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Hilti Chemical Anchor HIT-HY 200 System
- Thread starter upk
- Start date
- Thread starter
- #21
Consider columns.. the most edge bars would have more strain and stress than the intermediate bars via the strain diagram.. and if you don't use any intermediate bars.. the stress in the edge bars are the same. In the case of metal plates.. it also bends.. and the edge anchors would experience the same strain and stress.. what is the analogy in the case of columns.. just this so I can get your frame of reference. Thanks.
JStructsteel
Structural
I looked at your detail, and it shows the baseplate is stiffened, so I assumed that the plate would not bend, and the loads would be shared.
Maybe you need to post a new anchor layout so we can see how its laid out. Based on your detail i know would assume there are 8 anchor rods all at the same plane as the poor A307 rods.
Maybe you need to post a new anchor layout so we can see how its laid out. Based on your detail i know would assume there are 8 anchor rods all at the same plane as the poor A307 rods.
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- #23
Yes, the designer make it stiff because it is just rafter middle support. Moment is suppressed..
This is the 0.5x0.5 mtr base plate that enclose all the 8 anchors (the 4 were not yet put.. maybe tomorrow if weather permits)
The blue dot is the A307 bolts (1 foot embediment) located about 3" from edge corner. The red dots are the additional expansion bolts to be put (the designer colleague said it's up to us.. more anchors better). Unfortunately. There is no stocks of the Hilti chemical bolts so have to use local GI expansion bolts. The light blue wide flange is the 1 foot support of the rafter you saw with the stiffener.
This is the 0.5x0.5 mtr base plate that enclose all the 8 anchors (the 4 were not yet put.. maybe tomorrow if weather permits)
The blue dot is the A307 bolts (1 foot embediment) located about 3" from edge corner. The red dots are the additional expansion bolts to be put (the designer colleague said it's up to us.. more anchors better). Unfortunately. There is no stocks of the Hilti chemical bolts so have to use local GI expansion bolts. The light blue wide flange is the 1 foot support of the rafter you saw with the stiffener.
JStructsteel
Structural
If the capacity meets the demand of the loads imparted on the structure as specified by your engineer, it should be fine.
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- #25
In ACI 318 Appendix D illustration (see above), i'm more concerned of shear loading than moment loading.. anchor so close to edge can result in pryout. This is even without any moment but just the structure swaying left to right. That's why the direction of the shear is horizontal.
upk,
Unless you have calculated the shear you are worried about resisting, there is no way to check the adequacy of your design. You need to know your design loads, before you can compare to capacity. It does not sound like you have quantified your loads (due to sway or other) and does not seem like you are able to compute said loads. That being said, what country are you in? Sounds like you are acting as a contractor and designer, which would be fine, if you were qualified to do so. by all of your posts, I am assuming you all are not qualified to be the contractor nor the designer.
Unless you have calculated the shear you are worried about resisting, there is no way to check the adequacy of your design. You need to know your design loads, before you can compare to capacity. It does not sound like you have quantified your loads (due to sway or other) and does not seem like you are able to compute said loads. That being said, what country are you in? Sounds like you are acting as a contractor and designer, which would be fine, if you were qualified to do so. by all of your posts, I am assuming you all are not qualified to be the contractor nor the designer.
@upk
First check if the chemical anchors or any hilti anchors are compatible to the seismic zones you are working on. This is very important, some anchors cannot be used in SDC D, E, F.
Note that Adhesive anchors have different strength reduction factors that more conservative (ACI 318-11)
I don't know what you mean to reinforce the A307, if this was cast in place you can use hairpin style reinforcement to gain strength for shear.
in your case, may be you can group anchors and figure out the combined capacity of anchor family. Any edge distance less than 1.5 x embed and any spacing less than 3 x embed depth requires strength reduction due to overlapping of the cones.
First check if the chemical anchors or any hilti anchors are compatible to the seismic zones you are working on. This is very important, some anchors cannot be used in SDC D, E, F.
Note that Adhesive anchors have different strength reduction factors that more conservative (ACI 318-11)
I don't know what you mean to reinforce the A307, if this was cast in place you can use hairpin style reinforcement to gain strength for shear.
in your case, may be you can group anchors and figure out the combined capacity of anchor family. Any edge distance less than 1.5 x embed and any spacing less than 3 x embed depth requires strength reduction due to overlapping of the cones.
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- #28
I'm just verifying the design of the designer because he made mistakes before. He for instance forgot to put stirrups in places that needed it before.. later he just designed carbon fiber retrofit because he forgot. So now I'm cautious and just want to double check if he would make another mistake.. the contractor will implement the plan tomorrow.. so have a few hours to do a halt of the project if I see another mistake in the design.
JStructsteel
Structural
Just check your shear load against the shear capacity of the anchors. If you also have tension, be sure check the interaction for shear and tension.
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- #31
For months and years. I've learnt how to derive the computations in beams, columns, foundations, even seismic. I generally avoided wide flange and base plates because I just wanted to focus on reinforced concrete. But this situation forces me to try to understand it.
Ive been trying to understand the principle or physics for it the past 2 hours.. I still can't understand.. if one add new sets of bolts inside the edge.. why does it decrease the moment arm and make the edge anchor seems more load. See the illustration above for some questions.
After understanding it. I'd no longer ask others. Lol. Thanks.
Assuming you have a perfect couple for your two anchor bolt example, your applied moment which has the units of force*length will be equal to the unknown force in your anchor bolts multiplied by the distance between the anchor bolts. Therefore, when you have a smaller distance between anchor bolts, the load is higher. Move your anchor bolts out, and their loads will go down.
The example with the 4 bolts is more complicated, but essentially the outer ones are further away from the neutral axis and therefore see a larger share of the load. Imagine if your bolts were right in the middle spaced very close, you could imagine that this would not be very helpful to keep something (column) from tipping. Its the bolts applied closer to the edges of the base plate that will resist the overturning (moment).
The example with the 4 bolts is more complicated, but essentially the outer ones are further away from the neutral axis and therefore see a larger share of the load. Imagine if your bolts were right in the middle spaced very close, you could imagine that this would not be very helpful to keep something (column) from tipping. Its the bolts applied closer to the edges of the base plate that will resist the overturning (moment).
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- #33
Is there a counterpart of this principle in columns? What serves as the anchor there that depends on the moment arms? In columns. Putting the intermediate bars or not won't affect the forces in the edge bars because of the strain diagram.. and what is the equivalent in the concept of anchors and metal plates? also what is the moment arm in columns.. many thanks.
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- #34
I understood the second part.. it's like the outermost bars in columns where they are the most stress. But according to jrisebo, if you suddenly add internal anchors.. it would change the outermost anchors contibution. Well.. in columns.. adding internal intermediate bars won't affect the values of the stress/strain at the outermost bars. Why would there be effect in metal plates? This is the part the I don't get.
Note jrisebo statement is "Well if you use the A307 and a new set of bolts, you are still decreasing your moment arm, so yes the A307 will see more load."
It's as if adding intermediate bars would suddenly change the outermost bars in columns. It doesn't. So what is jrisebo point out?
JStructsteel
Structural
My comment has nothing to do with column bars. I was ONLY talking about the poor anchors.
You have jumped to the column and the bars. Not the same thing.
If you have a set of anchors, and add more anchors towards the inside, the moment arm changes, and the loads change. Thats what I was getting at.
You have jumped to the column and the bars. Not the same thing.
If you have a set of anchors, and add more anchors towards the inside, the moment arm changes, and the loads change. Thats what I was getting at.
JStructsteel
Structural
"It's as if adding intermediate bars would suddenly change the outermost bars in columns. It doesn't. So what is jrisebo point out?"
If you go from one set of bars to two set of bars, what happens to your 'd' distance for the group of bars. You increase the load, but with additional bars, you increase capacity.
Please prove me wrong.
If you go from one set of bars to two set of bars, what happens to your 'd' distance for the group of bars. You increase the load, but with additional bars, you increase capacity.
Please prove me wrong.
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- #37
i can understand it better using the concept of neutral axis. if you add more anchors inside. the outside anchors would still have same distance to neutral axis. yes or no? if same and you add more internal anchors. the outside anchors would still have same distance to neutral axis and have same load.. right? pls share references (even newtonian physics) so i can directly check them out.. tnx
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- #38
again extra anchors (expansion bolts) were put (the blue texts) to aid the poor A307. the following are the holes in the metal plate painted with grey.
jrisebo.. reflecting it today.. while it is true that shorter anchor distance would produce more force on the anchors.. the only way the edge anchor can be affected by adding or changing the middle anchors is if they are coupled.. so I think by adding middle anchors.. the stiff plate doesn't flex by moment but instead transfer the load to the edge anchor.. is this what you meant the load at edge increases when middle anchors were put?? if not.. please let me know why.. just this aspect.. thanks!
jrisebo.. reflecting it today.. while it is true that shorter anchor distance would produce more force on the anchors.. the only way the edge anchor can be affected by adding or changing the middle anchors is if they are coupled.. so I think by adding middle anchors.. the stiff plate doesn't flex by moment but instead transfer the load to the edge anchor.. is this what you meant the load at edge increases when middle anchors were put?? if not.. please let me know why.. just this aspect.. thanks!
JStructsteel
Structural
If the moment is left to right on the picture you posted, with the extra holes, the NA moves a bit, I would design using the NA of the original holes, & the extra holes.
Going back to the original post, how do you know the A307 are not adequate for the load? Do you know the load?
You need to get a competent engineer involved, and based on your other post, that does not involve the company you are dealing with now. This is basic engineering, and if they cant get this right, the rest of the building is in question.
Going back to the original post, how do you know the A307 are not adequate for the load? Do you know the load?
You need to get a competent engineer involved, and based on your other post, that does not involve the company you are dealing with now. This is basic engineering, and if they cant get this right, the rest of the building is in question.
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- #40
I went to the designer company this morning. The team leader said the A307 are adequate for the job. But they also give safety factors for construction error. Hence the 4 extra holes are just additional for extra margin.
So you are saying when the anchors are nearer to each other in a baseplate, there is a larger force in the anchors and at the same time the neutral axis rate of change would be faster.. hence there is more load in the tension side because the neutral axis moves a bit more... right?
The designer just says when the anchors are farther, there is less tension.. I asked him would there be greater load at the far edge.. he is silent.. he appeared not to consider what you were saying.
Anyway the 4 extra holes are just to strengthen the shear capacity (safety margin). Because the designer himself said moments are not large just enough to resist the wind load over the rafters. I discussed with him about pryout of the edge.. he seemed not to worry of it much.
Well. In our country. There is no course in structural engineering.. so ordinary folks can get the label of structural engineers by just 6 month short course and exam. That is why many don't even know the meaning of stress and strain diagram. This is exactly why I'm learning the theoretical foundation.. to analyze if they made possible mistakes.. like they had before. Because wherever I go.. the structural engineers don't put importance in knowldge of physics principle.. so they can't apply it in odd situation. Hence I need international assistance.
In a third world country. This is expected. So thank you so much for sharing even a bit. Don't worry I won't ask you on others things.. just this internal anchors affecting the load at the edge anchors.
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