Research on Using Fe-SMA Material to Actively Strengthen Fatigue Cracks of Arc-Cutouts in Diaphragms
This study investigates the feasibility of using the iron-based shape memory alloy(Fe-SMA)to actively strengthen fatigue cracks of arc-cutouts in diaphragms of the orthotropic steel deck.An in-service cable-stayed bridge with superstructure consisting of steel box girders was used as a case.Given the cracking characteristics of the arc-cutouts in the diaphragms,it was proposed to drill crack stop holes first,then to bond Fe-SMA plates to repair the cracks.Tests were performed to observe the strain responses and temperature variation of the Fe-SMA plates during the thermal activation process,and the interaction between the Fe-SMA material and steel diaphragm and the strengthening mechanism were analyzed.It is shown that bonding Fe-SMA plates is an effective and convenient way to apply pre-compressive stresses to the diaphragm,which takes good use of the thermal-driven shape memory effects of Fe-SMA material to achieve active strengthening of damaged locations.Combined with crack stop holes,the Fe-SMA plate can generate a pretensile stress of 200 to 240 MPa under the thermal drive,and impose a compressive stress of 43 to 90 MPa circling the crack stop hole,leading to effective hindrance of the further propagation of cracks.The Fe-SMA plate remained intact during the thermal activation process,when the temperature at the center of the heating zone reached 200 ℃,the temperatures at the center and back of the non-heating zone were below 60 ℃ and 90 ℃,respectively,due to the heat conduction effect.
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