Implications of a More Refined Damage Estimation Approach in the Assessment of RC Frames

Abstract eng:
This paper examines the influence of different definitions of demand parameters for the seismic assessment of ductile RC frames. Fragility functions used in the performance assessment of structures typically relate damage states in the structural elements, such as beams and columns, to the drifts determined during the structural analysis phase of the assessment. However, the use of such global demand parameters implies that damage is being estimated based on global response at each floor and not the local demand on the various damage zones, despite the local demand on the different elements being typically available from structural analysis. In this paper, a number of structures are designed using direct displacement-based design and a seismic damage assessment is conducted using two approaches at various intensity levels. The first is to calculate the probability of damage in the structural elements based on global demand, such as drift at the centre of mass. The second is a more refined damage analysis approach, where demand is defined in terms of local demand parameters, such as the drift at the particular grid line of the frame. By comparing these two approaches, the impact of different procedures when defining structural demand on both the damage and loss incurred on the different elements is investigated. The results show that the use of a single demand parameter at the centre of mass for regular and symmetric structures is sufficient for estimating the damage to the frame members at any location. However, the use of drift at the centre of mass is no longer adequate in cases where the structure is irregular and possesses some torsional behaviour. It is shown that this not only underestimates the damage to some frame members but also provides unconservative estimates of direct loss in the range of 15-30% for the case study structures examined. This paper’s findings, therefore, present the argument for more advanced tools in the assessment of RC frame buildings. In addition to the issue of torsional response, some further aspects relating to the assessment of RC frame buildings are discussed to illustrate other areas in which more sophisticated tools and rational approaches to defining damage may lead to better performance estimates.

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