Seismic retrofitting of six storied RC frame structure designed for gravity load only

Abstract

The occurrence of earthquakes is part of the natural process in the earth's geophysical system. It is not possible to stop such natural events and it should not be intervened such internal system of the earth. Rather it is better to put up this event and develop technology to live with this unpleasant incident. Locating the epicenters and examining the characteristics of each shock, it may improve the understanding considerably and lead to develop some preventive measures to live with earthquakes. Many buildings in Bangladesh were not designed and constructed properly which is really vulnerable to earthquake. It can be strengthened by designing and retrofitting properly that can save a lot of lives and properties. To scrutinize the changes in seismic retrofitting for variation of spans is one of the most important objectives of this study. As a result, the findings and methodology of this research will be the guidelines regarding costing and procedure of seismic retrofitting. Nine numbers of buildings having different area and/or aspect ratio have been selected to achieve the aims of this study. All the buildings have been designed for gravity loads and detail drawings and estimates have been done. The evaluation for degree of seismic deficiency of all buildings has been performed. As per deficiencies, the design and detail drawings for seismic retrofitting have been done for the buildings. Use of RC jacketing for retrofitting the beams and column of a building is a well established technique. Many buildings all over the world have been strengthened using this method. Even though, the magnitude of experimental and analytical investigation conducted on this method is fewer. It can be effectively used to increase stiffness, strength and ductility of existing members. RC jacketing of columns has one major advantage that increasing in lateral load resisting capacity of the building is distributed throughout the structure and therefore the new foundation or significant strengthening of existing foundation may be avoided. The quantities of materials for retrofitting works of every building have been estimated separately. The cost of seismic retrofitting on the basis of unit area exclusive of form work, propping, chipping, dismantling etc. as per PWD schedule of rates has been calculated. Finally various contour graphs have been drawn to explain the findings. Seismic retrofitting by RC jacketing is efficient but needs very high level of intervention in building causing hindrance to its functionality during retrofitting period. In addition to the problem of intervention, application of this method to joints as well as to achieve monolithic behavior of new material with the existing material is difficult task. However, to determine the performance of this technique both experimental as well as analytical verifications in conjunction with construction practice of Bangladesh are needed. As per findings it can be described for the six storied RC frame structures that the amount of excess concrete required to retrofit shall be approximately 54% of concrete required for gravity load design and the amount of excess rebar required to retrofit shall be approximately 37% of rebar required for gravity load design. On the other hand the average cost required for seismic retrofitting of six storied gravity load design RC frame structures exclusive of form work, propping, chipping, dismantling etc. shall be Tk.78.00 per sft.