Compressive Stress-Strain Model for Confined Lightweight Concrete Based on Brittleness Number

Typically, the stress-strain relationship of confined lightweight aggregate concrete (LWAC) exhibits lower stiffness in the ascending branch and more brittleness in the descending branch compared to counterpart confined normal-weight concrete (NWC). To describe the rational stress-strain relationship of confined LWAC according to these trends, the concept of concrete brittleness number ( ξ b ) was introduced. Specifically, ξ b values were determined as constants in the existing size effect equation. The constants were fitted via regression analysis of 164 datasets compiled in extant studies. The models of elastic modulus, strength gain factor, strain at maximum stress, and strain at 85% of the maximum stress in descending branch were proposed, including ξ b to describe the lower stiffness and more brittle behavior in confined LWAC when compared to those of counterpart confined NWC. Other existing models showed significant differences when compared with the test results in the descending behavior. These differences were significant in LWAC and counterpart NWC. Conversely, the proposed stress-strain relationship of confined concrete was in excellent agreement with the test results, irrespective of concrete type, compressive strength of concrete, and volumetric transverse reinforcement index.