Simplified Approach for Seismic Analysis of Structures

The seismic analysis of a structure using continuum mechanics approach may yield good results. However, this approach is difficult to apply for complex geometrical problems such as nuclear reactor containment building. To incorporate the entire structural behaviour, a full 3D model is best suited. However, a large number of modes are required to achieve at least 90% mass participation or frequency content up to 33 Hz. This consumes a large computational time due to large number of local modes present. Therefore, an equivalent lumped mass beam model, which as compared to 3D model, is much simpler and produces conservative global responses, has been considered in analysis. The lumped mass equivalent beam model of the system can be prepared after carrying out static analysis of 3D model using static energy equivalence approach. Forces and moments obtained by the seismic analysis of this beam model can be applied on the 3D model in order to obtain stresses in each element. It was found that the results obtained by this approach gives higher results because of higher mass participation. Experimental investigation is also performed on one of the case study to support the analysis. Hence it is concluded that analysis using beam model based on strain energy equivalence, in combination with 3D model is much simpler, economic and gives conservative results.