Effects of extreme gravity and seismic loads on short to medium span slab-on-girder steel highway bridges.
Creators: name: Dicleli, Murat.
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 1993
Subjects: subject: Engineering, Civil.

description: This study addresses two separate but related problems. They are detrimental effects of extreme gravity and seismic loadings, which were not considered in the original design, on slab-on-girder steel bridges. In the first part of this thesis the effect of extreme gravity loads on slab-on-girder steel bridges is studied. Currently, in many jurisdictions of North America, special permits are issued to extra-heavy vehicles considering only the ultimate capacity of the bridges. Based on this, a large number of special permits have been issued to extra-heavy vehicles, and therefore concerns have been raised since the cumulative effect of such overloads have never been assessed. In this perspective, the ultimate and cumulative effect of such overloads on bridge components is studied. Typical heavy permit-truck configurations are selected to investigate their effect on steel bridges. As a first step, influence line analyses are conducted to find the ranges of spans of simply supported and continuous bridges for which heavy permit-trucks have the most detrimental effects. In the light of these observations, a number of actual bridges within the estimated span length limits are analyzed to find the bridge members largely affected by such overloads. Next, a literature review is conducted to appraise the state-of-knowledge on the impact of infrequent stress-range excursions produced by heavy loads on fatigue life of bridge members. The effect of variable amplitude loading due to both Ontario truck traffic and heavy permit trucks on fatigue life of bridge members is investigated. Analytical expressions to calculate the fatigue life and the reduction in fatigue life of bridges due to heavy permit-trucks, without the need for a detailed analysis of each bridge, are derived and presented, along with a fatigue-based methodology to assess the reduction in service life of bridges attributable to heavy-permit trucks. Finally, using the derived equations, a sample permit-policy is presented assuming that a two percent reduction in fatigue life due to heavy permit-trucks is acceptable. In the second part, the response of bridge superstructure components to seismic excitations is investigated. Single span simply supported, continuous and multi-span simply supported bridges are studied by varying their geometric and structural properties. Linear and nonlinear dynamic analyses of these bridges are conducted for earthquakes of different characteristic and intensity considering only the superstructure. The forces and displacements of superstructure components which significantly affect the response, are determined as a function of the selected properties and earthquake types. Then, using these results, a methodology is developed for ranking and rapid seismic evaluation of existing steel bridges. Bearing forces due to seismic excitation in both transverse and longitudinal direction are found to be proportional to the mass of the bridge, span length, and bearings' stiffness. The effect of span length, number of spans, column size and steel strength on the seismic response of continuous and multi-span simply supported bridges are studied. Next, sliding of bridges after the bearings are severed is investigated. High intensity earthquakes are required to slide multi-span simply supported bridges when the bearings at the abutments are severed but single span simply supported and continuous bridges may have considerable sliding displacements depending on the $A\sb{p}/V\sb{p}$ ratio of earthquakes. The effect of cross-bracing as a retrofitting element for continuous and multi-span simply supported bridges is investigated. (Abstract shortened by UMI.)