Journal of Structural Engineering

Nonlinear finite element procedures are presented for the analysis of reinforced‐concrete shell structures. Cracked concrete is treated as an orthotropic material using a smeared rotating crack approach. The constitutive model adopted for concrete compression response accounts for reductions in strength and stiffness due to the presence of transverse cracks. The model used for concrete in tension represents the tension stiffening effects that significantly influence postcracking response. A heterosis‐type degenerate isoparametric quadrilateral element is developed using a layered‐element formulation, which rigorously considers out‐of‐plane shear response. Selective integration is used to avoid shear‐locking and zero‐energy problems. Good stability and convergence characteristics are provided by the iterative, full‐load secant stiffness solution procedure employed. Simple test elements are used to confirm the analytical procedure's ability to accurately model behavior under conditions of membrane load, flexure, and out‐of‐plane shear. Plate specimens and column‐slab strip specimens are used to investigate the ability to model complex structural behavior influenced by geometric and material nonlinearities.

Connecting a W‐shape beam to a hollow steel section (HSS) column using conventional bolts is difficult due to a lack of access inside the hollow section column to tighten the nut. Field welding the connection remains the common practice. The objective of this work is to propose a bolted moment connection for rectangular hollow steel columns using high‐strength blind bolts, and to evaluate such a connection in terms of its performance and its failure modes. An experimental program was conducted involving beam‐to‐column specimens subjected to beam tip monotonic loading. Moment‐rotation relationships of the tested connections were obtained while the response of the connection and its elements was investigated. Results show promising performance of such a connection type in terms of its stiffness, moment capacity, and ductility. Comparison is made with a similar connection using ordinary high‐strength A325 bolts. For the blind bolted connection, it was found that column flange thickness is a critical element that may govern the failure mode.

The multiple tuned liquid dampers (MTLDs), which consist of a number of TLDs whose first natural frequencies of sloshing are distributed over a certain range around the natural frequency of a structure, are studied. The simulations on the liquid motion in the MTLDs as well as the MTLDs‐structure interaction are carried out by using a shallow water‐wave theory. Then, two types of experiments, a forced‐excitation experiment and an MTLDs‐structure interaction experiment are conducted. The experiments and the simulation studies show that the MTLDs are efficient in the small amplitude range than the conventional TLDs, which have a single natural sloshing frequency, while the MTLDs efficiency is more or less the same level to that of the conventional TLDs in large amplitude range because of the damping nonlinearity of liquid motion. It is also shown that the control efficiency is not degraded, even though there is some offset in the tuning. This is the most significant point in actual engineering application. Finally, the application of the MTLDs to a high‐rise building is presented as an example.

Strength‐reduction factors that are used to reduce linear elastic design spectra to account for the hysteretic energy dissipation of the structure are evaluated. The paper presents a summary of results of a statistical analysis of strength‐reduction factors computed for single‐degree‐of‐freedom systems undergoing different levels of inelastic deformation when subjected to a relatively large number of recorded earthquake ground motions. Special emphasis is given to the influence of soil conditions. Results indicate that for a given displacement ductility demand, the use of period‐independent reduction factors is inadequate. Soil conditions can have an important effect on strength‐reduction factors, particularly in the case of soft‐soil sites. It is recommended that strength‐reduction factors to be used in design be specified as a function of the period and inelastic capacity of the structure, and of at least two types of soil conditions—one for rock and relatively firm sites and another for soft‐soil sites. Following these recommendations, simplified expressions to compute strength‐reduction factors are proposed.

Current inspection requirements for several countries are reviewed. Observations and modeling of general corrosion of steel‐girder bridges are described. A highway steel‐girder bridge is assumed to be subjected to dead load and heavy‐truck traffic load. Three failure modes of the steel girders are considered, i.e., bending, shear, and failure of the stiffened web at the supports. The safety margins for each failure mode and an event margin for repair are described, and the reliability index is defined. The three failure modes are modeled as a series system, and expressions for the failure probability after inspections have taken place are shown. The optimization problem is formulated, with an objective function and constraints, to select an optimal inspection strategy. For example, a typical highway steel‐girder bridge is investigated. The reliability indices are calculated for each girder as a function of time. Based on this an inspection strategy is proposed.

Cyclic‐loading tests were conducted on eight large‐scale welded flange‐bolted web steel moment connections. The objective was to investigate the need for supplemental welds on the beam web connection, for beam sections where the web accounts for a substantial portion of the beam's fluxural strength. Such supplemental web welds are currently required by model seismic codes in the United States. Results of the testing program showed highly variable performance among the eight specimens. Plastic rotations developed by the beams prior to connection failure were judged to be poor to marginal for severe seismic applications. All connections failed by fracture at or near the beam‐flange groove welds. Variability in the performance of the beam flange groove welds appears to have dominated the response of the specimens. This paper summarizes the test program and compares results to those of previous U.S. test programs. Concerns are expressed about the welded flange‐bolted web moment connection detail for severe seismic applications.

Earlier studies on the design of reinforced concrete structures by equilibrium‐serviceability methods (that simultaneously satisfy collapse and service criteria) are extended to continuous prestressed and partially prestressed concrete structures. The objectives of the paper are to present a practical design approach to nonlinear design for prestressed concrete structures and to identify its potential benefits. The paper also demonstrates the conflict between desirable plastic redistribution (at ultimate limit state) and zero or limited cracking (at serviceability limit state) for fully prestressed concrete structures. Optimization results suggest that partially prestressed concrete structures represent the most economical compromise between these conflicting criteria, and the optimal prestressing degree strikes a good balance between adequate service conditions (stresses, cracking, and deflection) and economy. Optimization of prestressed concrete beams is cast as a nonlinear programming problem and is solved by the projected Lagrangian algorithm. Examples of (three‐span and two‐span) continuous‐beam optimizations illustrate the method and its features, as well as resulting differences between full and partial prestressing design solutions.

The analysis to compute prestress loss and the stress redistribution in concrete and nonprestressed reinforcement due to the time‐dependent effects of creep, shrinkage, and relaxation of prestressed steel, in partially prestressed concrete members cracked under the influence of dead load and initial prestress is presented using the method of creep‐transformed sections. The method involves an easy‐to‐use procedure repeated a number of times depending on the desired accuracy of the results. No cubic equation need be solved to obtain the time‐dependent neutral axis. The method is convenient to use for members with multiple layers of prestressed and nonprestressed reinforcement and can be programmed on any desktop computer. In a cracked partially prestressed section, the neutral axes of stress and strain change with time and generally there is an increase in the neutral axis depth. In certain cases, there may be an increase in tension in the prestressed tendons due to creep and shrinkage, and the actual relaxation loss will be greater than the intrinsic relaxation in such cases. In the proposed method, the relaxation loss need not be assumed a priori, but can be accurately calculated based on the diagram provided in the paper. Two numerical examples are presented to illustrate the proposed method.

Cracked reinforced concrete in compression has been observed to exhibit lower strength and stiffness than uniaxially compressed concrete. The so‐called compression softening effect responsible is thought to be related to the degree of transverse cracking and straining present. It significantly influences the strength, ductility and load‐deformation response of a concrete element. A number of experimental investigations have been undertaken to determine the degree of softening that occurs, and the factors that influence it. At the same time, a number of diverse analytical models have been proposed by various researchers aimed at modeling this behavior. In this paper, a review is made of the experimental data available, of the various models proposed, and of the accuracy of the models in correlating to the test data. Based on new data, previously derived analytical models are updated. Parametric studies are made to investigate factors thought to influence the softening effect. As well, nonlinear finite element analyses of test panels are conducted to determine the relative significance of compression softening in accurately predicting behavior of reinforced‐concrete elements.

Ductile coupled flexural walls are the primary seismic load resisting systems of many structures. The coupling beams of these structures must exhibit excellent ductility and energy‐absorption ability. To achieve better ductility and energy absorption than previously possible, the use of steel link beams with their ends embedded in the reinforced concrete walls is proposed. Preliminary experimental results are reported for two full‐scale reversed cyclic‐loading tests of portions of ductile flexural walls coupled with steel link beams. The excellent performance, together with the ease of construction, demonstrate the feasibility of this alternative form of construction. To ensure ductile response, design and detailing guidelines for both the clear span and embedded portions of the link beams and the reinforced concrete embedment region are presented. An assessment, based on comparisons with other structural systems, of this new type of construction is presented.

Existing methods for calculating the LRFD design nomograph for an effective length $K$ factor utilize iterative algorithms such as the method of bisection. This paper presents a novel algorithm that computes the $K$ factor with no iterations. This algorithm computes an approximate $K$ factor, which is often within 2% of the true nomograph value of $K$. The initial section selection method offered in the LRFD Manual is primarily a hand‐calculation technique relying on the engineer's intuition for selection trial sections. A computer‐based algorithm is developed herein for the initial beam‐column section selection using the LRFD strength criteria (the beam‐column interaction equation). An example problem presents typical preliminary member sizes for girders and beam‐columns using these techniques. The computer program DFRAME, which uses these methods, is briefly described and is implemented in C++, an object‐oriented language, using Digital Equipment and Sun workstations.

The phenomenon of creep causes the deflection of a wood beam under sustained loading to increase throughout time. Current design codes include provisions to account for the time‐dependent deflections of wood members in bending, but these guidelines have been based, to a large extent, on past performance and engineering judgment only. Previous reliability studies for wood have not explicitly considered creep effects, and consequently, questions as to the true limit‐state exceedence probabilities associated with serviceability design procedures remain unanswered. In this paper, the effect of creep deformations on the reliability of single dimension‐lumber wood beams is examined. A stochastic viscoelastic stress‐strain relationship is used to model the time‐dependent behavior of wood, and stochastic pulse process models are used to account for the temporal variability of the loads. Reliability levels associated with current serviceability design procedures are then determined, and resistance factors that include creep effects are suggested for use in a checking equation for load and resistance factor design.