Moment Connections of Steel Structures 1

[KCRatnayake]

Hello All,
I am designing a multi-storeyed steel building for a church to be functions as a school. I want some steel connections to act as moment connections. Bolt size is M36 with clearance hole diameter of 40mm. Plate thickness is 35mm.

1. Since there is a gap between bolts and steel plate, is it possible to have a moment connection?

2. Hilti has Dynamic sets for bolted connection if you need a fixity there, but only sizes up to M20

3. One of my colleagues proposed to weld the bolts and base plate; but I think the purpose of bolted connection will be lost if we do that.

4. Can I use 2 Nos. 20mm thick plates instead of 35mm plate?

Appreciate your comments and ideas.

Regards,
Clefcon

 

[asixth]

clefcon,

It's good to see you are working with the correct units.

The oversize bolt holes are provided to facilitate tolerance on-site and to reduce the residual stresses that result from lack-of-fit.

A moment connection is analysed making the assumption that the connection fits perfectly and each plate acts rigid. However, the real behaviour of the "moment" connection is going to differ for many reasons including the slip that occurs from having oversized bolt holes.

To create a moment connection, the most important aspect is to ensure that you can transfer the flexural stresses in the flanges of your sections from one element to the next.

Without knowing too much about the connection under consideration, I'll list some references that I have always found useful.

Hogan & Thomas, 'Design of Structural Connections', 4th ed. (i.e. The Green Book which I believe will soon be updated).

Syam et. al. 'Steel Designers Handbook'

Trahair & Bradford, 'The Behaviour and Design of Steel Structures to AS4100'.

 

[hokie66]

It sounds as if this is a base plate connection. The hole size should not affect the ability to transmit moment, but rather the ability to resist sliding or shear. If this is the case, you could site weld plate washers with smaller holes after the column is set.

I don't know what you mean by using two plates instead of one, but the bending capacity of two 20 mm plates does not nearly match that of a 35 mm plate.

 

[apsix]

'The Green Book which I believe will soon be updated.'

The pinned connections section has now been published; refer

http://www.steel.org.au/_uploads/476_Connections_series_summary.pdf

The moment connections section is due for publication later this year.

NB the quoted references are for design to AS4100, although Trahair et al has broader application. 35mm plate is not a standard Australian size AFAIK.

 

[KCRatnayake]

Thanks.

hokie66,
I just wanted to know if there anyway we can use small multiple plates (one on top of the other) in place of a larger plate.

Clefcon

 

[hokie66]

Well, as I said, the strength in bending of two-20mm plates is smaller than one-35mm plate. Elastic section modulus is proportional to square of thickness, so the single 35 mm plate has about 1.5 x strength of the two thinner plates. For deflection, the difference is even greater. I hope this answers your question, but it is so fundamental I may have misunderstood your problem.