Abstract. In this paper the dynamic response of a complex double-string system traversed by extreme moving load is considered. The paper includes the study of a dynamic behavior of a finite, simply supported double-string flexible complex system subject to moving forces with a constant velocity on the top string. The strings are identical, parallel one upon the other and continuously coupled by a linear Winkler elastic element. The moving loads are around an extreme position of the shear wave velocity of the strings. The classical solution of the response of complex systems subjected to forces moving with a constant velocity has a form of an infinite series. But also it is possible to show that in the considered case part of the solution can be presented in a closed, analytical form instead of an infinite series. The presented method to search for a solution in a closed, analytical form is based on the observation that the solution of the system of partial differential equations in the form of an infinite series is also a solution of an appropriate system of ordinary differential equations. The closed solutions take different forms depending if the velocity of a moving force is smaller, equal or larger than the shear wave velocity of the strings. This follows from the fact that in string wave phenomena may occur. The solution for the dynamic response of the composite strings under moving force is important because it can be used also in order to find the solution for other types of moving loads. The double string connected in parallel by linear elastic elements can be studied as a theoretical model of composite system or prestressed structure in which coupling effects and transverse wave effects are taken into account.
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