Engineering FAQs

Q: Does the earthquake resisting column (ERC) have a code evaluation report?

A: We are currently performing final tests; we expect to have an evaluation report by July, 2018.

Q: How do I know if the ERC is right for me or my client?

A: ERCs offer the greatest benefit when any of the following applies:

  1. An R factor of 6.5 is needed. This is often the case if the code requires using the least value of R when combining systems in the horizontal direction, or when calculated forces throughout the system need to be reduced.
  2. Using a moment-resisting frame would require relocation of existing utilities
  3. Rapid replacement of earthquake-resisting elements for quick recovery and business continuity after an earthquake is desired.

Q: Are there any limitations for use of the ERC?

A: Currently ERCs are only rated to resist lateral loads. Further testing will determine safe vertical loads that can be supported in combination with lateral loads. For further information see "Earthquake Resisting Columns: Information for the Design Professional".

Q: What materials are used?

A: The Structural Fuses are laser-cut from ASTM A572 Grade 50 steel to give very predictable ductile performance.

Q: What seismic performance parameters apply to the system?

A: Testing and evaluation shows that the following seismic design parameters may be used:  R=6.5, Cd=4, and Ω0=3 (the same as used for WSP shear walls).

Q: What about column lateral torsional buckling?

A: Lateral torsional buckling (LTB) is not an issue with typical column heights used in existing buildings. The column is already sized for deflection rather than strength, and the allowable bending strength based on AISC equations for LTB is far greater than the actual yield stress. Even using twice the height of the column to calculate allowable LTB bending stress (as required in some jurisdictions) does not result in reduced allowable column strength for standard-height ERCs.

Q: Are custom sizes available?

A: To keep costs down, a limited selection of fuse capacities and ERCs will be available initially. However, the final code evaluation report should allow using the fuses on any size of wide-flange column that is needed to meet height requirements for the project. Completely custom structural fuses may also be available in the future based on expanded code evaluation reports.

Q: What are the advantages of the ERC?

A: The ERC has three distinct advantages over steel frame systems:

  1. Easily-replaceable elements—the structural fuses can be replaced upon removal of just three bolts; other systems with replaceable elements and similar capacity require removing 40 or more bolts in order to replace their yielding elements.
  2. Economy of installation—the ERC's inventor has extensive experience designing earthquake retrofits in San Francisco, where there is rarely room to install steel frames without first having to relocate electrical panels, gas meters, or other utilities. A single column has much greater flexibility for installation without the need for expensive preparation.
  3. Reduced construction time—ERCs are shipped fully assembled, with all necessary fasteners and connectors. Steel transition plates supplied with the ERC fasten to wood framing with structural screws, and adjust for commonly found joist spacing. No welding is required (and no special inspection).

Q: How much drift can the ERC system handle before failure?

A: Testing could not be completed because the laboratory equipment could not produce the range of movement needed to produce failure in the structural fuses. The hysteresis plot below show test behavior of a representative specimen that withstood multiple cycles at drift levels up to 10% of story height.

Cyclic lateral load-drift hysteresis

Q: What sort of footing does the ERC need?

A: The engineer of record is responsible for foundation design. The most common foundation is a reinforced concrete grade beam. For small ERCs the grade beam can be as small as 18" deep by 16" wide; for larger ERCs (ASD capacity of 12k) a footing 36 inches deep by 30 inches wide is practical. Footing length varies as needed to accommodate overturning forces and provide adequate soil bearing capacity.

Q: How many ERCs do I need to brace my soft story building?

A: The system was developed so that a single ERC could brace the front half of a four-story wood-framed apartment building typical of San Francisco. Building size or geometry may require using more than one ERC.

Q: What parts are included in an ERC kit?

A: You may download and print A detailed parts list and instructions can be downloaded Installation instructions for Earthquake Resisting Columns that includes a parts list and detailed illustrations.