A simplified procedure for assessing failure probabilities of reinforced concrete frame buildings under earthquake loading.
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The thesis argues the need for a more rational structural code, and as a major step in its attainment describes the development of a simplified technique for assessing the probability of failure of structures due to earthquake effects. Previous approaches to the development of a rational code are discussed critically and their limitations are described. A major problem is shown to be the difficulty of assessing failure probabilities for complete structures, even using the simplified First-Order Second-Moment approach. The difficulty is illustrated by applying the First-Order Second-Mount method to a simple portal frame structure. A consistent approach to the analysis of seismic failure probabilities of complete structures is then developed. Cumulative plastic strain energy is used as an overall damage measure, with an interstorey drift limit as a failure criterion. The relationship of the two is established using three separate analyses for estimating: 1. the total cumulative plastic strain energy absorbed by an entire structure; 2. the proportion of total energy absorbed by each storey; and 3. the maximum interstorey drift induced by the energy in each storey. Finally, a First-Order Second-Moment approach is used for obtaining probabilities of failure. The technique is developed in detail only for reinforced concrete frame structures, though the approach is more universally applicable. The analysis is relatively complex, but it nevertheless involves a number of simplifying assumptions. These are discussed, and are also the subject of sensitivity analyses. The analysis is applied to various trial structures. It is tentatively concluded that the seismic reliability implied by New Zealand codes is a little low, compared with results obtained elsewhere.