Journal of Structural Engineering

The failure of beam–column joints in RC frame buildings induced by a strong earthquake can lead to the collapse of buildings. Therefore, numerous experimental studies have been carried out on beam–column joints made with natural aggregate concrete (NAC). However, only a few experimental tests have been conducted on recycled aggregate concrete (RAC) beam–column joints. This paper presents an experimental investigation of the seismic behavior of various types of RAC beam–column joints. A series of five RAC beam–column joint specimens, including three interior joints and two exterior joints, were tested under quasi-static cyclic loading and their behaviors were evaluated in terms of strength, stiffness, cumulative energy dissipation, damping ratio, and damage indexes at different load steps. The influence of joint type, column axial compression level, stirrup ratio in the joint panel, and longitudinal reinforcement ratio on the seismic performance of RAC joints was evaluated. The validity of RC joint shear strength models proposed by different building codes to predict RAC joint shear strength were examined by comparing the experimental shear strength values with analytical results.

This paper investigates isodamage criteria for framed PVB (polyvinyl butyral) laminated glass panels subjected to blast load. Isodamage criteria are presented in the form of pressure-impulse (P-I) diagrams, and a methodology for the generation of the P-I diagrams for laminated glass was developed based on numerical simulation studies and the energy method. Three damage levels were classified in accordance with the conditions identified in standards, namely (1) the glass crack limit, (2) the PVB rupture limit, and (3) overall detachment with a specific velocity after the PVB ruptures. Based on nonlinear finite-element analysis, the governing failure modes of the glass panel in both impulsive and quasi-static regions for each damage level were identified and the corresponding deflection functions were determined. A simplified PVB tensile bar model is proposed to describe the local tensile failure of PVB laminated glass corresponding to Damage Level III under impulsive loading. The pressure and impulse asymptotes of framed PVB-laminated glass for different damage levels were derived using the energy balance principle. The proposed method was validated through comparison with published experimental data and further numerical results. This method can provide a reference for engineering design and hazard estimation of framed PVB-laminated glass against blast loading and can be extended to laminated glazing with other interlayers.

A fully prefabricated damage-tolerant beam-to-column connection is proposed as an approach toward an earthquake-resilient steel frame. By introducing a composite steel–ultrahigh-performance concrete (UHPC) joint and friction damper, the plastic deformation becomes concentrated on the designated plastic hinge region. Thus, the damage index and area of the connection can be limited to an acceptable level. In this paper, four full-scale specimens are tested to evaluate the cyclic performance of the novel connection. Some important design parameters are investigated, including the thickness of the UHPC layer, the length of the designated plastic hinge region, and the friction force. The experimental results confirm the expected damage-tolerance performance. Yielding does not occur in the main column and composite beams. The beam-to-column connection exhibits satisfactory energy dissipation and deformation capacity. Strength degradation is not observed, even when the beam–column relative rotation reaches $1/20$. Based on the experiment, an analytical connection model is proposed. This model performs well in estimating the initial stiffness and yielding force of the connection. Several design suggestions are presented on the basis of this analytical model.

This paper focuses on the identification of tension in suspenders equipped with supplemental dampers in through and half-through arch bridges. Although the differential equation governing the transverse vibration of beams can be modified to include the restraining actions and energy dissipative features of the damper, ensuing solutions relating suspender tension to suspender frequency can only be expressed implicitly, rendering the approach impractical in real bridge applications. This paper develops a simpler, practical identification method which takes into consideration the influence of the damper. Numerical results relating suspender frequency to suspender tension and damper lateral stiffness can be visualized as a surface plot, which in essence is a signature of the suspender system. Feasibility of the tension identification method is demonstrated using a recently completed 180-m-span bowstring arch bridge. Results are promising because suspender tensions are identified with acceptable accuracy. It is further contended that the proposed method is effective in identifying the tension in suspenders equipped with supplemental dampers at all stages of construction and the process can be readily extended to tension identification during the service life of bridges.

The present study investigated the effect of web distortion on the lateral torsional buckling strength of Gerber systems. Toward this goal, a number of modifications were introduced into two finite-element formulations for the distortional and nondistortional lateral torsional buckling analysis. The distortional formulation treated the web as a thin plate and the flanges as Gjelsvik members and captured load height effects. The nondistortional formulation was based on the Vlasov beam kinematics and enabled the enforcement of lateral restraints offset from the shear center while preserving the positive definiteness of the stiffness matrices. Both models were validated against shell finite-element solutions and then utilized to develop moment gradient coefficients for Gerber beams, assess the web distortional effects, and quantify the influence of various lateral bracing scenarios on the elastic lateral torsional buckling strength. Unlike rolled simply supported beams in which web distortion was considered to be insignificant, the present study indicated that web distortion heavily influences the lateral torsional buckling strength of Gerber beams.

This paper proposes a joint system that connects the thin-walled square reinforced concrete–filled steel tube (RCFST) column to RC beams at both sides of the joint. In order to delay the local buckling of square steel tubes with high width-to-thickness ratio and enhance confinement effect on infilled concrete, diagonal stiffeners were welded to adjacent sides of the internal square steel tube and longitudinal bars were embedded in the square RCFST columns. Four RCFST joints with internal diaphragms were tested up to a large drift ratio of 6.7% under combined axial compression and reversed cyclic loading. All four specimens were designed according to the strong-column-weak-beam concept, and the strong-joint-weak-member seismic design philosophy. The cross-sectional dimensions of the RCFST column were $300\times 300\mathrm{mm}$. The dimensions of the beam cross section were $200\times 350\mathrm{mm}$ and high-strength steel rebars (600 MPa) were adopted in the RC beams. The width-to-thickness ratio of the square joint tube and the level of axial load in the column were two important parameters to be studied. Two types of failure mode, i.e., beam flexural failure and beam flexural failure with bond failure, were observed. Both failure modes were ductile and the joints showed excellent seismic performance under cyclic loading. Based on the test results, some design considerations for the joints were recommended.

This paper focuses on the structural behavior and negative bending moment capacity of steel–timber composite (STC) beam-to-column connections with shear tabs. It is hypothesized that timber slabs with relatively high tensile strength acting compositely with steel beams can allow for large negative bending moment resistance despite their being a simple (or pin) connection between the steel beam and column. Four full-scale STC beam-to-column cruciform subassemblies with shear tab connections were fabricated and tested under a monotonically increasing load that produced negative bending moments at the beam-to-column connections. In addition, a steel–concrete composite (SCC) beam-to-column connection with identical geometry to that of the STC joints was fabricated and tested to evaluate the structural performance (stiffness, strength, and ductility) of the STC compared with SCC connections. The main variables in the experimental program were the type of connection (i.e., continuous, spline, and bolted steel plate) between the cross-laminated timber slabs across the column and the depth of the shear tab. Lastly, a simple method inspired by the component-based approach is proposed for estimating the peak load carrying capacity of the STC beam-to-column connections with a shear tab.

Experimental research on seismic behavior of structural columns is one of the most important and active research areas in structural engineering. Various methods with innovative loading configurations have been developed by researchers over the past several decades, and the research has enhanced our knowledge about the performance of structural columns, resulting in the improvement of design practice. This paper provides a state-of-the-art review of the testing setups for simulating earthquake loading on structural columns, to reveal the trend of sophistication of testing methods. Special attention is given to the large tonnage axial loading methods and the shortcomings of existing methods. Based on past experiences and a review of existing methods, a new multiuse structural testing (MUST) system is developed and described in this paper. Because the MUST equipment has the unique ability to maintain the axial load vertical during lateral loading, and the force inputs to the structural model can be directly measured, it is more suitable for simulating structural responses under horizontal and vertical ground motions.

Shear lag effects can significantly reduce the moment capacity of nonrectangular reinforced concrete walls. Although this phenomenon is recognized as an important component in the analysis and design of buildings, it is generally not well understood by practicing engineers. Furthermore, a paucity of experimental studies exists that have focused on the seismic performance of reinforced concrete C-shaped walls and virtually no studies that have investigated the shear lag effects for these types of walls. This research investigates shear lag effects in reinforced concrete C-shaped walls using an extensive number of finite element modeling results. The numerical analyses are conducted using VecTor3 version 1.1, a state-of-the-art finite element modeling program, to estimate the vertical strain distributions across the web and flanges of the wall. The results show that shear lag effects are significant and sometimes prominent in C-shaped walls, particularly for the wall sections perpendicular to the loading direction. An expression is derived to estimate the effective width of C-shaped walls and for the different loading directions. Moment-curvature analyses are conducted to illustrate how practicing engineers can implement the effective width method for future analyses and designs.

Base isolation is accepted as the method of choice for mitigating the seismic risk of critical facilities, including hospitals. However, while many studies have confirmed the effectiveness of isolation in reducing seismic demands on attached nonstructural components, only a few have investigated the performance of unanchored building equipment and contents (ECs), and especially mobile ECs supported on wheels/casters, in base-isolated buildings. Motivated by the fact that about one-third of ECs in typical hospitals are supported on wheels/casters, this study investigated the seismic response of such ECs in base-isolated buildings through shake table tests. A comparative approach was adopted to examine the performance of lead-rubber bearing (LRB) and triple-friction pendulum (TFP) isolation systems against a conventional fixed-base hospital in reducing displacement and velocity demands on mobile ECs. It was observed that base isolation is effective in reducing seismic demands, especially velocity, on ECs. It was concluded that, in base-isolated buildings, locking the wheels/casters on ECs reduces EC response. Fragility curves were developed for mobile ECs on unlocked wheels and casters in base-isolated buildings.

This paper proposes the use of an additional stiffening ring to prevent buckling of aboveground storage tanks (ASTs) under storm-surge inundation and presents an approach to obtain an optimal design for the additional ring. This study addresses the lack of methods to prevent storm-surge buckling of ASTs even though it has been identified as a common mode of AST failure. For this purpose, finite-element simulations were performed to study the effect of the proposed stiffening ring on the buckling response of ASTs. The critical surge height, i.e., the lowest surge height that causes AST buckling, is evaluated for a wide range of tank geometries, material properties, ring section moduli, and positions of the additional ring. The critical surge heights obtained from these simulations are used to obtain a multiparameter regression equation that can predict the critical surge height. The regression equation is further used to derive the optimal section property and the position for the additional ring as a function of tank geometry and material properties. In order to demonstrate the effect of the additional stiffening ring, the change in the critical surge height due to the installation of the additional ring is evaluated for five case-study tanks. The results show that installation of the additional stiffening ring can significantly increase the critical surge height of tanks. Furthermore, considering uncertainties from level of fill in the tank and geometric imperfections, fragility analysis for one of the case study tanks underscores the reduction in fragility, i.e., conditional probability of buckling failure given surge level, due to the additional ring.

In buildings, thermal bridging can be formed through structural components such as protruding balconies. For this reason, thermal break systems are used to limit heat flow in order to fulfill code requirements. With balconies exposed to significant variations of outside temperature, the thermal break systems undergo large horizontal deformations that might lead to yielding several times throughout its service life. Assessing the design in these conditions requires a low-cycle fatigue verification, which is unusual in the building design. As a consequence, the whole safety format must be redefined, with a proper account of the uncertainties in the definition of the actions and in the model for the resistance. This paper presents a reliability-based analysis for the calibration of the safety factor that takes into account these uncertainties. The energy-based fatigue life curve and the cyclic force-displacement relationship of the thermal break system are constructed based on the low-cycle fatigue experimental test data. The mechanical behavior of the thermal break system is modeled by a coupled plastic-damage model. For the fatigue verification, the climatic loads are defined based on the temperature history obtained from European Climate Assessment & Dataset (ECA&D). The limit state equation for fatigue failure is written based on the energy-based fatigue life curve and Miner’s rule to describe the reliability model. This reliability model includes the uncertainties related to the strength, the loads, and the accumulated damage. The effect of these uncertainties on the safety factor is discussed for the city of Embrun in France. At last, the sensitivity of the safety factor with the locations is expressed based on the data from 33 cities in France.