bolted tension connections. limit state: yield or ultimate?? yield: 36 ksi (strain = 0.0013)

Bolted Tension Connections

Limit State: Yield or Ultimate??

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.40

10

20

30

40

50

60Stress-Strain for A36 Steel in Tension

Strain (in/in)

Stre

ss (k

si)

Ultimate: 58 ksi (strain = 0.32)

Yield: 36 ksi (strain = 0.0013)

Limit State: Yield or Ultimate??

0 0.1 0.2 0.3 0.40

102030405060

Strain (in/in)

Stre

ss (k

si)

12’

24’

Limit State: Yield or Ultimate??

0 0.1 0.2 0.3 0.40

102030405060

Strain (in/in)

Stre

ss (k

si)

12’

24’

P

322” long brace

mmmm….. Maybe we should not let it yield

0 0.1 0.2 0.3 0.40

102030405060

Strain (in/in)

Stre

ss (k

si)

12’

24’

P

322” long brace

mmmm….. Maybe we should not let it yield

0 0.1 0.2 0.3 0.40

102030405060

Strain (in/in)

Stre

ss (k

si)

12’

24’

P

322” long brace

If we limit the stress to less than yield, then….

0 0.1 0.2 0.3 0.40

102030405060

Strain (in/in)

Stre

ss (k

si)

12’

24’

P

322” long brace

If we limit the stress to less than yield, then….

0 0.1 0.2 0.3 0.40

102030405060

Strain (in/in)

Stre

ss (k

si)

12’

24’

P

322.4” long brace

The brace would not extend more than 0.4” (do the math: eL = 0.4”)

If we limit the stress to less than yield, then….

0 0.1 0.2 0.3 0.40

102030405060

Strain (in/in)

Stre

ss (k

si)

12’

24’

P

322.4” long brace

The brace would not extend more than 0.4” (do the math: eL = 0.4”)And the column would be leaning by no more Than 0.45” (do the math: Pythagoran

Then again…. Yield is no where near the maximum the steel can take.

0 0.1 0.2 0.3 0.40

102030405060

Strain (in/in)

Stre

ss (k

si)

12’

24’

P

322” long brace

Then again…. Yield is nowhere near the maximum stress the steel can take.

0 0.1 0.2 0.3 0.40

102030405060

Strain (in/in)

Stre

ss (k

si)

12’

24’

P

322” long brace

I mean…. Even if it yields at 36 ksi, it doesn’t break, right?

0 0.1 0.2 0.3 0.40

102030405060

Strain (in/in)

Stre

ss (k

si)

12’

24’

P

322” long brace

I mean…. Even if it yields at 36 ksi, it doesn’t break, right?

0 0.1 0.2 0.3 0.40

102030405060

Strain (in/in)

Stre

ss (k

si)

12’

24’

P

322” long brace

It seems like yielding is no big deal

0 0.1 0.2 0.3 0.40

102030405060

Strain (in/in)

Stre

ss (k

si)

12’

24’

P

322” long brace

It doesn’t break at 36 ksi (yield)Why not just say that 58 ksi (ultimate) is the limit??

0 0.1 0.2 0.3 0.40

102030405060

Strain (in/in)

Stre

ss (k

si)

12’

24’

P

322” long brace

It doesn’t break at 36 ksi (yield)Why not just say that 58 ksi (ultimate) is the limit??

0 0.1 0.2 0.3 0.40

102030405060

Strain (in/in)

Stre

ss (k

si)

12’

24’

P

322” long brace

If we limit the stress on the brace to Anything Less than Ultimate (58 ksi), then…

0 0.1 0.2 0.3 0.40

102030405060

Strain (in/in)

Stre

ss (k

si)

12’

24’

P

322” long brace

If we limit the stress on the brace to Anything Less than Ultimate (58 ksi), then…

0 0.1 0.2 0.3 0.40

102030405060

Strain (in/in)

Stre

ss (k

si)

12’

24’

P

425” long brace

The brace would not extend more than 103” (do the math: eL = 103”)

132”

If we limit the stress on the brace to Anything Less than Ultimate (58 ksi), then…

0 0.1 0.2 0.3 0.40

102030405060

Strain (in/in)

Stre

ss (k

si)

12’

24’

P

425” long brace

The brace would not extend more than 103” (do the math: eL = 103”)And the column would be leaning by about 132”(do the math: its fun, complicated)

132”

Now, we’re in the world of 2nd order effects (the Statics are changed because of the huge change in

geometry

0 0.1 0.2 0.3 0.40

102030405060

Strain (in/in)

Stre

ss (k

si)

12’

24’

P

425” long brace

The brace would not extend more than 103” (do the math: eL = 103”)And the column would be leaning by about 132”(do the math: its fun, complicated)

132”

Gravity loads will make it collapse

0 0.1 0.2 0.3 0.40

102030405060

Strain (in/in)

Stre

ss (k

si)

12’

24’

P

425” long brace

The brace would not extend more than 103” (do the math: eL = 103”)And the column would be leaning by about 132”(do the math: its fun, complicated)

132”

So….We DO NOT WANT THE MEMBER TO YIELD

YIELD IS THE LIMIT FOR THE MEMBER

But…The connection is different

Around holes, a little bit of yielding is fine (holes are tiny).