The front of the building consists of the three story town homes with facades to remain, as well as one leg of the condominium tower that reaches the street. The main condo portion of the building is L shaped with the majority of the building set back from the street along the alley to the rear of the site. There are separate entrances to the town homes from F street and one entrance to the condominium tower, as well as the parking entrance from the alley in the rear. The portion of the tower that reaches the street is two stories shorter than the rest of the structure and houses some of the larger units. It is also distinct in appearance because the curtain wall is nearly entirely glass so that little distinction can be made between floors, whereas the rear leg of the building shows its skeletal structure with two story windows divided by a brick veneer that hides the members. Codes The building code used is the District of Columbia construction codes supplement of 1999 which includes revisions of the 1996 BOCA code, as well as the ICC international mechanical code of 1996 and plumbing code of 1995. It also includes the BOCA fire prevention code of 1996 and the NFPA electrical code of 1996. Zoning / Historical This lot is zoned DD/C-4, which is the shopping district overlay of the downtown historical district. There are 3 historic town homes on site that are to remain. The interiors will be selectively demolished and converted into retail stores and condos and the facades will be refinished. Demolition The historic buildings are currently wood framed structures with masonry exterior walls. Portions of both of these materials will be removed or replaced. The slab on grade will also be removed or relocated and much of the building will receive a new foundation system. One of the hazardous materials encountered in the building is asbestos, which can be found in numerous places. These include mastic in the floor tiles and roof flashing, and insulation around pipes. Another item that was encountered in the buildings was bird excrement, which also had to be removed prior to mobilization. Also in the buildings and on site were abandoned sewer tunnels, wood logs, piles and old foundations, all of which had to be addressed in demolition plans. 9
Excavation Support The National Union Building to the west was supported using bracket piles. They were used because the combination between poor soil conditions on site as well as the weight of the building resulted in a concern that traditional underpinning would be inadequate. The same was true of the Marriott Hotel to the east. Bracket piles were installed only where the pile caps from the new building would undermine an existing building footing. The historic buildings on site were, however, supported by traditional underpinning. The street side of the excavation was supported using soldier piles and lagging boards, as was the western portion of the alley side to support the existing sewer line. Structural The structural system of the building consists of reinforced columns and scattered beams with a two way flat plate slab. The foundation system is also cast concrete with auger piles and pile caps connected by a web of grade beams. Formwork for most of the concrete structure will be traditional hand built forms. For the round columns in the building, metal forms are used that are able to be clamped in place. For placement, concrete deliveries are made to the street side of the building and placed using the tower crane and a bucket. Mechanical System The building mechanical system consists of a number of split system heat pumps. An outdoor compressor is located on the roof for each individual condominium unit. Each unit also has a small mechanical room inside of it that contains an indoor unit to provide the compliment for the system and distribute air throughout the unit. The heat pumps use a fan to force air through a system of ducts in the units. There is also a separate set of pumps for the lobby with a mechanical room above on the second floor. 4 outdoor units will also be placed on the roofs of the townhouses to accommodate the retail stores after they become occupied. Air supply for the corridors runs off of a separate air handling unit which contains an indirect gas furnace and an outdoor condensing unit. There is a shaft which runs down the middle of the building to supply the corridor. Next to this shaft is ductwork for the pressurization of the stairwells for fire code purposes. Fans for stairwell pressurization range up to 10,500 CFM. Two other large fans are used to exhaust the garage in the basement at 3000 and 7500 CFM. Other exhaust fans in the building include those for dryers, kitchen exhaust and bathroom exhaust and range from 150-1600 CFM. 10
A main fire control room is located adjacent to the main lobby, between the lobby and a townhouse. It has its own entrance door from the exterior of the building. The fire suppression system in the building consists mainly of a wet pipe system, with the exception being the garage, which has been designed as a dry pipe system so that it doesn t freeze. The building is 100% sprinkler protected. Electrical system The electrical system in the building consists of 3 switchboards. One is a 1600A service that serves the retail space of the building. A second switchboard is sized at 2000A and mainly serves the condominium units for lighting and receptacles. The third switchboard provides power to many of the equipment systems in the building, including the elevators, the fire pump, the heat pumps, and the generator. The emergency generator is sized at 200kW and designed to run on diesel fuel for 8 hours. The electrical system throughout the building is a 208/120V 3 phase 4 wire system. Electricity is used for the systems already mentioned as well as baseboard and cabinet heaters in the condominium units and in the garage and lobby. The main electrical room is located on the basement level in a room adjacent to the room that houses the generator. The lighting system in the building is being redesigned due to cost considerations and preliminarily consists of a number of different lights, including fluorescent and incandescent light which could be recessed, surface mounted or in track lighting. Telecommunications The telecommunications systems in the buildings stem from the main telecommunications closet located in the basement with smaller closets on each floor. They consists of both a cable and telephone line which branches off at each floor and serves all units. Transportation There are 3 elevators located in the building. The first is a shuttle elevator designed to run from the lobby to the third floor. It runs on the street side of the building near the main entrance and serves only up to the height of the floors of the existing historic buildings. The other two elevators run together for the entire height of the building. The stairwells operate in a similar manner, with 1 stairwell going from floors 1-3 and two that cover every floor. Design Coordination MEP coordination was required by contract as noted in the specifications. The subcontractors were very hesitant to agree to the idea, and getting them to work together has been a difficult but 11
increasingly necessary process. The electrical contractor in particular initially saw little value in his participation, since he believed he took up very little space and could work around other contractors. Advantages of these meetings are now being realized as a number of conflicts have been discovered. During the course of their work, the subcontractors meet once a week to discuss the coordination drawings, with more frequent meetings used as necessary. The coordination process begins with the mechanical contractor, who creates a 2D drawing of the systems that they are responsible for. This is done one floor at a time a few weeks ahead of actual construction so that any changes that need to be made can be taken care of. An FTP server has been created on the internet for easier sharing of these drawings. The mechanical drawing is passed on to the fire protection contractor after the mechanical systems have been drawn in place. After the fire protection contractor overlays his pipes and sprinkler heads, he passes the drawing on to the electrical subcontractor, who finishes the drawing. After the trades have completed overlaying their systems, the master drawing gets sent back to the mechanical contractor, who then searches for and labels potential conflicts. They do this by drawing a revision cloud around the conflict with a brief description of the problem. The drawing is then passed along to Davis. At this point, the coordination meeting is held between the various trades and solutions to these conflicts are proposed and agreed upon. In attendance are the various MEP trades as well as the assistant PM and some of the field personnel. After a revised plan has been made, Davis creates a final overlay which is forwarded to the architect and structural engineer for approval. There have been a number of areas that have presented problems for the coordination of MEP systems. One of the largest is the architecture of the buildings. The historic building layout presents problems with the desired plans of the units located in them. The locations of pipes and fixtures relative to existing floor joists and walls are somewhat less than ideal. One example is that the floor joists will probably have to be cut and an area boxed out for tub boxes to be placed beneath the bathtub drains. The layout of the new building also presents a number of problems. The architect tried to keep floor to ceiling heights as large as possible, with a bulkhead along one wall to carry all of the mechanical systems 12
to the far end of the units. The result has been a fairly tight space in which to fit a number of systems. Another problem that has arisen resulted from an assumption by the mechanical contractor that the fire protection pipes would be attached close to the underside of the slab above, allowing him enough room to design floors in the manner that he wanted to. In some instances, this assumption does not hold true. Some ductwork has to be rerouted and two 45 degree angles are used to avoid other systems instead of one 90 degree angle around the point of conflict. Locations of other systems need to be adjusted as well as areas of overlap are discovered. A final example of a coordination problem resulted from the drawings, where light fixtures were represented by a symbol instead of being drawn to scale. In the bathroom, as well as in the area around the stove in the kitchen, there is not enough room to house the lighting unit along side of the other fixtures around it. The bathroom, for example, is calling for both an exhaust fan and a light to be centrally located in the room, which has caused a problem without seeing the size of the light fixture accurately represented. A number of problems have already been identified and far fewer conflicts will arise as a result of the efforts put forth so far. The owner s insistence on these meetings has turned out to be great foresight on their part, as several of the contractors probably would have refused to participate in this process, which would have resulted in at least the conflicts listed above, costing the owner valuable time and money. Masonry Masonry is used in the form of CMUs in the building for partition walls in the basement as well as brick for an exterior finish. Brick is also used alongside the curtain wall in the front and rear elevations of the building and in areas next to the existing buildings. There is also some architectural stone used on the front portion of the tower that extends to the street. In order to place all of this material, the masonry contractor is using a variety of different scaffolding systems. Along the front of the building, they are going to build tube scaffolding due to the limited amount of work involved. On the rear of the building they decided to use hydraulic scaffolding due to a fair amount of area to be covered as well as the height that they must reach. The portion facing the Marriott Hotel will be both hydraulic and swing scaffolding. 13
Material will be passed up to the masons as they proceed up the building through the use of a material hoist. Curtain Wall The curtain wall consists of metal panels, glass windows, and aluminum framing for the mullions and headers. The mullions are mostly prefabricated to ensure quality control as well as for quick installation. For installation, embeds are placed into the slab when the deck is poured. These embeds will be used to fasten the curtain wall headers and footers. Windows will then be installed from the interior of the building. The manufacturer of the curtain wall system worked with the architect to help develop the design and then proceeded to make detailed shop drawings of the system. There was a collaborative relationship between the two entities prior to the bidding of the work. 14