Stiffness of joint (spring value)

[dccd]

Say that I want to limit the moment formed at the beam –column joint = 100kNm (in fact the joint can take much higher moment) , how to calculate the spring at the joint in kNm/degree ??

 

[rb1957]

in a model or a hand calc ? I'm guessing a FEM, since in a hand calc you'd just say "100kNm is the moment".

I think in a FEM the easiest would be (if you're modelling a rotational freedom) would be to run the model with fixed and pinned joint. Then combine a fraction of the fixed cases (so that the moment is 100kNm) and the complementary fraction of the pinned case. If the joint is a horrible combination of shears, then that much less obvious.

another day in paradise, or is paradise one day closer ?

 

[Celt83]

a rotational stiffness value won't guarantee a moment value, it will only guarantee that at an x kNm moment the rotation of joint will equal 1.

Do you specifically want a 100kNm moment at the joint or not to exceed 100kNm at the joint? if you just want that moment you could pin/hinge the beam ends and apply a 100kNm very near to the beam end, but I'd probably advise against this because it could potentially be dangerous as the joint will attract moment based on it's stiffness which could result in much higher moment at in the column or negative flexure for the beam leading to a potential unsafe design.

My Personal Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

Open Source Structural GitHub Group:

https://github.com/open-struct-engineer

 

[Agent666]

Are you limiting the moment because that's the plastic moment capacity of your member?

You basically need to do a non linear analysis that models the plastic hinge behaviour. There's software out there that will do this.

A spring stiffness won't achieve this as Celt83 eluded to.

https://engineervsheep.com

 

[dccd]

Do you mean it 's unsafe to limit the moment over support to a value lower than the max moment that the support it can takes ?

My interest is to limit the moment transferred to the support at certain value (by modifiying the spring value of the support) to design the midspan bottom of beam .... Generally I want to limit the moment at support at ceratin value , and bring up the mispan bottom moment abit ... I am interested only in the midpsan bottom part .... (just take it i want to design the beam as pinned -pinned condition , but to in order to make the design more economical, i want the support to be partially fixed to attract some moment to it to reduce the mispan moment)....


How to calculate the stiffness of the spring to support certain value of moment ???

 

[dccd]

Normally in FEM sofwtare, we can specify the spring value of support, and we can get the moment value at the support...

My intention now is to get the spring value of support to support certain moment value... Is there any simple way to calculate the spring value of support to resist certain value of moment?

I have tried and error to input teh value of spring to resist certain moment.However, i find that it was time consumign and ineffective.

I know it may be impossible to get the exact value because the FE software use non-linear approach. Is there any way that I can get the approximate value of spring to resist certain moment ?

 

[Agent666]

Can you draw a picture of your arrangement so everyone understands what you're trying to achieve. The solutions been given in terms of using software that's capable of modelling an internal hinge.

If it's a simple matter of redistribution of gravity loads, what's so hard about doing it by hand?

https://engineervsheep.com

 

[Agent666]

Additionally, is it an internal joint or an external support? You've used both interchangeably? A sketch should clarify obviously.

https://engineervsheep.com

 

[dccd]

It's just a single span beam supported by column at both ends... I have been trying to back-calculate the value of spring the schieve certain moment value over the beam-column joint only