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EXPORT SLAB FROM ETAB TO SAFE
02-20-2012, 11:55 AM
Post: #1
EXPORT SLAB FROM ETAB TO SAFE
SALMO 2ALYKOM

we would like to discuss the best option to export the slab lateral force from etab program to safe

As we know we have three options to export the floor from etabs to safe

1-export floor loads only.

2-export floor loads and loads from above.

3-export floor loads plus column and wall distortion.

we knew most of engineers recommended option NO 3 and me too but I found the mentioned sentence in safe help

“For SAFE v12 it is not necessary to export distortions from ETABS to account for lateral
loads. The loads can be exported directly and the columns and walls modeled in SAFE will
account for the correct distribution of moments to the slabs. Back-calculation of the loads
from the distortions is sensitive to the differences in stiffness modeled in SAFE and ETABS
and is no longer needed”.


“That is mean option 03 is no longer used to export lateral force from etab to safe and option 02 is enough to design the slab and foundation under lateral load effect

please send me your advice for the mentioned subject

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02-25-2012, 05:57 PM
Post: #2
RE: EXPORT SLAB FROM ETAB TO SAFE
سوف نقوم بالمقارنة بين نتائج

1-export floor loads and loads from above
AND
2-export floor loads plus column and wall distortion.
تم عمل مودل ايتاب واصدار دور من المبنى بطريقتين
First let us see the punching result taking into consideration the lateral load effect

the link of file is mentioned below

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بجد فى فرق كبير فى النتائج

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03-04-2012, 12:36 PM
Post: #3
RE: EXPORT SLAB FROM ETAB TO SAFE
السلام عليكم

بعد قيام احد الاخوة بمراسله

CSI Technical Support
الاجابه كالتالى
If you have lateral loads in your slab Second or third options should be used. We are currently haven an issue with second option when exporting lateral loads that will be corrected in a future version; therefore, currently we recommend third option.

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03-04-2012, 10:40 PM
Post: #4
RE: EXPORT SLAB FROM ETAB TO SAFE
Dear Sea2007,

Till ETABS version 9.7.3, the only and correct way to export the lateral loads (seismic & wind) affecting the slab design from ETABS to SAFE is by using the third option available in exporting process, which is "Export floor loads plus columns and walls distortion".

Here, I would like to mention the followings:
First:
The distortions result from gravity load (i.e. dead & live) will be exported along with those caused by lateral loads as well.
So, it is high important to cancel the gravity distortions from all support points, otherwise you will duplicate the stresses result from gravity load.

These gravity distortions result from two things:
  • Support distortions result from the gravity load distributed on the slab itself.
  • Support distortions result from the cumulative shortenings of the columns/walls supporting the slab.
Under second point, some body may raise the following issue: why to cancel the distortions result from columns shortening as obtained from ETABS ?

The answer is:
  • the cumulative columns shortening is elastic one and doesn't include the long term shortening result from creep and shrinkage.
  • Even the ETABS's output is cumulative elastic shoretening only, however those values given by ETABS are fake and incorrect.
    The main reason behind this:
    As known, two major parameters affect the growth of elastic shortening by time history of loading, the first one is the ratio of reinforcement affect the transformed section enter in calculating the axial rigidity of columns, and the second one is the increasing of material modulus of elasticity by time. and both of those parameters are not considering in ETABS analysis. in another word, the axial rigidity of columns/walls stay fixed in all analysis steps of ETABS.

    For more details regarding this issue refer to the reference mentioned in the following thread:
    Code:
    http://www.structural-experts.com/Thread-Column-Shortening-in-Tall-Structures

conclusion to above:
  • Cancel all gravity distortions result from ETABS
  • Calculate columns/walls shortening: elastic term and long term result from creep and shrinkage from a separate module.
  • Distinguish between up-to and sub-to values of total columns shortening (i.e. shortening of columns up to time of casting the slab, and the later-on developed shortening after the time of casting the slabs in stories above.)
  • Consider the correction in shortening values during the construction. (i.e. increase columns length in pre-specified floors by designer).
  • Finally, the net values of columns/walls shortening to be consider in design of slab (i.e. entered in SAFE).


Second:
The exported lateral loads (seismic & wind) distortions, are caused by pre-specified degree of cracking entered in ETABS for all columns, walls, slabs and beams. I mean here the stiffness modifiers of all these elements.

As known,
Force = Axial Stiffness x Displacement.
Moment = Rotational Stiffness x Rotation.

When you export the distortions (displacements & rotations) from ETABS to SAFE, you need to deal with the same Stiffness that giving those distortions in ETABS to get the same Forces/Moments in SAFE. Accordingly the stiffness of elements in SAFE shall be modified/decreased as well to get the same outputs as of ETABS.

i.e. if the stiffness modifiers in ETABS are as follow: 0.7Ig for walls and columns, 0.25 Ig for slabs, and 0.35Ig for beams. then same value shall be entered in SAFE. Finally, always try to check the outputs of SAFE by comparing the strip forces result from lateral loads by those ones result from Section-Cut technique available in ETABS.

Important:
To determine the gravity load short term and long term deflection, so don't use the same SAFE model where the slab stiffness is reduced to get the same outputs of lateral loads as of ETABS. In this case, another SAFE model with Full elements stiffness shall be run using nonlinear long term cracked analysis option to obtain the actual deflection under gravity load.

Hope that the above general guidance is useful for you.

Hussein Rida

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 Thanks given by: alaa elesawey , ibrahim.hosny , Melekeen , kiranklk
03-05-2012, 08:14 PM
Post: #5
RE: EXPORT SLAB FROM ETAB TO SAFE
(03-04-2012 10:40 PM)hussein.rida Wrote: You are not allowed to view links. Register or Login to view.Dear Sea2007,

Till ETABS version 9.7.3, the only and correct way to export the lateral loads (seismic & wind) affecting the slab design from ETABS to SAFE is by using the third option available in exporting process, which is "Export floor loads plus columns and walls distortion".

Here, I would like to mention the followings:
First:
The distortions result from gravity load (i.e. dead & live) will be exported along with those caused by lateral loads as well.
So, it is high important to cancel the gravity distortions from all support points, otherwise you will duplicate the stresses result from gravity load.

These gravity distortions result from two things:
  • Support distortions result from the gravity load distributed on the slab itself.
  • Support distortions result from the cumulative shortenings of the columns/walls supporting the slab.
Under second point, some body may raise the following issue: why to cancel the distortions result from columns shortening as obtained from ETABS ?

The answer is:
  • the cumulative columns shortening is elastic one and doesn't include the long term shortening result from creep and shrinkage.
  • Even the ETABS's output is cumulative elastic shoretening only, however those values given by ETABS are fake and incorrect.
    The main reason behind this:
    As known, two major parameters affect the growth of elastic shortening by time history of loading, the first one is the ratio of reinforcement affect the transformed section enter in calculating the axial rigidity of columns, and the second one is the increasing of material modulus of elasticity by time. and both of those parameters are not considering in ETABS analysis. in another word, the axial rigidity of columns/walls stay fixed in all analysis steps of ETABS.

    For more details regarding this issue refer to the reference mentioned in the following thread:
    Code:
    http://www.structural-experts.com/Thread-Column-Shortening-in-Tall-Structures

conclusion to above:
  • Cancel all gravity distortions result from ETABS
  • Calculate columns/walls shortening: elastic term and long term result from creep and shrinkage from a separate module.
  • Distinguish between up-to and sub-to values of total columns shortening (i.e. shortening of columns up to time of casting the slab, and the later-on developed shortening after the time of casting the slabs in stories above.)
  • Consider the correction in shortening values during the construction. (i.e. increase columns length in pre-specified floors by designer).
  • Finally, the net values of columns/walls shortening to be consider in design of slab (i.e. entered in SAFE).


Second:
The exported lateral loads (seismic & wind) distortions, are caused by pre-specified degree of cracking entered in ETABS for all columns, walls, slabs and beams. I mean here the stiffness modifiers of all these elements.

As known,
Force = Axial Stiffness x Displacement.
Moment = Rotational Stiffness x Rotation.

When you export the distortions (displacements & rotations) from ETABS to SAFE, you need to deal with the same Stiffness that giving those distortions in ETABS to get the same Forces/Moments in SAFE. Accordingly the stiffness of elements in SAFE shall be modified/decreased as well to get the same outputs as of ETABS.

i.e. if the stiffness modifiers in ETABS are as follow: 0.7Ig for walls and columns, 0.25 Ig for slabs, and 0.35Ig for beams. then same value shall be entered in SAFE. Finally, always try to check the outputs of SAFE by comparing the strip forces result from lateral loads by those ones result from Section-Cut technique available in ETABS.

Important:
To determine the gravity load short term and long term deflection, so don't use the same SAFE model where the slab stiffness is reduced to get the same outputs of lateral loads as of ETABS. In this case, another SAFE model with Full elements stiffness shall be run using nonlinear long term cracked analysis option to obtain the actual deflection under gravity load.

Hope that the above general guidance is useful for you.

Hussein Rida


كعادة المهندس حسين فان مشاركاته مميزه وبها معلومات كثيره

ورغم اننى كنت اظن نفسى اتقنت برنامج الساف الا ان بعد مشاركتك ارى انى احتاج الى كثير من الوقت لتعلم هذا البرنامج وتطبيقاته


لقد قمت بذكر ثلاث نقاط هامه فى مشاركتك وهى


1-Shortenings in vertical elements

كل معلوماتى عن هذا الموضوع انه معقد جدا فى كيفيه حساب تاثيرة لذلك لن اسال فى هذة النقطه حتى انتهى من قراءه المرجع الذى قمت بذكرة فى المشاركه

2-you want to adjust all stiffness modifiers of all these (slabs ,beams and columns ) to be same as the etabs model

وهذه النقطه لم اسمع عنها من قبل كل الاستشاريين الذين تعاملت معهم

لذلك قمت بعمل مودل ايتاب
لمبنى مكون من عشره طوابق يقع فى

zone 2A as per ubc 97 or SDC C accroding to the new codes
وتم اعتبار البلاطه على انها جزء من النظام المقاول للزلازل لذلك تم تعريفا على انها
Shell

ونظرا ان كثير من المهندسين يعرف البلاطه على انها
Shell
وفى نفس الوقت لا ياخذ تاثير الاحمال الجانبيه فى تصميم البلاطه
مما يودى الى تقليل القوى الناتجه على الحوائط والاعمدة بسبب تاثير البلاطه
وهذا خطا مشهور

So we would like to clarify this point as mentioned below

When you define the slab as shell you have to take into consideration the effect of lateral load with the slab design
Otherwise you have to define the slab as membrane



We Used the following criteria for ETAB MODEL:

1- Seismic load (zone2A) UBC 97
2- Wind load (WIND SPEED 93 MPH) UBC 97
3-live load 200 kg/m2
4-Supper imposed 400kg/m2



And then We export the 6th floor from ETAB to SAFE program using option 3 as per our agreements
وتم عمل 2 مودل ساف احدهم طبقا لتوصيات التى قمت بذكرها وسوف نطلق عليه
ENG HUSSEIN MODEL

والاخر بالطريقه التى اعتاد عليها
اى بدون تعديل
The stiffness factor for concrete elements and keep the distortion of the dead load as it obtain from etab .

وسوف اسميها

ENG MOHAMED MODEL

Note :We define the columns strip width equal to columns width plus 1.5 slab thickness meaning {70cm column width +2*(1.5*25cm)=150 cm (AS PER ACI 318-05 clause 21.12.6).

وكانت النتيجه كالتالى ان قيم الحديد الاضافى المطلوب وقيم
Punching

فى مودل المهندس حسين تقريبا نصف المطلوب من مودل المهندس محمد وهذا جعلنى فى شك فى كل المشوعات السابقه على انها بها حديد اكثر من اللازم وكذلك حجم الاعمدة اكبر من المطلوب

The link of the model
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3-Another SAFE model with Full elements stiffness shall be run using nonlinear long term cracked analysis

وسوالى هنا اذا تم عمل 2 مودل لكل بلاطه الا ترى ان حجم الجهد المبذول لتصميم بلاطه سوف يكون كبيرا جدا

الا يمكن الاعتماد على مودل واحد لاستخراج النتائج


وفى اى مودل يتم التحقق من الترخيم تحت تاثير اخمال الرياح

According to IBC 2006 TABLE 1604.3

هل سوف تاخذ النتائج من

Safe model with reduction in stiffness modifier and without gravity distortion or model safe without reduction in stiffness modifier and without gravity distortion

نقطه اخيره

عند تصدير ملف السفق من الايتاب الى الساف ظهر العمود
as point
والطريقه الوحيده لاضافى العمود بابعاده الحقيقيه سوف تكون من داخل مودل الساف


اسف على الاطاله فالحديث مع من اكثر منك خبره له مذاق خاص

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 Thanks given by: kiranklk
06-02-2012, 06:39 PM
Post: #6
RE: EXPORT SLAB FROM ETAB TO SAFE
How can i Cancel all gravity distortions result from ETABS ??

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06-03-2012, 06:28 PM
Post: #7
RE: EXPORT SLAB FROM ETAB TO SAFE
after checking both attaced models , i think that removing all displacements from gravity loads (dead and live loads) from safe models means that the distorsions from etabs model are cancelled

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06-04-2012, 10:12 AM
Post: #8
RE: EXPORT SLAB FROM ETAB TO SAFE
الله عليك يا مهندس حسين والله انت مُمتع
Shortenings in vertical elements جزاك الله خيرا وارجو المناقشه تستمر فى موضوع

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01-15-2013, 11:40 PM
Post: #9
RE: EXPORT SLAB FROM ETAB TO SAFE
all of this make sense except for the part about entering inertia modifiers into safe , i think that is mistake specially when you preform cracked analysis ,I mean the whole idea behind this analysis is to get the Icr ,reducing the slab inertia by 0.25 will give huge error

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01-16-2013, 04:50 PM
Post: #10
RE: EXPORT SLAB FROM ETAB TO SAFE
Important:
To determine the gravity load short term and long term deflection, so don't use the same SAFE model where the slab stiffness is reduced to get the same outputs of lateral loads as of ETABS. In this case, another SAFE model with Full elements stiffness shall be run using nonlinear long term cracked analysis option to obtain the actual deflection under gravity load.

Hope that the above general guidance is useful for you.

Hussein Rida

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