Wind loads on Row Homes

[gls4286]

We do analysis and design of Brownstone dwellings in NYC. Most of the time we are working with one dwelling in a row of same sized dwellings (often more than 6 units in a row). Since these units were constructed at the same time, one could consider that the wind load applied to the structure perpendicular to the party walls that separate the units is shared by ALL of the units - but there is nothing we can find in the Code (IBC/ASCE 7 or NYC 1968 Bldg Code) that addresses this.

We've approached this conservatively and have considered load sharing for a smaller number of units, as if one of the middle units were gone... (e.g. our unit is #2 of 6 in a row and #3 burns down, so #1 and #2 share the wind load taking 50% each - this also means that #4, #5, and #6 will now see 33% of the wind each)

Is this a reasonable design approach to this? Any suggestions are welcomed!

 

[kieran1]

Don't know about NYC but I always ensure each dwelling has its only stability incase the adjacent one has to be demolished or altered in the future

Kieran

 

[DST148]

As per IBC 2006, Section 1609.1 - Decreases in wind loads shall not be made for the effect of shielding by other structures. There was some thing similar section even in UBC.
In a place like New York City a church may be sand witched by high rise buildings on three sides, yet shielding for design calculation purposes can not be made.

 

[msquared48]

If these are units on one building separated by fire/party walls, as in concdo construction, I would divide the longitudinal force by the shear walls available in the whole building.

I would assume that any individual unit in the structure would be quickly repaired, not upping the overall force to any portion of the structure. After all, we do not assume that a portion of any one residence will become disfuncgtional due to fire or other calamity in our designs. Why would that be different here, irrespective of any code requirements?

Mike McCann
MMC Engineering

 

[hokie66]

If no allowance for shielding is the US Code provision, it is at odds with the rest of the world. Oh, well... Don't you do wind tunnel testing on significant buildings to determine the effect of being in an urban environment?

 

[msquared48]

Shielding is not an issue with structures sharing one common wall, only if there is a breezeway, or a double party wall, where the removal of one part of the wall would still leave the other portion structurally functional.

Mike McCann
MMC Engineering

 

[MiketheEngineer]

I would probably check both cases. And maybe pick something in between unless code prohibited it. But you could always lose a row house to fire or someone with a chain saw!!

 

[Ron]

hokie66...wind tunnel testing is done on significant buildings, but I doubt that a single brownstone would constitute a significant building.

I would model independently.

 

[hokie66]

I wasn't suggesting that wind tunnel testing be done on row houses, but the principle of using wind loads based on the location is the same.

 

[Steve1415]

We've actually run into this problem before when dealing with 3 story very narrow townhouses. We were designing for structural independence, and another engineer got the job because of a clause in the IRC. Section R302.2.4 talks about the structural independence of townhouses. It says that they shall be structurally independent, except in the case of "5. Townhouses separated by a common 1-hour fire-resistance-rated wall as provided in Section R302.2." This is interpreted to mean that if they have this fire-rated wall, they can be designed as a single building. This would imply that your original assumption about the wind loads perpendicular to the party walls was correct.