Journal of Structural Engineering

This paper contains detailed analyses of an experimental study conducted to evaluate the ductility, stiffness degradation and energy dissipation characteristics of rectangular, flanged, and end-confined reinforced masonry (RM) shear walls failing in flexure. The test program consisted of seven two- and three-story RM shear walls, with aspect ratios of 1.5 and 2.2, tested under reversed cyclic lateral displacements simulating seismic loading effects. Documentation of the compressive strains at the wall toes, wall base curvatures, and ductility levels attained are presented. The paper focuses on determining the extent of plasticity over the wall height, evaluating the contribution of flexure and shear deformations to the overall wall lateral displacements, identifying the trend of stiffness degradation, and quantifying the amount of energy dissipation. The rectangular walls displacement predictions at ultimate loads using Canadian Standards Association (CSA) S304.1 were in better agreement with the experimental results compared to the Masonry Standards Joint Committee (MSJC) code predictions. However, both the MSJC code and the CSA S304.1 significantly overestimated the test results for the flanged and end-confined walls. Analysis of the measured displacements showed that the contribution of shear displacement to the overall wall displacement was, on average, 21 and 25% of the total displacement for the walls with aspect ratio of 2.2 and 1.5, respectively. The relationship between the energy dissipation and the ratio of the postyield to the yield displacements was found to be almost linear for the test walls. In addition, the wall stiffnesses degraded rapidly to about 60% of their gross stiffness at very low drift levels (0.1% drift). Measured compressive strain at the wall toes were almost double those specified in both North American codes. Extent of plasticity over the wall height was about 75% of the wall length. The data presented in this paper is expected to facilitate better understanding of RM wall behavior under in-plane load to researchers, practicing engineers, and code developers. This study aimed at presenting the flanged and end-confined categories as cost-effective alternatives to enhance the seismic performance of midrise RM construction in North America.

Since the early 20th century combined RC-masonry buildings have become more common in European, Mediterranean, and Southern America countries. Despite the diffusion of this combined building typology, the international guidelines have not followed building transformation evolutions and, in particular, for combined RC-masonry buildings, nowadays, international guidelines are not exhaustive to deal with specific issues of this building typology. Although there is a well-established background focused on the nonlinear analysis of masonry structures and RC frames, the knowledge of numerical and experimental criteria for the study of interaction effects in combined RC-masonry buildings is limited. In this paper, nonlinear static analyses (pushover analyses) on three-dimensional combined RC-masonry buildings have been performed to obtain capacity curves of single-resistant systems and of the whole building. The results confirm the code guidelines for the design of new combined RC-masonry buildings and provide interesting insights about the seismic behavior of combined RC-masonry buildings obtained from the rehabilitation of original masonry structures.

This paper presents the formulation of a time-dependent seismic fragility format for bridges, as well as new insights into the potential effects of aging and deterioration on seismic vulnerability traditionally neglected in fragility modeling, including joint impacts of multiple component deterioration not investigated to date. The study evaluates the impact of lifetime exposure to chlorides from deicing salts on the seismic performance of multispan continuous highway bridges, considering corrosion of reinforced concrete columns and steel bridge bearings. The components’ degradation and their influence on seismic response are illustrated through three-dimensional nonlinear dynamic analysis. A full probabilistic analysis accounting for variation in bridge, ground motion, and corrosion parameters is conducted to develop time-dependent seismic fragility curves. These fragility curves indicate the evolving potential for component and system damage under seismic loading considering time-dependent corrosion-induced deterioration. The results indicate that while corrosion may actually decrease the seismic vulnerability of some components, most critical components suffer an increase in vulnerability. Quadratic models depicting the change in lognormal seismic fragility parameters are proposed to capture the time-dependent effect of aging on the fragility of the bridge system. Overall, the seismic vulnerability significantly increases throughout the lifetime of the representative bridge geometry, with a 32% shift in the median value of complete damage fragility near the end of the bridge’s life.

The behavior and design of four-legged controlled rocking bridge steel truss piers to three components of seismic excitation are presented in this paper. The controlled rocking approach for seismic protection allows a pier to uplift from its base, limiting the force demands placed on the bridge pier and deck, and can allow the structure to remain elastic during an earthquake, preventing damage toward the goal of keeping the bridge operational immediately following the earthquake. Passive energy dissipation devices [steel yielding devices (SYDs) or fluid viscous dampers (VDs)] are used at the uplifting location to control pier response. The bidirectional kinematic and hysteretic cyclic behavior of controlled rocking piers with SYDs is presented and verified with nonlinear static pushover analysis. This fundamental behavior is used to develop design equations to predict peak pier displacements, uplifting displacements, and forces (frame shear and leg axial force). Dynamic response history analyses are performed, compared with the design equations, and shown to provide reasonably accurate results for design. The use of fluid VDs in the controlled rocking system is then discussed.

Shake table testing of a 1/5 scale model of a slender bridge steel truss pier that uses a controlled rocking approach as a means of seismic protection was conducted. The controlled rocking approach allows the pier to uplift from its base while passive energy dissipation devices (steel yielding devices or fluid viscous dampers) are implemented across the uplifting location to control the response. The fundamental static and dynamic bidirectional behavior of controlled rocking four-legged bridge piers has been developed and evaluated in past research. This paper discusses the experimental specimen’s design, setup, and results of the testing. The testing program included the use of three sets of steel yielding devices and a set of fluid viscous dampers as the passive control devices. The specimens were subjected to ground motion records with increasing amplitude. The results of the testing were used to verify and further investigate the behavior of piers designed by the controlled rocking approach. Much of the fundamental behavior (self-centering, hysteretic behavior, and higher mode participation) are evident in the experimental results. Comparisons between the experimental results with design predictions and nonlinear time history analysis are made that show reasonable prediction of response.

While it is well known that slender girders have less ductility than their compact counterparts, this reduction has not been explicitly quantified. This results in limitations on the use of slender girders, and consequently, potential reductions in economy. These limitations are particularly significant in the AASHTO moment redistribution procedures, which exclude the use of girders that fail to satisfy certain compactness requirements. Thus, this paper reports the results of finite-element analysis (FEA) that has been validated by experimental testing of a series of I-girders with plate width-to-thickness ratios and unbraced lengths exceeding the limits for use of these provisions. From the FEA results and the complementary experimental results, the ductility of this class of girders is quantified in terms of moment-rotation response. Furthermore, a moment-rotation model that may be used to represent the ductility of any I-girder that satisfies AASHTO’s criteria for general I-girders is proposed.

Concrete-filled tubes (CFTs) are composite structural members that consist of a steel tube and concrete infill. CFTs optimize the contributions of both components by improving their geometric efficiency and fully using their inherent strengths. The concrete infill is confined by the steel tube, resulting in a triaxial state of compression that increases the strength and strain capacity of the concrete. The perimeter steel is at its optimal location, and the concrete infill delays local and global buckling of the tube. CFTs are easily and rapidly constructed and provide significant compression, bending, and shear resistance. They may be used for bridge piers and building columns. However, current design specifications for CFTs vary significantly, thereby limiting the current understanding and use of these components. This study addresses combined axial and flexural loading and determines the best models for predicting the stiffness and resistance of circular CFT. A database of 122 test specimens was compiled and evaluated. The results indicate that the plastic stress method is a simple yet effective method to predict the resistance of circular CFT components under combined loading. These data show that current specifications provide inaccurate predictions of the flexural stiffness, and a new stiffness expression is proposed. The proposed models permit simple yet accurate predictions of stiffness and resistance and allow engineers to use CFT components routinely in structural design.

A general reliability-based methodology is proposed for developing capacity reduction and fire load factors for design of steel members exposed to fire. The effect of active fire protection systems (e.g., sprinklers, smoke and heat detectors, fire brigade, etc.) in reducing the probability of occurrence of a severe fire is included. The design parameters that significantly affect the fire design of steel members are chosen as random variables. Raw experimental data published in the literature was analyzed to obtain the statistics of parameters for which no statistical information was available in the literature. Model errors associated with the thermal analysis models are also characterized based on experimental data. It is found that uncertainty associated with the fire design parameters is significantly higher than that of room temperature design parameters. To illustrate the proposed methodology, capacity reduction and fire load factors are developed for simply supported steel beams in U.S. office buildings, and it is shown that for consistent reliability these factors should vary depending on the presence of active fire protection systems in a building.

A fatigue reliability model which integrates the probability distribution of hot spot stress range with a continuous probabilistic formulation of Miner’s damage cumulative rule is developed for fatigue life and reliability evaluation of steel bridges with long-term monitoring data. By considering both the nominal stress obtained by measurements and the corresponding stress concentration factor (SCF) as random variables, a probabilistic model of the hot spot stress is formulated with the use of the $S\text{-}N$ curve and the Miner’s rule, which is then used to evaluate the fatigue life and failure probability with the aid of structural reliability theory. The proposed method is illustrated using the long-term strain monitoring data from the instrumented Tsing Ma Bridge. A standard daily stress spectrum accounting for highway traffic, railway traffic, and typhoon effects is derived by use of the monitoring data. Then global and local finite element models (FEMs) of the bridge are developed for numerically calculating the SCFs at fatigue-susceptible locations, while the stochastic characteristics of SCF for a typical welded T-joint are obtained by full-scale model experiments of a railway beam section of the bridge. A multimodal probability density function (PDF) of the stress range is derived from the monitoring data using the finite mixed Weibull distributions in conjunction with a hybrid parameter estimation algorithm. The failure probability and reliability index versus fatigue life are achieved from the obtained joint PDF of the hot spot stress in terms of the nominal stress and SCF random variables.

Interstory drift, the relative translational displacement between two consecutive floors, is an important engineering demand parameter and indicator of structural performance. The structural engineering community would benefit well from accurate measurements of interstory drift, especially where structures undergo inelastic deformation. Unfortunately, the most common method for obtaining interstory drift, double integration of measured acceleration, is problematic. Several issues associated with this method (e.g., signal processing steps and sparse instrumentation) are illustrated using data from shake table studies and two extensively instrumented buildings. Some alternative contact and noncontact methods for obtaining interstory drift are then presented.

Building floors comprising timber joists connected to limecrete (lime concrete) slabs via timber headed studs have low carbon footprints. Such floors are not yet used owing to lack of underpinning research. This paper presents results from large-scale joint tests which show that by sloping the timber studs at 45° against the sense of slip so that the slab lifts off the joists during slip, not only does the joint exhibit good stiffness and strength, but also the joint fails in a highly ductile manner by double curvature hinging of each stud and by crushing of the adjacent limecrete and glulam near the slab-joist interface. With the studs sloped at 45° toward the sense of slip, joint ductility drops significantly while joint stiffness and strength rise dramatically. Test data are also given for a 4.6 m long timber joist-limecrete slab composite specimen with studs sloped at 45° against slip and loaded in four-point bending to failure. Nonlinear finite-element analysis (FEA) using the measured joint and material constitutive data is seen to reliably predict this specimen’s load response. The verified FEA is used to compare the effects of the two stud layouts on the specimen’s structural characteristics. An equivalent rectangular stress block is derived for the limecrete based on a polynomial fit of that material’s compressive stress-strain test data and assuming that the neutral axis of the timber-limecrete section lies in the slab. Finally, suggestions are made for future studies of this composite system.

A fully coupled 10-degree-of-freedom (DOF) beam theory is developed for the analysis of thin-walled closed piecewise straight beams of general quadrilateral cross sections. The developed beam theory can predict the structural response of arbitrarily shaped thin-walled quadrilateral sectioned beams that are curved or connected to each other through a number of angled joints. For accurate prediction, the local effects by four beam sectional deformations such as torsional warping, torsional distortion, bending warping, and bending distortion must be taken into account in addition to the structural responses by standard six translational and rotational DOFs of the Timoshenko beam theory. When two straight beams of general quadrilateral sections meet at an angle, all 10 DOF deformations become fully coupled. Furthermore, it is not easy to derive the exact interface conditions at the angled joint because 10 DOFs have different physical behavior. For the analysis of the beam system in consideration, the section deformation patterns corresponding to all of the 10 DOFs are presented. In particular, the cross-sectional shape functions for bending distortion and bending warping for general quadrilateral sections are derived for the first time. Then, a systematic method to match 10 DOFs of two straight quadrilateral beams meeting at a joint of an arbitrary angle is developed. Several numerical case studies are considered to check the validity of the developed beam analysis.

An investigation into the frequency nonstationarity in the response of primary-secondary (P-S) systems and the impact it could have in the analysis of such structures has been presented in this note. For this purpose, a torsionally coupled P-S system subjected to nonstationary support motion is considered here. Simulated time history records of relative displacement of the secondary system are used to evaluate the time varying power spectral density functions. This is achieved by using a wavelet-based time-frequency analysis, which shows the temporal variations in the frequency content. The numerical results presented in this study advocate the use of nonstationary analysis of the P-S system for their proper design as conventional methods using cascading approximation may fail to capture this phenomenon, especially in the light of tuning and torsional coupling. System parameters such as mass ratio and radius of gyration are also observed to have a significant impact on the time varying frequency content of the response which is evidenced from the constructed time varying power spectrum.

In this brief note, we present the results of a full finite deformation analysis of a system similar to the Oakland-San Francisco Bay Bridge saddle repair system. The dimensions used are for illustration purposes but are intended to be in the range of those associated with the real system. The saddle system is seen to be unstable as designed. With a small modification the system can be made stable (self-centering).

Many bamboo species are well regarded for their strength and rapid renewability, although the nonuniformity of bamboo poles has impeded use in developed countries. Described herein are the results of a pilot effort to develop engineered bamboo I-joists for use in common low-rise construction applications. Solid section bamboo materials were used to fabricate I-beams; flanges consisted of single-strand bamboo material and webs consisted of bamboo OSB or three-ply material. Experimental results indicate that flexural strengths were limited to 5.2 ksi (36 MPa) by the failure of the flange finger joints; shear strengths were 2.1 ksi (14 MPa) for the bamboo OSB and 3.3 ksi (22 MPa) for the three-ply web material. The modulus of elasticity averaged 2,000 ksi (14 GPa), while the shear modulus was 250 ksi (1.7 GPa) for the bamboo OSB and 140 ksi (0.94 GPa) for the three-ply material. Design values are developed from the test results following a hybrid approach based on ASTM procedures for wood I-joists and whole bamboo poles.