Shotcrete Magazine Article
Honorable Mention Shotcrete Project – 2016
Rehabilitation and Repair Construction Project
The Pacific
The Pacific, at 2155 Webster St. in San Francisco, is a concrete building with two levels below grade and nine levels above grade with a total of over 250,000 sf (21,925 m2) of usable space. The building was constructed and completed in 1967 and has spent most of its life as the University of Pacific School of Dentistry with the school moving in to a new location 2014. In the past several years the building was repurposed by converting the building into seventy seven condo units and ten townhomes.
As part of the repurposing of the project the existing façade of precast concrete was removed thus providing full height windows. This lightened the building considerably, but it also lost some of its structural strength and rigidity from the precast being removed. As part of the redesign and bringing the building up to current seismic codes the building required extensive new redesigning of the shear walls as well as column reinforcement. The additions to the shear walls were between 8” (20 cm) to 18” (45 cm) thick with typical field reinforcement of #7 (#22 metric bar ) bars at 6” (15 cm) on center with various boundary element conditions. In addition all of the columns that were not encased in existing or new shear walls were jacketed in shotcrete with typically over twenty columns per floor. Overall the project consisted of over 1,750 cy (1,338 m3) of shotcrete and 65,000 sf (6,039 m2) of surface area.
One of the difficulties of the project was coordination but this also provided one of the strengths of shotcrete. Due to existing site conditions there were a lot of redesign issues as well as wall modifications due to existing conditions not being plumb and straight. Because of the flexibility of shotcrete we were able to increase the wall thicknesses in areas to get the proper reinforcement clearances as well as moving from different walls, sometimes at the last minute, because certain walls were not signed off due to unanswered questions or new discoveries dealing with existing conditions. Also due to minimal formwork that is required by shotcrete the other trades were able to work above the walls up to the just before shotcrete operations started which would not have been possible with a standard cast in place operation. This included modifications of the reinforcement and demolition that could occur up the time that shotcrete started on that particular wall. Due to this flexibility the schedule of the General Contractor was significantly less impacted by these changes then would have occurred under a cast in place operation and the formwork not starting until all issues were resolved or the formwork having to be removed when additional issues arose.
One of the requirements of the project was the Owner’s desire for LEED certification. One of the ways that shotcrete was able to help their desire is by the use of slag and fly ash in the shotcrete mix. The design strength of the shotcrete was 6,000 psi (41.4 MPa) and the final shotcrete mix used a 45% replacement of the cementious material with 30% slag replacement and 15% fly ash replacement. Because of the high replacement the shotcrete mix was very difficult to pump, but with the use of pumping aids, such as Rheomac VMA, we were still able to get a production rate of over 90 cy (69 m3)per shift through over 500 lf (152 m) of system. The owner also had a concern for cracking in all of the concrete surfaces so this issue was resolved by using a shrinkage admixture, Masterlife SRA. Shrinkage tests were not performed on the project, so it is not known how much of a benefit the admixture provided, but the owner was very satisfied with the results.
The largest issue on the project that shotcrete was able to solve is with site logistics. The project is located in a very congested part of San Francisco with narrow streets, a lot of vehicles and pedestrian traffic, and numerous local businesses. When the project was bid it was bid under the conditions of using Sacramento St. (the long axis of the project) and Webster St. (the short axis of the project). However by the time that DHI’s portion of the work began the project only pumping location was from Webster St., which happens to be the narrower of the two streets. The General Contract had numerous difficulties through out the project with all of their pours because of this narrowness of the street and numerous times had to perform off shift pours due to space and traffic limitations. Due to the smaller footprint of a shotcrete operation we were able to easily slide into the single parking lane that was available and be able shotcrete the entire project from the far end of the project. As mentioned before some of the pumping distances were up to eight stories up (because of the slope gradient) and across the entire long length of the building for a total pumping distance of over 500 lf (152 m).
The Pacific was a difficult project to work through and had many issues that had to be resolved. Shotcrete was able to solve several of these issues and with the Owner, General Contractor, and DHI working together we were able to make this a mutually successful project for a building that has already served for fifty years and is ready for its next season of service.
Project Name The Pacific
Project Location 2155 Webster St., San Francisco, Ca
Shotcrete Contractor Dees Hennessey, Inc.
General Contractor Plant Construction Company
Architect Handel Architects
Structural Engineer Holmes Culley
Material Supplier Central Concrete
Project Owner Trumark Urban
Author
Jason Myers graduated from California Polytechnic University at San Luis Obispo in 1995 with a Bachelor’s Degree in Civil Engineering and from Golden Gate University in 2015 with a Master’s In Business Administration with an emphasis in Project Management. Jason started out his professional career working for an earth retention subcontractor where he learned the importance of budgeting, scheduling, and client relationships. Also during this time he was introduced to the use of shotcrete and its applications. After working for a General Contractor for a couple of years he realized that he enjoyed the tighter knit of working for a subcontractor and the ability to construct projects on a tighter time frame with several going at once. Jason also enjoys the process of handling most of the procedures that go into constructing a project rather then seeing only a small portion of the process. Jason joined Dees Hennessey in 2004 and has been a part owner of the company since 2007. Jason currently serves as the Vice President of Operations as well as the safety director.
