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+---- Thread: ETABS (/thread-167.html)
RE: ETABS - fashion - 08-29-2009
(08-29-2009, 02:31 AM)essenza Wrote:Although seismic excitation is a vibration, the way that it is considered, either by software or bt hand, is this:(08-24-2009, 04:23 PM)fashion Wrote:(08-24-2009, 01:19 PM)essenza Wrote:(08-24-2009, 01:14 PM)fashion Wrote: yes of course is static and of course trying to model earthquake as a static load or a dynamic load under static analysis is a bit aproximate, but what else can you practically do?
Oh no i think you don;t understand what i mean, dynamic load under static analysis I just get confuse:(
you mean that the formation of the stifness matrix refers to static only analysis?
no there are two different approach for vibration analysis which have different stiffness matrix. Just be careful if you are using the one used in ETABS, SAp and all those structural analysis software unless you understand the problem at hand.
Since we never know the exact accelerogramm of the earthquake that is going to hit us, we make envelope ones from past experience. Since we can't have all the necessary characteristics of the excitation under consideration, i.e. duration, cycles, we only consider basic characteristics such as period, max. accelaration, velocity.
Earthquake is an external imposed load, contrary to vibration that is the outcome of external load
(08-27-2009, 04:20 PM)aslam Wrote: (1) If we assign some stories as "similar stories" then reinforcement requirement for beams in such stories will be displayed same eventhough it is different?
(2) I want to flush columns with beam face using "cardinal point". At a paticular node(point) beam width is oriented centrally. When i flush columns using "cardinal point", column is flushed with node and not with beam face. To flush beam and column i need to offset beam by half beam width. it is too labourous. Is there any simple way?
Manual input of offset by a value will be exact but when column size is reducing towards top it is difficult to give offset to all columns.
(3) I have 300 x 1200 mm column with two beams falling at different locations on columns. Actually column is defined at a point. So only one beam meets column at a point, other beam which is actually falling on this column will fall on beam suppored on this column. How rigidity can be achieved between these two points on column where beams are falling. people use master-slave option in STTAD. Is there any option in etabs?
(4) Many seismic codes states that any mass in between two floor leves (say brick masonry, column mass) shall be equally lumped to two connected floors (levels). To follow this codal provision, how brick masonry mass shall be modeled?
By default, how etabs is lumping masses between two levels to defined levels?
1) I think so
2) cardinal point applies to beams as well, u have to make some tries
3)I can't have in my mind your node u describe, upload a pic or something. If you mean how to model rigid offsets, you have to input in the model members (beams) with very high stifness so as to model rigid links that transfer moments and forces as they are, without deforming.
4) by manually calculating the mass and applying it on a mass node (which must be connected to the structure by links. Most accurate and time consuming method.
BUT if you just apply the weight of the external masonry on the external beams and the go to define-seismic mass then according to your code you assign how the mass is calculated, e.g. from mass only, from mass and loads etc. according to EC it should be mass+1,35DL+0,3LL, or something like that
RE: ETABS - juice - 08-29-2009
(08-27-2009, 04:20 PM)aslam Wrote: (1) If we assign some stories as "similar stories" then reinforcement requirement for beams in such stories will be displayed same eventhough it is different?
(2) I want to flush columns with beam face using "cardinal point". At a paticular node(point) beam width is oriented centrally. When i flush columns using "cardinal point", column is flushed with node and not with beam face. To flush beam and column i need to offset beam by half beam width. it is too labourous. Is there any simple way?
Manual input of offset by a value will be exact but when column size is reducing towards top it is difficult to give offset to all columns.
(3) I have 300 x 1200 mm column with two beams falling at different locations on columns. Actually column is defined at a point. So only one beam meets column at a point, other beam which is actually falling on this column will fall on beam suppored on this column. How rigidity can be achieved between these two points on column where beams are falling. people use master-slave option in STTAD. Is there any option in etabs?
(4) Many seismic codes states that any mass in between two floor leves (say brick masonry, column mass) shall be equally lumped to two connected floors (levels). To follow this codal provision, how brick masonry mass shall be modeled?
By default, how etabs is lumping masses between two levels to defined levels?
hi aslam,
To answer item (4), model a simple 2D-frame 2 storeys high with infill wall. Compare the calculated mass from ETABS for each floor level with your manual calcs.
i hope this helps.
regards,
juice
RE: ETABS - carlofabie - 09-20-2009
(08-04-2009, 11:08 PM)promo8 Wrote:(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?
Yes it is possible, you define the boundary elements as columns, of the size you want, with the same pier name as the one you used for the wall, then ETAB will take the as a shear wall with boundary elements. Hope this help you.
Hi,
Just keep in mind that frame elements modelled with shell elements beside it as walls will have an overlapping of stiffness which is not recommended.
RE: ETABS - balboul83 - 09-20-2009
hi can some one explain how u can do the dynamic analysis using etabs ??? i mean how to calculate the reduction factor for spec x and spec Y ???? any clue
thank u all
best regards .
eng.bilal
RE: ETABS - fashion - 09-22-2009
what do you mean by reduction factor
RE: ETABS - balboul83 - 09-22-2009
i mean spec x and spec Y for the dynamic analysis after definig the sepctrum function .
how u can obtain in according to any code if u want :O
RE: ETABS - robertsas - 09-25-2009
(09-22-2009, 07:40 PM)balboul83 Wrote: i mean spec x and spec Y for the dynamic analysis after definig the sepctrum function .
how u can obtain in according to any code if u want :O
Dear Colleagues,
I know what you mean..
For SpecX and SpecY, Put Scale Factor value = 9.81/R ..... (read my note below)
R = Seismic Respons Factor
Note : I ussualy keep my unit on kN, meter
regards,
robertsasmita
regards
RE: ETABS - VCHFCE - 09-25-2009
(09-22-2009, 07:40 PM)balboul83 Wrote: i mean spec x and spec Y for the dynamic analysis after definig the sepctrum function .
how u can obtain in according to any code if u want :O
This scale factor strongly depends on the response spectrum function type as well on code specific additional coefficients and units used during input.
Please see attachment. Although it is elaborated for specific case you may find it useful.
Most codes used different multipliers ( Zone factor, Importance factor, behavior factor etc.) and diff. type of normalized response spectrum functions - normalized to g or ag, linear or nonlinear type resp. spectum. ;
Always check for the consistency of units:
Response Spectrum Functions * sf = Sa(T) - m/s2
Sa(T) is a response spectrum acceleration (without any modifications);
Sf = code prescribed multiplayers *factor(s) used to normalize resp. spectrum function ( if any)
RE: ETABS - balboul83 - 09-26-2009
thank u alot but that mean i can take the factor and i can take the result like dynamic analysis :O after ruunning the model.
or should i do something else.
RE: ETABS - core - 09-26-2009
(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
core: There are two kinds of analysis, Global and local analysis. If you are using shell in the global analysis "be very careful, specially is your bldg's period is to the limit. It would increase the stiffness of your bldg. And it might not match your detailing.
(2) One way slabs shall be modelled as MEMBRANE and NO need meshing
[color]core[/color]: Etabs default for membrane is automatic. Thats why you thought messing is not required. Check column reactions of your model to be sure loads are properly captured. A good way of checking is to export one flr and check in etabs if col loads are same as manual calcs.
(3) Stiffnes modifiers for beams,columns,walls,slabs needed on when nonlinear
analysis not performed.
core: modifiers should be provided, special for crack condition. UBC and other codes specifics this. There are no full 100% I value in reality.
(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.
Core: all can be check and design be etabs, except slab and slating walls.
(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