Budapest University of Technology and EconomicsFaculty of Civil Engineering - Since 1782

Currently in Hungary there is a significant shortage of labour in the construction industry which requires the application of less labour-intensive structural solutions. One of the possible solutions for this problem is the comprehensive use of concrete prefabrication. It means the application of new materials, like HSC, HPC or FRC for structural members, and it eventuates better concrete quality, larger precision and more durability, as well as faster construction. The application of prefabricated prestressed formwork panels together with in-situ concrete layer became a typical solution for concrete floors. Design and analysis of such floors is usually done by simple analytical calculations and/or linear elastic finite element analysis, which necessarily leads to suboptimal designs.

 

The aim of the research is to study the behavior such floor systems, using analytical and sophisticated 3D numerical modelling methods. The analyses should consider the applied constructions method, the long term behavior of materials, the cooperation of prefabricated and in-situ concrete layers casted at different times. The force transfer mechanisms on the contact surface of different concrete layers, and the role of shear reinforcement in this cooperation must also be studied. The effect of previous phenomena on the behavior, load bearing capacity and especially the deformation of floor slab systems made of formwork panels must be determined. Based on the results recommendations should be made concerning optimal floor configuration and the improvement of existing analytical calculation methods.

 

The candidate must solve the following tasks:

Literature review: (i) buildings, and especially floor slabs made from prefabricated concrete elements, solutions, element types, connections and constructions methods; (ii) materials available for prefabricated concrete construction, material properties including time-dependent behavior; (iii) force transfer between concrete layers casted at different times; (iv) design methods, appropriate analytical calculation and numerical modelling methods for prestressed concrete structures; (v) test results and practical experiences.

Analysis of simply supported and double span floor systems made of prefabricated prestressed concrete formwork panels, considering the applied construction method (with or without temporary support) and time dependent material behaviour regarding concrete layers casted at different times: (i) analytical calculation and verification of floor systems in ULS and SLS according to EC2 standard (ii) development of a numerical model for the floor system in question, using an appropriate FE software suitable for the consideration of internal steel reinforcement and prestressing tendons including they anchorage mechanism, time dependent material behavior, while force transfer between concrete layers casted at different times should be taken into account by developing a suitable contact element for the numerical model; (iii) verification of the numerical model by test results (it is expected that test results will be available at the time of research, but depending on the timing, test could be done with the participation of the candidate); (iv) time dependent numerical simulation of different floor configurations considering long term effects like shrinkage and creep of concrete and relaxation of prestressing tendons, determination of structural behavior (internal forces, stresses, cracks, deflections), analysis of failure modes.

Evaluation of the results of analytical calculation and numerical simulation, sensitivity analysis of the main parameters influencing the load bearing capacity and deflection of the floor, explanation of structural behavior. Based on the results recommendations should be given for a more optimal structural configuration and construction of the floor systems in question, as well as for the possible improvement of existing analytical calculation methods used in practice.