Journal of Bridge Engineering

This paper reviews eight previous studies on the variable-amplitude (VA) fatigue strength of structural steel details: (1) four studies in the finite-life regime in which the number of cycles to failure of the specimens are equal to or shorter than the number of cycles at the intersection between the sloped S-N line and the VA fatigue limit, hereafter called the transition life; and (2) four studies in the infinite-life regime that is, at numbers of cycles greater than the transition life. The VA data correlate well with the constant-amplitude data when the former are plotted in terms of an equivalent root-mean-cube stress range. The effects of the following variables on the fatigue strength of structural details are discussed: block sequence in a stress range spectrum, spectrum size, type of spectrum, minimum stress, and type of steel. A so-called long-life factor quantifies how far a type of detail was cycled into the finite-life regime. Based on the results of the literature review, the writers recommend that the current AASHTO log-log bilinear equations for calculating the fatigue life be replaced with a single equation similar to the equation for predicting the fatigue crack growth rate in metals. This simplified model more accurately predicts the fatigue life near the VA fatigue limit.

Current American Association of State Highway and Transportation Officials (AASHTO) bridge specifications for compact composite steel girders in positive bending with adjacent compact pier sections limit the allowable maximum strength to a value between the full plastic moment and the hypothetical yield moment of the cross section as a function of the depth of web in compression. The strength prediction equations derived using these methods provide conservative values when compared to the results of the parametric studies used to develop the equations. Recent experimental tests coupled with finite-element analysis and mechanistic evaluations of the cross-section flexural capacity suggest that larger capacities may be achieved than those determined from AASHTO’s prediction equations. This paper presents an assessment of the behavior of composite positive bending specimens. A summary of a comprehensive literature review is provided coupled with results of the analytical and experimental evaluation of the nominal moment capacity of composite girders. Lastly, a less conservative design moment capacity expression developed from this assessment is provided.

Aerial guideways are elegant transportation structures that are seen at airports, theme parks, and crowded urban areas. The guideways generally consist of continuous, prestressed concrete beam spans, precast concrete columns, and steel beam-column connections. Although there are guidelines prepared as a supplement to conventional highway and railway bridge design codes, aerial guideways form a different class, relatively less studied compared to common highway bridges. The primary objective of this paper is to present a study to better understand the structural behavior and capacity used in an existing guideway structural system which has been in service for about $35\text{years}$ . The load demand on the guideway system has increased by about 50% over the years. The structural system is composed of six-span continuous prestressed concrete bridge segments. In order to develop models that bound the possible existing condition of the structure, several models are developed by changing the most critical parameters. The critical parameters are categorized as material properties, prestress losses, boundary conditions, and continuity conditions. Sensitivity studies are conducted using eight parametric models for simulations with moving loads for the two different train types. The load rating and reliability indexes are computed for all the cases under different loading conditions. The parameters that have the most influence on the load rating and reliability are also presented. The information generated from these analyses can be utilized for better-focused visual inspection and can also be used for developing a long-term structural monitoring plan.

A novel approach to evaluating safety of existing bridges based on monitored structural responses and component conditions is presented in this paper. A limit state equation is developed for the measured strain data from structural health monitoring (SHM). The new concepts of the condition function, $\alpha (s,t)$ , and prediction function, $\zeta (s,t)$ , are introduced. The condition function is utilized to estimate the strains at locations other than the strain gauge locations. This function is related to the structural condition assessment results, strain gauge locations, and failure modes under consideration. The prediction function is used to predict the extreme values of the SHM data in the future. An illustration of the proposed approach is provided on an existing highway bridge in Pennsylvania, which had been monitored from 2001 to 2005 by the Advanced Technology for Large Structural Systems Center, a National Engineering Research Center at Lehigh University, Bethlehem, Pa. This study provides the basis for integrating achievable SHM data into structural safety evaluation, and establishes a valid platform for life-cycle, cost-oriented, and reliability-based infrastructure management systems using structural health monitoring.

Vulnerability of a structure under terrorist attack can be regarded as the study of its behavior against blast-induced loads. A structure is vulnerable if a small damage can trigger a disproportionately large consequence and lead to a cascade of failure events or even collapse. The performance of structural vulnerability depends upon factors such as external loading condition and structural properties. As many of these factors are random in nature, it is necessary to develop a vulnerability assessment technique in the probabilistic domain. In this study, one such assessment framework is proposed for cable-stayed bridges. The framework consists of two stages of analysis: determining the probability of direct damage due to blast loads and assessing the subsequent probability of collapse due to component damage. In the first stage assessment, damage of the bridge component is defined as the exceedance of a predefined limit state such as displacement or yielding. The damage probability is obtained through a stochastic finite-element analysis and the first-order second-moment reliability method. The second stage assessment further calculates the probability of collapse due to direct damage of some component via an event tree approach. The proposed assessment methods are illustrated on a hypothetical single-tower cable-stayed bridge. It is seen that the proposed methods provide a quantitative tool for analyzing the vulnerability performance of cable-stayed bridges under terrorist attack.

Interaction between steel cables and concrete is complicated in prestressed concrete bridges, especially in curved prestressed concrete bridges. The most significant behavior of curved beam bridges under the loads is that, at the same time of vertical flexure, torsion occurs on the cross section, which complicates the mechanical analysis to curved beam bridges. Based on coordinating relations of steel cables and concrete (CRSC), the grillage structure finite-element method was adopted to analyze the spatial effect of curved beam bridges. This way, the effect of all prestressing procedures can be simulated properly, including the prestressing loss due to concrete shrinkage and creep, batch prestressing of the cables, etc. Furthermore, it is effective to analyze the integrated behavior of the combined steel cables space out and concrete. The efficiency and reliability of the CRSC method is demonstrated by our analysis system WXQ2.0 developed for curved-skew bridges.

Clarke was one of the leading engineers in Canada and the United States in 1848 to 1901, working on railroads, waterways, buildings, and primarily bridges. He was a prolific writer with articles not only in ASCE publications but in British technical journals. He also published many articles in Scribners’ and other popular magazines. He was a leader in the formation and running of several major bridge design and construction companies and worked with many leading bridge engineers of the period. He served ASCE for many years starting as a director in 1870 and was elected President of the Society for 1896–1897. Despite his noteworthy career, he is one of the unknown giants of 19th century civil engineering.