United States Department of Transportation
i
Load rating of Bibb Graves Concrete Arch Bridge.
-
2014-07-01
[PDF-3.92 MB]
Details:
-
Creators:
-
Corporate Creators:
-
Corporate Contributors:
-
Subject/TRT Terms:
-
Publication/ Report Number:
-
Resource Type:
-
Geographical Coverage:
-
Corporate Publisher:
-
Abstract:To assess the strength of the Bibb Graves Concrete Arch Bridge, the Alabama Department of Transportation sponsored an
investigation by Auburn University. In one of the spans, the arches are experiencing severe longitudinal cracking from Alkali-Silica
Reactivity (ASR). The significance of ASR on the load carrying capacity of the bridge is unknown for two reasons. First, the effects of
ASR on cross section capacity are not well understood. Second, a load rating for the bridge has never been performed. As an initial step
for planning maintenance activities for the bridge, a load rating is performed in this project. Ratings are provided for the vertical
columns, vertical tension hangers, transverse floor beams, and arch ribs. Rating factors were calculated for components of the bridge
based on the as-designed condition. Ratings were provided for eight standard trucks and the AASHTO lane load. Evaluation of the
impact of ASR on the ratings was outside the scope of the project.
An operating rating factor significantly less than 1.0 was calculated in preliminary ratings of one arch. The low rating was
attributed primarily to slenderness effects calculated using the moment magnifier from AASHTO Standard Specifications for Highway
Bridges (2002). An investigation was conducted to identify a more accurate method for including slenderness effects in the arch rating
calculations. An analysis that combines an elastic second-order analysis for dead loads and a linear analysis for moving live loads was
found to be very practical and sufficiently accurate. This combined analysis approach resulted in significant increases in the arch ratings
beyond those found by using the AASHTO moment magnifier method.
Sensitivity analyses were performed to assess the effects of ASR-expansion on the bridge components’ internal forces and arch
vertical deflection. Effects of changes in concrete strength and modulus of elasticity on member forces, deflection, and ratings were
examined.
Load ratings of the Bibb Graves Concrete Arch Bridge resulted in multiple operating rating factors less than 1.0. The lowest
operating rating based on the as-designed condition is 0.86 for shear in an arch rib. This rating factor was increased to be greater than
1.0 by using a higher concrete compressive strength that was justified by concrete core test results. The final load ratings are controlled
by the positive bending capacity of the transverse floor beams. The controlling operating rating factors are 0.93 and 0.97 for the
standard tri-axle truck and concrete truck, respectively.
-
Format:
-
Collection(s):
-
Main Document Checksum:
-
Download URL:
-
File Type:
