bookowski
Structural
- Aug 29, 2010
- 971
I've got a few situations/connections here that are outside of my knowledge base.
This is a beachfront resort, these details will be repeated on around 15 of the same structures. I've designed the concrete buildings for this project and various canopies and accessory structures are theoretically designed by others. However, I've been asked to opine on the proposed details beyond only the loads imposed on my structure. There are a lot of mixed materials and the drawings do not indicate any measures to mitigate corrosion potential. I'm not sure how much I'll be able to make them change these but in my review I'd like to at least note the problems and possible solutions for them to consider to push the risk back to them. The concrete buildings will get stucco as their finish.
Condition 1: A small trellis like canopy mounted to the face of the concrete building. This is about a 3 ft cantilever of open repeating fins, imagine a ladder turned sideways and bolted to the face of a building. Currently proposed detail shows a steel perimeter frame (think ladder side rail) and aluminum infill members (the ladder rungs). The Al and steel are shown directly connected. The overall frame is shown as being mounted with post installed anchors to the concrete. Forget about loading/demands here, just corrosion. They've already suggested that they could change this all to aluminum. If this is all aluminum would it be sufficient to apply a coating to the face of the concrete to separate the Al from the concrete? Stainless anchors for the post installed with a separation coating or washer? All of this is more or less exposed.
Condition 2: A much larger exterior canopy/pergola type structure. This one has long spans and some big cantilevers. Again, they are proposing steel for the main spans and cants and infill being done in Al. This one also interfaces at one side with concrete. This one has an extra corrosion twist. The long spans are shown as wf steel which then gets clad in bent plate to make it a sharp square. To accomplish this they show a lot of small "cold formed framing as required", presumably shot into the steel to hold it in place and likely touching some Al here and there even if inadvertently. It feels like that cf steel would not last long to me. Similar questions to #1 - what is a robust separation detail for these various interfaces, and what happens to cf steel in an exposure like this?
Being beachfront and fully exposed is it sufficient in general to separate the Al and steel by a coating alone? This is an aggressive environment, is there a more robust measure that should be used for separation? Note that in some cases the connections do hold cantilevers or other members with non negligible demands. As usual this is an "this is what we've always done" situation.
This is a beachfront resort, these details will be repeated on around 15 of the same structures. I've designed the concrete buildings for this project and various canopies and accessory structures are theoretically designed by others. However, I've been asked to opine on the proposed details beyond only the loads imposed on my structure. There are a lot of mixed materials and the drawings do not indicate any measures to mitigate corrosion potential. I'm not sure how much I'll be able to make them change these but in my review I'd like to at least note the problems and possible solutions for them to consider to push the risk back to them. The concrete buildings will get stucco as their finish.
Condition 1: A small trellis like canopy mounted to the face of the concrete building. This is about a 3 ft cantilever of open repeating fins, imagine a ladder turned sideways and bolted to the face of a building. Currently proposed detail shows a steel perimeter frame (think ladder side rail) and aluminum infill members (the ladder rungs). The Al and steel are shown directly connected. The overall frame is shown as being mounted with post installed anchors to the concrete. Forget about loading/demands here, just corrosion. They've already suggested that they could change this all to aluminum. If this is all aluminum would it be sufficient to apply a coating to the face of the concrete to separate the Al from the concrete? Stainless anchors for the post installed with a separation coating or washer? All of this is more or less exposed.
Condition 2: A much larger exterior canopy/pergola type structure. This one has long spans and some big cantilevers. Again, they are proposing steel for the main spans and cants and infill being done in Al. This one also interfaces at one side with concrete. This one has an extra corrosion twist. The long spans are shown as wf steel which then gets clad in bent plate to make it a sharp square. To accomplish this they show a lot of small "cold formed framing as required", presumably shot into the steel to hold it in place and likely touching some Al here and there even if inadvertently. It feels like that cf steel would not last long to me. Similar questions to #1 - what is a robust separation detail for these various interfaces, and what happens to cf steel in an exposure like this?
Being beachfront and fully exposed is it sufficient in general to separate the Al and steel by a coating alone? This is an aggressive environment, is there a more robust measure that should be used for separation? Note that in some cases the connections do hold cantilevers or other members with non negligible demands. As usual this is an "this is what we've always done" situation.
