Our first question this month asks if nuts & bolts can be used instead of beam clips and our second asks about load testing a mezzanine floor
Nuts & Bolts
Q. We are being asking to fix beams on site with nuts & bolts to prevent beam dislodgment as a permanent fix instead of using manufacturers beam clips.
Their argument is that beam clips can be removed or dislodged easy and a therefore pose a risk. SEMA training that I have had says that only manufacturer’s safety clips should be used and beams should not be bolted on standard APR.
Can you please refer me to the SEMA code of practice which states that bolts should not be used or clarify SEMA’s position?
A. I do not think any SEMA or other code specifically bans the use of nuts and bolts in place of beam connector locks however they do pose a serious risk and should be used with caution.
In some circumstances, for instance with the front beam of a pallet live storage installation their use is essential to take the force from the pallet end-stops and prevent the front beam from falling out under repeated impact. In other circumstances their use can increase the risk of a ‘progressive collapse’ and therefore should be used with extreme caution.
The purpose of the beam connector lock is to prevent accidental uplift of the connector by being required to take a ½ tonne uplift force and is not designed to take any horizontal load. Thereafter it is expected to ‘shear’ and allow the beam to come free of the upright without causing great damage to the upright. It acts as a kind of ‘shear pin’ in this situation. In the event of an accident this will usually result in a small collapse of one or two pallets.
If a nut and bolt fix is used the bolt will often have a greater shear value than the ½ tonne mentioned and in addition will restrain the connector close to the upright so the connector will be wedged into the slots of the upright. Most trucks will, lift well over the ½ tonne design force and eventually will tear the connector away from the upright taking a substantial amount of upright material with it in the process. This can often reduce the remaining upright section to the level that it cannot carry the imposed load so also collapses. Once this upright begins to move downward in the collapse it takes with it all the beams attached and they in turn also rotate at the next upright down the aisle tearing the upright here as they come to the point of disengaging from it. This upright in turn then cannot carry the weight and also collapses which in turn causes the next one down the aisle to collapse in a similar manner giving the progressive collapse situation which can bring down a complete run, or on some occasions all the racking in a warehouse!
Sometimes a nut and bolt fix is used as a cure for a symptom, without addressing the main problem, which might be poor driving techniques, or lack of clearances causing repeated impacts of a back beam. Certainly SEMA would recommend that an experienced engineer, possibly from the rack manufacturer be requested to look at the whole problem to see if there was a simpler solution (sometimes merely changing training techniques).
If there is no other solution then bolted connections may be used however in SEMA’s opinion the weakest possible bolt should be used (normally nothing more than a 6mm gutter bolt) and if possible this should not be fully tightened allowing some movement in the connector away from the face of the upright under accidental impact. The manufacturer’s engineer should be able to make specific recommendations in this area. It is recommended that a full and open discussion with the client take place considering the relative risks of this technique before implementation.
Load Testing Mezzanine
Q. We have had a Mezzanine floor relocated to a different part of our workshop, how can I get it load tested?
A. Load testing a Mezzanine floor that has been moved is likely to be very expensive and probably would not cover all the issues required.
Probably you would require a qualified structural engineer to inspect the floor and confirm the build is to the same standard as in the original location and there are no issues with damaged or rusted components. If all that is OK, then if this is done by the original supplier the calculations should be available for checking and confirming the carrying capacity is OK without physical tests needing to be carried out. If the original supplier and calculations are no longer available you might have to retain the services of a chartered structural engineer to inspect and in effect reverse engineer the design of the structure but again the need to load test is removed.
Other checks are necessary however, such as means of escape and escape distances, which are critical for mezzanines and it is possible that your building control department would demand a new application for this new location that would look at other issues as well as design, and would want fire escape distances and fire protection of the structure reviewed, rules governing which may have changed since the original construction. As an example we still come across cat ladders as a means of emergency escape on old structures while a second stair would be expected today.
Sorry this is not at all as straight forward as it sounds!
SEMA
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