Seismic Design Theory And Method Of Long Span Bridges

As one of the most devastating natural disaster, earthquakes always cause tremendous losses of life and property. Under great earthquake, bridge may go into nonlinear phase, for example, unseating caused by excessive seismic displacement of bearing, pounding between adjacent structures, etc. As the development of modern traffic system, long span bridge are adopted more widely, for the complexity and the particularity, it's important to intensify the research of structural nonlinear theory for the sake of improving the level of seismic analysis and design of bridge structures. Based on the previous research achievements in this field, nonlinear analyses of bridge structure including pounding effect are studied in this dissertation. As a result, finite element models suitable for large scale structure are introduced and a program for seismic analysis of bridge system is developed on the basis of IDARC-BRIDGE program. The dynamic analyses of some bridges are carried out using this program and then some insights in comprehension of the structure dynamic characteristics are brought into. The main contents of this dissertation are described as follows: 1. In this paper, a study of the seismic response of long span curved bridges is conducted. Multiple-span bridges with up to seven spans are analyzed. The in-situ responses and analysis results were evaluated. The combined effects of the earthquake excitations in the two horizontal directions are also discussed. The coupling between the flexural modes and torsion modes, which exists in the curved bridge, is significant. This is determined by the characters of the curved bridges, but it, cannot be identified when the bridge regarded as straight beams. 2. A simplified bridge model suitable for use in a parametric study of curved highway bridges with stiffness eccentricity is presented. The proposed model is simple, yet it captures essential features that affect the dynamic response of these bridges. Using this simplified model, formulas for computing earthquake response of the bridges are presented and parameters that significantly influence the dynamic response of curved bridges are identified. The study indicates that the response of a given curved bridge depends on the radius of the curved bridges, width of the deck and central angle of the curved bridges. The calculated results of natural frequencies for the proposed bridge system are illustrated in tables and diagrams. These results can be employed in primarily seismic design. 3. IDARC-BRIDGE is extended for seismic assessment of long span bridge through adding Pounding Element and Tension-Gap-Yield element. The dynamic characteristics and seismic response for pounding effect of elevated bridges is computed with this program and ANSYS. The results of analyses and comparisons demonstrate the modified procedure is accurate. 4. Pounding of adjacent superstructure segments in elevated bridges during severe earthquake can results in significant damage. In the study, analytical modal are used to examine the factors affecting the global responses of a multi-span bridge due to pounding of adjacent frames. The results show that the influence of pounding on the structural response is significant in the longitudinal direction of the bridge and significantly depend on the gap size between superstructure segments. Parameters studies of one-sided pounding are conducted to determine the effects of span stiffness ratio on the pounding response of bridge frames. This paper also proposes a method to estimate the maximum relative displacement between adjacent elastic structures subjected to seismic traveling waves. The method, seeks the cross-correlation between the responses of adjacent structures subjected to earthquake excitation with time lag. 5. For highway bridges being as lifeline structures, it is essential that residual displacement after an earthquake should be smaller than the acceptable maximum value so that the bridges can be easier repaired. Both the maximum displacement and the residual displacement are important in seismic design. Residual displacement is undesirable because it causes difficulty in repair and reconstruction after earthquake. Damage indices available in the literature, either based on ductility, energy dissipation or a combination of both are discussed. The concept of residual deformation as a critical complementary indicator to cumulative damage is introduced in the paper. In addition the P-Delta effect is corporated into the corresponding post-yield stiffness and...