Influence of contact layers on cracking resistance of bending three-layer structures

Introduction. In the present-day construction practice, multilayer building envelopes are applied; their layers are made of concretes having different physical and mechanical characteristics. When different concretes are poured in successive layers, contact layers are formed; their physical and mechanical properties are unlike those of the adjacent layers. The strength and stress-strain characteristics of the contact layers can affect the behaviour of a multilayer structure. Materials and methods. Numerical and experimental methods are applied to study the stress-train state of such structures exposed to loading. Bending three-layer structural models, having external layers made of strong structural concrete and the middle layer made of low-strength concrete, were applied in the research project. A contact layer is formed in the process of their manufacturing; its geometrical, strength and stress-strain characteristics are simulated in the process of numerical studies. Results. The co-authors have identified the effects produced by geometrical, strength and stress-strain characteristics of contact layers on the analysis of bending multilayer structures. Design models and a novel method of analysis have been developed for bending multilayer reinforced concrete structures with account taken of the influence of geometrical, strength and stress-strain characteristics of the contact layer. According to the results of numerical calculations, differences between cracking moments can reach 4.3 % or more for three-layer reinforced concrete beams. As for the practical calculations, if the thickness of the contact layer is below 0.4 cm, one can ignore the influence produced by the contact layer on the calculation result. Conclusions. The results of the research help to identify the rational parameters for the design of multilayer enclosing structures having varying strength reinforced concrete layers interconnected by the monolithic contact layer.