GENERAL BUILDING DATA
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Worcester Apartments
Massachusetts
WITHHELD
Mixed Use/Residential
418,400 total square feet
20 stories above grade and a mechanical penthouse
214'-3"
October 2013 - October 2015
~$85,000,000
Design-Bid-Build (Fast Track)
WITHHELD
Add Inc.
Suffolk Construction
Acentech
Aquatics Group
Commercial Construction Consulting Inc. - C3
Nitsch Engineering
Haley & Aldrich
Ground Inc.
LAM Partners
WSP│Flack + Kurtz
Kalin Associates
Odeh Engineers, Inc.
Howard/Stein-Hudson
ARCHITECTURE
The project consists of two towers with a total of 378 units and a parking garage that holds 180 spaces. The first building is an 11 story mid-rise tower that features a mix of retail and residential space on the first and second floors and the above floors consisting entirely of residential space. In total, the mid-rise has 170 apartments. The second structure is a 20 story high-rise tower that features retail and residential amenities on the first floor. The second and third floors have a mix of residential amenities and rental apartments, and all of the floors from the fourth story upwards are residential, which has a total of 208 apartments.
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Major national model code/s
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Massachusetts State Building Code, 8th Edition (IBC 2009/ASCE 7-05, amended)
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Massachusetts Electrical Code (2011 National Electrical Code, amended)
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Massachusetts Elevator Code (2004 ASME A17.1, amended)
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2009 International Mechanical Code
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Zoning: Residential
BUILDING ENCLOSURE
Building Façade:
The building façade has many different panel types. The panels are mix of precast concrete, metal veneer and glass curtain walls hanging from building columns. Many of the precast panels feature sprayed foam insulation, however some are uninsulated. The metal veneer panels are primarily aluminum and backed by 3” rigid insulation and fastened to the columns. However, the insulation is different for panels attached to the concrete shear wall, as they feature 3” closed cell spray foam instead. Some of the metal panels also feature louvres. I am still looking into determining what the glazing on the glass panels are.
Roof Systems:
The roofing features a series of insulated membrane systems. One is a monolithic membrane roofing system which is comprised of rigid insulation and a root barrier in instances where there are planters. Another roofing membrane assembly features an adhered roof membrane that has rigid tapered insulation. The assemblies are supported by either a composite or metal deck, depending on where they are located in the building. Different roofing assemblies utilized in the rooftop terrace and mechanical penthouse are pictured below.
SUSTAINABILITY FEATURES
Sustainability was a key consideration during the design, construction and operation of Worcester Apartments. Per the building’s website, it was designed to operate 25% more efficiently than a code-compliant building. One approach utilized to accomplish this is through the use of a localized co-generator, which produces 100% of the building’s hot water and 54% of its heat. Additionally, the building contains a great deal of recycled material; the floor features 82% post-industrial recycled content flooring while some portions of the structure were crafted from recycled steel and concrete. It also features rooftop terraces with planted gardens as well as bicycle racks. These, and other factors, contributed to the building being rated LEED Gold.
STRUCTURAL SYSTEM
Foundation:
The foundation system of the taller Worcester Apartment tower consists of concrete piles, concrete grade beams and a thickened mat pile cap foundation. The concrete piles are capped by mat pile caps varying in thickness from 2’-0” to 6’-6”. Additionally, some of the mat caps are designed to resist uplift, as are the piles that they sit on. As noted previously, during the initial exploration of the site, it was discovered that an older caisson foundation was still intact beneath the building’s intended location. However, because of careful collaboration with the geotechnical engineer and contractor, a system was designed that allowed the new piles to be constructed without having to remove a majority of the existing caissons. The grade beams are reinforced and located at the perimeter of the building between reinforced pile caps. They range in thickness from 15” to 20” and some feature shelves. Each beam uses #8 sized bars at both the top and bottom.
Gravity Framing:
Specially fabricated beams are used for the flooring system of this building. Known as “D-Beams,” they range in size from a DB8x37 for shorter spans to a DB8x46 for longer spans, with the longest span measuring 18’-0”. The beams work with 8” thick hollow core precast concrete panels that span across the 21’-0” distance, and frame into columns that are connected by W10x26 girders on the perimeter.
The building primarily uses size W14 steel columns, with sizes ranging anywhere from W14x43 to W14x370. At the roof level, the columns are HSS shaped and sized as HSS12x8x1/2 and HSS10x10x1/2. Column splices are located every other floor, with some being compressive splices and others being tension splices. Tension splices are required at all column locations with braced frames and moment frames.
Lateral System:
The lateral load resisting system utilizes a combination of concrete shear walls and concentric steel braced and moment frames. There are two concrete shear walls located on the first level that run in the plan East/West direction. Both are 24” thick and have a minimum compressive strength of 5000 psi. The larger of the two runs 62’-6” long and is located on column line C. The wall uses #6 bars @ 12” O.C. for horizontal reinforcement, while using #6 bars @ 8” O.C. in the vertical direction. The smaller shear wall measures 11’-9” in length and is located on column line F. Concerning reinforcement; this wall uses #6 bars @ 8” O.C. in the horizontal direction and #9 bars @ 6” O.C. in the vertical direction. Both walls have columns built into the walls at ends and are capped at the top with embedded transfer beams.
Since the shear walls only reach the second level, moment and braced frames are utilized to provide lateral reinforcement throughout the rest of the tower. Some of the framing surrounds the elevators and stairwells. The members used in the braced frames change with elevation, ranging from W14x145 to W14x48
MECHANICAL SYSTEM
The mechanical system utilizes four 100% Outside Air packaged rooftops to provide ventilation to the building. The Central Plant consists of natural gas boilers and a cooler tower to provide heating and cooling, and it is located on the building penthouse level at the top of the structure. Water cooled heat pumps serve each unit to supply the heating cooling from the central plant.
LIGHTING SYSTEM
The lighting system for Worcester Apartments consists mainly of LED fixtures in order to reduce energy consumption. These have a consistent color temperature of 3000K throughout the building and generally operate on 277V circuits. However, residential lighting is tied into individual load centers at 120V. On the ground floor, the elevator lobby utilizes custom LED downlights, while the main lobby features recessed LED cove lights. The back of house lighting consists of primarily fluorescent fixtures. In the penthouse lounge space, there are decorative opal globe LED pendant fixtures that vary in diameter. These create a fun and welcoming environment.
ELECTRICAL SYSTEM
Electrical services are provided to the building by NSTAR. Worcester Apartments has two main transformers that feed five main switchboards. The first is a 4000 A, 480/277 V switchboard that serves the tower penthouse, as well as the mid-rise switchboard and the retail spaces. The second switchboard is 5000 A with 208/120 V that serves the vertical busway for the tower and the mid-rise. The third switchboard is 480/277V and feeds a fire pump. The fourth switchboard is 1600A with 480/277V and feeds the mechanical equipment. The fifth feeds to light controls and miscellaneous mechanical equipment. Outside, a 600KW/750KVA diesel generator powers elements such as life safety, elevators, and legally required systems in the event of a power failure.
CONSTRUCTION
The focus of this project during construction was to complete construction in a quick and efficient manner. This is represented in the fast track Design-Bid-Build project deliver method. Construction began in October 2013. The building primarily utilized precast concrete planks in the floor system instead of metal deck floors. This made it easier to erect floors, which allowed other trades to begin work sooner. Additionally, lower floors were rapidly enclosed out of necessity to prevent exposure to the harsh New England weather. This reduced construction time significantly, which allowed the building to be topped off 10 months after construction began. The building was completed in October 2015.
FIRE PROTECTION
Worcester Apartments contains four different occupancy classifications: light hazard, ordinary hazard group 1, ordinary hazard group 2 and residential. As such, the fire protection system is designed to handle these conditions. It utilizes a dry pipe sprinkler system throughout the tower. The pump room and control panel are located on the north side of the building next to the stairwell. Every floor in the building has sprinklers. Standpipes run all the way up to the mechanical penthouse at the top of the structure.
The fire protection system complies with relevant codes. The sprinkler protection system is in compliance with NFPA 13. Standpipe systems are in compliance with NFPA 14, and fire pump systems in compliance with NFPA 20.
TRANSPORTATION
Worcester Apartments has a main elevator and stair core located towards the southern part of the building. Located in this core are three elevators as well as a stair well. There is also a stairwell located at the very northern part of the building. All elements run from the ground level all the way up to level 20.
TELECOMMUNICATIONS
The ground floor has a wireless access point in the main lobby of the building. There are two television outlets that serve as Voice/Data/CATV outlets in the elevator lobby, as well as one in the mail room. Voice/Data outlets are spread across the floor as well. The third floor features two wireless access points in the lounge and fitness area, as well as multiple floor boxes.
The telecommunications layout is typical amongst apartment units. All come equipped with at least one Voice/Data/CATV outlet, however some come with two. Also included is a recessed multimedia panel, which is used to provide power and service to the cable and television.