Feasibility Study--Technical Report on Air Rights Development over the Dulles Corridor, Appendices A and B

8/7/2019 Feasibility Study--Technical Report on Air Rights Development over the Dulles Corridor, Appendices A and B

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APPENDIX A

AIR RIGHTS FEASIBILITYSUMMARY OF TECHNICAL FINDINGS

January 28, 2011

This summary provides a brief update on the study related to the technical feasibility of air rights in theDulles Corridor and to evaluate the level of investment required (if any) concurrent with the Phase 2 railconstruction in order to not preclude future air rights development. This study was authorized by theAirports Authority for Dulles Rail Consultants to prepare the technical analysis and resulted in a finalreport delivered in November 2010. The following outlines the basis for the evaluation and summaryfindings:Basis of Design Concepts and Technical Evaluation

. The Reston Parkway Station was selected as the prototype Phase 2 station location selected forthe air rights evaluation based on its proximity to Reston Town Center and other commercialdevelopment and interest expressed by the Reston community and Fairfax County in this location.

. Three initial locations for the air rights deck location (see Figure 1) were developed including:o Air Rights Deck Directly Over the Reston Parkway Stationo Air Rights Deck Straddling Reston Parkwayo Air Rights Deck West of the Reston Parkway Station

. The DRC team utilized the prior work developed by Davis Carter Scott (DCS) and structuralengineer Fernandez Associates Structural Engineers (FASE) which had designed a structuralframing system that would permit construction of an air rights deck while maintaining Metrorailand vehicular operations on the DTR/DIAAH below.

. The underlying premise of the framing concept is the installation of a continuous reinforcedconcrete footing/foundation system supported by a series of auger-driven piles following eachside of the Metrorail right-of-way with a pier cap/barrier wall that serves as the guide for thetravelling form system. This permanent foundation system and barrier wall (indicated as Stage 1 inFigure 2) would be installed as part of the Phase 2 project and would serve as the perimeter wallsfor the rail right-of-way. Stage 2 would be installed when the future air rights deck would beconstructed, and Stage 3 when the future air rights development would be built. A similarfoundation system would be installed at a future date below the Jersey barrier walls between theDIAAH and the DTR and along the outside property lines of the DTR.

. The framing system for construction of the air rights deck consists of a series of collapsiblemodular forms that would travel along the existing barrier wall system to be built as part of theinitial Phase 2 construction along the site of the future air rights deck. The air rights deck would bebuilt in 3D-foot segments spanning between 50 and 60 feet depending on the location of thefoundation system (see Figure 3).

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. The original study concept design included minimal span lengths for the air rights deck framingsystem of 60 feet on 30 foot centers over the Metrorail right-of-way. This concept requiredinvestment in the foundation system as part of the Phase 2 project that would not preclude futureconstruction of air rights development, since there are insufficient clearances adjacent to theactive railroad to construct a foundation system at a future date. Cross sections showing theoriginal design concept are shown in Figure 4.

. The alternative design concept provides a clear span over the Metrorail right-of-way for an airrights deck framing system, with 150 foot spans on 30 foot centers. The alternative designreduces (or rather eliminates) the initial investment required as part of Phase 2 to not precludefuture air rights development. The system of Jersey barriers being used to build Phase 1 of theDulles Corridor Metrorail project along the DIAHH median would be used for this construction.Temporary shutdowns of the operating railroad would be necessary during off hours and selectedweekends for placement of structural beams and building the initial parking deck slab. Once theinitial deck is in place, construction can continue without any disruption to rail operations. A crosssection showing the alternative design concept is shown in Figure 5, with a rendering of thealternate concept shown as Figure 6.

Summary of Findings. Based on the analysis described above, it was determined that using a long span structuralframing and foundation system would not require any additional investment in the Phase 2

Metrorail Project:o The cost premium associated with the alternate concept with the framing systemfeaturing longer lSD' spans and building the basic air rights deck at a future date over

the operating railroad is approximately 30 percent greater than the original conceptfeaturing 60' spans and building the initial substructure concurrent with Phase 2.o Building the 60' span framing and foundation system as part of Phase 2 would still resultin having to shut down rail operations intermittently after hours and on weekends to

build the balance ofthe air rights at a future date.o Building the lSD' span over Metrorail at a future date would also result in having to shutdown rail operations intermittently after hours and on weekends to build the air rights

deck.o For either span concept, lane closures would stil be required for construction of the

balance ofthe foundation systems between the DIAHH/DTR and the outside lanes andshoulder of the DTR

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Figure 1: Air Rights Deck Location Options at Reston Parkway Station

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Station~~ Cross Section A Cut Location (see Figure 21Cross Section B Cut Location (see Figure 21.3

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Figure 2: Typical Foundation and Column/Bent Frame Design Concept

FUTUREAIR RIGHTS

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Figure 3: Foundation System Elements

Phase 1

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Figure 4: Original Design Concept with 60' Spans

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Feasibility Study--Technical Report on Air Rights Development over the Dulles Corridor, Appendices A and B

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