This paper addresses the influence of the local soil type (firm or soft) on the reliability-based optimal load combination factors for seismic design of buildings. The approach aims to minimize the total expected life-cycle cost (LCC) of a structure. As a constraint, it is established that the mean annual rate of structural failure should be less than or equal to a certain prescribed value. The LCC of the structure includes 1) initial cost, 2) cost due to damages, and 3) social costs. The methodology is applied for two sets of reinforced concrete buildings; the first set is located on firm ground and the second on soft soil. The reinforced concrete buildings are designed using different load combination factors, and the total expected cost is estimated for each set of buildings. It is concluded that the optimal load combination factors for the buildings on soft soil are different from that obtained on firm ground. Finally, some recommendations are provided to estimate the seismic load factors for structures located at firm and soft soils.

本文探讨了局部土壤类型（坚硬或柔软）对基于抗震性能的建筑物抗震设计最佳荷载组合因子的影响。该方法旨在最小化结构的总预期生命周期成本（LCC）。作为约束条件，可以确定平均每年的结构破坏率应小于或等于某个规定值。该结构的LCC包括1）初始成本，2）损害成本和3）社会成本。该方法适用于两套钢筋混凝土建筑。第一组位于坚固的地面上，第二组位于软土上。钢筋混凝土建筑物的设计采用了不同的荷载组合系数，并且估算了每套建筑物的总预期成本。结论是，在软土上建筑物的最佳荷载组合因子不同于在坚硬地面上获得的荷载组合因子。最后，提供了一些建议来估算位于坚硬和软土上的结构的地震荷载系数。