FEATURES OF DETERMINATION OF THE DYNAMIC AMPLIFICATION FACTOR UNDER IMPULSE LOADS

It is accepted to lead non-stationary loads to equivalent static loads in practice of construction design. Different methodologies are used to calculate the effects of dynamic impact on building structures. This article describes evaluation methodology of dynamic amplification factor under impact loads, arising in case of explosions, falling of massive bodies, hydraulic impact. To calculate the dynamic amplification factor it was determined frequency of fundamental tone of natural oscillation. A shortcoming of described evaluation method of dynamic amplification factor under impact loads is the assumption that oscillation process of each element happens at a certain frequency (usually at the fundamental tone frequency); though in fact oscillations happen in all range of natural frequencies of elastic element. Besides, any boundary conditions for this methodology can be set with certain approximations. Nevertheless structural analysis of building constructions in conditions of emergency situation, when the maximum possible loadings have been taken as initial data, such approach in determination of Kdyn is justified in a certain degree. The integrating equations for different types of loads and various ratios between load duration and natural oscillation period has allowed to determine values of dynamic amplification factor for such ratios at five types of loads. It have been shown that temporality of loading influences dynamic amplification factor only at certain ratios between load duration and natural oscillation period. This fact can be attributed to a sufficiently long (in ratio to the natural oscillation period), but not to impulse loads. Values of dynamic amplification factor for various ratios between load duration and natural oscillation period under the impact forces and under the growth phase load were given. The type of load have not affect numerical values of dynamic amplification factor for the presented ratios. The main influence on dynamic amplification factor is the pressure pulse.