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Fire-Resistant Steel: Bolted Connection

Sakumoto et al. (1993) reported the results of experimental studies on the tensile and shear strength of high-strength FR bolts materials and joints at high temperatures. The FR bolts are a Grade F10T torque-control bolt made of BOLTEN110N-FR steel and prepared in accordance with the JSS II-09-1981. The bolts had a nominal 0.2% yield strength and tensile strength of 1090 and 1130 N/mm2 respectively. For comparison, the fire tests for the original high-strength bolts made of BOLTEN110N steel were also carried out in this study.

Figure 1 shows the reduction factors for 0.2% yield strength, Young’s modulus and tensile strength of FR and original bolts derived from the fire tests. The tensile strength was corresponding to 2 to 3% strain. It can be seen that the tensile strength of FR bolts at high temperatures is superior to that of original high-strength bolts. Compared to the design values for tensile and shear strength of original bolts in accordance with prEN1993-1-2 (see Section Bolted Connections), the FR bolts have a much higher reduction factor of tensile strength throughout the temperature range. However, it is found that the design curve of prEN1993-1-2 follows closely the test values of the original bolts.

Figure 1 Strength Reduction Factors for Nippon Steel FR Bolts at Elevated Temperatures

Fujino et al. (1993) reported a kind of FR steel manufactured by Kawasaki Steel (denoted as KSFR) and the compatible high-strength bolts of Grade F10T (FR) for joining KSFR steels. Figure 2 shows the reduction factors for the tensile properties of the bolts at elevated temperatures. For comparison, the test results given by Sakumoto et al. (1993) on another kind of F10T (FR) bolts which was developed by Nippon Steel were included. It can be seen that the two batches of test results generally match very well, indicating the consistency in the quality of the bolt.

Figure 2 Strength Reduction Factors for Kawasaki Steel FR Bolts at Elevated Temperatures

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