RETROFIT OF A NONDUCTILE REINFORCED CONCRETE BUILDING WITH UNBONDED BRACES
M. Arif Bozaba
(Thesis Supervisor: M. Nuray Aydınoğlu)
The main objective of this study is to retrofit a nonductile reinforced concrete building with unbonded braces ( Buckling restrained braced frames ). For this purpose, a typical eightstorey reinforced concrete building - designed according to the Turkish Earthquake Code 1975 (TEC-75) - has been evaluated. The seismic performance of the model has been investigated using nonlinear static analyses. As a result of the analysis, it is seen that the column and beam strains exceed the limits, so the building need to be retrofitted. The basic principle in the construction of unbonded brace is to prevent buckling of a central steel core by encasing it over its length in a steel tube filled with concrete or mortar. In the first model, namely reinforced concrete building with UB-I, response spectrum analysis was conducted and brace sections are determined. After obtaining brace sections, pushover analysis was performed using SAP2000 structural analysis computer program. In the second model, namely reinforced concrete building with UB-11, all loads are assumed to be carried by unbonded braces and unbonded brace sections are determined. After obtaining brace sections, pushover analysis was performed . As a result of the analysis, it is seen that when the building is retrofitted with the unbonded braces-I, the strains become smaller but they exceed the limits. In case of the building is retrofitted with unbonded-11, because of the big axial forces only the strains of columns at ground floor exceed the limits. For the solution the columns at ground floor should be retrofitted. In case of the building is retrofitted with the unbonded braces-I , the retrofitting cost is 680.000 $, it is retrofitted with unbonded brace-11, the retrofitting cost is 799.000$.