Journal of Structural Engineering

Aluminum alloys are used in a wide range of engineering applications and are gaining increasing usage in the construction sector, offering high strength-to-weight ratios and good durability. In this paper, a series of stub-column tests on aluminum alloy box sections with and without internal cross stiffeners is carried out to investigate cross-section capacity and to explore the possible exploitation of strain hardening in design. All existing stub-column test results from the literature were also collected. A database containing the results from 346 tests on aluminum alloy stub columns of box, channel, and angle sections, with a wide range of cross-section slendernesses, was formed. The test strengths were compared with the design strengths predicted by the current American, Australian/New Zealand, and European specifications. Furthermore, the test strengths were compared with those predicted by the deformation-based continuous strength method (CSM). Following reliability analyses, the design strengths predicted by the three current design specifications were found to be generally conservative, whereas the CSM offered improved design capacities, owing to its allowance for strain hardening.

In collapse-resistant design of structures, understanding primary structural failure-mechanisms and alternative load paths under accidental extreme loads is important. A quasi-static experimental method is used to simulate the sudden loss of a column in a single story concrete flat slab-column structure. In a series of experiments on two identical large-scale models, an interior, exterior, and corner column of the structure were replaced by mechanical jacks during the fabrication of the structure. After application of uniform loads of increasing intensity, the jack representing the lost column was unloaded. In the first model test wherein an interior column was removed, a downward concentrated load was also applied on the upper end of the interior column until the structure collapsed. Elastic behavior, yield-line mechanisms, and compressive and tensile membrane actions in the flat slab-column structure were observed during the collapse tests. The results provide valuable information on the load transfer mechanisms in a flat slab-column structure when critical columns are removed.

Recently, a new plating system was proposed based on a strain localization mechanism for addressing the critical debonding problem in externally bonded reinforcing systems for reinforced concrete (RC) structures. The system delays or inhibits debonding by localizing the large strain of the externally bonded reinforcement in certain areas and leaving other places in a smaller strain condition to ensure that global debonding does not occur. This debonding avoidance strategy is in line with the concept of controlling a flood by channeling water away rather than blocking it. Two techniques have been used to achieve strain localization: (1) a nanotechnology called surface mechanical attrition treatment and (2) variation in the cross-sectional area of bonded reinforcement. To better understand this newly developed system, this paper presents a numerical study of RC beams strengthened with such plating systems. This study leads to a better understanding of the mechanism for inhibiting debonding and the development of a general design strategy for the system. In particular, a critical location is identified for strain localization, which forms the basis for the design of such a system in the future.

This study examined the seismic performance of reinforced concrete beams with corrosion only induced in the transverse steel reinforcement by using cyclic loading. The beams were designed with closely spaced steel hoops as transverse reinforcement conforming to the seismic design provisions of the ACI 318 code. Seven beams were constructed. One beam was used as a control without corrosion. The other six beams were subjected to six levels of corrosion in the potential plastic hinge region by using an electrochemical method. Corrosion test results indicated that pitting corrosion increased with an increasing corrosion level. The hoops fractured at a corrosion weight loss of 35%. Cyclic test results indicated that the beams could sustain a corrosion weight loss of 6% in the hoops and still maintain ductile flexural behavior. The corrosion of hoops adversely affected the deformation capacity of the beams significantly, yet did not significantly influence the load-carrying capacity of the beams. The residual shear strength provided by concrete and steel was still sufficient to develop flexural yielding, even for beams with hoops corroded to fracture. Methods were developed to estimate the residual shear strength and ductility of reinforced concrete beams with corroded hoops. The amount of corrosion substances filled in the cracks’ volume was approximately 25% of the reduced volume of steel due to corrosion. Although shear strength estimation based on the average corrosion weight loss was not conservative, the shear strength estimation based on the minimum residual cross-sectional area was too conservative at a high corrosion level due to severe pitting corrosion. Shear strength estimation based on average weight loss and minimum residual cross-sectional area produced results that describe the experimental behavior more reasonably.

This paper describes an experimental study of the seismic performance of cantilever-reinforced concrete masonry shear walls. As part of a research project on displacement-based design of masonry structures, 30 cantilever shear-wall specimens, made of fully grouted reinforced concrete masonry, were tested under reversed cyclic loading at the University of Texas at Austin and at Washington State University. Based on test results, the relationship between key design parameters and the nonlinear hysteretic response of the specimens was evaluated. The specimens exhibited predominantly flexural behavior, as intended, and their behavior was generally in good agreement with that reported in previous research work. Specimens constructed with masonry units containing recycled materials behaved similarly to otherwise identical specimens constructed with ordinary units, indicating the structural equivalence of those two types of units. Lap splices in the longitudinal reinforcement caused a reduction in wall performance. Walls with longitudinal reinforcement concentrated at jambs behaved similarly to walls with evenly distributed longitudinal reinforcement.

Buckling-restrained braced frame performance at high drifts is improved by providing beam splices that reduce demands in the gusset regions. Existing experimental data only consider web splices without a slab present. An alternative top-flange splice, proposed by others, was investigated experimentally and numerically. Two full-scale top-flange beam splices from a prototype frame were tested using the qualifying buckling-restrained brace frame cyclic loading protocol. During experimental testing, the gusset connection regions remained essentially undamaged through multiple cycles at 0.06 rad drift. The splice plates experienced low inelastic strains, but fatigue analyses indicate they could withstand over fourteen similar loading histories without requiring replacement. Finite-element models were used to investigate the influence of slabs on connections with web splices or top-flange splices. When slabs were considered, the top-flange splice transmitted over 70% less moment than the web splice.

Load-carrying capacity of confined masonry walls in the out-of-plane direction after being damaged is crucial for overall stability and is affected by the type of interface present at the wall edge and column, such as toothing. Shake table tests were conducted to investigate the effectiveness of a toothed connection on the out-of-plane behavior of damaged confined masonry walls. Four half-scale clay brick masonry walls were subjected to a sequence of slow cyclic in-plane drifts and shake table–generated ground motions in the out-of-plane direction. Specimens included one regular RC infill frame and three confined masonry panels, two with different densities of toothing and one with no toothed connection. The specimen with the infill panel demonstrated a higher risk of out-of-plane collapse, whereas the other three confined masonry wall specimens maintained structural integrity and out-of-plane stability even when severely damaged. The confined masonry walls with or without toothing enhanced the interaction between masonry walls and RC confining elements and were able to delay the failure by controlling out-of-plane deflections even after an in-plane drift cycle of 1.75%.

This paper presents selected results from an experimental and computational evaluation on the behavior of slender concrete-filled steel tubes (CFTs) under combined axial compression and biaxial flexure. A complex loading protocol was used in the experimental program, including monotonic and cyclic loading that allowed detailed evaluation of the complete beam-column response. This paper principally addresses the experimental determination of the maximum stable axial load–bending moment ($P-M$) interaction strength. The experimental $P-M$ interaction strengths extracted at incipient instability shows that for very slender specimens, the bilinear interaction diagram proposed in the current design provisions of the AISC is somewhat unconservative. This experimental observation is also confirmed by detailed computational results. However, the results also indicate that current AISC provisions provide an accurate and conservative approach for evaluating axial load–flexural interaction for most practical CFT column sizes and lengths (i.e., composite beam columns with low and intermediate slenderness).

This paper describes the closed-form and discrete computational models for a geometrically nonlinear and linear static analysis of the adaptive tensegrity module presented in the companion paper. Due to the symmetry of the spatial tensegrity system, a simplified closed-form analysis is based on a two-dimensional (2D) solution of an equivalent prestressed triangular cable truss acting under a vertical point load. Novel concrete forms of the cable and deflection equations are derived. The analytical models serve to determine the response, i.e., horizontal components of cable forces and deflections as the basis for control commands. A three-dimensional (3D) discrete geometrically nonlinear analysis of the adaptive tensegrity module is based on the application of a nonlinear finite-element method. The results obtained by the nonlinear finite-element analysis are compared with those obtained by using both the simplified linear and nonlinear closed-form solutions. Physical relevance and mathematical correctness of the applied theoretical approaches were confirmed by the results. Finally, the numerical model is applied to assess the response of the prestressed tensegrity module considering the effects of large deformations and slackening of cables.

This paper describes a newly developed adaptive tensegrity module which has the ability to alter its geometrical form and prestress properties in order to adapt its behavior to current loading conditions. The novel adaptive structure and its connections create a new aspect which is presented in the paper. This system contains sensors that sense forces from the environment and an actuator that adjusts its shape accordingly, depending upon the load applied. The structure, in the form of an octahedral cell, consists of eight prestressed cables, four circumferential compressed struts and a central compressed strut which is designed to function as an actuator. Five types of tests were carried out, namely a prestressing test, a static loading test, and three adaptation tests. Tests confirmed the functionality of the developed adaptive system and the applicability of the proposed equipment, software, computational models, and control commands. Responses of the structure obtained analytically and numerically are compared with experimental results. The results demonstrate that the experimentally obtained behavior of the adaptive tensegrity system can be theoretically predicted.

This paper presents detailed analyses of experimental shake table test results with the goal of providing a better understanding of the seismic performance of lightly reinforced fully grouted masonry shear walls. The paper first gives a brief summary of the experimental program followed by detailed analyses of the inelastic behavior characteristics of the walls. This includes quantifying the walls’ displacement ductility levels, extent of plastic hinge zones, and equivalent plastic hinge lengths based on the experimental results. Separation of the various energy components of the system, including those of the shake table, the walls, and the external mass support system, based on the experimental results, is also carried out. Utilizing the evaluated energy components, the characteristics of the system, including the change of input energy levels with time and the contributions of the different energy dissipation mechanisms (e.g., hysteretic, viscous damping, and coulomb friction damping), are quantified. In general, the results from this study demonstrate that the displacement ductility capacity of the reinforced masonry (RM) walls and their capability to dissipate energy through plastic hinging are higher than what is currently recognized by the National Building Code of Canada. In addition, the effective dynamic properties of the walls including the effective secant stiffness, period, and equivalent viscous damping are quantified, and their variations at different response levels are characterized. A single-degree-of-freedom (SDOF) substitute structure model, based on the aforementioned properties, is subsequently used to predict the experimental base shear demands of the walls. The study forms a part of the ongoing efforts to quantify the seismic performance parameters of RM wall systems to facilitate their adoption in the next generation of seismic codes in North America.

A curve-approximated hysteresis model of the lateral load-displacement behavior of steel bridge columns is proposed for nonlinear seismic response assessment of single-column-type bridges using single-degree-of-freedom (SDOF) analysis. Instead of multiple straight lines, a series of curves are adopted to precisely describe complicated force-displacement hysteresis behavior of the column. The $P\text{-}\delta$ effect, hardening effect in unloading-reloading hysteresis loops, deterioration of strength, and stiffness are taken into account. Parameters of proposed hysteresis model for three types of steel column specimens used in this study are calibrated by six quasi-static cyclic tests. To verify the accuracy of the proposed model, eleven pseudodynamic tests are conducted. By comparing the simulation and the test results, the differences between the predicted nonlinear seismic response using the proposed model and pseudodynamic tests are found to be, on average, 5% in maximum response displacement, 22% in residual displacement, and 4% in the amount of energy dissipation.

Pushover analysis is one of the most-used nonlinear static procedures for the seismic assessment of structures; therefore, nowadays it is extensively used by practicing engineers for the seismic analysis of virtually every type of building. This paper proposes a bidirectional pushover analysis (BPA) method to overcome the limitations of current pushover methods to assess the seismic response of irregular (both in plan and in elevation) buildings subjected to bidirectional ground motions. The extended N2 method and the proposed BPA method were applied to estimate the nonlinear response of six highly irregular reinforced concrete frame structures designed according to the requirements of Eurocode 8. Results in terms of interstory drifts and floor rotations are compared with those given by nonlinear response history analysis (NRHA). For the latter, a suite of twenty Italian bidirectional seismic ground motions was selected. It was found that results given by the proposed BPA method match those given by NRHA when the earthquake loadings are considered to act simultaneously in two principal orthogonal directions ($X$ and $Y$) with load factors of 1 and 0.6, respectively. These load factors are different from the values of 1 and 0.3 indicated in the European seismic code for bidirectional linear analysis.

Results from a series of tests intended to study loss of pretension force in bolted assemblies are presented. The test matrix included ASTM A325 assemblies with various direct tension indicators (DTIs), some through-hardened and some not, as well as assemblies without direct tension indicators. Bolt length and diameter and grade of nut were also varied. Load losses were monitored for 42 days (1,000 h). However, load levels generally stabilized after 14 days. Pretension losses were linearly dependent on initial pretension and not affected by DTI or washer configuration. Bolt diameter and length did affect the magnitude of losses over time but not the general linear relationship with initial pretension.

This paper presents a combined study of wind tunnel experiment and numerical simulation of the wind-induced pressures on the long-span roof of the Hangzhou East Railway Station Building. Wind tunnel tests were performed on a $1:250$-scale rigid model of the station building. Based on the measured pressure data, the third and fourth statistical moments of the pressure processes were evaluated to quantify the non-Gaussian nature of the wind-induced pressures on the station roof. Using the recently reported Hermite moment model, an analytical form of the non-Gaussian peak factor was proposed for a given hardening load process and was verified using numerical integration. The currently available simulation algorithm was revised to generate sample functions of skewed hardening load processes. The simulated pressure data samples provide a basis for the direct statistical analysis of extreme peaks. The peak factors for non-Gaussian wind load effects were estimated by employing various state-of-the-art methods and compared to the mean extreme values of wind pressure data from simulations.

The work presented in this paper aimed to evaluate the diagonal strut model for the design of reinforced concrete (RC) infilled frames, already broadly used as a design tool in the case of masonry infilled RC frames. The assumptions on which the strut model provisions in codes are based are reviewed. In parallel, some of the results of an experimental study on the response of eight $1/3$-scale RC infilled frames subjected to quasi-static cyclic horizontal displacements are summarized. Two different aspect ratios and different types of connection of the infill to the frame have been investigated. Design provisions for infilled frames included in codes are applied to describe the behavior of the specimens tested in terms of stiffness, ultimate strength, and expected mode of failure. The results are discussed and some suggestions are made for improving the design procedures.

This paper describes structural optimization formulations for trusses and applies them to size and geometrically optimize lateral bracing systems. The paper provides analytical solutions for simple and limit cases and uses numerical optimization for cases where analytical solutions are not available. The analysis is based on small displacements, constant or no connection costs, static loads, and elastic behavior. This work provides guidance to improve the common engineering practice of locating the bracing point at the middle or at the top of the bay/story panel.