Influence of near‐field ground motions with fling‐step and forward‐directivity characteristics on seismic response of stilted buildings in mountainous area

SummaryNear‐field ground motions with fling‐step and forward‐directivity characteristics contain large‐amplitude pulses in velocity history, causing severe damage to stilted buildings in mountainous areas. In this study, three groups of 20 near‐field ground motions with fling‐step and forward‐directivity characteristics and 10 far‐field ground motions were selected as seismic inputs. Nonlinear response history analysis (NLRHA) was performed on plane finite element models of two seven‐story stilted frame structures, one with steel braces in the stilted story and the other without steel braces in the slope direction. Structural seismic response obtained from NLRHA was discussed in terms of inter‐story drift ratio (IDR) and peak floor acceleration (PFA). In addition, damage to two structures was assessed using the modified Park–Huang damage model. The results show that stilted structures exhibit greater inter‐story ratios and damage index values under near‐field ground motions with fling‐step characteristics and forward‐directivity characteristics than far‐field ground motions, where the stilted story has the highest amplification ratio in both IDR and damage index among floors. Designers should pay sufficient attention to the influence of ground motions with fling‐step and forward‐directivity characteristics on seismic demands and damage to stilted structures. The peak inter‐story ratio and damage index of stilted structures with steel braces were significantly lower than that of stilted structures without braces, proving the validation of setting steel braces on reducing the seismic demands of stilted structures and improving structural seismic safety. Additional NLRHA performed using artificial pulses shows that the seismic response of stilted buildings is related to pulse periods of near‐field ground motions and the greatest seismic demands and damage are obtained when the pulse period is 1.5–1.6 times the fundamental period of the stilted building.