Effect of Infills on the Global Behaviour of R/C Frames. Energy Considerations from Pseudodynamic Tests

A series of pseudo-dynamic tests were conducted on a full-scale four-storey reinforced concrete building designed according to Eurocodes 2 and 8. The building was 10 m long, 10 m wide, and 12⋅5 m high. It was designed as a ductility class ‘High’ structure, for typical live loads and for a peak ground acceleration of 0⋅3 g and medium soil conditions. A first test was conducted on the bare frame. The project was carried out within the framework of the European Association of Structural Mechanics Laboratories (EASML), and was designed to assess the adequacy of the damage indicators to be used in the calibration of Eurocode 8. The pseudodynamic test was conducted by using an artificially generated earth-quake derived from a real earthquake (Friuli, 1976), with nominal acceleration 50 per cent larger than the value adopted in design. The structure performed as expected. The pattern of the measured rotations was that of a weak-beam, strong-column mechanism. The fundamental frequency of the structure after the test was found to be half of the initial value, but the damage was limited and uniformly distributed. A second experimental programme was conducted as part of the work of the Network Prenormative Research in support of Eurocode 8, to study the influence of masonry infill panels on the global behaviour of the frame. Two pseudodynamic tests were conducted, with different infill patterns. A test was performed by infilling the two external frames with hollow brick masonry in all four storeys (uniform infill distribution). The test was then repeated on the structure without infills at the first storey, to create a soft-storey effect. The input signal was the same as in the tests on the bare frame. The purpose of the tests was to study the effects of the different layouts of infills, as well as to calibrate the computer models for the infills to be used in parametric analyses. In this paper the test results are presented and the performances of the structure with different infill configurations are compared. The global behaviour of the structure is compared with the predictions which could have been made with simplified approaches. In particular, single degree of freedom energy concepts are used to verify if the differences in the global behaviour could have been predicted. The differences in the single degree of freedom energy demands with respect to the bare frame may be used as a means of accounting for the presence of irregular distributions of non-structural infills in the simplified design of the frame.