Evaluate lateral load on portal frame

[RD2EN]

I have this 3 story residential house that contains a portal frame together with plywood and metal strap bracing at the ground floor. My question is how do I work the proportion of lateral load that will apply on the portal frame either by a simplified method or 3D computer model? Is it based on the tributary area or stiffness? I believe that it is stiffness dependent as the timber joists work as a diaphragm but I still have no idea how to work out the stiffness of the plywood or metal strap. The standards only gives you the lateral limit state capacity (eg. 3kN/m for metal strap bracing) that I have no idea how to convert to stiffness. Say the 1.8 meter long metal bracing capacity is 1.8 * 3 = 5.4 kN. How much is its stiffness?

In another word, as the drift of bracing is very small compared to portal frame, almost all of the lateral load will go to the bracing?

 

[Ron247]

it will probably be based on equal lateral drift. The portal frame will probably be less than the strap bracing although a Superman Portal Frame will take more than a Woody Allen x-brace.

Relative stiiffness