Project Description

Grade Beam for Braced Frame – San Francisco

1940s retrofit - expanse of the grade beam with 2 inch thick column bases

Integration of rebar with the existing column footings

Integration of stirrups at the proposed column base

Grade beam construction in progress

Integration of stirrups and epoxied dowels in existing footings i

Integration of stirrups and epoxied dowels in existing footings ii

Installation of one and half inch anchor bolts

Two inch base plate with anchor bolts and drag rebars

Two inch base plate with anchor bolts and drag rebars

Structural Strengthening Using Grade Beams and Braced Frames

When it comes to building the design specifications, we are tenacious…

The Challenge: A six-story apartment building in San Francisco required a substantial earthquake retrofit to enable it to withstand high stresses of seismic racking. It was a typical large building with soft story construction. The rigid steel frame and the foundation for the frame were quite substantial in proportion, so complex construction skills were necessary.

The placement of the reinforcing steel bars in the foundation required a thorough understanding of how and in what sequence they should be positioned. A highly skilled construction crew would be needed to implement the installation.

Our Solution: The soil composition for this site was dune sand, and the Geotechnical Engineer had specified implementing a soil stabilization program before building the grade beam. Before we began the excavation for the grade beam, we engaged a specialized company to inject grout into the sand in 12’ columns below the bottom of the footing. The pressure grouting took place under the observation of the Geotechnical Engineer of record as well as our own resident engineer. Subsequent to the injection operations, soil sampling was performed by an independent firm to assure the competency of the soil before the construction of the large grade beam for the steel frame.

We constructed a concrete grade beam that measured 35’x9’x5’ on the stabilized sand to support the steel frame, which rose from the basement floor to the second floor of the building.

Click here to see Construction of the Frame

To discuss your structural strengthening project, please contact grade beam and braced frame contractors SteelCore Builders at: 415-331-0525.