flexular development length for existing beam (newbie) 2

[delagina]

if i have an existing concrete beam and i add a load at the center. if for example i will need extra 4-#8 bar 6'long for flexure.

how do i develop this rebar?

should i just chip 6' long of concrete then drill the rebar at both ends with Ld length. so the total length of addtnl rebar is 6 + 2(Ld) ?

i understand if this is new concrete i just have to extend the rebar by d or 12db distance.

thanks,

 

[BAretired]

Provide a sketch of what you are attempting to do. Your proposal sounds dangerous to me.

BA

 

[delagina]

here.. am just trying to ask how do i develop the additional rebar..

thanks,

 

[BAretired]

How do you place the 4-#8 bars into the drilled holes?

BA

 

[hokie66]

The stirrups are in the way of adding more reinforcement as you propose.

 

[delagina]

so how do i solve this if i need additional rebar at the center? how do i increase the flexure capacity of that existing beam?

sorry for this newbie question.


thanks,

 

[hokie66]

A number of ways come to mind: 1) Add to the sides of the beam to accommodate additional reinforcement, ensuring that the sections work together by dowels, etc. 2) Add to the bottom of the beam with same precautions. 3) Steel plating to bottom of beam. 4) Carbon fibre reinforcement. 5) Provide steel beam under to take the load. 6) Others.

Not a simple job to either design or build. If you haven't done it before, seek help from your mentor.

 

[delagina]

at BA ,

i am just basing this solution similar to increasing the size of foundation and adding hilti rebar to develop the additional concrete.

not sure if it will work for beam as well.

 

[delagina]

thanks hokie66,

do you recommend any book about this?
not only beams, but columns, foundations, etc..

basically how to increase the capacity of reinforced concrete "the right way" ahahaha

 

[rscassar]

If your concrete beam is required to take more load and you have performed an engineering assessment to determine the beam needs to be strengthened for flexure only (i.e. the structure works for shear, service considerations and all the other good things that need to be checked when it comes to reinforced concrete design). I would highly recommend the use of externally bonded carbon fiber reinforcement (refer to hokie66 design option #4).

Do your require an additional 4-#8 bars for a 6' long zone at the centre of the span? 6' will not be long enough to develop a #8 bar (maybe just).

If, and only if, externally bonded carbon fibre reinforcement can prove to be a viable method to strengthen this beam, then you will need to hit the books for the weekend and study up on the latest in structural applications of carbon fibres (usually takes a good weekend). This is a structural material which requires prudent engineering judgment and as a result you will need to become very learned on the topic.

I hope you haven't been given something to look at by a senior colleague and told 'make it work'.

 

[csd72]

One option that may be considered is changing how the load is applied to the beam, can you provide a spreader to spread the load across a width and thus reducing the peak of the moment grapph.

Agree with the others that your original proposal is not buildable.

 

[delagina]

hi guys.. thanks..

this is not real case
i am in a project doing retrofit of existing plants so just decided to ask in case i encounter this problem..

i am still searching for a good concrete book that deals with different good methods/approach of strengthening reinforced concrete beam, column, slab and foundation..

 

[rapt]

Delagina,

It is not as simple as what you suggest. There are code rules about termination of reinforcement in the tension zone, relating to shear etc. You need to look into those rules in your code. To terminate them where you are suggesting would probably require extra shear reinforcement and introduce more tension into the member at the termination point.

You would also need to check the effects of increased deflection.

As Hokie said, talk to your mentor. If you do not know you should either not be considering doing it yourself or should be working under someone who does know the rules. Getting information from this site only masks your lack of understanding of design. It would be better if your mentor knows what you do not know so he can help you!