1 Senior Staff II – Structures, Simpson Gumpertz & Heger Inc., 41 Seyon Street, Waltham, MA, 02453, USA, bpstrohman@sgh.com
2 P.E. (CA), Malden, MA, gunjeetjuneja@gmail.com
ABSTRACT
A failure investigation of a historic unreinforced masonry arch bridge with two 11.3 m (37 ft) span arches is presented. The unreinforced masonry arches were 7.0 m (23 ft) wide with a rise of 2.0 m (6.5 ft) and consisted of uniformly sized exterior granite arch-ring stones that were cut to precisely fit radially along the arch. The arches were bearing on granite skewback stones, which rested on unreinforced spread footings. The retrofit of the bridge envisioned two spans of reinforced concrete supported on two integral-abutment pile caps and one center pier with the two arches preserved for visual effect. During construction, large horizontal and vertical movements and cracks were observed. Finite-element analysis (FEA) models were created in PLAXIS and NASTRAN to assist in the structural failure investigation. The PLAXIS finite-element model evaluated the impact of the construction sequencing on the loading conditions and displacements of the bridge superstructure and surrounding soil. The NASTRAN model provided detailed response of the arches, including the development of cracks in the mortar that the PLAXIS model could not. An evaluation of the results from the PLAXIS and NASTRAN finite-element models and a comparison of these results to the structural damage observed are provided.
KEYWORDS: bridge, failure, investigation, FEA
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