When is Moment Reduced in Reinforced Concrete Design?

[niz]

Hi!
I'm having some difficulty trying to clear some things when designing r.concrete slab and beam.
My question is : when do you reduce moment ?
I am aware we reduce moment over support...but when that support is in middle of beam .(continuous beam)
For simply supported beam we don't make reduction of moment.
Then i read on one place that we do not reduce moment over support in cantilever beam...is this true..?
can anyone give me cases when we do reduction of moment for beams and slabs..?
Thanx in advance!

Niz

 

[radou]

Hi!
I'm having some difficulty trying to clear some things when designing r.concrete slab and beam.
My question is : when do you reduce moment ?
I am aware we reduce moment over support...but when that support is in middle of beam .(continuous beam)
For simply supported beam we don't make reduction of moment.
Then i read on one place that we do not reduce moment over support in cantilever beam...is this true..?
can anyone give me cases when we do reduction of moment for beams and slabs..?
Thanx in advance!

Niz

You do moment reductions over supports on continuous beams (middle supports) in general because the bending moment function you get (by using a simple statical system approximation for your beam) has greater values (in the neighbourhoods of these points) and a different 'shape' than a more realistic moment function.

 

[niz]

what about cantilever beam and cantilever arm?
do we make moment reduction for these two cases as well?
or...because of the safty we dont..?

 

[radou]

what about cantilever beam and cantilever arm?
do we make moment reduction for these two cases as well?
or...because of the safty we dont..?

I think there is no need to do moment reduction in the case of a cantilever beam, at least I didn't see a case/argument to do so yet.

 

[niz]

thank you so much for your help :)

 

[radou]

thank you so much for your help :)

No problemo, I'm glad I helped.