Journal of Structural Engineering

Composite beams comprised of concrete slabs and steel beams joined by mechanical shear connectors are commonly used in modern building design. The use of innovative deconstructable high-strength friction-grip bolt (HSFGB) shear connectors and reduced-emissions precast geopolymer concrete slabs in composite beam design can greatly enhance the sustainability of building infrastructure. Hitherto, research contributions that address the behavior of composite beams with HSFGB shear connectors and precast geopolymer concrete slabs are very limited. To provide a contribution to this area of research, an effective finite element model of push-out testing is developed to investigate the ultimate strength and the load-slip characteristics of shear connection using HSFGB connectors and geopolymer concrete slabs in this proposed sustainable composite beam application. The accuracy of the proposed finite element model is validated by comparing its predictions with experimental results on push-out test specimens also reported in the paper. The effects of the change in the bolt pretension, its clearance between the hole in the steel flange, its diameter and tensile strength,and the compressive strength of the geopolymer concrete are elucidated through parametric studies. Practical design recommendations in algebraic form are proposed and verified for predicting the ultimate strengths and the load-slip relationships for composite beams with HSFGB shear connectors.

As magnetorheological (MR) control devices increase in scale for use in real-world civil engineering applications, sophisticated modeling and control techniques may be needed to exploit their unique characteristics. Here, a control algorithm that utilizes overdriving and backdriving current control to increase the efficacy of the control device is experimentally verified and evaluated at large scale. Real-time hybrid simulation (RTHS) is conducted to perform the verification experiments using the nees@Lehigh facility. The physical substructure of the RTHS is a 10-m tall planar steel frame equipped with a large-scale MR damper. Through RTHS, the test configuration is used to represent two code-compliant structures, and is evaluated under seismic excitation. The results from numerical simulation and RTHS are compared to verify the RTHS methodology. The global responses of the full system are used to assess the performance of each control algorithm. In each case, the reduction in peak and root mean square (RMS) responses (displacement, drift, acceleration, damper force, etc.) is examined. Beyond the verification tests, the robust performance of the damper controllers is also demonstrated using RTHS.

Twelve ultrahigh-strength concrete (UHSC) columns confined by rectangular hoops and crossties were constructed and tested under pure axial load. Primary variables of the investigation were the amount, spacing, and configuration of transverse reinforcement, and concrete compressive strength, ranging from 50 to 200 MPa. The amount of transverse reinforcement ranged from 53 to 151% of that required by the American Concrete Institute (ACI) seismic design provisions. Four different configurations of transverse reinforcement were investigated that included hoops as well as hoops and crossties. The behavior of UHSC columns are characterized by sudden spalling of the concrete cover and extremely brittle failure unless the columns are adequately confined with transverse reinforcement. Therefore, more confinement is required in a column with higher concrete strength than in a column with lower concrete strength to achieve a reasonable postpeak response and sufficient deformability. The amount of transverse reinforcement has a pronounced effect on the postpeak behavior of UHSC columns. It is concluded that the ACI provisions overestimate the maximum axial load by 8–21%; however, the seismic design provisions provide for significant postpeak response of the UHSC columns in this test series. A design expression is proposed for the amount of seismic confinement for 200 MPa UHSC columns, based on the effective confinement index.

Based on the previous research results of the authors, this paper presents an accurate and consistent equation for determining the ultimate shear-out capacity of a structural steel bolted connection. The equation is verified against independent laboratory test results obtained by other researchers around the world. Comparisons against alternative equations found in the design specifications and literature are also included. The paper explains why certain equations appear to be accurate for particular configurations, but are grossly inaccurate for others. This paper describes the various assumptions embedded in the existing equations, some optimistic and others pessimistic. It shows that the current code equations lead to very significant errors on either side of conservatism, while the proposed equation is consistently accurate for all test specimens known to fail in shear-out. A resistance factor of 0.85 is recommended for the proposed equation in order to achieve a reliability index of 4.0. The use of the proposed equation instead of the current AISC specification’s equation will facilitate structural designs that are more economical yet reliable.

A simplified procedure is developed for estimating the seismic sidesway collapse capacity of frame building structures incorporating linear and nonlinear viscous dampers. The proposed procedure is based on a robust database of seismic peak displacement responses of viscously damped nonlinear single-degree-of-freedom systems for various seismic intensities and uses nonlinear static (pushover) analysis without the need for nonlinear time history dynamic analysis. The proposed procedure is assessed by comparing its collapse capacity predictions on 1,190 different building models with those obtained from incremental nonlinear dynamic analyses. A straightforward collapse capacity-based design procedure aimed at achieving a predetermined probability of collapse under maximum considered earthquake event is also introduced for viscously damped structures without extreme soft story irregularities.

Unable to generate sufficient ductility and continuity, RC flat slab structures are vulnerable to progressive collapse, in which the relatively brittle failure mechanism attributable to punching shear failure may lead to catastrophic consequences. Thus, it is necessary to evaluate the effectiveness of approaches for improving the ability of flat slabs to mitigate progressive collapse. Previous studies have indicated that integrity reinforcement may enhance the behavior, particularly postpunching behavior, of newly designed flat slab structures. However, limited tests have been conducted to determine reliable approaches for strengthening existing flat slab structures to resist progressive collapse. In this study, a series of seven multibay flat slab substructures were cast and tested to assess the effectiveness of proposed glass fiber-reinforced polymer (GFRP) strengthening schemes for improving the progressive collapse behavior of existing flat slab structures, owing to its low density, high strength, rigidity, and excellent resistance to corrosion. Three specimens without strengthening were used as control specimens and the remaining four specimens were strengthened by GFRP strips. Test results indicated that proposed strengthening schemes effectively improved the initial stiffness and flexural resistance of flat slab structures. However, they did not sufficiently enhance the postfailure resistance and deformation capacity: there was significant debonding of the GFRP strips from the concrete interface in the large displacement stage, even when specially designed fiber anchors were employed.

Tests regarding the long-term behavior of posttensioned timber connections have been performed at the ETH in Zurich. The aim of these tests is to estimate the loss in tendon force that can be expected during the lifetime of a structure. Several posttensioned beam and beam-column timber specimens exposed to controlled and uncontrolled environmental conditions and loaded only with the axial prestressing force have been monitored for more than one year. The force in the tendon was measured together with the strains in the specimens and temperature and relative humidity in the testing environment. Creep tests performed on small glulam timber blocks loaded in compression have been started as well. The estimated creep coefficients parallel and perpendicular to the grain are used to calculate the losses with an analytical model for the larger posttensioned specimens. A prestressing loss in the range of 5–10%, depending on the geometrical properties and environmental conditions, has been found at the end of the one-year testing. Such a percentage is likely to increase up to 30% at the end of a 50-year service. Careful consideration has been given to identify the different variables affecting the losses of prestressing force in the long-term, including the environmental conditions. The tendon force losses were compared to the results obtained by a simple analytical model. A parametric study based on the model was performed in order to check whether the suggested ash reinforcement in the column is beneficial regarding tendon force losses in the long-term.

Due to their typical high slenderness ratios, glass structural elements can be often subjected to buckling phenomena. Major difficulties in a correct estimation of their effective buckling strength and load-carrying behavior are generally given by a combination of multiple mechanical and geometrical aspects, especially in presence of laminated cross sections or interacting applied loads. In this paper, buckling experiments are performed on laminated glass beam-columns eccentrically compressed. Extended numerical and analytical comparisons are performed with test results in terms of Euler’s critical loads or load-displacement paths. As shown, appropriate calibration of numerical and analytical models generally can provide good agreement between buckling predictions and experimental results. Viscoelastic numerical models, in particular, if well-calibrated in terms of mechanical [e.g., creep effects in polyvinyl butyral (PVB)-foils] and geometrical properties (e.g., initial imperfections, load eccentricities) can provide interesting correlation with experiments, both in the form of global load-carrying behavior and ultimate loads. At the same time, simplified analytical methods based on the equivalent thickness concept can be used for rational analytical predictions—although in well-defined load-time and temperature conditions—and simplified buckling verification procedures.

A comprehensive analytical model is developed for a pressurized fire sprinkler piping system of a hospital building. A suite of ninety-six artificial triaxial floor acceleration histories is used to generate seismic fragility parameters of the sprinkler piping system. The analytical model accounts for the inelastic behavior of braces, hangers, and wire restrainers. It incorporates an experimentally validated hysteresis model developed, as part of this study, for the moment-rotation relationship of grooved fitted joints. Component fragility parameters were obtained for lateral restrainers, hangers, and pipe joints. Three system-level damage states were defined based on the level of functionality of fire sprinkler systems and severity of leakage after a seismic event and a joint probabilistic model were utilized to obtain system-level fragility parameters. Finally, the seismic fragility of fire sprinkler systems with grooved fit joints is compared to that of a piping system with threaded joints.

Corrosion of reinforcement is a predominant reason for reduced service lives of reinforced concrete (RC) structures exposed to aggressive environments. This deterioration process can lead to damage resulting in capacity loss or even structural failure, especially in coastal marine environments or where deicing or antiicing applications occur. Based on data from the National Bridge Inventory in 2010, the average bridge age in the country is 40 years old. Thirty percent of the bridges have exceeded 50 years, 7% have exceeded 75 years, and 25% are deemed deficient. For bridges exposed to chlorides (coastal areas or deicing or antiicing exposure), these older bridges often experience corrosion of the reinforcement. When reinforcement corrodes, the capacity of the structure is likely reduced, although little work has been reported on quantifying the reduction in performance and reliability. In seismic areas, this reduction in capacity may be magnified due to the loading demands during a seismic event. Therefore, understanding the time-variant risks associated with corroding structures will assist engineers and decision makers in making sound decisions with respect to optimization of design, inspection, repair, strengthening, and/or replacement of RC structures. This paper develops a new deterministic corrosion rate model and then uses the new model to assess the time-variant reliability of a corroding column subjected to a seismic event. The results indicate that corrosion can significantly reduce the reliability of an existing bridge column over relatively short durations.

The results of an experimental program investigating the dynamic increase factors of light-frame wood stud walls under blast loading are presented in this paper. A total of 20 walls with two different sheathing types and thicknesses were tested to failure under static and dynamic loading. The study found that the observed failure mode for both static and dynamic loading was flexure; however, a difference in the type of flexural failure was observed. Average increase factors of 1.40 and 1.18 on the resistance and stiffness, respectively, were found. A detailed literature review combined with the test results from the current project yielded a strong correlation between the increase in strain rate and the relative increase in strength and an equation relating the dynamic increase factor (DIF) on the resistance to strain rate was proposed for strain rates in the ranges of 1.67– ${1.65\times 10}^3{\mathrm{s}}^{-1}$ .

Research was conducted to investigate the seismic performance of steel plate shear walls (SPSWs) having infill plates designed to resist different percentages of the applied lateral loads. The FEMA P695 methodology, which defines the performance in terms of collapse potential under maximum considered earthquake (MCE) ground motions, was used to compare the performance of the SPSWs under consideration. This paper describes the development of component strength deterioration models that are needed to perform the collapse assessment of SPSWs, focusing on stress-strain or force-deformation relationships for infill plates and boundary elements. The approach began with identifying the deterioration and failures modes of SPSW from 36 tested specimens. Cyclic deformation capacities of these SPSWs when reaching their ultimate strength, failure points, and rates of degradation were statistically quantified. Based on these statistical results, initial deterioration models for SPSW components were developed in a format compatible for use with the FEMA P695 procedures. The chosen deteriorated material models for infill plates and boundary elements were calibrated to four selected SPSW specimens varying from one to four stories. A companion paper presents the steps and results of the seismic performance assessments.

Assessment of collapse potential and seismic performance was conducted for steel plate shear walls (SPSWs) having infill plates designed per two different philosophies. This assessment was first conducted on SPSWs that were designed neglecting the contribution of their boundary moment resisting frames to resist story shear forces. This assessment of collapse potential was repeated for SPSWs that were designed considering the sharing of story shear forces between the boundary frames and infill plates. Based on these assessments, seismic performance factors [i.e., response modification coefficient ($R$-factor), system overstrength ${\mathrm{\Omega }}_0$ factor, and deflection amplification $C_d$ factor] for both types of SPSWs were identified and compared. Adjustments to improve collapse performance and factors that affect collapse potential were presented. Collapse fragility curves for archetypes with various structural configurations (i.e., panel aspect ratio, intensity level of seismic weight, and number of stories) were investigated. Findings from these analyses demonstrate that the infill plates of SPSWs should be designed to resist the total specified story shears, and that SPSWs designed by sharing these story shears between the boundary frame and infill plates will undergo significantly larger and possibly unacceptable drifts.

The NIST Building and Fire Research Laboratory developed 29 recommendations for research based on the findings from the investigation of the World Trade Center (WTC). This paper discusses the results of a collaborative research effort conducted to address recommendation R9.1 from that report, namely to “Develop and validate analytical tools, guidelines, and test methods necessary to evaluate the fundamental behavior and fire performance of components and the structure as a whole system.” Specifically, it describes the development of a closed-form analytical model to represent moment-curvature-thrust-temperature ($M\text{-}\mathrm{\Phi }\text{-}P\text{-}T$) behavior of steel beam-columns in strong or weak-axis bending. The model considers uniform temperature distributions through the cross sections, and it is developed from parametric studies using a fiber-based analytical approach calibrated to experimental and finite-element results. The section-constitutive model was developed to provide a computationally efficient alternative to fiber-based or finite-element analysis (FEA) models and facilitate development of analytical approaches that do not require sequentially coupled thermal-mechanical analyses.

The self-centering energy-dissipative (SCED) brace is a new steel bracing member that provides both damping and recentering capability to a structure, while reducing or eliminating residual building deformations after major seismic events. Previous SCED brace designs exhibited full self-centering capability over frame lateral deformations ranging from 1.5 to 2.0% of a typical building story height owing to the elongation capacity of the tendons comprising the system. To overcome this limitation, a new enhanced-elongation telescoping SCED (T-SCED) brace has been developed that allows for self-centering response over two times the range achieved with the original SCED bracing system. A prototype design of this proposed system was fabricated and tested quasi-statically and dynamically in a full-scale vertical steel frame. It exhibited full self-centering behavior in a single story frame that was laterally deformed to 4% of its story height. This new T-SCED brace also satisfied standard testing protocols for buckling restrained braces.

Parameter selection is a key step in finite-element-model updating (FEMU) because it determines whether the task of FEMU is successful or not. The as-built engineering structures are inevitably subject to many sources of uncertainty such as geometric dimension variability due to manufacture process, inherent random variation of materials, and imprecisely known boundary conditions. Uncertainty involving parameters challenges the task of parameter selection in FEMU. In this paper, the powerful global sensitivity analysis (GSA) is proposed to perform parameter selection in FEMU when uncertainty exists. The Monte Carlo simulation (MCS) method is extensively adopted to perform GSA. However, the brute-force MCS method is likely to be unaffordable and impractical because it entails a large number of model evaluations due to its slow convergence. Therefore, the Gaussian process metamodel is used as the surrogate model of the time-consuming finite-element model to ease the heavy computational burden. Gaussian process metamodel is favored here because of its probabilistic, nonparametric features and high capability of modeling a complex physical system. The space-filling Sobol sequence sampling method is utilized to generate the informative training data for establishing the Gaussian process metamodel. Finally, two study cases of the simple flat steel plate and full-scale arch bridge are presented to detail the procedure of employing the proposed GSA method to select parameters for FEMU.

This paper investigates the mechanical behavior of dowelled steel-to-timber moment-resisting connections. Two configurations of joints were tested, and the experimental results were used to validate a three-dimensional (3D) nonlinear finite element method (FEM) model. The model uses the Hill criterion to manage the plastic yielding of timber. The brittle character of timber in shear and tension perpendicular to grain is managed through the damage evolution based on the Hoffman failure criterion. The numerical model represents with good accuracy the behavior observed during experiments. The analytical model based on the theory of plastic limit analysis was evaluated through the application to the tested connections.