Torsional effect will occur in pile-supported wharves under bi-directional horizontal ground motions.The Chinese code for wharf seismic design does not provide specified provision for that phenomenon.Nevertheless,in domestic code for seismic design of buildings and foreign wharf codes,similar problem is addressed by combining the effects of action in two principal horizontal directions of the structure under single directional ground motion.To verify applicability and accuracy of the combination rules from aforementioned codes in pile-supported wharves,30 pairs of horizontal ground motion records are selected to conduct time history analyses and modal response spectrum analyses for different wharves.The internal forces of pile determined by spectrum analyses were combined in accordance with rules in codes,and the internal force ratios of combined values and forces from time history analyses are calculated.Then statistical analysis is conducted on the internal force ratios,and the formula of correction coefficient for internal forces is proposed by the regression analysis of average values for force ratios.The results show that:1)The internal forces of pile under bi-directional ground motions are much larger than those of single ground motion.Thus,the seismic analysis of wharf should consider the effect of bi-directional motions.2)The correlation between the internal forces determined by the square root of the sum of the squares(SRSS)rule in the Chinese building code and the time history method is better than that of the combination rule in foreign wharf design code.The internal force ratio determined by the combination rule in Chinese code obeys lognormal distribution and its average values approach the value of one,with a smaller dispersion of force ratio.Consequently,SRSS rule is recommended for seismic analysis of wharves under bi-directional ground motions.3)For long-term pier structures,the combination method may underestimate the seismic response,and the proposed formula should be used to correct the internal forces of the pile foundation.