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| Influence factors and formula for dynamic stress reduction coefficient |
| WANG Ke，SUN Rui，YUAN Xiaoming |
(Institute of Engineering Mechanics，China Earthquake Administration，Key Laboratory of Earthquake Engineering and Engineering Vibration，Harbin，Heilongjiang 150080，China)
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Abstract The reduction coefficient of dynamic shear stress is the key in the methods of liquefaction evaluation. The reliable and easy method of calculating is very important for liquefaction evaluation and seismic response analysis. The influencing factors of were therefore studied based on the results of site response analysis to 508 records of seismic motion at 32 actual sites. The variation pattern of and the trends of shape parameter are uncovered. The necessary factors are selected and thus a new 3-parameter formula and a single-parameter formula of are proposed. The proposed formulas are compared with the existing formula. The results show that the depth is the most significant factor affecting ，the seismic magnitude and the shear wave velocity are the second significant factors which cannot be neglected，and PGA is the least significant factor. The curve follows the Logistic model，and is controlled by three shape parameters：asymptotic line，reference depth of influence and shape index. The proposed 3-parameter formula depends on d， and ，and the single-parameter formula depends on d. Both formula are applicable in the depth range of 0–50 m，and change continuously with depth，which overcome the disadvantages of existing formula in terms of splicing lines. The single-parameter formula is more accurate in comparing with the curve recommended by Seed and by NCEER. Comparing with the formula proposed by Cetin，the 3-parameter formula has the similar accuracy in the range of shallow depths，and has the higher accuracy in the range of deep depths. The new 3-parameter formula has a simpler form than Cetin curve and is more applicable for engineering applications.
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2018, Vol. 37 
