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 本文针对巴西混凝土结构设计规范中的分项安全系数（partial safety factors）开展基于可靠性理论（reliability theory）的校准研究。本研究依托可靠性理论，可清晰表征抗力（resistances）与荷载（loads）相关的各类不确定性。针对抗力维度，本研究考虑五类混凝土强度等级（C20、C30、C40、C50及C60）的受弯梁构件，设置3种基高与有效高度之比（0.25、0.50和0.75）、3种纵向配筋率（最小配筋率$
ho_{ ext{min}}$、0.5%及最大配筋率$
ho_{ ext{max}}$），以及3种横向配筋率（最小横向配筋面积$A_{s,s, ext{min}}$、5倍最小横向配筋面积$5cdot A_{s,s, ext{min}}$及最大横向配筋面积$A_{s,s, ext{max}}$）。荷载维度方面，本研究设置7种活载与恒载之比（$q_n/g_n$），以及7种风载与恒载之比（$w_n/g_n$）。本研究采用单一的目标可靠指标（target reliability index，$eta_{ ext{target}}=3.0$）。研究结果表明，优化后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分布更为均匀一致。