Journal of Structural Engineering

Use of carbon fiber–reinforced polymer (CFRP) strengthening of structural elements has been gaining increased traction over the past few years. Although some research has been carried out on the behavior of CFRP-strengthened steelwork under static and fatigue loads, no single study exists that experimentally captures the response of CFRP-strengthened steel beams under impact load. In the present study, a series of tests was conducted to gain insight into the effect of impact load on such beams. The parameters examined in the experiments were the thickness and length of the CFRP layers. The impact test was performed by dropping a 91-kg impactor with a velocity of $4.43\mathrm{m}/\mathrm{s}$. A finite-element analysis (FEA) model was developed in which the bond between CFRP and steel, strain rate effects for steel, and failure of both CFRP and adhesive material were included. Comparing the test data with corresponding finite-element results confirmed a high level of accuracy of the predicted results. A series of detailed analyses on the impact behavior of CFRP-strengthened steel beams was performed using the validated finite-element model to provide further insight.

The seismic performance of nonstructural components, including suspended ceiling systems, plays a significant role during and after an earthquake. Damage to these systems can leave buildings inoperable, causing economic losses and extensive downtime. Therefore, it is necessary to better understand the response of these systems in order to enhance the seismic resilience of buildings. A series of full-scale system-level experiments conducted at the University of Nevada, Reno, Network for Earthquake Engineering Simulation site aimed to investigate the seismic performance of integrated ceiling-piping-partition systems. In this paper, the seismic behavior of suspended ceiling systems is discussed. Experimental results include acceleration amplification factors for different ceiling configurations. In addition, fragility curves are presented for perimeter displacement, support axial force, and overall ceiling performance. Some major findings from this experiment show that the median acceleration amplification was 2.71 and that unseating of grid members in 22.2-mm (7/8-in.) wall angle configurations was one of the dominate failure modes.

Backbone curves are used in seismic design standards as the basis for developing component models for nonlinear static and dynamic analysis. Herein, data from 240 tests of rectangular, barbell, and flanged shear-critical walls are assembled and analyzed to develop an improved cyclic backbone curve for use in nonlinear response-history analysis. Values of drift ratio and normalized lateral force at the control points on the cyclic backbone curve are identified. The effects of design parameters, including wall aspect ratio, axial load, day-of-test concrete compressive strength, vertical and horizontal web reinforcement ratio, reinforcement ratio in the boundary elements, and yield strength of reinforcement, on the coordinates of the control points are addressed. The accuracy of equations for peak shear strength is assessed using the collected test data.

Postyield steel–concrete bond has been the subject of considerable investigations using pull-out or direct tensile tests; however, the degradation in bond due to reinforcement yielding in RC beams subjected to lateral loading has not been fully scrutinized. Conventional measuring instruments (strain gauges or LVDTs) cannot precisely measure strain distribution along the yielded reinforcing bar with a minimum level of interference to the bond. Therefore, this study reports the postyield behavior of bond in RC cantilever beams subjected to monotonic lateral loading monitored using a distributed fiber-optic strain sensing system (DFOSSS). The DFOSSS enabled accurate monitoring of deformations of the embedded reinforcing bars and the strains on the concrete surface. This allowed slip, steel stress, bond stress, bond deterioration length, and the locations of cracks to be determined. Using the new values for maximum bond stress, a model was proposed to predict pre- and postyield bond behavior, including steel strain effect. Finally, the mean bond stress values were presented for the simple assessment of bond strength in both pre- and postyield regions.

Steel plate shear walls (SPSWs) have been shown capable of remaining stable under seismic loading due to their satisfactory hysteretic performance. However, since the thin steel web infills within these walls only yield under tension and in most cases exhibit no significant compressive resistance, their behavior is uncertain under long duration of shaking. The scope of this research was to investigate whether there is a point in time where the SPSW behavior becomes that of its own bare frame when subjected to extensive shaking, which would indicate that the steel web plates no longer contribute to response. In this parametric study, SPSWs of various configurations were analyzed using nonlinear inelastic dynamic analyses, for which response modification factor and duration of repetitive synthetic ground motions were varied. Two single-story SPSWs (with panel aspect ratios of $1:1$ and $2:1$) and one 3-story SPSW (having panel aspect ratio of $1:1$) were modeled using the commonly used diagonal strip model. Spectra-compatible synthetically generated ground motions were used in the analyses. SPSW responses were then compared against those of their respective boundary frames. Performance of SPSW over the duration of the repeated stochastic ground motions was characterized by inelastic and residual drifts. The objective of this research was to provide an understanding of the expected ductile performance of SPSWs when subjected to prolonged seismic excitation, and hopefully, an improved confidence in their seismic behavior under such conditions.

This paper investigated the confinement mechanism of steel-confined concrete in steel-reinforced concrete (SRC) columns. Six axially loaded SRC-core columns were tested and the corresponding structural performance data were collected and assessed. Considering the confinement mechanism of both steel-confined and hoop-confined concrete, the concrete in the SRC columns was divided into four regions: highly steel-confined concrete (HSCC), partially steel-confined concrete (PSCC), partially confined concrete (PCC), and unconfined concrete (UCC). Based on Mander’s model, a theoretical stress–strain model for each concrete region was proposed and implemented in an analytical model to predict the mechanical behaviors of axially loaded SRC columns from the results of the tests described in this paper and of previous tests; satisfactory agreement was observed.

The incremental dynamic analysis (IDA) is a powerful methodology that can be easily extended for calculating probabilistic seismic damage curves. These curves are metadata to assess the seismic risk of structures. Although this methodology requires a relevant computational effort, it should be the reference to correctly estimate the seismic risk of structures. Nevertheless, it would be of high practical interest to have a simpler methodology, based for instance on the pushover analysis (PA), to obtain similar results to those based on IDA. In this article, PA is used to obtain probabilistic seismic damage curves from the stiffness degradation and the energy of the nonlinear part of the capacity curve. A fully probabilistic methodology is tackled by means of Monte Carlo simulations with the purpose of establishing that the results based on the simplified proposed approach are compatible with those obtained with the IDA. Comparisons between the results of both approaches are included for a low- to midrise reinforced concrete building. The proposed methodology significantly reduces the computational effort when calculating probabilistic seismic damage curves.

Progressive collapse behavior of RC infilled frames is studied experimentally under quasi-static loading and numerically by using macro (strut) and micro (finite-element) models to simulate the damage propagation within infill walls. A three-strut model is proposed to simulate the overall behavior of infill walls based on the observation that corner regions of infill walls play an important role even after the cracking of the diagonal region in infill walls. The proposed three-strut model is implemented using commercially available software. The accuracy of the proposed method is evaluated by comparing the experimental data with simulated responses from detailed finite-element models and simplified strut models. The modified three-strut model is also compared with other widely used strut models. The comparison shows that the proposed three-strut model predicts the maximum resistance force with higher accuracy. Finally, a simpler model is developed based on the proposed three-strut model for infill walls. This simpler model can easily be implemented by practicing engineers to predict the overall behavior of the infilled frame with acceptable accuracy.

For a seismically designed concentrically braced frame with hollow structural sections as braces, the typical connection design consists of a slotted brace that is field welded to a gusset plate. During an earthquake, the brace is expected to buckle out-of-plane and the gusset plate is expected to yield. This makes it difficult to repair or replace the brace and connection, and the out-of-plane brace buckling caused by this connection can also damage surrounding walls and cladding, with potential life safety implications. This paper proposes an alternative connection that is expected to result in reduced erection costs by avoiding site welding, and also to simplify structural repairs following a major earthquake by confining all damage to a replaceable brace module. Additionally, the new connection causes the brace to buckle in-plane during a seismic event, reducing the potential for damage to the surrounding walls and cladding. This paper discusses large-scale quasi-static cyclic testing of eight brace modules with two variations of the new connection, one with a single-shear eccentric splice and the other with a double-sided concentric splice. All tested specimens had the desired failure progression and buckled in-plane, as intended. Bolt slip in the connection had very little effect on the overall force-deflection response after the brace compressive strength degraded to less than the slip load. The brace module was replaced after each test without observable damage outside the module. Although both connection variations behaved in a desirable manner, the single-shear eccentric splice was preferred because of the simpler constructability and improved performance.

The bias factor of the Eurocode 2 [CEN (European Committee for Standardization) (2008). Eurocode 2: Design of Concrete Structures–Part 1-1: General Rules and Rules for Buildings] and ACI 318 [ACI (American Concrete Institute) (2014). Building Code Requirements for Structural Concrete and Commentary] flexural resistance models of reinforced concrete beams are compared with emphasis on the effect of the incorporation of coarse recycled aggregates sourced from concrete waste. The bias factor of the yielding moment calculations according to both codes is also investigated, and the bias in the cracking moment when Eurocode 2 material clauses are used. The database was composed of 174 beams, and the criteria that led to its development are discussed. The effect of recycled aggregate incorporation on the statistical descriptors of the bias factor is evaluated and probabilistic modeling using lognormal distributions is argued for. Preliminary partial safety factors for the bias factor of recycled aggregate concrete beams are proposed. No significant differences in the bias of the ultimate moment were found between the two comparison vectors: Eurocode 2 versus ACI 318 specifications and recycled versus natural coarse aggregate. The bias of the cracking moment increased when coarse recycled aggregates were incorporated, most probably due to the higher heterogeneity of recycled aggregates.

This paper presents an experimental study and numerical simulation analyzing the seismic performance of low- and midrise cold-formed steel-framed buildings using shear walls sheathed with corrugated steel sheets with slits. A new testing method considering both lateral and gravity (vertical) load was used to investigate the behavior and strength of the cold-formed steel-framed shear walls. The test results indicate that the perforated shear walls demonstrate desirable ductility and initial stiffness with relatively high shear strength compared with nonperforated shear walls. To further study the seismic performance and determine the seismic performance factors, incremental dynamic analysis was performed of six building archetypes in which the new shear walls were installed. Seismic performance assessment was evaluated according to FEMA methodology. The results indicate that a set of seismic performance factors ($R=C_d=6.5$ and ${\mathrm{\Omega }}_0=3.0$) is appropriate for the perforated cold-formed steel-framed shear wall systems using corrugated steel sheathing. The proposed new shear wall can be used as a substitute for flat steel sheet or wood-based panels in Type I and II constructions in high wind and seismic regions. Detailed full-scale test results and nonlinear finite-element modeling results of this new lateral force resisting system are discussed and reported herein.

In the design of steel structures, composite effects of stud shear connectors are generally measured using ordinary push-out tests. Furthermore, based on those results, the evaluation formulas of the ultimate shear strength are given in design guidelines. However, a concrete slab is subjected to reversed stress during an earthquake, whereas existing tests consider only compressive stresses on concrete. The mechanical behavior in existing structures thereby might be different from that under compressive force alone. This research proposes a component model of a composite beam modeling the stress in actual buildings. Furthermore, cyclic loading tests were conducted on 14 specimens with different specifications of the stud shear connector, concrete, and rebar. The results showed that the ultimate shear strength is considerably lower than that under compressive stress. Consequently, this paper presents equations to assess structural performance precisely considering various influential factors of composite structures.

Current US seismic design provisions allow structures in areas of lower seismicity (e.g., the Midwest and eastern North America) to be designed with modest seismic requirements as compared with the requirements that must be satisfied in areas of higher seismicity (e.g., western North America). Because of the reduced seismic detailing and proportioning requirements in these areas of moderate seismicity, seismic force–resisting systems (SFRSs) within these regions are classified as low-ductility, in contrast to the high-ductility systems common in areas of higher seismicity. Considering the prevalence of low-ductility concentrically braced frames (CBFs) in moderate seismic regions of the US, a thorough performance assessment of these low-ductility CBFs was conducted using detailed OpenSees building models and dynamic numerical simulations. A matrix of 12 buildings was assessed, which varied by number of stories (3, 6, and 9), system configuration (chevron and split-x), and system type [$R=3$ CBF and ordinary CBF (OCBF)]. An additional set of six buildings was designed, using $R=4$ with modified seismic detailing and proportioning, to investigate an alternate prototype low-ductility SFRS with improved seismic performance. Using the established seismic performance evaluation framework, $R=3$ CBF systems did not pass, whereas all but one of the OCBF systems passed. All but one of the prototype $R=4$ CBF systems passed the seismic performance evaluation, and for the majority of cases, the weight-normalized performance was better than the corresponding OCBF systems.