Highlights

Abstract

Keywords

۱٫ Introduction

۲٫ Numerical analysis models for the existing members and a column retrofitted by wing walls

۳٫ Optimal seismic retrofit method using wing walls

۴٫ Applications to seismic retrofit

۵٫ Conclusion

Acknowledgments

Appendix A.

Appendix B.

References

Abstract

Seismic retrofit of reinforced concrete (RC) columns using wing walls can be used to improve the shear and flexural strength of the column through a relatively simple process. However, the feasibility and efficiency of the seismic retrofitting of RC frames with wing walls heavily depends on the selection of number of columns to be retrofitted, the cross-sectional dimensions of wing walls, and the quantity of re-bars of the wing wall. In this study, an optimal seismic retrofit design method is proposed to minimize not only the initial retrofit cost but also the earthquake-induced damage expected during the life cycle of the building. The seismic performance of structures before and after the application of the retrofit has been verified with the comparison of four response parameters: pushover curves, the inter-storey drift ratios, the energy dissipation capacities, and failure modes. The proposed retrofit method is applied to seismic retrofit of a six-storey RC building example and an actual RC building structure in use. For the retrofit of actual building structure, with an initial retrofit weight of 70.85 kN, which corresponds to 1.85% of the weight of the non-retrofitted building, the energy dissipation capacity was increase by 3.02 times and the life cycle cost (LCC) of the retrofit was reduced to 69.47% of the required LCC for the non-retrofitted building. In addition, it has been confirmed that no storey collapse occurred in collapse prevention level, which indicates the most severe failure mechanism of a structure due to an earthquake.

۱٫ Introduction

During and prior to the 1980 s, when the concept of seismic design had not yet been established in developing countries, buildings were designed without consideration of seismic performance. Accordingly, those buildings tended to suddenly collapse under an external force, such from an earthquake, due to displacement capacity not being considered [1]. In particular, the sudden failure of columns, which are structural members bearing vertical loads, leads to failure to support building weight. This causes the collapse of the entire building and enormous human and structural damages [2–۴]. To prevent such damage, various seismic retrofit studies have been conducted on old buildings that have not been seismically retrofitted, and the number of seismically retrofitted buildings is therefore on the rise [5–۱۰].

Seismic retrofit methods, which are practically applicable to the improvement of the seismic performance of existing buildings, can be classified as either strength and stiffness retrofit methods or ductility retrofit methods. Seismic retrofitting of building structures with steel bracings and bearing walls is a representative strength and stiffness retrofit method. Although this method can sufficiently improve seismic performance, a building may still have brittle behavior, which can result in sudden failure [11–۱۳]. On the other hand, ductility retrofit using carbon fiber jackets or steel jackets has a confinement effect on structural members, which partially improves strength and significantly enhances ductility capacity. However, the number of structural members to be retrofitted must be increased, which increases both the working duration and retrofit cost [14–۱۷]. For this reason, many studies have attempted to find the most appropriate retrofit method that can increase strength and ductility capacity satisfactorily