Journal of Structural Engineering

Several stages of performance need to be considered during the design of curved I-girders, including both the construction stage and the in-service conditions. Girder stability during the early stages of construction can be difficult to assess because the girders, at times, have little or no bracing present. One stage when there is no bracing present occurs when the girders are picked up from the ground or transport trucks by cranes and lifted into place. To better understand girder response during this critical stage, field studies were conducted on horizontally curved I-girders to measure rotations and stresses during the lifting process. This paper provides details of a semianalytical solution to predict the buckling and deformational responses of straight and curved girder segments during lifting. The deformations can be compared with rotational limits that were established to minimize problems with making connections to previously erected girder segments. The total rotational deformations of a horizontally curved girder result from two distinct components: (1) rigid-body rotation and (2) rotation caused by the girder cross-sectional twist owing to torsion from the girder’s self-weight. A spreadsheet design tool, UT Lift, was developed to provide critical information for evaluating the rotational behavior of a horizontally curved I-girder during lifting and to estimate its lateral-torsional buckling capacity. An example of UT Lift’s capabilities is presented along with background information on its development. Recommendations are given for safely lifting and erecting horizontally curved steel I-girders.

This paper presents an approach for modeling the fire insulation damage in steel columns. Both experimental and numerical studies were carried out to investigate the failure pattern and damage phenomenon of fire insulation on steel columns under monotonic and cyclic loads at ambient conditions. As part of the experiments, three fire-insulated steel columns were tested, and the horizontal load and displacement at the top of the column were monitored. The test results show that the adhesion of fire insulation with steel columns is generally weak and that the fire insulation peels off from the column surface under large moments induced at the ends of the column. Under cyclic loading, the adhesion of fire insulation weakens significantly because of the damage-accumulation effect. A finite-element model was developed to evaluate interlaminar stress between the steel plate and the fire insulation, and the effect of critical factors on insulation damage was studied. Results from experimental and numerical studies are utilized to develop an approach for modeling the fire insulation damage in steel columns. In this approach, two damage criteria, namely, maximum stress and distortion energy, are considered for evaluating the insulation damage and damage length. Results from case studies indicate that either of the damage criteria can be applied for evaluating insulation damage and also that both of the criteria predict similar damage patterns.

The 2009 International Building Code (IBC) structural integrity provisions include a minimum tensile capacity requirement for simple shear steel connections. An all-bolted single-angle connection has been physically tested and analytically modeled to determine its ability to meet this code requirement. The single-angle connection studied was an ASTM-rated A36 $102\times 76.2\times 9.53\text{-}\text{mm} (\mathrm{L}4\times 3\times 3/8\text{-}\text{in.})$ connection having four A325 19.1-mm-diameter (0.75-in.-diameter) snug tight bolts on each angle leg. This connection’s tensile capacity, calculated by prying equations from the current AISC Steel Construction Manual, does not meet the new IBC requirement. Six full-scale tests were performed. For three tests, a lateral restraint was included to examine the effect of beam restraint on connection tensile capacity. The ultimate tensile failure load of the connection was observed to be three times the value predicted by the current AISC prying equations. Both tensile rupture of the web-framing angle leg and bolt tensile failure modes occurred. Presence of lateral restraint decreased the variability in tensile capacity. Finite-element analysis was performed to explore observed connection behavior. Results of the physical tests and computational analysis were used to make recommendations to modify the AISC prying equations to more accurately predict the tensile behavior of single-angle connections. The proposed equations use a plastic-hinge model to determine the effects of prying action on bolt strength for single-angle connections, accounting for their inherent flexibility. Using the proposed equations, the connection meets the IBC tensile requirement.

Large-scale shake table tests were conducted at E-Defense, Japan, to examine the dynamic response of a steel concentrically braced frame. The specimen was a single-bay, single-story frame with a pair of square hollow structural section braces placed in a chevron arrangement. The gusset plates connecting the brace to the framing elements were provided with an elliptic fold line to accommodate out-of-plane rotation of the brace in compression. The specimen was subjected repeatedly to a unidirectional ground motion with increasing magnitude until the braces buckled and eventually fractured. The bracing connections performed as intended; the gusset plates folded out of plane, and no crack was observed in the gusset plate or in the critical welds. Consequently, the test results demonstrated excellent performance of the bracing connections. Elastic deformation of the beam prevented the braces from developing their full tensile strength. Yielding in the middle of the beam, which was predicted by monotonic loading analysis, did not occur. The specimen response was reproduced by a numerical model using fiber elements. This model was able to predict the occurrence of brace buckling and fracture and thereby accurately trace the dynamic behavior of the frame.

Steel concentrically braced frame (CBF) systems are widely used in buildings to resist lateral loads, because they possess high lateral strength and stiffness. For seismic applications, braces dissipate energy through tension yielding and compression buckling, and the lateral response of the CBFs is dominated by the complex cyclic inelastic behavior of the braces. Significant effort has gone toward developing accurate and efficient brace models, and these models fall into three broad categories: finite element, phenomenological, and physical theory. Finite-element models are accurate but computationally expensive, and phenomenological models are computationally efficient but depend on experimental results for calibration. Physical theory models, which are based on fundamental structural behavior, provide a balance of efficiency and accuracy. The present research implements an existing brace physical theory model for use in the force analogy method, which is an accurate, efficient, and stable algorithm for conducting dynamic analysis when coupled with the state space formulation. The brace model, which uses two sliding plastic mechanisms to capture axial and lateral brace deflections and to relate these to the brace force, is validated against prior experimental results. The brace model is also implemented in a frame, where inelastic response occurs in both the frame and the braces, to demonstrate application of the model and the potential for simulating complex inelastic dynamic CBF behavior with the force analogy method.

Masonry walls subjected to in-plane loading exhibit a complex behavior because of the influence of several parameters such as axial load, aspect ratio, and the strength of materials. In high-rise buildings or seismic areas, large tensile stresses may arise in these walls, and vertical and horizontal reinforcement is often used to provide proper resistance, which increases the complexity of the structural behavior. This work presents (1) an overview of the experimental behavior of unreinforced and reinforced masonry walls; (2) an overview of distinct design methods aimed at calculating the in-plane lateral resistance; and (3) a proposal of a new design model for reinforced masonry walls subjected to in-plane loading. The proposed model considers the coupling interaction of the flexural and shear resisting mechanisms and updates the role of the vertical and horizontal reinforcement to the lateral resistance. A database composed of experimental results of the in-plane lateral resistance of 101 masonry walls available in the literature was used to evaluate the performance of existing models and to validate the newly proposed model, which exhibits much better performance.

Experimental observations on 11 RC columns tested at Nanyang Technological University and existing experimental data of 79 shear-critical RC columns are presented. Significant arch action is found in columns with a small shear span-to-depth ratio and high axial-load ratio under shear force. Using the sectional method for shear strength of these types of columns, which does not consider arch action, would give a more conservative prediction. On the basis of the truss-arch model, an expression to predict the shear strength of shear-critical RC columns is presented, which considers both the contributions of concrete and transverse reinforcement to shear strength in the truss model, as well as the contribution of arch action through compatibility of deformation. The proposed model is compared with other shear strength models using the available column test data consisting of 90 shear-critical RC columns, and the results show that the proposed model can improve the accuracy of shear strength predictions for shear-critical RC columns.

This paper describes the implementation of a three-dimensional (3D) concrete constitutive model for fiber-based analysis of RC members subjected to combined loadings including torsion. The proposed model is formulated to address the interaction between the axial force, bidirectional shear, biaxial bending, and torsion. The shear mechanism along the beam is modeled using a Timoshenko beam approach with 3D frame elements with arbitrary cross-sectional geometry. The model considers the 3D equilibrium, compatibility, and constitutive laws of materials at the section and structural level. The concrete constitutive law follows the softened membrane model with a tangent-stiffness formulation. The emphasis of the paper is on evaluation of the effect of the different stress states on the global and local behavior of the member. The ability of the model to assess the ultimate strength, stiffness, energy dissipation, failure modes under 3D loading is evaluated by correlation of analytical results with experimental tests of RC specimens.

In this study, a method of strengthening circular columns using high-performance ferrocement (HPF) is proposed. This is achieved by replacing the concrete cover by HPF (i.e., comprising rendering material and wire mesh). Direct tensile tests were carried out on HPF specimens. For rendering material with high tensile strength, it is necessary to incorporate its tensile strength in the estimation of the tensile strength of HPF. Nineteen full-scale circular plain or RC columns were tested under monotonic compression. Eleven were detailed with a volumetric ratio of transverse reinforcement ${\mathit{\rho }}_s$ at 0.230%. HPF, having three different rendering materials and with one or three layers of wire mesh, was used to confine eight of these columns. Test variables included volume fraction of wire mesh and tensile strength of rendering material. Plain-concrete columns strengthened with HPF have peak strengths at 30–59% higher than control specimens. RC columns having a low ${\mathit{\rho }}_s$ at 0.230% and strengthened with HPF can achieve peak strengths comparable with columns having a high ${\mathit{\rho }}_s$ at 0.918%. A set of empirical equations for predicting the peak strength of plain-concrete or RC columns strengthened with HPF is derived, showing good agreement with the test data. Lastly, a design procedure for strengthening a RC column by replacing the concrete cover using HPF is proposed.

The vulnerability of conventional RC structures to structural failure caused by the loss of corner columns has been emphasized over the past years. However, the lack of experimental tests has led to a gap in the knowledge for the design of RC building structures to mitigate the likelihood of progressive collapse caused by losing a ground corner column. Seven one-third scale RC beam-column substructures were tested to investigate their performance. The variables selected for the test specimens included beam transverse reinforcement ratios, type of design detailing (nonseismic or seismic), and beam span aspect ratios. Shear failure was observed to have occurred in the corner joint, and a plastic hinge was formed at the beam end near the fixed support in the nonseismic detailed specimens. However, plastic hinges were also formed in the beam end near to the corner joint for the seismically detailed specimen. Vierendeel action was identified as the major load redistribution mechanism before severe failure occurred in the corner joint, but a cantilever beam redistribution mechanism dominated after the corner joint suffered severe damage. The test results were compared with the Department of Defense design guidelines to highlight the deficiencies of the recently updated guidelines.

This paper describes the development and validation of an analytical multispring plastic hinge element that can predict elongation of ductile RC plastic hinges together with its flexural and shear responses. The element consists of layers of longitudinal and diagonal springs that represent the behavior of concrete, reinforcing bars, and diagonal compression struts. Beam tests reported in the literature, for which elongation of plastic hinges was measured at different stages of the lateral cyclic loading, were used to validate the effectiveness of the newly developed plastic hinge element. Comparisons of the analytical predictions with experimental results show that the proposed element predicts elongation of plastic hinges satisfactorily. The ability of the model to predict elongation of a plastic hinge together with its flexural and shear deformations offers a significant advancement in seismic performance assessment of RC structures.

A new force visualization and design tool employing hybrid topology optimization is introduced for RC and prestressed concrete structural members. The optimization scheme couples a minimum compliance (maximum stiffness) objective function with a hybrid truss-continuum ground structure that can generate a strut-and-tie model for any general concrete member, loading, and set of boundary conditions. The truss ground structure represents discrete steel reinforcing bars (tensile load paths) that can be sized based on axial forces output directly by the optimization routine, whereas the continuum elements simulate concrete compression struts. This separation of compressive and tensile load-carrying elements is achieved through bilinear elastic models with an orthotropic constitutive relationship for the continuum. Examples are provided demonstrating the potential value of the optimization tool to RC design. Reinforcing layouts that can minimize cracking and reduce steel quantities when compared with traditional designs are provided for a prismatic beam, a hammerhead pier, a stepped beam with a cutout, and the local anchorage zone of a prestressed concrete block. A minimum length scale constraint is employed to control complexity of the strut-and-tie topology, accommodating design solutions that balance material savings, structural performance, and constructability.

This paper seeks to examine the concrete contribution to shear strength and determine the inclination of the compressive strut within the variable truss model for slender RC shear-critical beams with stirrups. Using the modified compression field theory in place of the conventional statistical regression of experimental data, the expression for the concrete contribution to shear strength was derived, and the inclination of compressive struts was determined. A simplified explicit expression for shear strength was then provided, with which shear strength can be calculated without extensive iterative computations. This method was then verified using the available experimental data of 209 RC rectangular beams with stirrups and compared with the current methods from the American Concrete Institute and the Canadian Standards Association. The theoretical results are shown to be consistent with the experimentally observed behavior of shear-critical RC beams.

The objective of the present paper is to analyze the free vibrations of thin-walled beams with arbitrary open cross section, made of cross-ply laminates with midplane symmetry, by means of an exact solution. The theory of thin-walled composite beams is based on assumptions consistent with Vlasov’s beam theory and classical lamination theory. The governing differential equations for coupled bending-torsional vibrations were obtained using the principle of virtual displacements. To simplify the coupled system of differential equations, an ideal center of gravity and shear center were introduced. In the case of a simply supported thin-walled beam, the closed-form solution for the natural frequencies of free harmonic vibrations was derived. The frequency equation, given in determinantal form, is expanded in an explicit analytical form. To demonstrate the validity of this method, the natural frequencies of nonsymmetric thin-walled beams having coupled deformation modes are evaluated and compared with results available in the literature as well as with FEM results.

A second-order equilibrium analysis is developed for the calculation of the collapse load of an eccentrically compressed beam with an annular cross section in the presence of a no-tension material. Unlike the case of a rectangular cross section, extensively treated in the literature, no rigorous closed-form solution is possible, in this case, but semianalytical results can be obtained, which may be useful for engineering applications.