Railway Track & Structures - November 2007 - (Page 20)

TTCI R&D spun hook bolts. Fasteners under a moveable bridge joint When a two-piece casting moveable bridge joint was installed on the bridge, the hook bolt and nailed washer with double nut and adhesive system was used on every tie beneath the joint. 1,2 On those ties, the high dynamic loads of 40mph train operations vibrated the hook bolts loose daily (one mgt). Several hook bolts also broke. Breaks occurred at both the bottoms and the tops of the hook bolts. On those ties beneath the joint castings, locking clips were soon added to prevent turning and loosening of the hook bolts (Figure 5a). The addition of the locking clips significantly reduced the amount of hook bolt maintenance required on ties beneath the casting joint (five to 10 mgt intervals). Figures 5a and 5b show some typical conditions that required maintenance. Only when the casting joint was removed from the bridge did the need for fastener maintenance drop to the levels experienced on the remainder of the bridge. The combination of hook bolts and nailed washer nuts, with double nuts, threaded fastener adhesive, and locking clips were installed on one girder to repair damage incurred by a derailed car. This combination of fasteners has performed well for over 750 mgt with no maintenance required. This test is ongoing with additional tonnage being accumulated. In conjunction with a rail change, the deck fasteners on two girders were changed. On one girder, hook bolts with spring lock washers and locking nuts were used (Figure 6a). In theory, the spring washer should keep the hook on the hook bolt in contact with the bottom of the flange at all times. On the worn ties at FAST, this system required maintenance after about 30 mgt of HAL traffic. Failure modes for individual fasteners included turning of the hook bolts, breaking of hook bolts and springs. A concern is that there is no recommendation for the tightening of the spring lock. If too loose, the hook bolt is likely to turn. If too tight, either the spring or the hook bolt is likely to break (Figure 6b). Each of these problems was experienced on this particular girder at FAST. Concurrently with the above installation, the second girder was equipped with www.rtands.com Figure 4, top, shows a double nut and washer nut with nail hole. Figure 5 shows hook bolt fasteners with locking clips, (a) typical, (b) turned hook bolt with locking clip, and (c) broken hook bolt with locking clip. Figure 6, center, shows (a) locking nut, spring lock and washer, (b) broken spring lock and hook bolt. Figure 7, bottom, shows (a) HCP-25 spring clip with single nut, (b) rotated spring clip and gouge in girder flange, (c) HCP spring clip with double nuts. hook bolt and 22 spun hook bolts out of a total of 56 on the bridge (Figure 3). Due to the relatively deep girder flanges, the fluting of the hook bolts was only minimally engaged into the ties. In many cases, the hook bolts turned loose over time. In the process, they rounded the holes in the deck ties so that the fluting could no longer engage the ties. In some cases, the nail worked out of the washer nut, allowing rotation. After aligning and tightening all hook bolts, the original hook bolts and nailed washer nuts withstood about 150 mgt of additional HAL traffic before a 20 Railway Track & Structures similar number of hook bolts became loose or rotated for the same reason. This case served as a baseline for comparison to the other cases, as the ties were now considered to be worn. After establishing the performance of the original system with both new and worn ties, a common field retrofit was applied. The hook bolts were again aligned and tightened, with double nuts and a threaded fastener adhesive applied to keep the nuts from loosening (Figure 4). This system lasted in service for 511 mgt on a portion of the bridge until maintenance was required due to loose or November 2007 http://www.aar.com http://www.rtands.com

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Railway Track & Structures - November 2007 Contents On Track Industry Today Supplier News AREMA News NRC News TTCI R&D Seattle Retrofits Downtown Transit Tunnel Switch Stand, Switch Machines Planning M/W with Modern, High-Tech Tools Products & Literature People Calendar Advertisers Index Sales Representatives Website Directory Professional Directory Classified Advertising Chicago Perspective

Railway Track & Structures - November 2007

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