Wind on Shoring/Bracing for tiltwall panels during construction
Wind on Shoring/Bracing for tiltwall panels during construction
(OP)
Project is in 120mph basic wind speed zone. Are there any Code-allowed reductions to that design wind speed for the shoring/bracing of the tiltwall panels while they are being constructed? Tiltwall Contractor is claiming they "always" use 90mph since "temporary condition". I'm inclined to make them design the shoring/bracing for the full 120mph, but want to make sure I'm not missing something... Anyone know?






RE: Wind on Shoring/Bracing for tiltwall panels during construction
If the job is going on during hurricane season then you may need to consider the consequence of failure.
RE: Wind on Shoring/Bracing for tiltwall panels during construction
RE: Wind on Shoring/Bracing for tiltwall panels during construction
RE: Wind on Shoring/Bracing for tiltwall panels during construction
Seems like we have covered this wind gust reduction/mitigation scenario very recently.
I could see a reduction outside of the June to September hurricane season (October to May), but not during it. So what if the contractor has to use super struts instead of the normal ones. Include it in the bid. Failure is not an option.
Mike McCann
MMC Engineering
RE: Wind on Shoring/Bracing for tiltwall panels during construction
RE: Wind on Shoring/Bracing for tiltwall panels during construction
When we receive shop drawings, the design wind speed is 72 mph (we are located in a 90 mph area), so it seems reasonable to me that the reduction from 120 is 90.
Titlwall needs to be braced until you get the roof structure (and, obviously the LFRS, if not entirely tiltwall) in. If you get a major hurricane during construction, well that's just really bad luck, but it's not like anyone will be at the job site during construction. I don't think it's reasonable or cost effective to design every stage of construction for the maximum possible loading.
RE: Wind on Shoring/Bracing for tiltwall panels during construction
If there was a hurricane then people wouldnt be hanging out at the construction site and most of these sites are in the middle of a vacant lot. So very unlikely to be alife safety risk.
BUT if the panel could fall on say a public highway, a school, a hospital or similar then I would design the propping for the full wind load.
RE: Wind on Shoring/Bracing for tiltwall panels during construction
Mike McCann
MMC Engineering
RE: Wind on Shoring/Bracing for tiltwall panels during construction
ANY FOOL CAN DESIGN A STRUCTURE. IT TAKES AN ENGINEER TO DESIGN A CONNECTION."
RE: Wind on Shoring/Bracing for tiltwall panels during construction
by that logic we should reduce all highway speeds to 30mph to allow for the occasional kid that may try to cross it!
Rowingengineer,
This reduction of wind speed is standard practice for temporary works. The cost of the additional bracing would far outweigh the risk. I think you will find that the onus is on the construction insurance policy rather than the owners.
Lets make this clear, we cannot completely eliminate risk! We can only allow for those reasonably foreseen risks and do our best to reduce them to an acceptable level.
Even if we designed for a hurricane, there is always the chance that nature will hit us with an even bigger hurricane.
This is not just a matter of bigger props, the footing or structure at the bottom of the prop needs to be designed for uplift and would need to be twice as big if the higher pressures were used. If these anchors are into the building structure then it may not be possible to make them work without completely rechanging the whole structure.
RE: Wind on Shoring/Bracing for tiltwall panels during construction
I almost always agree with you. However, a kid in a construction site during a hurricane?!
csd72 hit the nail on the head. We cannot eliminate risk. We can only try to manage it in a reasonable and, frankly, conservative way. 90 mph is already at the upper end of a category 1 hurricane.
RE: Wind on Shoring/Bracing for tiltwall panels during construction
RE: Wind on Shoring/Bracing for tiltwall panels during construction
RE: Wind on Shoring/Bracing for tiltwall panels during construction
this maybe true for us law, but in Australia if the propping is design below the code requirements it will fail the insurance requirements and the onus will fall on the owner.
ANY FOOL CAN DESIGN A STRUCTURE. IT TAKES AN ENGINEER TO DESIGN A CONNECTION."
RE: Wind on Shoring/Bracing for tiltwall panels during construction
I know exactly what you are talking about but AS1170 does have provision for seasonal and short term factors (I think this is in the importance factor now) in the wind section. This is also acknowledged in much of the correspondence from workcover, worksafe e.t.c.
By the way, I think the regulations in Australia regarding tilt-up and precast are some of the best in the world. Many things that you would never get away with in Australia are still regular practice in the US and UK as well as most other parts of the world.
A few good australian references:
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RE: Wind on Shoring/Bracing for tiltwall panels during construction
Since a braced tilt wall during construction usually has no axial load other than dead load, the failure mode we all agree on is pullout failure of the bolts at the slab level?
RE: Wind on Shoring/Bracing for tiltwall panels during construction
RE: Wind on Shoring/Bracing for tiltwall panels during construction
The panel is unlikely to fail as the span is much less and the critical bending stress is usually during the lift from the casting bed.
Actually, thats one more point, I expect you will find that at 120mph wind most panel propping arrangements will fail due to uplift of the panel!
RE: Wind on Shoring/Bracing for tiltwall panels during construction
RE: Wind on Shoring/Bracing for tiltwall panels during construction
And if the contractor and shoring engineer adhered to the established "standard of care", certainly not them.
So it's out of the owner's pocket. Wonderful, just wonderful. So the insurance companies get richer and the clients, who pay us and create thae projects, get poorer.
Just can't agree here guys. I see nothing wrong with the 120 mph provision and extra bracing as needed, maintaining the protection of insurance for the client to a higher level in area prone to these winds during the construction season. This is a minor project cost compared to the potential level of risk. In fact, in the southern areas, that "season" is year around.
Now I'll step back and dodge the flack.
Mike McCann
MMC Engineering
RE: Wind on Shoring/Bracing for tiltwall panels during construction
The reduced wind force is per the code. People are not making it up, it is in ASCE 37, Loads on Structures During Construction. If every stage of every project had to be designed for full 500 year return periods, the costs of engineering and bracing them during construction would be astronomical (not to mention at some stages of construction not even feasible). As always, you have to weigh risks vs costs vs life safety. The risk of a hurricane or storm strong enough to exceed the reduced wind loads hitting the structure during construction is very small compared with the costs of designing and bracing the structure to withstand the full forces. Could we design all buildings with an R=1 to withstand the full force of an earthquake? Sure - but we don't - because it is too expensive and we are willing to take some risk.
RE: Wind on Shoring/Bracing for tiltwall panels during construction