Journal of Structural Engineering

A method has been developed for the design of reinforced concrete (RC) members when subjected to blast loadings based on the nondimensional energy spectrum. Numerical analyzes showed good agreement between the approximate responses of RC members designed to their respective levels of target response. This paper further verifies this method through the actual response of a RC column and beam subjected an actual denotation of explosives at a short standoff. When subjected to blast loading from a short standoff distance, the cantilever column behaved predominantly in direct shear. Thus, ways to mitigate the damage of a cantilever column should draw focus on the robustness. The developed design procedure provides a feasible method for the blast resistant design of members, subjected to blast loads at a short standoff distance.

A series of large-scale shaking table tests is conducted for a high-rise building structure subjected to long-period ground motions. A test method is developed to preserve the original dimensions of structural members of a prototype building that has 21 stories with a total height of 80 m. The test specimen consists of a four-story, two-span by one-bay steel moment frame and three substitute layers placed on top of the moment frame. The substitute layers, which consist of concrete slabs and rubber bearings, are arranged to represent the upper stories of the prototype. From preliminary vibration tests, equivalence between the test specimen and the prototype is verified in terms of the lower mode natural periods and corresponding mode shapes. The test specimen when subjected to long-period ground motions exhibits cumulative ductilities more than four times those expected in Japanese seismic design, while the maximum story drifts remain nearly the same as those considered in the design. A number of cyclic inelastic deformations caused fractures at the bottom flanges of beam ends. According to these observations, the combination of large cumulative ductility demand, the weld quality of the field weld connections, and the promotion of strain concentrations at the toe of the bottom flange weld access hole by the presence of floor slabs caused the fractures and resultant smaller cumulative ductility relative to that observed in the bare beam tests.

A study investigating the modal properties and dynamic response of several laboratory-constructed and in situ floors supported with cold-formed steel C-shaped joists for floors was conducted. The tested floors were typical of residential midrise applications, with oriented-strand board, FORTACRETE, and cold-formed steel deck subfloors, both with and without lightweight concrete topping. Details including span, large lip-reinforced web openings, subfloor, topping, strongback, and framing condition were varied to observe their influence on the fundamental frequency, damping ratio, and deflection. Suggestions for the design and remediation of floors where vibration serviceability is a concern are given. Laboratory tested floor systems were generally found to be the worst-case scenario for the natural frequency and damping ratio. Furniture and finishes were found to not appreciably change the performance of a floor system. The responses of the floor systems tested in this study were evaluated against the ISO 2631 limit for maximum acceleration and Onysko’s static deflection limit, as presented in ATC Design Guide 1: Minimizing Floor Vibration. The in situ floors examined were found to have performed within the acceptable range, as defined by the two criteria.

A computational study was conducted to investigate the nonlinear response of composite frames consisting of rectangular concrete-filled steel tube (RCFT) beam-columns and steel framing subjected to static and dynamic loads. Following mixed finite-element principles, a three-dimensional fiber-based beam finite-element model was developed, allowing slip deformation between steel tube and the concrete core. Comprehensive material constitutive relations were developed for the steel tube and the concrete core through examining the experimental results in the literature. The uniaxial stress-based steel and concrete constitutive relations include modeling of the effects of confinement, steel tube local buckling, cycling concrete into both tension and compression, cyclic softening, and other key cyclic phenomena observed for steel and concrete in RCFT members. The finite-element model was verified against a wide range of experimental tests under monotonic, quasistatic cyclic, and pseudodynamic loading conditions. The mixed finite-element model produced strong correlations with experimental results to simulate the nonlinear response of RCFT members with excellent computational efficiency.

Consistent with capacity design principles and requirements of ductile behavior, the 2005 AISC and 2001 CSA seismic design codes require that the intermediate horizontal boundary elements (HBEs) of steel plate shear walls (SPSWs) be designed to remain essentially elastic with the exception of plastic hinges at their ends when the infill plates fully yield under seismic loading. However, the unexpected failure observed during the tests on a full-scale two-story SPSW suggested that the current design approach does not necessarily lead to an intermediate HBE with the expected performance. This paper presents analytical models for estimating the design forces for intermediate HBEs to reliably achieve capacity design. Those models combine the assumed plastic mechanism with a linear beam model of intermediate HBE considering fully yielded infill panels and are able to prevent in-span plastic hinges. Design forces predicted using the proposed models are compared with those from nonlinear finite element analysis. Good agreement is observed. Finally, the proposed models are also used to explain the observed premature failure of intermediate HBE.

In this paper, seven reinforced concrete-block shear walls with aspect ratios of 1.5 and 2.2 (two- and three-storey high) were tested under displacement-controlled cyclic loading. The response of rectangular, flanged, and end-confined walls, designed to have the same lateral resistance when subjected to the same axial load, is discussed. In general, high levels of ductility accompanied by relatively small strength degradation were observed in all walls with a significant increase in ductility and displacement capabilities for the flanged and end-confined walls compared to the rectangular ones. For both aspect ratios evaluated, the drift levels at 20% strength degradation were 1.0, 1.5, and 2.2% corresponding to the rectangular, the flanged, and the end-confined walls, respectively. The ductility values of the proposed flanged and end-confined walls were, respectively, 1.5 and 2 times those of their rectangular wall counterparts (with the same overall length and aspect ratio). In addition to the enhanced ductility, a saving of more than 40% in the amount of vertical reinforcement was achieved using the proposed alternative strategies while maintaining the same lateral wall resistance. Existing design clauses were used to predict the wall capacities using the American and the Canadian masonry codes and showed excellent agreement. This will facilitate adoption of the new construction categories with minimal modifications to existing code clauses. The test results indicate that higher ductility than the currently endorsed values by North American codes should be used for rectangular walls. Moreover, higher values should be expected when the proposed strategies are adopted which would significantly reduce the seismic demand on reinforced concrete-block shear wall construction.

Long-period pulse components in near-field ground motions have been known to cause significant damage to flexible structures. In this paper, an empirical mode decomposition (EMD) approach is used to identify and separate the dominant pulse, high-frequency, and long-period components in near-field ground motions. The pulses synthesized by an analytical pulse model recently proposed by the authors are compared to the extracted pulse components from recorded earthquake records using EMD, and the responses of linear and nonlinear structures subjected to these components are analyzed. The results demonstrate that (1) the characteristics and effects of the pulses generated by the analytical pulse model are similar to those of the extracted pulse components and (2) the pulse components are responsible for the peak responses of elastic structures subjected to near-field ground motions and govern the extent of inelastic structural damage in all frequency ranges.

Light-frame wood buildings represent most of residential structures throughout the United States. Approximately half of the U.S. population lives within 50 miles of the coast with many of those dwellings in the Gulf Coast region or along the eastern seaboard, both of which can be negatively impacted by hurricanes. The majority of damage during a hurricane is the result of wind-driven rainwater entering a building through openings caused by strong wind. To date, wind fragility approaches to examine the probability of damage to a light-frame wood building have focused only on component or subassembly strength, thereby providing information up to the point of first failure of the building envelope. These previous analyses, while valuable, will not allow hurricane engineering research to progress to fully mechanistic loss modeling, which is needed to mitigate losses caused by these events. In this paper a methodology to develop fragility curves and fragility surfaces for the volume of rainwater intrusion is summarized and demonstrated on an example structure. To do this, nonlinear structural analysis, computational fluid dynamics, and reliability theory are combined with particle dynamics for rainwater trajectory modeling, essentially providing the first fragilities of their kind and going beyond first failure of the building envelope. It should be emphasized that it is the methodology that is the focus and some level of calibration is still necessary.

A finite-element model (FEM) is developed to predict the load-displacement behavior of a composite wood-concrete floor/deck system under short-term loading. The interlayer connection was modeled with link elements dedicated for connection modeling. Results of past tests of two full-scale layered floor/deck specimens are employed to confirm the FEM model. The specimen had a layer of solid sawn lumber overlaid by concrete and interconnected to it with a pattern of notched shear key/anchor details. The FEM results agreed closely with the measured deflection data for the loadings considered. The efficiency of composite behavior achieved by each of those specimens is quantified by a conventional and three improved approaches based on the computer modeling and measured test results. The new approaches better capture the overall efficiency of the entire floor/deck.

A three-dimensional nonlinear finite-element model of single nail connection was developed based on transversely isotropic plasticity. In order to have the connection model account for crushing behavior of wood during the nail embedment, a procedure was studied to implement the theory of a beam on a nonlinear foundation in the solid element modeling. Within a prescribed volume of wood surrounding a nail, a wood foundation was defined with the foundation material parameters, which were determined through nail-embedment tests. Introduction of the wood foundation to the connection model was justified by comparing the results of nail-embedment simulations with or without a wood foundation. Three-dimensional finite-element analyses of single nail connections incorporated with wood foundations were compared with the results of lateral resistance tests of the connections under parallel to grain loading and perpendicular to grain loading. The model predictions showed good agreement with the load-slip relations and the actual deformed shapes of the connections.

This paper presents the results of an experimental study on the critical buckling load and lateral bracing force of metal plate connected wood truss assemblies. Material property tests—including the modulus of elasticity of dimension lumber, flexural stiffness of plywood panels, and load-slip relationship of nail connection—and full-scale tests of individual trusses and truss assemblies were conducted. The critical buckling load and lateral bracing force were recorded. The continuous lateral bracing, the load sharing and distribution effects, and the residual deformation at the metal plate connections were studied for their influence on the system’s stability performance. The adequacy of the 2% rule of thumb, which is used by some design engineers for lateral bracing system design, was also discussed by comparing to the test results of the lateral bracing forces. The generated database can be used as input parameters and for verification for numerical analysis models and therefore contributes to the improvement of the design methods in the long term.

Results from 50 bond tests conducted using the so-called direct tension pullout specimen type are presented. Anchorages of steel bars with machined deformations were tested so as to enable a targeted study of the effect of rib height and related rib area on bond behavior; tests were conducted with or without the combined presence of external confinement over the embedded length. The novel specimen form presented in the paper was designed to simulate the state of stress arising in usual bar anchorages in the tension zones of flexural members (where both cover concrete and bar are stressed in tension). This development was motivated by the need to eliminate spurious influences of the test setup on specimen behavior, which are known to interfere with bond mechanics in conventional bond tests leading to unconservative estimates of bond strength and misleading interpretations as to the true parametric dependencies of the bond problem. Additional parameters studied in the experimental program were the development length, the cover thickness, the effect of confinement, and the tensile strength of concrete. Data reduction (local bond strength and slip estimates) was possible by fitting the exact solution of the differential equations describing the state of stress along the anchorage to the test measurements, while accounting for important phenomena such as yield penetration or debonding, and bond plastification. Next, the obtained values for local bond strength were used for calibration of the frictional analog for bond strength (a Mohr-Coulomb failure criterion). Milestone values for bond and slip were estimated with reference to the code limit-state model for bond.

Peak bending moments are compared for a set of steel portal frames of industrial buildings in an open terrain calculated using database-assisted design (DAD) techniques and ASCE 7-05 Standard plots. The comparisons indicate that, depending on the building dimensions, the peak bending moments at the knee based on DAD techniques are generally larger by 10–30% than their counterparts based on the ASCE 7-05 plots. (In one case with a relatively steep roof slope of 26.6° the discrepancies exceed 70%.) For the buildings considered, the discrepancies increase with increasing roof slope and with increasing eave height.

Prestressed concrete sleepers (or railroad ties) are the crosstie beam support in railway track systems. They are designed and constructed under flexural constraints in order to carry and transfer the dynamic wheel loads from the rails to the ground. Under perfect wheel and rail conditions, the dynamic loading on railway tracks could be treated as a quasi-static load using a dynamic impact factor. The current design method for the prestressed concrete sleepers taking into account the quasi-static effect is based on allowable stress where crack initiation is not permitted. In reality, the impact events are often detected due to the uncertainties of wheel or rail abnormalities such as flat wheels, dipped rails, etc. These loads are of very high magnitude but short duration. Over the design life span of the prestressed concrete sleepers, there exists the feasibility of extreme and repeated impact loading events. These have led to two proposed limit states for the consideration of structural engineers: ultimate limit states and fatigue limit states. Prestressing techniques have been long used to maintain the high endurance of the sleepers under repeated impact cycles. In spite of the most common use of the prestressed concrete sleepers, their impact behavior and capacity under the repetitions of severe impact loads are unclear. This paper presents the experimental investigation aimed at understanding the dynamic crack propagations in prestressed concrete sleepers in railway track structures under repeated impact loading. The impact forces have been correlated against the probabilistic track force distribution obtained from an Australian heavy haul rail network. The effects of track environment including soft and hard tracks are highlighted in this paper.