Owner: Douglas Development Corporation & CarrAmerica

Construction Manager: James G. Davis Construction Corporation

Architect: Pei Cobb Freed & Partners Architects LLP w/ Shalom Baranes Associates

The Square 320 Project is favorably located at 1199 F Street NW, the corner of 11th and F, in the resurgent East End submarket of Washington DC.  Square 320 incorporates the renovation of four historic buildings with the construction of a new 12-story concrete building to create Class A office space.  This exciting renovation project sits on top of 5-stories of below-grade parking totaling 74,300-SF and offering 167 parking spaces.  Above grade, the new 12-story concrete structure will create 302,000-SF of rentable office space.  Construction began in October of 2007 and is expected to last for 41 months through February of 2011.  This project is a joint venture between owners Douglas Development Corporation and CarrAmerica, now part of Equity Office, and is expected to reach an overall project cost of $110 million.  At this stage there are no significant tenants committed but Square 320 is expected to attract larger law firms from the central business district.    

Architecture
The main exterior skin of Square 320 consists of a stone and aluminum curtain wall system which becomes bronze below the third floor and down to the street level.  The interior will be flexible office space offering high-end standard finishes and amenities.  The buildings being renovated date back to the early 1900’s and are constructed of brick masonry with timber joists and terracotta flooring.  The historical integrity of the brick buildings will be maintained with special attention shown to the wooden windows, exterior masonry, brown stone, ornamental copper, and galvanized sheet metal.  It is evident that the architecture of the new building was based heavily on consideration of such materials.  The historic storefront will be replicated with an aluminum system of decorative stone and cast iron ornaments at the street level.  The most exciting architectural element of this project is the adjoining structure that encompasses the new and historic buildings, a six-story glass atrium.  Structural steel bridges will connect the bronze and aluminum curtain wall system to the restored historic masonry buildings, all under the cover of a 110-foot skylight. 

Some of the major National codes include: 2003 Int’l Building Code, 2003 Int’l Mechanical Code, 2003 Int’l Plumbing Code, 2003 Int’l Electric Code, and ADA Accessibility.  The District of Columbia has very strict zoning restrictions to both protect the historic nature of the city while stimulating economic growth.  Square 320 is located in the downtown core, C-4, which comprises the retail and office centers of the District of Columbia.  This designated district allows office, retail, housing and mixed uses to a maximum lot occupancy of 100% and a maximum height of 110 feet and 130 on 110-foot adjoining streets.  Additionally, this subsection of DC is called the Downtown Development District (DD) permitting incentives and requirements for Downtown sub-areas to a maximum floor area ratio (FAR) of 6.0 to 10.0, and a maximum height of one hundred-thirty (130) feet.

Building Statistics Part 2
Construction
With the renovation work occurring alongside of new construction there was a considerable amount of demolition required on this project.  Demolition was required on both parts of the site.  The renovation site consisted of 7,400 SF removal by hand with the allowance for selective appurtenances to remain intact.  Some of the work included lead paint abatement and the removal of interior framing, finishes, and roof system keeping intact the terracotta flooring system. 
On the tower site there was a small two story brick building with a basement that resulted in just over 32,000 SF of demolition and removal from the site.  The majority of the hazardous material was remediated and removed from that portion of the site prior to Davis’ involvement.  For that reason little is known of the contents and materials present prior to excavation.

 Excavation Support
The Square 320 project excavated nearly 100 feet below the ground level in order to prepare the way for the 5-story 76,000 SF parking garage that would become the foundation for the 12-story office tower.  Before the excavation would be allowed to move forward an extensive dewatering plan had to be created to account for heavy water infiltration into the sight.  The dewatering plan consisted of 6 well points along the perimeter of the site continuously discharging directly into the storm sewers in excess of 30,000 GPM.  The system was monitored frequently from piezometers on the west and south of the site.  Once the system was in place the site was excavated and the support system was built.  The supports consisted of a comprehensive system of tiebacks, lagging, tangent piles along 12th street, heavy steel diagonal bracing, and discontinuous underpinning at each level.  The majority of the support system was a permanent system with the exception of the large tubular supports that can be seen in the image below. 

Lighting & Electrical System
As the basement level of the office tower, the buildings power comes from a 4000Amp and 3000Amp.  The 4000 Amp switchboard feeds a 4000A 480/277V, 3ø, 100,000 A.I.C.Amp feeder busway running the full height of the tower while the 3000A 480/277V, 3ø, 100,000 A.I.C. switchboard offers the redundancy for emergency power.  For additional emergency precautions,  the hospital has a single 600 kW, 480/277V, 3ø generator with a 4W Diesel GENSET w/ 50 Gal. day tank.
In the office tower, each floor has an electrical room with houses a 400-Amp fusible plug-in busway switch in addition to both 120V and 277V J-boxes.  Throughout the historical buildings side, electric rooms are set-up the same way.  This project is not working to gain credit from the TP1 transformer standard.  The historic buildings are led by a 225 kVA dry type transformer powering every floor while a team of weaker ones ranging from 30-113 KVa. 
The lighting system consists of three real cores groups, metal halides for the garage, recessed fluorescents, and low-voltage adjustable accent-lights all over the class-A interior spaces.    

Mechanical System
The mechanical system is built upon a series of variable volume (V-VAV) self contained water cooled AC units with one on every floor.  Next in line are two plate and frame heat exchangers leading to the HVAC penthouse on the roof.  There, two inducted draft propeller fan cooling towers rest integrated into the green roof, each weighing 28,000 lbs and capable of pushing 1800GPM and 149,090 CFM.  In addition, on each floor a series of traditional ductwork transfers the treated air throughout the spaces.  Both cooling towers will be picked by the tower crane located in the atrium space between the tower and the BW Annex.  With tight plenum space ranging from 9” at its tightest point and 18” at its widest point, coordination will be key.   
The plumbing plan takes advantage of a wet stack attached to alternating concrete columns to minimize on excess piping.  The system includes and requires hot water heaters at not only the fitness center on B1 but also two in the bottom of the basement B-5 and two in the penthouse. 

Structural
Cast in Place Concrete
Due to the height restrictions in the District of Columbia, cast-in-place was chosen as the structural system for the 12-story office tower.  The construction of the 5-story underground parking garage included a series of foundation walls ranging between 12”-16”, just under 4,000 CYs for a 42” mat foundation, and nearly 80,000 SF of 8” suspended drop slabs.  In order to achieve the desired full span, the garage did include post-tensioning in selected girders.  The formwork for the garage portion was all multi-use plywood and the tower crane enabled the use of placement with crane and bucket.         
As the garage transitioned to the tower, the design changed slightly as the live load requirements altered.  The tower utilized 210,000 SF of 7” suspended slab design with 10” drop panels and 100 CYs of post tensioned transfer girders.  The tower construction utilized more multi-use plywood as the tower crane placed the concrete with crane and bucket over the course of 24 weeks.           

Structural Steel Frame
The new construction consisted of solely cast-in-place concrete and the only place structural steel was implemented was in the support of the restoration projects.  Great effort was made to preserve the original terracotta flooring of the historic buildings but additional support was required.  On the first floor of the Nordlinger building metal deck was filled with concrete to achieve the desired design load. 
The structural systems consist mainly of W14X22 and W16X36 girders supporting 3”-20guage composite metal deck with a lightweight concrete slab of 3 ¼”, 6 ¼” total depth.  The project utilized two tower cranes with one located directly between the concrete tower and the historic BW building facing F street

Special Systems
Curtain Wall
Douglas brought in the highly respected architectural firm of Pei Cobb Fried & Associates to design a fully custom, signature curtain wall that would represent the high-end luxury that that Douglas wanted to convey to tenant.  The curtain wall consists of full height glazing panels with architectural bronze and decorative stone.  Sections are installed by tower crane and hung from concrete levels.  At each concrete floor a sill plate extends out and down creating a lip-like channel for the hooks of the curtain wall system to fall into and transfer weight to.  The steel tubing bolted to the concrete floor runs horizontally down the length building and provides an additional support 5/8” steel plate sill for the curtain wall system to rest on.  Above and below each of the connections are solid panels of bronze that add the style and color to the curtain wall.  The curtain wall system went through mock-up testing at two locations off-site.  It was graded on infiltration, water penetration, and structural performance against referenced test standards.  The curtain wall system experienced significant leaking during the testing period and required three mock-up tests before successfully passing.  Additionally, the highly customized glazing mullion required significant effort to ensure proper installation.       

Masonry
CMUs were used to form a series of walls on the first level both for utility sake and to back-up stone façade.  In addition, 13,000 SF of CMUs formed walls on the North elevation.  These walls were mostly not load bearing and formed a firewall between the tower and the existing buildings to the north.  Pei Cobb Fried & Associates implemented a custom design curtain wall that incorporated a repeating pattern of masonry separated by two glazing panels on the first two floors and five panels for the remaining levels.  Stonework on the façade of the ground level is scheduled to begin in October of 2008 and last for 30-45 days.  The high-end appointed stone in the lobby is scheduled to occur towards the end of the project around January for 2009.  There is some masonry restoration of the historic buildings, but those items are off the critical path and won’t take place until foot.  The historic buildings will already have scaffolding up from the paint abatement and façade cleaning so will not be a need to rebuild a scaffolding system when the time comes to hang the bring, etc.