Analytical Stress–Strain model for steel spirals-confined UHPC

Abstract

Ultra-high performance fiber reinforced concrete (UHPFRC), which for short is commonly referred to as ultra-high performance concrete (UHPC) is an advanced cementitious composite material with superior mechanical properties that could transform future structural design. This paper presents a new comprehensive analytical stress-strain model for confined UHPC with steel spirals, which could be readily implemented in analytical studies to enable and expand structural design of future UHPC axial members such as columns. The validity of several existing confinement models for normal strength, high strength, and fiber reinforced concrete was evaluated first for predicting the uniaxial compressive behavior of UHPC. The evaluation results indicated the need to develop a unique confinement model for UHPC, which was pursued in this study. The proposed model was calibrated and validated using material tests data from about 100 UHPC specimens with varied volumetric ratios of steel fibers and spirals. Thus, the model accounts for combined confinement effects of steel fibers and spirals on compression behavior of UHPC. The developed model was further evaluated using additional experimental data and was shown to adequately represent the uniaxial compressive behavior and full stress-strain curves of both unconfined and confined UHPC with transverse reinforcement.