The Fire Damage To The Reliability Assessment Of Reinforced Concrete Structures, Reinforcement, And Maintenance

Fires do serious damage to human being s lives and properties, and some times even to nature resources, among which building fires accounts for a great proportion. Due to the fire effects, the material properties of steel and concrete in reinforced concrete structures deteriorate significantly, such as strength and elastic modulus, which results in the decrease of load bearing capacity of members, and then the reliability of whole structure fails to meet the criterion of current designing code. More often than not, the re-inhabitancy of fire-affected structure is evaluated by personal experiences. The problems of fire-affected structures associated with reliability assessment, optimized amelioration scheme, and so on are dealt in the dissertation, which is an essentiality issue in the view of economy and society.Based on the domestic and oversea development in fire engineering and taking advantage of the fundamental theories of reinforced concrete structure, probability, reliability and structure optimization, the safety assessment, maintenance and repair strategy of fire-affected structures are studied in the paper. The main ideas are listed as following:1. The comprehensive influences of fire on material properties and section dimension for reinforced concrete structure are studied in detail. The structure anti-fire capacity includes the ability of the load bearing, deformation, stability and integrity etc. Accordingly research includes the high temperature character of structural material ( being in high temperature and after high temperature cooling ) and structural anti-fire performance property ( strength, rigidity and stability ). After fire, the plane assumption is still tenable. When we compute the structuralresidual bearing load, the width of pressing section and the strength of reinforcing bar of the pulling section shouJd be reduced. Taking advantage of the width discount coefficient, the pressing section can be converted into ladder shape ( fire in pressing section ) and rectangle ( fire in pulling section ). In the case of catching fire on four sides, the effective section of rectangle section column is changed into two axle symmetrical ladder shapes, and the equal temperature line of the reinforcing circular column is a cluster circle with the same concentric.2. The evaluation procedure for residue load bearing capacity for beam and column in frame-structure is put forward after the introduction of collaboration coefficient of reinforcement and concrete.3. The characteristics of load effect and structure resistance effect are summarized in different stages for fire-affected structures. The concept of "safety rate is defined for various kinds of structures, such as concept structure, designing structure, in-service structure, fire-affected structure and maintenance structure.4. The safety rate evaluation process is recommended for key sections of fire-affected reinforced concrete members. And the similar work is done for ductile structures. Considering the attenuation of the limit stress of the material of reinforcing bar and concrete because of the influence of fire temperature site, the bonding strength between reinforcing bar and concrete becomes reducing. Which results the change of cooperation working mode between reinforcing bar and concrete, as well as the change of geometry size. The safety function of component section can be show ascorrespondingly the section safe degree can be show as definite rateQSF , when Z F > 0 , when considering randomness only, it is PSF ?The safe degree analysis for ductility structure must combine the structural specific condition and the characteristic of environment. And the most serious failure mode of structural safety function can be determined with the way of stage analysis. For the mode of overall safety, which leads by the eventual forming of flexible system, the overall safe degree coefficient can be computed by taking the system as series one approximately. If there are n plasticity ream occurring in the overall safe f...