Failure load and collapse mode of an RC beam in a large collapsed roof

The present work focused on the determination of the collapse load and of the failure mode of a collapsed framed structure constructed in the South of Italy and failed in 2004 under its self-weight. Information available was the results on extensive experimental test campaign, for the determination of mechanical properties of concrete and steel bars of beams, floors and columns involved in the failure. Moreover, draws of original design with construction details and design rules valid in Italy at the time of construction were found. A simple monodimensional beam model for prediction of load-deflection curve, able to include degradation of constituent materials (concrete, steel and bond) was developed. Ultimate load predicted analytically at the time of the failure was very closed to that estimated on the structures at the time of collapse and due to the self-weight justifying the failure of building. Results obtained highlighted that concrete degradation phenomena were the main causes of collapse. In addition, numerical analyses with Response (2000) and ATENA 3D (2004) were carried out to predict ultimate load, failure mode and crack patterns at failure. Results obtained numerically showed good agreement with available experimental data and with proposed one-dimensional model. Comparison between simplified analytical and numerical responses showed that although the use of refined nonlinear finite element models give much more detailed information with respect to the one-dimensional model, but the latter can be very useful for preliminary check of the structures