slab and beam modeling

[yasir1989]

I'm trying to model a two-way concrete slab and beam system in etabs. I have the slab elements( h=150 mm) and rectangular beams (400 mm depth x 300 mm width) , but when I view in 3-d, it appears that everything is being modeled from the centerline of the elements. How can I change my model so that the top of the slab and top of the beam are at the same elevation.
someone tell me to make insertion point of beam is top center but i do not know how much the depth of beam after change the insertion point
please help me

Thank you

 

[MrHershey]

In my experience, beams are usually modeled with top of beam at the level they're being modeled at.

But you can change this by changing the cardinal insertion point of the beam.

 

[yasir1989]

Thank you for your interest
but can you tell me the dimension of beam should i insert in program if have beam (0.4 m depth x o.3 width)
and slab depth (0.15 m) ?
so the dimension of beam in program (0.55 x 0.3) or still the same (0.4 x0.3) .i have some confused which is the best method for modeling the beam.

 

[johnbridge231]

The beam should be modeled as it is, eg 0.55x0.30.
If you want to be more precise, you can assign a reduced bending stiffness modifier for the slab elements.

Analysis and Design of arbitrary cross sections
Reinforcement design to all major codes
Moment Curvature analysis

http://www.engissol.com/cross-section-analysis-design.html

 

[inggelu]

Hi there, I think you should use the beam 0,40m x 0.30m if you model has the beam as 0.40m height (depth), otherwise you will have a beam with 0.55m height. You should not add the depth of the slab to the beam. Only if you need a beam with 0.55m height (depth) you can use this value for the beam. Usual the depth of the slab is common on beam, so in the 0.40m height is included the 0.15cm of the slab, of course you must define the beam on the top center. You can play with this, select the beam, go to menu Assign > Frame > Insertion Point and take what you need Cardinal Point (Top center, Middle Center etc....). But remember if you use for define section of the beam as 0.55m the design will be for this beam depth (height), not for 0.40m depth as should be. You can check this when you design the beam to see what section is take it. from 0.55 to 0.40 can be a big difference, special if you don't need a beam so big.
If you decide to use the influence of the slab (take in consideration as "T" beam) you should define in other way the beams and the slab. But you can ignore this influence because it is an plus for bending moment. But this is different discussion.
As conclusion from my point of view you should not ad the depth of the slab to the beam height, if you design a beam as 0.4m depth, otherwise you will affect the results.
You can play with an easy model, four columns, four beams, an slab and one story and see the difference of the results. Choose the different Cardinal Point insert and different beam size.
Good luck.

 

[yasir1989]

Thanks all for important notes
as i conclude form notes i use beam (0.4m x0.3m) and top insertion point to get good modeling of beam and slab