ENTRY FORM. DVASE 2014 Excellence in Structural Engineering Awards Program

Transcription

1 ENTRY FORM DVASE 2014 Excellence in Structural Engineering Awards Program PROJECT CATEGORY (check one): Buildings under $2M Buildings Over $100M Buildings $2M-$10M Other Structures Under $5M Buildings $10M - $30M X Other Structures Over $5M Buildings $30M - $100M Single Family Home Approximate construction cost of facility submitted: Entry Fee: Name of Project: Location of Project: $26 Million FREE 159 First Street Cambridge, Massachusetts Date construction was Under Construction Estimated Completion Late 2014 completed (M/Y): Structural Design Firm: Michael A. Beach & Associates Affiliation: Architect: General Contractor: All entries must be submitted by DVASE member firms or members. Kitchen and Associates Callahan Construction Company Logo (insert.jpg in box below)

2 Provide a concise project description in the following box (one page maximum). Include the significant aspects of the project and their relationship to the judging criteria. The project is comprised of a 126,000 square foot, 6-story, 115 unit apartment building. The building is located on First Street in the heart of East Cambridge approximately 1/2 mile from the Massachusetts Institute of Technology campus. The building is comprised of a 5-story wood framed bearing wall structure with open web wood floor and roof trusses above a steel framed podium structure with a mixed-use occupancy. A parking garage with accommodations for ninety vehicles is located in the basement. The foundations for the building are comprised of a mixed system of secant pile bearing walls and conventional spread footings. The design of the foundation was the first challenge of this project because of the structure s close proximity to two adjacent existing buildings and busy streets to the north and south. In addition, the parking garage below the new building created an excavation and shoring challenge for the adjacent buildings that did not have basements. At each of the adjoining buildings, the exterior wall of the parking garage is essentially up against the exterior wall of the existing building. The adjacency of the other buildings required the installation of a secant pile excavation shoring system. The system was selected over many other considered systems because of property line concerns and vibrations. The secant pile wall is comprised of 21 inch diameter drilled concrete filled piles spaced at 18 on center. At this spacing, the adjoining piles overlap and interlock with each other. A wide flange W10x54 soldier pile was installed in the concrete of every other pile (3-0 on center) creating a wall for both the shoring of the existing grade and the final finished wall of the basement. The secant pile system was only used at the perimeter of the basement garage adjacent to the existing buildings where vibrations were a concern. A conventional steel sheet pile system was utilized for the remainder of the excavation. In order to save money and eliminate complex strap foundations along the secant piles, the wall was also designed as a bearing wall with allowable loads provided by the geotechnical engineer. A concrete cap beam was designed by our office to distribute perimeter column loads onto the secant piles to satisfy the design loads established by the geotechnical engineer. Another unique design requirement was that the secant pile wall is also the finished basement wall product. This unique aspect of the shoring system required two design processes. The first design for the wall was done by the shoring and bracing engineer with the final design checks for the wall with the first floor of the building in place was performed by our office. The wide flange soldier piles needed to be increased in size to W10x68 sections at the location of the elevator pit which required excavations 6 feet below the garage floor slab. Another challenging aspect of the building design was the steel framed podium over the first floor mixed use area. The podium level supports the five story wood bearing wall structure above. Due to concerns over placement of concrete in winter months Callahan Construction suggested a steel framed structural system over cast in place concrete. Limited continuity of columns from the garage level to the second floor and open space requirements at the first floor made the installation of braced frames impossible. Therefore, a fully welded moment connection lateral force resisting frame system was designed. Column sizes were analyzed with the large fixed end moment reactions and W12 sections were utilized. The weights of the column were increased during design to reduce stiffener and web doubler plate fabrication/erection difficulties. The final and most complicated portion of the design was the five story wood bearing wall structure over the podium. In order to construct a wood framed building of this size and height Type 3B construction was necessary. Type 3B construction required all exterior perimeter walls to be 2 hour fire rated. This meant that fire retardant treated lumber needed to be utilized for the studs and plywood sheathing. The fire-retardant treatment process reduces the strength of the members from both a gravity and lateral perspective and was a significant part of the design. Another complicated detail of the two hour fire rating is the continuity of the rating through the floor construction. This meant that the floor framing could not bear on the walls as is typical in platform construction. The framing instead was supported off the walls with pre-engineered metal hangers from the wall double top plate which extended to the underside of the floor sheathing. The hanger selection for this application was critical because the drywall needed to be behind the hanger which required the top flange of the hanger to cantilever from the wall top plate over the drywall. Technical bulletins from Simpson for this type of condition were followed and reduced hanger capacities were utilized. The 2 hour fire rating also meant that engineered lumber headers and posts could not be utilized in the 2 hour walls since these products are not available in fire-retardant treated materials. Therefore, headers for longer span openings needed to be designed with a steel flitch plate. Using a steel flitch plate of up to 3/8 thick plate sandwiched between dimensional fire retardant treated lumber members the larger openings in the fire-rated walls were able to be accommodated. Plywood sheathed shear walls were utilized to resist lateral wind and seismic forces with a continuous rod hold-down system at the wall ends. Lateral seismic drift for the shear walls was calculated considering the effects of rod elongation, plate crushing and nail slip. The rod diameter for the hold-downs ranged from 3/4" diameter ASTM A36 rod to 1 1/4" ASTM A193 (120 ksi) high strength rods with hold-down tensions in excess of 45 kips. Chord members at the ends of the highly loaded non-fire rated shear walls are comprised of up to (3) 3 1/2 x 7 1/4" PSL posts. Wood shrinkage for the building was also a major consideration and estimates for the total shrinkage at each floor were provided on the drawings for contractor reference especially for the plumbing risers. Estimated shrinkage for the roof of the building was calculated to be approximately 1 1/8. Wood framing was isolated from the CMU shafts of the stairs and elevator.

3 The following 5 pages (maximum) can be used to portray your project to the awards committee through photos, renderings, sketches, plans, etc Secant Pile Layout on site. Detail for Secant Pile Wall from Structural Drawings.

4 Cap beam reinforcing around installed secant piles. Excavation for basement parking garage at elevator pit adjacent to secant pile wall.

5 Finished secant pile foundation wall in basement parking garage. 2 nd floor podium steel under construction. Temporary excavation bracing being removed with 1 st floor diaphragm over parking garage installed.

6 Compression chords of high load shear wall. 3 rd and 4 th floors under construction. Steel podium structure at first floor fireproofed.

7 2 nd floor walls under construction as viewed from crane. Rendering of project scheduled for completion in late 2014.

8 By signing, signatory agrees to the following and represents that he or she is authorized to sign for the structural design firm of record: All entries become the property of DVASE and will not be returned. By entering, the entrant grants a royalty-free license to DVASE to use any copyrighted material submitted. Submitted by: Print name: Paul Constantini Signature: Date: 04/21/14 Submitting Firm: Mailing address: Telephone: Michael A. Beach & Associates 200 Birchfield Drive Suite 205 Mount Laurel, NJ Fax: paulc@mabeachassoc.com