Continue to Site

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

  • Congratulations waross on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

thin existing concrete slab - adding new support? 1

Status
Not open for further replies.

mats12

Geotechnical
Dec 17, 2016
181
Well hello!

I have existing concrete slab - it is only 140 mm thick.
Reinforcement is sufficient for self weight only - No top reinforcement, bottom reinforcemenet just sufficient,
I'd like to add screed and other layers on top - so permanent and imposed load will be increased.
Since existing reinforcement is insufficient I am planning to add extra support in the middle - steel beam that is supported on columns and existing walls.
That way my reinforcement at the bottom is still OK after the load is incresed.
I also get one-way slab.

My question - I have no top reinforcement in the middle of the span, but since I intend to add steel beam as support I will get tension in the top zone of the slab (above steel beam).
I was thinking about using FRP straps but I have never worked with it. Is this solution alright since there is no top reinforcement in the slab - so all tension forces are taken care of by FRP? or is there something better that comes to your mind?

Hope for some help.

Bye


EXISTING SLAB:

a_klgyqm.png



AFTER ADDING STEEL BEAM AS NEW SUPPORT:

b_ffljpn.png
 
Replies continue below

Recommended for you

Bottom reinforcement seems to be adequate for a simple span slab.
I was thinking to sawcut the top of the slab over the new/added support (steel beam).
That way I get simple span slab with no reinforcement needed at the top.

New screed + ceramics will be added afterwards. Should I expect cracks in screed (above sawcut)? Putting a reinf. mesh in screed may prevent that.

nwq_y9gqya.png
 
mats12 said:
1) Should I expect cracks in screed (above sawcut)?

2) Putting a reinf. mesh in screed may prevent that?

1) Yes. Consider deflection of the two, one-way, simple spans:

one-way_slab-400_wiagpr.png


2) No.

Put a joint in the screed directly over the saw cut. If the screed is continuous, you are right back where you started... a slab without proper reinforcement for negative moment over the support.

[idea]
 
I agree with SlideRuleEra.

My question regarding this topic - How deep the sawcut should be? 1/3 of the slab thickness? 1/2?
 
n3jc - The slab is so thin (140mm) that existing rebar could be anywhere in the concrete (there is not really a "top" or "bottom" inside the slab for the rebar). To make sure the two slabs are truly independent, I would cut deep enough to guarantee that all rebar was cut. That means the saw cut would be essentially full depth.

If the saw cut was not deep enough, there is a real chance that existing rebar is cut in some places but not in others... not good.

[idea]
 
Status
Not open for further replies.

Part and Inventory Search

Sponsor