Journal of Structural Engineering

This paper provides perspectives on multihazard engineering in the contemporary structural engineering context in order to frame the breadth and multiple dimensions it encompasses, to summarize recent activities on selected relevant topics, and to highlight possible future directions in research and implementations. A comprehensive overview of all research and points of view on these broad topics is beyond the scope of this paper. Rather, the objective is to provide selected examples to illustrate the nature of the issues and possible solutions, with the understanding that multihazard design is a relatively new endeavor and that the accomplishments in this field for the most part lie ahead. Topics covered include description of the political context that led to multihazard design, review of current return periods and safety indices for various hazards in model design codes, issues related to hazard interaction and cascading effects, considerations for interdependent systems, and structural element optimization to provide multihazard resistance.

A fiber-section model for nonlinear analysis of shear-critical reinforced concrete frames is developed. The model incorporates a new procedure for the computation of an exact shear strain profile and corresponding shear stress distribution over the cross section. Longitudinal axial strains are evaluated based on the plane section assumption, whereas transverse strains are determined from equilibrium in the vertical direction, following classical beam assumptions. Axial-shear interaction at the fiber level is based on a smeared-crack orthotropic constitutive model, which uses equivalent uniaxial material models for concrete and steel in the crack and reinforcement directions, respectively. Shear strain components at the crack, arising from deviations between principal and crack directions, are related to shear stresses by means of a shear stiffness term that fully satisfies compatibility and equilibrium conditions. The procedure was implemented into a force-based element and applied to monotonic and cyclic analysis of lightly reinforced beams, shear-critical frames, and columns.

The steel-plate shear wall with coupling (SPSW-WC) system is a natural extension of the conventional steel-plate shear wall (SPSW) seismic force–resisting system. The SPSW-WC configuration is created by linking a pair of SPSW piers together with coupling beams at the floor levels. Two half-scale, three-story specimens were tested using hybrid controls to simulate the bottom three stories of six-story prototype structures. The experimental SPSW-WC specimens demonstrated robust cyclic performance. Both specimens reached 4% lateral drift, the maximum displacement that could be imposed by the facility, with minimal strength degradation. Additionally, a large amount of energy was dissipated during each test, with over 20% equivalent viscous damping observed in the 4% drift cycles. The web plates, horizontal boundary elements, and coupling beams all exhibited ductile response through large inelastic deformations. The SPSW-WC configuration was shown to be a viable seismic lateral force resisting system for use in high seismic regions.

This paper investigates the time-dependent behavior of concrete-filled steel tubular (CFST) tensile members subjected to coupled long-term loading and chloride corrosion. A series of experiments for CFST members under both 120-day sustained tensile load and electrically accelerated corrosion in chloride solution are conducted, with loading ratio and corrosion rate as the main parameters. A finite-element analysis (FEA) model is established and validated by the test data for the full-range analysis of CFST tensile members considering the long-term behavior of the core concrete as well as the corrosion of the outer steel tube. The FEA model then is used for further analysis on CFST tensile members, including the interface performance, interaction between the steel tube and the core concrete, load distribution mechanism through the cross section, and ultimate strength. Parametric studies also are conducted, based on which a simplified method is suggested for calculating the tensile strength of CFST members under coupled long-term loading and chloride corrosion.

Mass timber is an attractive and sustainable alternative structural engineering material to concrete and steel. Despite successful midrise to high-rise timber building projects around the world, such buildings have not been implemented in regions with high seismicity due in part to a lack of research and development on appropriate ductile seismic load resisting systems for heavy timber construction. This paper describes experiments conducted to develop a resilient lateral force-resisting wall system that combines cross-laminated timber (CLT) panels with vertical posttensioning (PT) to provide postevent recentering. Supplemental mild steel U-shaped flexural plate (UFPs) are intended to yield under cyclic loading while the PT and CLT components remain undamaged until large interstory drifts are experienced by the wall. The experiments were designed to explore various limit states for self-centering CLT (SC-CLT) walls, including their dependence on design variables and their effect on performance, and to investigate strength and stiffness degradation at large interstory drifts. It was found that the SC-CLT walls were able to recenter even after large drift cycles and the crushing of the CLT material was the governing limit state for most specimens. A hierarchy of desirable limit states was identified consisting of UFP yielding, CLT splitting, PT yielding, and CLT crushing.

In this paper, to supplement the Canadian building code for a timber-steel hybrid structure, over-strength, and ductility-related force modification factors are developed and validated using a collapse risk assessment approach. The hybrid structure incorporates cross-laminated timber (CLT) infill walls within steel moment resisting frames. Following the FEMA P695 procedure, archetype buildings of 3-story, 6-story, and 9-story height with middle bay infilled with CLT were developed. Subsequently, a nonlinear static pushover analysis was performed to quantify the actual over-strength factors of the hybrid archetype buildings. To check the FEMA P695 acceptable collapse probabilities and adjusted collapse margin ratios (ACMRs), incremental dynamic analysis was carried out using 60 ground motion records that were selected to regional seismic hazard characteristics in southwestern British Columbia, Canada. Considering the total system uncertainty, comparison of the calculated ACMRs with the FEMA P695 requirement indicates the acceptability of the proposed over-strength and ductility factors.

Towers or tower-line systems within a power network can experience damages under rare earthquakes or strong winds. The estimation of the failure probability of a tower-line system is rarely addressed for scenario wind or earthquake events. One of the difficulties to evaluate the reliability of a tower or tower-line system is associated with the computationally demanding task of assessing the nonlinear inelastic dynamic responses or capacity curves of the towers under spatiotemporally varying wind or earthquake loads. An assessment of the capacity curve of a tower within the tower-line system (i.e., considering tower-wire interaction) under the spatiotemporally varying wind or earthquake loads is presented based on the incremental dynamic analysis. The estimated capacity curves are compared with those obtained using the nonlinear static pushover analysis for a single tower. The comparison indicates that the use of the nonlinear static pushover analysis could lead to useful results, although in such a case the uncertainty in the capacity curve caused by the record-to-record variability of the spatiotemporally varying loads cannot be captured. Moreover, a simple procedure to evaluate the reliability of a tower-line system for scenario wind or earthquake events is proposed by considering the spatial correlation of winds or ground motion measures. The results emphasize that the consideration of the spatial correlation of natural hazards could be important to estimate the failure probability of a tower-line system.

This paper develops new models predicting the initial stiffness and ultimate moment of top-seat angle connections without web angle (TSACs). The TSACs, bolted to the beam flange and the column flange, are studied to investigate the effect of the material properties of the angle, gauge distance, angle thickness, angle length, rows of bolts, depth of beam, bolt diameter, and thickness of column flange in their moment-rotation behavior. The finite-element method is used to analyze the nonlinear behavior of TSACs. Identical geometric and material properties with previous experiments by others are utilized to verify finite-element models. A more accurate equation for the initial stiffness is suggested, and good agreement between the proposed model and the various test data is shown. The type of collapse mechanisms for TSACs is established. The ultimate moment capacity modified from Kishi and Chen’s equation also is proposed, and it agrees well with the various test data.

This paper presents experimental and analytical investigations on the creep response of full-scale laminated glass panels. The experimental study comprised relatively long-term (350-h) flexural creep tests on full-scale 3-layer Polyvinyl butyral (PVB)-laminated and 4-layer SentryGlas (SG)-laminated glass panels. The experimental data were fit using Findley’s power law, and the resulting creep deformation predictions were compared with those obtained considering different interlayers’ material models available in the literature, most of which are based on dynamic mechanical analyses (DMA). The results obtained confirm that PVB-laminated glass panels present significantly higher creep deformations than those made of SG. Findley’s power law was able to accurately simulate the deflections of both laminated glass panels measured in the tests. For the PVB panel, long-term (50-year) deflection predictions using the DMA-based material models from the literature were considerably higher than those using Findley’s power law. For the SG panel, although an overall better agreement was observed between Findley’s power law and deflection predictions from material models available in the literature, significant differences were still encountered, namely for the DMA-based material model.

Seven full-scale curved T-stubs connected to concrete-filled circular hollow sections (CFCHSs) using groups of double-headed anchored blind bolts (DHABBs) have been cyclically tested in this paper considering different configurations of the DHABBs and the addition of a through bolt (TB) and shear blind bolts (SBs). The cyclic testing consisted of axial forces being applied to the T-stub stem and transmitted to the column through the bolted T-stub flange connection. The relative contributions of the embedded heads, TB, SBs, and heads bearing on the tube wall to the total applied force obtained from finite-element analysis (FEA) for each specimen considered in the experiments have been summarized. Furthermore, a parametric study has been performed using FEA software to make an assessment of which parameters are the most influential in achieving a higher secant stiffness at 0.6 $F_u$ provided that the bolts are fully pretensioned, sufficient concrete strength is provided, and the embedded heads have sufficient embedment depths. The results show that the thickness of the T-stub flange is the parameter that is most influential in increasing the secant stiffness of the connection, and it is recommended that a flange thickness of $1.25d_{bb}$ be used. The second most important parameters are the addition of a TB and SBs because these are effective in preventing premature stiffness degradation resulting from concrete cracking.

The reinforced concrete squat wall, which demonstrates high stiffness and load capacity, is one of the most effective earthquake-resisting members. It has been widely used in seismic design and retrofitting and thus is crucial to an understanding of the lateral load-displacement behavior within. Based on the strut-and-tie concept, a trilinear model is proposed to predict the lateral load-displacement curves for reinforced concrete squat walls failing in shear. This paper proposes a curve with three turning points: the cracking point associated with the apparent decrease in stiffness as the crack occurs; the strength point as the squat wall fails in shear; and the collapse point as the squat wall finally loses its axial load-carrying capacity. With a simplified calculation process, the proposed model is proven suitable for application in engineering practice and achieves successful predictions of lateral load-displacement curves for squat walls. A further comparison between the proposed model and other available models is carried out so as to further explain the differences among those models and describe their physical configurations.

This paper presents a novel bioinspired actuator that mimics the sacrificial bond and hidden length mechanism, a highly efficient energy dissipation mechanism found in bio-organisms such as abalone shell and bone. The effectiveness of the bioinspired actuator implemented in a tuned mass damper application is investigated with illustrative examples. As a basic and simple example, a single-degree-of-freedom system was studied both numerically and experimentally while subjected to a range of frequency near its resonance as the first step toward application for control of tall buildings under vortex shedding. It was found that the peak displacement of the damped system was decreased as much as 43% as compared with that with a conventional tuned mass damper. With the confirmation of both theoretical and experimental results for this basic example, a more practical and realistic example of a wind-excited 76-story benchmark building was studied. In this example, the current bioinspired tuned mass damper, although passive, showed better performance than the conventional passive tuned mass damper and was also comparable with the semiactive tuned mass damper in its capability of reduction in displacements and accelerations at various floors.

Surface and subsurface inspection of concrete structures provides useful information for the maintenance of these structures. Remote sensing techniques such as radar and microwave sensors enable engineers to assess structural condition with ease and efficiency. This paper reports the performance of a 10.5 GHz portable imaging radar system for the quantitative, surface, and subsurface sensing of concrete structures in field configuration. Ranging, size determination, crack imaging, and subsurface interface determination are conducted using stripmap synthetic aperture radar (SAR) images. Three concrete structures are selected for field measurements. Ranging accuracy, size determination procedure, and effect of background noise are studied. Issues with background subtraction are discussed. Image-based, quantitative condition assessment criteria for ranging and size determination are proposed.

Evaluation of the seismic performance of masonry-infilled reinforced concrete (RC) frames is challenging because a number of damage patterns can be induced by the interaction between the infill and the frame. In this paper, the extended finite-element method (XFEM) is adopted to model the cracking behavior and the compressive failure of concrete in frame members as well as masonry units in infill panels, and the discrete interface element is employed to simulate the behavior of the masonry mortar joints and the joints at the frame-to-infill interface. With the XFEM, the crack can propagate in an arbitrary manner during the analysis. In addition, multiple continuous cracks are allowed in this model. The nonlinear finite-element model is validated by the available experimental data. It can be concluded that the proposed model is capable of predicting the load-displacement response of a masonry-infilled RC frame structure. The damage patterns regarding cracking and crushing of frame members and masonry panels, tensile fracture and compressive compaction in mortar joints, and shear sliding of masonry units along mortar joints are also reproduced very well.

Strength of lead rubber bearings (LRBs) deteriorates as a function of temperature rise in the lead core under cyclic motions. Accordingly, the isolator exhibits a gradual change in its hysteretic behavior that affects both the energy dissipation capacity and lateral strength of isolator. Thus, the superstructure response may change due to variation in the characteristics of LRB. This paper focuses on the effects of lead core heating on the superstructure response of seismically isolated buildings (SIBs) in terms of peak floor accelerations and story drift ratios. A parametric study was performed for two different seismically isolated buildings by conducting bounding analyses (nondeteriorating hysteresis loops for LRBs) and temperature-dependent analyses (deteriorating hysteresis loops for LRBs). A 20-story reinforced concrete (RC) and a 3-story steel structure were subjected to earthquake excitations to assess the effects of isolator properties such as isolation period and characteristic strength-to-weight ratio on the superstructure response. Results revealed that the success of bounding analyses to provide a safe envelope for superstructure response depends on the characteristics of SIB.

This paper presents a novel enriched force-based formulation for beam-column elements. The enrichment was developed on the basis of the concept of evolutionary plastic hinges and incorporated with conventional force-based element formulation. The evolutionary plastic hinge was activated on the basis of the crushing of concrete and/or yielding of reinforcement, whereas its length was calculated adaptively according to real-time sectional forces. Several representative numerical examples are demonstrated, verifying that the proposed model can achieve accurate and objective responses regardless of the number of integration points. The spreading of plasticity in strain-hardening problems and the localization of deformation in strain-softening problems can be captured well by the proposed element.