News Details
Vehicle crash testing on a GFRP-einforced PL-3 concrete bridge barrier
Corrosion-induced degradation of steel-reinforced barrier wall. (Source: Schöck Canada Inc)
Glass fiber reinforcement in the barrier wall. (Source: Ryerson University)
Sequential photographs of the crash test (frontal views). (Source: Ryerson University)
Barrier wall before vehicle impact. (Source: Schöck Canada Inc)
Corrosion of steel reinforcement due to environmental effects is a major cause of deterioration problems in bridge barriers. Glass fiber reinforcement not only addresses this durability problem, it also provides exceptionally high tensile strength and Young’s modulus. The special ribbed surface profile of the studied glass fiber bars and end anchorage heads ensures an optimum bond between the concrete and the bar, and thus eliminates the need for custom-made bent bars. A recent design project conducted at Ryerson University on a PL-3 bridge barrier proposed the use of 16 mm and 12 mm diameter glass fiber bars as vertical reinforcements in the barrier front and back faces respectively, with 16 mm diameter bars as horizontal reinforcements in the barrier wall, all at a spacing of 300 mm. The connection between the deck slab and the barrier wall utilized the glass fiber headed end bars for proper anchorage.
Background
In November 2007, The Residential and Civil Construction Alliance of Ontario (RCCAO), Canada, released a report on the state of Ontario bridges, entitled “Ontario’s Bridges: Bridging the Gap.” The report warns that the integrity of Ontario’s municipal bridge infrastructure and public safety are at risk after years of deferred maintenance, irregular inspections, and lack of government oversight. Recent media coverage on bridge collapses in Laval, Minnesota, Quebec and Minneapolis has highlighted the serious consequences of postponing moves to rehabilitate or reconstruct deteriorated bridges and the urgent need to take timely responsible action to safeguard the public from potential infrastructure failure. The study noted that many of Ontario’s bridges were built in the 1950s and 1960s, and “it is expected that most bridges will require costly rehabilitation or replacement after 50 years of life.” According to the Provincial Auditor’s report in 2004, almost one-third of the approximately 2,800 provincial bridges under Ministry of Transportation of Ontario’s (MTO) jurisdiction are in need of major rehabilitation or maintenance based on MTO’s own figures. The RCCAO report contains recommendations to promote public safety and the sustainability of Ontario’s bridges. One of these recommendations includes promoting bridge engineering designs that improve the life expectancy and reduce maintenance costs of bridges. This can be achieved by using glass fiber reinforced polymer bars.
FRP technology
Fiber reinforced polymers (FRPs), as non-corrodible materials, are considered an excellent alternative to reinforcing steel bars in bridge decks and other elements such as barriers, sidewalks and wingwalls to overcome steel corrosion-related problems. Since they are less expensive than carbon and aramid FRPs, glass fiber reinforcing bars are more attractive for bridge deck and barrier applications. Until recently, the installation of glass fiber bars was often hampered by the fact that bent bars have to be produced in the factory because FRP bars cannot be bent at the site. Also, bent FRP bars are much weaker than straight bars due to the redirection and associated rearrangement of the fibers in the bend. As a result, the number of bent FRP bars has increased and even doubled at such locations where bar bends are required. The use of headed-end FRP bars is intended to eliminate the unnecessary and expensive use of custom-made bent bars.
Design of a glass fiber reinforced barrier system
The design process of bridge barrier walls specified in the Canadian Highway Bridge Design Code (CHBDC) is based on the American Association of State Highway and Transportation Officials (AASHTO) Guide Specification for bridge railings and the AASHTO Guide for Selecting, Locating and Designing Traffic Barriers. CHBDC Clause 12.4.3.5 specifies that the suitability of a traffic barrier anchorage to the deck slab shall be based on its performance during crash testing of the traffic barrier.
The test wall was designed according to the CHBDC. The design was based on the results of material tests on headed glass fiber reinforcing bars and on the results of two full-scale tests on 1,200 mm long PL-3 wall segments performed at Ryerson University in 2010.
The final design called for 16 mm and 12 mm diameter GFRP bars as vertical reinforcements in the barrier front and back faces respectively, with 16 mm diameter bars as horizontal reinforcements, all at a spacing of 300 mm. The connection between the deck slab and the barrier wall utilized the GFRP headed end bars for proper anchorage.
Crash testing of the developed GFRP-reinforced barrier system
In November 2010, a vehicle crash test was conducted in accordance with Test Level 5 (TL-5) of MASH, which involves the 36,000V van-type tractor trailer (cab-behind-engine model of 36,000 kg gross weight) impacting the barrier at a nominal speed of 80 km/h and an angle of 15 degrees.
The remote controlled tractor trailer impacted the barrier at 620 mm upstream of the control joint located at 10.8 m from the barrier downstream end. At 0.100 s, the cab of the test vehicle began to redirect, and at 0.203 s, the lower right front corner of the van-trailer made contact with the barrier near the top. At 0.403 s, the cab of the test vehicle was traveling parallel with the barrier at a speed of 79.7 km/h. The van-trailer began traveling parallel with the barrier at 0.667 s, and was traveling at a speed of 76.3 km/h. At 0.695 s, the lower right rear corner of the van-trailer made contact with the barrier near the top, and at 0.748 s, the right rear edge of the van-trailer ruptured. As the test vehicle continued driving along the barrier, it righted itself and rode off the end of the barrier wall. The brakes on the test vehicle were not applied, and the test vehicle subsequently came to rest 35.66 m downstream of the end of the barrier and 2.7 m towards the field side.
The test showed that the barrier withstood and redirected the vehicle. It did not penetrate, underride or override the parapet. No elements, fragments, or other debris became detached from the barrier that could potentially penetrate the cab, or cause undue hazard to others in the area. No deformation occurred to the cab. The 36,000V test vehicle remained upright during and after the collision.
After the crash test, minor cracks in the front and back faces of the barrier were observed, but there was no severe damage. In practice, these minor cracks may need to be repaired to avoid possible crack propagation resulting from other possible vehicle impacts.
In February 2011, a Ryerson University research team conducted static load failure tests on the barrier segments to provide research information that will be used to further evaluate the extent to which the AASHTO-LRFD yield-line equations that were developed for reinforcing steel bars can be applied to the design of glass fiber reinforced barrier walls under equivalent static vehicle impact loading.
Authors:
Khaled Sennah: Professor, Civil Engineering Department, Ryerson University, Toronto, Ontario, Canada
Benjamin Juette: Product Manager ComBAR, Division of Glass Fiber Reinforcement, Schöck Bauteile GmbH, Germany
André Weber: Head R&D, Division of Glas Fiber Reinforcement, Schöck Bauteile GmbH, Baden-Baden, Germany
Christian Witt: President, Schoeck Canada Inc., Kitchener, Ontario, Canada
