Αριθμητική και πειραματική μελέτη της διεπιφάνειας χάλυβα - σκυροδέματος στις σύμμικτες πλάκες με χαλυβδόφυλλο μορφής

Abstract

Composite construction is becoming increasingly popular worldwide as a reliable alternative construction method, due to its many advantages such as high construction speed, limited timber shuttering and small steel sections. Composite construction is applicable to commercial, residential and industrial buildings as well as to factories and bridges. The analysis of composite structures is complex and can be classified into nonsmooth mechanics due to the existence of contact and frictional phenomena. In the case of composite slabs with profiled steel sheeting, the critical point of the analysis is the interaction between steel and concrete at the interface of the slab. The shear connection between concrete and profiled steel sheeting in composite slabs is a highly nonlinear problem concerning boundary conditions, material and geometry. In this dissertation the composite slab with trapezoidal steel sheeting is treated as a unilateral contact problem where sticking, sliding and frictional phenomena at the interface of the bodies are all present. The problem is approached mathematically, experimentally and computationally. For the mathematical approach of the problem, a novel mathematical theory based on hemivariational inequalities is proposed. The composite slab with profiled steel sheeting is classified as a unilateral contact problem, where the contact and noncontact regions between bodies or structures are not a priori known. These problems are described using nonmonotone material laws. In our case, the Signorini-Fichera conditions have been applied in the normal direction to the interface of the composite slab and a nonmonotone friction law has been implemented in the tangential direction to the steel-concrete interface. After the appropriate mathematical processing, a hemivariational inequality, describing the aforementioned problem, has been formulated. Further, a two dimensional numerical model, that simulates the physical problem, has been implemented using the MATLAB software package. For the experimental approach of the problem, a series of full-scale tests has been carried out. In order to investigate the shear connection between concrete and profiled steel sheeting, the composite slab specimens have been subjected to static and cyclic loads. The strength of the shear bond has been measured using the partial connection method and necessary experimental data. Load-deflection and load-slip 148 curves were also produced. The tests presented in the thesis have been carried out according to the rules and the restrictions of Eurocode 4. The experimental results have been processed by using the PSC method. The theoretical curve of the composite slab according to the Partial Shear Connection method has also been constructed. For the computational treatment of the problem, a three-dimensional finite element simulation of the composite slab is proposed. The numerical analysis is nonlinear and has been realized using the ANSYS software package. The interface has been simulated by the use of surface contact elements and the application of unilateral contact conditions. The developed friction forces at the steel sheet-concrete interface were also taken into consideration. A computational model of the composite slab with shear studs is also presented. The outcomes of every approach of the problem are presented and evaluated. The models and mathematical formulations presented in this thesis, combined with the Eurocodes, can be used as an effective tool for the design of composite slabs with profiled steel sheeting. The dissertation ends with four appendices. In the first of them the design rules of the composite slabs, according to Eurocode 4, are presented. In the second appendice some elements of convex and non convex analysis are given. The third appendice has the data of the model presented in chapter 4, whereas the last one contains photos and diagrams from the experimental analysis