S-N curve fatigue study and the stress-strain properties on the refurbish NITI SMA for reinforcing bar in concrete

Abstract

The earthquake load in structures is assumed as a low-cycle loading type load in structures that may cause low-cycle fatigue in earthquake resisting structures. Hence, this paper is to highlight and compare the fatigue properties of refurbish pseudoelastic shape memory alloy (SMA) and structural steel for used as seismic reinforcement features in concrete structures. This experiment study on the stress (S) against the number of cycles to failure (N) known as an S-N curve were conducted using INSTRON 8801 Servo hydraulic Fatigue Testing System with 3Hz of loading frequency with the stress varies between 0.9Fyield and 1.45Fyield for 8 SMA samples and 2 steel samples with stress varies of 0.64Fyield and 1.15Fyield. Two type of SMA samples were used including three 12.7mm SMA samples with Af-25, 6 SMA samples with Af-6.3 with 12 mm diameter respectively. As a result, the structural steel were observed could with stand approximately 93710 cycles before failure if loaded up to its yield stress, while SMA of diameter 12.7mm can withstand until 19040.75 cycles. Type 1 of refurbish SMA rebar that were reused shows a much better behaviour against fatigue than structural steel rebar and is more reliable in seismic periodic loads. However, for second type refurbish and reused of SMA shows the vice versa and can only sustain maximum 23674.25 cycles.