Bridge Structures - Volume 6, issue 3-4

Authors: Mahmoud, Khaled M.

Article Type: Other

DOI: 10.3233/BRS-2010-014

Citation: Bridge Structures, vol. 6, no. 3-4, pp. 81-82, 2010

Authors: Rahai, Ali Reza | Shokoohfar, A.

Article Type: Research Article

Abstract: Some existing bridge girders do not satisfy current shear strength requirement and so study of this strength seems essential. Shear strength of pre-stressed concrete bridge girders with and without vertical prestressing is studied in this paper. First several models of prestressed concrete beams are selected and analyzed using the finite-element method. In this regard the validity of modeling is evaluated based on some test performed on an existing bridge girder in Switzerland. In the second part of the study several beam specimens are built and tested and their load-deformation curve and cracking pattern are studied. Using all numerical and experimental …studies, the slope of shear cracks and shear reinforcement ratio are investigated and the effect of horizontal and vertical pre-stressing on the noted parameters is evaluated. The findings should be of interest to researchers as well as practicing engineers involved in analysis and design of prestressed concrete beams. Show more

Keywords: Shear strength, post-tensioned bridge girders, vertical prestressing, tendons, testing, stress field

DOI: 10.3233/BRS-2010-009

Citation: Bridge Structures, vol. 6, no. 3-4, pp. 83-94, 2010

Authors: Karunananda, Kamal | Ohga, Mitao | Kaita, Tatsumasa | Dissanayake, P.B. Ranjith

Article Type: Research Article

Abstract: This paper presents a reliability-based condition assessment procedure of multispan masonry arch bridges. Considering axle load as assessment criterion, safety margins (limit state functions) are introduced for each arch of the bridge. The introduced safety margins consist of two variables: provisional axle load (PAL) which is estimated using MEXE methods and actual axle load (AAL) which is estimated using weigh-in-motion measurements of the bridge. Both variables are assumed to follow log normal distribution. Then, failure probabilities of each arch which were estimated from statistical parameters of variables are combined to get the failure probability of the bridge using reliability bounds. …The reliability index of the bridge is estimated from the failure probability. Bridge condition is predicted by comparing the reliability index with its acceptable reliability index. Further, when the statistical parameters behave as interval numbers, corresponding reliability index changes are discussed. The introduced assessment procedure is illustrated by a four span brick masonry arch bridge in Sri Lanka. Show more

Keywords: Multispan masonry arches, condition assessment, reliability index, MEXE method

DOI: 10.3233/BRS-2010-011

Citation: Bridge Structures, vol. 6, no. 3-4, pp. 95-106, 2010

Authors: Edalatmanesh, Rahman | Newhook, John P.

Article Type: Research Article

Abstract: A method for the identification of vehicle axle loads on slab-on-girder bridges is presented in this paper. The method is based on the development of a bridge specific static influence line matrix and the use of an optimization method combined with a pattern search algorithm. A 1/3 scale laboratory model of a six girder bridge was used as part of the case studies which demonstrate the development and implementation of the method. A finite element model of the bridge was developed and calibrated against experimental data. The search based optimization procedure was necessary to provide an estimate of vehicle characteristics …when noise was present in the recorded data and when error was present in the numerical model. The estimated vehicle characteristics therefore did not exactly match the actual vehicle; this deviation was designated as an identification error. The statistical behavior of the identification error with respect to the level of noise in the measured response or error in the model was studied. Methods for reduction of the identification error were numerically evaluated. It was shown that a field calibrated bridge model is important and that averaging of multiple vehicle estimates for different positions on the bridge can decrease the identification errors. Show more

Keywords: Weigh-In-Motion, bridges, vehicle loads, optimization, pattern search method, statistical analysis

DOI: 10.3233/BRS-2010-012

Citation: Bridge Structures, vol. 6, no. 3-4, pp. 107-119, 2010

Authors: Alampalli, S. | Ettouney, M.

Article Type: Research Article

Abstract: Load testing is gaining popularity among bridge owners to take advantage of the actual load capacity that can not be estimated using conservative analyses. This paper provides an easy, generalized model for evaluating the value of load testing using costs and benefits of load tests. Both quantitative and qualitative benefits are included. Also explored are the effects of load tests on the life cycle analysis of bridges and quantification of extended life of bridges due to load testing.

Keywords: Load testing, cost-benefit modeling, load testing value, bridge testing

DOI: 10.3233/BRS-2010-010

Citation: Bridge Structures, vol. 6, no. 3-4, pp. 121-127, 2010

Authors: Esposito, Steven | Najm, Husam

Article Type: Research Article

Abstract: In October of 2007 the AASHTO LRFD Bridge Design Specification became the mandatory design specifications for highway structures in the United States. This has introduced a number of changes in the design and analysis procedures that engineers have to follow. This paper evaluates the differences between the ASD standard specifications and the LRFD specification and how they apply to the design of earth retaining structures. Several design examples were carried out to examine the effect of the new design standards on structural proportioning and cost. For cantilever abutments and retaining walls 4.6 m and taller, the difference between the LRFD …specifications and the ASD standard specifications was insignificant. However, designing shorter abutments and retaining walls using the LRFD specifications can result in an increase in footing length of about 30% and an increase in cost of approximately 10% of the cost of the retaining structures. While these cost impacts to a structure can be significant in some designs, the AASHTO LRFD specifications provides a safe and reliable method of design which is of paramount importance to engineers and the public. Show more

Keywords: LRFD specifications, ASD specifications, abutments, retaining walls, design, cost

DOI: 10.3233/BRS-2010-013

Citation: Bridge Structures, vol. 6, no. 3-4, pp. 129-138, 2010

Authors: Shoukry, Samir N. | William, Gergis W. | McBride, Kevyn C. | Riad, Mourad Y. | Wriston, Jimmy D.

Article Type: Research Article

Abstract: This paper presents a case study of the Buffalo Creek bridge structure under two conditions, one with an empirical sandwich deck referred to as “old deck design” and the other with traditional deck referred to as “new deck design”. The focus of the study is to assess the performance of the empirically designed reinforced concrete bridge decks versus those designed using traditional analytical design methods and to check the adequacy of both design methods by correlating the theoretical results with field observations. For this purpose, two 3D finite element models of the old deck and new deck designs were developed …together with the bridge superstructure. Both models were subjected to real life loading configurations of self weight and temperature variations. A comparison of the stresses induced in both models indicates that the stresses developed in the empirically designed concrete deck (old design) at the levels of the reinforcing mats are similar to those developed in the traditionally designed deck. The connections between the steel main girders and the concrete deck are the main constrains for deck expansion and contraction in the transverse direction, hence high tensile stresses were developed over the girders in the transverse direction. Additionally, the sharp edge of the clip angle protruding into the concrete deck as well as the top of the slope of the stay-in-place forms were identified as stress risers that contribute to the longitudinal cracking problem. Show more

DOI: 10.3233/BRS-2010-008

Citation: Bridge Structures, vol. 6, no. 3-4, pp. 139-153, 2010