Property Line Setback for tall buildings/Maximum inelastic response displacement
Property Line Setback for tall buildings/Maximum inelastic response displacement
(OP)
Hello-
I am in charge of designing a hirg-hrise tower in California. The developer wants to use every square foot of the site. However, on one side of the site there is a restriction that a potential future development might happen. So as per ASCE 7-10, 12.12.3 the tower needs to set back by at least "Maximum inelastic response displacement δM from the property line. The current tower is 330 ft high, so allowing for max. 2ft elastic displacement (H/165) at top and considering Cd=5.0 and Ie=1.0, δM will be equal to 10ft. This is a substantial set back from the property line and conducive to loss of a lot of squad footage!!
The question is what else i can do to avoid this clause? Do you expect to achieve smaller values if you conduct an analysis based on inelastic response to design ground motions?
any help is greatly appreciated.
I am in charge of designing a hirg-hrise tower in California. The developer wants to use every square foot of the site. However, on one side of the site there is a restriction that a potential future development might happen. So as per ASCE 7-10, 12.12.3 the tower needs to set back by at least "Maximum inelastic response displacement δM from the property line. The current tower is 330 ft high, so allowing for max. 2ft elastic displacement (H/165) at top and considering Cd=5.0 and Ie=1.0, δM will be equal to 10ft. This is a substantial set back from the property line and conducive to loss of a lot of squad footage!!
The question is what else i can do to avoid this clause? Do you expect to achieve smaller values if you conduct an analysis based on inelastic response to design ground motions?
any help is greatly appreciated.
RE: Property Line Setback for tall buildings/Maximum inelastic response displacement
Per ASCE7, I believe that your maximum drift will limited to H/50 as opposed to H/33 as you've indicated. So that gets you down to 6.6' which is an improvement.
This is often the case, yes.
You can't avoid the clause but what you can easily do is simply design the structure to be stiff enough to control deflection as you see fit. del_M varies linearly with del_max, the elastic drift. And you can control your elastic drift by simply providing a stiffer structure. Therefore, you can control del_M. Stiffening the structure will cost the owner some money. It's up to the owner as to whether or not the extra SF is worth the trade. Even in quake country, H/50 is a lot of drift for a 330 ft building.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Property Line Setback for tall buildings/Maximum inelastic response displacement
DaveAtkins
RE: Property Line Setback for tall buildings/Maximum inelastic response displacement
You are likely correct but the maximum inelastic response displacement would be much larger.
RE: Property Line Setback for tall buildings/Maximum inelastic response displacement
RE: Property Line Setback for tall buildings/Maximum inelastic response displacement
If the architect (or whoever) is fighting the extra structure, may want to bring this up. Even if you can technically do it, it isn't free.
RE: Property Line Setback for tall buildings/Maximum inelastic response displacement
Thaidavid