Seismic Retrofit

[BrianMCE]

Typically with new construction, a multi-story wood framed building would have holdowns that transfer from the roof to the foundation. With seismic retrofit, this is different since it is only necessary to retrofit the first floor. With this in mind, the existing shear walls on the stories above the first usually remains existing and only the collector element is strengthened on the first floor. My main question is, how would you evaluate and properly size the collector? With new construction, it is quite easy to place an uplift force that transfers floor to floor but older construction does not use holdowns. I want the collector on the first floor to be sized for the drag force while taking into account the overturning moment from the floors above. How do you usually design the collectors for overturning on the first floor for seismic retrofits?