Load to A.B. 1

[sandman21]

I am using this detail as a hold-down at the end of a shear wall. I got a comment on how I determined the load in the bolts; I tried a few different methods and got fairly close results. I was just curious on how you guys would determine the load in the bolts.

 

[msquared48]

I'm not really sure what I am looking at, plus the material and orientation... Where is the shear wall with respect to this?

Mike McCann
MMC Engineering

 

[sandman21]

Sorry I thought I wrote more, it has been a long month.

At the end of a shear wall, I am using the HSS as a hold-down. This condition occurs at the end of a footing inside the wall on top of a curb. Therefore, I am unable to space out the A.B. to get an even distribution, so I was wondering what method would you guys use to determine the load to each of the bolts.

 

[Lion06]

I am assuming this is a plan detail, is that true? How are the anchor rods attached to the HSS - are you using a thick plate?

 

[Lion06]

I would probably use an equal number of anchors on both sides of the HSS.

 

[nutte]

Check prying action to get the tension in the closest anchor bolt. I wouldn't count on the other three to resist any tension. The right-hand sketch in Fig. 9-4, page 9-10 of the 3rd edition steel manual, shows a configuration with a one-sided bolted connection resisting tension.

If the plate was thick enough, there wouldn't be any prying effects, and the tension in the closest anchor could be taken as the tension in the column.

 

[sandman21]

I wanted to use an even number of bolts that was not possible at the time; we have since changed the detail. Yes the first one is a plan view the second is an elevation; a plate is used to transfer the load. Thanks I figured the AISC prying would be the one that would come up. Anyone else have a method they use?

 

[swearingen]

This is a zipper situation where failure of the first row is the only way to load the next row. The first row must be able to take the entire tension load plus prying forces.


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[Tomfh]

First bolt carries all the load.

Add 30% for prying.

 

[hokie66]

I disagree that the first bolt takes all the load. How much it takes is dependent on the stiffness of the column and the plate. But I do agree that it is a poor detail.

 

[DaveAtkins]

You can assume whatever you want about how the load is resisted, but you must be consistent. If you assume all the bolts are loaded equally, you must design the base plate for bending (which should not be a problem) and design the steel HSS post to throw the bending induced back into the shear wall via the plywood (which could be a problem).

Eccentrically loaded holddowns are frowned upon because of the moment created.

DaveAtkins

 

[msquared48]

In addition to the prying actio0n here, which will happen regardless of the stiffness of the bearing plate, I would be concerned that the shear cones of the bolts are overlapping, reducing the capacity of the bolts in pullout.

I do not like the detail at all...

Mike McCann
MMC Engineering

 

[matrix333]

Why not try some gusset stiffeners to the plate and connected to the column. There will be a much greater sharing of the load. Not equal, mind you, but better than detailed.

 

[sandman21]

Well per AISC you can make the plate thick enough to prevent prying action. The question at hand is how to determine the load to the bolts, the detail has been changed so no need to worry. I design the plate to be thick enough to prevent prying, then used the vector analysis to determine the load to the bolts. Anyone have a way to determine the load to the bolts other than assuming that the load plus prying is on the first bolt.

 

[mudflaps]

When confronted by a nasty problem with an equally nasty solution, do as Captain Kirk would do. Change the problem, in this case move the HSS tube away from the end of the shear wall till you can get a better bolt pattern. This assumes you can live with a slightly shorter shear wall and aren't getting any uplift from upper stories. If you are, maybe a skewed column is in order. It's no worse than the mess you're dealing with now. In any case, question the assumed restrictions.

Old CA SE