Journal of Structural Engineering

Low‐volume road bridges are currently designed according to the same specifications as urban highway bridges. Thus, many of the low‐volume bridge designs are overly conservative and uneconomical. This paper addresses this issue and proposes modifications of the existing specifications in the area of fatigue, deflection, allowable stress, composite action of timber decks, bridge width, lane loading, and the use of guardrails. All of the systems selected were combinations of prefabricated components. Jointless bridges received very high rankings and are strongly recommended for the 60‐ft and 100‐ft span ranges. A precast voided slab system and a timber deck and steel stringer system received the highest ranking on the 30‐ft span range. This study proposed a method of selecting the type of bridge system to be built in a particular area and a priority scheme to select which bridges must be replaced first. The scheme models the Federal Highway Administration (FHWA) sufficiency ranking with some of the ranking criteria being changed to better meet the needs of low‐volume road bridges.

Most of the badly deteriorated bridges in the United States are those built prior to the 1950s, and many of these are on low‐volume roads where they receive little attention. This paper deals with the use of value engineering principles to study the economics of various low‐volume bridge systems along with miscellaneous bridge components so that potential savings through proper choices of innovative bridge systems can lead to better utilization of the funds available. Value engineering principles such as functional analysis and fast diagramming, value analysis and innovation/evaluation techniques have been used to develop and evaluate different design scenarios. The optimal designs derived through this study are of generic nature. Certain geographical factors or other concerns depending on site locations have to be incorporated in the value analysis before the final selection of a bridge system. Specifically, the value engineering analysis revealed that initial material cost, maintenance aspects, durability, service life, availability of components, and ease of erection have turned out to be the most important items in the selection of a low‐volume road bridge.

Space trusses of the double‐layer grid type, because of their large degree of static indeterminacy, are often assumed to have sufficient redundancy such that the loss of one member would cause force redistributions that can be accommodated by the remaining structure. However, the results presented in this paper of the analyses performed on a hypothetical space truss and on a constructed space truss show that progressive collapse could occur following the loss of one of several potentially critical members when the structures are subject to full service loading. However, when the structures were evaluated using the American National Standard ANSI A58.1‐1982, the structures were found to survive with a small margin of safety. It is suggested that to improve resistance to progressive collapse the compression members and diagonal members along and adjacent to the column line should be designed with higher factors of safety than those currently used, particularly in the middle half of the span. Further research directions are suggested.

A U.S.‐Japan cooperative project to improve the safety of buildings included static and dynamic tests of reinforced concrete structures of various sizes. The results from a large‐scale, seven‐story structure built and tested in Tsukuba, Japan, were complemented by results from static and dynamic tests of models and from experimental investigations of individual members and member assemblies. The large‐scale test structure was loaded laterally by forces at each story, simulating the force distribution for the lowest translational mode. Load history was determined by calculating how the planar wall‐frame combination with a fixed base would respond to a strong ground motion, using measured incremental stiffness. The strong influence of floor slabs and of strain hardening in the reinforcement on base shear observed in the test of the large‐scale structure was confirmed by results of the complementary investigations. This report contains a brief description of the conclusions of practical importance derived from the tests and their analyses.

A closed form solution for predicting the generalized slip response of reinforcing steel bars anchored inside beam‐column joints is presented. It allows computation of bond stresses, steel stresses, and slip distribution along the bar anchorage length under given generalized steel stresses at the boundaries. The solution takes advantage of some theoretical and experimental observations regarding the bond and steel stress characteristics inside a beam‐column joint. The main features of the proposed model is that it depends only on the monotonic ascending portion of the local bond stress‐slip relationship of the reinforcing bar, and it bypasses the definition of its local bond stress‐slip relationship under severe slip reversals. Results predicted by the model are found to be in good agreement with experimental results and finite element predictions.

A methodology to apply linear and nonlinear analysis rationally in the seismic design, vulnerability evaluation or upgrade design of RC buildings is presented. Some of the initial steps in this methodology are discussed and exemplified, while the remaining steps will be discussed in a separate paper. It is recommended to apply analysis to study in a step‐by‐step interactive manner the bounds of critical section, the critical element, and the complete structural response as a structure is loaded to failure under static load increments which are monotically and simultaneously applied in both lateral directions. This analysis procedure is assessed to be more rational than conducting time‐history analyses of detailed models. The reliability in the bounds of generated static response would naturally depend on perceiving and accurately modeling all the critical local and global mechanisms which influence response. Some of the parameters and mechanisms which significantly influenced the test response of idealized assemblies and building specimens are described. The influence of these parameters and mechanisms on element response bounds is illustrated.

Ten one‐way reinforced concrete slabs were tested to investigate the effects of shear stirrups and stirrup details on ultimate capacity and tensile membrane behavior. The slabs were rigidly restrained at the supports and were loaded with a uniformly distributed pressure. Support rotations between 13°–21° (0.23–0.37 rad) were observed. The test series was unique due to the uniform loading and the large support rotations experienced for the conventionally reinforced concrete one‐way slabs. The results of these tests indicate that requirements for shear reinforcement found in current blast‐resistant design manuals are overly conservative.

Seismic design parameters are inherently imprecise and fuzzy. Formal models of inexact inferences are therefore highly relevant to the interpretation of such inexactly described seismic parameters. Application of such techniques becomes even more relevant if it is envisaged that, in the future, provisions for seismic design may be more effectively represented by encoding them as fuzzy expert systems. The linguistic representation of imprecise variables is presented. More importantly, how an evidence‐based scheme, the Dempster‐Shafer theory of evidence, can be used to infer conclusions about imprecisely stated problems is demonstrated. A set of seismic parameters, namely the seismic performance category (SPC), the seismic hazard exposure (SHE), and the seismic intensity (SI), are selected from a seismic design code. How the relationship between the three parameters can be “softened” is demonstrated using a linguistic representation; such a representation involves setting up conditional IF … THEN types of rules describing how different states of rule‐antecedents, SI and SHE, will lead to different states of a rule‐consequent, SPC. A frame of discernment (θ) is then defined which comprises several hypotheses about SPC. Thereafter evidence about SI and SHE is used to infer conclusions about SPC. The conclusions are represented by a combined degree of belief and plausibility in the hypotheses in θ.

In 1984 the ASCE Committee on Design of Steel Building Structures created a task committee to investigate the state of the art of designing for drift of steel‐framed buildings. To accomplish this task, a poll of structural engineers was taken to determine the drift control and philosophies that are in use today. The intent of the questionnaire used in this survey was to summarize design practice regarding the need to control steel‐building drift and considerations used for this task. This paper summarizes the results of that poll. It is evident that structural engineers vary considerably in their practice in this aspect of their field.

A method of analysis is presented that concerns the inelastic stability of beam columns subjected to transverse loads. A computer program based on the ALGOL‐60 language is developed to analyze three different loading cases. The computed results are also compared with those for eccentrically loaded columns. These results show that the lateral stability of a beam column is dependent not only on the position of the loads within the span but also on the point of the application of such loading relative to the shear center of the cross section. The latter affects the strength by as much as 26 percent. The influence of the beam column slenderness ratios and the distribution of the residual stress affects the lateral‐torsional buckling strength. Some discussion and suggestions for design formulas of beam columns are also presented. The design formula for lateral‐torsional buckling strength suggested in this paper is simple and convenient to use in practice.

In this paper particular investigation is directed towards the combined effects of horizontal and vertical motions of real earthquakes to structures resting on sliding base. A simplified method is presented to treat the nonlinear effects of time dependent frictional force of the sliding base as a function of the vertical reaction produced by the foundation. As an example, the El Centro 1940 earthquake record is used on a structural model to show the structural responses due to a sliding base with different frictional and stiffness characteristics. The study shows that vertical ground motion does affect both the superstructure response and the base sliding displacement. Nevertheless, the sliding base isolator is shown to be effective for the reduction of seismic response of a superstructure.

A new formula that represents both ascending and descending portions of uniaxial compressional stress-strain relation is suggested. This formula consists of two parameters, one governing the steepness of ascending portion and the other controlling the steepness of descending portion. For all possible variations of the parameters, the suggested formula implicitly satisfies the basic properties of a complete stress-strain relation that the stress ascends, reaches its peak value, and then descends, as the strain increases. Expressing the parameters in term of concrete strength, the suggested formula automatically satisfies the behavior of concrete under uniaxial compression that the descending portion becomes steeper as concrete strength is higher. Using the suggested formula, the entire range of strength-stress relation can be favorably determined upon comparing to available test data.