Table 11.29 lists the allowable stresses for railroad bridges recommended in the AREMAÂ Manual. The stresses, ksi, are related to the specified minimum yield stress Fy , or the specifiedÂ minimum tensile strength Fu , ksi, of the material except where stresses are independentÂ of the grade of steel. The basic stresses may be increased for loading combinations (Art.Â 11.35.12), or may be superseded by allowable fatigue stresses (Art. 11.38).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 These stressesÂ may also be increased for loading combinations (Art. 11.35.12), or may be superseded byÂ allowable fatigue stresses (Art. 11.38). The designer should review the AREMA Manual forÂ complete provisions, including prohibited types of welds and joints. Special provisions mayÂ apply for fracture critical members.
Allowable Bearing Pressures on Masonry
For bearing assemblies with specified edge distances, with or without shock pads, the followingÂ allowable bearing stresses may be used for the indicated supporting material:
Concrete â0.25 of specified compressive strength
Granite â800 psi
11.37.2 High Strength Bolts
Steel fabrication may be detailed for 7â8 in diameter A325 or A490 bolts in 15â16 in diameterÂ holes. The designer should determine the ownerâs requirements for fastener sizes, materials,Â use of oversize or slotted holes, etc. Often, 7â8 in diameter A325 high strength bolts are usedÂ because bridge owners generally have maintenance equipment for installing and removingÂ these fasteners. Attention is directed to the AREMA Manual, Chapter 15 Commentary, forÂ additional information.
High strength bolts must be installed to specified minimum tension values. The requiredÂ tension for installed bolts of various sizes is given in Table 11.31.