Anchored Concrete Barrier (405160-3)

Problem Statement

Bridge replacement projects often require the use of phased bridge construction techniques to maintain traffic operation during construction. An important safety requirement is to use temporary concrete barriers to protect vehicular traffic from extreme drop-offs resulting from existing bridge decks. There are few restrained bolted down temporary concrete barriers that have been crash tested to provide limited deflection requirements. TTI crash tested a long 30 ft temporary NJ barrier using pinned connections under Report 1959 in 1993 for NHCRP Report 350. Louisiana DOT is currently using an “F” shaped Oregon TL-3 approved barrier that has a 32 inch deflection without restraints.

Background

In 1993, TTI developed a limited-slip portable concrete barrier connection for Texas Department of Transportation (TxDOT) (Beason 1993) that passed the NCHRP Report 350 evaluation criteria. This connection was developed for 30 ft TxDOT portable concrete barriers (PCB) placed on bridge decks and/or concrete pavements. Four steel pins (1.25 inch diameter and 20.5 inches length) were inserted into holes drilled through each of the barriers. The pins were inclined at an angle of approximately 40.1 degrees from the ground and were installed from one side of the barrier only. A TL-3 crash test for this system resulted in maximum static and dynamic deflections of 9.6 inches and 15.6 inches. In 2001, Midwest Roadside Safety Facility (MwRSF) developed an NCHRP Report 350 compliant tie-down system for 12.5-ft long temporary concrete barriers with pin-and-loop type connection (Bielenberg 2002). This tie-down system was designed for installation on bridge decks. It consisted of a steel strap that was connected to the joints between the barriers and at the same time bolted to the bridge deck. The strap was a 3 inch x 0.25 inch x 36 inch steel piece bent at four points to form a trapezoidal. Holes were punched into the strap to allow the pin connecting adjacent barriers to pass through and to bolt the strap to the bridge deck. The maximum static and dynamic deflections of the system were 33.5 inches and 37.75 inches, respectively.

In 2002, MwRSF developed a tie-down system for attaching Iowa H-section steel barriers to bridge decks (Polivka 2003). Four angle brackets were welded to the base of each steel barrier and anchored to the concrete bridge deck by passing bolts through the holes in the angle brackets. The maximum static and dynamic deflections were 9.5 inches and 12.4 inches, respectively. In 2003, MwRSF developed a concrete bridge deck tie-down system for Kansas temporary barriers (Polivka 2003). Three anchor bolts were passed through the holes in the barrier and fastened to the bridge deck on the traffic side of the barrier. The maximum static and dynamic deflections were 3.5 inches and 11.3 inches, respectively.

TTI has previously researched the staking of Oregon Department of Transportation’s (DOT) pin-and-loop pre-cast PCB (FHWA Contract DTFH61-97-C-00064). A detailed analytical analysis was performed to examine the behavior of the stakes under different stake angles and friction coefficients. Analytical analysis was also performed to examine the strength of the staking configuration. Based of these analyses, optimum stake inclination angle, appropriate stake length and the barrier concrete load capacity levels were suggested.

Objective

Develop a restrained (pinned or bolted to existing bridge deck or roadway) 12.5 ft – 15 ft long temporary “F” shape concrete barrier that meets NCHRP Report 350 TL-3 and limits dynamic deflection to meet space requirements in a work zone.

Benefits

This project is expected to result in a restrained temporary concrete barrier design that results in limited deflections while meeting the NCHRP Report 350 TL-3 criteria. The design will be used for shielding motoring public and construction personals at various construction sites.

Results of Project

Under this project, a new restraining design that limits lateral deflections of F-shaped precast concrete barrier was developed through a program of finite element simulation analysis and full-scale vehicle crash testing. This design uses the pins to restrain the barriers in a manner that is easy to install, inspect, and remove. It also minimizes damage to bridge decks or concrete pavements and no through the deck bolting is required. The design uses steel pins which are simply dropped into inclined holes that pass through the toe of the barrier and continue a short depth into the bridge deck or concrete pavement underneath.

The new F-shaped pinned-down barrier successfully passed NCHRP Report 350 Test Level 3 requirements. The maximum permanent and dynamic barrier deflections measured in the crash test were 5.76 inches (483 mm) and 11.52 inches (293 mm), respectively.