ETABS

[VCHFCE]

Hi,

1. Modeling slabs in ETABS :
*option membrane - intended to transfer vertical loads according programmed and described in Manual rules - mainly relaying on geometric properties ( like yield line method ) and support condition, without bending stiffness; can be applied for two and one way slab;although elements can be meshed this is not need - load transfer is not affected;
*opt deck - properties similar to membrane but to model one way slabs - direction of load transfer can be changed by the user by rotating local axes; meshing is not need
Above opt. are recommended when loads are distributed - there is not point and line loads across slab
* opt. plate or shell - vert. loads are transferred according bending thickness (and boundary condition of course ) ; can model all types of slab; meshing is recommended; user can "regulate " proportion" of the load transfer :
** mainly by stiffness modifiers - bending m11, m22, m12;
** stiffness of the surrounding beams - if any
Last opt. - shell is the most general - allows user to model situation with point and line loads on the slab. Results on the support columns - flat slab with/without drop panels are strongly dependent on bending stiffness.

Later I can give more comments and share experience - if this is of interest
- for beam and col design
- for beam stiffness modifiers

[juice]

Hi,

1. Modeling slabs in ETABS :
*option membrane - intended to transfer vertical loads according programmed and described in Manual rules - mainly relaying on geometric properties ( like yield line method ) and support condition, without bending stiffness; can be applied for two and one way slab;although elements can be meshed this is not need - load transfer is not affected;
*opt deck - properties similar to membrane but to model one way slabs - direction of load transfer can be changed by the user by rotating local axes; meshing is not need
Above opt. are recommended when loads are distributed - there is not point and line loads across slab
* opt. plate or shell - vert. loads are transferred according bending thickness (and boundary condition of course ) ; can model all types of slab; meshing is recommended; user can "regulate " proportion" of the load transfer :
** mainly by stiffness modifiers - bending m11, m22, m12;
** stiffness of the surrounding beams - if any
Last opt. - shell is the most general - allows user to model situation with point and line loads on the slab. Results on the support columns - flat slab with/without drop panels are strongly dependent on bending stiffness.

Later I can give more comments and share experience - if this is of interest
- for beam and col design
- for beam stiffness modifiers

Thanks VCHFCE; all forum members are encouraged to share their experiences, lessons learned, etc. from using ETABS. Let us learn more about ETABS from each other's thoughts :cool:

[junaid]

To All:

Always define your slabs (one way or two way) as shell or plate. and Shear wall as membrane. (As per CSI recommendation in Manual)

Meshing size should be at least 4x4.

The difference between shell and plate is DOF (Degree of Freedom).
Shell has 6 DOFs (require more computational efforts) n Plate has 3 DOFs.

Last but not least Plz do not trust software generated result, use your fundamental engineering know how while analysing or designing any structure.

regards

Junaid
Structural Engineer
Mott MacDonald Pakistan (Pvt.) Ltd.

[Yasir]

Dear All;

How many of you have designed composite beams on ETABS? I tried to design but it differ from manual calculations. Moreover for the same model AISC LRFD 99 doesnot give the result but 94 gave... Some of our friends also experienced same problem...


Please share your experience and tips if any..

Regards

[juice]

Yasir, personally I didn't use ETABS to design the structural components of buildings that I designed. ETABS is trustworthy when it comes to analysis but I am not comfortable with getting the complete design done by ETABS as I may not be able get a good feel at the outcome of what I am designing. ETABS should be not be taken as a black box for structural design of buildings. Also, look at structural engineering as an art--with a designer's personal touch.

What you have done, designing or analyzing the composite beam outside of ETABS environment is a better approach, in my opinion.

;)

[junaid]

Dear All,

Has anyone performed THA (Time History Analysis) in ETABS? If yes then plz guide me how should i do that and what are the important checks that should be consider while using THA feature?

Regards,

Junaid
Mott MacDonald Pakistan (Pvt.) Ltd.

[Yasir]

@Juice

Thnx for ur correspondance. I tried to design it with ETABS but due to wrong answers i had to revert back to manual calcs.... m still in search of it and will research for this... but da same happened with some of my fellows .. they used to have in-house worksheets to solve...

May be somone else have some experience... that is why the forum is still open.. isn't it?

[yucapareja]

Dear All;

How many of you have designed composite beams on ETABS? I tried to design but it differ from manual calculations. Moreover for the same model AISC LRFD 99 doesnot give the result but 94 gave... Some of our friends also experienced same problem...


Please share your experience and tips if any..

Regards

Dear friend, I dont really trust in the module of etabs for composite beams. The results differ from manual calculations in the perimetral beam, i believe the problem is with the effective width.

Also i use other equation to calculate vibration.

regads

[Yasir]

ya i agree with "yucapareja".. same problem here

both of the above mentioned problems i.e. eff width calcs and vibration calcs have problem...

[robertsas]

Agree with you both, I ussualy use hand calculation based on code to calculate them..
Never trust your software, check again with manual.

Anyone have an experience to design BELT TRUSES (Outtrigger) on highrise/Tall Building design ?


Regards,
RobertS