The Grande San Diego
The Grande in San Diego is a large landmark twin tower project in Downtown San Diego, close to San Diego Bay. The towers are distinctively triangular-shaped, 40 storeys tall, 400 ft. high, and constructed of reinforced concrete with post tensioning and with three levels of underground parking. Being in San Diego and near the bay, presented unique design engineering challenges. In addition to intense seismic challenges, site soil conditions are poor, with a high groundwater table and design water levels close to the ground surface. Significant effort and successful advancements were made in gaining approval from the San Diego Building Department for innovative structural design features.
The project was awarded the “Multi-Family Residential Award” by the American Concrete Institute (ACI).
- An efficient “dual” seismic load-resisting system, combining the seismic load resisting efficiency of a ductile reinforced concrete core, with a rigid frame system
- A reinforced concrete raft slab foundation to spread the weight of the tall concrete towers over sufficient area to limit pressure on the poor soils, and hence limit foundation settlement
- The three levels of the underground parking structure designed as a fully tanked, watertight “container” in order to resist large hydrostatic pressures acting against the sides of the parkade walls and large hydrostatic uplift pressures acting on the underside of the raft slab foundation
- “Hold-down” soil anchors were designed to provide the strength needed to resist the large hydrostatic uplift pressures in areas outside the large towers where there was insufficient structural weight to ‘hold down’ large hydrostatic uplift forces
- The seismic core served the additional function of providing a fire safety enclosure to exit stairwells and also to elevators and building services shafts.
- Three independent seismic resisting rigid frames were designed for each tower, in the north-south direction of each structure
- Rigid frames were incorporated into the structure of the reinforced concrete core walls eliminating the need for and cost of separate independent rigid frames in the east-west direction
- Tower columns were located so they could continue down to the foundation and accommodate parking under the large footprint towers, without the need for costly column transfer beams.
- The use of mechanical ducts inside the concrete floor slabs for exhausting kitchens, washrooms, and laundry dryers, as well as providing fresh air intake (new to Southern California at the time) – all done without compromising the structural integrity, or the fire separation and fire rating of the floor slabs