Reinforcing In-place Structural Steel

[RobPSUAE]

I have a debate going on right now, and I am looking for help in clarification on the methods of analysis and implementation of reinforcing structural members.

First: When using a flat plate to reinforce a beam for deflection, the beam doesn't care whether it is A36 or Gr. 50, as the increased Ix and Sx are acheived either way and deflection is aided by the reinforcing. BUT, if I am looking to reinforce for stress, and I have a Gr 50 beam, wanting to use a A36 Plate, shouldn't I increase the area of the plate by the ratio of Fy50/Fy36? The total area of the plate would effectively be capable of handling the same amount of force that a Gr. 50 plate of smaller dimention could transmit. The weld can be designed based on shear flow between the two members as normal.

Second: If I wanted to use an A36 channel, angle, or WT, what would be the proper way to run the analysis on the member. Since two types of material are being used, it appears that the A36 would limit the design, as it is now the extreme fiber under stress. (assuming non-composite beam being reinforced)

Any help would be appreciated. There's an article out there by John Ruddy "Reinforcing In-place Structural Elements" given in 1987 at the National Engineering Conference, but I can't seem to find a copy of this.

(warning, results of these answers will lead into reinforcing composite beams too,.... )

Thanks
Rob

 

[RobPSUAE]

Just received the Paper by John Ruddy from AISC, I'll post my findings, please provide me with your thoughts in the meantime.

 

[UcfSE]

If you mix yield strengths in your section you have two options: design the whole section as having the lower yield strength, or find the design strength taking into account the non-linearity after the weaker steel yields.

Increasing the area of the plate would help with the capacity of the plate, but only because it increases both your section modulus and moment of inertia. I would not try any sort of scaling based on yield strength, but rather I would use one of the two approacheds mentioned above. You have to take into account that as soon as you hit 36 ksi, your plate extreme fiber yields and can not take any additional stress. This yielding will continue alomg the section depth as more load is added until you reach the junction of the two materials. You might then have a strain compatibility problem where one fiber is yielding and straining much more than the next fiber, depending on exactly what the stress state is.