The Westside Media Center is one of the new flagship office buildings in the trendy West Los Angeles/Santa Monica area. In addition to the rehabilitation of an existing warehouse, this project consists of two new 4-story buildings that provide 300,000 square feet of office space and over 340,000 square feet of parking in 2 subterranean levels. At the ground level, an additional 100,000 square feet of landscaped area creates a campus-like feel that helps attract employees of the entertainment and software industries.

Concrete was selected for the framing system to create large uninterrupted interior spaces, commonly preferred by prospective tenants. The floor system was required to span 45 ft with no vertical supports between the core and the edges of the building. The shallow concrete floor system allowed greater than usual open office space, since the required floor-to-floor heights are 15 ft.

The floor framing consists of 7-in.-thick cast-in-place one-way slabs spanning between precast beams. Using modular formwork supported at the edges of the precast beams allowed the elimination of conventional full-height shores and reshores, thereby saving both time and money. The 16-in. by 30-in. precast, prestressed beams are supported by 20-in. by 30-in. precast, prestressed girders. Aesthetic demands of the project required all the beams and girders to have a dapped end, supported by rectangular corbels flush with the bottom of the framing members. Where only one beam frames into a column, pockets were provided in the column, which eliminated the need for corbels. Precast concrete columns 24 in. by 24 in. are utilized for the entire 85-ft height.

Two types of lateral-force-resisting systems are utilized in these structures. In the long direction, precast hybrid moment-resistant frames are provided. Cast-in-place concrete shear walls are used in the short direction. Precast columns at each end of the shear walls constitute boundary elements.

The precast hybrid moment-resistant frames utilize post-tensioned cables anchored at both ends of the frame, running concentrically with the axis of the beams. In addition to the restoring force it provides, the post-tensioning steel, which remains elastic during a seismic event, generates a clamping force between the beams and columns, and enables the shear forces to be transferred by friction at the beam-column interface. Mild reinforcing steel, the straining of which provides the necessary energy dissipation during a seismic event, is placed at the top and bottom of the beam through the joint and is grouted in place.

Typical frame columns are 36 in. by 36 in. with a concrete strength of 6,000 psi. Frame beams are 24 in. by 41 in. with 24 strands (0.6 in. diameter) at typical floors, and are 24 in. by 48 in. with 19 strands at the roof level. The beams have 3-No. 9 mild reinforcing bars at the top and bottom, placed inside the 3-in.-diameter duct filled with high-performance non-shrink grout.

These buildings, which are the first application of the ICBO-approved Precast Hybrid Moment-Resistant Frame in the city of Los Angeles, were each constructed in approximately 13 months. Concrete framing satisfied the needs of the owner, and provided cost-effective buildings that were occupied in a relatively short amount of time.

Case Studies:

Cultural Buildings
Educational Institutions
Green Buildings
Healthcare
Hospitality
ICF Buildings
Luxury Residential
Mixed Use
Office Buildings
Religious Structures
Tilt-Up Buildings

Owner: Kilroy Realty Corporation, Los Angeles, CA Architect: HKS, Los Angeles, CA Structural Engineer: Englekirk Partners Consulting Structural Engineers, Inc., Los Angeles, CA General Contractor: Charles Pankow Builders, Ltd., Altadena, CA

 
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