TTI Research Supervisor:
William F. Williams, P.E.
Texas Transportation Institute
Texas A&M University System
College Station, Texas 77843-3135
(979) 862-2297 [email protected]
Pooled Fund Technical Representative:
Louisiana Department of Transportation
P.O. Box 94245
1201 Capitol Access Road
Baton Rouge, LA 70804-9245
(225) 379-1323 [email protected]
Adequate storm water drainage is necessary for safety on vehicular bridges. For bridges utilizing continuous cast-in-place concrete bridge rails with no openings, storm water drainage is typically provided on the ends if drainage scuppers are not provided. During heavy rainfall events, drainage water can accumulate on the bridge structure. Drainage through the bridge railing can provide better drainage of storm water, thus improving vehicular safety. LaDOTD has developed an F-Shape barrier with drainage slots to accommodate drainage through the bridge rail into scuppers or off the sides of the bridge (see Figure 1).
Figure 1. Details of F-Shape Concrete Barrier with Slotted Drain Holes.
The objective of this project was to evaluate the geometry and placement of the drainage slots on the LaDOTD Concrete F-Shape Barrier with respect to vehicle impact performance requirements for National Cooperative Highway Research Program (NCHRP) Report 350, Test Level 4 (TL-4) specifications. This project will provide LaDOTD with a viable option to provide drainage through the cast-in-place concrete F-Shape bridge rail.
A few similar barriers were compared to the proposed barrier for this project. The TXDOT Wildlife Crossing Barrier has a taller opening in the base compared to the Washington Pin & Loop Barrier design. The drainage slot used in the Washington Pin & Loop Barrier appeared to perform well in LS-DYNA impact simulations with both the small car and pickup truck. Although the WSDOT barrier did not meet the MASH test specifications, the 9‑inch high drainage slot used in the WSDOT Pin & Loop Barrier system did not adversely affect the performance of the crash vehicle. In addition, the potential for vehicle interaction with the drainage slot opening was considered low to marginal with respect to the criteria as provided in AASHTO Section 13 specifications. Figure 2 shows the side-by-side comparisons between the size of the openings between the TXDOT Wildlife Crossing Barrier, Washington Pin & Loop Barrier, and the LaDOTD F-Shape Barrier with drainage slots.
Figure 2. Barrier Comparisons
TTI researchers have reviewed the current details of the LaDOTD Cast-in-Place Barrier Railing (F-Shape Barrier with Drainage Slots) details as shown in Figure 1. Based on TTI researchers’ review, the F-Shape barrier with drainage slots as shown on Figure 1 (LaDOTD Drawing Cast-in-Place Barrier & Transition (Transition on Wingwall)) is considered acceptable with respect to NCHRP Report 350 TL-4 performance criteria.