Anchor Base Plate Connection - Allow for Thermal Expansion?

[Redacted]

Hi there,

I am working on a strut design and I am finalizing the connection details.

The steel strut is 5.2m long and has a temperature range of 32 degrees C. This results in a thermal expansion of 2mm. When converting this into a force it would result in 1337kN (which I do not want to impart into the buttresses that the strut is connected to). The existing buttresses are stiff as they increase in depth as you go down (triangular), so I can't see these deflecting to relieve the expansion.

For an anchor base plate connection as shown below, would there be enough give in the bolted connection to account for a 2mm expansion? If so, is there any literature to back this up that you can share or name?

I am trying to determine if I need to include some form of elastomeric bearing material under the base plate to accommodate this 2mm expansion movement. Is there a better/simpler way to approach this?

I am also thinking of ways to increase the construction tolerances on site. I have allowed for 2" of non-shrink high strength grout on both sides but I am wondering if any additional measures should be added such as oversized/slotted holes to the base plate etc? The contractor would essentially place the steel beam with a crane from above. I'm thinking that the anchor holes will need to be pre-drilled prior to placing the beam and the anchors put in after the beam is levelled and in position.

Any advice would be greatly appreciated.

 

[desertfox]

Hi

You could cut the strut short and use belville washers to act like a spring between the strut and buttresses to take up the expansion, although I can’t tell whether that would work for you or not based on the information you have posted.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[HTURKAK]

Will you post the full picture? Are the walls ( butresses ) retaining walls ?

IMO, do nothing.. If you solve the strut both sides fixed ( axially fixed ) , the mentioned 1337kN could develop ..however, both butresses will also deflect ..

Try to solve the full model ( with retaining walls ) and see the force developing..

 

[desertfox]

If the buttresses don’t deflect then the strut might buckle.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[Redacted]

@Desertfox, thanks I haven't seen those used before but seems like an interesting concept. I'm using an HP 16x88 section, which based on a quick check in Tedds just now, the beam I was planning to use seems to have enough capacity to take the axial compression load of 1120kN and the thermal expansion load of 1337kN without buckling(I'll do a hand check later to verify that).

@HTURKAK yes the walls adjacent to the buttresses are retaining walls see image below (new struts will connect directly into buttresses). Essentially I will be demolishing the existing concrete struts and replacing them with new HDG HP16x88 steel struts. Based on previous calculations, axial load from retaining wall buttresses into struts is 1120kN compression.

 

[desertfox]

Hi Redacted
Something else to consider, if the strut expands it might well take all or most of the preload on the bolt, imagine that the fixing doesn’t heat up at the same rate as the strut, so in effect the nut stays in its original position but the plate on the strut base wants to move away from the nut and thereby reducing the pre load.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[bones206]

The load path for axial thermal expansion is the same load path as the axial compression that the strut is designed to resist. I don’t see how you can have one without the other.

Does the existing strut have the same boundary conditions? If so, then these walls should have already experienced strut thermal expansion forces over the life of the structure, and any adverse effects of that should be visible.