Figure 1 shows a water tank which includes a gate ABC which holds water from the tank.The gate is 3m wide (into the page) and is pin supported (hinged) at

point A. The strut BDE supports the gate and prevents its rotation about a pin at A under the pressure of the water. The strut is pinned at both ends for buckling about X and Y axes and laterally restrained at its mid-length (point D) in X-direction only (this influences buckling about theY-Y axis). The strut BDE is made from steel rectangular hollow section (RHS) of E =200,000 MPa, Oy = 350 MPa. Using the attached table (Figure 2) determine the smallest RHS section size for the strut BDE that will prevent the strut from failing and releasing the water. Which mode of failure (squashing, buckling about X or buckling about Y) governs the axial compressive capacity of the strut BDE? Support your answer with appropriate calculations and description. Neglect the self-weight of the gate.

Fig: 1

Fig: 2

Fig: 3