基于广义可靠指标相对安全率的地基承载力安全判据研究

Safety criteria for bearing capacity of foundation based on the generalized reliability ratio of safety margin

相对安全率搭建了岩土工程确定性设计和可靠度设计安全判据的桥梁。广义可靠指标相对安全率克服了相对安全率受分布类型限制的局限,拓宽了相对安全率准则的应用范围。提出了在给定目标失效概率(或目标可靠指标)的条件下基于广义可靠指标相对安全率,标定允许安全系数的方法和流程。将所提允许安全系数标定方法应用于地基承载力安全判据研究,分别标定了传统抗力荷载比值法和强度折减法对应的地基承载力允许安全系数。通过地基承载力算例说明了不同工况下可靠指标相对安全率与广义可靠指标相对安全率的相互关系,探讨了不同参数和计算模型对地基承载力允许安全系数的影响。根据所标定的允许安全系数得到的确定性设计可行域与可靠度设计可行域相同,验证了所提方法在地基承载力允许安全系数标定中的有效性。

Ratio of safety margin(RSM)provides a useful tool to bridge safety criteria of deterministic design method based on safety factor and reliability-based design(RBD).Generalized reliability RSM(RRSM)overcomes the limitation on the distribution type of uncertain parameters,which restricts the application of the principle of the ratio of safety margin(RSM),and makes the RSM principle feasible in general design situations.This paper proposes a calibration method and framework for determining the allowable safety factor(FSa)based on generalized RRSM for a given target failure probability(or target reliability index).The proposed approach is applied to study the safety criteria for foundation bearing capacity.The FSa values of foundation bearing capacity are calibrated for the traditional method based on the ratio of resistance over load and strength reduction method,respectively.The proposed approach is illustrated using a design problem of foundation bearing capacity,and the relationship between RRSM and generalized RRSM is also discussed.And then,the influence of different parameters and calculation models on the allowable safety factor of foundation bearing capacity is discussed.It is shown that the feasible design domains of the deterministic design method based on FSa values calibrated from the proposed approach are identical to those of RBD under different design situations.This validates the proposed method for bearing capacity design problems.