The three-story, $9 million building located at 3700 Henry Hudson Parkway in The Bronx, N.Y., is the new home of The Hebrew Institute of Riverdale. It encompasses a new 24,000-square-foot addition and a renovated 11,000-square-foot building. The project team included general contractor Mc Gowan Builders Inc. (MGB), East Rutherford, N.J.; architect SLCE Architects, New York; and structural engineer DeNardis Engineering, White Plains, N.Y.
Engineering and construction challenges
The building team faced numerous engineering, design revision, staging, site management, and scheduling challenges, especially with the foundation.
The new building was originally to feature foundations bearing on rock. During excavation, it was discovered that the bedrock sloped down at a 70-degree angle, rendering the initial design unbuildable. The initial testing did not reveal this condition, as there was a residential structure located on the site, which prohibited testing in a large section of the new building’s footprint.
Following a collaborative review of the issue, MGB suggested a new foundation system supported by mini caissons with pile caps. This solution was more cost effective than refilling the areas where the bedrock was significantly lower than expected. DeNardis Engineering accelerated the design process and the team presented the solution to the client within days of the discovery of the sloping bedrock.
To minimize the impact of this significant engineering design change on the schedule, MGB immediately mobilized a specialty contractor and within two weeks installed 20 80-ton caissons with rock sockets driven 5 feet deep into the bedrock. This rapid response allowed the team to complete the entire project on schedule in spite of the significant design revision implemented when the project was already under construction.
The caissons vary in length from 6 1/4 to 7 feet. The system encompassed 5-foot-long rock sockets driven into the rock and pile caps installed 11 inches below the foundation slab level. Following completion of the caisson installation, MGB built reinforced concrete blocks atop each caisson. Selected caissons, located beneath the new building’s 15 steel columns, also received concrete piers with anchor bolts. Grade beams span the pile caps. The team inspected the caissons and installation of the rock sockets with a video camera. The caissons are filled with 4000-psi grout of portland cement and water.
The excavation process was revised to include removal of a large amount of rock in order to create rock shelves in the locations of the foundation footings, and placement of some of the rock debris in other sections of the site. However, the majority of the bedrock elevation issue was addressed by installing the mini caissons.
Staging and phasing
The new building was constructed while the adjacent, pre-existing structure remained in operation. During the entire project, MGB accommodated the client by halting the work in observance of Sabbath, Jewish holidays, and community events.
MGB delivered the project in three phases. The first, from October 2008 to September 2009, encompassed construction of the addition. The second phase, from September 2009 to January 2010, included structural upgrades to the cellar of the pre-existing building. The third and final phase, from January 2010 to June 2010, was renovation of the old building and completion of spaces occupying both buildings, such as the sanctuary and the assembly hall.
During the second phase, MGB made structural reinforcements and revisions to the old building while the top floor was still occupied. This necessitated close collaboration and scheduling with the client and elaborate safety measures.
Two of the new building’s exterior walls are located within 1 inch of the property line and are adjacent to two streets with high pedestrian and vehicular traffic. This necessitated very strict control of the structural and concrete work. Due to the location, MGB collaborated with the New York City Department of Transportation in order to develop a complex staging plan, including temporary and partial street closures.
In anticipation of a future upward expansion, the client requested that the new building accommodate the addition of a fourth floor. The engineering team accommodated this potential expansion by designing oversized foundation footings and structural steel.
The Hebrew Institute of Riverdale opened in 2010.