Table 11.29 lists the allowable stresses for railroad bridges recommended in the AREMA Manual. The stresses, ksi, are related to the specified minimum yield stress Fy , or the specified minimum tensile strength Fu , ksi, of the material except where stresses are independent of the grade of steel. The basic stresses may be increased for loading combinations (Art. 11.35.12), or may be superseded by allowable fatigue stresses (Art. 11.38).
Allowable stresses for welds for railroad bridges are given in Table 11.30. These stresses may also be increased for loading combinations (Art. 11.35.12), or may be superseded by allowable fatigue stresses (Art. 11.38). The designer should review the AREMA Manual for complete provisions, including prohibited types of welds and joints. Special provisions may apply for fracture critical members.
Allowable Bearing Pressures on Masonry
For bearing assemblies with specified edge distances, with or without shock pads, the following allowable bearing stresses may be used for the indicated supporting material:
Concrete 0.25 of specified compressive strength
Granite 800 psi
Sandstone 400 psi
Limestone 400 psi
11.37.2 High Strength Bolts
Steel fabrication may be detailed for 7â„8 in diameter A325 or A490 bolts in 15â„16 in diameter holes. The designer should determine the owners requirements for fastener sizes, materials, use of oversize or slotted holes, etc. Often, 7â„8 in diameter A325 high strength bolts are used because bridge owners generally have maintenance equipment for installing and removing these fasteners. Attention is directed to the AREMA Manual, Chapter 15 Commentary, for additional information.
High strength bolts must be installed to specified minimum tension values. The required tension for installed bolts of various sizes is given in Table 11.31.