Trying to figure out this section i

[JStructsteel]

Trying to figure out this section in the code. The first passage highlighted reads to me that existing framing can be checked with prior loads. The second makes it seem like the whole structure needs to be up to the current code.

I have some rafters damaged/blown off due to tornado. Its a old timber framed structure, main beams and trusses appear to be fine. I read this as everything needs to be updated to current code, other than the yellow highlighted passage saying no. Seem to contradict in the same paragraph.

How are you folks reading this?

3405.3 Substantial structural damage to gravity load-carry-ing
components. Gravity load-carrying components that
have sustained substantial structural damage shall be reha-bilitated
to comply with the applicable provisions of this code
for dead and live loads. Snow loads shall be considered if
substantial structural damage was caused by or related to
snow load effects.[highlight #FCE94F] Existing gravity load-carrying structural
elements shall be permitted to be designed for live loads
approved prior to the damage.[/highlight] Existing gravity load-carrying
structural elements that were damaged due to snow loading
shall be rehabilitated to comply with snow load requirements
of this code for new buildings. [highlight #F57900]Non-damaged gravity load-carrying
components that receive dead, live or snow loads
from rehabilitated components shall also be rehabilitated or
shown to have the capacity to carry the design loads of the
rehabilitation design.[/highlight] New structural members and connec-tions
required by this rehabilitation design shall comply with
the detailing provisions of this code for new buildings of sim-ilar
structure, purpose and location.

 

[jayrod12]

The orange highlighted text appears to read very clear, your load path from the rehabilitated member down to the ground needs to be good for new code-level loading, the rehabilitation level loads and if that results in further reinforcing required, then so be it.

edit: However, coupling that with the yellow highlighted portion, it reads to me that they can be designed for the loads at the time of original design. Therefore my opinion is, you must restore the original structural integrity of the building prior to the damage. But not necessarily obligated to upgrade it.

 

[rb1957]

I think you're good to work with the original loads, rather than current code.

The point to the repair is to restore the structural strength to what it was before the storm (or better).

You can see the problem if you removed three rafters but put back 2 (even 2 with 50% more capacity).
So the idea is to restore the structure to what it was before, so the loadpaths are the same.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[phamENG]

The orange seems to be an extension of the snow load language. So if you have to replace rafters because they were damaged by snow loading, the new rafters have to be designed for the new snow loads, and the ridge beam, headers, and everything else in the load path also have to be upgraded for the new snow load.

But if the rafters are allowed to use the old loads, the rest of the load path can also be checked with old loads.

 

[JStructsteel]

phamENG, I think you are right.