Keywords: eccentric steel bracing, masonry infills, seismic retrofitting, numerical models.

The seismic performance of a non-ductile reinforced concrete (RC) frame with and without masonry infill panels and the assessment of a retrofitting intervention using eccentric steel bracing were investigated using numerical analyses. The main objectives of this study were: (a) the development and calibration of numerical models capable of predicting the seismic response of RC frames designed only for gravity loads; (b) the evaluation of the masonry infill effects on the global structural response; (c) the assessment of the effectiveness of a retrofitting solution for masonry infilled RC frames based on the replacement of infill panels by eccentric steel bracing with vertical shear links. The numerical models developed were calibrated with the results of the experimental tests carried out on RC structures at the JRC ELSA laboratory [1], and satisfactory agreement was obtained. The effect of distributing the steel bracing retrofitting system over the height of the RC frame on the seismic performance of the structure was investigated. The retrofitting intervention carried out on all the storeys of the frame was not experimentally verified but just numerical simulations were carried out. Non-linear dynamic analyses with increasing earthquake intensities were performed on the retrofitted model. The retrofitting system reduced the top displacement with respect to the infilled frame for high values of the acceleration intensity level. The infilled frame became highly vulnerable, showing significant damage and the development of a soft storey mechanism at the first floor. The response of the infilled frame showed a high sensitivity to increases in the acceleration intensity level. The brittleness of the infilled structure after reaching the maximum strength was observed. The infilled structure did not show the necessary ductility and energy dissipation capacity for high values of the acceleration intensity level. The analyses pointed out a clear soft-storey mechanism with demands strongly concentrated in the first storey which was not capable of developing further strength. A significant characteristic of the eccentric bracing system was the effective energy dissipating property of the shear link. A significant and regular increase in the energy dissipation capacity was observed with the increase of the peak acceleration. The shear-strain hardening of the web of the shear link resulted in an increase of the lateral resistance allowing the shear links to compensate for the progressive failure and loss of resistance of the infilled panels. The numerical results showed that the stiffening effect provided by the masonry walls was kept while their low ductility was compensated by the energy dissipation capacity of the shear link.

1

A. Pinto, G. Verzeletti, J. Molina, H. Varum, R. Pinho, E. Coelho, "Pseudo-dynamic tests on non-seismic resisting RC frames (bare and selective retrofit Frames)", Joint Research Centre, Ispra, 2002.

purchase the full-text of this paper (price £20)

go to the previous paper
go to the next paper
return to the table of contents
return to the book description
purchase this book (price £130 +P&P)