Reliability-based calibration of Brazilian structural design codes used in the design of concrete structures

Abstract This paper presents a reliability-based calibration of partial safety factors for Brazilian codes used in the design of concrete structures. The work is based on reliability theory, which allows an explicit representation of the uncertainties involved in terms of resistances and loads. Regarding the resistances, this study considers beams with concrete of five classes (C20, C30, C40, C50 and C60), three ratios between base and effective depth (0.25, 0.50 and 0.75), three longitudinal reinforcement ratios (ρmin, 0.5% and ρmax) and three transverse reinforcement ratios ( A s s m i n, 5 . A s s m i n and A s s m a x). In terms of loads, this work considers seven ratios between live loads and permanent loads (qn/gn), and seven ratios between wind loads and permanent loads (wn/gn). The study also adopts a single value for the target reliability index (βtarget = 3.0). Results show that the optimized set of partial safety factors leads to more uniform reliability for different design situations and load combinations.

摘要 本文针对混凝土结构设计所用的巴西规范，开展基于可靠性理论的分项安全系数校准研究。本研究以可靠性理论为支撑，该理论可对抗力与荷载相关的不确定性进行显式表征。就抗力维度而言，本研究选取的梁构件采用5个强度等级的混凝土（C20、C30、C40、C50及C60），截面宽度与有效高度之比分为3组（0.25、0.50、0.75），纵向配筋率设置3种水平：最小配筋率ρ_min、0.5%以及最大配筋率ρ_max，横向配筋率同样设置3种水平：最小横向配筋面积$A_{s,s,min}$、5倍最小横向配筋面积$5·A_{s,s,min}$以及最大横向配筋面积$A_{s,s,max}$。荷载维度上，本研究考虑了活荷载与永久荷载之比的7种取值（$q_n/g_n$），以及风荷载与永久荷载之比的7种取值（$w_n/g_n$）。本研究同时设定目标可靠指标为单一值（$β_{target}=3.0$）。研究结果显示，经优化得到的分项安全系数组合，可使不同设计工况与荷载组合下的可靠度更为均匀一致。