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I have questions regarding the installation of a thrie beam bridge rail on a brush curb using epoxy anchors in lieu of the case in place anchors used in your standard. I wish to install the thrie beam bridge rail shown in the attached detail to near the front and on top of the brush curb shown in the second attached plan. The thickness of the bridge deck and curb at the proposed installation region is approximately 16". The standard for the thrie beam railing calls for four 7/8" dia. A325 anchor bolts to be cast in place into the concrete. Because this installation is a retrofit, that is not possible. Thus, the desire to install the railing with epoxy anchors. The speeds of the bridge in question are 35-45 mph which would suggest TL-2 impact conditions for the railing.

I am writing to summarize our discussion over the phone regarding the installation of a thrie beam bridge rail on a brush curb using epoxy anchors in lieu of the case in place anchors used in your standard. To review, you wish to install the thrie beam bridge rail shown in the attached detail to near the front and on top of the brush curb shown in the second attached plan. The thickness of the bridge deck and curb at the proposed installation region is approximately 16". The standard for the thrie beam railing calls for four 7/8" dia. A325 anchor bolts to be cast in place into the concrete. Because this installation is a retrofit, that is not possible. Thus, the desire to install the railing with epoxy anchors. The speeds of the bridge in question are 35-45 mph which would suggest TL-2 impact conditions for the railing.

In order to determine the proper epoxy anchor configuration for the railing, I began by analyzing the existing 7/8" anchors. The 7/8" A325v anchor has yield and tensile strengths of 92 ksi and 120 ksi, respectively and a threaded area of 0.462 in^2. These capacities and areas provide a tensile yield force of 42.5 kips, an ultimate tensile force of 55.44 kips, and an ultimate shear strength of 32 kips. The spacing of the anchors from your place is 6".

We have recently been using HILTI RE-HIT-500 epoxy for the concrete barrier anchorage project that we are working on for WisDOT and have found that the published strengths of this material is very consistent with the results of our dynamic testing. Review of the ultimate strength data for HILTI RE-HIT-500 epoxy shows that a 7-7/8" embedment of a 7/8" dia. anchor with HILTI RE-HIT-500 epoxy is capable of developing a tensile load of 63.5 kips and a shear load of 72.86 kips. Reducing these capacities to adjust for the spacing of your anchors leads to an ultimate tensile load of 49.53 kips and a shear load of 56.71 kips. These values exceed the tensile yield and ultimate shear capacities of the 7/8" A325 anchor, but are approximately 10% less than the ultimate tensile capacity. We do not believe that the slight reduction in the ultimate tensile capacity is a concern in this situation as the railing was designed for TL-3 and the roadway speeds for this installation reflect a TL-2 impact condition as noted above. Thus, we would recommend that the thrie beam railing can be safely retrofitted on the brush curb shown using 7/8" dia. A325 anchors bolts or rods embedded a minimum of 7-7/8" into the brush curb. We could recommend the anchor rods or bolts be fully threaded to better develop strength in the epoxy.