Journal of Structural Engineering

This paper describes the behavior of wood-concrete composite beams in which the wood layer is composed of recycled utility poles. Two full-scale laboratory specimens of $7,500$-mm (295-in.) span were constructed, with the concrete slab cast on the timber poles left unshored. The connection was obtained by cutting six notches in the timber poles. A threaded steel dowel is placed in each notch extending through both layers with a nut on the bottom of the beam that can be tightened once the concrete has cured. Since the material in each layer exhibits a time-dependent response, it is necessary to examine the effects of sustained loading. After 28 days of initial curing of the concrete layer during which the midspan deflection was monitored, both beams were subjected to the service load to estimate the composite efficiency. The beams were very stiff and values of 96% and 98% were obtained, respectively, demonstrating the high efficiency of the notched connection system used. A comparison was made with results obtained in the literature for ramp load tests of two similar specimens, which had exhibited composite efficiencies of about 94% and 96%, respectively. A sustained load of approximately 11% of the estimated static ultimate load capacity was then applied to one of the specimens, which was monitored over time. The applied load resulted in a midspan moment of $24\mathrm{kN}·\mathrm{m}$ ($212\mathrm{kip}·\mathrm{in}.$) while the calculated ultimate capacity corresponded to a midspan moment of $226.5\mathrm{kN}·\mathrm{m}$ ($2,005\mathrm{kip}·\mathrm{in}.$). The final deflection was found to increase to 44.4 mm (1.75 in.) after 256 days, which was more than twice the initial elastic deflection owing to the application of the dead and live loads. The deflection attributable to the dead load was 19.1 mm (0.75 in.), and the deflection attributable to the live load was 2.54 mm (0.10 in.). An existing one-dimensional (1D) finite-element program was utilized to predict the time-dependent deflection at the end of a 50-year service life. The comparison with experimental results showed good approximation, particularly for the midspan deflection. The software predicted a 54-mm (2.14-in.) midspan deflection at the end of a 50-year service life, corresponding to $1/139$ of the span. This was sufficiently high to suggest that either larger cross-section and/or precambering of the wood layer could be needed when the serviceability limit state of maximum deflection in the long-term is a required performance criterion.

In this paper, an experimental and analytical investigation of concrete-filled steel tubular (CFST) laced columns is presented. These columns consist of four concrete-filled steel tubes that are laced together. A total of 27 experimental tests were conducted to quantify the column failure mechanism at ultimate loads. The experiments were designed to obtain the load-deflection curves. These curves were subsequently used to quantify the structural behavior for each element of the hybrid column. Experimental results indicate that the compression force in the longitudinal members dominated the failure mechanism in the CFST columns. In-plane bending occurred when member segments reached the compression failure load. The forces in the lacing members (diagonal and horizontal bracing) were found to be small and remained in the elastic range through failure. The experimental study was used to validate an analytical parametric study. The analytical study showed that increasing slenderness ratios and eccentricities reduced the ultimate load capacity. Additionally, finite-element analyses of CFST columns based on four in situ structures were performed to determine the ultimate load-carrying capacity and were subsequently compared to several building codes. On the basis of the analytical results, a new methodology for calculating the ultimate load-carrying capacity is proposed. This purposed methodology is compared with five different building codes to quantify the increased accuracy.

An experimental investigation was conducted to achieve engineered infilled frames in two stages. The first stage was aimed at discovering methods to raise infilled frames’ ductility, through testing six single-story single-bay infilled steel frames; three general techniques were studied, disregarding their manufacturing details. Results show that supplying a sliding fuse in the infill highly efficiently increases ductility; however, this presents some problems that can be avoided by improving fuse configuration. The second stage of the testing was conducted with two specimens with an improved sliding fuse configuration, in which the influences of fuse sliding strength on the behavior of the infilled frames were studied. On the basis of these results, the infills, provided with frictional sliding fuses, can be considered to be engineered elements of high ductility, of transversal stability, and capable of being adjusted for desired strengths.

An experimental study was performed to investigate the cyclic behavior of walls that are composed of reinforced concrete boundary frames and thin steel infill plates. For this purpose, three-story steel plate infilled walls (SPIW) were tested. The parameters in this test were the reinforcement ratio of the columns and opening in the infill plates. A reinforced concrete infilled wall (RCIW) and a reinforced concrete frame (RCF) were also tested for comparison. The deformation capacity of the SPIW specimens was significantly greater than that of the RCIW specimen, though the specimens exhibited an identical load-carrying capacity. Similar to the steel plate walls with steel boundary frames, the SPIW specimens showed excellent strength, deformation capacity, and energy dissipation capacity. Furthermore, by using the steel infill plates, shear cracking and failure of the column-beam joints were prevented. By using the strip model, the strength and initial stiffness of the SPIW specimens were predicted. The prediction results were compared with the test results.

The behavior of coupled-wall buildings primarily depends on the performance of coupling beams. Existing coupled-wall buildings designed and built prior to the 1970s contain coupling beams reinforced with horizontal and vertical bars. Seismic evaluation of these older buildings is commonly performed using nonlinear static or dynamic analyses techniques. Results from nonlinear analyses depend on the quality of backbone curves that characterize the behavior of the individual coupling beams. Backbone curve construction must, therefore, focus on reliable estimates of the strength and deformation values used to characterize the behavior of the structural component. This paper presents experimental results of four conventionally reinforced coupling beams designed to exhibit different behavior modes during cyclic loading. The effect of different amounts of longitudinal and transverse reinforcement on behavior is highlighted. The measured shear strength of the beams is compared with values calculated using existing equations. The deformation components that contributed to chord rotation are identified and discussed in light of response parameters, such as measured strains and observed cracking. The tests also highlight the importance of accounting for reduction in shear stiffness to accurately determine the deformation response of coupling beams.

This paper describes a displacement-based method of analysis for the performance-based seismic design of regular buildings with reinforced-concrete bearing walls acting as the lateral-force resisting system. The method considers two performance levels: immediate occupancy (IO) and life safety (LS), each anchored at a specific seismic hazard level. It explicitly accounts for the combined effects of inelastic first mode of response, kinematic system overstrength, and higher modes of response. Quantification of these effects is required to capacity-protect the structure and to ensure the intended performance. As an example, the method is applied to a full-scale 7-story reinforced-concrete building slice, built and tested on the George E. Brown Jr. Network for Earthquake Engineering Simulation Large Outdoor High-Performance Shake Table at the University of California–San Diego. The response of the test building largely verified the method discussed in this paper.

This paper is a companion to “Displacement-Based Method of Analysis for Regular Reinforced-Concrete Wall Buildings: Application to a Full-Scale 7-Story Building Slice Tested at UC–San Diego” and presents key results obtained from a full-scale 7-story reinforced concrete building slice built and tested on the George E. Brown Jr. Network for Earthquake Engineering Simulation Large Outdoor High-Performance Shake Table at the University of California, San Diego. The building was tested in two phases. This paper discusses the main test results obtained during Phase I of the experimental program. In this phase, the building had a rectangular load-bearing wall acting as the main lateral force–resisting element. The building was subjected to four historical California input ground motions, including the strong-intensity near-fault Sylmar record, which induced significant nonlinear response. The test addressed the dynamic response of the building, including the interaction between the walls, the slabs, and the gravity system as well as four issues relevant to construction optimization: (1) reduction in the longitudinal reinforcement; (2) use of a single curtain of reinforcement to transfer shear; (3) constrain of plasticity in the first level of the wall using capacity design; and (4) use of resistance-welded reinforcement in the boundary elements of the first level of the walls. The building responded very satisfactorily to the ground motions reproduced by the shake table and met all performance objectives. The effects of kinematic system overstrength and higher modes of response in the experimental response were important; this verified to a large extent the displacement-based method of analysis presented in the companion paper.

A full-scale 7-story reinforced concrete building slice was tested on the unidirectional University of California–San Diego Network for Earthquake Engineering Simulation (UCSD-NEES) shake table during the period from October 2005 to January 2006. A rectangular wall acted as the main lateral force resisting system of the building slice. The shake table tests were designed to damage the building progressively through four historical earthquake records. The objective of the seismic tests was to validate a new displacement-based design methodology for reinforced concrete shear wall building structures. At several levels of damage, ambient vibration tests and low-amplitude white noise base excitation tests were applied to the building, which responded as a quasi-linear system with dynamic parameters evolving as a function of structural damage. Six different state-of-the-art system identification algorithms, including three output-only and three input-output methods were used to estimate the modal parameters (natural frequencies, damping ratios, and mode shapes) at different damage levels based on the response of the building to ambient as well as white noise base excitations, measured using DC-coupled accelerometers. The modal parameters estimated at various damage levels using different system identification methods are compared to (1) validate/cross-check the modal identification results and study the performance of each of these system identification methods, and to (2) investigate the sensitivity of the identified modal parameters to actual structural damage. For a given damage level, the modal parameters identified using different methods are found to be in good agreement, indicating that these estimated modal parameters are likely to be close to the actual modal parameters of the building specimen.