Linked Column Frame with 5 shear links

The linked column frame (LCF) is a new lateral braced-free structural steel system intended for rapid return to occupancy performance level. LCF is more resilient under a design level earthquake than the conventional approaches. The structural system consists of moment frames for gravity and closely spaced dual columns (LC) interconnected with bolted links for the lateral system. With increasing emphasis on performance based design, the link’s replaceability becomes a desired quality. The LC links are sacrificial and intended to be replaced following a design level earthquake. Practical connection details for the link components are used in an effort to provide elastic connections that shift plastic strains away from critical welds, thereby avoiding some of the failures observed in past tests on similarly detailed link-to-column eccentrically braced frames. The centerpiece of this work is a unique full scale experiment using hybrid testing; a combination of physical test of a critical substructure tied to a numerical model of the building. This presentation outlines the experimental setup, testing and validation of the LCF steel frame system. Hybrid testing allows for full scale study at the system level accounting for the uncertainties via experimental component and having the ability to model more conventional behavior through numerical simulation. The experimental substructure consists of a two story LCF frame with a single bay while the remainder of the building is numerically modeled. Two actuators per story are connected to the specimen. All steel is 345 MPa nominal yield stress and the resulting LCF specimen design is summarized as follows: gravity and linked columns (W14x132), gravity beams (W16x57), and links (W10x45). The LC links have been considered to be short and plastically shear dominated and the LCF design met the design intent of 2.5% inter-story drift limits. For evaluating the LCF response, hybrid testing is performed for ground motion at three different intensities; 50%, 10% and 2% probability of exceedence in 50 years for Seattle, Washington ground motions. The system overall had exhibited three distinct performance levels; linearly elastic, rapid return to occupancy where only the replaceable links would yield, and collapse prevention where the gravity beam components also become damaged. Experimental results indicate a viable system under seismic loading, offering a new ductile structural system with the ability to rapidly return to occupancy.