Steel Joists Supporting Parking 1

[cal91]

Hello,

I have a steel framed building currently in design phase. It will have rooftop parking, no Trucks, so 40 PSF live load. The spans will be 55'-0", will have a 4" topping slab, over 3" structural slab over W3 deck, so 10 total thickness. With the spans being 55'-0", we are looking into using joists in lieu of wideflange. The main concern is vibration.

I'm looking for vibration input and acceptance levels for parking but cannot find any. AISC's vibration design guide says nothing about parking, and AISC's parking design guide says nothing about vibration. Does anyone have a reference I could use?

Also, I've only been able to find two jobs that have used steel joists to support parking. Does anyone else have experience in this regard?

Thanks,

Cal

 

[lexeng18]

Not sure that you will be able to find any publications that will have dealt directly with this issue, however short of enlisting a vibration specialist to do some FEA you can be proactive and use good practice methods to reduce vibrations. Things like specifying minimum Ix requirements for the joists, increase joist spacing as much as the decking will allow, or even rotating/interrupting framing between bays will all help to reduce the amount of vibrations that the structure will transmit.

 

[cliff234]

I would never use joists for a parking deck. The two joist-framed garages I've seen over the years were in absolutely horrible condition. I suggest contacting SJI and asking if they have any recommendations for the use of joists in garages. I'll bet they recommend against it.

 

[dik]

I'd be reluctant using OWSJ (long span 40"+/- deep for parkades... have to be real careful with corrosion issues and fatigue on the welded connections... You have to be very careful about coating systems. It can be done, but need to be careful. In the last 50 years, I've been involved with about 50 parkades, but no OWSJ... due to the lack of mass, OWSJ may be more prone to vibration.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik

 

[sbisteel]

I'll add a 3rd vote to avoid OWSJ for parking garages. Only seen one in my life but it had many problems; cracking slab, corrosion, popped welds among the big ones.

 

[HTURKAK]

Open web steel joists is not recommended for Steel-Framed parking structures. Vibration and deflection in joist systems could create crack problems for the deck system. Open joist system can also create problems for the application and maintenance of coating systems.

Refer to AISC Steel Design Guide 18.

 

[BAretired]

I agree that Open Web Steel Joists should not be used for parkades.

BA

 

[GeorgeTheCivilEngineer]

This won't be very useful so I mention it out of interest... In the UK the IStructE did a tiny amount of research which basically concluded that the suspension in cars meant you could get away with natural frequencies down to 3Hz.

"...In stand-alone car parks with lightweight
construction and spans up to 16.0m it has been
found that a minimum natural frequency of 3Hz is
satisfactory. This vibration frequency is that calculated
for simply-supported primary beams and floor slabs,
together with secondary beams where appropriate
within the effective width. Cars parked on the decks
provide additional damping to the structure by their
mass supported on damped suspension. Additional
guidance for such situations with cars present and
absent within the structure is provided on page 14 of
Steel-framed car parks published by Corus. Any
end restraint will assist in damping the vibrations and
its contribution should be considered if justification of
the vibration characteristics is by in situ testing of the
completed structure.

Unusual or long span structures may be more
sensitive to dynamic loading and their response to
vibration should be checked. Irregular surfacing,
badly aligned movement joints, and speed-retard
humps can have an adverse effect on dynamic
movement."

The Corus document I did eventually find and it basically said no one had complained yet about wobbly car parks.