Question

1- For the Pratt type bridge reinforcement and the load shown in the figure. 1. Determine the average normal stress on the BE element, knowing that the element's cross-sectional area is 350 mm².

Make the free body diagram and explain step by step.

B D 4 m A C E --3---3-- -3m- -3 m 360 kN 360 KN 360 KN Fig. 1

Answer 1

solution : (0) B D f o 04m A the C E G OH TT HA Y 360KN 0 360 360kn V 360KN VA lun — Эт—Ж— Зm-3-Ж— Зm 7 Step I calculate Support Reactions By applying equilibrium conditions TVA 360 360 -360 + VH = 0 VA + VH = 1080 EMA=0 Sum of moments at point A (360x3) + (360x6) + (360x9) - 12VH = 0 VH = 540 KN & VA = 540 kN

step 2 i Applying method of sections cut the truss - at section - FBP B. FED 10 FB2 D FBE orn BE A For 360KN LE 540 KN H all 360kW 360kW 1540kn Lef side of section 0-0 Right side HA=0KN Because No Horizontal force is actiong on a Truss

step 3 : Applying equilibrium conditions left side of section 0-0 to o = tant 4 "G (5) 53,13 FBD 53.13 F BECOso FBET sino FBE FCE 540KN 360kn iii EVS Sum of Vertical forces iz +540 FBE sino - 360 = 0 540 - 360 FBE sino

180 - FBE sin 53.13 FBE = 225 KN Tension * Average Normal stress in stress in member BE force in member BE Garg Cross sectional area = FBE 225 x 10 3 = A 350 [ Janar ] se = 642.857 MPa Ans.