One Rincon HillCONDOMINIUM RESIDENCESOne Rincon Hill511 Harrison Street ♦ San Francisco, CaliforniaArchitect:Solomon, Cordwell, Buenz Associates Structural Engineers:Magnusson KlemencicConstruction Company:Bovis Lend-LeaseConcrete Sub-Contractor:WebCoreProject BackgroundThis two phase project includes two condominium towers, and a set of town homes connected by an underground parking structure. Currently they are working on the first phase which consists of the town homes, parking structure and the South Tower. The scope of our project covers the South Tower.The project began in August 2004 and the structural system of the South Tower is expected to be finished by June 2007.The South Tower has roughly 350 units ranging from 620-2000 sq. ft. Their prices range from $0.5 million to $2 million.Project BackgroundThe South Tower, which is the main tower, will reach over 620 feet making it the second tallest building in San Francisco. It is comprised of a concrete shear core reinforced with steel K-bracing linked to out-rigger columns to resist earthquake loading. The bracing strengths the weak axis of the core. The core has been designed twice as strong as the codes require it to be. It carries the majority of the load support for the building and provides structural stability in the N-S direction.The building makes dual use of its fire-water reserve system. The water reserves sit on top of the building serving as an un-tuned liquid mass damper which is a first in the country.Concrete DesignFoundation Mat (F’c = 5000 psi)8.9Fine Aggr.10.6 (max 1”)Course Aggr.1.2Fly Ash2.0 (Type II Mod. PC)Cement3.9Water0.4AirSlump: 5”Mix Design (ft3)The foundation mat is composed of three separate mats which are connected by expansion joints. This enables the isolation of earthquake forces of each tower.Concrete DesignCore – Lower Floors (F’c = 12000 psi)1.7Slag8.7Fine Aggr.9.2 (max 0.5”)Course Aggr.0.8Fly Ash1.6 (Type II Mod. PC)Cement4.3Water0.5 Spread: 24”-28”AirSelf-Consolidating MixMix Design (ft3)Self-consolidating concrete was needed for the first few floors of the core due to the congestion in the area and the density of rebar.Concrete DesignCore – Upper Floors (F’c = 8000 psi)1.7Slag7.3Fine Aggr.11.0 (max 0.5”)Course Aggr.0.7Fly Ash1.5 (Type II Mod. PC)Cement4.3Water0.5AirSlump: 8”Mix Design (ft3)Core walls are approximately 2.5’ thick. Strength of the walls are graded so that it is 12000 psi at the base and tapers to 6000 psi at top.Concrete DesignPT Floor Slabs (F’c = 5500 psi)8.7Fine Aggr.10.3 (max 1”)Course Aggr.1.7Pronto Cement1.7 (Type II Mod. PC)Cement4.3Water0.4AirSlump: 4”Mix Design (ft3)Floors reach a minimum strength of 3000 psi after the third day of curing.Concrete DesignColumns (F’c = 8000 psi)Unlike the core the columns are not continuous members running through the building. The floor slabs are the continuous members with the columns being poured on top at each floor. The strength of the floor is less than that of the column creating weaker sections in the column where the slab is poured in. This is unavoidable and code allows for this type of variation in strength. To prevent punching shear, the columns have stud rails inside.All concrete on the tower is placed using a single placement boom. It is pumped from the ground floor through a pipe, which runs along the inside of the core. There are two different pouring schedules running simultaneously for this project, one for the core and the other for the floor and columns.Construction MethodsPlacement of the rebar for the foundation took four weeks. Formwork was only needed on one side, taking two weeks and occurring simultaneously with the rebar. Foundation depth varies, from 6 ft to 16 ft depending on the planned superstructure. The South Tower’s foundation is 12 ft deep.Foundation was poured in a single 16 hour pour. Four pumps were used, each starting from a corner and working inwards, to prevent cold joints and congestion. Construction MethodsFoundationThe interior formwork is a self-climbing slip-form, allowing for fast and easy form placement. Exterior formwork is placed by the crane and held together with snap ties.Rebar cages for the core are assembled onsite and lifted in place. For the first few floors the rebar was assembled in place since their weight exceeded the crane’s lifting capacity.The core is on a different cycle than the floor and columns, being poured on a different day. Two stories are poured at one time for the core and it is always ahead of the floor slabs by two stories.Construction MethodsCoreThe floor slabs and columns are poured on a 3-day schedule. The first day the formwork is set in place, the second day is for rebar and the third is for the pour. The slabs use a fly-form for most of the formwork. The fly-form mounts to the core wall removing the need for any shoring. The forms are moved up and placed by the crane in parts. There are two sets of fly-forms so that after a floor is poured, the formwork will stay on for another three days, for curing, until it is needed for the following floor. After three days of curing the slab is tensioned. Construction MethodsPT SlabsRebar for columns are placed the same time as the floor. The length of each column segment is 2 ½ floors. They are assembled off-site and lifted directly in place when they arrive on site. The rebar is continuous through the floor slabs, being joined in the middle of a floor. Formwork is assembled the same day as the floor. Initially the formwork does not reach the floor and only after the floor has been poured does the formwork get extended down to the finished floor.The columns are poured the same day as the floor slab, only 10 hours later.Construction MethodsColumnsProblem: Creating a sufficient connection with the rebar between the core and the floor slabsSolution: For the floor slabs within the core, the rebar had to be bended into place. For the floor slabs outside the core, formsavers were used. Styrofoam was used to create keyways for embedded pieces, allowing rebar to be screwed into the core.Problem: Punching shear around the columnsSolution: Stud rails were used around the columns to resolve the problem of punching shears.Problem: Over congestion at the core’s base due to the amount of necessary rebar, making it impossible to vibrate properly.Solution: Self-consolidating concrete was used for the first few floors because