Experimental and numerical study on cracked steel bridge diaphragm reinforced with bonding Fe-SMA plate

Abstract

This study proposes a novel iron-based shape memory alloy (Fe-SMA) plate covered crack-stop hole method for repairing fatigue cracks at the arc-shaped cutout of the transverse diaphragm on the orthotropic steel bridge deck (OSD), which aims to reduce stress levels and increase the stiffness of the cracking part, in order to alleviate the stress concentration problem at the edge of the crack-stop hole. Firstly, a static tensile loading test on specimens strengthened by the proposed method was conducted. Results revealed that the edge stress of the crack-stop hole repaired by Fe-SMA plates with thicknesses of 1.75 mm activated at 150 °C, 2 mm activated at 200 °C, 2 mm activated at 150 °C, and 1.75 mm unactivated was reduced by 83.93%, 88.45%, 81.84%, and 66.76%, respectively, compared with those repaired only by the crack-stop hole method. Then, numerical simulations were carried out to analyze the geometric parameters and activation temperatures of the Fe-SMA plate, with the prestress of Fe-SMA simulated by an equivalent temperature method that had been validated through an activation test. Results showed that with the thickness of the Fe-SMA plate increasing from 1 mm to 3 mm, the stress concentration factor K of the hole edge decreased from 2.5 to 0.5. In practical application, it is recommended to use 2 mm-thick Fe-SMA plates, with a width just exceeding the crack-stop hole by approximately 10 mm to completely cover the cracking part and the hole. Further analysis indicates that the recommended activation length is 50–100 mm. Moreover, the repair effect is positively correlated with the activation temperature of Fe-SMA plates, indicating that higher activation temperatures can be used to improve repair efficiency within the acceptable temperature range.