Type: Strauss Heel Trunnion Bascule
Location: Buffalo, NY
Stafford Bandlow Engineering (SBE) was called to investigate an issue affecting the operation of a 1914 vintage, 129.75 ft. long Strauss heel trunnion bascule bridge that spans across the Buffalo River and operates mainly in winter months to accommodate ice-breaking operations to alleviate flooding concerns to the Buffalo Southtowns communities. The reported issue was that the north rack and pinion teeth were skipping which prevented the movable span from opening.
SBE’s investigation included strain gage testing to determine the operating loads span imbalance and a limited inspection of the mechanical machinery to confirm that the teeth were skipping and to determine the cause of the skipping. The mechanical inspection of the structure also focused on the operating strut yoke assembly, rack and main pinion, north counterweight trunnion, and span drive machinery.
It was confirmed that the teeth were skipping as reported, with the root causes determined to be a combination of four issues; 1) excessive clearance between top guide rollers in the operating strut yokes an the operating struts; 2) deterioration of the operating strut yokes; 3) rack segment that was engaged with the leaf seated appeared to be improperly adjusted; and 4) ongoing counterweight repairs had increased operating loads to the extent that the separating force was greater than the dead load of the strut with the leaf in the closed position.
To restore operation of the bridge, steel bars were welded to the top of the operating struts to reduce the clearance between the top guide roller in the operating strut yokes and operating struts. Recommendations for additional repairs were also provided.