Conventional structural steel frame systems have been primarily developed to effectively resist gravity loads. In areas of moderate to high seismicity, these structural systems have been made to effectively resist earthquake induced motion through specific and often complex detailing requirements. The basic seismic design philosophy has been to engage sufficient plasticity in the gravity system in order to prevent loss of life. However, the expectations of building owners and society are, in general, no longer satisfied with merely providing life safety, and new structural systems are needed to target specific seismic performance levels. One of these targets needs to include rapid return to occupancy, especially for hazard levels that are less than the maximum expected. The overall vision of this project is to develop a lateral load resisting system for unbraced steel frames capable of achieving specific target performance levels. The system, referred to as “Linked Column Frame” (LCF), includes the use of dual columns interconnected by specially designed links coupled with ordinary moment resisting frames that together provide ductile response with recoverable deformations through replacement of the non-gravity load carrying link components.

The performance objectives of the LCF system is to achieve multiple design objectives as set by the engineer during design and include:

1. •Elastic behavior – Under wind and service loads, the entire structure remains elastic. The primary stiffness is provided by the linked column assembly.
   

1. •Extreme event rapid return to occupancy – Under extreme lateral loads, the links plastically deform while the rest of the structure remains elastic. The structure can be immediately occupied following the event as the gravity system remains undamaged.
   

1. •Collapse prevention – During events exceeding the design base earthquake and rapid return to occupancy performance level, moment hinges could form in the gravity system.