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Previously, you had inquired into the allowance for alternative anchorage hardware within the bridge railing system noted above. According to the MwRSF test report (No. TRP-03-53-96), four anchor rods were used to attach the upper tubular steel rail, tubular steel posts, and welded base plate to the top of the reinforced concrete parapet. As noted, these anchor rods were modified from ASTM A307 grade material to ASTM A325 grade material. The report also noted that ASTM A193 Grade B7 material was used due to the unavailability of A325 hardware for testing. Therefore, the final crash-tested system utilized 7/8-in. diameter anchor rods configured with ASTM A193 Grade 7 alloy material with the expectation that either A325 or A193 B7 material could be used in the future.

A comparison of structural properties for 7/8-in. diameter fasteners using A193 B7 and A325 material is noted below, along with information for ASTM A449 material.

As shown above, the structural strength for ASTM A193 B7 material is only slightly greater than that provided by ASTM A325 material. As such, it would seem reasonable that steel anchor rods or bolts meeting the ASTM A325, A449, or SAE Grade 5 material specifications would also adequately retain the rails, posts, and plates to the concrete parapet.

Based on the successful crash testing program, the MnDOT combination bridge railing system was found to provide acceptable crash performance according to the NCHRP Report No. 350 Test Level 4 guidelines. Since higher strength anchors were utilized within the concrete parapet for attaching the metal railing, it would not be appropriate to utilize ASTM A307 anchors in lieu of the higher strength anchors unless deemed acceptable through the use of full-scale vehicle crash testing.

Although the testing program was successful, there was insufficient data collected in order to determine or estimate the actual impact loads imparted to the entire bridge railing system. As such, it is not possible to determine what peak lateral load was actually distributed to the upper metal railing system, including the individual posts, plates, and vertical anchors. Thus, it is difficult to now substitute the use of epoxied, high-strength (HS) anchors for the cast-in-place, high-strength anchors which were used in combination with an embedded steel anchor plate.

If epoxied, HS anchors are desired, it would seem appropriate to construct a short segment of the RC parapet with the alternative vertical anchor systems spaced 6 ft or more apart along the wall. With the posts attached to the parapet, dynamic component testing could be performed at each post location in order to determine the peak load capacity of the various anchored posts when impacted at the upper rail height. If the alternative anchor options are found to provide equivalent or greater load capacity through dynamic component testing, then it would seem reasonable to allow their use within the bridge railing system.