Non-Destructive Determination of Serviceability and Load Bearing Capacity of Floor Slabs Using Dynamic Methods

Abstract : Due to dwindling resources and the aging of the building infrastructure, many future activities in civil engineering will focus on building conversions and refurbishments. The key prerequisite in this case is the verification of the serviceability and the load bearing capacity towards the certification authorities. In most of the practical cases the current loading status, the internal stresses and deformation under static loads are unknown. As a result, the immanent load reserves canÕt be exploited, which often leads to a very conservative approach or even to demolition. Refurbishing of existing slabs means dealing with many uncertainties. Material properties like densities or elasticity modules as well as geometries or boundary conditions are often unknown. For this reason thereÕs a strong need to make efficient use of all information derived from measurements under static and dynamic test loads. In this context, in the field of modal analysis especially output-only methods utilizing only response measurements have proved particularly powerful. The big advantage is that the exciting forces need not to be measured. As a consequence high demands on signal analysis and the subsequent system identification are made. This paper describes a procedure to automatically update a numerical model by means of a prior identification of modal parameters with the Frequency Domain Decomposition (FDD). The modal parameters are used to calibrate the numerical model, which uses a-priori information on the construction. The updated model is subsequently capable to describe the dynamic behavior of the slab within the considered frequency range. The different steps of the methodology are shown using the example of a wooden beam ceiling.