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# Plate yeild line theory

## Plate yeild line theory

(OP)
HI everyone,
I'm struggling to design cross braced frame connections. I would highly appreciate if someone could explain the design steps and how to determine the plate thickness using plate yield line theory.
The brace members are SHS square hollow section and the collector is 250PFC channel beam.

Each brace is subjected to 60kN tension force.

Connection:

Thank you

### RE: Plate yeild line theory

Has your professor provided any guidance whatsoever? What did he/she suggest?

Dan - Owner
http://www.Hi-TecDesigns.com

### RE: Plate yeild line theory

1. Yield line theory is fine for some things, but you don't need it here. You indicate a 15mm plate but you don't indicate a width. Make sure you allow room for the fillet weld.

2. An all round weld is not possible because the angle is too small.

3. The iron workers will not appreciate having a common plate for two braces above and below the beam. Makes them awkward to handle on site, more so if the braces are long. Better to use separate base plates. If you do use a common plate, put a bolt between the two braces. It reduces the moment.

4. Braces above and below the beam do not align. Much better to make them align, even if they don't intersect at the exact center of the beam.

5. Draw a section through the connection to demonstrate how the SHS and channel align. The flange of the channel is 90mm wide, which is almost identical to the SHS. If the 15mm plate is centered over the channel flange, the load will be eccentric to the channel, causing a bending moment in the flange and web. The web of a 250PFC is only 8mm thick. Why use a channel? A wide flange would be better. You may need to add some stiffeners. The stiffeners you have are not well placed.

6. For the design, resolve your 60 kN force into a vertical and horizontal component. Design the 15x? plate for the bending moment resulting from the vertical force. The horizontal force is resisted by shear in the bolts.

BA

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