Beam with opening 2

[dccd]

Supposed we have a long beam , there's an opening along teh span of the beam.

My question is how to calulcate the bendign moment capacity of the beam at the opening location.

1.) Does it still act as the deep beam with effective depth of hb + ht + do ?

2.) Or the part where the beam is on top of the opening is effective in taking the bending moment only ? I shall consider the hb as the beam to take the load only ? Bottom beam just provide nominal rebar since it doesn't effective in taking the load above ?

 

[dik]

You distribute the shear at the opening in flexure at the top and the bottom of the opening. It's good to keep the opening within the middle 1/3 of the span and within the middle third of the beam depth (generally small shear areas). It doesn't work so well with large point loads; these need special treatment. The beam has to be deep enough to accommodate the flexure above and below the opening. I'm also not an advocate of adding the diagonal reinforcing. It just clutters up things in the vicinity of the opening (many engineers differ with this).

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[dccd]

Can i still treat it as whole deep beam (ht + hb + do) ? Or I shall treat the beam above opening with effective depth ht only to take the flexure @ opening area) ?

 

[wrantler]

I would do a strut and tie model on this.
If it truly is a deep beam you need to do this per code in my area.

 

[dccd]

If i want to do it as normal beam approach , can i consider as deep beam (ht + hb + do) ? or only consider ht to be effective only ?

 

[HTURKAK]

The picture depicted has an opening less than 40% of the depth .. In this case ,

- You may use classical beam bending theory,

- Regarding shear strength , you may reduce the effective depth to ( d- do)

I will suggest you to look to the book for further info.: CONCRETE BEAMS WITH OPENINGS (By M.A.Mansur )

Is the picture taken from this post ?

https://construction-site-vn.blogspot.com/2011/12/design-of-reinforced-concrete-beams.html

Don't underestimate a nail. A nail saves a horseshoe, a horseshoe saves a horse, a horse saves a commander, a commander saves an army, an army saves a whole country.. GENGHIS KHAN

 

[dik]

In the vicinity of the opening, two beams having a depth of ht and hb. I'd distribute the loads based on ht^2 and hb^2 (not strictly correct, but close). I'd also treat it as a rectangular opening. Very conservative.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[KootK]

If i want to do it as normal beam approach , can i consider as deep beam (ht + hb + do) ? or only consider ht to be effective only ?

For primary flexural design, you can and should consider your reinforcement to be acting over the full depth of the beam. The hole will primarily impact the beam design in these ways:

1) Significant impact to shear capacity for significant holes and;

2) Local increase in rebar demand at all levels as result of the Vierendeel behavior across the hole which may result in:

a) small stirrups across the hole.

b) flexural rebar at the top and bottom of the small concrete members that span the hole.

c) longitudinal rebar that is additive to the primary flexural rebar.

It would be very useful for us to know the following:

- the depth of your beam.
- the diameter of your hole.
- where your hole is located within the depth of your beam.
- whether your primary flexural rebar is the top of bottom steel at the location of interest.