Test 12--NCHRP Report 350 Test 3-11 of the Modified Texas Type T6 Bridge Rail on Bridge Deck
Author(s):
C.E. Buth, W.F. Williams, R.P. Bligh, W.L. Menges, B. Abbot
Publication Date:
February 2000
Abstract:
The Texas Type T6 Bridge Rail was developed under a previous Texas Department of Transportation (TxDOT) project with the Texas Transportation Institute (TTl). The Texas Type T6 was crash tested and evaluated under National Cooperative Highway Research Program (NCHRP) Report 230 guidelines. However, with the adoption of NCHRP Report 350, the bridge rail needed to be reevaluated using the 2000-kg pickup truck specified in NCHRP Report 350 test 3-11.
Earlier in this study NCHRP Report 350 test designation 3-11 (test no. 418048-2) was performed and the Texas Type T6 did not perform satisfactorily. Although the bridge rail contained and redirected the vehicle, some of the anchor bolts pulled out allowing post baseplates to be displaced from the bridge deck. The vehicle rolled onto its left side upon exiting the installation. Static load tests on posts taken from the prototype rail installation showed that the strength of the welds between the baseplates and the posts exceed the plastic moment capacity of the posts.
The project team selected two revised weld details for dynamic testing. In all tests, failure in the welds occurred before rupture of the post steel. The team then modified the breakaway connection by welding the tension flange to the baseplate with a 10 mm long, I0-mm fillet weld and welding the compression flange with two 19 mm long, I0-mm fillet welds. Results of the second full-scale crash test (test no. 418048-3) on the revised design were similar to the first test and indicated unacceptable performance.
Design of the post welds was further revised. Two welds that were located along the back flange of the T6 Post were relocated along the web of the post. In addition, two slots (6 mm x 29 mm) (1/4 in x 1-1/8 in) were machined in the tension flange of the posts to reduce the ultimate strength of the post. A third full-scale crash test (test no. 418049-8) was then performed. The modified T6 posts broke away readily but allowed the rail element to deflect enough to allow one side of the pickup to go down into the ditch behind the bridge rail. This deflection was considered unacceptable.
Based on results of additional pendulum testing, a full scale crash test was performed on the T6 Bridge Rail with the T6 Posts modified to include the following:
1) a larger and thicker baseplate (241 mm x 304.8 mm x 25 mm plate)
2) two 6.4 mm x 13 mm machine-cut slots on the tension flange of the posts
3) a 51 mm x 83 mm x 13 mm plate welded on the field side of the flange just above the baseplate.
Reported herein are the details and results of the full-scale crash test performed with the abovementioned modifications.
The modified Texas Type 1'6 Tubular W-beam Bridge Rail contained and redirected the vehicle; however, the vehicle rolled one complete revolution after exiting the bridge rail.
Report Number:
0-1804-10
Electronic Link(s):
Document/Product
http://tti.tamu.edu/documents/TTI-1999-ID5240.pdf
Publication/Product Request
TTI reports and products are available for download at no charge. If an electronic version is not available and no instructions on how to obtain it are given, contact the TTI Library.