Journal of Structural Engineering

Nominations are being sought for the 2003 ASCE and SEI Awards.

The objective of the ASCE and SEI Honors and Awards Programs is to advance the engineering profession by emphasizing exceptionally meritorious achievement. Traditionally, such accomplishments have been in the form of technical papers, although many awards are based on other considerations.

Several of the ASCE and SEI awards are listed below. Complete descriptions of the respective awards and criteria that apply are found in the ASCE 2002 Official Register (available on request from the Society).

This report presents an overview of construction methods for the most commonly used composite steel-and-concrete floor system in U.S. buildings. The report was prepared by a subcommittee of the ASCE Committee on Composite Construction and is intended to assist practitioners by summarizing practical and effective means to avoid common construction problems. Four principal components of the floor system are considered: (1) steel section, (2) steel deck, (3) headed shear stud, and (4) concrete slab. Proper construction procedures for each component are discussed and summarized. Reasonable adherence to specifications and communication between designers and builders will minimize difficulties in the construction of composite steel-and-concrete floor systems.

The seismic performance of a posttensioned energy dissipating (PTED) connection for steel frames is investigated analytically and experimentally. The PTED connection incorporates posttensioned high-strength bars to provide a self-centering response along with energy dissipating bars that are able to yield in axial tension and compression. The analytical study involves the development of an equivalent iterative sectional analysis procedure to predict the moment-rotation relationship of the PTED connection. Based on this analytical model, a simple design procedure for PTED connections is described. In the experimental study, a cyclic component test was performed on two energy dissipating bars and a cyclic test was conducted on a large-scale exterior beam-to-column PTED connection. The results of the tests show that the PTED test specimen was able to undergo large inelastic deformations without any damage in the beam or column and without residual drift. The proposed analytical model and design procedure were also validated against the experimental results.

This paper describes a seismic design procedure for rib-reinforced steel moment connections based on an equivalent strut model. It is shown from the results of finite-element analysis that the force transfer mechanism in the rib connections is completely different from that predicted by the classical beam theory and that a diagonal strip in the rib acts as a strut. By treating the rib as a strut, an equivalent strut model that could be used as the basis of a practical design procedure is proposed first. A step-by-step design procedure is then recommended based on the proposed model.

This paper presents practical methods for predictions of strength and ductility capacity of thin-walled steel box girders with longitudinally stiffened webs predominantly loaded in shear. The shear behaviors of the girders under monotonic and cyclic loadings are simulated through inelastic large deformation analysis, in which a modified two-surface model is incorporated to trace the material nonlinearity. Geometric and material imperfections are taken into account. During the analysis, the variation of stresses in the webs and flanges is monitored, and the observed shear-resisting mechanisms of the girders are discussed. An extensive parametric study is carried out to investigate the effects of structural parameters on the shear strength and ductility capacity. From these investigations, the application of available shear strength prediction methods, originally developed for plate girders, to box girders is verified. Some method is found to be appropriate for practical design, since it gives satisfactory predictions and relies on rational assumptions regarding the shear-resisting mechanism. Considering key structural parameters, a simple formula is proposed for the assessment of the ductility capacity.

Finite element microanalysis using fiber technique was carried out to study the buckling mechanism of reinforcing bars. It was found that reinforcing bars under inelastic axial compression exhibit lateral deformation defined as buckling due to the geometrical nonlinearity. Further investigation revealed that the postbuckling average compressive stress is less than the local stress corresponding to the same strain due primarily to the different stiffness for loading and unloading fibers in the laterally deformed section. It was clarified that the average compressive stress-strain relationship including the softening in the postbuckling range can be completely described in terms of the product of square root of yield strength and the slenderness ratio of the reinforcing bar. Moreover, a unique relationship between the average stress and average strain of reinforcing bars including the effect of buckling is established through various parametric analyses. The comparison of the analytical results and proposed model with some experimental results showed good agreement, thus verifying the reliability of the microanalysis and proposed computational model.

This paper presents a method of analysis for evaluating the softening behavior of reinforced concrete (RC) members. To obtain mesh objective results, a nonlocal fiber element model is introduced. The resisting force of each section, in the nonlocal fiber element model, is calculated using a proposed differential hysteretic model, which is especially developed for modeling softening behavior under cyclic loading. The section hysteretic response is determined using microplane constitutive law for concrete and bilinear elastoplastic law for reinforcements. The calculated hysteretic behavior of sections is employed to scale the parameters of the differential hysteretic model. The proposed method is verified by the available experimental results. Close agreements between the numerical and experimental results are obtained. The method provides insight to the procedure of flexural localization. Also, due to computational efficiency of the method, it is possible to extend its use for analyzing RC frames with softening members.

This paper deals with finite-element (FE) modeling and nonlinear analysis of steel–concrete composite plate girders under negative bending and shear loading. A three-dimensional FE model, using a general purpose finite-element software, has been used to carry out the nonlinear analysis. One steel plate girder and four composite plate girders tested to failure by other researchers have been analyzed by the FE model proposed in the study. Various models, which attempted to overcome the difficulties in modeling of steel–concrete composite plate girders, are presented and discussed in this paper. Results obtained from the FE analysis are compared with the corresponding experimental results. It is observed from the comparison that the proposed nonlinear FE model is capable of predicting the ultimate load behavior of steel–concrete composite plate girders to an acceptable accuracy.

A new type of steel and concrete composite bridge with steel U-shape girders has been proposed. The U girder can be cold formed from one steel sheet, and the amount of welding required is substantially small and mass production could be possible. This new bridge would be therefore very economical. The steel U girder is composite with the reinforced concrete slab at the span center, whereas concrete is poured into the steel U section and prestressed at the intermediate supports of a continuous bridge. Bending tests were carried out to investigate the static bending behavior of the girder models. The girder model at the span center behaved as a composite beam. The girder model at the intermediate supports behaved as a prestressed beam and the filled concrete restricted the local buckling of steel plates in compression. A design calculation method for the girder section has been proposed assuming the Bernoulli-Euler principle, and was verified by the test results. This study shows that the new composite girder has sufficient bending strength and deformation capacity, and this bridge system is practical and feasible.

This paper presents the results of a pilot study of the web crippling performance of two common exterior load-bearing wall conditions (rim joist and rim track with a framing joist) in light framed cold-formed (light-gauge) steel construction. The intent of the study was to develop some preliminary data on the web crippling performance of built assemblies. The test results show that the ultimate strength for the two web crippling conditions considered may be greater than the sum of the individual strengths of the components (based on current American Iron and Steel Institute Specification equations). Further, on the basis of the configurations tested, it appears that the measured higher strengths may be due to a beneficial distribution of load at the corners of a track section. The tests also showed that although the measured strengths may be high, the associated cross-sectional deformations tend to be relatively large. For gravity load design, this deformation may be treated as a serviceability limit state, however, where lateral load design is a concern, this deformation may impact the performance of a braced wall. Thus, it may be prudent to impose a deformation limit on web crippling design equations.

Presented herein is an experimental study that focuses on the shear splitting failure of composite concrete encased steel beams. Nine full-scale specimens were constructed and tested in this study. Significant horizontal cracks along the interface of steel flange and concrete, referred to as the shear splitting failure, appeared in five tested specimens. Observations from the experiments indicate that the steel flange width ratio, defined as the ratio of steel flange width to gross section width, has a dominant effect on the shear splitting failure of composite beams. The test results reveal that the shear splitting failure occurs when the steel flange width ratio of a composite beam reaches 0.67. The test results also show that the application of shear studs has a positive effect on preventing this type of failure for beams with large steel flange ratio. In addition to the experimental study, a new method for predicting the failure mode of composite beams is proposed. The proposed method gives satisfactory predictions as compared to the test results. Finally, a new equation is derived for the design of the stirrups to prevent shear splitting failure of naturally bonded composite beams.

When fiber reinforced polymer (FRP) bars are used as reinforcement in concrete sections in flexure, it is necessary to control the width of cracks by limiting the tensile stress in the FRP in service to a small fraction of its tensile strength. Parametric studies show that when the cross-sectional area of the FRP reinforcement is based on a permissible strain at service, rectangular and T-sections exhibit large deformation before failure; thus, there is no need to check the deformability.

Closed form solutions are derived for the buckling loads of unidirectionally loaded rectangular orthotropic plates with (1) free and built-in unloaded edges and (2) free and rotationally restrained unloaded edges. These expressions can be used in the design of local buckling of the flanges of fiber-reinforced plastic beams. The accuracies of the formulas were determined and the usefulness of the formulas was demonstrated by numerical examples.

Adhesive bonding of plates of advanced composite materials (ACMs) to reinforced concrete structural members is increasingly used to strengthen such members in flexure. The integrity of the strengthened member under load depends on the level of hybrid structural action developed between the concrete member and the plate through the adhesive. High shear stresses at the adhesive-to-concrete interface trigger fracture of the concrete, and so induce failure by loss of this hybrid action. In zones of varying moment along the member, these high interface shear stresses can arise from the requirement, after the steel yields, for high axial stress gradients to develop in the ACM plate. In these moment-varying zones of elastoplastic activity, the steel and concrete are into their nonlinear regimes of material behavior, and the height of the neutral axis changes nonlinearly along the member. These nonlinear effects, which generate complex behavior in elastoplastic zones, are not represented in existing approaches for predicting interface shear stresses. This paper fills that gap by presenting analytically exact expressions for interface shear stress which allow for vertical shift of the neutral axis and for material nonlinearities. The expressions reveal that distinct nonlinear disparities exist between the interface shear stress variations and the shear force variations in moment-varying elastoplastic zones. The model is verified against test data, and is then used to establish magnitudes of elastoplastic interface shear stress in a plated member under different types of load. The stresses are shown to reach critical values, and their variations along the plated member are seen to be load sensitive. It is concluded that this model for elastoplastic interface shear stresses is suitable for incorporation into procedures for design of ACM-strengthening schemes.

This study investigates the axial load behavior of concrete-filled steel tubular (CFT) columns with the width-to-thickness ratios between 40 and 150, and proposes an effective stiffening scheme to improve the mechanical properties of square cross-sectional CFT columns. Seventeen specimens were tested to examine the effects of cross-sectional shapes, width-to-thickness ratios, and stiffening arrangements on the ultimate strength, stiffness, and ductility of CFT columns. Moreover, nonlinear finite element analysis was also conducted to investigate cross-sectional axial stress distribution at the ultimate strength. Comparing the measured ultimate strength with estimates by using some current specifications suggested that current specifications may considerably underestimate the ultimate strength of circular CFT columns, particularly for columns with a small width-to-thickness ratio. Results in this study demonstrate that the proposed stiffening scheme can significantly enhance the ultimate strength and ductility of square CFT columns.

It has been illustrated in the past that a modal synthesis gives incorrect modal properties and seismic response of nonclassically damped coupled systems when all the modes of uncoupled primary and secondary systems are not included. The effect of missing mass contained in the truncated high frequency modes can be represented using residual modal vectors. This paper illustrates two possibilities in which the residual modal matrix may contain redundant vectors leading to a breakdown of the originally proposed method. First, secondary systems with a support inclined to the primary system orthogonal connecting degrees of freedom can have residual vectors that are scalar multiple of each other (parallel). Second, the number of residual and nonrigid modal vectors can be more than the total number of secondary system modes (equal to the number of secondary system degrees of freedom) in multiply connected simple secondary systems. A solution is presented to identify and eliminate both these types of redundant vectors using an alternative form of Gram-Schmidt’s orthogonalization.