Markus SUMMER
Comparison of seismic design procedures for a reinforced concrete frame (in German)
In engineering practice, force-based design procedures have been used in recent decades due to the low calculation effort. The response spectrum method is the standard method for predicting the structural response. The internal forces obtained are compared with component resistance. Thus, this design strategy is referred to as force-based. The basis of this linear elastic structural analysis is the so-called behavior coefficient q which is used to estimate any inelastic deformation capacity as well as the overstrength in advance according to the standard. The value of q can be selected by the engineer within a relatively large range suggested by the standard.
Modern earthquake engineering proposes the use of deformation-based design procedures. The structural response is obtained by non-linear static or dynamic analysis methods. In the design procedures, the calculated non-linear deformations or rotations are compared to the corresponding capacities depending on the component. This type of design is referred to as deformation-based and fully utilizes the non-linear load reserves.
The basis of this master thesis is a reinforced concrete frame structure, asymmetrical in ground plan and vertical section, designed according to the modal response spectrum method based on a 3D-model by the engineering office BHM-Ingenieure. The proof of the earthquake resistance is carried out on a selected cross frame by means of a non-linear static and a non-linear response history analysis. The adequate representation of geometric nonlinearity, appropriate modelling of damping and the effects of mass distribution are discussed. The results of the nonlinear analysis are compared with the results of the modal response spectrum method. It can be shown that requirements of over-dimensioning and the fact that the earthquake load case was not decisive for the design of some nodes lead to bending moments in the response history analysis that are many times higher than the design moments of the reference project. Subsequently, the static capacity is compared with the dynamic capacity of the structure and the overstrength is estimated by a non-linear static analysis. In addition, for the frame structure as well as for a single column, the influence of cyclical deterioration on collapse capacity is studied. This leads to the conclusion that for the structures under consideration the effects of cyclical deterioration are small and that not all deteroriation mechanisms are equally important for overall deterioration.