148 Summary

High-performance steels offer many advantages over conventional steels in bridge design and construction. Some of the major benefits are

• Improved weldability and lower preheat temperature.

• Enhanced weathering characteristics and durability.

• Higher fracture toughness and crack tolerance.

• Wider girder spacing may help lower fabrication and construction cost.

• Shallower members may help solve or alleviate vertical clearance problem.

• Increased span lengths may help reduce the number of piers needed to support the superstructure.

• Lighter structure.

• Lower initial, or perhaps even life-cycle, costs.

Despite these advantages, the use of smaller/shallower and fewer girders in a HPS bridge means the possibility of excessive deformations, global/local buckling, and increased load-induced fatigue. Care must be exercised to ensure that both strength and serviceability limit states are satisfied. In addition, it has been reported that difficulties were encountered in the drilling (Wasserman et al. 1998) and reaming of HPS70W plates. The use of a larger quantity of lubricant in the holes and on the drill bits and reamers may be needed. Moreover, there have been reports that show HPS70W steel has a tendency to leave tiny pitting residue after blast cleaning, and mill scale removal by descaler is not particularly effective. Finally, if HPS70W steel plates fabricated using the Q&T process are used, its limited length (50 ft or 15 m) means more splice plates are needed to build a long girder. The increase in the number of beam splices, the more expensive flux, and the higher material cost mean the unit cost of a girder made of HPS70W steel is likely to be higher. However, a higher unit cost does not necessarily translate to a higher overall cost because of the benefits outlined above for using HPS70W steel in bridge construction.

The AASHTO load and resistance factor design (LRFD) Specifications (AASHTO 1998) have been updated (AASHTO 2000a, 2000b) to allow for the use of HPS70W steel in bridge design. Studies have shown that these specifications are adequate for use with HPS70W steel provided that the issues of girder deformations, global and local buckling, and tension field action are properly addressed in the design.

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