Impact Load from Car/SUV on a concrete column 2

[Mike188613]

I am designing a 3 story wood structure with parking underneath. The structure is open at the parking level, and I have one post in the structure that is critical to the structure. If it failed, the structure could collapse, and it is exposed to vehicle traffic. Does anyone have an idea of how much impact load I should be designing the column for. I know that it is F=MA, but is there a code requirement for size of the vehicle, and speed that needs to be designed for. I don't think it makes sense to look at bollard design, as bollards can fail and deflect, whereas this post needs to remain standing.

Any thoughts would be much appreciated!

-Mike

 

[TehMightyEngineer]

A lot, probably more than is realistic to support safely. Highway traffic barriers are designed to be able to be damaged during impact and are designed to redirect traffic; not to withstand a direct, perpendicular impact, undamaged. The loads for a direct impact without damage are going to be probably in the 20+ kip range at least as a rough guess.

I'd design a protective system to armor the column. I've seen steel plates embedded into the concrete columns with shear studs used in mill take a lot of hits from forklifts without excessive damage.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[Ingenuity]

This October 2008 Structure Magazine article entitled "Designing Edge Barriers in Parking Structures" may be a starting point: Link

 

[MotorCity]

For the scale of structure you are dealing with, I would guess that it would be prohibitively large to design a column to continue to function after being struck full speed by a car. I think the public would expect some degree of collapse after a car runs through it. That is an extreme event, kind of like designing a skyscraper for being hit by a 747. I seem to remember seeing somewhere (maybe in an AASHTO spec) that (bridge?) piers should be designed to resist an impact force of 600k. To get an idea of scale, think of the size of tree trunk or bridge pier when you see a horrific accident with a car wrapped around it. I'd say its on the order of 3' diameter. What about the exterior walls? I would imagine there would be collapse if the car hit an exterior wall assuming its load bearing. That's exactly the point of bollards....they fail and deflect instead of your column.

 

[Mike188613]

This is never going to be designed for 600 kips, but maybe 20kips.

I am at worst picturing an SUV going 15 MPH and hitting this.

I am right now looking at a 14 x 14 concrete column. The column will be attached to a steel beam at the top which is into the floor diaphram, and then creating a thickened slab, maybe 10 feet by 10 feet around the column to create a reaction at the base. I would then run the column as a simply supported beam, and run the load case of perhaps a 20 kip load at 4-feet up from the base, dead load. I know these numbers are kind of out of left field, but I am looking to see if I am in the right ballpark with this. Just gut feeling is that this all seems reasonable.

Thank you for sending along that article, I will check that out as well.

 

[IRstuff]

You could also "guard" the column with concrete/steel barriers or posts.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[Lomarandil]

Another vote for bollards here. Plenty of pre-engineered systems available that will guard your column.

----
The name is a long story -- just call me Lo.

 

[hokie66]

I have designed plenty of columns in underground car parking garages, with multistory buildings above. Unless in the way of a truck, and headroom normally takes care of that, they are never protected.

Having said that, my columns have always been at least 16" square, and as part of a concrete structure with concrete floors above.

Perhaps you could design the supported beam for more robustness, similar to earthquake and blast design principles, so that the entire building retains some integrity with damage to that column.

 

[bridgebuster]

I thought there was something in IBC about a 12 or 16k force but I couldn't find it. Maybe my memory is failing me and it was a specific requirement on a project I did a few years ago. IBC implies do nothing unless you have vehicles over 10K but then it doesn't say what to do.

Anyway I came across this link on ET Link, which doesn't say much. If you're really worried and can't use a bollard, how about a steel jacket?

 

[KootK]

Similar to hokie's experience, I've designed oodles of low rise parking level columns in north america and almost none have had any kind of explicit protection. Mostly not open but still... And columns with one face 12" wide are very common owing to their being invisible to parking stall layouts in most jurisdictions.

I think that the "threat" in these situations is mostly a bumper impact induced shear failure from relatively slow moving vehicles. The 15 MPH SUV as you say. Consequently, were I to do anything, I would probably pound the bottom three feet of column full of ties. That, combined with integrity reinforcing compliance above, strikes me as reasonable. In your particular case, some ductility and/or reserve capacity in the connection between your concrete column and the steel beam above probably makes sense too.

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.

 

[dik]

Can you use PWF treated lumber and cast a concrete 'elephant's foot' around it? like a 30" or 36" dia 'bollard'?

Added: I used PWF since the structure is wood...
Dik

 

[wannabeSE]

Now, the IBC (2105 section 1607.8.3) references ASCE 7-10 section 4.5.3 for vehicle barrier systems. Vehicle barriers need to resist a 6,000 lbs load. See ASCE 7 for more details