Unreinforced concrete masonry under compression: Brazilian statistics, reliability analysis and code calibration

Abstract

Although the new Brazilian code is considered an advancement, it still lacks a reliability-based calibration of partial safety factors. Therefore, this paper presents a comprehensive set of reliability analyses oriented to structural masonry members under compression in Brazil. This study was based on structural reliability theory, which allowed a safety assessment through the reliability index (β). Walls with hollow concrete blocks of three classes (A, B and C) and two modular sizes (M-15 and M-20), two ratios between the prism strength and the block compressive strength (η = 0.5 and 0.6), and three ratios between effective height and effective width (λ = 14, 19 and 24) were evaluated. Considering that each one of the 36 elements is described by five ratios between live and dead loads and the five ratios between wind and dead loads, 900 configurations were analyzed. Reliability procedures, the structural configurations and the calibration methodology were implemented and solved in the StRAnD – Structural Reliability Analysis and Design software. Results showed that the reliability indexes are greater for unreinforced masonry walls under compression with modular size M-20 than modular size M-15. It can be noted that the block compressive strength not only represents the greatest impact on the masonry’s safety level, but is also the most relevant random variable. Based on the reliability-based calibration of the Brazilian code, it is recommended that unreinforced masonry presents different partial safety factors (ɣm) than reinforced masonry. This work represents a stepping stone in evaluating the safety of Brazilian masonry structures, indicating a possible path in terms of achieving a more uniform reliability in masonry design.