Report No.: CCEER-91-1

Authors: M. Saiidi, E. Hwang, E. Maragakis, and B. Douglas

Date: February 1991

Sponsoring Agency: Nevada Department of Transportation

Performing Organization:

Department of Civil Engineering/258

University of Nevada, Reno

Reno, NV 89557

Abstract:

The project presented in this report involved a brief study of the vertical dynamic characteristics of the old Flamingo Road Interchange located in Las Vegas, Nevada. The interchange consists of two parallel, side-by-side reinforced concrete bridges, each with five spans. Cast-in-place box girders formed the superstructure of the interchange. The bridges had been designed in 1959, constructed in 1964, and were taken out of commission in 1984 due to the realignment of the road. The bridge was tested in January 1990.

The purpose of the study presented in this report was to determine the actual effective moment of inertia of the superstructure in a box girder bridge, and to determine (a) if any unusual behavior can be detected at the location of an intermediate hinge in one of the spans, and (b) any interaction between the two parallel bridges at the longitudinal joint.

The study included field testing of the bridge using impact caused by a heavy truck travelling over a wooden block. A total of ten data sets were collected corresponding to five different truck impact locations. The data were then analyzed and the frequencies and mode shapes for the first two vertical modes were extracted. A relatively simple computer model of the bridge was developed, and calculated and measured frequencies and mode shapes were compared. The moment of inertia of the superstructure was varied to match the measured and calculated frequencies, and therefore, determine the actual effective moment of inertia of the superstructure. It was concluded that the effective moment of inertia of the bridge superstructure was close to its gross inertia (Abstract by authors).