Civil Engineering Association

To ETABS newbies, always check your "GLOBAL FORCE BALANCE RELATIVE ERRORS" in Last Analysis Run Log.

Don't get too excited at once on the output. ;)

heyy juice... please explain.. how to check it... thanks in advance

Hi Yasir, go to File menu after analysis is complete, click on Last Analysis Log, and check the text file for GLOBAL FORCE... The errors are in percentage.

hello, Juice, Yasir,

Plz correct (guide) me if i am wrong :
(1) Two way slabs shall be modelled as SHELL and need meshing
(2) One way slabs shall be modelled as MEMBRANE and NO need meshing
(3) Stiffnes modifiers for beams,columns,walls,slabs needed on when nonlinear
analysis not performed.
(4) ETABS only gives area of reinforcement for columns & beams (section to be
designed & not to be checked) and not the dia of bars and its arrangement.
(5) for beam we get steel requirement at column face, mid span only and not at
other sections of beam. How to decide upto which distance extra top steel at
support and extra stirrups at end required?
Regards

(02-02-2009, 06:37 AM)aslam Wrote: [ -> ]hello, Juice, Yasir,

Plz correct (guide) me if i am wrong :
(1) Two way slabs shall be modelled as SHELL and need meshing
(2) One way slabs shall be modelled as MEMBRANE and NO need meshing
(3) Stiffnes modifiers for beams,columns,walls,slabs needed on when nonlinear
analysis not performed.
(4) ETABS only gives area of reinforcement for columns & beams (section to be
designed & not to be checked) and not the dia of bars and its arrangement.
(5) for beam we get steel requirement at column face, mid span only and not at
other sections of beam. How to decide upto which distance extra top steel at
support and extra stirrups at end required?
Regards

Hi Aslam,

Answers to your queries:
1) Two way slabs - model these as membrane; preferably with meshing
2) One way slabs - yes; as membrane; preferably with meshing
3) modify your beam and column stiffness; if you're doing linear analysis
4) ETABS will give you the required area of reinforcements
5) Remember ETABS is not a black box for design; use your engineering judgement -- we're supposed to be structural engineers not encoders ;)

I hope these help.

juice

Thanx Juice,

Can u suggest me most common values of stiffness modifiers for columns, beams, walls etc.

I read somewhere that two slabs shall be modeled as shell to have both Membrane(in plane forces) +Plate (bending) behavior. If u model it as memebrane there will not be any bending.

Plz clearify.

Regards

(02-02-2009, 08:05 AM)juice Wrote: [ -> ]

(02-02-2009, 06:37 AM)aslam Wrote: [ -> ]hello, Juice, Yasir,

Plz correct (guide) me if i am wrong :
(1) Two way slabs shall be modelled as SHELL and need meshing
(2) One way slabs shall be modelled as MEMBRANE and NO need meshing
(3) Stiffnes modifiers for beams,columns,walls,slabs needed on when nonlinear
analysis not performed.
(4) ETABS only gives area of reinforcement for columns & beams (section to be
designed & not to be checked) and not the dia of bars and its arrangement.
(5) for beam we get steel requirement at column face, mid span only and not at
other sections of beam. How to decide upto which distance extra top steel at
support and extra stirrups at end required?
Regards

Hi Aslam,

Answers to your queries:
1) Two way slabs - model these as membrane; preferably with meshing
2) One way slabs - yes; as membrane; preferably with meshing
3) modify your beam and column stiffness; if you're doing linear analysis
4) ETABS will give you the required area of reinforcements
5) Remember ETABS is not a black box for design; use your engineering judgement -- we're supposed to be structural engineers not encoders ;)

I hope these help.

juice

(02-02-2009, 08:05 AM)juice Wrote: [ -> ]

(02-02-2009, 06:37 AM)aslam Wrote: [ -> ]hello, Juice, Yasir,

Plz correct (guide) me if i am wrong :
(1) Two way slabs shall be modelled as SHELL and need meshing
(2) One way slabs shall be modelled as MEMBRANE and NO need meshing
(3) Stiffnes modifiers for beams,columns,walls,slabs needed on when nonlinear
analysis not performed.
(4) ETABS only gives area of reinforcement for columns & beams (section to be
designed & not to be checked) and not the dia of bars and its arrangement.
(5) for beam we get steel requirement at column face, mid span only and not at
other sections of beam. How to decide upto which distance extra top steel at
support and extra stirrups at end required?
Regards

Hi Aslam,

Answers to your queries:
1) Two way slabs - model these as membrane; preferably with meshing
2) One way slabs - yes; as membrane; preferably with meshing
3) modify your beam and column stiffness; if you're doing linear analysis
4) ETABS will give you the required area of reinforcements
5) Remember ETABS is not a black box for design; use your engineering judgement -- we're supposed to be structural engineers not encoders ;)

I hope these help.

juice

Hi everyone

1) Agree
2) Agree
3) not really sure about that
4) For beams ETABS will give you the required area of reinforments, but for columns also check the reinforments that you asign for the column.
5) Agree

Bye..

yucapareja

Can u suggest me most common values of stiffness modifiers for columns, beams, walls etc.

1. Best source of recommended values - the concrete design code used in your country
2. Paulay and Priestly's book
3. Charles Salmon's book on reinforced concrete
4. ACI 318-08 (recently posted in the forum), etc.


I read somewhere that two slabs shall be modeled as shell to have both Membrane(in plane forces) +Plate (bending) behavior. If u model it as memebrane there will not be any bending.

If you intend to design your slab for needing bending, go for SAFE instead of ETABS. Membrane - no out-of-plane stiffness; load distribution to your supporting beams will be roughly similar to how you would distribute the loads with 45deg angle for tributary area.

Hello everybody,

Is it possible to define & design Boundary element (size larger than regular wall) in shear wall in etabs?

(02-05-2009, 01:18 PM)aslam Wrote: [ -> ]Hello everybody,

Is it possible to define & design Boundary element (size larger than regular wall) in shear wall in etabs?

If the intention is to model boundary elements that are thicker than the wall; then the answer is yes, it is possible.

It will be nice if other members of the forum could give aslam some guidance on how to do this; i.e., share your ETABS knowledge.