Case Study Santa Clara Semiconductor Manufacturer
Seismic Strengthening Of Semiconductor Test Facility

The Challenge
Marvel Corp., a major manufacturer of semicon­ductors, needed to build test facilities at their North American Headquarters in Santa Clara. A large existing structure was being gutted and turned into a test laboratory.
In order to bring the building up to the demand­ing seismic specifications that were critical for the functioning of the sensitive equipment, the existing columns needed to be braced against any uplift motion. The design called for each column base to resist an uplift force of 440 kips.

Action:
RWR Construction provided a design-build pro­posal to install helical pier tiedowns around all columns, consisting of (6) piers each with a 73.3 kip design rating and a 110 kip test (150%) rating per pier. 3.5” galvanized tubular helicals were installed to a depth of 56 ft. The helicals were driven through and below a 7 ft. thick dense sand lens located at an invert elevation of 28 ft. The sections in and below the sand lens were then pres­sure grouted. This locked the helicals into and up against the bottom of the sand lens, which increased the uplift resistance to the required specifications. The piers were then cut off at the proper elevation, anchor plates and nuts were installed and the pier caps were cast into the new foot­ings surrounding the column bases.

Results:
All helicals were tested to 150% of design load and passed. The test facility is now able to keep functioning through any minor seismic event, and is structurally protected from major events.

Captions:
Installing helicals around perimeter column base
Starter sections with helix flights visible
Existing column and base surrounded by installed helical pier group
Pressure grouting operations for test pile
Detail of end section of typical helical pile showing sand lens, helix flight configurations and grout ports.
Performing helical test pile installation in parking lot adjacent to testing facility.

RWR Construction Inc. 200 Gary Place, San Rafael, CA 94901 (415) 457-5658 www.RWR-inc.com

Case Study: Beresford Arms Hotel Earthquake retrofit

The Challenge
This hotel was built on unstable fill and sands and was in danger of collapse in the event of a severe earthquake. A structural analysis showed that the inner core of the building needed to be reinforced with shear walls and underpinned with cast-in-place reinforced concrete piers.

Action:
The inner courtyard was inaccessible except for an 8 ft. tall x 5 ft. wide opening. The height of the build­ing prevented the use of cranes to place equipment or material into the courtyard. Furthermore, since the soils were noncohesive, all piers had to be cased for the top 25 ft.
A small track rig was used that fit through the narrow opening. Groups of 4 piers 40 ft. deep were placed in each of the 4 corners. 18” diameter contin­uous flight augers and steel casing were used for the pier drilling.
The cages were winched through the opening in sections and then assembled to full length with rebar couplers. They were then raised over the piers and lowered in using temporary tube steel pole and winch systems bolted to the sides of the building. The piers were then poured as the casing was re­tracted.

Results:
This initial phase of a multi-phase retrofit program helped bring the Beresford Arms Hotel up to current earthquake standards.

Captions:
Multi-story Hotel, San Francisco
Detail showing rebar couplings
Starting a new pier hole before inserting casing
Overhead shot of pier drilling in corner of courtyard
Raising a reinforcing cage consisting of #8 rebar and spiral ties
Overview of construction site showing continuous flight augers and one set of completed piers at upper left corner.
Placing a reinforcing cage into a pier hole in the corner
Lowering a cage down into a pier hole with the temporary winch system
Picture showing temporary winch systems bolted to building and suspended cage at right side. Access opening visible at center bottom.

RWR Construction Inc. 200 Gary Place, San Rafael, CA 94901 (415) 457-5658 www.RWR-inc.com