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We are trying to figure out if we need to bolt through a parapet for a BEAT-SSCC crash cushion.
Manufacturer's recommendation is:
"Anchorage systems that develop the full capacity of the bolt may be used as an alternative to drilling through the concrete section."
Manufacture indicates that the bolt that is used to mount the BEAT-SSCC to the parapet is:
1" x 16" Hex Bolt Grade 5
Total parapet width at the height that the bolts are going to be installed at is 11". Concrete strength is 4000 PSI.
Is it possible to use epoxy or mechanical anchors?
|Date||September 17, 2012|
I have reviewed the BEAT installation you sent to see if the end bolts can be installed with epoxy.
Typically, when we determine if the bolts can be epoxied rather than through bolted we assume that the epoxied installation must be capable of developing the full tensile and shear capacity of the bolt in question. The ultimate shear and tensile capacity of the 1" dia. Grade 5 bolt are 41.98 and 72.72 kips, respectively. If the bolt shear occurs through the shank rather than the threaded section, the max shear load is approximately 94.2 kips.
I calculated the epoxy anchors based on Hilti RE 500 epoxy and assumed an embedment depth of 9". I also used an anchor spacing of 15.625" and an edge distance to the top of the parapet of 7". Hilti lists the ultimate bond/concrete capacity in shear and tension for a 1" anchor with 9" of embedment as 95.2 kips and 69.5 kips, respectively. When factors for anchor spacing and edge distance are applied, the shear and tension capacities of the concrete/bond become 95.2 kips and 54.2 kips, respectively. The tension number is likely too conservative as Hilti assumes unreinforced concrete. Thus, the actual tensile capacity is likely greater than 54.2 kips. I would assume that that the anchorage can safely achieve 60 kips with reinforcing steel present. Comparing those capacities with the steel strengths above, it is apparent that the epoxy anchor has sufficient shear capacity and is slightly lower in tension. We do not believe this is an issue as the combined loading on the end anchor bolts is primarily shear with some tension due to prying of the box beam away from the face of the parapet. This prying action will create some tensile loads in the bolt, but the box beam tubes cannot generate tensile loads in excess of 60 kips at the anchor locations prior to yielding. In fact, the yield of the tubing limits the pryout tensile loads on the anchor to under 40 kips.
However, a problem exists if you are installing the anchors with the epoxy. The epoxy bond capacities assume the use of all threaded rod of similar grade or fully threaded bolts. The thread will develop the epoxy capacity more effectively than a smooth shank. A smooth shank will tend to decrease the bond capacity significantly. Thus, we cannot depend on the epoxy anchor capacities above will be true unless a fully threaded section is used. The BEAT system may be designed such that the smooth shank is required to take the shear loads in the design rather than a reduced section due to threads. As such, we cannot recommend epoxy anchorage of the bolts due to concerns that the use of fully threaded sections would reduce the shear capacity of the anchorage below the design intent. You could contact the BEAT manufacturers to get their feedback if the use of fully threaded anchor sections is acceptable.
|Date||September 20, 2012|
I talked with the manufacture. Threaded rods are acceptable. Do you have a recommendation on grade of threaded rod?
|Date||September 20, 2012|
I would make the grade equivalent to the Grade 5 rod specified in the plans. Thus, A449 is the appropriate threaded rod spec. A193 B7 would be acceptable as well.
|Date||September 21, 2012|
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