The protection and use of historic buildings is a difficult and costly task. Most often, these objects are under conservatory protection and any interference in their structure requires appropriate consent. On the other hand, conducting construction works on historic buildings carries a high risk of their damage or even destruction. Therefore, proper prior diagnostics is an extremely important factor affecting the scope and manner of works to be conducted. The paper presents the use of 3D scanning to determine the deflection of the ceiling under the Column Hall of the historic Palace, the floor of which showed elasticity, recorded during changing service loads. After identifying the places with the greatest deflections, based on data from 3D laser scanning, test holes were made and wood samples from the ceiling were taken to perform moisture content and mycological tests. An endoscopic inspection camera was inserted into test holes, providing the basis for recognizing the structure of the ceiling, i.e. arrangement of layers as well as dimensions and spacing of ceiling beams. Strength calculations were made with the limit state method resulted in the determination of the maximum permissible service load on the ceiling. The presented course of action in diagnostics of the analysed historic building may be an example of a preliminary procedure to be taken before deciding on changes in the manner of use of historic buildings or the functionalities of their individual parts.

The non-linear analysis of hollow-core concrete slabs requires the use of advanced numerical techniques, proper constitutive models both for concrete and steel as well as particular computational skills. If prestressing, cracking, crack opening, material softening, etc. are also to be taken into account, then the computational task can far exceed the capabilities of an ordinary engineer. In order for the calculations to be carried out in a traditional design office, simplified calculation methods are needed. They should be based on the linear finite element (FE) method with a simple approach that takes into account material nonlinearities. In this paper the simplified analysis of hollow-core slabs based on the generalized nonlinear constitutive law is presented. In the proposed method a simple decomposition of the traditional iterative linear finite element analysis and the non-linear algebraic analysis of the plate cross-section is used. Through independent analysis of the plate cross-section in different deformation states, a degraded plate stiffness can be obtained, which allows for iterative update of displacements and rotations in the nodes of the FE model. Which in turn allows to update the deformation state and then correct translations and rotations in the nodes again. The results obtained from the full detailed 3D nonlinear FEM model and from the proposed approach are compared for different slab cross-sections. The obtained results from both models are consistent.