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 (ρ_min, 0.5% and ρ_max) and three transverse reinforcement ratios (${\left(\frac{\mathrm{A}\mathrm{s}}{\mathrm{s}}\right)}_{\mathrm{m}\mathrm{i}\mathrm{n}}$, $5.{\left(\frac{\mathrm{A}\mathrm{s}}{\mathrm{s}}\right)}_{\mathrm{m}\mathrm{i}\mathrm{n}}$ and ${\left(\frac{As}{s}\right)}_{max}$). 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 (w_n/g_n). The study also adopts a single value for the target reliability index (β_target = 3.0). Results show that the optimized set of partial safety factors leads to more uniform reliability for different design situations and load combinations.

Keywords:
code calibration; concrete structures; structural safety; reliability; safety; NBR 8681; NBR 6118