View Q&A

We have a question from a
contractor regarding the acceptability of the attached anchorage system for use
in temporary concrete safety barrier applications.  I have not seen a system
like this used before.  Could you please take a look at the attached
information submitted to KDOT and let us know if you have any concerns with
this anchorage system?  I have also attached our Standard Drawing
depicting our typical anchorage system. 

Thanks for your help,

The system that was tested for Kansas to anchor the TCB through the holes in the toe of the barrier used ⅛-in. diameter, ASTM A307 anchor bolts with heavy hex nuts and 3-in. x 3-in. x ½-in. thick washers spaced evenly across the traffic side of each PCB segment. Each anchor bolt was epoxied into the concrete with an embedment depth of 12 in. The test installation consisted of sixteen 12-ft 6-in.) long, redesigned F-shape PCB segments placed adjacent to a simulated bridge deck edge with a total system length of 204 ft. During test no. KTB-1, a 4,448-lb (2,018-kg) pickup truck impacted the system 5 ft – 5 in. upstream from the joint between barrier nos. 8 and 9 at a speed of 62.0 mph (99.8 km/h), and at an angle of 25.3 degrees. The system contained and redirected the vehicle with maximum lateral dynamic and permanent set deflections of 11.3 in. and 3½ in., respectively, and was considered successful according to TL-3 of NCHRP Report No. 350.

In the past, we have often been asked what embedment depth was required for the epoxy anchorage of the A307 rods used in that system. Adhesive anchorage capacity depends on many factors, including anchor size, anchor embedment, concrete strength, adhesive bond strength, spacing effects, edge effects, and other factors. Thus, we have typically recommended that the embedment for the anchor rods should be selected to develop the ultimate shear and tensile capacities of the anchorage. For the 1 1/8” dia. A307 rod, the ultimate shear and tensile capacities are 26.4 kips and 45.8 kips, respectively.

In the case of the alternative anchorage shown, we would make a similar recommendation. Thus, the cast in anchor shown would need to develop shear and tensile capacities of 26.4 kips and 45.8 kips, respectively. It appears that the system shown has an allowable anchor capacity of 27 kips and a max capacity of 54 kips in tension. The shear loading is not listed. Thus, I would check the shear loading and confirm it is sufficient.

Do they install these cast-in-place anchors when the concrete is poured and then set the barriers in those exact locations? This seems difficult.