Optimal fortification load decision-making and life-cycle cost design for aseismic structures according to Chinese codes

A new model of life-cycle cost for aseismic structures is put forward in the present paper, which includes the minimum initial cost and the expected seismic loss under the future earthquakes during the design reference period. The function relationship between the minimum initial cost and the fortification load is derived through a series of minimum-cost seismic design subjected to the provisions of the Chinese codes by successively adjusting the fortification load. The expected seismic loss is the sum of the products of seismic risk probabilities with the corresponding economic losses. The probabilistic seismic risk analysis (PSRA) includes probabilistic seismic hazard analysis (PSHA) and probabilistic seismic fragility analysis (PSFA). The type IIIextreme distribution of the seismic intensity is adopted for the seismic hazard in the mainland of China. The simplified seismic fragility curves of four damage states are provided according to the three-level fortification principle in the Chinese seismic design codes of buildings, and then, the damage probability matrix can be developed by way of this practical seismic risk methodology. A twostage life-cycle cost design methodology is presented for aseismic structures, in which the decision of the optimal fortification load (OFL) is made during the first stage, while the minimum-cost design under the optimal fortification load is taken in the second stage. The feasibility of the proposed procedure is demonstrated in a numerical example where the methodology is applied to the life-cycle cost design of a four-storey three-bay steel frame building.