Linked Elements in Etabs 1

[hsn199]

Hey,

I have a project where I have to model two 130m towers connected by 7m bridges at 5 levels. I was asked to consider as a senario the bridges pinned from one side and a roller from the other , and the only way I could think of is by introducing link elements.

Now here's the question: is it wrong to elevate the bridge by lets say 20 cm, plant columns on bridge ends and assign link property to the planted columns? What will be the difference between this and between introducing a null frame section and assigning it as a link?

And is there a standard value for the stiffness we input (flexural,shear,axial), so that the direction taken into consideration would be considered restrained, or shall it be calculated in some way?

Please share me your thoughts about this matter.

 

[slickdeals]

I would suggest that you extend "rigid" elements, say 12" long, with amplified stiffness properties (I and A) at each of these locations.

You can assign your releases to this member, which can be an axial release + moments releases for the roller end and only moment releases at the pinned end. You will have to transfer shear at each end.

 

[hsn199]

That's a thing I shall try. If I may ask another question: the drift in my model accounting for combination "EQUAKEX" is exceeding 0.02, which is not allowed by UBC 97.

The natural period in my building is about 5.89 s which is too much in my belief. I've checked the elasticity of concrete materials, and stiffness modifiers were only applied for slabs (.35 for flexure). Everything seems to be right.

I've provided an attachment of my model (connectivity at bridges ends is Rigid-Hinge). Any help given in relation to this matter is really appreciated. Thx. I'll post this question as a single thread for everyone to see.

PS: When running the analysis without application of stiffness modifiers, the period is somewhere near 4.45 s. Application of stiffness modifiers for SLABS ONLY, made the period 5.89. I believe if something was done wrong, it was done wrong here.

 

[hsn199]

slickdeals, may you demonstrate the difference between assigning releases for the column, and assigning it a link property?