What is the source of the 0.4SDS max. diaphragm shear found in ASCE7?
What is the source of the 0.4SDS max. diaphragm shear found in ASCE7?
(OP)
In ASCE 7 there is a seismic design section for diaphragms. (12.10.1.1 in ASCE 7-05)
There it specifies a formula to determine the lateral seismic force to be used in diaphragm designs.
It also includes an upper limit on the shear (0.4SDS x I x wpx) and a lower limit (0.2SDS x I x wpx)
Does anyone know where the 0.4SDS value comes from or how it was developed - or what the philosophy is behind it?
The lateral force resisting system is designed based upon other derivations earlier in Chapter 12 and these don't apply to diaphragms.
However, it seems weird that you would design your vertical brace system and collectors, but then have cases where the diaphragm itself is designed for a lower (0.4SDS) load.
Thanks
There it specifies a formula to determine the lateral seismic force to be used in diaphragm designs.
It also includes an upper limit on the shear (0.4SDS x I x wpx) and a lower limit (0.2SDS x I x wpx)
Does anyone know where the 0.4SDS value comes from or how it was developed - or what the philosophy is behind it?
The lateral force resisting system is designed based upon other derivations earlier in Chapter 12 and these don't apply to diaphragms.
However, it seems weird that you would design your vertical brace system and collectors, but then have cases where the diaphragm itself is designed for a lower (0.4SDS) load.
Thanks





RE: What is the source of the 0.4SDS max. diaphragm shear found in ASCE7?
I have never had a diaphragm design force lower than a vertical distribution force for SFRS design. Cs is Sds/(R/I), or some other variation, which should always be smaller than the 0.2 Sds or 0.4Sds.
The diaphragm is not supposed to behave plastically - if it were to create a plastic hinge a rigid diaphragm would lose the ability to act rotationally. That is why the diaphragm is designed for a high load. I think it also has to do with the notion that a diaphragm will see a higher load the ELF provides, due to the whipping action of the structure, but I am not 100% on that idea.
RE: What is the source of the 0.4SDS max. diaphragm shear found in ASCE7?
RE: What is the source of the 0.4SDS max. diaphragm shear found in ASCE7?
I can dig through my dynamics stuff to see if I can find a more solid explination / reference.
RE: What is the source of the 0.4SDS max. diaphragm shear found in ASCE7?
RE: What is the source of the 0.4SDS max. diaphragm shear found in ASCE7?
I saw that the typical spectral response curve always starts with 0.4SDS for T = 0 but this doesn't make sense for a diaphragm as they would have their own "period" higher than zero of course.