STEEL STRUCTURES

Inspections of corroded. weakened, or damaged areas are essential for determining the best methods or needs for repair coating or replacement of steel members in the various structures. Main members are normally replaced when 30 percent or more of the section has been removed by corrosion or when seriously deformed. In the planning of replacements, consideration must be given to the rate of corrosion or actual decrease in section. If adjacent members show signs or serious deterioration, it may be best to replace whole frames or bents. Never remove a stressed member until the stress has been relieved by temporary bracing, shoring, or jacking because, if the stress is not removed, the member may sprint out of place when loosened, making it very difficult to replace the member. In the replacement of piles, the load should be shifted temporarily to adjacent piles by means of temporary beams or jacks. The replacement of wales on bulkheads may require the excavation of the fill to relieve the lateral loads. The structures must retain their structural stability at all times. In most cases, the maintenance and repair of metal structures will be handled by the SWs. At times, though, the BUS may be working with the SWs in these operations, so let us consider some of the common methods of maintenance and repair.

New members must be accurately fabricated to match the old work. Special care must be taken to be sure that all bolt-and-rivet holes line up with original members. Before the placement of the new member, all old rivets or bolts must be removed in the most expeditious manner by using hand or pneumatic chisels, saws, and wrenches, or by burning them off before removing the old member. Place the new member in position and line up all holes by adjusting the jacks or the bracing as necessary. Place a few bolts to hold the member, then fasten securely in place by riveting, placing additional bolts or welding.

In the replacement of bearing piles, the new pile is generally driven alongside the old one at a slight angle. It is then cut off at the proper elevation, capped, usually by welding on a steel plate, and pulled into position by block and tackle. If the old pile is pulled and a new one driven, care must be taken to transfer the load temporarily until the new pile can assume the load. Care must be taken to bore or punch the bolt holes in the cap to conform with the holes in the floor beam or stringer.

Precautions may be necessary when replacing wales and sheet metal bulkheads because they often retain materials that have a low angle of repose. The old wales are left in place or at least until new wales are installed just above or below the originals. Occasionally, they can be connected to existing tie rods; however, in most cases, new tie rods and deadmen should be installed.

Badly deteriorated sheet pile is generally protected by new sheetpiling being driven outside the old piling and provided with new wales, rods, and deadmen. The space between the piles must be filled with well-tamped earth, sand, gravel, or concrete, depending upon conditions at the site.

Steel members that have corroded in only limited areas may be repaired by welding fishplates onto the flanges and the web. The corroded area should be first thoroughly cleaned and featheredges burned off back to a point where the metal is of sufficient thickness to hold a weld. Fishplates should be of sufficient cross-sectional areas to develop the full strength of the original section and should extend beyond the top and bottom of the corroded zone. Another method is to encase the corroded section in reinforced concrete.