Slab with opening

[EJS23]

Hi guys,im designing a slab with 2 openings would you design it as a slab with no openings ?

 

[oneintheeye]

no I would deign it as a slab with openings. Unless they are very small.

 

[rowingengineer]

I second Herewegothen’s suggestion and would also suggest that you check punching shear if the opening is near a column.

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it

 

[oneintheeye]

it would also be helpful to have more details, is it suspended, ground bearing, composite deck?

 

[rowingengineer]

maybe even the size of the opening and location?

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it

 

[EJS23]

Hi guys heres a sketch

 

[oneintheeye]

can't download. have you used the attach file option in the message box at the bottom? The file you used is filtered out by company server.

 

[EJS23]

Sorry herewegothen please try this link guys

 

[oneintheeye]

those are some big holes (in relation to total area). Slab looks a little thin as well at 170mm if it is suspended. You will need to design as strips around the holes to enclose them.

 

[EJS23]

Thanks herewegothen just please check the drawing that ive attached and what do i do with the area's arround the holes marked "X" on the sketch

 

[oneintheeye]

i would design then as spanning (as beams ) to strips 1 and 2 as the slab will tend to span across the page (the 3500 dim). This will increase the load on an effective beam spanning on strips 1 and 2. I would also put diagonal bars around the corners of the holes to resist cracking from the corners of the holes. Hope this helps.

 

[hokie66]

I would add beams at the ends of the openings. The "X" areas would just span to the upstand beam at the sides of the openings, and the upstand beams would span to the new downturned beams.

 

[oneintheeye]

not sure if I'm interperating hokie correctly. My aaproach would be to ensure enough steel for the x sections to span up/down the page for a span of slab opening + effective depth. Then say effective depth is x then provide enough steel in a strip going across the page of width (effective beam) x times 2. This strip will take the UDL on the slab plus the reactions from the x sections. Then you will have enough capacity to take the load and distribute it back to the walls.

 

[hokie66]

herewegothen,
I was just saying that I would provide a thickened slab band spanning across at each end of the opening rather than making the whole slab thicker.

 

[asixth]

It's not uncommon. I designed a service passage spanning similar dimensions supported on a blockwall one side and dowelled into an existing rc beam the other, 200 thick and spanning 2500. Typical 1000x1000 peno's to access a water tank below. Your peno's look like they are mechanical risers. The slab has a hob which you could reinforce so it behaves like an upstand beam to help trim around the opening in the direction opposite to the span.

Check the long term deflections of the strips spanning either side of the opening. Because they are going to have a higher load the may deflect more with time.

 

[paddingtongreen]

I haven't anything to add to the good advice, but asixth, what is a "peno"? I think I can guess but I would rather know for sure.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[asixth]

I should of wrote "opening" instead of "peno" referring to penetrations.