Slab check for Truck wheel load. 3

[malikasal]

Hey guys,

i have an existing slab ( Steel Joists With metal deck), and i need to check it against the wheel load of a truck during construction.

are there any references / books that can guide me through the process, especially for the punching shear check under the wheel.

thanks .




ôIf you don't build your dream someone will hire you to help build theirs.ö

Tony A. Gaskins Jr.

 

[hokie66]

That type construction is not typically designed for truck loading, so I doubt you will find a reference. How thick is the slab? What type truck?

 

[Agent666]

It's not that unusual in this part of the world, so a design aid was created by one of our local steel industry bodies. I've used this before (it's NZ based though, and then based on BS5950 approach to composite slab design).

One of the main issues I seem to remember is the breakdown of the bond between the deck and concrete under higher point loads, especially at the ends of the deck.

 

[malikasal]

hey hokie,

this the detail of the slab

the max wheel load is about 2.25 mton.

the approach i am thinking of is this :

i will assume a 2kn/m2 as a construction live load + the concentrated wheel load+ slab dead load to find the moment and assume a 1 m strip to design for flexure.

for the punching shear i will take the max wheel load and check under the wheel , (the question here is how could i calculate the contact area of the wheel)





ôIf you don't build your dream someone will hire you to help build theirs.ö

Tony A. Gaskins Jr.

 

[hokie66]

When you said you had a system with steel joists, I thought you mean bar joists like they use in North America. That would be a much more flexible system than a composite slab on steel beams as shown in your picture. Do you have composite decking?

 

[malikasal]

yea it is a composite deck.





ôIf you don't build your dream someone will hire you to help build theirs.ö

Tony A. Gaskins Jr.

 

[BridgeSmith]

Is it a composite deck or a composite superstructure? I'm not sure from the note whether the studs are attached to the decking (composite decking) or the joists/beams (composite superstructure). It could make a difference in how it's analyzed. Under the AASHTO LRFD, we have what's called 'empirical deck design', which recognizes the that the failure mode of concrete bridge decks is strictly a punching shear failure mode, at a much higher load (about 5 times higher) than assumed for the flexural failure capacity. However, one of the restrictions on using it is that it has to be a composite superstructure. The horizontal arching (load distribution) mechanism may not fully develop without the restraint of the beams/girders.

The AASHTO specs get pretty detailed for slab capacities. When I'm back in the office tomorrow, I'll see what I can dig up related to the configuration you show.

It looks like a prefab superstructure, so if you have info on who designed/fabricated it, you could contact them for the design loading. That assumes you don't have plans showing a design load. If you have that, you can post that, and that would help us sort it out.

 

[txeng91]

I use this for point loads on metal deck. It goes by the AASHTO method for determining effective slab widths for flexure and shear.

http://www.calculatoredge.com/download/DECKSLAB.xls

 

[txeng91]

Do you know what the design wheel load is? With that slab depth I’m not sure you could do anything heavier than passenger vehicles. I’ve found that I usually need around 10”-12” thickness with AASHTO HS-20 Loading (heavy trucks) for punching shear.

 

[BridgeSmith]

txeng91, there are many 7" decks on highway bridges designed for, and carrying, HS-20 or higher loads. The I-35W bridge in Minneapolis did just fine for decades with the original 6" deck. Eventually, it required an overlay and then another, due to wear and deterioration, but not punching shear failures. You may want to reexamine your assumptions of the punching shear capacity of concrete slabs.

I'm having some trouble locating the documentation of the research findings on the empirical deck design (Ontario method) from 1983 at the moment, but the testing proved that an 8" concrete deck, with minimal reinforcing was adequate for wheel loads around 5 times that of an HS-20, before failure. Granted, the failure mechanism was punching shear, but 10-12" thickness is greatly excessive for an HS-20 loading.

 

[WARose]

We were just talking about this on another thread:

https://www.eng-tips.com/viewthread.cfm?qid=451967