Loading phase & Applied loads

02-Getting started with the modelling
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Sheheryar2015
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Joined: 24 Jul 2017, 19:24

Loading phase & Applied loads

Post by Sheheryar2015 »

Hy
I am little confused in applying loads. Let suppose there is a node "N1". I have applied 10 mm displacement in "y" direction as an incremental load from the "Applied load" tab on this node. Now in the next step I am defining loading phase, I have selected response control phase and now applying a displacement of lets say 20 mm on the same N1 node in the same direction. After analysis the said node is displaced 20 mm in y direction. which shows the displacement value entered in "Response Control phase" is followed rather than that entered in "Applied Load" Tab.
My question is what is the purpose of entering the displacement value in "Applied Load" tabs if we are using the "Response Control Phase" as this phase type again requires the displacement value and direction of displacement, which is already defined in Applied Loads tab.
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seismosoft
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Joined: 06 Jul 2007, 04:55

Re: Loading phase & Applied loads

Post by seismosoft »

When applying displacement loads the Load Control or the Response Control phases are indeed equivalent. However, there is a big difference in the structural behaviour between Load Control or the Response Control , when applying forces instead. Please refer to the help system or the User's Manual for further guidance on the issue.

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Ralazem
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Joined: 08 Feb 2019, 02:38

Re: Loading phase & Applied loads

Post by Ralazem »

Hi, can I have some clarification on this issue? I have referred to the manual and I am still confused regarding this. If I want to push my element to a specific displacement, should I set the load phase ( response control ) and the load (displacement load) to the same displacement value?
huffte
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Re: Loading phase & Applied loads

Post by huffte »

For a simple, non-adaptive pushover with a target displacement, incremental forces with response control seem to work just fine, Ralazem. You might give this a try and see if it meets your intended modeling strategy. In the response control loading phase, just specify the node and corresponding displacement to which you want to push the structure. Your applied incremental loading pattern should correspond to your anticipated force distribution and the magnitude of incremental loads is not critical, typically. In response control, the software will compute appropriate load factors to produce the desired displacement increment from the loading phase.
Tim Huff
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seismosoft
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Joined: 06 Jul 2007, 04:55

Re: Loading phase & Applied loads

Post by seismosoft »

A simpler (and less scientific) way of describing this is as follows:
1) Load control (with forces as lateral loads) is like pushing the structure with constant increments of forces 5, 10, 15, 20... kN
2) Response control (with forces as lateral loads) instead is like pulling the structure at constant displacement increments 5, 10, 15, 20... mm, and then measuring the lateral forces that correspond to these deformation levels.
Hope this is clear now
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Ralazem
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Joined: 08 Feb 2019, 02:38

Re: Loading phase & Applied loads

Post by Ralazem »

Thank you both for taking the time to reply.

Huff, your explanation is quite helpful, except, I am unsure of the anticipated force distribution. How can I get the software to automatically apply the distribution? such as a triangular loading distribution?
huffte
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Re: Loading phase & Applied loads

Post by huffte »

You will need to make the decision as to where the loads are to be applied. If, for example you had a three story frame and you wanted the triangular distribution you describe, then you could apply loads of 1 kip at one node of the first elevated level (or 0.5 kips at two nodes at this level, etc.), 2 kips at the second elevated level (or 1 kip at two nodes at this level, etc.), and 3 kips at the third elevated level (or 1.5 kips at three nodes at this level, etc.). These must be identified in the loading application to be incremental loads - that is the key. The actual load values are not so important, since, as mentioned in the help system, the scale factor will be internally adjusted to produce the desired displacement increment (as specified in the loading phases dialogue). It is the relative values of the loads specified as incremental which is critical. Best of luck, Ralazem.
Tim Huff
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