Question

5. The figure shows a cast-iron bearing block that is to be bolted to a steel ceiling joist and is to support a gravity load of 18 kN. Bolts used are M24 ISO 8.8 with coarse threads. The joist flanges are 20 mm in thickness, and the dimension A is 20 mm. The modulus of elasticity of the block is 135 G Pa. Find the safe tensile shear load F that can be applied to this connection to provide a minimum factor of safety of 2 for the following failure modes: shear of bolts, bearing on bolts, bearing on members, and tension of members. Problem 5

Answer 1

Write the equation for initial bolt tension for permanent connection. Here, A, is the tensile stress area, and Sp is the proof strength. Obtain proof strength from the table 8-11, "Metric Mechanical-Property Classes for Steel Bolts, Screws, and Studs" and also obtain tensile stress area from the table 8-1, "Diameter and Areas of Coarse-Pitch and Fine-Pitch Metric Threads" in the textbook. A 353 mm2 S, 600 MPa Substitute 353 mm2 for A, and 600MPa for Sp F 0.9x353x 600 -190.62 kMN

Calculate the wrench torque required for permanent connection as follows: Here, K is the torque coefficient, and d is the nominal diameter. Obtain the torque factor from the table 8-15 in the textbook. K 0.18 Substitute 0.18 for K, 190.62 kN for F, and 24 mm for d. T_0.18x190.62x103 x24x10-3 -823 N m Therefore, the wrench torque requied i the tasteners are lubncated duing assembly and the joint is to be permanent is 823 N m