The historic high-rise building at One Market Street once served as the headquarters for Southern Pacific Railroad Company. The large-scale architectural and structural renovation included the addition of significant new floor space. This eleven-story, 420,000 sf building was constructed in 1917 on a foundation of timbers driven into the deep deposits of bay mud. Its structure consists of a vintage riveted steel frame with in-fill masonry façade walls. The original design provided little in the way of lateral bracing. The retrofit scheme needed to address a variety of challenges, including poor soil conditions, limited access for construction, historic preservation, and space planning. The design team added two 33-ft-square, 150-ft-tall, hollow concrete cantilever towers in existing light wells and two solid concrete shear walls to provide strength, stiffness, and toughness. The hollow concrete towers and their foundations were constructed completely within the interior spaces of the structure and are seamlessly integrated with the existing building. The solution increased usable square footage, avoided exposed bracing, and accommodated the new mechanical systems. The design accounted for soil-structure interaction with a foundation of post-tensioned drilled piers, which are as deep as the building is tall.

Project executed as Tipping Mar