diaphrgam analysis 1

Before you go any further, you need to determine whether your diaphragm is rigid or flexible. That will determine how your diaphragm loads are distributed to the structure. Once you know how the diaphragm loads are applied, you can check the diaphragm capacity, drag struts, connections, openings, etc

it is single story light gauge metal.
I assumed rigid.

I don't understand your reactions.

A diaphragm is a beam. The reactions occur at the shear walls. As MotorCity mentioned, if the diaphragm is flexible, you should treat the diaphragm as two, separate, single span beams. If it is rigid, it is one two span beam.

DaveAtkins

Actually, it will only act like a true two span beam if all three shear walls are of equal stiffness. If they are not, the stiffness of the shear walls relative to one another comes into play, affecting where the lateral loads go.

DaveAtkins

If its light metal roofing, then I'd tend to think it's behaviour would be more at the flexible end of the spectrum than fully rigid behaviour. With diaphragms it's a good idea to do some sensitivity on the stiffness. I don't think I'd ever assume rigid for a steel roof diaphragm.

is there a book or reference material someone can suggest?
i bought an ICC book by Terry Malone but it seems the material is too advanced. the problem are very complex

Perhaps have a look at these free standards/design guides:-

AISI free standards. Scroll down for AISI D310-17: AISI Design Guide - Design Examples for the Design of Profiled Steel Diaphragm Panels Based on AISI S310-16, 2017 Edition and AISI S310-16: North American Standard for the Design of Profiled Steel Diaphragm Panels, 2016 Edition. There is also a few other older versions available.

NEHRP technical briefs. There are a few design guides relating to diaphragm design related to concrete, which while not directly related to your situation they do cover the basics which also can extend to the philosophies involved in your problem. Specifically related to light gauge steel, refer to Design Guide 12 (Seismic Design of Cold-Formed Steel Lateral Load-Resisting Systems: A Guide for Practicing Engineers), this refers back to the AISI standards linked above for your situation.

Hopefully they are of use!

THANKS