Research On Value Of Performance Index Of Bridge Structures In Performance Based Seismic Design Theory

The lessons learned from significant earthquakes that have occurred recently has led to the conclusion that performance-based seismic design (PBSD) theory is recognized step by step in earthquake engineering field and the research about it is becoming a principal topic. The core content of PBSD is to improve the target performance level of structures and make the structure achieves a group of anticipated performance objectives under different design earthquake levels.Current seismic deign code for PBSD in bridge sturcture are based on empirical considerations of the authority. In this paper, it is focused on the quantitative anysis of failure mode and performance index in reinforced concrete bridge columns. The major contributions of the work presented in this thesis are listed as follows:1. On the basis of guidelines for seismic design of highway bridges, it is compared that the provisions about seismic fortification aims, seismic design categories, ground types, response spectrum, earthquake action, detailing of ductile piers and structural integrity of the bridge among guidelines for specifications of earthquake resistant design for highway engineering and Eurocode8for bridges. The results indicate that it is similar in seismic fortification aims, seismic design categories and response spectrum between guidelines for seismic design of highway bridges and Eurocode8for bridges. It is very different in strength reduction factors between guidelines for seismic design of highway bridges and Eurocode8for bridges. At the end, the existing problems in strength reduction factors, performance index, seismic fortification level, isolation and energy dissipation design are pointed, and the trends of future study are discussed.2. In order to help engineers better understand the behavior of reinforced concrete columns, columns failure characteristics and failure mode are analysed. A database containing results of lateral-load tests of reinforced concrete columns is compiled and assembled. It is well recognized that the relation between plastic shear demand and shear strength provides usefull information in the determination of column failure modes. In order to investigate the relation of plastic shear demand to shear strength ratio on concrete compressive strength, longitudinal reinforcement ratio, transverse reinforcedment ratio, longitudinal reinforcement index, transverse reinforcement index, axial load ratio, aspect ratio and hoop spacing to depth ratio, correlation analysis and partial correlation analysis are used. A failure mode index model is developed to identify column failure modes:flexure failure, flexure-shear failure and shear failure. It is difficualt to distinguish flexure-shear failure mode in practice. Hence, a two-zone classification method is proposed to approximately distinguish the flexural response dominated columns (Zone F) and the response dominated columns (Zone S). The predictions of two-zone classification method are shown to be in close agreement with available test results of column flexure failure.3. According to the failure characteristics of reinforced concrete bridge columns and the need of performance based seismic design in bridge, reinforced concrete bridge column performance levels, which are categorized into fully operational, temporarily operational, reparably operational, life safe, and near collapse levels are established. To relate bridge damage to socio-economic descriptions and field investigations at the five designated performance levels, qualitative indices are established. Based on the statistical data of seismic performance tests of reinforced concrete bridge columns with circular section subjected to flexural failure, five indices for the same five designated performance levels are put forward. Comparing the drift ratio of five designated performance levels with the provisions among New Zealand standard, Japan design code, and American design code, the results show that the drift ratios for five designated performance levels is reasonable.4. Considering the quite simple in earthquake hazard level and the marked difference in probability of exceedance between earthquake action El and earthquake action E2in guidelines for seismic design of highway bridges, a new definition of earthquake action El’ and earthquake action E2’is proposed. Based on five designated performance levels and four earthquake action levels, seventeen strcuture performance objectives and four seismic fortification creteria are formed. To relate bridge component to its mechanical properties at the five designated performance levels, component performance levels for different seismic fortification criterion in bridge structures are establishded. It is expected that performance-based seismic design for bridge structure can be improved.5. Damage indices have the potential to play vital role in defining performance objectives and retrofit decision-making in earthquake regions with the development of performance based siemic design recently. Based on test results by Kunnath, eight damage indices are evaluated by comparison with a series of bridge pier tests. On the basis of these comparisons, it appears that the indices which attempt to take account of the damage caused by repeated cycling give no more reliable an indication of damage. The Park&Ang model provides a more reliable indication of the various damage levels. The equivalent ductility damage criteria which takes account of low-cyclic fatigue is clear concept and easy for application.