Question

Please help me answer part B.....i couldnt answer it.

A tunnel of length L - 180 m, height 9.4 m, and width 6.1 m (with a flat roof) is to be constructed at distance d - 62 m beneath the ground. (See the figure.) The tunnel roof is to be supported entirely by square steel columns, each with a cross-sectional area of 1180 cm. The mass of 1.0 cm of the ground material is 2.4 g (a) What is the total weight of the ground material the columns must support? (b) How many columns are needed to keep the compressive stress on each column at one- half its ultimate strength? To all emergency services workers, thank you Units IN (a) Number 11.682 (b) Number Units No units

Answer 1

weight = 2400 x 68076 x 9.8 = 163382400 X9,8 = 1.6 xlop n or 160l 47520N # 6 let a numbers of pillars / square steel Colums are requered. Area = nx C. S Area of 2 Column 6 - Force I Area= nx 1180 x 10-4 m² area 6 = Lem² = 10-4 m2 1601147520 nx 1180 x 10-4 Also i 6= 4 x Ultimate strength of steel - 2 x 420 MPa 6 = 2 x 420 x 106 N SPA = IN m2 m2 210 1 920 x 106 = 1601147520 nx 1180 X 104 n = 160ll 47520 210 x 108 x 1180 x 204 n = 64.64 so i Approx 65 pillars are required.