Thursday, 9 July 2015


Optimizing a joint in csJoint module

    We often receive complains, where it is asked that why the utilization of a joint model is not reacting to the changes of certain component parameters.

    It is a fact, that in some cases, to make a joint adequate, may look like a complicated task on first sight, (since there are a lot of component parameters to set), but if we know the basics about the background of the calculation, it is going to be a simple, logical and consequent process.

    The Eurocode 3 design approach consists the component method, that supplies procedures for the evaluation of the resistance, stiffness, and rotational behaviour of a moment end plate joint.
The summation of the mechanical parameters of each components, gives the mechanical parameters of the whole joint. The resistance of the weakest component dominates the resistance of the whole joint as a result.
Configuration, and functional model of a moment end plate beam to column joint can be seen below:

    For the determination of the Resistance and stiffness of this joint, the behaviour of the following components has to be checked under the acting of the internal forces:
1. Column web in shear
2. Column web in compression
3. Beam flange in compression
4. Column flange in bending
5. Bolts in tension
6. End plate bending
7. Column web in tension
All of these components has their own resistance and stiffness.

    When checking a joint in csJoint, it is strongly advisable, to always check which are the weakest components of the joint, since it will determine the resistance of the whole joint. These dominant compression and tension components can always be checked on the result view window.
Those parameters should be strengthened, which are related to the weakest component, otherwise the changes will not affect the utilization. For example, in case of:
  • Mode 1:Complete yielding of the flange (end-plate in bending) Only the end plate properties should be strenghtened, like material, and thickness of the plate
  • Mode 2: Bolt failure with yielding of the flange (end plate in bending): Size, and material of the bolts, and thickness and material properties of the end-plate can also be increased
  • Mode 3: Bolt failure: the size of the bolt should be increased, or a higher grade material should be chosen, or haunch can be applied on the beam to increase the level arm of the tension force
  • Column web in shear: Shear stiffeners on the column should be applied
  • Column web in compression: Web stiffeners should be applied
  • Column flange in bending: Flange stiffeners should be applied
  • etc...

Strengthening the parameters of the weakest component should be continued until another component will replace it, and become dominant. Beyond this point, strengthening the previous component will not affect the utilization of the joint.

Since the calculation of the whole joint is automatically executed after every change in the component parameters, the process of joint optimization can be monitored dynamically.