A practical method of progressive collapse analysis of reinforced concrete flat-plate buildings using yield-line method is suggested. Methods for calculation of punching shear and evaluation of inelastic deformations are proposed and illustrated using a building example. The outlined procedure allows the designer to evaluate the resistance of flat-plate structures to progressive collapse, using tools already available in most design offices. The proposed method also allows the designer to clearly identify places where additional reinforcing will effectively increase building robustness, thereby reducing the total use of material and labor in field.

My company has recently negotiated a contract to provide design services for wind turbine foundations. The turbine manufacturer will provide the allowable soil pressure and forces at the tower base (including shear and overturning moment due to wind as well as dead load due to turbine and tower weight). I plan to size the footings using the service loads and an allowable soil pressure. For design of the reinforced concrete in the footing, should I factor the reactions or the loads? It makes a difference to the pressure distribution because under service loads, the footing is in full contact with the soil, but with factored loads, there is footing uplift.