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Structural Steel Designers Handbook Part 5

Tham khảo tài liệu 'structural steel designers handbook part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 5.64 SECTION FIVE V . Pv V 5.14 n where n is the number of fasteners in group. The resultant stress must be less than the allowable capacity of the fastener. Depending on the fastener pattern the largest resultant stress does not necessarily occur in the outermost fastener. Vectorial addition of shear and bending stresses may have to be performed for the most critical fasteners in a group to determine the maximum. In computing the fastener stresses designers generally find that the computations are simpler if the forces and distances are resolved into their horizontal and vertical components. Advantage can be taken of the fact that J Ix ly 5.15 where Iy sum of squares of distances measured horizontally from centrr of gravity to fasteners in2 Ix sum of squares of distances measured vertically from center of gravity to fasteners in2 Ix and Iy are analogous to moment of inertia. Fatigue need not be considered when calculating bolt stresses but should be taken into account in designing splice plates subjected to bending moments. Example AASHTO ASD. The 48 X 5 16 in A36 steel web of a plate girder in a highway bridge is to be field spliced with 7 8-in-diameter A325 bolts Fig. 5.43 . Maximum shear is 95 kips and maximum bending moments are 700 and - 200 ft-kips. The moment of inertia Ig of the gross section of the girder is 14 670 in4. Design the web splice for A36 steel. With an allowable stress of 12 ksi the shear capacity of the web is Vc 12 X 48 X 5 16 180 kips One design criterion then is 0.75Vc 0.75 X 180 135 kips. A second design criterion is the average shear FIGURE 5.43 Example of design of a girder-web splice. CONNECTIONS 5.65 Vav 1 2 95 180 137.5 kips 135 kips This governs for the bolts in the web splice. The gross moment of inertia of the web is 2 880 in4. From this should be subtracted the moment of inertia of the holes. With the bolts arranged as shown in Fig. 5.43 and area per hole 1 X 5 i6 0.313 in2 Ix 2 5 2 10 2 15 2 20 2 0.313 1500 X 0.313 470 in4 Hence