Confusing software terminology 1

[Aleeeex]

Hi guys,

I am just learning a new software and I came across some new terminology I am not sure about like Axial load release top, and torsional load release top and bottom.

I don't understand what axial load release means? the axial force doesn't go through the column like there is compressible material between the column and the bottom flange of the beam so the beam forces don't go to the ground through the column.

Similarly to torsional load release.

If there is a real connection example with picture with a simple explanation.

Please bare with me!

Thanks

 

[Aleeeex]

I didn’t understand how the slotted connection will prevent transmitting the load from the primary beam to the column?

 

[human909]

I didn’t understand how the slotted connection will prevent transmitting the load from the primary beam to the column?

Sorry what exactly are you asking ? As BAretired mentioned a slotted connection can be designed to prevent load being transferred in the direction of the slots.

Really what you need to do is recognise that each beam has a set of local coordinates and specify your joint fixities to match the behavior of your desired connection.

From your diagram it seems that you have not adjusted to the local coordinate system. A pinned column would normally have Mx-fixed. (X-axis being along the memnber and thus a torsional restrain.)

 

[r13]

A few notes on your concerns.

- Horizontal shot slot hole connection - mainly used for convenience/ease of erection, especially in limited space. It is usually designed as pined connection.
- Horizontal long slot hole connection - mainly used as movement joint to relieve undesirable tension/compression, such as piping sudden shutdown thrust, and excessive expansion/contraction. Properly tightened, the joint will only support the horizontal force to a specified level, then become loose. The connection needs to be inspected periodically to ensure proper tightness.
- Vertical slot hole connection - I've never used it, so no comment.
- Torsion fixity - similar to bending moment, there are compatibility torsion, and equilibrium torsion. Equilibrium torsion is easier to spot, such as eccentrically loaded beam, or externally applied torsional load, for these conditions, the rotational freedom (usually Mx) must be fixed to generate reactions to counter the applied torsion. The compatibility torsion is everything besides the torsion required for equilibrium. The fixity of rotational freedom is seldom an issue, as either way the resulting effects are usually small and negligible. I almost always leave it free, unless the joint is to be fixed for other concerns.

 

[human909]

Torsion fixity - similar to bending moment, there are compatibility torsion, and equilibrium torsion. Equilibrium torsion is easier to spot, such as eccentrically loaded beam, or externally applied torsional load, for these conditions, the rotational freedom (usually Mx) must be fixed to generate reactions to counter the applied torsion. The compatibility torsion is everything besides the torsion required for equilibrium. ...<snip>... I almost always leave it free, unless the joint is to be fixed for other concerns.

Interesting... Assuming we are talking about the same thing. This is the opposite of what I would be doing. For a couple of reasons:
-most connections do provide torsional rigidity, modelling it otherwise is liable to yield incorrect and sometimes non-conservative results
-A typical secondary beam which has only end connections would have not torsional restraint beyond its end connections. Thus it is left with a complete degree of freedom that will cause errors in many solvers.

**I assume we are both talking using the same terminology regaining torsional fixity. That is restrain to rotation about the axis that runs parallel to the member.

The fixity of rotational freedom is seldom an issue, as either way the resulting effects are usually small and negligible.

I would agree with this. In contrast I always leave it fixed and resultant torsion in my steel models are generally completely negligible. Though the typical model wouldn't explicit ally cater for eccentric connections to beams to that is something that can't be ignored if the connection has significant eccentricity.


Just as an addendum... For the steel structures I've designed and reviewed I have only once felt the need to check torsion. In AS4100 the steel code has no provision addressing torsion so the software I use will stamp AS4100 PASS on beams that would be twisting and yielding. It was a 20m span landing on a bearing plate significantly eccentric to the supporting beam. Not a fun combination. Regardless, it was an interesting find, something to remember before I become too reliant on computers.

 

[r13]

Two examples of equilibrium torsion, for which reactions are required to hold the structure in position (no rotational displacement at support), so torsional freedom must be fixed. The reaction serve to check the anchors/bolts, as well as the member torsional capacity.

 

[Agent666]

Natsmith, here's a practical example. Connection is free to slide vertically, but can take some load in both horizontal directions.