Journal of Structural Engineering

Assessing the stability of steel building frames exposed to fire conditions is challenging because of the need to consider the elevated temperature properties of steel, nonuniform heating of structural members, and large deformational demands on the frames. This challenge is further intensified if the stability of the frame is also influenced by the lateral forces of an earthquake that preceded the fire. Although there has been significant progress recently in simulating the response of frames using finite-element methods, there is a need for computationally efficient tools that would minimize the modeling effort and allow for accurate and rapid assessment so that a large number of simulations can be conducted. To this end, the present study aims to develop a framework for conducting a stability analysis of steel columns subjected to demands imposed by lateral loading followed by fire. A nonlinear formulation is proposed to assess the stability of W-shaped steel columns under multihazard loading scenarios. Results from the proposed formulation show good agreement with available strength design equations of steel columns at ambient and elevated temperatures. This computationally efficient tool can be used to investigate the effects of a wide variety of variables on the stability of steel columns subjected to fire and fire following earthquakes.

Pneumatically driven steel pins have been successfully used for attaching structural sheathing to cold-formed steel framing in both load-bearing and nonload-bearing applications. The design of these types of connections is exclusively based on published manufacturer data. Attempts to analytically quantify/estimate the shear and withdrawal (tensile) strength of pin connections is nearly nonexistent. This paper proposes a mechanics-based equilibrium model for withdrawal strength and presents test data for wood structural panels connected to cold-formed steel with pneumatically driven steel pins. The tests include a range of wood panel and cold-formed steel thicknesses commonly found in light-frame construction. Using the proposed model, empirically modified to reflect observed behavior, equations are presented to estimate the withdrawal strength of connections made with helically knurled pins. The proposed equations are shown to provide reasonably good estimates of strength with a reliability consistent with that of the more commonly used screw fastener.

The development of models to predict the inelastic behavior of the individual components of a building system at different performance levels is an essential step in performing nonlinear static and dynamic analyses, as recommended by ASCE/SEI-41. However, current methodologies for generating nonlinear models for reinforced masonry shear wall (RMSW) buildings do not adequately account for various system-level aspects, such as the influence of the floor slab stiffness. Several recent studies have shown that these aspects would significantly alter the overall building response under seismic loading. In addition, although ASCE/SEI-41 defines the capacity parameters of reinforced masonry shear walls (RMSWs) with rectangular cross sections through standardized force-displacement backbone relationships, no corresponding relationships are available for RMSWs with boundary elements. Moreover, ASCE/SEI-41 does not provide the necessary hysteretic parameters required to define the cyclic behavior of any type of RMSWs under seismic loading. To address these issues, this study focuses on developing two ASCE/SEI-41 relevant models for RMSW buildings, based on the currently available provisions pertaining to their reinforced concrete (RC) counterparts. The first model is a backbone model for RMSW buildings without and with boundary elements that can be used to perform nonlinear static analyses. The experimentally validated modeling approach shows that RC parameters are applicable, but it is critical to include the out-of-plane stiffness of the floor diaphragms when evaluating the overall building response. The second model is a concentrated plasticity (spring) model in OpenSees used to simulate the hysteretic response of RMSW buildings with different configurations, to conduct nonlinear dynamic analyses. Finally, the developed numerical hysteretic responses are compared with experimental results in terms of the most relevant characteristics, including the initial stiffness, peak load, and stiffness and strength degradation as applicable. This study aims at presenting useful system-level response prediction tools for the nonlinear static and dynamic procedures specified by ASCE/SEI-41.

In U.S. building construction, typical simple (shear) connections are often bolted for flexibility during fabrication and construction. This paper summarizes the results of experimental investigations of bolted lap-splice joints at elevated temperatures. This paper provides a comprehensive overview of previously tested bolted lap-splice joints at elevated temperatures and a new testing series performed by the authors. Bolted lap-splice joints represent a simple approximation of simple bolted connections. The authors tested specimens using steady-state conditions at targeted temperatures. The tests considered two failure modes: bolt shear fracture and bolt bearing. The authors considered varying parameters within the connection such as bolt diameter, edge distance, and thickness of plate. The results of these experiments are temperature-dependent bolt shear fracture capacities and experimentally measured axial force–deformation–temperature relationships. The temperature-dependent bolt shear fracture capacities are compared with those capacities previously measured by other researchers and the temperature-dependent retention factors provided in Eurocode. The axial force–deformation relationships are compared with previously developed numerical models.

This paper reports the results of an experimental investigation of the shear behavior of beams made using hybrid fiber–engineered cementitious composites (HFECC). The paper specifically deals with the shear behavior of beams made using strain hardening engineered cementitious composites that incorporate relatively low volume ratios ($V_f\le 2\%$) of discontinuous, randomly distributed hybrid fibers (steel and polyethylene) and how the strain hardening characteristics of the fiber composite impact the shear behavior of the beam. A total of 21 beams reinforced with longitudinal steel bars and with various combinations of polyethylene (PE) and steel (ST) fibers were tested in a three-point loading setup at a shear span to depth ratio of 3. The total volume fraction of the fibers in the composites ranged from 0 to 2%, and the matrix was either cementitious paste or cementitious mortar. The beams were tested in controlled deformations to enable capturing the postpeak behavior. It is shown that HFECC made using cementitious paste was effective in increasing the shear strength by up to 8 times relative to the nonfibrous matrix. In addition, the ductility, multiple cracking behavior, and shear strain capacity of the beams were considerably improved. Improvements were also observed in the HFECC beams made with cementitious mortar but to a lesser extent, in which the shear strength increased up to 3 times relative to the nonfibrous matrix. The results also showed that when used in HFECC, the PE fibers were nearly as effective as steel fibers in increasing the shear strength. The addition of fibers allowed the beams to reach or exceed their calculated flexural capacity in spite of the relatively large longitudinal reinforcement ratio used. A fiber volume of 1% is shown to be an adequate minimum shear reinforcement for beams with compressive strengths ranging from 40 to 65 MPa, irrespective of the hybridization ratio and the binding matrix.

Caribbean-style hybrid concrete-masonry structures consist of a RC frame infilled with partially grouted and reinforced masonry walls that are connected to the RC frame with cast-in-place dowels along one or more edges of the infill. Currently, there is little guidance in existing codes for the assessment of infills with such connections to the bounding frame. This paper proposes a finite-element modeling scheme for hybrid concrete-masonry structures combining smeared crack and interface elements. The model is used to predict the behavior of two hybrid concrete-masonry frames subjected to cyclic loading. The proposed finite-element modeling scheme closely predicts the peak capacity, the displacement at peak capacity, and the damage patterns of the test structures. Finally, sensitivity studies are conducted with the validated numerical models to investigate the influence of the dowel connections and masonry properties on the seismic performance of these structures. The results indicate that increasing the amount of reinforcement in the masonry infill makes the influence of the dowel connections become more pronounced, increases the strength of the structure, and lowers its ductility.

The self-centering modular panel with a slit steel plate shear wall (SCMP-SW) is a new seismic load-resisting structural component that combines recentering capabilities and energy dissipation ability. The self-centering modular panel is designed as a posttensioned steel moment resisting frame and in this study two types of SCMP-SWs with slightly different configurations are fabricated and tested, which could be potentially inserted into framed structural systems. In this paper, the prefabricated SCMP-SW is installed into a beam-through steel frame, while the slit wall is intended to serve as replaceable fuse elements for energy dissipation purposes. A series of experimental tests were conducted to investigate the cyclic loading behavior of the SCMP-SW with two different types of self-centering modular panels and slit walls. The experimental results show that SCMP-SW is capable of recentering upon unloading while retaining the moderate energy-dissipation capacity of the slit walls. It is also observed that due to the self-centering modular panel, after severe cyclic loading the system with newly replaced slit walls and a reused main frame exhibits almost identical structural performance (stiffness, strength, and recentering ability) to the original system.

Allowing a wall to rock and uplift during a seismic event can cap the forces and minimize the postevent residual damage. Slip friction connections comprised of flat steel plates sliding over each other have been experimentally tested as the hold-down connectors in timber shear walls and performed well in terms of the hysteretic behavior and the energy dissipation rate. However, the main disadvantage of these joints is the undesirable residual displacements. In recognition of this fact, a novel type of friction joint called a resilient slip friction (RSF) joint is proposed. The innovative configuration of this joint provides the energy dissipation and self-centering behavior all in one compact package. This paper describes the large-scale experimental test conducted on a rocking cross-laminated timber (CLT) wall with RSF joints as the hold-down connectors. Additionally, a series of capacity equations are presented and validated by comparing the analytical results with the experimental data. The results confirmed that this technology has the potential to provide a robust solution for seismic-resilient structures.

This paper puts forward a risk-based approach to prioritize a portfolio of buildings for retrofit. A new set of local sensitivity measures is proposed to rank the buildings based on the optimal mitigation of risk to the entire portfolio. The proposed measures employ the derivative of various risk measures with respect to the cost of retrofit for each building. These risk measures are the mean and higher moments of the total portfolio cost probability distribution. The total portfolio cost comprises the construction cost due to retrofit and the repair cost due to damage. The proposed sensitivity measures quantify the reduction of risk to the entire portfolio per dollar spent on retrofitting each building. They provide the flexibility to prioritize under risk-neutrality and risk-aversion. To quantify the risk, reliability methods were employed in which many interacting probabilistic models evaluate the costs. The proposed methodology was applied to prioritizing 114 masonry school buildings in Iran for seismic retrofit. To this end, models were developed to predict the repair and the retrofit cost of masonry structures.

In this study, the behavior of posttensioned reinforced concrete (PC) beam-column subassemblages subjected to the loss of a middle column is investigated experimentally. The influence of unbonded posttensioning strands (UPS) with a parabolic curve on the behavior of reinforced concrete (RC) frames to resist progressive collapse is also quantified. Test results indicated that UPS have little effect on the yield load and first peak load of frames to resist progressive collapse. However, UPS could significantly increase the ultimate load capacity of the frames because stretching of strands could provide considerable additional vertical load resistance. UPS will aggregate the damage in the beam ends near to the middle column, although they may relieve the damage in the beam ends near to the side column. Moreover, UPS may change the load-resisting mechanism of the RC frame. No reliable compressive arch action developed in PC beams to resist progressive collapse because the UPS changed the distribution of the compressive stress along the beams. In addition, the effects of span/depth ratio and effective prestress in UPS on the progressive collapse resistance of PC frames are investigated. It is found that the span-depth ratio has a significant effect on the performance of RC frames to resist progressive collapse, but not the PC frames. The effective prestress in UPS has little effects on the yield load and initial stiffness of the PC frame, but it may significantly affect the ultimate deformation capacity and ultimate load capacity of the PC frame.

An improved analytical evaluation model considering both the interbuilding coupling caused by the link and the intrabuilding structural coupling caused by eccentricities is developed for linked building systems (LBS). Expressions for the modal properties of four representative configurations of the eccentricities are derived. Applying these expressions to an example LBS shows that the intrabuilding structural coupling can cause significantly coupled modes. The wind-induced responses of a series of LBS with different intrabuilding structural couplings are calculated. It is found that there are a few favorable configurations of the intrabuilding structural coupling that can enhance the performance of wind-excited LBS. The results can provide guidance to researchers and engineers on designing a favorable configuration concerning the intrastructural coupling of linked buildings at the initial design stage.

Structural engineering is undergoing a profound change toward a life-cycle-oriented design philosophy. An effort is ongoing within SEI/ASCE to promote the transition toward this new design paradigm by using life-cycle cost analysis in conjunction with the Grand Challenge of reducing life-cycle costs of civil infrastructure projects by 50% by 2025. A Special Project approved by the SEI Technical Activities Division Executive Committee is part of this effort and includes a survey on the life-cycle performance of civil structure and infrastructure systems. The main results of the survey are presented by addressing life-cycle concepts and methods, deterioration and damage evaluation, life-cycle performance indicators, inspection and maintenance procedures, life-cycle cost analysis, and implementation in design practice. These results are expected to complement information on the state-of-research and -practice, promote a better understanding of life-cycle concepts in the structural engineering community, and foster methodologies and tools to incorporate life-cycle concepts into structural design codes and standards.