End PLate Moment Connection (with Large Moment) for SDC D SMF 1

[FRACH23]

I was designing an end plate moment connection for a SMF Building at SDC D, and having trouble with very large demand moment (3,000 kN-m) due to overstrength. My girder is 800mm deep. I

1. I checked DG and it seems the most i could do was 8 tension bolt connection (2 hor x 4vert each flange, 16 total bolts at joint). Since my column was fairly large and is a built-up section, i was thinking of making more tension bolts, say 16 tension bolts (4 hor x 4 vert each flange, 32 total bolts at joint), but was worried i may have deviated any AISC seismic design rule.

2. I could make a haunch under the girder, but also worried i may deviate the "protect zone rule"

3. My other option into make Bolted Flange Plate (BFP). But at a given overstrength connection force, i may need to provide 4 columns of bolts. Could i do this without deviating any AISC rule (typical detail i see shows only two bolt columns (1 each side of flange)

4. How do we establish the particular location of protect zone for a SMF frame?

Any guidance would be highly appreciated.

 

[sandman21]

If you are trying to following AISC for the design and detailing of a SMF. You need to read AISC 358, connection forces are not based on overstrength but on the capacity of the member.

 

[FRACH23]

Thanks sandman21. Yes i was starting to study AISC 358 as well as 341. But i only came up with the protect zone length to width ratio 7 limit, highly ductile columns and girders. I might miss all other rules as i was new with this procedure.

I tried to follow through some example on seismic design guide for SMF and saw column design taken with redundancy factor Axial and Moments, but only verified with Overstrength at Axial force (no moment). In my understanding, joints, say my concerned end plate moment connection, must be designed with all forces taken at seismic overstrength factors to consider connection ductility.

I hope somebody could enlighten me at this point.

 

[sandman21]

I am not sure I understand your question. This link is for the design of a RBS SMF, the requirements protected zones, column and beam strengths, etc are about the same Stteltips - RBS Design The force in the connection will be the probable maximum moment Mpr + Vh*Sh. This is then converted into axial loads on into the plates. The Mpr is defined in section 2.4.3, which has a number of factors that account for overstrength in the connection. These overstrengths are different then system overstrength in ASCE7-10. Hopefully that helps you along, SMF are very important

 

[FRACH23]

Thanks sandman. I was reading through with AISC 358-10, and i gave up with using end plate moment connection as it could not satisfy the demand moment in need. I resorted with Bolted Flange Plate (BFP) moment connection.

As i read through Chapter 7, some notes troubled me:

A. Please share some thoughts about the wisdom in the idea of beam limitation at Section 7.3.1 (4) "Beam flange thickness is limited to a maximum of 1 in. (25 mm)". I used Japanese built-up girder BH800x300x16x32 as i need higher stiffness against drift. I could not go to deeper beam as i have SMF frame span to depth ratio limit also. I wish to understand the logic, and if could be possibly waived.

B. As with another item Section 7.3.1 (3, beam weight is limited to maximum of 224kg/m. My section 261 kg/m. How strict is this rule?

C. There was prequalification exception saying "Bolted flange plate connections in SMF systems with concrete structural slabs are only prequalified if the concrete structural slab is kept at least 1 in. (25 mm)
from both sides of both column flanges." The building was SMF Steel frame with 200mm thick slab on metal deck, sitting just above the top flanges with stud provision. I could not comprehend the English construction. Please help me interpret.

 

[FRACH23]

D. Do I really need to course trough probable moments and shears? As previously mentioned, I only arrived at large sections due to drift requirement (my base plates are pinned), so my stress ratios are only around 50% or less. We suggested to Contractor to use SS400 material, other than SM490 just to save a bit to the least, since issue is serviceability. Mpr and Vpr are both size and span-related. Thus, coursing through this requirement gets me in trouble. Could i forget about this as long as i satisfied the actual magnified joint forces (with seismic redundancy factor for member design and overstrength factor for joint design)?

 

[sandman21]

(A/B) All connections in AISC 358 are prequalified. The limitations given for each connection are the parameters used in testing of the connections. No wavier you could talk with the authority having jurisdiction and setup a connection review committee and then have your connection tested. This option is neither quick or inexpensive.

(C) I dont have time to draw a detail. But, picture a plan view of the column, from each face would be a 1" gap which would have no concrete.

(D) No, drift requirements assume that the building is going beyond elastic. This comes from forming plastic hinges in the beams. The checks given in AISC 358 are to ensure that the column or connection do not fail prior to the develop of Mpr and Vpr. If you are relaying on the extra energy dissipation from a SMF you need to ensure that you can properly develop all the forces.

 

[FRACH23]

Thanks lot sandman21, its really a big help for my understanding. It seems im busted if something happens with the project. We did not follow the prequalification requirement and it was now under construction. I explained to my boss and he said that such prequalification is too strict and we forget about this (by the way we are structural engineers on the contractor's side). The project is in Indonesia, the PE endorsed it, which seems not also well versed about the proper requirements.

 

[sandman21]

I have not worked in Indonesia but if you are relaying on the improved performance of a SMF system you should be complying with the pre-qualified connections or providing testing justifying the connections.