Adam0917
Structural
- Oct 3, 2019
- 6
Hello everyone,
I have a simple question/discussion topic that I want to bring up, share some of my thoughts, and maybe more senior SE can correct me if I'm wrong and provide me with some expert opinions in this regard.
So in my working industry, I have come across many steel wall mount designs that using adhesive/mechanical wall anchors for simple structure that supports telecommunication equipment, e.g. antennas.
Sometimes I have to deal with special requirements, for example, I have a 1.3m parapet (concrete with min. reinforcing I assumed), from the top of the parapet to the proposed antenna is another 1.7m (center of the antenna on which I consider the wind load is acting). In my original design, I left 200mm to concrete parapet edges all around so my anchors can develop full capacity according to the anchor manufacturer's recommendation. Last year, I did not design this type of wall anchor connection to take any moment (i.e. I used pinned connection type).
Recently client has proposed to rise up the antenna so now my total cantilever distance is increased to about 2.1m (from the centerline of the antenna to the top anchor connection). With my re-assessment of the wall anchors, and a closer look at my connection type, I think instead of using the full pinned connection, I tried fixed type, the reason for this is I want to see if the existing connection can take moment at all. Cause I don't have full details of the reinforcement for this parapet, I could only assume none to 15m reinforcing rebars for this parapet, cracked, and 25MPa concrete strength.
So the result was just like what I expected, all the anchors are fine in both tension and shear (far away from their capacities), but I have a problem with the concrete breakout. Now, by just considering the y-axis as my fixed axis, the concrete breakout is at a 169% utilization ratio. I'm now more leaning towards the latter approach cause I know there will be a moment transfer at my top connection. However, I have also seen so many designs by others that had a similar cantilevered structure with wall anchors like this, but they never had a single issue. In addition, My intention is not to touch the existing installation (so this eliminates the option for installing the full penetration rods to engage the entire local parapet wall). So am I overthinking this or my assumptions for parapet were too conservative or am I missing anything?
Loading Case: Fw+Fd, where Fw=1.66kn, Fd=2.88kn (both factored loads). Fw is acting 2.2m above the first connection. overall mount assembly and anchor layout see below screenshot
Therefore, if you are the engineer that deals with this simple design situation, what would you do? Thank you in advance and any advice and input would be greatly appreciated!
I have a simple question/discussion topic that I want to bring up, share some of my thoughts, and maybe more senior SE can correct me if I'm wrong and provide me with some expert opinions in this regard.
So in my working industry, I have come across many steel wall mount designs that using adhesive/mechanical wall anchors for simple structure that supports telecommunication equipment, e.g. antennas.
Sometimes I have to deal with special requirements, for example, I have a 1.3m parapet (concrete with min. reinforcing I assumed), from the top of the parapet to the proposed antenna is another 1.7m (center of the antenna on which I consider the wind load is acting). In my original design, I left 200mm to concrete parapet edges all around so my anchors can develop full capacity according to the anchor manufacturer's recommendation. Last year, I did not design this type of wall anchor connection to take any moment (i.e. I used pinned connection type).
Recently client has proposed to rise up the antenna so now my total cantilever distance is increased to about 2.1m (from the centerline of the antenna to the top anchor connection). With my re-assessment of the wall anchors, and a closer look at my connection type, I think instead of using the full pinned connection, I tried fixed type, the reason for this is I want to see if the existing connection can take moment at all. Cause I don't have full details of the reinforcement for this parapet, I could only assume none to 15m reinforcing rebars for this parapet, cracked, and 25MPa concrete strength.
So the result was just like what I expected, all the anchors are fine in both tension and shear (far away from their capacities), but I have a problem with the concrete breakout. Now, by just considering the y-axis as my fixed axis, the concrete breakout is at a 169% utilization ratio. I'm now more leaning towards the latter approach cause I know there will be a moment transfer at my top connection. However, I have also seen so many designs by others that had a similar cantilevered structure with wall anchors like this, but they never had a single issue. In addition, My intention is not to touch the existing installation (so this eliminates the option for installing the full penetration rods to engage the entire local parapet wall). So am I overthinking this or my assumptions for parapet were too conservative or am I missing anything?
Loading Case: Fw+Fd, where Fw=1.66kn, Fd=2.88kn (both factored loads). Fw is acting 2.2m above the first connection. overall mount assembly and anchor layout see below screenshot
Therefore, if you are the engineer that deals with this simple design situation, what would you do? Thank you in advance and any advice and input would be greatly appreciated!
