Analysis of Foundation Slab of Commercial Building in Prague Těšnov

The use of foundation slabs for large structures is relatively common case. Foundation slabs are significantly thick in such cases and a problem with casting arises due to hydration heat generation. Apposite numerical models have to be used for the validation of the casting procedure. One of the possible numerical models was implemented in the SIFEL code.

The casting procedure of the foundation slab can be solved as a coupled thermo-hydro-mechanical problem in this software. The KŁnzel and Kiessl-FĘs models are available for the simulation of the heat and moisture transport processes. The BazantĘs B3 model -A can be used for the description of concrete creep and shrinkage, damage can be modelled by the scalar isotropic damage model. The subsoil under the foundation slabs was modelled by the system of spring supports as a result of the complexity of the computation process. The stiffness of the springs can evolve nonlinearly depending on the settlement of the foundation slab.

Several important modifications of the SIFEL code were performed on the basis of experiences from the previous analyses performed in 2006. These modifications improved the simulation of the real process of the casting procedure. First of all, the code was extended by the implementation of the gradual construction process using time controlled switching on/off of particular degrees of freedom and elements. In addition, it was implemented and successfully used numerical solution of the B3 model using a continuous retardation spectrum method. A new solver of time dependent problems was implemented and used. The solver contains the Newton-Raphson iteration method which significantly improved results.

A scalar damage model was modified to respect the time variability of Young modulus and tensile strength and correction of dissipated energy depending on the size of element was implemented. Advanced models of anisotropic damage were theoretically derived and partially implemented. The methods were used for the two-dimensional model of a cranked foundation slab which was cast in three layers. The behaviour was solved as a coupled problem in which the mechanical behaviour was assumed together with heat and moisture conduction and their interactions. Material parameters were obtained from the project of a foundation slab of commercial building in Prague-Těšnov.

The resulting deformed shape of lower slab step.