Reliability-based design of fiber reinforced concrete slabs-on-ground in flexure as per ACI 360

Abstract

Modern design codes apply the Load and Resistance Factor Design (LRFD) format to account for all uncertainties involved, primarily manufacturing, fabrication, and modeling errors. In this format, load effects are scaled-up by load factors while a resistance factor scales down the resistance. In this way, the LRFD design format ensures that all designs meet, consistently, a certain safety level. To determine the most appropriate factors, a reliability-based procedure is required, in which a target reliability index is selected, which corresponds to an acceptable probability of failure. Unlike most of the American Concrete Institute (ACI) design codes, which adopted the LRFD design format, the current ACI 360R for slabs-on-ground design is based on the concept of safety factors. The present work aims at calibrating the resistance factor,ϕ, for the flexural design of fiber reinforced concrete slabs-on-ground. A total of 56 laboratory tests gathered from previous studies were analyzed to determine the statistical parameters of the resistance model. Then a series of reliability analyses were conducted to calibrate the resistance factor. In the calibration process, dead and live loads with and without impact were considered in the load combinations. This study suggests that for a flexural design of fiber reinforced concrete slabs-on-ground subjected to dead and live (with or without impact) loads, to meet the target reliability index, a resistance factor ϕ = 0.8 is recommended. An example is presented to showcase the application of LRFD for the design of FRC slabs-on-ground.