Journal of Structural Engineering

Ductile end cross frames have been proposed in the past as a seismic design and retrofit strategy for steel plate girder bridges. In this paper it is shown that with good connection details, single angles are able to undergo large cyclic deformations in excess of 6% average axial strain before failure occurs. Large-scale shake table experiments were performed on a straight steel I-girder bridge model to evaluate the performance of a superstructure with ductile end cross frames using single angle X braces. The cross frames exhibited no apparent overall strength degradation, but also a comparatively low postyield stiffness, allowing the cross frames to act as effective structural fuses. The measured base shear was 61% of the elastic base shear in response to 2.0 times the El Centro earthquake at an average drift of 3.4%. Large girder drifts were achieved without distress in the deck slab by removing selected studs between the slab and top flange of the girders at the end cross frame locations, with axial deformations in the angles well below their deformation capacity based on component experiments.

Ductile end cross frames have been proposed in the past for seismic design of steel plate girder bridges. In this paper buckling-restrained braces (BRBs) are investigated as ductile end cross frames and compared against the performance of yielding X braces. Component experiments on the BRBs showed that these braces dissipated energy very efficiently and have stable hysteretic behavior. Shake-table experiments on a large scale bridge model investigated the performance of braces with both pin-ended connections and fixed-end connections. Despite slippage, the pin-ended connections are considered more effective as flexural action in the relatively short braces is prevented. The base shear in the bridge model in response to 2.0 times the El Centro earthquake was 69% of the elastic base shear at an average drift of 2.5% during experiments. The relatively large deformation capacity of the BRBs, although not as great as the X braces, is necessary to achieve a significant reduction in base shear. The maximum cross frame displacements with the BRBs are consistently smaller than those in X braces at the same level of base shear.

An experimental study was conducted to investigate the seismic behavior of reduced beam section (RBS) moment connections to a deep wide-flange column. The test matrix for the experimental program consisted of six full-scale interior RBS connections, where the column for the specimens ranged in depth from a W24 to a W36 wide flange section. Five of the specimens had a composite floor slab, with the remaining specimen having no floor slab and a supplemental lateral brace at the end of the RBS. The results from the study show that a composite floor slab provides restraint to the beams, reducing the magnitude of beam top and bottom flange lateral movement in the RBS, column twist, and strength degradation due to beam instability in the RBS. The performance of each of the test specimens was found to meet the seismic connection qualification criteria in Appendix S of the AISC seismic provisions. The results of the experimental study were used to develop a procedure for predicting the torque applied to a column from an RBS connection.

An analytical study was conducted to investigate the seismic behavior of reduced beam section (RBS) moment connections to a deep wide flange column. Calibrated three-dimensional finite element models of RBS connections in perimeter special moment resisting frames with deep columns were used to perform parametric studies under inelastic monotonic and cyclic loading. The parameters in the study included: beam-to-column connection type, column section, composite floor slab, panel zone strength, and beam web slenderness. The results from the parametric study show that a composite floor slab provides restraint to the top flange of the beams, reducing the magnitude of beam top and bottom flange lateral movement in the RBS, column twist, and strength degradation due to beam instability in the RBS. The effect of beam web slenderness contributing to an increase in the lateral movement of the beam flange in the RBS and column flange is significantly reduced when a composite floor slab is present. A weaker panel zone results in higher potential for ductile fracture in the connection region. An RBS connection to a deep column is shown to have less potential for ductile fracture in the connection region than a welded unreinforced flange connection. The potential for fracture is increased in RBS connections when the column section properties are reduced, leading to larger stress and strain.

A series of static strength tests were performed on full-scale precracked square-to-square hollow section welded T joints. These joints were subjected under brace end axial load until failure using a special purpose designed test rig. An alternating current potential drop technique was employed to monitor the crack propagation during the tests. In addition, three sets of linear variable displacement transducers were used to record the crack mouth opening displacements. The tests were performed at room temperature; therefore, the material is on the upper shelf of the ductile-brittle transition curve where failure occurs in a ductile manner. In all these tests, a stable ductile tearing was observed with a small tearing region. Based on the yield line theory, the plastic collapse load is estimated, and then applied to the failure assessment diagram (FAD) of BS7910. The results show that BS7910 Level 2A FAD provides an adequate procedure for the assessment of cracked square-to-square hollow section T joints.

For assessing the integrity of damaged hollow section joints, the plastic collapse loads of the joints containing cracks is an important parameter. Very little published information is available in the literature concerning the residual strength of square hollow section (SHS) joints containing defects or cracks. In this paper, an accurate numerical modeling of SHS T joints with cracks is proposed, whereby the entire finite element mesh is generated automatically. To validate this numerical model, several T joint models are studied and compared with the experimental data. A good agreement is obtained on the ultimate loads. Based on this model, the plastic collapse loads under different geometrical ratios are studied, and they are compared with the results calculated from the yield line theory. It is found that the yield line theory can give a reasonable prediction of the plastic collapse loads when the brace width to chord width ratio $\beta$ is less than 0.8. The failure assessment diagrams (FAD), constructed using the $J$ -integral predictions, have confirmed that the standard BS7910 Level 2A FAD is appropriate for determining limits of safe loading of cracked SHS T joints, provided the plastic collapse load is calculated using the yield line formulae neglecting the influence of the welds.

The ACI standard 318-02 permits the use of a moment magnifier approach for the design of slender composite steel-concrete columns. This approach is strongly influenced by the effective flexural stiffness $\left(\mathit{EI}\right)$ , which varies due to the nonlinearity of the concrete stress-strain curve and the cracking along the column length among other factors. The $\mathit{EI}$ equations given in the ACI code are approximate when compared to the $\mathit{EI}$ values computed from the axial load-bending moment-curvature relationships. This study was undertaken to determine the influence of a full range of variables on $\mathit{EI}$ used for the design of slender, tied, composite columns in which steel shapes are encased in concrete, and also to examine the existing ACI $\mathit{EI}$ equations. Approximately 12,000 isolated square composite columns, each with a different combination of specified properties of variables, were simulated and used to generate the stiffness data. The columns studied were subjected to short-term ultimate loads and equal and opposite end moments causing symmetrical single curvature bending about the major axis of the encased steel section. A new nonlinear equation for $\mathit{EI}$ was then developed for use in design of slender composite columns subjected to major axis bending and is proposed as an alternative to the existing ACI $\mathit{EI}$ equations.

This paper presents test results of ten single-story reinforced concrete masonry shear walls. Test results are summarized and compared with design formulae specified by the New Zealand masonry design standard NZS 4230:1990 and by the National Earthquake Hazards Reduction Program. It was determined that the test walls exhibited shear strength significantly exceeding the NZS 4230:1990 maximum permissible shear stress, confirming that NZS 4230:1990 was overly conservative in accounting for masonry shear strength. It was also confirmed from the test results that masonry shear strength increases with the magnitude of applied axial compressive stress and the amount of shear reinforcement, but that the shear strength decreases inversely in relation to an increase in wall aspect ratio. In addition, it was shown that the postcracking performance of shear dominated walls was substantially improved when uniformly distributing the shear reinforcement up the height of the walls.

The focus of this paper is to describe the idea and the theory behind a finite-element model developed for analysis of timber trusses with punched metal plate fasteners (nail plates). The finite-element model includes the semirigid and nonlinear behavior of the joints (nonlinear nail and plate elements) and contact between timber beams, if any (bilinear contact elements). The timber beams have linear-elastic properties. The section forces needed for design of the joints are given directly by the finite-element model, since special elements are used to model the nail groups and the nail plate area over the joint lines. The finite-element model is based on the Foschi model, but with further improvements. After the theory of the model is described, results from experimental tests with two types of nail plate joints are compared with predictions given by the model. The model estimates the behavior of the joints very well at lower load levels. At higher load levels the stiffness is overestimated due to development of cracks in the timber and the linear-elastic timber properties in the finite-element model.

William Howe’s 1840 patent truss was intended to be posttensioned by tightening nuts on iron rods. Since the wood diagonals simply bear on node blocks, the two diagonals in a panel are both functional only if precompressed. To properly rehabilitate Howe bridges and to guide new designs, it is important to understand the prestress forces that are induced initially and how they change with time. Results of linear elastic analyses for the actions of tensioning vertical rods and temperature changes are reported. Tensioning vertical rods at one location induces forces primarily in the two adjacent panels and causes very small upward vertical displacements. An increase in temperature decreases prestress forces; therefore, prestressing should not be done at low temperatures. A linear viscoelastic analysis is formulated using a standard-linear-solid constitutive model. The formulation is used to predict the time-dependent behavior of the Pine Bluff Bridge in Indiana. Time histories of forces and displacements are computed. Displacements increase and prestress forces decrease over time because of the viscous behavior of wood. Prestress losses decrease as the relative axial stiffness of the metal rods decreases.

Use of finite-element simulations in designing and analyzing roadside hardware has increased significantly over the past decade. Due to considerable progress in computer technology in conjunction with nonlinear finite-element software, outcome of complex vehicle-roadside hardware collisions can be accurately predicted using simulation programs. In this paper, the finite-element simulation program LS-DYNA was used to analyze and improve the crash test behavior of New York Department of Transportation Portable Concrete Barrier (NYPCB). A full-scale crash test demonstrated that the current NYPCB design was unable to meet national standards. Inspections after the test revealed that the welding at metal connectors forming the joint between the barrier segments was not properly fabricated. A finite-element representation of the crash-tested barrier was developed with a special fillet weld with failure model and subjected to crash testing using the nonlinear finite-element code LS-DYNA. This baseline model simulation was intended to replicate the failed crash test and validate the fidelity of the finite-element models. Qualitative and quantitative comparisons show that the baseline model simulation was successful in replicating the failed crash test. Upon validation, an improved NYPCB model was developed by using proper welding details and subjected to full-scale impact simulation to determine whether this design would satisfy the crash testing requirements. Results of the simulation were encouraging. It was predicted that the barrier would successfully contain and redirect the impacting vehicle in a stable manner. Subsequent full-scale crash testing on the NYPCB with proper welding details passed the NCHRP Report 350 requirements and substantiated LS-DYNA predictions.

First-order reliability analyses were performed for wood connections, using bolts, nails, lag screws, and wood screws, including both wood and steel side plates, designed to ASCE 16-95. The reliability analyses were performed using the European yield model to determine the connection capacity. Using reasonable statistics for the random variables in the yield equations, a reliability index was determined for each of the possible failure modes for both single and double shear connections. Simple bounds were then determined for the reliability index of the series system consisting of multiple failure modes. These reliability analyses show that designs to ASCE 16-95 do not exhibit consistent reliability across the range of possible designs. One way to increase consistency is to use the full set of yield equations rather than the simplified set of design equations now present in ASCE 16-95 for most of the connectors. Other modifications may also be necessary since there are inconsistent reliability levels even for those connectors designed to the full set of equations.

This paper presents a nonlinear model used to predict the load–deflection responses and axial load–moment interaction curves of pretensioned concrete-filled circular composite tubes. The model accounts for the prestressing effect, which not only improves serviceability, but also activates a confinement mechanism of the concrete core restrained by the tube. The enhanced performance of confined concrete is considered. In the compression side, the tube is modeled as a biaxially loaded membrane, subjected to longitudinal compressive and hoop tensile stresses, and failure is detected using the Tsai–Wu biaxial strength envelope. Progressive failure of layers of fibers at various directions within the tube leads to stiffness degradation, and is modeled using the classical lamination theory–ultimate laminate failure approach. The model is verified using experimental results and used in a parametric study to evaluate the effects of prestress level, amount and material type of prestressed reinforcement, and thickness and laminate structure of the tube. It was shown that ignoring concrete confinement would highly underestimate the flexural strength. The tube’s thickness and laminate structure have a much larger effect on flexural strength than the number of prestressing strands.

In this paper, a procedure is proposed for calculating the interaction diagram of a vertical pile group subject to axial load and biaxial moments; equations are then applied to the AASHTO LRFD code. Several cases are presented, depending on the efficiency of the pile group, and it is shown that the interaction diagram can be a pentahedron, a hexahedron, an octahedron, a nonahedron, or a decahedron. It is shown how the use of convex analysis and computational geometry leads to a rational calculation of the load effects and of the relationship between load effects and an interaction diagram. When the design entails evaluating several design alternatives, the methods of computational geometry yield a fivefold to tenfold computational saving with respect to considering all load combinations. A simple numerical example shows the application of the proposed procedure in a typical design setting, and highlights the advantages of the proposed procedure.

Although multiple-mode pushover analysis methods have been proposed for general use in the seismic analysis of moment-resisting frames, difficulties have been encountered in their implementation with specific structures. Two alternative multiple mode methods were developed to overcome these difficulties. Estimates of four response quantities determined with the alternative methods are compared herein for a set of five buildings subjected to suites of scaled ground motions. The uneven accuracy of the estimates, relative to the range of values determined by nonlinear dynamic analysis, suggests that results obtained by both alternative methods should be regarded with caution, until such time that the scope of applicability of the methods has been clearly established.

A properly designed two-way stiffened (stiffened both in longitudinal and transverse directions) shear panel can sustain large deformation without pinching and consequent strength degradation. Hence it can be used as an effective passive energy dissipating damper (PEDD) in building and bridge structures to absorb seismic energy. In this Technical Note, a series of steel shear panels with 1, 2, or 3 two-way stiffeners has been analyzed under cyclic loading by the general-purpose finite element program ABAQUS, in which a modified two-surface model is incorporated to trace the material nonlinearity. Slenderness of web, $R_w$ , is employed as a key parameter to investigate the hysteretic performance of stiffened shear panels. The sensitivities of the ratio of stiffener rigidity to optimum stiffener rigidity, ${\gamma }_s∕{\gamma }_s^{*}$ , the ratio of flange thickness to web thickness, $t_f∕t_w$ , and aspect ratio, $\alpha$ , are also investigated. Finally, a simplified bilinear model for stiffened shear panels acting as a PEDD is presented in this Technical Note based on FEM results. The proposed model is expected to get use in the time-history analysis of engineering structures that employ the PEDD to mitigate seismic hazard.

In characterizing the mechanical properties of oriented strand boards (OSBs), the punching shear capacity is not normally determined. Any attempt at developing a failure theory for punching shear from the planar shear strengths and a hypothetical shear perimeter that is similar to the approach in concrete should be most welcome by OSB designers. Fortunately, the planar shear strengths of OSBs are gradually being documented. The planar shear strengths and the punching shear capacities under a 25-mm-diameter load applicator of six OSB panels with thicknesses ranging from 9 to 18 mm have enabled a preliminary assessment of the optimum position of the hypothetical shear perimeter in an empirical punching shear failure theory for OSB. It is shown that a hypothetical shear perimeter that is a distance equal to the thickness away from the boundary of the loaded area enables the prediction of punching shear capacities that are roughly 75% of the measured punching shear capacity for one panel and within 10% of the measured punching shear capacities for the other five panels. Given that punching shear capacity of OSBs is rarely documented, and subject to future validation by other OSB panels, this empirical failure theory could be potentially useful for estimating the punching shear capacity of oriented strand board.