Members built integrally with supports

[DB1521]

When is it appropriate to consider a continuous concrete beam to be built integrally with its supports? Does it apply only to a monolythic pour or does it also apply to a beam or slab bearing on a wall with dowels joining them?

ACI 318-08 Section 8.9 addresses what the appropriate span length is for members built integrally and not-integrally, but doesn't specify what is meant by "integrally." This also comes up in Section 8.3.3. The equations in Section 8.3.3 seem to be independant of Section 8.9 since "ln" is defined as the clear distance from face to face of supports.

Can anyone help clarify and possibly provide a source for this info?

 

[hokie66]

Integrally and monolithically have different meanings. A concrete beam should not be built monolithically with a vertical supporting element, but is commonly built monolithically with horizontal supporting elements. While monolithically means cast at the same time, integrally means incorporated so that the two elements act together for resistance of moments and shears.

 

[sdz]

If the beam/slab bears on the wall, with or without dowels, it is not integral with it since there is no continuity of reinforcement across the joint.
(assuming by dowel you mean a round bar that can allow slip)

 

[RHTPE]

It really depends on how the reinforcing is detailed through the joint. Do you have a detail?

 

[DB1521]

Thanks to all for their responses.

The detail would show vertical reinforcing coming up and hooking into the slab or beam with hooks long enough to develop the bar. The slab / beam reinforcing are not specifically spliced or lapped with the hooked dowel bars. Intuitively I think the hooked bars will transfer some moment across the joint. So it's not a pinned connection but it's not exactly fixed either. It would be partially fixed, but I'm wondering if it would technically qualify as being built 'integrally with the support.' The question arises when determining which span to use for calc'g moments.

I really need to back this up with a solid reference such as an ACI commentary or by some other acceptable literature.

 

[sdz]

Post the detail.

 

[RHTPE]

Properly reinforced, it is integral (but not monolithic). The vertical bars on the far wall face should hook into the top of the slab and will be your negative moment reinforcing for the slab. The bottom slab bars (or a portion of them) should extend over (into) the wall at least 6".

Walls & columns are most always cast & forms removed before setting up slab formwork & reinforcing. This has been the norm for my 40 years in concrete construction.

Ralph

 

[RHTPE]

Correction to my previous post - I meant to say 'beam', not 'slab'.

ralph

 

[DB1521]

Ralph - Your post confirms my gut feel for the detail. That's the way I had been taught to interperet details like that. But proving it (with code verbage) to someone who might challenge the interpretation is not easy when ACI is not specific.

Thanks to all for their posts. It has been helpful. I need to research ACI subcommitee papers and find out if they address this topic. I just don't have a lot of time to put towards research right now since I'm swamped with more pressing work.

 

[RHTPE]

DB1521: Constructing beams monolithic with their supports is practically an impossible task. And at what point do you allow a construction joint? Must the supporting members also be cast monolithic with their supports? How far down do you carry it?

Elevated concrete floors often have construction joints to break a floor into 2 or more concrete placements. Yet the completed structure is still considered to be a continuous structural entity.

I suspect that finding a code statement to the effect that "integral with the support" means that the support can be cast independent of the supported member will be difficult. I do not recall ever having come across a statement (in a code document) to that effect.

Ralph

 

[hokie66]

DB1521,

It is never good practice to cast a beam or slab monolithically with a supporting column or wall. The column or wall should always be allowed to harden before the beam or slab is cast to prevent plastic settlement in the vertical element from creating a discontinuity under the horizontal element.