Reliability Analysis Of Reinforcement Concrete Members After Exposure To Fire

Mechanical performance of reinforcement concreter (RC) member after fire duration is complicated, For example, materials strength and elastic modulus of reinforcement and concrete and bond strength between reinforcement and concrete deteriorate significantly, which result in the decrease of load bearing capacity of member, so the resistance decrease. Under the action of regular service load, the reliability of structural member fails to meet the criterion of current code if the resistance is lower than the total load effect.Some RC members post- fire can continue to serve after they are repaired and strengthened, all which are based on some theoretic calculations. So reliability analysis can supply some theory basis to damaged assessment, maintenance-strengthening and life forecast of RC member after fire exposure, and the reasonable maintenance-strengthening method can be determined, the synthesized ability of disaster resistance is increased, the maintenance costs are decreased. Based on the previous research results, besides systematic analysis and conclusions are made other studies in this thesis are included as the following:1. The calculation method of residual bearing capacity of RC member post-fire was perfected in order to improve calculate precision. Against to degeneration on mechanical performance of materials and reduction on section dimension of RC member post-fire, primarily discussion was carried out on the calculation method of residual bearing capacity, such as stratification and equivalent cross-section economization. Resistance reduced coefficient of member was given. All which provide theory basis for reliability analysis of RC member post-fire under some condition.2. Influence factors of reliability of RC member post-fire were discussed .On the one hand, degeneration of member resistance was considered, which was caused by degeneration of mechanical performance of reinforcement and concrete materials. On the other hand, equivalent fire-load was considered, which is caused due to change of stress under fire duration and is equivalent as fire load, so the load effect made up to limit state equation increase. Performance function of RC member post-fire was established and digital character of member resistance was analyzed.3. Time-dependent reliability was introduced, the reliability of RC member subject to fire after long-time serve was analyzed. Degeneration of resistance with active time was considered before fire; Degeneration of resistance under high temperature was also considered after fire. Correlation of resistance between the two procedure was considered simultaneously, and formula of the resistance correlation was deduced. The numerical example indicated that it is more suitable for engineering case to consider the change of resistance fore-fire with active time and the change of resistance post-fire with temperature were considered generally, simultaneously introduce the correlation of resistance between the two course.4. The resistance model and limit state equation of axial compression columns subjected to four-side fire are established .The influences on reliability of RC member after fire exposure are analyzed , which is caused by different parameters such as fire duration, strength of reinforcement and concrete, ratio of reinforcement, section dimension and slenderness ratio and so on.5. Reliability analysis method of eccentric compression column after fire exposure was given. Under the situation that correlation and independence between axis and moment were considered comprehensively, reliability of the eccentric compression column after fire exposure was analyzed, analysis results of the two conditions were compared comprehensively and the difference was disclosed. Results indicate that the method of reliability analysis on eccentric compression column after fire exposure is more coincident with real case than only the single factor of axis or moment is considered.