Selection of the rational height of the steel roof trusses taking into account the effect of the impulse load

The objective function of the aggregate steel consumption for the steel truss of the roof with a cross-lattice is described, taking into account the dynamic coefficient and the time of action of the concentrated impulse in the middle of the span of the structure. The objective function of the steel consumption describes the nonlinear patterns of the influence of the impulse load on the aggregate steel consumption for the steel trusses. The numerical research effects of the pulse action time on the selection of the rational height of the steel trusses with a cross-lattice with a span of 15.0 m and 18.0 m are carried out. It is established that when the dynamic coefficient for the bending moment is less than 1.0, a tendency to reduce the rational height of the steel truss of the covering is revealed relative to the constructive solution in the absence of an impulse load or a short time of its action. When the pulse load action time is increased to a value relative to the natural oscillation period τ1 /Тtr,1 > 0.2, the dynamic coefficient increases quite rapidly, which leads to an increase in the rational height of the steel truss structure of the roof with a cross-lattice. It is confirmed that a decrease in the pulse action time can result in a decrease in the values of the dynamic coefficient for deflection and bending moment, and the values of these quantities can be less than unity. It is also confirmed that an increase in the pulse action time to half the natural oscillation period (τ1 /Тtr,1 = 0.5) gives an approximation of the dynamic coefficient of the impulse for deflections to the value of the impact load kdin,η,2→2.0. The described patterns are related to two other patterns of influence on steel consumption. An increase in the overall bending stiffness of the structure leads to an increase in the dynamic coefficient, and accordingly to an increase in steel consumption for the structure, on the other hand, an increase in the height of the structure reduces steel consumption due to a decrease in steel consumption for the roof truss belts. Thus, taking into account two opposing trends leads to finding a rational height of the steel roof truss. The dynamic coefficient is also affected by the duration of the impulse and the ratio of the quasi-static load from the impulse to the self-weight of the protective enclosing structures.