Axial reinforcement info needed

mchoa696

In my exam we may be asked about beams with axial reinforcement. Is this the same as shear reinforcement?

yourpics

mchoa696 wrote: »

In my exam we may be asked about beams with axial reinforcement. Is this the same as shear reinforcement?

No, 2 different things.

RC is usually designed for shear but not axial although it can also fail by axial forces.

breadmonkey

A beam with axial reinforcement seems quite unusual. Could you be a bit more specific about the type of question you're expecting?

mchoa696

The lecturer was naming things that may be asked and two specific ones were: Biaxially bent columns and beams with compression/axial reinforcement!
Dont know if that helps at all. Is Ned usually used to indicate axial?

bnt

The question is a bit confusing, since you don't specify what the reinforcement is supposed to prevent. It won't be to prevent purely axial deformation since that is simply a function of the material strength and cross-sectional area, you don't "reinforce" against that. (ε = N/AE or δ = NL/AE).

If I got this question I would be thinking about reinforcement or bracing against Buckling, and break out Euler's Buckling Load formula. This is used in Eurocode too, but with various modification factors.

bnt

It just occurred to me that the question may be about concrete beams specifically. In that case you could have axial reinforcement to increase its axial capacity. But I imagine it would be problematic, though, since it would need to be designed to transfer its end loads to some other members directly. It could not be permitted to impose high stresses on concrete, obviously. In the design calculations I've learned it was assumed that the concrete alone would handle axial compression, and the steel would take all the tension due to bending moments imposed on the beam.

breadmonkey

mchoa696 wrote: »

The lecturer was naming things that may be asked and two specific ones were: Biaxially bent columns and beams with compression/axial reinforcement!
Dont know if that helps at all. Is Ned usually used to indicate axial?

Do you have any specific examples of questions from the course to date? And yes, NEd would be the design axial force.

bnt

In the most straightforward sense, any reinforcement steel in a RC column can act as axial reinforcement, if designed appropriately and you're happy with what happens at the ends. Increasing the axial reinforcement is a matter of increasing the area of the steel relative to the column area. There are limits on how much of that you can get away with before it causes problems with the concrete pour - I was taught to limit the steel to ~2% of the column area for that reason, but these days the use of self-compacting concrete might let you get away with more.

Eurocodus

Refer to Reinforced Concrete Design, Mosley et al, Palgrave

Beams with axial loads, pg 83 to 89.
Biaxial short columns using interaction diagrams, pg 273 to 275.
If slenderness ratios, short or long columns and design chart construction are examinable, maybe pg 252 to 280

Max reinforcement 4%, 8% at laps.