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Appendix D 3
- Thread starter FeSE
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"Does anyone really use Appendix D on real structures? Or has everyone, like me, just developed simplified 'work arounds' that we know are conservative, but we use to get the work done without wasting too much time? "
That's exactly what I'm typing about. Rather than being hurt my App. D, you came up with a better way. It's probably a small step to develop something like this into a formal simplified procedure and publish it for all to use. Then the problem seems to vanish.
That's exactly what I'm typing about. Rather than being hurt my App. D, you came up with a better way. It's probably a small step to develop something like this into a formal simplified procedure and publish it for all to use. Then the problem seems to vanish.
I'm currently writing a spreadsheet for use based on appendix D and so far it doesn't look too bad. Certainly not requiring a PhD. But some limitations I've put on it will be necessary (i.e. only cast-in anchors, only tensile plus ONE lateral load - i.e. no x and y forces laterally -just one direction)...that kind of thing.
I think a lot of Appendix D reaction is based more on [red]Who moved my cheese"[/red] than anything else. There has always been, and will always be, resistance by engineers to changing design methods as it threatens our self-knowledge and security when we suddently [red]can't[/red] design per code because of a newly percieved code provision. After you get into it a bit the fear and loathing go away rather quickly.
But I do remember my old mentors designing concrete based on a 1950's era method...in 1985.
I think a lot of Appendix D reaction is based more on [red]Who moved my cheese"[/red] than anything else. There has always been, and will always be, resistance by engineers to changing design methods as it threatens our self-knowledge and security when we suddently [red]can't[/red] design per code because of a newly percieved code provision. After you get into it a bit the fear and loathing go away rather quickly.
But I do remember my old mentors designing concrete based on a 1950's era method...in 1985.
Overall Appendix D is an improvement. One can now actually understand what failure mode is controlling there design. With this knowledge and engineer can more accurately evaluate the risk, the approach taken, alternative designs, etc.
My gripe is with the symbols. Its like the committee members got in an argument. Some wanted lower case. Some wanted capitols, and some wanted greek. So they compromised and used all three for each symbol. Its hard to tell when reading it when one symbol begins and one ends.
That said I was able in about a day to write a really good excel sheet for a joist embed connection to the top of a concrete tilt-up panel or concrete wall tie beam in about a day.
Cavemen could have come up with better symbols than these guys. They could have used the symbols above the numbers on the keyboard. They could have used F1, F2, F3, F4, etc... Anything would be better than what they've done.
On codes and specs. I we should lobbie congress for a special law to jail specification writers who want to put out a new code or spec every two years. Everytime I just about get a good feel for a new code they decide to change. Now good ole steel is $!@#^$# me.
See how convenient those symbols above the numbers on the keyboard are!
My gripe is with the symbols. Its like the committee members got in an argument. Some wanted lower case. Some wanted capitols, and some wanted greek. So they compromised and used all three for each symbol. Its hard to tell when reading it when one symbol begins and one ends.
That said I was able in about a day to write a really good excel sheet for a joist embed connection to the top of a concrete tilt-up panel or concrete wall tie beam in about a day.
Cavemen could have come up with better symbols than these guys. They could have used the symbols above the numbers on the keyboard. They could have used F1, F2, F3, F4, etc... Anything would be better than what they've done.
On codes and specs. I we should lobbie congress for a special law to jail specification writers who want to put out a new code or spec every two years. Everytime I just about get a good feel for a new code they decide to change. Now good ole steel is $!@#^$# me.
See how convenient those symbols above the numbers on the keyboard are!
- Thread starter
- #44
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1
- #45
bretrooks
Structural
- Mar 25, 2008
- 1
Sorry to resurrect an old thread, but I was hoping I could shed a little light on why (at least) engineers in high-seismic areas are unhappy regarding ACI 318-05 Appendix D.
The biggest reason has to do with The D.3.3 section. D.3.3.3 takes 25% of your strength away off the top in medium- and high-seismic areas. D.3.3.4 and D.3.3.5 then require that a ductile steel yielding failure must govern. The CA Building Code has modified this to state that where steel yielding doesn't govern, you have to multiply your applied forces by 2.5.
This means that the anchorage condition which will often govern is a (low) concrete breakout value, reduced by 25% and then forced to cope with 2.5x the design forces. (I haven't personally dug into the concrete breakout calculations too deeply for situations other than sill anchor bolts, but my impression is that they are broken for some cases.)
For example, this means that a 5/8" anchor bolt with a 1.75" edge distance, which was worth ~1500 lb. under ASD in the previous CBC, now ends up being worth the equivalent of 285 lb. Yes, 285 pounds...that's not a typo. And 562 lb. for a 2.75" edge distance. The wood isn't even close to governing.
As you can see, it's not just that Appendix D is a hassle--hassles can be dealt with. But I think anyone looking at the massive drop in allowable values would admit that something needs fixing, at least for certain situations. Changing the ductility requirements and reviewing the shear-parallel-to-an-edge breakout values would be a good start.
Hope this helps...
Bret
The biggest reason has to do with The D.3.3 section. D.3.3.3 takes 25% of your strength away off the top in medium- and high-seismic areas. D.3.3.4 and D.3.3.5 then require that a ductile steel yielding failure must govern. The CA Building Code has modified this to state that where steel yielding doesn't govern, you have to multiply your applied forces by 2.5.
This means that the anchorage condition which will often govern is a (low) concrete breakout value, reduced by 25% and then forced to cope with 2.5x the design forces. (I haven't personally dug into the concrete breakout calculations too deeply for situations other than sill anchor bolts, but my impression is that they are broken for some cases.)
For example, this means that a 5/8" anchor bolt with a 1.75" edge distance, which was worth ~1500 lb. under ASD in the previous CBC, now ends up being worth the equivalent of 285 lb. Yes, 285 pounds...that's not a typo. And 562 lb. for a 2.75" edge distance. The wood isn't even close to governing.
As you can see, it's not just that Appendix D is a hassle--hassles can be dealt with. But I think anyone looking at the massive drop in allowable values would admit that something needs fixing, at least for certain situations. Changing the ductility requirements and reviewing the shear-parallel-to-an-edge breakout values would be a good start.
Hope this helps...
Bret
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