Journal of Structural Engineering

Light gauge metal decking is commonly used in the building and bridge industries for concrete formwork. In addition to supporting the concrete, the metal forms also improve the lateral-torsional buckling capacity of the beam or girder they are fastened to as they behave as a shear diaphragm and restrain the warping deformation of the top flange. However, the stability bracing requirements for shear diaphragms are not well established. This is the first part of a two-part paper on diaphragm bracing of beams. The first part of the paper focuses on behavior whereas the second part focuses on general design requirements. The diaphragms in the study were connected along two edges to the top flanges of adjacent girders. The parameters that were investigated include the diaphragm stiffness, load type, and load position. The type of loading has a significant effect on the stability bracing behavior of the shear diaphragm. Other factors that have an effect on the bracing behavior include the web slenderness and the presence of intermediate discrete braces. The results presented in the first part of the paper create the foundation for a diaphragm bracing design methodology that is developed and presented in the second part of the paper.

Light gauge metal decking is commonly used in the building and bridge industries for concrete formwork. In addition to supporting the wet concrete, the metal forms also improve the lateral-torsional buckling capacity of the beams or girders they are fastened to since they behave as a shear diaphragm and restrain the warping deformation of the top flange. The design requirements for shear diaphragm bracing are not well established. This is the second part of a two-part paper. The first part of the paper focused on the general stability bracing behavior for shear diaphragms connected to the top flanges of adjacent beams or girders. This part of the paper outlines the design requirements for shear diaphragm bracing and focuses on both the stiffness and strength requirements for beam stability. Design expressions are presented for the stiffness and strength requirements as well as a model that can be used to estimate the forces in the fasteners that connect the diaphragms to the top flanges of the beams. An example is presented at the end of the paper demonstrating the use of the design expressions.

A two-phase experimental program was generated on a full-scale two-story steel plate shear wall with reduced beam section connections and composite floors, to experimentally address the replaceability of infill panels following an earthquake and the seismic behavior of the intermediate beam. In Phase I, the specimen was pseudodynamically tested, subjected to three ground motions of progressively decreasing intensity. The buckled panels were replaced by new panels prior to submitting the specimen to a subsequent pseudodynamic test and cyclic test to failure in Phase II. It is shown that the repaired specimen can survive and dissipate significant amounts of hysteretic energy in a subsequent earthquake without severe damage to the boundary frame or overall strength degradation. It is also found that the specimen had exceptional redundancy and exhibited stable force-displacement behavior up to the story drifts of 5.2 and 5.0% at the first and second story, respectively. Experimental results from pseudodynamic and cyclic tests are compared to seismic performance predictions obtained from a dual strip model using tension only strips and from a monotonic pushover analysis using a three-dimensional finite-element model, respectively, and good agreement is observed.

Although concentrically braced frames are an efficient means of providing lateral support in steel structures, many such frames designed to resist seismic loading and featuring hollow structural section braces have performed poorly in recent earthquakes—primarily due to unexpected connection failures. To address this issue, the use of a cast steel connector that fits between a tubular brace and a gusset plate is presented as an alternative to the reinforced, fabricated connections that are commonly used in seismic load resisting braced frames. The resulting connector was shaped using solid modeling software, verified by finite-element analysis, and finally cast to ASTM A958 standards. Laboratory results from static and cyclic testing of concentrically loaded brace-connector assemblies showed that the use of a cast steel connector is a viable means of connecting to tubular brace members for seismic (or even static) applications. Further, as the connector was crafted to fit a range of tubular members and can be mass produced, the proposed solution is an economical alternative to conventional tube-to-gusset connections under seismic loading.

The behavior of I-shaped steel girders with flanges made from concrete-filled tubes is investigated experimentally, focusing on concrete-filled tubular flange girders (CFTFGs) in positive bending regions where the concrete-filled tube is the compression flange. The investigation included CFTFGs that are either composite or noncomposite with a concrete deck. For the composite CFTFGs, girders with rectangular tubes and either a flat web or a corrugated web are studied, and for the noncomposite CFTFGs, girders with round tubes and flat webs are studied. The objectives are: (1) to provide experimental data demonstrating the load carrying capability of CFTFGs and the advantages of CFTFGs over conventional I-girders; and (2) to verify the adequacy of analytical models by comparing experimental and analytical results. The experimental results demonstrate the improved lateral torsional buckling capacity of CFTFGs, and their capability to carry factored design loads under construction conditions and in the final constructed condition. The comparison between experimental and analytical results shows the adequacy of simple analytical models for CFTFGs.

This paper presents the development of a parametric equation for predicting the ultimate capacity of tubular circular hollow section joint with complete overlap of braces based on the experimental and numerical investigation. In the experiment, a joint specimen with complete overlap of braces is tested to failure under lap brace axial compression for verification of the finite-element (FE) model. The comparison of results showed that the FE model simulates very well the current and the previous test specimens with differences in ultimate capacity and lap brace axial displacement of less than 1.52 and 3.5%, respectively. In the parametric study, the joint ultimate strength is found not significantly affected by the boundary conditions and the chord prestresses. The developed parametric equation based on 3,888 FE models has been verified against the current and the previous test and FE data. A simplified equation in characteristic format for limit state design is also proposed. A comparison with the existing T/Y-joint equations showed that the joint ultimate strength at small gap size is higher. However, the joint ultimate strength decreases with increasing gap size and is found equivalent to that of T/Y-joints at a gap size greater than through brace diameter.

Stainless steel structural sections possess several features that result in a significantly different response to that of equivalent carbon steel sections. To date these features have not been fully recognized in design codes, which have largely adapted rules devised for carbon steel in a rather simplistic fashion. Recently, a new approach for dealing with local buckling and the associated loss of effectiveness that does not utilize the concepts of either cross-sectional classification or effective cross-sectional properties has been developed for stainless steel and has also been applied to other nonlinear metallic materials. The method is based directly on the deformation capacities of cross sections and covers the behavior of stainless steel members subjected to flexural buckling and combined axial load plus bending. The proposed method has been verified using test results and its performance has been compared against the existing ASCE and Eurocode design guidance for structural stainless steel. Significantly improved and more consistent predictions have been obtained using the proposed method without any extra calculation effort.

This paper presents a set of parametric equations for predicting the stress concentration factor (SCF) at the crown toe, saddle, and crown heel of completely overlapped tubular circular hollow section joints under lap brace axial compression. In the study, a joint specimen is tested within the elastic limit of steel material for the verification of finite-element (FE) models. The comparison of results showed that the 8-node thick shell and the 20-node solid FE models simulate reasonably well the test specimen with average difference in strain concentration factor (SNCF) of 7.9 and 8.8%, respectively. The mean SCF-to-SNCF ratio of the joint is 1.15. The parametric equations are developed based on 5,184 8-node thick shell FE models and have been assessed against the Fatigue Guidance Review Panel criteria, the current and previous test data and the FE database. The results of the statistical analysis, which based on the frequency of occurrence of predicted-to-measured SCF, showed that the performances of the proposed parametric equations are acceptable.

The finite element method was used to develop accurate stress intensity factor (SIF) solutions for two-tip web cracks and symmetric three-tip cracks in I-beams under tension or bending. Governing parameters for cracked I-beams were determined. For web cracks, the SIF is a function of applied stress, crack length, eccentricity, and flange-to-web area ratio of W shape. For three-tip cracks in web and flange, the SIF is a function of applied stress, web and flange crack lengths, and flange-to-web area ratio. The flange-to-web area ratio accounts for the constraining effect of the flange on two-tip web cracks and the interaction effect on three-tip cracks. A total of 2,106 combinations of type of crack, type of loading, crack length, eccentricity, and flanges-to-web area ratio were analyzed. Numerical results were fitted with polynomial equations for ready use by practicing engineers.

The paper investigates the influence of cyclic and sustained loading on the performance of layered wood–concrete composite beams interconnected by a notched connection detail. A number of composite beams were conditioned in a climate chamber in order to raise the wood moisture content from the ambient value (5–7%) to about 12%. Then the beams were subjected to $\mathrm{21,600}\text{cycles}$ of loading and unloading to simulate the typical live load frequency experienced by the floor of a commercial building over a $30\text{-}\text{year}$ service life. Finally, each individual beam was ramp loaded to failure to determine the ultimate load carrying capacity and composite efficiency. Additional beams were subjected to sustained load for $133\text{days}$ in an unconditioned environment and then tested to failure. The main outcomes of the experimental program were: (1) relatively high beam stiffness and strength were achieved despite the use of few connectors; (2) two types of failure mechanisms were detected: either shear in the wood between the exterior notch and the beam end, or wood bending failure at midspan; (3) the cyclic loading increased the initial elastic deflection by 18% and reduced the beam stiffness by 9%, on average; (4) after $133\text{days}$ of sustained load, the deflection increased by 59%, on average; and (5) the reduction in stiffness and in load capacity due to sustained loading was greater than that due to the cyclic loading.

Many studies have approached the problem of mixed beams with a slip at the connection. An analysis of the problem has been carried out globally and Eurocode-5 solves the problem for the use of simple supported beams or similar structures in a precise way and with a simple formulation. Other methods to solve the structural analysis of this issue include matrix as well as several finite-element procedures. Nevertheless, the design process for selecting the connection is now iterative and the variables of the problem can be presented in a more condensed and useful way. The problems of strength and stiffness in this research have been separated. Variables in a powerful nondimensional way and their exact relationships in simple supported beams are presented here. These variables show the nature of the problem in a clear way, and provide a rational basis for selecting the connection.

The influence of concentrated reinforcement in the immediate column region, the use of high-strength concrete slabs, as well as using puddled fiber-reinforced high-strength concrete in the slab in a region close to the column were investigated. The slab concrete strengths of the specimens were 30, 35, 40, 55, 65, and $90\mathrm{MPa}$ . The performance of the slab-column specimens tested was investigated, including the punching shear capacity, cracking on the top of the slabs around the columns, and the stiffness of the slab-column connections. Predictions using different code equations are compared to the experimental results obtained from the slab-column connections tested in this study and those tested in other studies. The beneficial effects of using concentrated flexural reinforcement, high-strength concrete and puddled fiber-reinforced high-strength concrete are demonstrated.

This paper proposes the concept of “equivalent load for stiffness” (ELS) and presents the applicability of this concept to a variety of structural problems. ELS is a set of additional forces applied to an original structure to produce the same response as that of a modified structure. That is, ELS is equivalent to the changes of stiffness in the original structure. The novelty of the proposed algorithm is that it requires computational operations of an order of $qmn$ , as compared to the full analysis requiring $m^{2}n$ , where $m=\text{half}$ -bandwidth of the global stiffness matrix; $q=\text{number}$ of degrees of freedom (DOF) associated with the modified members, and $n=\text{number}$ of DOFs. Therefore, the proposed algorithm is particularly efficient for such situations as a limited number of members are modified. In addition, the algorithm involves a clear physical concept based on static condensation and is applicable to a variety of problems, including sensitivity analysis, nonlinear analysis, dynamic analysis, and so forth.

Linear elastic and nonlinear elastic analytical investigations are reported for a nearly conventional, laminated glass curtain wall with split screw spline mullions subjected to low-level blast loading. Responses (dynamic stresses, deflections, and accelerations) of the rectangular glass lites within the curtain wall are compared to those of identical glass lites that are (1) simply supported and (2) supported on structural silicone sealant beads along all four edges. The elastic finite element model of the curtain wall was calibrated to small-amplitude static and dynamic experimental results in a previous effort, where effective mullion moments of inertia, connection stiffnesses, and system damping ratios were determined. This calibrated curtain wall model and the two other glass lite models were subjected to uniform blast pressures represented in time by a triangular pulse. These comparisons are made to illustrate the reduction of principal stresses of the glass lites due to the flexibility of the structural silicone bead and, more significantly, the global flexibility of the curtain wall system. Changes in modal frequencies and the appearance or disappearance of significant response modes due to the different boundary conditions of the glass lites are illustrated. For the cases studied, maximum principal stresses were typically halved when the flexibility of the curtain wall members supporting the lite was considered. This paper also shows that: (1) the dynamic behavior of a given glass lite varies dramatically with support conditions as shown in corroborating modal and transient analyses and (2) geometric nonlinearities typically reduce dynamic responses only slightly when compared to linear geometry for the low-amplitude loads considered in this study.

Progressive collapse resistance of an actual six-story reinforced concrete frame structure is evaluated following predefined initial damage. The initial damage was caused by the simultaneous explosion (removal) of two adjacent exterior columns, one of which was a corner column. The mechanism of load redistribution and change in column axial forces (strains) are discussed. In the structure studied, the development of bidirectional Vierendeel (frame) action is identified as a major mechanism in redistribution of loads. Through careful instrumentation, the change in the direction of beam bending moments in the vicinity of the removed columns is demonstrated. In general, if such a change in the bending moment direction results in high tensile stress in bottom beam reinforcement at the face of a column, brittle local failure in the absence of proper anchorage can occur. This failure did not take place in this building. The nearly century old structure, without satisfying integrity requirements, resisted progressive collapse with a recorded maximum vertical displacement of only $1∕4\mathrm{in.}$ $\left(6.4\mathrm{mm}\right)$ .

In the United States, currently there are three consensus test methods for determining the wind uplift capacity of mechanically-attached single-ply roofing membrane systems. Each is based upon a specific specimen size and static loading regime. However, few studies have examined the relationship, if any, of failure loads among these methods. This study was conducted to determine the effects of varying specimen sizes on the static wind uplift performance or failure loads of mechanically-attached single-ply roofing membranes. Full-scale wind uplift pressure tests were performed in three phases, using six specimen sizes, and three membrane materials. The results were used to determine the minimum acceptable specimen sizes to be used for testing. In Phase 1, fastener failure loads were monitored, while in Phases 2 and 3, the failure experiments were repeated without measuring fastener loads. A significant difference in the apparent failure loads occurs among different specimen sizes for the same membrane materials. The results suggest that correction factors are necessary for comparing tests on different test beds and that the performance of membranes in the test chamber may not produce the same results on full scale structures.

A system safety performance metric is a tool to quantify the degree of safety of a structural system for a given performance objective. Classically, safety of skeletal structure as a complete system, designed by member-based structural codes, was evaluated by checking for system stability. Reliability oriented research has focused on ultimate strength and probability of failure as system safety performance objectives, whereas earthquake engineering evaluations have considered displacement as the performance objective. This paper explores and clarifies the connection between system safety and structural redundancy concepts, provides alternative interpretation of structural system redundancy, and proposes two nondimensional system safety performance metrics for skeletal structures with stability as the performance objective. The proposed structural system safety performance metrics conveniently range from 0 to 1, and use algebraic properties of stiffness matrix to (1) measure the minimum distance of stiffness matrix from a set of singular matrices; and (2) quantify the degree of linear dependency of column vectors of the stiffness matrix, respectively. Also, approaches for identifying critical structural member and quantifying failure path importance are addressed.

The present test summaries present the experimental research carried out at the “Politehnica” University of Timisoara, Romania, with the scope of investigating the influence of different column web stiffening solutions on the performance of beam-to-column joints of moment-resisting steel frames. The response parameters, such as resistance, rigidity, and ductility have been monitored. Five different types of panel web stiffening are compared in regard to a reference test. A quasilinear relationship between the moment capacity and the total shear area of the web panel resulted from the experimental tests. The initial rigidity has increased nonproportionally with the same parameter. The investigation of the failure modes proved that fragile failures have been obtained for the specimens with web reinforcement.

Cracking, yielding, and softening of reinforced concrete cross sections influence the response of reinforced concrete structures to strong ground shaking. The accuracy of peak roof displacement estimates made using relatively simple “equivalent” single-degree-of-freedom (SDOF) models is investigated. Peak roof drifts of four multistory frames were determined by nonlinear dynamic analysis using high-fidelity models, in which cracking, yielding, and softening of components are explicitly represented in the multidegree-of-freedom model. Estimates of peak roof drift are made using low fidelity “equivalent” single-degree-of-freedom models, in which nonlinearity is represented using simple stiffness-degrading models that capture yielding and the initial stiffness of the model is set equal to the cracked stiffness. Roof drifts are examined for the four frames, each subjected to a suite of ten ground motion records scaled to five intensity levels, representing ordinary “far-field” motions. As might be expected, the influence of the uncracked stiffness on the accuracy of peak roof drift estimates was found to diminish with increasing roof drift. Of greater significance is that the uncracked stiffness had a negligible effect for roof drifts greater than approximately twice the yield drift. The simple estimates were reasonably accurate at these drift levels.