Journal of Structural Engineering

A quasi‐static loading procedure is utilized in the pseudodynamic test method to simulate the seismic response of a structure. Hence, a major concern with the results of such tests is the rate‐of‐loading effects. This problem is addressed in the paper by studying the response of an elastic/viscoplastic system that has the rate‐dependent characteristics of a steel structure and is calibrated with the dynamic yield strength of mild steel obtained from prior experimental studies. While a wide scatter of experimental data can be observed, results of this study indicate that the dynamic yield strength of mild steel attained in the seismic response of a structure can be 30% higher than that developed in a pseudodynamic test, depending on the plastic strain rate induced. As a result, the inelastic response developed in a pseudodynamic test tends to be higher than that induced by an actual earthquake excitation. Nevertheless, the discrepancies are small for structures that have relatively low fundamental frequencies, provided the inelastic deformation is within a reasonable limit.

A new elasto‐plastic cracking constitutive model for reinforced concrete is presented. The nonlinear effects considered cover almost all the nonlinearities exhibited by reinforced concrete under short term monotonic loading. They include concrete cracking in tension, plasticity in compression, aggregate interlock, tension softening, elasto‐plastic behavior of steel, bond‐slip between concrete, and steel reinforcement and tension stiffening. A new procedure for incorporating bondslip in smeared steel elements is described. A modified Huber‐Hencky‐Mises failure criterion for plastic deformation of concrete, which fits the experimental results under biaxial stresses better, is proposed. Multiple cracking at Gauss points and their opening and closing are considered. Matrix expressions are developed and are incorporated in a nonlinear finite element program. After the objectivity of the model is demonstrated, the model is used to analyze two different types of problems: one, a set of four shear panels, and the other, a reinforced concrete beam without shear reinforcement. The results of the analysis agree favorably with the experimental results.

The present study addresses the loading or deformation rate effect on the yield loads of nailed timber joints. Four different types of joints, which differed with respect to the thickness of the members and the angle of load to grain, were tested. The bearing strength of the wood and the bending strength of the nails were also tested in order to analytically verify the dynamic ultimate capacity of the joints. All tests were run with deformation rates from static loading values up to approximately 1 m/s (40 in./s). The pilot study results show that the strength of the nailed joints can be expressed in terms of the deformation rate. A logarithmic expression for the strength of the joints was obtained from regression analysis of approximately 200 results. The values obtained analytically agreed well with the experimental ones for the various joints tested.

Concentrically braced frames dissipate severe seismic energy inputs mainly through inelastic deformations in the bracing elements. Thus, an accurate brace model is essential for improving the accuracy of the computed inelastic seismic response of braced frames. A computationally efficient formulation capable of closely predicting the hysteretic behavior of the physical theory brace models is presented. This formulation is consistent with the displacement method of analysis in the sense that it uses displacement as input. The developed brace model also involves a limited number of degrees of freedom and can be efficiently incorporated into the conventional computer programs for nonlinear dynamic analysis of structures. The developed model requires limited input data and little computer storage capacity, Comparisons are also made between the analytical predictions of the model and cyclic test results on steel struts. The results indicate a reasonable degree of accuracy in theoretical predictions. The developed brace model can be useful in nonlinear analysis and design of brace frame systems. It can also provide researchers with an efficient tool for investigating the details of nonlinear dynamic response characteristics of braced structural systems.

Use of a layering technique in general nonlinear finite element (FE) analysis of reinforced‐concrete flat shell elements is introduced. Stack of simple four‐node plane stress and Mindlin plate elements is used to simulate RC elements subjected to membrane and bending loads. Transverse shear deformations are taken into account and compatibility between layers is satisfied by means of nodal constraint equations. The method along with nonlinear constitutive models for concrete and steel are implemented in a FE program. Efficient stiffness calculation, assembly, and solution algorithms are employed to minimize the computational effort. Experimental specimens are analyzed. The results indicate the effectiveness and efficiency of the layering technique in simulating the behavior under membrane as well as flexural loading cases. The provided flexibility in the thickness direction makes it possible to model transverse shear deformations and to simulate bond degradation between concrete and steel. The importance of simulating such phenomena in predicting realistic cracking patterns is demonstrated.

The classical smeared cracking model widely used in finite‐element analysis of concrete and rock cannot describe the size effect experimentally observed in brittle failures and exhibits spurious mesh sensitivity with incorrect convergence to zero energy dissipation at failure. The crack band model circumvents these deficiencies but has limitations with respect to mesh refinement, shear locking on zig‐zag crack bands, and directional bias of the mesh. It is shown that all of these problems can be avoided by a nonlocal generalization, in which the damage that characterizes strain softening is considered to be a function of the spatial average of the positive part of the maximum principal strain. Two alternatives are presented: (1) Smeared cracking whose direction is fixed when cracks start to form; and (2) smeared cracking whose orientation rotates with the maximum principal strain. Furthermore, fracture tests on specimens of various sizes are analyzed by finite elements. It is shown that the model correctly reproduces the experimentally observed size effect and agrees with Bažant's size effect law. Orthogonal and slanted meshes are shown to yield approximately the same cracking zones and propagation directions. The model is easily programmed and computationally more efficient than the corresponding local version.

The postbuckling behavior of thin‐walled fabricated steel tubes under transverse shear and bending shows a stable carrying mechanism largely consisting of a banded tension field. This phenomenon, coupled with the possibility that the ultimate load is severely affected by residual stresses due to cold bending in the fabrication process, suggests the use of this stable postbuckling mechanism as a design basis. Hence, an equivalent truss mechanism composed of a helical tension field and inclined compression struts is proposed. The corresponding shear‐carrying capacity relations are developed. The magnitude of postbuckling shear capacity is controlled by the banding phenomenon of the tension field, the local “across‐the‐buckles” bending moments, and the inclination of the compression struts. The developed relations recognize the upper and lower bounds of these phenomena. A comparison is held to existing test and numerical data.

A model for predicting the moment‐rotation relationship of partially prestressed concrete beam‐column joints under generalized excitations is presented. The model accounts for both the inelastic rotation in the beam inelastic region and the “fixed end rotation” at the beam‐column interface crack arising from the slip of reinforcement inside the joint. In addition to its simplicity and computational efficiency, results predicted by the model are found to be in good agreement with limited experimental results and finite‐element predictions.

The AISC‐LRFD (American Institute of Steel Construction‐Load and Resistance Factor Design Specification for Structural Steel Buildings) Specification provides rules for design of built‐up members. The slenderness ratios of built‐up members that may buckle out‐of‐plane, say, about the Y‐Y axis for a two‐back‐toback‐angle member are discussed. Based on the LRFD equation (E4‐1) and the usual concept of the effective length factor, a modification of the slenderness ratios $(\mathrm{Kl}/r{)}_m$ for built‐up members as given in the present LRFD Specification is proposed. The proposed formula with local effective length factor $K_m$ is concise, simple, and physically clear. It is consistent with the effective length factor recommended by the LRFD Specification, and has only one equation considering the effects of shear and connectors on buckling of built‐up members. The calculated results of the proposed formula are found to be in good agreement with available test results.

The distortional response and slip behavior of curved composite box girders were investigated. Three curved composite box girders with only end diaphragms were tested in order to provide additional information on the distortional and slip behavior of curved composite box girders. The test specimens were fabricated to exhibit different radii, cross sections, and placements of shear connectors. The test results were compared with analytical results based on the curved beam theory and the distortional theory proposed by Dabrowksi, as well as on the finite strip method. These results are in good agreement. A parametric study was also conducted to evaluate the effects of cross‐sectional deformations on the stresses of the girder.

The majority of structural failures, whether collapse or functional, are attributable to errors in design, construction, or operation. This paper attempts to review selected literature on the subject of errors in structural engineering. Various features such as the frequency, magnitude, classification, and detection of error are considered, together with causes and environments for error propagation and the role of control strategies in error abatement. In this last respect, the viewpoint on costs largely drives the professional attitude to error. If the full costs fall on the perpetrator, then a lively interest in controls prevails. If the costs are spread among practitioners, then the interest abates and changes to the detection of socially tolerable levels of error and failure incidence. The relation between errors and aspects of professional life and education is also discovered. The significance of frequent personnel changes, compressed design‐construction time, belief in codes and complex calculations, low pay, professional inexperience, and novelty of the structure are considered.

Reports are given of: (1) A field investigation of the significant characteristics of current designs and construction methods; (2) development of “bench mark” designs for the inclusion of significant variables; (3) controlled variation of the design parameters in the bench mark designs in order to estimate the corresponding quantities of input resources; and (4) derivation of the input resource curves. The input resource curves are unique in the sense that they do not change with monetary inflation. Thus, for any given design within the range specified (up to 30 stories high) one can refer to the relevant input resource curves and obtain the quantities of the basic resources. These are then converted into their equivalent monetary sums using the respective rates. Worked examples illustrate how design concepts can be investigated, first in terms of construction feasibility considering such matters as the proposed construction method, the craneage requirements, cycle time, and cycle program evaluation; and second in terms of potential cost competitiveness and the evaluation of the overall project economics.

An analysis of elastic buckling in beam‐columns was undertaken to develop a general interaction equation for use in timber design. The derivation of a general buckling criterion and the determination of moment modification factors following the method of Southwell (1922) are presented. Biaxial bending, axial compression, and water ponding on flat roofs are all considered. Simple support is assumed, but results may be applicable to other support cases. The results are of interest to code developers and to designers of space frames, towers, and trusses, where biaxial bending and axial compression are combined, or whenever axial compression and water ponding may be combined.