Shake, Rattle, and Roll!

Subjecting a test building to seismic forces

DCI partnered with the University of California in San Diego to sponsor a series of shake table tests conducted on a six-story building made of cold formed steel (CFS). UCSD’s Jacob School of Engineering designed and developed the building, which was the tallest of its kind to be performed on the school’s outdoor shake table last summer. The tests demonstrated how this type of building would perform during multiple low level and design level seismic events typically experienced in California. DCI Engineers inspected the building for damage and calculated the longitudinal and transverse loading for the roof and floors. According to DCI Principal Harry Jones, the damage to the building was minor and was much less than what would be predicted by the current California Building Code (CBC).

Harry determined the building’s high performance was related to two key factors:

1. The balloon framing for the walls provided a more direct load path for the building shear to transfer loads down to the ground (shake table).

2. The compression post and rod tie-down systems provided a high degree of seismic resilience, which is not adequately incorporated in the determination of the R-factor of 6.5. This is particularly true because the compression post and rods were designed for omega level forces (ASCE 7-10 for an R=6.5). While this force amplification was a somewhat arbitrary code requirement and not based on explicit research, it does seem to reduce the level of damage you might see at the ends of the shear walls in a typical building.

UCSD’s building contained a lateral system consisting of Sure-Board Series 200S diaphragms spanning between Sure-Board Series 200 shear walls. A standard Zone 4 tie-down system was installed at the end of each shear wall along with standard CFS compression studs.

On behalf of Sure-Board, Harry submitted his assessment for the UCSD six-story CFS shake table tests to the City of San Jose. His structural testimonial informs San Jose’s Department of Planning, Building, and Code Enforcement about the seismically sound design of CFS buildings with Sure-Board shear walls and the feasibility of building them as tall as eight stories.

About the author

Harry Jones

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