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Aadelaadel Fd

Assigning Of Temperature Load In Etabs And Safe

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Dear Sir,

 

thank you in advance  for kind helping, please  I need your advise for the  following:

 

how  to assign  temperature load and its relative load combinations in etabs and safe. 

is it applicable for slabs only or for other elements as  well.

if there is  a file as an example that  would be appreciated 

 

 

thanks a lot

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Hello Aadelaadel Fd,

 

I can tell you how to do it in SAP2000. I don't have ETABS or SAFE installed but I hope that will help you since the interface for all three software is similar.

 

In SAP2000, Go-to: Define>Load Pattern. Create a new load pattern and assign the type as temperature.post-1-0-33916400-1440546860_thumb.jpg

 

The next thing to do is to select the frame member you want to apply this load, and go-to: Assign>Frame Loads>Temperature.post-1-0-42259500-1440546868_thumb.jpg

 

That is it. Run the analysis and you are done. I have checked the results using an online website and they matched. post-1-0-00004600-1440546878_thumb.jpgpost-1-0-80786300-1440547230_thumb.jpg

 

Technically speaking, you should be checking all the limit states. So you can apply the temperature loads along with other loads to see what you get. You can also use judgement for the cases where you are confident. Please  see ASCE 7 for details about what companion loads to consider with temperature load .

 

Thanks.

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Is it necessary to apply temperature loads to all frame members ? plz shed some light. I want to skip "expension joint" in the building so I need guidence. what will be the steps and limits during temperature analysis to avoid expension joint?

 

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For islamabad how much temperature (degree celcius) should I apply to my external members because in islamabad temperature varies from five degre in winter and upto  46 degree in summer.........also what if internal temperature (in rooms) is also not controlled then in this case we have to take temp affect on internal members also???

 

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@ZOHAIB SATTAR NAGRA Application of temperature loading and provision of expansion joint depends on engineering judgment of an engineer, keeping in view construction tolerances.What is the length of your building, and how many storey it is? I would like to draw your attention to following comments

  1. You can ignore expansion joints till "60m" as per PCA suggestion, however it is not hard n fast criteria.Building Geometry also play an important role in provision of expansion joint. Please refer to ACI Committee report 224.3 Table 1.2.
  2. As far as Islamabad is concerned, basically when concrete is poured it generates heat of hydration, your concrete will not be at 5c when it will be poured it ll have some temperature. The structure will not be subjected to difference of 45 degree, it will actually be subjected to difference at the time of casting and mean temperature. Generally we take _+20 C. You can ignore temperature loading on intermediate floor and assign temperature loading to exposed roof surface.
  3. Sometimes the assignment of improper temperature loading would attract too much axial load on beams which will not happen in reality.Also concrete will try to relieve it with minor unnoticeable cracks 

 

Edited by SALMAN CH

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@SALMAN CH my building is 227 ft x 170 ft with 60 ft x 60 ft opening in centre.as per ACI report 224.3 if diifference of annual mean temperature and  maximum low or high temp (which ever is high ) is less than 20 C then we will give expension joint after 90m.but if it is greater than 60m then we will provide it after 60m. plz check image attached.

plz explain third point

17 hours ago, SALMAN CH said:

Sometimes the assignment of improper temperature loading would attract too much axial load on beams which will not happen in reality.Also concrete will try to relieve it with minor unnoticeable cracks

I have a model file in office in which they have applied 27 degree only on roof .Why they have not applied it on buildiing exterior sides expose to climate like expterior columns and exterior beams and exterior walls on each story.?

how to overcome the (axial load on beams) problem which you have explained in third point.? do we have to play with stiffness modifires? procedure?

 

aci report expension joint.png

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@ZOHAIB SATTAR NAGRABefore replying to your question, I would like to clarify that I don’t know the plane of your building, you have big opening whose nature and geometry is unknown to me.  Expansion joint might play an important role in your building, if there is abrupt change in the plan, I would recommend to provide expansion joint. In connection to your question, keeping in view the conditions of frame end conditions and heating of the building, briefly, I would like to explain as follows:

1.       Intermediate floors will not be exposed to weather conditions; they will be much cooler than roof. Ask yourself what will happen if you will put this load on intermediate floors? Axial tensile or compressive stresses will be developed in your structure.

SOLUTION: There will be no loading on intermediate floors at that time, except workers or temporarily loading, the reinforcement you already provided would be sufficient enough to cater theses build up stresses. Nothing will happen to your structure.

2.       Your structure will act together, slab will not behave alone; in fact these volumetric changes will occur about Centre of Stiffness. Your frame will try to contract or expand as whole. Connection are not ideal rigid connection, the structure will have some relief from theses axial stress through joints, shrinkage/temperature steel and also through micro cracking which will not be visible.

 

 

12-13-2017 11-37-01 AM.png

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Thank you salman sb you have cleared alot of things and what I understand uptill now  is (that there will come an extra reinforcement to balance the forces due to temperature in addition to seismic and gravity reinforcement) but I still have a question (what will happen to vertical shear walls directly facing sunlight?) what will happen if we apply temperature loading on these walls?axial stresses develop in wall?reinforcement?

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@ZOHAIB SATTAR NAGRA..  Applying temperature to vertical elements (Wall) will hardly effect your design, this is my observation.

     "It is pertinent to mention that biggest trouble for frames/walls will arise due to the application of temperature loading on slab area".

 

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On 12/11/2017 at 4:31 PM, miqureshi77 said:

temperature load can be assigned to the members that affected with the temperature variation only (like exterior members)

not true in all cases. uncontrolled internal temperature has the same effects like outside sun heat on the structure.

On 12/12/2017 at 12:09 PM, ZOHAIB SATTAR NAGRA said:

For islamabad how much temperature (degree celcius) should I apply to my external members because in islamabad temperature varies from five degre in winter and upto  46 degree in summer.........also what if internal temperature (in rooms) is also not controlled then in this case we have to take temp affect on internal members also???

 

There are usually documents stating weather station data. You should use mean yearly average highs and lows not daily.

On 12/12/2017 at 5:01 PM, SALMAN CH said:

You can ignore expansion joints till "60m" as per PCA

It also depends on approval authority. For example in Dubai, limit is 45m.

On 12/13/2017 at 12:42 PM, SALMAN CH said:

I would recommend to provide expansion joint

Expansion joints are nice from structural point of view only. As a structural engineer, Id try my best to avoid them. Construction isnt that easy for expansion joints. What about water leakage?

On 12/13/2017 at 4:39 PM, SALMAN CH said:

Applying temperature to vertical elements (Wall) will hardly effect your design, this is my observation.

Except ground floor columns and walls that will have huge forces due to restrain (supports).

On 12/13/2017 at 2:17 PM, ZOHAIB SATTAR NAGRA said:

will come an extra reinforcement to balance the forces due to temperature in addition to seismic and gravity reinforcement

This is my opinion. I don't think T+E should be added.

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