections, which was validated using the experimental results. An updated empirical equation considering the contribution made by the weld collar is proposed to estimate the shear strength of a single headed stud. Finite-element models were developed to evaluate the shear strength of each stud in a densely arranged group of headed studs. The results reveal that the interaction between headed studs mitigated the confining effect on studs, and the studs thus sustained less shear strength than those with larger stud spacing. Studs placed in different positions sustain different shear forces, and this difference is greater when smaller stud spacing is used. Formulas with which to estimate the reduction in the strength of headed studs in SFRCC are suggested according to a parametric study of the finite-element analysis. [ABSTRACT FROM AUTHOR]

Concrete-filled steel tube (CFT) beam-columns are categorized as compact, noncompact, or slender depending on the governing slenderness ratio (width-to-thickness b/tb/t or D/tD/t ratio, λλ) of the steel-tube wall. The current AISC specification recommends the bilinear axial force-bending moment (P-MP-M) interaction curve for bare steel members for the design of noncompact and slender CFT beam-columns. This paper compiles the experimental database of tests conducted on noncompact and slender CFT beam-columns, and demonstrates the overconservatism of the AISC P-MP-M interaction curve. This paper also presents the development and benchmarking of detailed 3D finite-element models for predicting the behavior and strength of noncompact and slender CFT members. The benchmarked models are then used to evaluate the fundamental P-MP-M interaction behavior of CFT beam-columns, and the influence of material and geometric parameters such as the tube slenderness ratio (λλ), material strength ratio (Fy/f'c), member length-to-section depth ratio (L/D), and axial load ratio (P/Po). The parametric analyses indicate that for L/D ratios up to 20, the P-M interaction curves are governed by the relative strength ratio (csr=AsFy/Acf'c). The parametric analysis results are used to propose revisions to the current standard's interaction equations for designing noncompact and slender CFT beam-columns. [ABSTRACT FROM AUTHOR]

This paper presents a triangular shell heat transfer element that is used to simulate the thermal response of nonuniformly heated structures. The formulation uses a combination of finite-element and control volume techniques to arrive at a layered shell element that is used to solve the 3D conduction heat transfer problem in a highly efficient manner. This paper considers a 3-node linear element and a 6-node quadratic element. The element formulation is verified against a converged continuum heat transfer model for a thick steel plate exposed to a concentrated heat flux, a thick steel pipe exposed to a concentrated heat flux, and a concrete slab exposed to a localized fire. The verification studies demonstrate that the linear and quadratic elements consistently converge to the continuum model and require a fraction of the computational cost. The verification study involving the concrete slab exposed to a localized fire demonstrates that the formulation can readily handle steep temperature gradients as well as temperature-dependent material properties. [ABSTRACT FROM AUTHOR]

Many terrorist attacks have been carried out in recent years, such as in Oslo, Norway (2011), and more recently in Boston, Massachusetts, and in Volgograd, Russia (both 2013). Terrorist attacks target primarily public facilities, such as railway stations, government buildings, embassies, and the transport infrastructure. Research on the effect of blast loading on structures and interiors has gained considerable attention. Although there are many types of terrorist attacks, this paper focuses specifically on bomb attacks. Two different types of bomb attacks can be distinguished. In Oslo and Boston, the explosion occurred in an open space. In Volgograd, the explosion occurred inside a confined space. This paper primarily focuses on the type of bombing observed in Volgograd by presenting reduced-scale experiments on the effect of rigid barriers on blast wave propagation in the confined space of a railway station. The experimental data set was used for calibrating numerical finite-element models for use in predicting pressure-wave propagation. Very good agreement has been achieved between the experimental results and the numerical model results. The experimental results and also the numerical modeling results showed no significant effect of solid rectangular barriers in reducing the peak overpressure of the air shock wave in the area behind the barriers. Although the results indicate some effect on lowering the peak overpressure, this is limited to the area directly behind the barrier. At a greater distance, the effect diminishes rapidly and the pressure wave reverts to almost its original strength. In front of the barriers, the overpressure is increased, because the shock wave is reflected by the rigid barrier surface. The main benefit of such barriers would be that they absorb potentially harmful flying debris carried by the blast winds. [ABSTRACT FROM AUTHOR]

Although multiple-model structural identification (MM ST-ID) approaches appear to offer clear, conceptual benefits over singlemodel approaches, they have not yet been employed within a transparent scenario that will allow quantitative comparison, critique, and refinement. To fill this gap, the research reported in this paper aimed to (1) implement and compare current MM ST-ID approaches on a physical laboratory model to establish their accuracy and identify their merits and shortcomings, and (2) identify the ability to refine MM ST-ID methods by weighing observations based on their correlation with the desired predictions. The scenario implemented used modal parameters as the observations, and static displacements and strains as the desired predictions. The various MM ST-ID methods were evaluated based on how their prediction distributions agreed with the actual responses of the physical model. The results indicated that while all methods were successful in bounding the actual responses, the Bayesian updating approach proved to be the most efficient in terms of required number of simulations, and was able to produce prediction distributions with the smallest bounds (while still incorporating all measured responses). In addition, the mean of the MM ST-ID prediction distributions did not coincide with the model that had the largest weight (i.e., the highest likelihood), which indicates that single model approaches not only are unable to provide estimates of variability, but may produce biased predictions. Finally, through a second set of scenarios, the research reported in this paper showed how prediction distributions may be improved by weighing observations based on their correlation with the desired predictions. [ABSTRACT FROM AUTHOR]

The aims of this study are to generate experimental data and develop numerical models for aluminum alloy continuous beams, and to utilize the results to underpin the development of revised design methods for indeterminate structures. This paper presents an experimental program and finite-element (FE) analyses for two-span continuous beams (i.e., five-point bending) of square and rectangular hollow sections (SHSs and RHSs). The experimental program comprised 27 five-point bending tests with three different positioning of loads. The testing procedures and key results are reported. The test specimens were manufactured by extrusion, with 18 of grade 6061-T6 and 9 of grade 6063- T5 heat-treated aluminum alloys. The test specimens were nonslender sections, and mostly of Class 1 proportions. Generally, the specimens failed by the formation of a collapse mechanism comprising three plastic hinges. The distances between the supports and the loading points were varied in order to form the first plastic hinge in different locations, to achieve different load levels between the first hinge and collapse, and to change the rotation demands on the first hinge that formed. The FE models were developed and failure was defined as either when a plastic collapse mechanism was formed or the material fracture strain was reached on the tension flange, whichever occurred first. The numerical models were first validated against the experimentally obtained load-deflection responses, as well as the failure modes. The experimental and FE ultimate loads were both found to be beyond the theoretical loads corresponding to the formation of the first hinge as well as the calculated plastic collapse loads. A key characteristic of aluminum alloy, strain hardening, is shown to be particularly significant in both the experimental program and the numerical investigation. The validated FE models are used to generate numerical results through parametric studies in the companion paper. The development of design rules for indeterminate aluminum alloy structural systems is then described. [ABSTRACT FROM AUTHOR]

This two-part paper is an application of advanced nonlinear finite-element analyses (ANFEA) for the design or assessment of large concrete structures. It presents an innovative application of ANFEA that reveals many important aspects of numerical modeling and safety verification, starting from the material up to the structural level and going from calibration and validation to the prediction level. A complex hydraulic structure with large members and nonconventional boundary conditions is taken as the target design structure (TDS). Following a two-step procedure that was proposed in a previous paper, the model error is first computed for two candidate concrete models (part 1). Using the selected concrete model and the corresponding model error, the global resistance factor is computed in a second step for the TDS (part 2). This first part is related to the calibration and validation assessments for the ANFEA models of concrete structures. These issues can be viewed as two basic steps within the verification and validation process (V&V) that has been adopted in other engineering fields. In the calibration procedure, the size effect phenomenon, which is a major parameter for the TDS, is considered. The distinction between size effect statistical (material) and deterministic (energetic) components is highlighted, and a new approach for considering each contribution is presented. The validation process is undertaken from the material to the structural level. It is shown through this process that the use of only the compressive strength of concrete and the yield stress of reinforcement are sufficient with one candidate concrete model in order to obtain a relatively low coefficient of variation of model error. The paper illustrates a general methodology that can be applied with any ANFEA software to design or assess the safety level of unusual concrete structures. [ABSTRACT FROM AUTHOR]

This paper develops both a three-parameter power model and a Ramberg-Osgood model for quantifying the moment--rotation characteristics of a blind-bolted flush end-plate system that connects a composite beam to a concrete-filled steel tubular (CFST) column in a steel framed building structure. By default, these connections are semirigid, and accurate analyses of structures including them necessitate quantitative knowledge of their moment-rotation response. A detailed three-dimensional (3D) nonlinear-continuum-based finite element model of the connection region including the composite beam, flush end-plate, blind bolts and the concrete-filled steel tube is developed in this paper. This sophisticated FE model can capture the pertinent physical, geometrical, and contact nonlinearities, and its accuracy is verified against experimental data reported elsewhere in the literature. The calibrated FE model is then employed for a parametric study in which the effects of the slab reinforcement ratio, the thickness of the slab, the degree of the shear connection, the diameter of the blind bolts as well as the pretension force in them and their yield stress, the depth of the beam, and the thickness of the flush end-plate are investigated. The results of the parametric study are employed to calibrate moment-rotation relationships, which are proposed in a convenient analytic form. It is shown that the proposed model predicts the moment-rotation response of blind-bolted flush end-plate composite beam-to-CFST column connections with good accuracy, and it provides a valuable empirical modeling that can be used in the computer design of composite framed building frames in the new paradigm of design by advanced analysis. [ABSTRACT FROM AUTHOR]

This second-part article presents applications of advanced nonlinear finite-element analysis for the design of large reinforcedconcrete structures. Because shear and the size effect are fundamental aspects of these structures, the first section of this paper is devoted to the prediction of shear failure for very large members more than 3 m deep. It is shown that the tendency of shear strength is much less sensitive to size effects for very large members than the predictions of some design code equations. Applications to the draft tube complex structure are then presented in a second part. A comparison of cracking patterns with an existing powerhouse is performed at the service level. It is shown that thermal effects have an important effect on the final cracking pattern. The draft tube model is then analyzed up to failure. Following a new design methodology proposed by the authors in a previous paper, and using the model error properties computed in part 1, the global resistance factor is computed for the ultimate level. The effects of temperature, nominal shear reinforcement, and lateral confinement are discussed. [ABSTRACT FROM AUTHOR]

This paper presents a technique for computing the time-dependent behavior of reinforced and prestressed concrete as a composite material. This technique, when implemented in a finite-element model and assuming that the concrete and steel reinforcement act as a composite material, is computationally advantageous compared with explicitly modeling the concrete and steel materials separately. The method is developed assuming linear viscoelasticity and uncracked sections. The approach starts by first approximating the creep compliance functions for the viscoelastic concrete as a Kelvin chain model. This approximation allows the viscoelastic behavior to be framed as a rate-type creep law, which converts the analysis to an equivalent elastic problem, simplifying the computations. This approach, originally developed for plain concrete, is extended in this paper to account for the effects of linear elastic reinforcement. Several implementation examples are provided documenting the viability of the method for problems of uniaxial, multiaxial, and bending behaviors. For the presented cases, the composite method is shown to provide similar results compared with models containing explicitly modeled reinforcement. The paper concludes with a discussion regarding how to extend the methodology to the general case with linear viscoelastic reinforcement and matrix materials. [ABSTRACT FROM AUTHOR]

This paper presents the results of an investigation of the decrease in residual axial force in corroded high-strength bolts in friction joints for steel bridge girders. The results of a finite-element analysis revealed that the root-mean-squared value of the thickness reduction near the washer was a useful parameter for evaluating the residual axial force for the corroded bolts. Furthermore, the effect of the corroded bolt's shape on the residual axial force could be evaluated based on the thickness reduction near the washer. To verify the validity of this approach, measurements were carried out on corroded bolts cut from a steel bridge girder. The results indicated that the proposed method can estimate the residual axial force to an accuracy of ±15%. [ABSTRACT FROM AUTHOR]

The solution of impact problems requires advanced computational techniques to overcome the difficulties associated with large short-duration loads. Such cases typically use the explicit time integration method because it provides a stable solution for problems such as the analysis of structures subjected to shock and impact loads. However, most explicit-based finite elements were developed for continuum models such as membrane and solid elements, which renders the problem computationally expensive. On the other hand, the development of fiber-based beam finite elements allows for the simulation of the global structural behavior with very few degrees of freedom, while accounting for the detailed material nonlinearity along the element length. However, explicit-based fiber beam elements have not been properly formulated, in particular for the case of the emerging force-based beam element. This paper develops two fiber plane beam elements that consider an explicit time integration scheme for the solution of the dynamic equation of motion. The first element uses a displacement-based formulation, whereas the second element uses a force-based formulation. For the latter case, a new algorithm that eliminates the need for iterations at the element level is proposed. The developed elements require the use of a lumped mass matrix and a small time increment to ensure numerical stability. No iterations or convergence checks are required, which renders the problem numerically efficient. The developed explicit fiber beam-column models, particularly the force-based element, represent a simple yet powerful tool for simulating the nonlinear complex effect of impact loads on structures accurately while using very few finite elements. The traditional implicit method of analysis typically fails to provide numerically stable behavior for such short-duration problems. Two correlation studies are presented to highlight the efficiency of the developed elements in modeling impact problems in which the material models consider the strain rate effect. These examples confirm the accuracy and efficiency of the presented elements. [ABSTRACT FROM AUTHOR]

This paper presents a numerical investigation to examine the bond-slip behavior of column longitudinal reinforcing bars embedded in oversized pile shafts and to determine the minimum embedment length required for the column bars to prevent anchorage failure. Three-dimensional nonlinear finite-element models of column-pile assemblies incorporating the bond-slip behavior of the longitudinal reinforcing bars have been developed for the numerical analyses. The capability of the models in capturing the response of column bars along their embedment length has been verified with experimental results from four full-scale column-pile assemblies tested under cyclic lateral loads. The study has shown that the bond-stress distribution along the bar anchorage length is highly nonuniform and that the embedment length specified for the column reinforcement in current design standards is very conservative. A new design formula that significantly reduces the embedment length has been evaluated. The numerical results have indicated that the new embedment-length formula provides a good margin of safety against the pull-out failure of the column bars. The results have also shown that the use of an engineered steel casing to provide lateral confinement for the pile is an effective means to enhance the bond strength and reduce the slip of the column longitudinal bars in the anchorage region. [ABSTRACT FROM AUTHOR]

The material presented in this paper refers to a part of the investigation on cross-laminated (XLam) wall panel systems subjected to seismic excitation, carried out within the bilateral project realized by the Institute of Earthquake Engineering and Engineering Seismology (IZIIS) and the Faculty of Civil and Geodetic Engineering at the University of Ljubljana (UL FCGE). The full program of the research consists of basic tests of small XLam wooden blocks and quasi-static tests of anchors, then quasi-static tests of full-scale wall panels with given anchors, shaking-table tests of two types of XLam systems including ambient-vibration tests, and finally analytical research for the definition of the computational model for the analysis of these structural systems. In this paper, the full-scale shaking-table tests for one XLam system type (i.e., specimen 1 consisting of two single-unit massive wooden XLam panels) that have been performed in the IZIIS laboratory are discussed. The principal objectives of the shaking-table tests have been to get an insight into the behavior of the investigated XLam panel systems under seismic excitations, develop a physical and practical computational model for simulation of the dynamic response based on the tests, and finally correlate the results with those from the previously performed quasi-static tests on the same wooden panel types. The obtained experimental results have been verified using a proposed computational model that included new constitutive relationships for anchors and contact zones between panels and foundations. Because a reasonable agreement between the numerical and experimental results has been achieved, the proposed computational model is expected to provide a solid basis for future research on the practical design of these relatively new materials and systems. [ABSTRACT FROM AUTHOR]

The behavior of semirigid partial-strength connections has been investigated through either experimental component testing or detailed three-dimensional (3D) finite-element (FE) models of beam-column subassemblies. Previous experiments on semirigid partial-strength connections were conducted under idealized loads and boundary conditions, which do not represent real situations. In addition, the developed 3D FE models are computationally expensive and have primarily been used under monotonic loadings. Evaluating the full potential of any connection requires a system-level investigation, whereby the effect of the local behavior of the connection on the global response of the structural system is considered. Moreover, the connection should be tested under realistic load and boundary conditions and/or analyzed using an accurate yet computationally affordable analytical model. This paper represents a new system-level hybrid simulation application aimed at investigating the seismic performance of semirigid partial-strength steel frames with top and seat angles with double web-angle connections. The analytical component of the simulation comprises a detailed two-dimensional nonlinear FE model. The experimental component of the simulation consists of a full-scale beam-column subassembly with loading and boundary conditions that are in full interaction with the rest of the frame. The paper provides an overview of the hybrid simulation application and highlights the major results. The simulations were conducted at the Multi-Axial Full-Scale Sub-Structured Testing and Simulation Facility at the University of Illinois, which is part of the National Science Foundation Network for Earthquake Engineering Simulation. [ABSTRACT FROM AUTHOR]

This paper presents procedures for the design of fixed- and pin-ended equal-leg angle columns with short-to-intermediate lengths. First, some remarks concerning the buckling and postbuckling behavior of the angle columns are presented that (1) illustrate the main differences between the fixed- and pin-ended column responses and (2) demonstrate the need for specific design procedures. Then, the paper reports an in-depth investigation aimed at gathering a large column ultimate strength data bank that includes (1) experimental values collected from the literature and (2) numerical values obtained from shell finite-element analyses carried out in the code ABAQUS. The set of experimental results is comprised of 41 fixed-ended columns and 37 pin-ended columns and the numerical results obtained include 89 fixed-ended columns and 28 pin-ended columns; various cross-section dimensions, lengths, and yield stresses are considered. Finally, the paper closes with the proposal of new design procedures for fixed- and pin-ended angle columns based on the direct strength method (DSM). The two procedures adopt modified global and local strength curves, and it is shown that the proposed DSM approach leads to accurate ultimate strength estimates for short-to-intermediate columns covering a wide slenderness range. [ABSTRACT FROM AUTHOR]