NDS Load Duration for Rain
NDS Load Duration for Rain
(OP)
Could someone direct me to the NDS Load Duration Factor for RAIN? I am analyzing an old building with a flat roof for a client and I must provide, verify and/or justify all data. I need the information for the evaluation the roof structure for the Rain Load and a stability analysis for ponding.
Thanks in advance;
JD
Thanks in advance;
JD





RE: NDS Load Duration for Rain
RE: NDS Load Duration for Rain
I would think that the duration of the ponding load is more pertinent than the 'label' of Live Load. A load duration of 24 hours permits a CD of 1.33. A duration of 7 days permits a CD of 1.25.
The 2005 NDS, Appendix B, does not explicitly assign a CD of 1.15 for Live Load (though it does for Snow Load - 2 month duration).
A freely draining roof might then be evaluated by an estimation of the depth of water at any point in time (based on the intensity of the rainfall) over the duration of a rainstorm.
JMHO.
Ralph
Structures Consulting
Northeast USA
RE: NDS Load Duration for Rain
YES I do agree with RHTPE that some consideration needs to be taken for your individual environmental conditions and building configurations which may modify these values. Some good information in the NDS commentary about this.
RE: NDS Load Duration for Rain
Sure you could argue for 1.25 or 1.33 or even 1.6 BUT WHY??
Most building officials will accept 1.15 for just about any load situation - because they have seen that for like 50 years or so. Anything else will catch their attention and then you got some 'splaining to do - Lucy
RE: NDS Load Duration for Rain
I would be hard pressed to see a owner that would allow the rain to pond for a cumulative of seven days over the life of a structure. But it is possible so I would use the 1.15 factor if it works to be safe, unless the Building Department had a writen policy of a 1.25 factor to be used.
Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.
RE: NDS Load Duration for Rain
For example, I could think the ponding load duration risk could be considered different in Portland, OR when compared to Tuscan AZ. Thankfully I work in a completely normal region where every thing is just right.