Aluminium facade fixing to buidling

[m_struct]

Hi.

Looking at the fixing of an 2mm aluminium cladding system to face of a building. The system is understood to have the detailing to allow for expansion and contraction of the panel. My engagement was specifying the fixing of the brackets to the wall.

However, in one zone, the wood framed walls were not constructed per plans. The cladding installer is asking to direct fix the top of the 5' tall by 2' wide panel (25lb) to the wall. The sides and bottom of the panel are free to expand and contract. The top and bottom are restrained in and out of plane. The proposed fixing detail would be 10mm dia hole in the aluminium panel, with a rubber washer in hole with 10Ga screw (5mm) through the center of hole and washer. It would theoretically allow for 2.5mm expansion and 2.5mm contraction at the top.

What to you think? If the panel is allowed to expand and contract on 3 of 4 sides, can other side (top) be restrained from thermal expansion? Considering durability (normal environment) and performance, what type of rubber washer would you recommend?

 

[NorthCivil]

Careful of only being engaged to "design the fixings"

often clients look for "fixing design only" as its cheaper, quicker, and the engineer does not look at the rest of the design which often needs work.

Then they will pass on your sign off documents to the consent authority as a "sign off" of their entire scope of works.

if it ever winds up in court, you'll be ripped to shreds trying to argue your engagement was to sign off on the screws only

 

[Ron]

Agree with NorthCivil...look at the system, not just the fixings. Check the Alucobond website. They give details for what you need.

 

[jjl317]

In terms of the technical question, one potential option might be to fully fix one of the two upper corners, and add a horizontal slot to the opposite upper corner, to allow for the horizontal thermal expansion.

I wouldn't think that the amount of potential expansion across the 2' width would be very large (not sure the environmental conditions of the project). An appropriate detail would be required for the fastener in the slot to allow movement.

In terms of the overall engineering responsibility, I do agree with the other commenters that these types of "limited scope" projects have the potential to be problematic, and care should definitely be taken to try and ensure that your scope is clearly defined, and you clearly identify any potential issues you might see.

 

[brut3]

Per the Aluminum Design Manual the coefficient of thermal expansion is 13 x 10^-6/Degree Fahrenheit. If you were to provide a single fixing point on one side of the upper panel flange then the pane would expect to experience a 0.00936" growth over its 5'-0" length at a change in temperature of 120 degrees Fahrenheit. Your 2.5mm expansion/contraction gap would work in this scenario. In my opinion you can accomplish the expansion/contraction accommodation with oversized holes on one flange as long as you provide sufficient room for the panel to move based off of your design change in temperature.

 

[dhengr]

M_struct:
Don’t forget, that at least in the vertical direction, the wood structural frame will shrink due to drying and long term settlement and creep. The magnitude of this movement may be as great as the alum. panel movement in the opposite direction in some consitions. Pay attention to the temps. and sun direction/exposure during panel installation, as this should/might influence some off-center placement of fasteners in holes and slots, or slot sizes. Think a bit about the structure movement due to lateral loads, as this racking may take up all your slot/hole movement allowance. Aluminum and vinyl are difficult to work with, and match to the rest of the structure, because their thermal expansion/contraction coefs. are so much greater than those for steel, concrete and wood. And, they are typically part of the exterior surface and directly exposed to the worst of the hot and cold conditions, literally baked by the direct sun light, or from reflected/radiated heat.

 

[m_struct]

Good points there with scope and wood framing shrinkage.

RON - I looked through the Alucobond website, but could not find the appropriate detail.

Here is an elevation of the panel and proposed fixings. One fixed point on top corner of panel, an oversized connection at other top corner. Max panel length is 5'. Designing for a +-100C, gives approximately +-3.5mm total thermal movement. The bottom fixing allows for 3.5mm contraction and +10 mm expansion.

 

[jjl317]

I would still advocate for a horizontal slot instead of an oversized hole. While theoretical, I would think that as drawn thermal expansion/contraction could cause the hole panel to rotate in plane around the fixed connection, potential bringing the panel out of plumb vertically.