Wind on Shoring/Bracing for tiltwall panels during construction

[steeledan]

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?

 

[msquared48]

So then, who pays the bill when the brace fails at 73? Certainly not the "insurance" company... They'll litigate until the cows vcome home and never pay.

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

 

[WillisV]

Mike-

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.

 

[spats]

Here here! I agree with Willis V wholeheartedly. Renting braces is not cheap, especially when you wind up with 3x the number of braces. I've been designing tilt-up in Florida for 30 years, including doing a lot of bracing design. I can only think of one instance in all that time where a hurricane hit one of my tilt-up buildings under construction. In preparation for the storm (there was plenty of warning) they buried the base of the panels using sand, and tied the panels together across the joints to facilitate load sharing. Maybe we were lucky (I can't recall the actual wind speed) but, again, there is a factor of safety. 72 mph design is good for 90 mph plus, at a minimum. It's not often that braces are at their full capacity under ultimate loads.