Finite element analysis of prestressed concrete slabs under impact loading

Abstract

Many structures use prestressed concrete slabs as roof or floor elements. Such elements can be impacted by precast walls during construction work, and safety on construction sites carries utmost importance. For impact problems, the use of empirical formulae is often sufficient for a conservative structural dimensioning. However, if the task is to obtain an accurate computational response that matches experimentally observed results, then empirical formulae and even most off-the-shelf material models readily available in commercial finite element methods software fail to produce consistently satisfactory results. This study conducts a finite element analysis on the effects of collisions between prestressed concrete slabs and precast wall elements to take precautionary measures for such events.

This thesis adopted the Enhanced Concrete Damage Plasticity model to accurately capture the dynamic response of concrete in Abaqus/Explicit used for the three-dimensional finite element modeling. The material model requires user-defined features, including user-defined subroutines. The study involved a sensitivity analysis with respect to internal concrete model parameters to obtain a set of values that can be used universally in any hard missile impact simulation on concrete. The finite element models with the chosen set of parameters are validated with the experimental data provided by VTT in Finland. The validation involved the comparison of the impactor’s residual velocities and the ultimate capacities of the struck slab, which yielded a good overall agreement.

The developed models were used to investigate 15 concrete-to-concrete collision scenarios on 200 and 300 mm prestressed concrete slabs hit by precast walls. The scenarios included impact velocities of 10.85 and 18.80 m/s with impactor masses of 3, 5, and 10 t and two different angles of strikes. The finite element study showed that the construction work under the slabs must be halted during the installation of precast wall elements in these conditions.