Strength Evaluation of the Nelson Street Bridge


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Title: Strength Evaluation of the Nelson Street Bridge

Author(s): Frank F. Liou

Publication: Special Publication

Volume: 88


Appears on pages(s): 225-236

Keywords: arch bridges; bridges (structures); computer programs; deterioration; evaluation; loads (forces); reinforced concrete; strength

Date: 11/1/1985

The Nelson Street Bridge in downtown Atlanta, Georgia is a ten-span continuous concerete arch bridge. Designed for carrying electric street cars, it was built in 1906. The bridge is present-ly carrying local street traffic over active tracks of the Southern Railway System and automobile parking areas. Strength evaluation procedures contrasted the latest design speci-fications and modern analysis techniques with the original design approach in every aspect. A slab-grid model was used for analyzing lateral wheel load distribution on a multiple arch and slab system. The distribution factors were then compared with those recommended by current AASHTO specifications for concrete slabs on concrete T-Beams. Arch geometry was accurately simulated, and moving axle loads were generated in a computer program. Force envelopes were produced for arch sections spaced from one foot to six feet along the arch, using critical loading positions. Sections were then checked for combined compression and bending. This approach is particularly effective when the spacing of arches is unequal and span lengths vary. Concrete cores were taken from the bridge and tested for compres-sive strength and chemical properties. Test results were satisfac-tory when compared with recommendations in the AASHTO Manual for Bridge Rating and turn-of-the-century books on concrete design. Sound arch sections from original contract plans, and existing sec-tions with concrete and steel losses determined by field inspection were used for evaluating section capacities.