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原文传递 Load Path Evaluation of the I-40 Bridge; Interim rept. Sep 93-Apr 94

题名：	Load Path Evaluation of the I-40 Bridge; Interim rept. Sep 93-Apr 94
作者：	Idriss, R. L.; Jauregui, D. V.
关键词：	Highway bridges; Loads(Forces); Load bearing tests; Joists; Girders; Rio Grande River
摘要：	The I-40 bridges over the Rio Grande in Albuquerque, New Mexico, were scheduled to be razed in the summer of 1993 due to geometry and traffic safety considerations. The structure is a three-span continuous non-composite two-girder steel bridge. The bridges represent a common design in the U.S., popular in the 1950s and early 60s. They are classified by AASHTO as "fracture critical" two-girder steel bridges. This research study evaluates the alternate load paths present in the two-girder steel bridge. It looks at the after-fracture behavior of one three-span unit of the I-40 bridge with a near full depth crack in one main girder. A preliminary analytical evaluation of the bridge was conducted. A three dimensional finite element model was used to determine the effect of a near-full depth girder crack on the structure. It predicted a stable structure, with minimal movement and no yielding. A three-span continuous unit of the structure was field tested to determine the impact of a near full depth girder fracture on the redistribution of loads, the load capacity, and the potential for collapse. Four levels of damage were introduced in the middle span of the north plate girder by making various torch cuts in the web and the flange of the girder. The final cut was to simulate a near full depth crack in the girder. The cut in the girder was done in four stages. The first stage cut was a two foot deep cut in the web, originating at floor beam connection level. Next the cut was continued to the bottom of the web. The third stage was to cut the flange halfway in from each side, directly below the web cut. Finally, in the fourth stage, the flange was severed completely, leaving the upper 4 ft (1.22 m) of the web and top flange to carry load at that location. The final cut resulted in a 6-ft (1.83-m) deep crack in the 10-ft (3.05-m) deep girder, extending from the bottom flange to the floor beam to girder connection. After data were accumulated for the bridge in its intact state, the defects were imposed and the data retaken at every level of damage. The fractured bridge proved to be stable, with no yielding, and very minimal deflection of 1 3/16 in. (30.2 mm) under dead plus live load at the fracture. The test data were analyzed and the load redistribution mechanisms of the damaged bridge established. The main load path proved to be the fractured girder itself as it redistributed the load longitudinally to the interior supports through cantilever action. The floor beams, lateral bracing system, and deck transferred the load to the intact girder, through torsional stiffness of the system. This load transfer in the transverse direction occurred mainly at the vicinity of the crack. Experimental and analytical results correlated well.
总页数：	158p
报告类型：	科技报告