Numerical simulation with fibre beam-column models of thin RC column behaviour under cyclic tension-compression

Rosso, Angelica Saraiva Esteves Pacheco De Almeida, João [UCL] Beyer, Katrin

(fre) Damage to structural walls in the recent earthquakes in Chile (2010) and New Zealand (2011) demonstrated that modern reinforced concrete (RC) wall behaviour can be largely governed by out-of-plane displacements triggered by instability. Thin walls are the most vulnerable to this deformation mechanism, especially if they have a single layer of reinforcement. These wall types can be easily found in some Latin American countries such as Colombia, with minimum thicknesses as low as 8 cm. Relatively little is known about the response of these members, mainly due to the lack of experimental testing and numerical simulations. The out-of-plane buckling of RC walls is often studied by idealizing the boundary element—which represents the part of the wall mainly involved in the instability mechanism—as an equivalent column axially loaded in tension and compression. This is also the approach followed in the present paper. Further, past experimental campaigns identified the magnitude of the maximum applied tensile strain prior to subsequent loading in compression as the key parameter that triggers the out-ofplane instability. In order to study the effect of this and other variables—e.g., loading history, thickness, and reinforcement ratio—on the out-of-plane response, efficient modelling techniques are required. Such a numerical simulation is challenging because of the need to account for a complex interaction between nonlinear geometric and material effects. The present study illustrates the application of a beam-column model to simulate the out-of-plane response of equivalent columns, representative of the boundary elements of a wall as mentioned above. In the present work, the response of the beam-column model is first described and discussed in detail. Secondly, the simulation accuracy is assessed by comparison against experimental results from a campaign on equivalent RC columns with a single vertical reinforcement layer that is ongoing at École Polytechnique Fédérale de Lausanne. The results show that the numerical model provides a good estimate, although slightly non-conservative, of the maximum out-of-plane displacement attained and of the maximum tensile strain that causes out-of-plane failure. Finally, the model is used to simulate the out-of-plane response of the boundary element of a thin wall with a single layer of reinforcement tested in the past. This work shows that such a numerical model is a relatively simple tool yet reliable for assessing the vulnerability of thin RC walls to out-of-plane instability.