Tek-Tips is the largest IT community on the Internet today!

Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!

Register Log in
  • Congratulations TugboatEng on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Converting moment into couple for two connections? 1

Status
Not open for further replies.
Redacted

Redacted

Structural
Joined
Mar 12, 2016
Messages
160
Location
BM
Hi there,

I need to check an existing connection and I want to make sure I'm going about this in the correct way.

To provide some background there is a metal pole that is connected to a hollow masonry CMU block wall with some mechanical anchors. I would like to check if this existing connection is adequate for the pull out loads.

I've drawn a sketch of the system below:

20220421_095322_1_-_Copy_-_Copy_xglabq.jpg


I guess my main question is to understand the structural system. It seems logical to me that if a bending moment is applied to the base of the pole from a wind force, connection 1 would be fully in tension and connection 2 in compression. Therefore, can I just convert the moment of 1.2kNm into a couple :

1.2/.711 = 1.7kN tension and 1.7kN compression.

As in both bolts in connection 1 will take the 1.7kN (0.85kN each) tension and both bolts in connection 2 will take 1.7kN compression?

Any advice would be appreciated if I am going about this analysis in the wrong way or if there is a better way to do it I would be happy to learn.

Thanks
 
Sort by date Sort by votes
analyze the pole as a beam (simply supported) on two supports ... which is the same as a cantilever built in at the midpoint of the two supports.

but I think the real question is is the moment a couple on the fasteners or is the "tension" force of the couple taken by the bolt and is the compression force the result of a distributed load against the wall ? If the pole is clear of the wall, is there a spacer around the bolts ... which would then provide a localised loadpath.

another day in paradise, or is paradise one day closer ?
 
Upvote 0 Downvote
1) I think that you've got the right idea in general.

2) I get slightly different numbers than you. I'm sure that you'll be able to parse out my reasoning based on my math.

3) As rb1957 intimated, your compression connection may well be a direct bearing of the connection plate on the substrate rather than passing the force through the bolts there. That depends on the detailing of course.

C01_gglw8v.png
 
Upvote 0 Downvote
Thanks very much rb197 and Koot, your comments are very helpful!

 
Upvote 0 Downvote
the overhand is 4000-852 = 3148mm
the max moment is at the upper fastener. The airload on the overhang is 600N *(3148/4000) = 472N, assume UDL,
and the moment is 472*3148/2 = 743243 Nmm

but this is IMHO a bad way to approach the problem. Always start with the reactions. Take moments about the lower fastener ...
600*(2000-141) = Ru*711, Ru = 1569N, Rl = -969N

my numbers slightly different to KootK's ... he overlooked the 141mm offset

another day in paradise, or is paradise one day closer ?
 
Upvote 0 Downvote
rb1957 said:
my numbers slightly different to KootK's ... he overlooked the 141mm offset
Click to expand...

That was intentional. I believe that is most correct to take the moments about the center of the lowest fastener group, not the lowest fastener.
 
Upvote 0 Downvote
sure, but then the load isn't applied 2000mm away

another day in paradise, or is paradise one day closer ?
 
Upvote 0 Downvote
I see the system as a cantilever beam with a short backspan. The two outriggers are the supports and the bolt groups support each outrigger reaction. I took the liberty of using a 100mm cantilever below the lower outrigger based on your initial sketch which is why my numbers are slightly below KootK's.

Capture_gxiwua.png


I'm making a thing: (It's no Kootware and it will probably break but it's alive!)
 
Upvote 0 Downvote
why 100mm, when OP has 141mm ?

another day in paradise, or is paradise one day closer ?
 
Upvote 0 Downvote
Because the OP's sketch appears to show a 141mm spacing between fasteners, not from the lower bracket to the bottom of the tube.
 
Upvote 0 Downvote
oh, ok ... I read as 141mm to the bottom of the tube.

another day in paradise, or is paradise one day closer ?
 
Upvote 0 Downvote
Status
Not open for further replies.

Similar threads

lexeng18
  • Locked
  • Question Question
Steel Frame Moment Connections Layout and Detailing
Replies
0
Views
2K
lexeng18
lexeng18
NickDePinhoPE
  • Locked
  • Question Question
Help Pipe Support Engineer with Moment Connections
Replies
7
Views
4K
DrZoidberWoop
DrZoidberWoop
mohamed hassan 2014
  • Locked
  • Question Question
Converting Stress to Moment in a Foundation Slab Model: Best Practices?
Replies
6
Views
3K
SWComposites
SWComposites
StrEng007
  • Locked
  • Question Question
Applying moment to beam on elastic foundation; single point or couple?
Replies
2
Views
607
KootK
KootK
mferg318
  • Question Question
Rigid Diaphragm - Decking Connections
Replies
4
Views
791
mferg318
mferg318

Part and Inventory Search

Sponsor

Back
Top