Steel Detailing 101 Questions - Bolted Double Angles 1

[271828]

Some of you will think these are pretty funny questions, but I'll ask it anyway. I've been wondering about these for a while.

Say I have a bolted-bolted dougle angle connection with bolts in-line rather than staggered. Folks often use L4x4x5/16 with a 2-11/16" angle gage in each leg of each angle. This is no good according to the 13th Ed. Table 7-16 with "no good" being defined ask not being able to get a socket on either bolt.

So what's the deal here? Do erectors just use a wrench for these situations, so it doesn't matter if Table 7-16 is violated? If that's the case, then what's the use of Table 7-16?

While I'm at it: What are the common angle sizes and gages that you guys see for this type of connection?

When this kind of connection is made to a girder, I've heard it referred to as a "suicide connection" because the first installed beam must somehow be supported without bolts while hte second is installed. Is there a standard procedure for dealing with this issue? I've seen people show temporary seats at some connections, but don't know if this is mandatory. Commentary on this would be appreciated.

Thanks in advance.
100000e

 

[hokie66]

With a bolted-bolted angle connection, I think you need to use larger angles. I haven't worked in the US for a long time, but we used to use 6 x 4 angles in that type connection, and my AISC Manual, 8th Edition, 1980, has some examples using 6 x 4 angles.

 

[271828]

That's how I see it too, although I think a L5x seems to work also. Still, I know for sure that people routinely use L4x4.

 

[spats]

I see 3 1/2" and 4" angles most commonly. Also, if you mostly using bearing connections rather than friction connections, the bolts only need to be snug-tight, and you don't need a socket/impact wrench to tighten. A simple crescent or box wrench does fine.

Regarding the "suicide connection", it is normal practice to provide one extra row of bolts on one of the beams, so that row can be used to temporarily secure the first beam.

 

[Dinosaur]

I have the eighth edition so I do not know specifically which table you are speaking of when you ask, "If that's the case, then what's the use of Table 7-16?"

My copy of the AISC Manual shows 'g' as 2-1/2 inches for a 4 inch angle.

I presume this has to do with minimum clearances needed to get the hardware in place, not the tool. In many connections, the opposite face is open so the tool can enter from that side and a wrench used on the difficult side.

My copy of the AISC Manual also offers guidance on staggered holes for tight situations as you describe. Maybe a good detail would follow these guidelines. Or as you suggest, a larger angle might be the best solution.

For myself, I have always found the information in the AISC manual to be of very high quality, bringing attention to aspects I might have overlooked, and amazingly free of typographical errors by contemporary standards.

 

[JAE]

I thought that OSHA (in the US) didn't allow these "suicide" connections. I thought you had to provide offsets.

 

[vincentpa]

why do you need to use bolted-bolted connections? Most fab shops use 3" and 4" angles welded to the beam and bolted to the column. That's what our typical details use. I have never used a bolted-bolted connection. You can call a fab shop to ask them. They are usually very helpful. They can tell you better than an engineer what fits up properly or easier. I personally have never welded a connection or tightened a "tight" connection. Although I have watched before welding and tightening. Watching doesn't qualify me as an expert. Those tables i AISC are good if you really need to get into a space. The fab shop might give you a larger angle that will make fabrication easier.

 

[nutte]

Vincentpa, your comment that most fab shops use welded clip angles is sweeping. I'm aware of many shops that use bolted-bolted clip angles.

JAE, the problem with the "suicide connections" and OSHA is avoided if one of the angles is extended longer and an extra bolt added, as Spats described.

 

[271828]

Thanks everybody.

Vincent,I'd say that the fabricators I've worked with are about half and half when it comes to the conn you described and bolted-bolted. In this case, I've just been asked by a pal to take a look at some bolted-bolted ones.

 

[JAE]

nutte - yes, I agree...but then with the extra bolt it is not, by definition, a "suicide" connection. That was simply my question - why is this even a question to begin with if you shouldn't use suicide connections.

 

[hokie66]

JAE,

The OP was only partly about "suicide" connections. The other part was about clearance for tightening in bolted-bolted angle connections.