Wind interference effect due to adjacent buildings 9

[Er KCJ]

Hello,

I need to calculate the wind load on a building height 32m that sits next to a 55 m building six meters away horizontally. What will be the effect of the taller building on the face of the shorter building that is towards the taller building? Is there any technical note or code reference for this?

 

[WARose]

I don't know of any (at least as far as any kind of cookbook formula). For as long as I can remember, ASCE 7 has prohibited any kind of shielding consideration when figuring wind loads. (Almost forcing you into a wind tunnel test if you want to get precise.)

 

[phamENG]

If you want to lower your wind load, you can't. Can you guarantee the adjacent building will stand longer than yours? No, so you can't count on it a shielding.

If you want to be sure the wind load won't be larger, you'll either need a robust simulation (solidworks, maybe?) Or a physical, scale wind tunnel test.

 

[BulbTheBuilder]

Others have mentioned not being able to reduce your wind. You'd have to consider full wind on the structure. However, wind tunnel test is the best approach to something like this. You could encounter issues related to vortex and crosswind which are properly accounted for in the wind tunneling method.

 

[driftLimiter]

These responses are right. I heard Dlubal software has a wind module that can do wind simulation now, I don't know if it can handle your separation problem or not though.

 

[Er KCJ]

Thanks a lot everyone for your responses! I have decided not to lower the wind load. See the attached extract from IS 875 Part 3. This includes a table and a figure and provides factors for interference effects. Since all factors > 1, this means the loads would increase as per this reference.

 

[human909]

Wow... You learn something new everyday. Down under we have a whole section on shielding in our wind code. You can gain as much as a 30% reduction in wind loads due to shielding.

However the recent code update reduced it to buildings under 25m.

 

[bkal]

EN 1991-1-4 states the following:
4.3.4 Large and considerably higher neighbouring structures
(1) If the structure is to be located close to another structure, that is at least twice as high as the
average height of its neighbouring structures, then it could be exposed (dependent on the properties
of the structure) to increased wind velocities for certain wind directions. Such cases should be taken
into account.

 

[MultiVar]

TURBULENCE is the word/concept everyone's toeing up to. Also Venturi Effect. While not trivial to model turbulence, there's never been a time with so many proven mature tools, most good enough to avoid having to build physical wind-tunnel models. Will this be a steel-framed or concrete structure?

NOT a Civil/Structural Eng., but in a prior century, I developed Mechanical/Structural CAD S/W that incorporated ACI 318. NOT a Computational Fluid Dynamics (CFD) wizard, but plenty of consultants/uni professors are.

You're probably not in a HVHZ, but I am (So. Florida), and have seen real-world inter-building turbulence "work" things loose over a 5-15 hour hurricane passage. Fasteners and anchors that would hold indefinitely under the constant steady load of the proverbial stationary testing via aircraft engine + propeller, will fail after just a couple hundred turbulence-induced push-pull "work" cycles. Think about it, you only ever see PULL-OUT values for anchor failure (performed in slow-mo, with a hydraulic jack). I've never seen a "PUSH-then-PULL, M times, at N strokes per minute" test value... hmmm... (OTOH I only use these items at the handyman/homeowner level.)

If you want a dramatic example of (rapidly-varying) Venturi Effect suctioning windows off a high-rise bldg., see L'Hermitage Condos, Fort Lauderdale, FL, Oct. 2005, Hurricane Wilma. This property is 2 identical concrete-core towers, ~100m height, whose plan is shaped like 3-leaf clovers, "notched" into each other, resulting in a very "snakey, S-turn" wind-path between the towers. That was only a mid-range Cat 2 at that location. Keep in mind these twin towers are post-Andrew, late 1990s construction, built to the latest strictest codes. (If I had a PE stamp, I wouldn't want it on that structure... architects got artsy with the complex shape--which IS way nicer than a boring rectangle--but it seems the PE/SE didn't do the "fancy" modeling...?)

You don't say how much "face" your proposed bldg. presents to the existing tower, and if parallel or angled, but 6 meters seems "tight", and could create significant NON-steady Venturi pressure-drops with wind velocities well below hurricane strength. I assume this is some dense urban area, and other towers could be erected equally close to the other faces/aspects of your bldg...?

Just based on case-studies and anecdotes, if I were the AHJ, I'd specify the attachment of the glazing should be BETTER than what was used on the 55m tower. "Not fair!..."

 

[Er KCJ]

Thanks all for your responses and sharing knowledge!

@MultiVar:
Will this be a steel-framed or concrete structure?
Concrete

You don't say how much "face" your proposed bldg. presents to the existing tower, and if parallel or angled, but 6 meters seems "tight", and could create significant NON-steady Venturi pressure-drops with wind velocities well below hurricane strength. I assume this is some dense urban area, and other towers could be erected equally close to the other faces/aspects of your bldg...?
Proposed building is 21 x 42 meters in plan.
Existing 55 meter tall building has same plan.
Long sides of both the buildings are aligned and not at an angle.
On south side of existing building is a lake, on north is a vehicle street. On the east there is a garden. And on the west is the 55 meter building. So I don't foresee much changing on south / east and north.