Seismic assessment and strengthening of existing old, under-designed buildings for seismic forces is a subject that has received a lot of attention from civil engineers and researchers in many areas of high seismicity around the world. Existing buildings with various strengthening systems have quite different seismic performances from one to another. A summary of the damage and retrofitting of an unreinforced masonry structure in Hanwang town which suffered slight damage during Wenchuan Earthquake was presented, and the role of the strengthening system was evaluated. A seismic retrofitting building which had excellent performance during 1985 Mexico Earthquake was also assessed. Numerical simulation on seismic retrofitting performance of one building located in Dujiangyan was conducted based on ANSYS. Comparison of analysis results and the two case buildings shows that: seismic assessment of existing building is crucial to choose the retrofitting system; global seismic performance of one building should be optimized after being retrofitted and not but simple repair; less increase of the weight of one retrofitted building is an important factor in success of retrofit solution; some retrofitting solutions may lead to higher increase in weight which would lead to reduce the efficiency of the stiffening, and lead to higher seismic roads; and large earthquake force may be developed due to retrofitting systems.
