抄録
The formula of ultimate shear strength of headed stud is shown in the design recomendations in Japan. However, the shear strength based on the design formula is not corresponded to the ultimate shear strength obtained by the push-out tests if both the specified design strength of concrete and the Young's modulus are large. In previous studies, some calculation method of ultimate shear strength of headed stud have been considered, but these methods are completely changed from the design formula. Considering structural design, the formula of ultimate shear strength should be simple and easy to use.
This study proposed the new method of the ultimate shear strength of headed stud by multiplying simply modified coefficient to the design formula. In the first step, the database of ultimate shear strength and some elements affected the strength are organized. In the database, basic correlations of main elements are considered. The elements of sca, Ec, and Fc which are already used in design formula have large variabilities, but the average values of them are able to use the representative value. The ratio length to diameter (L/d) and the tension strength of headed stud (Fu) also have large variabilities. As the tensile strength of stud material determined by standard is used as Fu when buildings are designed, and the real value of Fu is seldom obtained. Moreover, large shear displacement of composite structures as much as the headed stud occurring the tensile strength is not considered in design. Therefore, in this study, Fu is treated as one of element, not required element.
Based on the above confirmation of each correlation, a series of the multiple regression analysis for some elements in database are conducted. Using the combination of the elements in the case which the adjusted R-Square value is best, the modified coefficient is created separately both in case of flat slab and deck slab. In flat slab, the modified coefficient include sca, Ec, Fc, L/d, and Fu. In order to simplify, and correspond to the ultimate shear strength obtained in test, Ec, Fc, and Fu are changed to real number using by the average values. The correlation coefficient between modified formula and the ultimate shear strength obtained in test increased.
In deck slab, the modified coefficient include Ec, Fc, L/d, nd, bd, and Hd. However, using the average value of Ec, nd, and Hd are poor correlation to the ultimate shear strength obtained in test. Therefore, the part of calculation of Ec, nd, and Hd is represented by Ec. The correlation coefficient between these modified formula and the ultimate shear strength obtained in test also increased.
The proposed formulas in this study do not depended on the diameter of headed stud, the construction direction of deck, pitch or gage of headed studs, however, they are enough effective to calculate the ultimate shear strength close to the ultimate shear strength obtained by the push-out tests. The calculation is simple because all needs are that the calculation of the modified coefficient. Therefore, the formulas are also useful because of rising the accuracy of the structural design of headed stud.
