Jeffrey A. Laman

Fatigue reliability of steel bridges

Abstract A fatigue reliability analysis is performed for steel girder bridges. The data base for the live load model is obtained by weigh-in-motion (WIM) measurements. Bridge structures were selected to determine the site-specific truck parameters and component-specific stress spectra. Stress cycles are presented as cumulative distribution functions. The WIM measurements confirm a significant variation in stress spectra between girders. Fatigue limit state function is developed using the number of cycles to failure as the structural resistance, and the number of applied cycles as the load. The statistical parameters of steel are based on the available test results. Reliability indices are calculated for several equivalent stress ranges.

EXAMINATION OF RESPONSE OF A SKEWED STEEL BRIDGE SUPERSTRUCTURE DURING DECK PLACEMENT

The response of a 74.45-m (244-ft 0-in.) skewed bridge to the placement of the concrete deck was monitored to compare measured and predicted behavior. This comparison was completed to (a) determine theoretical deflections and rotations with analytical models for comparison to actual deformations monitored during construction; (b) compare the results of various levels of analysis to determine the adequacy of the methods; and (c) examine variations on the concrete placement sequence to determine the most efficient deck placement methods. Two levels of analysis were used to achieve the objectives. Level 1 was a two-dimensional finite element grillage model analyzed with STAAD/Pro. Level 2 was a three-dimensional finite element model analyzed with SAP2000. These studies are discussed and findings are presented.

Comparison of Experimental and Analytical Load-Rating Methodologies for a Pony-Truss Bridge

Vehicle and environmental loading, combined with the effects of deicing salts and inadequate maintenance, have resulted in a large number of structurally deficient bridges in the United States. Because of the limited resources of county and district bridge owners, aging structures must be evaluated and rated to facilitate suitable bridge repair, replacement, and posting strategies. A 1937 riveted pony-truss bridge in Pennsylvania was studied to evaluate the effect of increasingly refining rating parameter inputs to the analysis of the bridge. The study considered results from experimental field testing of the bridge, a detailed sectionloss inspection, and a refined analytical modeling using STAAD III, a commercially available software package, to increase the accuracy of the rating analysis. The research team evaluated the relative effect of using (a) allowable stress versus load-factor design methodologies; (b) experimentally derived versus code-specified impact and distribution factors; (c) experimental stress measurements versus manual- and computer-stress calculations; and (d) member fixity and composite action for both inventory and operating rating with an AASHTO HS20-44 and ML-80 rating vehicle. Results for selected truss members, floor beams, and stringers are presented. The investigators found that the rating increased with increasingly refined parameter input, with the rating factor increasing as much as 60 percent over a standard manual rating analysis when an experimentally based rating analysis was used. The best agreement with experimental results was obtained by using reduced deck stiffness to model deck deterioration, fully composite action between stringers and the deck, pinned stringer-floor beam connections, and fixed floor beam-to-truss connections. The study procedures can be applied to other similar bridge structures.

Causes of Early Age Cracking on Concrete Bridge Deck Expansion Joint Repair Sections

Cracking of newly placed binary Portland cement-slag concrete adjacent to bridge deck expansion dam replacements has been observed on several newly rehabilitated sections of bridge decks. This paper investigates the causes of cracking by assessing the concrete mixtures specified for bridge deck rehabilitation projects, as well as reviewing the structural design of decks and the construction and curing methods implemented by the contractors. The work consists of (1) a comprehensive literature review of the causes of cracking on bridge decks, (2) a review of previous bridge deck rehabilitation projects that experienced early-age cracking along with construction observations of active deck rehabilitation projects, and (3) an experimental evaluation of the two most commonly used bridge deck concrete mixtures. Based on the literature review, the causes of concrete bridge deck cracking can be classified into three categories: concrete material properties, construction practices, and structural design factors. The most likely causes of the observed early-age cracking were found to be inadequate curing and failure to properly eliminate the risk of plastic shrinkage cracking. These results underscore the significance of proper moist curing methods for concrete bridge decks, including repair sections. This document also provides a blueprint for future researchers to investigate early-age cracking of concrete structures.

Prediction of Concrete Integral Abutment Bridge Unrecoverable Displacements

Synopsis: Integral abutment bridges (IABs) have performed successfully for decades and have demonstrated advantages over traditional, jointed bridges with respect to first cost, maintenance costs and service life. However, accurate prediction of IAB response to loading is complex and challenging; behavior is typically nonlinear due to the combined influence of thermal and long-term, time-dependent effects. Summarized herein are measured and computational results from examination of four interstate highway IABs located in central Pennsylvania. The collected data indicates that current AASHTO prediction methods are very conservative with respect to displacements. New computational models are used to perform a parametric study that considers the effects of seasonal thermal loading, thermal gradient, time-dependent material effects, abutment-backfill interaction and pilesoil interaction on deformations that occur over a 75-year bridge life. The measured and parametric study results provide a basis to establish an approximate method for predicting (1) maximum abutment displacement, (2) maximum bridge bending moments and (3) maximum pile moments over the bridge life.

Heavy axle study: impact of higher rail car weight limits on short-line railroad bridge structures

The fundamental objective of this study, sponsored by the Pennsylvania Department of Transportations Bureau of Rail Freight, Ports, and Waterways, is to establish and implement a methodology to quantify the financial impact of higher gross car weights (GCW) on the infrastructure load carrying capacity of short-line railroads (SLRRs) operating within the Commonwealth of Pennsylvania. The research team developed a stratified random sampling methodology to establish a bridge sample due to the large number of railroad bridges in Pennsylvania. A stratified random sampling plan was developed to ensure that the bridge sample contained bridges of each material type and bridge type expected to significantly influence the strengthening cost estimate. Collecting and creating a complete database of railroad bridges was a large task due to the number of SLRRs and inconsistent record keeping by many SLRRs. There are an estimated 2000 bridges serving Pennsylvania SLRRs of which the eventual study population included 1174 bridges for consideration. The 25 sample bridges, drawn from this population, were evaluated structurally based on the American Railway Engineering Association (AREA) 1996 Specification and field inspections conducted by the research team. The structural evaluations were used as a basis to establish load-carrying capacity predictions and required strengthening for under-capacity structures. Five of the 25 sample bridges will not safely support either the 1273-kN (286,000-lbf) or the 1402-kN (315,000-lbf) GCW load. Bridge strengthening schemes were developed for each of the five under-capacity bridges. Cost estimates for each strengthening scheme were obtained from contractors and based on recent similar work completed in the Commonwealth of Pennsylvania. Upgrade costs for the bridge sample were then extrapolated to the entire SLRR bridge population, resulting in an estimated state-wide bridge upgrade cost of

Short‐line railroad management system for bridge prioritization

8,500,000 with a 32% width for a 95% confidence level. The study presents a procedure adaptable to transportation agencies faced with a significant inventory of SLRR bridges that may be subjected to increased railcar loading. Email: glg@psu.edu Email: cal158@psu.edu

Discussion of “Live Load Radial Moment Distribution for Horizontally Curved Bridges” by Woo Seok Kim, Jeffrey A. Laman, and Daniel G. Linzell

Purpose – Limited funding to maintain and preserve short‐line railroad (SLRR) bridge infrastructure requires that important priority decisions be made on an annual basis. The compartmentalized, dispersed, and diverse nature of many SLRR owners and operators is such that there is a need for a coordinated and centralized effort to evaluate the state‐wide system as a whole, to ensure the most effective overall resource allocation and also identify assets that either outperform predictions or consume disproportionate levels of resources for maintenance and operation, allowing for review of design and construction practices. The purpose of this paper is to examine the state of the art for railroad bridge population management and resource allocation decisions and to develop a state‐wide SLRR bridge prioritization methodology, to be used as a tool by a state agency to assist in allocating limited public funding for bridge maintenance, rehabilitation and replacement activities.Design/methodology/approach – A lit...

Long Gage-Length Interferometric Optical Sensors for Condition Assessment in Bridge Structures

The authors state that two and three AASHTO HS25 trucks and lane loads were applied based on the bridge width and that “a trial and error protocol was established for radial truck position to establish critical wheel load paths.” Further, that “HL-93 loadings were systematically placed at 305 mm 1 ft. increments from the outside girder.” This raises several issues. HS25 trucks are associated with the AASHTO Standard Specifications while HL-93 loadings are associated with the AASTHO LRFD Code. It is not correct to mix the two in an analysis. It is not clear if the two codes have been somehow combined. Both the AASHTO Standard Specifications, 17th edition, Article 3.6.2, and LRFD Code, 4th edition, Article 3.6.1.1.1, require that truck and lane loads be positioned within 3.65-m 12-ft. wide lanes. It appears that this requirement has not been met in this study.

Fatigue Impacts on Bridge Cost Allocation

Optical sensor technology is a potentially important element in the development of a bridge monitoring system. The present research has utilized the inherent characteristics of fiber-optic cable to develop a variable gage-length interferometric sensor. The major objective of the research was to develop a sensor for detecting changes in bridge structure dynamic response to be used in conjunction with pattern recognition techniques. Because sensor location is critical when using point sensors, long gage-length sensors are expected to be more effective in detecting changes in global dynamic response, effectively integrating the response along predetermined lengths of the structure.