Flexural Resistance Factors for Structural Ultra Lightweight Engineered Cementitious Composite Slabs

Abstract

Many problems associated with the use of normal weight concrete have been solved with the development of structural ultra-lightweight engineered cementitious composite (SULWECC) that has the capability to exhibit strain-hardening behavior prior to failure. However, the feasibility and standards that address the design of such engineered cementitious composites (ECC) in flexural slab systems are not available. In this study, reliability analysis and calibration process are carried out on three different SULWECC slab systems with the intention of estimating the potential flexural resistance factors. Although the high volume of randomly dispersed synthetic short fiber is considered the main reinforcement, SULWECC slab systems internally reinforced with carbon FRP mesh are also considered. The reinforcement ratio is selected so that the section is under-reinforced. Relevant load and resistance random variables are used, and appropriate statistical parameters are selected. The target reliability indices are chosen to be consistent with those used to develop current design code specifications. The nominal moment capacity is calculated based on a new model that consists of: elastic linear stress distribution in the compression zone and elastic-perfectly-plastic uniform stress distribution in the tension zone. The determined flexural resistance factors ranged from 0.59 to 0.69, although higher values are justifiable in special circumstances. The average slab thickness needed to satisfy the strength requirements ranged from 1/37 to 1/22 times the slab length. Flexural toughness to measure ductility is evaluated using load-deflection curves of experimentally tested SULWECC specimens.