in construction mechanics the design of a supporting structure that is formed by a combination of systems differing in how they function under a load.
In a combined system, one of the structural elements is usually designed to work basically under tension-compression conditions and the other for flexure or lateral force. A braced system (arch or suspension system) is most often combined with an unbraced one (girder or beam). The merits of the one system compensate for the shortcomings of the other. For example, girder systems, which have considerable rigidity, can be combined with suspension systems, which have great supporting power, to create light and economical combined systems for long bridge spans.
Combined systems can be made from a single or from different materials (for example, a reinforced-concrete girder and a steel chain with suspenders for support), in the form of flat or spatial systems, and as statically determinable or indeterminable systems. The essential consideration in calculations of the combined system is the choice of the dimensions of its elements, so that the combination will achieve maximum effectiveness.
L. V. KASAB’IAN