HS BOLT IN PIN CONNECTION

[bridgetrool]

Designing a pinned connection. Want to use HS bolt for pin. A325 assume ductile therefore plastic design is coming out better than A490 assume brittle therefore use elastic design. Is this thinking correct? Thoughts on the matter would be appreciated.
thanks
bridgetrool

 

[dhengr]

Bridgetroll:
You say... “Thoughts on the matter would be appreciated.” And, enough problem development info. so we could get our heads around what you are trying to do would be appreciated from this end. We can’t see what you are trying to do from here. Maybe a sketch with dimensions, loads, load cycles, what kind of a structure is this, etc. would be helpful.

 

[bridgetrool]

dhengr, sorry about lack of info.
Want to use 7/8dia HS bolts in temporary pin connection. Just wondering if the way I applied plastic and elastic is correct.
A325 HS ductile, Mn = Mp = FyZ = 92ksi*.112 (Z) = 10.304k" <= 1.6 My = 1.6*92ksi*.066 (S) = 9.715k" gov., factor*.67 = 6.509k"
A490 HS brittle, Mn = My = FyS = 120ksi*.066 (S) = 7.92k" factor*.75 = 5.94k"
Thought the 490 would calc. better.

 

[dhengr]

Bridgetroll:
With the latest generations of codes and engineers, we have become so interested in (been forced to) manipulating numbers, formulas, and factors which increase or decrease a result depending upon the direction of the breeze, that we have forgotten to look at the problem and understand it in its simplest form, before we start all the numerical manipulations. Is this a pin plate, with two side plates and the bolt through them, as a pinned connection; is this a single shear plate and a WF web temporarily pinned with the bolt? What are the plate thicknesses and forces on the pin? Is the pin in single or double (or more) shear, or is it a actually a bending member by the nature of the way the joint is detailed? Why are you looking at bending stresses? Or, when you say “temporary pin connection,” do you mean a bunch of bolts in a connection, but it’s not a moment connection or slip critical connection? I dare say that the bearing stress on the plates will more likely be the controlling condition. So, I say again, “ Maybe a sketch with dimensions, loads, load cycles, what kind of a structure is this, etc. would be helpful.” The new info. you’ve given doesn’t explain the problem well enough so that we can comment on your numerical manipulations.

All the crap we have to wade through in the current codes does a disservice, without producing better structures; in that it clouds the picture to the point that trying to get all that crap right completely negates a fundamental/basic/simplified understanding of the problem. For this old man, at least, it is becoming more and more true that we don’t teach or approach these problems the same way as we used to; hell, we barely speak the same language any longer. Furthermore, the difference btwn. A325 and A490 bolts probably wouldn’t be best described/characterized as ductile and brittle, they are both quenched and tempered. And, I’m not sure you are making the right distinction about when elastic, plastic or LRFD design is appropriate. And, unless there is redundancy in the detail I’m not sure plastic design has a place here.

 

[ishvaaag]

I as always (as I have here seen) have to be in agreement with dhengr ... it is easy today to find people outreaching the limits of their true knowledge using some program or programs for the design of structures that has not the minimal understanding necessary to produce appropriate designs. The urge of governments for political correctness -and image competence between institutions- trying to feign that they use the best and latest technical info to ensure public convenience and safety compound in the problem and, in the effort of trying to see the trees, many don't see the wood.

Other view is that specialization requires everyone just knowing quite on something and just that to be incardinated with the work of others, you can find tons of project management and system approach books that tell much and (sometimes) very reasonable things about that. But the fact is that for now, building (and tons -but not all- structural) designs need be closely tailored to single or very short run cases, and that (basically industrial) approach does not fit at all the (design and construction) needs of the actual practice, experience demonstrates that, whatever the size or complexity of the piece at work is. Not having a competent designer at the helm shaping the whats and hows from the whys is then a big problem and so generates not only functional misfit but also aesthetical disgust, when all the "trees" are massed in what built as a collection of items glued without natural order ... much of the ugliness being produced today comes from this, and the usual tactics of covering all with some dress is neither satisfactory ... architecture, architectonics always was from old "more than tecton", more than a roof.

Everyone in the field has seen his or her collection of technical moron bosses of whatever the kind boasting knowledges they really don't have. With the currently being impelled trend of placing users of programs and public servants -and quality control inspectors of lower qualification than the designers, this happens here through the vagaries of cheap salaries- blind to any other reality than some particular interpretation of code letter, a new collection of people obstructing making construction meet ends needs to be dealt with. And really, not having at the head someone that has the more ... rarefied ... idea of what is going on with the architectural or engineering design from one structural viewpoint is not going to help. This is an unwelcome departure of the merits of thought, understanding and merit, and no doubt, many bad things are resulting from this.

 

[BAretired]

The problem is not clearly defined. I am not sure the proposed pin joint is permissible by code. Provide a sketch and adequate explanatory material as requested by dhengr.

BA

 

[bridgetrool]

dhengr, are you thinking that C,QT material may not be assumed ductile? This is what we are wrestling with. As you can see, it makes quite a diff. in the calc.s thanks

ishvaaag, are we manipulating the numbers or is this an acceptable method? this is what we are trying to determine. thanks

BAretired, your post and the above posts reflect what we are trying to get a handle on. thanks

dwg. attached

 

[Archie264]

>>>...All the crap we have to wade through in the current codes does a disservice, without producing better structures; in that it clouds the picture to the point that trying to get all that crap right completely negates a fundamental/basic/simplified understanding of the problem. For this old man, at least, it is becoming more and more true that we don’t teach or approach these problems the same way as we used to; hell, we barely speak the same language any longer.<<<

dhengr,

Hear, hear! Preach on, brother!

I'm beginning to wonder if it isn't a symbiotic relationship between the building code writers and the software code writers. They each keep each other in business, for the benefit of the public, of course.

It reminds me of the short story by O. Henry wherein a cat constantly chases a mouse but never quite catches him but is rewarded with a saucer of cream for his efforts...until one day when his owner notices the cat and the mouse sharing the saucer of cream...

 

[dhengr]

Bridgetroll:
That sketch is a good start, but it is still like pulling teeth to get enough meaningful info. out of you people. Is this an adjustable height splice (in 3" or 6" increments) of the two different sized HSS sections? What are the lengths of the two different HSS sections and what is the total load on that temp. column. Where in the height of this temp. column is this splice, and what is the total height of this temp. column? Am I right in assuming that you think you will have a total of 9 bolts taking this total load? Without literally match boring the 15/16" holes in the two column sections, which then become permanent mates which should not even be rotated w.r.t. each other, you will not get all the bolts bearing, without some bearing yielding in the HSS walls, at some holes. Can you even buy a 14" long by 7/8" A325 bolt? I do now see how you can get some bending in the bolts, but I still suspect that bearing on the HSS walls will be the controlling design criteria. In terms of bearing stress, you have the same reaction force (F) on the 3/8" outer wall as you do on the inner 1" wall. And, this connection may have to take some beam/column bending moment too.

Why don’t you show 4 - .5" reinf’g. plates on the left 10x10 HSS, and why are the holes at 3" o/c in the reinf’g. plate you do show? You mean the holes are at 6" o/c, but offset by 3" from one side to the other, don’t you? The only thing I can understand about the right section through the bolt hole is the 15/16" hole dia. I would have shown where that section is cut on the middle side view of the connection, and then shown dimensions .5", .5", .125", .375" (that’s 1/2,1/2,1/8,3/8"). No one understands your thought process in getting the dimensions you show, and if you can’t afford dimension arrows, that confuses things too. Now, on this bolt hole section draw a FBD (free body diagram) which shows the two triangular bearing stress blocks and the slope of the bent bolt. This is where some engineering judgement and experience comes into play unless you want to spend a day farting around with FEA on this detail. The left (upward) bearing reaction will be .33" from the clearance space and the right (downward) bearing reaction will be .125" approx. right of the clearance space, plus the .125" clear. Now draw your bolt/beam with forces (F) .58" (.33+.125+.125) in from the two outer reactions, which are about 11.5" apart. Draw the shear and moment diags. for this beam and take a shot at its slope at the reactions, and its center deflection. You will get some significant bearing yielding in the HHS walls and the reinf’g. plates, and most of that force (F) is on the reinf’g. pl., so is the 5/16" fillet weld enough. I would look at a larger dia. round bar material for the pins which met my bending needs and was somewhat harder than the HSS material. I’d weld a driving head to one end, and taper the other, as you show, and provide a washer and locking pin (cotter pin?) at the tapered end. You might also consider making the holes 29/32" dia. which will improve the bearing stress picture, but make assembly a bit more difficult. I would still match bore the holes and then consider only 80-90% of the pin cap’y; otherwise use a lesser pin cap’y., since all of them won’t come into play until some HSS wall bearing stress yielding has occurred. You probably don’t want any bending yielding or much bearing yielding in the pins or it will be tough to extract and drive them again.

If height adjustment didn’t have to happen at this joint, I probably wouldn’t use your detail. These temp. columns are going to have to sit on a base plate and some cribbing at their foundation; and also have some cribbing up under what they are supporting. And, I’d be tempted to try to do my height adjustment at one of those locations, and avoid this difficult pin shear/bending load transfer splice detail if I could.

 

[BAretired]

The proposed detail should be avoided as it uses bolts in a way they are not intended to be used, namely in bending. A better detail would be to provide HSS 10x10x0.5 for upper and lower column sections, each with an end plate field bolted together or separated by steel packing of variable thickness.

BA