Robert Mroskey | Construction Option
The majority of the Annex's structure consists of structural steel. A combination of W and HSS sections are used throughout the new addition. The W shaped steel is ASTM A992, with a yield strength of 50ksi. A composite deck is placed on the steel to distribute the loads from the building. The deck is continuous over 3 or more spans and ranges from 1-1/2" to 2" in thickness. Normal weight concrete is placed over the deck and is to have a strength of 4,000 psi after 28 days. Additionally, a braced frame consisting of W shaped beams and columns as well as HSS cross braces are used to help resist the lateral loads imposed on the building. Shear loads ranging from 50K to 100K are experienced at the bases of the braced frames and are absorbed by large footings.
Cast-in-place concrete was also used throughout the construction of the Chevron Annex. Footers, pile caps, grade beams, slab on grades, slab on decks all required the use of cast-in-place concrete. All of the concrete used on the project was to be in accordance with ACI 318. Pile caps were placed in the existing slab on grades and stepped slabs, with the thickness of these pile caps ranging from 24" to 60" in depth. Stepping grade beams and mat slabs were also used to support concrete walls for the generator room.
Three new air handling units will serve the new addition and are located on the new penthouse level. Two of the units (AHU -1, 2) will serve the chemical lab and administration areas, which are located on two of the new floors. The third unit (AHU-3) will service the Ashe Lobby infill area located on the ground floor. All three of these units are designed as heating-cooling, single duct, variable volume reheat systems.
Additionally, three laboratory exhaust fans are used to remove any fumes from the lab areas. Each fan is sized to provide 50% of the design flow rate. Two of the fans operate in parallel under normal operation, while the other fan is in standby mode. These fans are located in the southeast corner of the penthouse level and are enclosed by louvers.
The electrical system for the Chevron Annex consists of transformers, switchboards and an emergency generator. The distribution transformer for this project has a maximum rating of 300kVA with a primary voltage of 400 volts through three phases and three wires. The secondary voltage for the transformer is 208Y/120 volts through three phases and four wires. Additionally, the main switchboard consists of 1600 amps, 480,277 volts through three phases and four wires plus a ground. The emergency generator that is specified for this job is located at the northwest corner of the building and delivers 1500kW of power at 480Y/277 V. Additionally, multiple panelboards of different rating and sizes are located on each of the floors throughout the project.
Chemistry research is the primary use for this facility, which needs an abundance of light for the precision needed for the experiments. The lab area is predominantly lit by pendant fluorescent lights that use a combination of direct and indirect light to minimize glare. Additionally, the student desk area is lit by a combination of lighting. Staggered strup fixtures that are concealed in a cover are provided, as well as surface mounted lighting integrated into the student desks. Both of these areas also rely on a significant amount of natural light from the vast amount of curtain wall facade.
The Chevron Annex shares two passenger elevators and one freight elevator with the existing Chevron Tower. A stairwell is also shared between the two buildings. The Annex also added an additional stairwell in the northwest corner of the building to accomodate the current building codes.
The Chevron Annex is protected by a dry-pipe system that fills water once smoke as been detected. Additonally, the system includes a fire pump and jockey pump.
Support of Excavation
Although the project did not require a large amount of excavation, the excavation that was performed needed to be supported. This was accomplished by using the method of soil nailing. Roughly 40 soil nails were drilled and installed, which consisted of a single rebar tieback in each of these 6" diamter holes. Each hole took about 1 cubic yard of grout to fill. The tiebacks were then followed by 22 cubic yards of shotcrete to help support roughly 1800 square feet of 4 inch coverage.
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