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Kicker Stair Support 1

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EntryLevelEIT

EntryLevelEIT

Structural
Jun 24, 2010
42
Hey Gentlemen,

I'm reviewing a stair submittal sent by the fabricator. The top landing is anchored to a concrete wall by a kicker. My goal is to check the adequacy of the connection (in particular the bolts anchoring into the concrete). As you can see by the attached pic the bolts are not eccentric. An example in my book has a tension-shear interaction check, but the bolts are eccentric, and the centroid can easily be found. Does anyone have any examples or guidance for the senario I have here. Plz see both pics, help is much appreciated.
 
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I'm not even sure what you are asking or why you are saying your bolts aren't "eccentric".

Are you asking for advice on the anchor design or on the analysis of the system?
 
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I want to analyze the system per 100 psf and make sure the given design is adequate. The closest example I have in my book doesn't really represent this situation. The book uses the eccentricity of the bolts to sum moments about the neutral access. After equating the resisting and applied moments a tensile force per bolt is found and compared to the design tensile strength. Since the bolts in my case are not eccentric I'm not sure what to do, so I'm asking if anyone has any examples similar to this situation.I want to determine that the design strength is greater than the factored loads.
 
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I'm still not 100% sure what you are saying.
However, you can sum forces/moments about the neutral axis of the bolt group and resolve this into compression and tensile forces on your bolts. Anchors above the n.a. will have tension and shear and the bolts below will have compression and shear.

I caution you this:
The area load on the landing will amount to reactions at the ends of the C10.
On the left side of the C10, the force will wind up in the knee brace. The bottom pair of anchors in the wall should take the full shear force resulting from the knee brace.
On the Right side of the C10, the shear will be taken by the top pair of bolts.
I would NOT share the shear force amongst all bolts.
 
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I would say the shear is taken by all five bolts, and the tension from the C10 is taken by just the top two bolts.

DaveAtkins
 
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Dave,
I was assuming pairs of bolts as far as "into the page".
 
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I started in this business as a clerk,drafter when I was sixteen. I retired at sixty seven and I still don't know what is meant by "kicker", I have seen it used so many different ways. I presume it is the knee brace in this case.

Michael.
Timing has a lot to do with the outcome of a rain dance.
 
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EntryLevelEIT,
I don't see by the pic that the bolts are not eccentric. Not eccentric to what? Please explain what you mean.

Whose expansion bolts are being used and how deep are they embedded? What is the minimum spacing between bolts according to the manufacturer? 3" seems too close to me for the upper two which carry most if not all of the tension.

Maybe through bolts should be used, at least for the top two.

BA
 
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This is one of those simple structures that's an analytical challenge, to say the least.

As for your book example, I'm fairly sure that the eccentricity referenced is actually the distance of each bolt from the point of rotation of the knee brace. OK...now where's the point of rotation? It can be anywhere from the bottom of the knee brace to the vertical center of the bolt group. It will also depend on the bolt spacing and stiffness of the vertical member.

Perhaps the easiest analysis method would be to consider the vertical member a continuous beam with 5 support points and an applied moment at 2/3 the distance from the bottom.

Another way is to use the AISC base plate approach, considering your vertical leg to be a base plate.
 
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BA-
I had the same thought....but I was so confused about the eccentricity that i didnt even know how to ask a question. I mean, eccentricity is not an intrinsic trait. Some have accused me of being eccentric, with reference to no physical point, but we can't do that here can we?
 
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I would check the connection with forces as shown in the attached sketch. Each bolt resists a shear of 2P/5 = 0.4P. The upper two bolts carry a tension of 1.94P (0.97P each).

I am not comfortable with the two top bolts being expansion bolts, especially at 3" centers because the rupture cones overlap. I would prefer to see either through bolts or a weld plate anchored in the wall using headed studs. Then the attachment angle could be welded to the weld plate on site.

BA
 
 http://files.engineering.com/getfile.aspx?folder=abf7f920-080a-4887-822a-2caa4092f648&file=Stair_with_kicker.pdf
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Toad,

I still don't know what he meant by eccentricity, but the sketch seems clear enough.

BA
 
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I am still of the opinion that the bottom bolt must take all of the shear from the "P" as BA shows on the outside of the knee brace. To me there is some shear lag in this set up....I am probably knit-picking.

Pad- Yes, I think "kicker" is used to too often.
 
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BA-
The only "e" I can think of is that which is out-of-plane.
That would exist, no?
 
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Do you think the 'e" may be at the top of the knee brace? it goes to the top at the connection with the stringer. I dont see how that matters but I'm wondering what the detail is there, how is the angle connected?

Michael.
Timing has a lot to do with the outcome of a rain dance.
 
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