Hairline crack in beam 1

[akgtm]

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1650946160/tips/01_kwl9qn.pdf[/url][URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1650946194/tips/02_cjoagm.pdf[/url]I found hairline crack running diagonally in newly constructed beams. The crack is visible and very small in size, should I be concerned about it?. I also see similar cracks in top of beams but running horizontally below slab. The structure span is 7 meter and has primary beam of depth 500m, sec beam depth is 400mm and has cantilever of span 1.5 meter.

 

[HTURKAK]

The picture implies the horizontal beam is the primary beam with depth 500 mm and the vertical one is secondary beam with depth 400 mm.. In this case, most probably max. span moment of primary beam would develop at junction and these are tension cracks..Moreover, if the span 7.0 m, the depth 500 for the primary beam may not be sufficient for displacement control.

Beam to beam junctions may require bent -up hangers .

If you provide more info ( a sketch, plan showing the structural plan and junction reinf., ..) you may get better responds.

 

[akgtm]

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1650945939/tips/02_a8oxpt.pdf[/url][URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1650945955/tips/01_chr612.pdf[/url]

 

[HTURKAK]

Er . akgtm (Structural),

I looked to the snaps of dwgs which you have posted. Apparently the depth of the primary beams 15 in and that makes 375 mm not 500 mm.. The reinf. of the primary beams 1,2,4 E-F should not be the same .. I am not familiar with the notation and just asking a clear answer ;

- The bottom reinf. 2 Φ 20 is continuous and there are only 2 Φ 20 at section M-M is this true?

- Additional bottom reinf . 2 Φ 20 is provided only at spans of 11'-8'' beams and there are 2 Φ 20 + 2 Φ 20 reinf at section N-N is this true?

If these are true , The span /sagging moment of the primary beam is max. at junction with S.Beam where addtional bottom reinf SHALL BE provided but only 2 Φ 20 rebar is there .. In this case,most probably the cracks are tension cracks due to insufficient amount of bottom reinf.

Other comments ;

- The additional top reinf . at span is meaningless ( section M-M) .. they only should be provided at column support locations

- The reinf of P Beams at axis 1,2,4 should be different

- The top reinf . for S.Beams should be provided at junctions with P. beams not two S beams junction..

 

[akgtm]

@HTURKAK There are 4-20Φ bar at bottom in section M-M and 2-20Φ,2-16Φ bar and 2-16Φ extra at top.
And additional reinforcement is provided in every beams and there are 4-20Φ at section N-N. I used 500mm as effective beam depth as reference with slab. I’m Unsure whether it is critical or not and what method should i take to resolve the crack? I’m also seeing minor hairlike crack running in full depth of P beam, that goes all the way from bottom to its side.

 

[HTURKAK]

Dear akgtm (Structural),

Still it is not clear for me the bottom and top reinf. at the junction ..

I suspect the structure modelled with different beam no's and the software provided the span and both support reinf. amounts.. The interpretation of section M-M at midspan of P. Beam implies the reinf. is not accurate interpreted ..

I will strongly advise to ask the services of an experienced structural engineer . It is better to run the model with existing concrete quality..