1. The problem statement, all variables and given/known data "Design a bridge over a valley 300m wide. Road surface is supported by a truss underneath." My problem: With calculations Now calculation for buckling says i need to design the truss for compression such that I > (P. L^2) / (pi^2 x E ) or Pcr > P where I = reduction value P = unfactored load L = length E= modulus pi = Pi. Pcr= Critical Load Now the information I'm given doesnt give me a value for I, just the rest. Not sure what I'm meant to do, just estimate a value and insert it in and do calculations from this or another method or if I'm meant to know the value fro plastic piping (?) - diameter (can work out effective area) - modulus - yield strength - length 2. Relevant equations Sum Fx= 0 Sum Fy= 0 Sum M(hinge) = 0 3. The attempt at a solution Not sure where to start, as it doesnt seem to be enough information?