Bridge Analysis Simplified By Bakht Jaeger.pdf !!TOP!!

Bridge Analysis Simplified By Bakht Jaeger.pdf !!TOP!!

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Load distribution factors have a substantial role in the analysis and design of highway bridges. In this research, the effect of load distribution factors on the design parameters of bridge superstructures are studied by a numerical semi-continuum method. Three different case studies are carried out in the research to compare the accuracy and performance of the method. The objective of the first case is to control the outcomes of the method with the results of finite element method as well as AASHTO LRFD method. The second case is presented to study the effect of design parameters on load distribution factors between longitudinal girders through the three methods. Finally, a field test investigation is studied in the last case to compare all three methods with an actual field test study. It has been shown that the AASHTO LRFD method is not precise enough in comparison with the present method. The AASHTO LRFD formulas for live load distribution are quite unreliable and can give design parameters far too low or far too high. Moreover, minimum calculation time, convenient performance and high accuracy in the solution process are the other advantages of the method proposed in this research.

Distribution factors (DFs) for one typical cross-section as specified in the AASHTO LRFD specification can be varied when the bridge parameters such as span length, loading lanes and skew are changed. The diversity between design and actual DFs may be varied as the bridge parameters changed. To study this diversity, this paper presents an evaluation of lateral load DFs for prefabricated hollow slab bridges. The response of the bridge was recorded during the field test. This field test was divided into two stages: a concentrated force loading test on the prefabricated girder that settled on the bridge supports before the girders were connected transversely and a vehicle loading test after the girders were connected transversely. The instruments used to record the response of the bridge were strain gauges and dial indicators. The measured data in the multi-stages of the field test could be used to calibrate the support condition of the bridge and transverse connection between adjacent girders in the finite element model (FEM) using beam and plate elements. From the FEM, DFs for this hollow slab bridge were determined and compared with the DFs in the AASHTO LRFD specification. A parametric study using the calibrated FEM was then used to investigate the effect of various parameters including span length, skew and bridge deck thickness on the DFs. It was found that AASHTO LRFD specification is conservative compared with the analysis in the FEM, while this conservatism decreased as the span length and skew of the hollow slab bridge increased.

This loading phase was performed after the prefabricated girders were installed and the adjacent girders had not been connected transversely. Before this loading test, a preloading test was carried out on the tested girders to ensure the accuracy of the instruments. G1 (exterior girder), G4 (interior girder) and G7 (medium girder) girders were selected to be the test girders. The loading girder, which weighed 160.44 kN, was also a prefabricated hollow slab girder. One end of the loading girder was simply supported on the bearings in the mid-span of the two tested girders and the other end of the loading girder was simply supported outside the abutment (Fig. 3). As a result, the analysis of the tested girder could be simplified to be a prefabricated girder with a concentrated force on the mid-span. So the concentrated force applied on the mid-span of each tested girder was 80.22 kN. The concentrated force loading tests were performed on the G1 and G4, G4 and G7, respectively. The dimension of the girder and material properties were measured in this loading phrase.

Elastic spring elements were used to simulate actual behavior of supports as shown in Fig. 10 (Eom and Nowak 2001). To model this kind of connection, general connection options in elastic connection were selected in MIDAS CIVIL, while the combin14 elements were modeled in ANSYS model. In this calibrating process, main girders were not connected transversely. Elastic spring elements were added to restrict the horizontal movement of the bridge on the base of the simply support condition according to the design plan. The stiffness of the spring elements was represented by K values. The suitable K values were found by comparing the deflections at the mid-span from FEM analysis with those from the concentrated force loading test by trial and error analysis. The K values used in the analysis are shown in Table 1, in which, girder 1 and 13 had different K values with the other girders because of their different section from the others. The K values that acquired from different FE models were the same. 2b1af7f3a8