A parametric study is conducted to investigate the effect of lead rubber bearing (LRB) isolator and ground motion characteristics on the response of seismic isolated bridges. The purpose was to investigate the most favorable parameters of the LRB for minimum earthquake response of the isolated bridge system for different ground motions. The important parameters included are: ground motion characteristic by considering peak ground acceleration to peak ground velocity, PGA/PGV ratio as damage index; characteristic strength, Q d of the LRB isolator normalized by the weight acting on the isolator; flexibility of isolator by varying post yield time period, T d ; and yield stiffness to post yield stiffness, K u /K d ratio. The performance of seismic isolated bridge is measured by the variation of maximum isolator displacement (MID), maximum isolator force (MIF), deck acceleration and pier base shear. For a specified ground motion, smaller MID and MIF are regarded as indicator of better seismic performance. It is found that there exists a particular value of Q d /W, T d and K u /K d for which the MID, MIF, deck acceleration and pier base shear attain the minimum values. Finally the recommendations are made which are useful for the design engineers at the preliminary seismic isolation design of the bridges with LRB isolator for the ground motion having different characteristics.

In recent years, steel box-girders have been used extensively and especially for long span due to its high torsional rigidity and rapid erection. In order to decrease the amount of costly steel material, the variations in thickness of web, top flange and bottom flange are always considered in cross sectional design. This design depends on the notable changing of the moment distribution along the length. Variation in plate thicknesses may represent a girder with the least weight; however, this may not be the most economical girder due to the increase in fabrication costs, which are associated with excessive variations in plate thicknesses. A parametric study is carried out to determine the optimum cost design of changing thickness of continuous beam over equal span. The objective function includes material and welding fabrication cost. The parameters varied are the length of span, the loading and the number of segments in each span. Both closed rectangular and open trapezoidal sections are considered. Finally, the relationship between cross-section dimensions of steel box girders is defined. The recommended design guidelines can be useful to the designer in the first stage of the designing procedure when he faces the problem of defining basic structure dimensions that would be close to the optimum ones.

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<p>Among various types of highway bridges, the precast prestressed girder bridge has been one of the most popular and economical types adopted. General analyses of this kind of composite deck-girder bridge are made by beam element. Therefore the details of behaviours such as the stress in the strands along the length of girder, the stress and deformation of concrete, especially the mechanical behaviours at the interface between the girder and slab can’t be obtained exactly. Actually it is full of challenge to model prestress tendons in solid element. In this paper it is attempt to simulate this kind of composite bridge by 20-node solid element in ABAQUS. Six approaches of modelling the prestressing are introduced. Accompanying subroutine code for shrinkage and creep based on Kabir’s creep compliance curving fitted according to AASHTO LRFD Bridge Design Specification (2007) is used. Whole construction procedures are modelled by “remove” deck element firstly in non-composite section, resisting the self-weight of girder and sequent wet weight of deck, and thereafter “reactivate” them into composite section, resisting additional dead load and live load. Using a “perfectly elastic element” to model the cast-in-situ deck, the deck element can be reactivated at an appropriate stage based on the deformed girder. A prism is used for the verification of the subroutine and the primary results of a single span composite girder-deck bridge are obtained.</p>

<p>The purpose of this paper is to investigate the behaviour of steel box girder bridge during up-down construction method. The steel box girder with open-trapezoidal cross section, partial prefabricated concrete slab and double composite section by cast-in-place bottom concrete slab is considered in this study. The three-dimensional finite element (FE) models, considering construction sequence in modelling, have been used to carry out the analysis. A parametric analytic study is used to investigate the effects of some structural characteristic on the behaviour of steel box girder. These parameters include the variation of lifting upward and lowering downward height, the length and depth of bottom concrete slab and the length of partial pre-fabricated concrete slab. An overview of the effect of lifting upward and lowering downward method to the stability design such as web buckling and top lateral bracing are also given. Results of the study with potential design recommendations are outlined.</p>