The Research Of Reliability And Equivalent Linearization Methods For LRB Isolated Bridges

Earthquake is one of the most serious natural disasters that human society faces, China is located between circum-Pacific seismic belt and Eurasian seismic belt, earthquakes are characterized by high frequency, intensity, wide distribution, large casualties and severe loss. Work as a lifeline, bridges play a key role in disaster relief and reconstruction. Isolation technology can reduce earthquake disaster of bridge effectively, but its reliability is often in doubt because of the cancellation of the fixed piers and the adoption of the isolation bearings, the domestic research seldom invlovs this field; in addition, currently most of the bridge design software used in China Design Institute can not simulate the nonlinear characteristics of isolation bearings, so equivalent linear for nonlinear isolated bridges is starved for meeting the design requirements. View of the lead rubber bearings (LRB) is the most widely used isolation system, LRB isolated bridge is selected as the research object in this dissertation and corresponding study includes the following aspects:1,The riding comfort of LRB isolated bridge was evaluated. The vehicle load was transformed into dynamic load by self-compiling program, the process for calculating the response of bridge under dynamic load was summarized; the result that only the vertical stiffness of LRB beared on the riding comfort among all of its factors was pointed out by analyzing the impact of the stiffness of LRB on the riding comfort; the riding comfort of different forms of LRB isolated bridges was analyzed with ISO standard, Diechmann indicator and Sperling indicator, the result showed that there riding comfort were well-drawn, which is determined by there own inherent characteristics, because the vertical stiffness of LRB and the bearings used in non-isolated bridges was basically the same.2,The possible pounding response of LRB isolated bridge subjected to seismic excitation was analyzed. Kelvin impact model was selected based on comparing characteristics and scope of application of various impact analytical models, because it could reasonably account for physical nature of pounding phenomena and relevant parameters were easy to determine, the problem that simulation of pounding element in ANSYS was solved; the suggestion of scope of period ratio for avoiding pounding of LRB isolated bridge subjected to seismic excitation was given, and reasonable value of the pounding stiffness was determined by deeply analyzed some factors which influenced pounding characteristics; the result that smaller horizontal stiffness of the bearing induced greater risk of pounding and pounding response for bridge was pointed out by analyzing the impact of the horizontal stiffness of LRB on pounding response, so the horizontal stiffness of the bearing can't be reduced blindly to pursuit isolation effect, pounding of isolated bridge subjected to seismic must be checked; the result that isolated bridge played a protective role for the piers when earthquake happened was pointed out by comparing the pounding response between isolated and non-isolated bridges, guidance was proposed for project application.3,Two kinds of dynamical stability problems for LRB isolated bridge subjedted to seismic excitation were analyzed. The problem that use first approximation method to determine the first dynamical stability of multi-degree of freedom complex structure was solved based on Liapunov dynamic stability concept; a specific method for analyzing the first dynamical stability was proposed, the method of time-history combined with eigenvalue and self-compiling program were adopted; based on nonlinear theory of fiber model, the method that IDA combined with B-R criterion was proposed to analyse the second kind of dynamical stability problem of LRB solated bridge; two kinds of dynamical stability problems of different structure forms of LRB isolated-bridges were studied, the conclusion was that LRB isolated bridges had very good dynamical stability subjected to seismic excitation, the reason was that the displacements of pier tops were significantly reduced after isolation, the piers didn't come to range of plastic; recommendations for engineering applications was given:for isolated bridges with higher piers and larger earthquake displacements, dynamic stability needs to be checked, because their dynamic stability might be weakened after use of isolation technology.4,The equivalent linear method of LRB isolated bridge was studied systematically. The equivalent linear method for LRB isolated bridge is proposed by comparing various equivalent linear methods for isolated bearing, analysis approach of spectrum subjected to seismic excitation and checking standard subjected to other horizontal loads for LRB isolated bridge were given, the contradiction between linear and nonlinear problems wh en calculating seismic response of isolated bridges was solved, a simple and effective method for calculating eismic response was provided to engineers and technicians.