Question

Problems 9.1 Compute the influence lines for the forces in the members AB, DI, IJ and CI of the truss shown in the figure. Live loads are transmitted to the top chord of the truss Is this a through- truss bridge or a deck truss bridge? Draw the influence lines in one page vertically aligned with the free-body diagram of the truss. Submit your computations in separate pages. 3 m 6 panels at 4 m-24 m

Answer 1

Live loads are transmitted to top chord of the truss. Hence, it is a deep type truss bridge. Member AB: This is a compression member opposite joint is H So, height of ILD = a(l - a)/lh (corresponding to joint H) = 4 times (24 - 4)/24 times 3 = 4 times 20/24 times 3 = 1.11 Member IJ: This is a tension member opposite joint is D So, height of ILD = a(l - a)/lh (corresponding to joint D) = 12 (24 - 12)/24 times 3 = 12 times 12/24 times 3 = 1 Member CI: Pass a section through member CD, CI & MI Let the unit load is anywhere on the top chord on the left side of joint C Then consider right portion of section Solving, we get F_ei = R_g (vertical reaction at G) \r\n ILD for reaction R_g is drawn on the ILD section page.