Park My Viaduct: Alaskan Way Elevated Park

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3 Revision Description Issued by Date Checked 00 Feasibility Study of Viaduct Davood Liaghat 8 May 2015 KA This report has been prepared for the sole benefit, use and information of Park My Viaduct Kate Martin for the purposes set out in the report or instructions commissioning it. The liability of Buro Happold Limited in respect of the information contained in the report will not extend to any third party. author Davood Liaghat signature date 8 May 2015 approved Kate Ascher signature date 8 May 2015 Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 3

4 Section Ref Author Date Full document DL 8 May 2015 Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 4

5 Team Client Park My Viaduct Kate Martin Project Principal BuroHappold Engineering Kate Ascher Project Director BuroHappold Engineering - Davood Liaghat Architect Donald Macdonald Architects Don Macdonald Cost & Construction Advisor The National Constructor s Group - Paul Silvestri Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 5

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7 Contents 1 Executive Summary 13 2 Introduction Background Aim of Project Purpose of this report 17 3 Workshop in Seattle and site visit 18 4 Design Development and structural options Introduction Base unit of existing viaduct Option 1: Double deck truss Option 2: Single deck truss Option 3: Moment frame Option 4: New design Bents Structural Analysis Idealization of the structure Structural performance of the retrofit options Structural Performance of a new bridge Modal analysis Summary 28 5 Seismic Retrofit Strategy Introduction Foundation issues Foundation retrofit strategy Column retrofit strategy Lower Deck Strategy Lower Deck Longitudinal and Transverse Beam Strategy 31 Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 7

8 5.7 Upper Roadway Strategy Upper Roadway Longitudinal and Transverse Beam Strategy General Seismic Retrofit Comments 32 6 Construction Cost Estimate Introduction Conceptual Construction Cost Estimates Summary of the Conceptual Construction Cost estimate for Project Alternatives #1 and # Construction Schedule Introduction Program Development Costs Suggested Project Delivery Strategy Program Risks Program Opportunities 37 8 Other considerations Access and circulation for pedestrians and bikes Surfaces Graded routes Stairs Elevators Segregation People and Bike Movement Levels of comfort Design competition/outreach 41 9 Conclusion 42 Appendix A Workshop in Seattle Appendix B Site Visit Appendix C Drawings Appendix D Structural Analysis of Viaduct and Options Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 8

9 Appendix E Cost Estimate Appendix F Construction Schedule Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 9

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11 Glossary Term Definition Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 11

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13 1 Executive Summary The Alaskan Way Viaduct is currently a concrete bridge in Seattle running along the waterfront on the west side of Downtown. There is an aspiration to create a mile-long elevated park that would preserve public access to the spectacular 360-degree view currently available from the upper deck of the Alaskan Way Viaduct. Portions of the Alaskan Way Viaduct are proposed to be converted to a linear park (similar to the High Line in New York City). The proposal commences on the northern segment of the Alaska Way Viaduct at Bent 60 between Pine and Pike Street, progresses to Bent 121 parallel to Dearborn Street, then extends on a new alignment to a terminus in close proximity of the athletic stadiums. This report is the engineering and cost estimation chapters of a feasibility study for the realization of the park. It also covers the delivery program and schedule of construction. A team led by BuroHappold Engineering studied a number of options for the structure that would be required to support the elevated park, ranging from seismic retrofitting the existing structure to constructing a new garden bridge. A detailed assessment of the cost of several options was carried out. Two preferred alternatives were presented: Alternative No. 1 (see illustration) Consisting of the following scope of work: Existing structure retrofit as a single deck moment frame 1,600 lf New structural design (cast in place concrete box girder) 3,000 lf Bent 60 to 55 Optional Retrofit 400 lf A pedestrian/cycle bridge at Union Street The cost of construction this alternate was estimated to be $262m. The schedule for this alternative commencing with the Request for Proposals and proceeding through completion of construction, is 32 months. Alternative No. 2 (see illustration) - Consisting of the following options: New structural design (cast in place concrete box girder) 4,600 lf Bent 60 to 55 Optional Retrofit 400 lf A pedestrian/cycle bridge at Union Street The cost of construction for this alternate was estimate to be $165m. The schedule for this alternative commencing with the Request for Proposals and proceeding through completion of construction, is 41 months. Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 13

16 2 Introduction 2.1 Background The Alaskan Way Viaduct is a concrete bridge / by-pass route (see Figure 1) in Seattle. It runs along the waterfront on the west side of Downtown. Built in two phases in the early 1950s it is approximately 50 wide and 55 high with a northbound upper deck and a southbound lower deck. The Seattle Transportation Department built the north segment from Battery Street to Dearborn Street and Washington State Transportation Department built the south segment, which has already been removed, south of Dearborn St. a few years later. In the 1960s, downtown on and off ramps were added at Seneca St and Columbia St. Figure 1 Alaskan Way Viaduct, Seattle, WA The viaduct was constructed so that traffic on State Highway 99 could by-pass the congestion of the surface streets on the west side of downtown Seattle. It is owned by the State of Washington and is reported to have had many structural and seismic problems as well as neglected maintenance issues. A number of studies (e.g. TY Lin s report of June 28, 2001 on Structural Sufficiency) have considered options to stabilize, update and restore it for continued longterm use as a highway. A related problem has been the nearby aging seawall - less than 100 west that threatened to give way during a storm surge and take the viaduct with it. Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 16

17 Over many years, government agencies and debated whether to retrofit and restore the viaduct for continued highway use, build a tunnel to replace it or move the traffic to surface routes. In 2009, it was decided to build a deep bore tunnel and subsequently take the viaduct down. The tunnel is currently under construction but the boring machine Bertha has broken down and requires repairs. Meanwhile, construction of the new seawall continues. 2.2 Aim of Project The aim of this project is to create a mile-long elevated park that preserves public access to the spectacular 360- degree view currently available from the upper deck of the Alaskan Way Viaduct. The 5-acres of car-free open space from Pike Place Market (north) to the stadia (south) would serve pedestrians, slow-moving cyclists and dogs. Proponents of the Alternative Waterfront Vision, that includes the elevated park, have brought experts together to undertake a Feasibility Study that investigates many aspects of the proposal including Engineering, Construction + Costs, Planning + Design, Economic, Environmental and Socio-Cultural Benefits, Finance and Legal + Legislative Issues. The team responsible for carrying out the Engineering, Construction + Costs chapter of the Feasibility Study is led by BuroHappold Engineering (New York, NY and London, UK) and assisted by Donald Macdonald Architects (San Francisco, CA) and The National Constructor s Group (Napa, CA). The team has studied a number of options for the structure required to support the elevated park ranging from retrofitting the existing structure to constructing a new garden bridge. 2.3 Purpose of this report The purpose of this report is to carefully assess the following criteria and to enable the development of feasible viaduct retrofit and new designs. This report will provide a detailed basis for design and development of the project should a decision be taken to proceed. It assesses the following criteria: Structural solutions Seismic retrofit strategy Cost estimation Construction Schedule Access and circulation of bikes and people Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 17

18 3 Workshop in Seattle and site visit A workshop was held in Seattle on October 17 th, 2014 for team and project introduction, review of objectives of the project and exploration of initial ideas for the retrofit of the viaduct. It was followed by an evening meeting with community members and activists interested in this project. The minutes of this workshop are attached in Appendix A. The discussion covered a number of areas: Access and circulation for bikes and pedestrians Landscaping and degree of soft and hard landscaping Structural options Drainage Services Stakeholder consultations and outreach Program for delivery of study In order to understand the site constraints and assess the condition of the existing viaduct, an initial examination and walkover of the existing Alaskan Way Viaduct was carried out on October 17 th and 18 th 2014 over a nearly mile-long stretch of the structure from the stadia in Pioneer Square / SODO (south) to Pike Place Market (north). Details of this visit are provided in Appendix B. The main conclusions from the site visit were: The viaduct is generally in a good condition. Certain elements of the viaduct have undergone some damage due to the 2001 Nisqually earthquake. It appears that these areas, including some columns, have evidently been seismically retrofitted. Some upper deck beams are being repaired. Both upper and lower decks of the viaduct are showing signs of crack, water leakage and leaching but this is to be expected of a structure of this age (over 60 years). Under the lower deck, the structure is carrying an array of services and cables which will need to be relocated in any retrofit, remedial or replacement works. There are a number of strategic locations along the viaduct, and in particular at Union Street, where a pedestrian link to the viaduct could be considered to improve permeability and accessibility. At certain locations along the viaduct, columns are in very close proximity to existing buildings along Alaskan Way. This will necessarily have some impact on construction works to the viaduct. The current drainage from the viaduct is via pipes which run down columns and into the ground. Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 18

19 4 Design Development and structural options 4.1 Introduction Five structural analyses of a typical unit of the Alaskan Way Viaduct were carried out. Four models have been prepared: a. Basic un-strengthened unit (used as a benchmark) b. Option 1 Retrofit Double Deck Truss Frame c. Option 2 Retrofit Single Deck Truss Frame d. Option 3 Retrofit Moment Frame e. Option 4 New design - Single pier option (cast in place and precast) A simple Finite Element frame model of the unit has been made using structural analysis program MIDAS employing beam and plate elements to model the beams, columns and the deck of the viaduct for the base model and options 1, 2, and 3. Structural program ROBOT was used for option 4. The models were analysed under static loading, wind loading and seismic in accordance with loadings from AASHTO. AASHTO load combinations were used in assessing the strengthening requirement of the viaduct. Modal analyses were also carried out to assess the pedestrian comfort and vibration levels. The assessment was done on the superstructure from an engineer s point of view only. Other important aspects such as foundation, construction program and cost have not been addressed yet. Stair/elevators are also excluded. Drawings of the base unit and all the options are given in Appendix C and a full report of the analysis of them is given in Appendix D Base unit of existing viaduct The typical unit consists of 3 bays with a total length of 184 made from reinforced concrete. The width is about 50 7 ¼. The top deck is about 55 above ground. The deck is made up of five concrete beams in the longitudinal direction with transverse beams spaced at about 14. The breakdown dimensions for each element shown are extracted from the drawings held by Washington State Department of Transportation. These dimensions are used to set up the base models and options 1, 2 and 3 models. Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 19

20 Figure 2 Typical Unit Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 20

21 4.1.2 Option 1: Double deck truss This option is similar to the Gray s retrofit proposal (July 2006) for upgrading the existing viaduct. The base unit is modified with new bracings in the lower deck. Figure 3 Option 1 Double deck truss frame retrofit Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 21

22 4.1.3 Option 2: Single deck truss The existing base unit is modified with new bracings in the upper deck. The lower deck is being removed. Figure 4 Option 2 - Single deck truss frame retrofit Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 22

23 4.1.4 Option 3: Moment frame In this option the existing frame is strengthened (moment framed) by installing HSS (Hollow Structural Sections) or I-shape beams. Figure 5 Option 3 Moment frame retrofit Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 23

24 4.1.5 Option 4: New design The new design is assumed to consist of a single pier and a deck beam made entirely from reinforced concrete. The pier is a hollow concrete box. The deck beam is a concrete box with internal diaphragms. The pier is spaced at 100 and the deck is 56 6 above ground. Typical unit is shown in figure below. Figure 6 Option 4 New design Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 24

25 4.3 Bents At Bents 55 to 60, where the southbound lanes of Highway 99 pass under the northbound lanes west of Pike Market, there are six architecturally interesting outriggers where the beams supporting the upper deck stretch out over the southbound lanes just north of where the structure becomes a double-deck highway (see Figure below). It is this 400 long section of the viaduct that the project proponents recommend for preservation in its entirety. The structural conditions are unique to this section and are not explored in the scope of this study. Placeholder costs for retrofitting this section are, however, included in the estimates along with assumptions about for how the retrofit would be achieved. Figure 7 Viaduct at Bents Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 25

26 4.4 Structural Analysis Idealization of the structure The idealized Finite Element model for the base model and the options are shown below. Figure 8 Base Model Figure 9 Option 1 - Double deck truss frame retrofit Figure 10 Option 2 - Singled deck truss frame retrofit Figure 11 Option 3 Moment frame retrofit Figure 12 Option 4 New design Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 26

27 4.4.2 Structural performance of the retrofit options Given the limited scope of this project, the process selected for making structural performance comparison between the base unit and the options is: a. Obtain the load effects for the beams, columns and deck under dead load, pedestrian live load, superimposed dead load, wind and seismic loads and the load combinations to American Association of State Highway and Transportation (AASHTO) for the analysis. b. Compare options 1, 2 and 3 with the base unit by considering the ratio for corresponding load effects and structural members to determine vulnerable sections of the viaduct. The results are imported into a spreadsheet. Load effects for each of the options are compared by dividing the option figure over the base figure. Ratios greater than 1 are potential deterioration caused by the options. Below is a summary of the number of areas in which strengthening is required under each of the options: Option 1 Option 2 Option 3 Upper Lower Lower Deck Lower Deck deck deck Marginal required Requires strengthening Strengthening not required Of the three options, option 3 repair can be targeted to areas that require strengthening while the other two only address the global repair and do not relate to local repairs. Since the degree of damage caused by the past earthquake events is not known, there is a risk that the existing structure is beyond repair or strengthening associated with these options. Extensive investigation will be required Structural Performance of a new bridge The design load effects for option 4 are obtained. The reinforcement content for the deck and pier are estimated using AASHTO design guidelines. They are 2.8% and 3.5% for the deck and pier respectively. Since this is a new build, investigation on existing structure is less intense than the retrofit options. Nominal investigation is required for demolition purpose Modal analysis Since the retrofit and options for the bridge are primarily for pedestrian and cycle use, there needs to be an assessment made of the dynamics of the bridge for the intended use. The bridge has been designed for vehicles and the acceptable vibration and comfort criteria are different from that required by pedestrians. The first stage in this analysis is to calculate the natural frequency of the first few modes of vibration of the structure. These have been compared with US and European standards and in general were found to be satisfactory. In simple terms, the change use would not have detrimental effect on the viaduct and the users. Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 27

28 4.4.5 Summary The findings of this assessment can be summarized in the table below: Option 1 Retrofit Double Deck Option 2 Retrofit Single Deck Option 3 Retrofit Moment Frame Option 4 New Design Single Column Demolition None Lower deck Lower Deck Complete superstructure Foundation + Retrofit & strengthening Retrofit & strengthening Retrofit & strengthening New (piled) Seismic Investigation New structural material Extensive Extensive Extensive Nominal In terms of retrofit, more than 2 and 3 In terms of retrofit, least of all options In terms of retrofit, less than option 1 and more than 2 but can be targeted Complete new superstructure and foundation Structure form Needs modification to accommodate stairs, planters and elevators, handrails and parapets Needs modification to accommodate stairs, planters and elevators, handrails and parapets Needs modification to accommodate stairs, planters and elevators, handrails and parapets Efficient form can be developed Residual Risk * High High Nominal Not applicable + This assessment is made purely qualitatively at this stage * Option 3 repair can be targeted to areas that need strengthening and hence the residual risk is less. From the table above (notwithstanding costs), option 4 (new design) and option 3 (moment frame) forward are preferred because: Option 4 is least reliant on the existing structure and minimizes the risk of redesign if the existing structure is weaker than expected. Option 3, among the three retrofit options, carries least risk. Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 28

29 5 Seismic Retrofit Strategy 5.1 Introduction The documents listed below have been reviewed by the National Constructor s Group for the purpose of developing a conceptual seismic retrofit strategy for the portion of the Alaskan Way Viaduct proposed to be converted to a park. The seismic retrofit strategy of this report addresses each of the structural elements discussed in the reviewed documents, providing a solution for each of the structure elements. No. Title Author(s) Pages 1 Alaskan Way Viaduct, Report of the Structural Clark, Gerwick, Goodyear, Grant, Mast, 37 Sufficiency Review Committee 2 Alaskan Way Viaduct, Phase 1 Retrofit Option, April 24, 2002; and cover letter from committee chair Theodore Bell, July 12, 2002 Stanton ASCE Expert Team: Arnold, Baska, Bell, Locke, Mageau, Myhre, Sand, Scott, Symonds, Tuttle, Upeahi 11 3 Rebuild/Retrofit Alternative Report Parsons Brinckerhoff Quade and Douglas, Inc. 47 Analysis Method Base Isolation Retrofit Approach Appendix C Joint Shear Analysis of Double Deck Beam Column Construction Typical Double Deck Frame Analysis 4 Preliminary Deep Foundation Engineering Analyses, Existing Piles, Alaskan Way Viaduct Project Shannon & Wilson 12 5 Rebuild/Retrofit 500 Executive Summary, 500 year Design Earthquake Parsons Brinckerhoff Quade and Douglas, Inc. 8 6 Rebuild/Retrofit 500, 500 year Design Earthquake Parsons Brinckerhoff Quade and Douglas, Inc Alaskan Way Viaduct Summary: Safety and Services Limitations of the Alaskan Way Viaduct T.Y. Lin International 5 8 Proposed Retrofit of Alaskan Way Viaduct Using Fluid Viscous Dampers: Preliminary Phase Miyamoto International, Inc. 23 Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 29

30 9 Alaskan Way Viaduct, Evaluation of Gray s Retrofit Proposal (with November 2006 addendum, Additional Retrofit for Gray s Modified Proposal) T.Y. Lin International Cost Report: AWV T.Y. Lin Retro Ken Florentino, Jacobs Civil Seismic Vulnerability Analysis Report PB, Inc Seismic Vulnerability of the Alaskan Way Viaduct Summary Report University of Washington: S.L. Kramer, M.O. Eberhard Evaluation of Seismic Retrofit Options FPFF Engineering 22 The seismic retrofit strategy for the individual structure members has either been extensively utilized by the Departments of Transportation in the states of California and Washington or recommended in various literature sources by structural engineers considered to be experts in the field of seismic engineering. The spans of the Alaskan Way Viaduct currently proposed to be converted to a park begin at Bent 53 between Pine and Pike Street to Bent 21 parallel to Dearborn Street. This includes the horizontal curve at the south end of the existing viaduct. It should be noted that the horizontal curve has been rated as high risk in the documents reviewed. It is suggested that in future the strategy for the curved portion of the viaduct be analyzed independent of the northern portion of the project. The current Phase 1 reconstruction of the seawall begins at Virginia Street and proceeds south, parallel to South Washington Street. The planned completion for Phase 1 is Spring The potential Phase II portion begins at the Olympic Sculpture Park and proceeds south to connect with the Phase 1 seawall at Virginia Street. The potential completion of Phase II is 2019/2020. A seawall south of Washington Street is not currently planned for construction. South Washington Street is approximately adjacent to Bent No. 95. The seawall construction ties to the details of the seismic reports indicating that the area south of Washington Street is of high risk. It is recommended that the Park My Viaduct project not be involved in constructing a seawall that would depend upon approval by the railroads and the Port of Seattle. If it is desired to go to the stadium, that portion of the park viaduct should be a new structure founded on a single column. 5.2 Foundation issues The previous reports identify the following issues in relation to the foundation of the viaduct; Liquefaction of surrounding soils Condition of the existing seawall Shear capacity of the existing foundation pile Shear capacity at interface of the existing concrete footing and column (reinforcing steel capacity) Deck and live load capacity of existing pile (settlement) Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 30

31 5.3 Foundation retrofit strategy A new seawall is currently under construction, which minimizes the concern of liquefaction in the area of the proposed viaduct park. It is worth noting that the seawall ends at S Washington St because south of that point Option 1, 2 and 3 are not viable. The placement of additional foundation drilled shafts and the encapsulation of the existing concrete footings limit any exposure and avoid the risk of catastrophic failure of the foundations. The current foundation retrofit strategy is to construct a 10 0 diameter drilled shaft outside of each footing, approximately 135 in length and tip grouted. The drilled shaft and the existing concrete footing will be totally integrated into a new concrete footing block including ± 2 0 above the existing footing to provide for required column reinforcing steel embedment. 5.4 Column retrofit strategy The existing column remains in place. A steel jacket will be placed around the column (standard seismic retrofit procedure) and the column dimension will increase approximately 1 0 on each side, providing for #14 reinforcing steel bars with seismic requirements of length into the transverse and longitudinal beams shear keys will be constructed in the existing columns. The steel plate jacket will be 0.5 in thickness with vertical steel bonding strips. 5.5 Lower Deck Strategy The lower roadway will be removed between the transverse and external longitudinal beams. The removal process will require temporary falsework and sawing of the deck element into sections, which will be removed. 5.6 Lower Deck Longitudinal and Transverse Beam Strategy The existing structural section of the longitudinal and transverse beam will be embedded into a new concrete encasement. The new concrete encasement will include containment reinforced steel as well as post tensioning ducts, strands, trumpets, and stressing load reinforcing steel. The existing beams will have shear rock pockets ground into the existing concrete, spalled concrete will be removed and the surface cleaned. The legs of column rebar will extend as seismically required into the beams. A similar procedure was utilized on the modification to the San Francisco Oakland Bay Bridge when the lower deck was modified from streetcars to cars and trucks in the 1950s. The procedure is not new. 5.7 Upper Roadway Strategy The existing roadway will remain in place with the exception of deck areas to be removed for planting. The remaining deck will be cleaned, cracks will be epoxy injected, and spalled concrete will be removed and cleaned. Upon completion of the deck preparation, a preservation coating will be placed. The existing rail will be modified for code requirements or replaced. 5.8 Upper Roadway Longitudinal and Transverse Beam Strategy The strategy will be similar to the lower roadway, in that geometric complexities will occur where the deck intersects with the beams. These areas will require individual detailing; however, the fundamental concept of post tensioning will be employed as well as the beam to column knee and tee reinforcing steel details. Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 31

32 5.9 General Seismic Retrofit Comments A) Chlorine deterioration of concrete (e.g. reinforcing steel corrosion) is undefined as to location. Samples have been taken and the results have found two pounds of chlorine per cubic yard of concrete, whereas the threshold is 1.4 pounds per cubic yard. This problem is removed for the columns and beams by the complete encasement of the existing concrete. The issue thus becomes the upper deck, which will require further chlorine content testing, visual inspection, and surface repairs (which may include partial removal and replacement). If it becomes apparent that sections of the upper roadway require replacement, a solution would be the utilization of precast concrete double tees as a replacement procedure. B) It is assumed that Seattle Light and Power is relocating its power ducts attached to the Alaskan Way Viaduct as required when the viaduct is removed and should not be considered a cost to the Park My Viaduct project. C) Consideration of base isolation as a seismic retrofit strategy was analyzed within the documents review. The findings were extremely clear that the existing structure is not sufficiently stable to transfer the seismic loading to a base isolation system. D) As the project progresses, testing of various elements of the concrete would prove to be beneficial: Strength testing of various elements of the structure Core borings to determine the bond conditions between the reinforcing steel and concrete Chlorine testing of columns/bents E) A pending issue is the development of a strategy relative to the open 2 expansion joint. This may prove to be very complex, but a solution can be developed. Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 32

33 6 Construction Cost Estimate 6.1 Introduction Portions of the Alaskan Way Viaduct are proposed to be converted to a park (similar to the High Line in New York City). The proposal commences on the northern segment of the Alaska Way Viaduct at Bent 60 between Pine and Pike Street, progresses to Bent 121 parallel to Dearborn Street, then extends on a new alignment to close proximity of the athletic stadiums. The plan originally included the horizontal curve at the south end of the existing viaduct. It should be noted that in the documents reviewed, the horizontal curve has been rated as high risk. It was suggested that the strategy for the curved portion of the viaduct be analyzed independently of the northern portion of the project. The current Phase 1 reconstruction of the seawall begins at Virginia Street and proceeds south, parallel to South Washington Street. Completion of Phase 1 is planned for Spring The potential Phase II portion begins at the Olympic Sculpture Park and proceeds south to connect with the Phase 1 seawall at Virginia Street. The potential completion of Phase II is 2019/2020. A seawall south of Washington Street is not currently planned for construction. South Washington Street is approximately adjacent to Bent No. 95. The seawall construction ties to the details of the seismic reports indicating that the area south of Washington Street is of high risk. It is recommended that the Park My Viaduct project not be involved in constructing a seawall that would depend upon approval by the railroads and the Port of Seattle. If it is desired to go to the stadium, that portion of the park viaduct should be a new structure founded on a single column. Bents 60 to 55 (a 400 lineal foot section) of the Alaskan Way Viaduct is a section that project proponents recommend for preservation in its entirety. Therefore, its retrofit strategy has been developed to maintain consistency with the existing geometry and surface texture. A full assessment of the cost of the various options in section 3 of the report has been completed. This is included in Appendix E. The following is a summary of this assessment. 6.2 Conceptual Construction Cost Estimates Conceptual construction cost estimates have been developed for the following structural options, as defined in Section 3 Design Development and Structural Options: Option #3 Existing structure retrofit as a single deck moment frame for a length of 1,600 lineal feet Option #4 New Structure Design a. As a cast in place concrete box girder for a length of 3,000 lineal feet b. As a cast in place concrete box girder for a length of 4,600 lineal feet Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 33

34 Option #5 retrofitting the existing structure consisting of straddle bents 60 to 55, for a length of 400 lineal feet Additional Item A Union Street Bridge It should be noted that for Option #1 Retrofit/Double Deck Truss Frame, and Option #2 Retrofit Single Deck Truss Frame, a detailed conceptual construction cost estimate was not developed due to the high residual risk and extraordinary cost. When Options 1 and 2 are compared with the scope of work and cost of Option #3, it is apparent that Options 1 and 2 are neither economically or environmentally feasible. 6.3 Summary of the Conceptual Construction Cost estimate for Project Alternatives #1 and #2 The extent of Alternatives #1 and # 2 are shown graphically in Appendix C. Alternative No. 1 (see Figure below) Consisting of the following scope of work: Option #3 Existing structure retrofit as a single deck moment frame 1,600 $90,902 $145,443,308 Option #4(a) New structural design (cast in place concrete box girder) 3,000 $30,780 $92,339,903 Option #5 Bent 60 to 55 Optional Retrofit 400 $48,524 $19,409,793 Additional Item A Union Street Bridge 15,000 $300/sf $4,500,000 Total Conceptual Construction Cost for Alternate #1 $261,693,004 Figure 13 Alternative #1 Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 34

35 Alternative No. 2 (see Figure below Consisting of the following options: Option #4(b) New structural design (cast in place concrete box girder) 4,600 $30,780 $141,280,052 Option #5 Bent 60 to 55 Optional Retrofit 400 $50,980 $19,409,793 Additional Item A Union Street Bridge 15,000 $300/sf $4,500,000 Total Conceptual Construction Cost for Alternate #2 $165,189,845 Figure 14 Alternative #2 Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 35

36 7 Construction Schedule 7.1 Introduction A conceptual construction schedule for each of the two separate structural alternatives that are currently offered to Park My Viaduct has been prepared, see Appendix F. The schedule for Alternative #1, commencing with the Request for Proposals and proceeding through completion of construction, is 32 months. The schedule for Alternative #2, commencing with the Request for Proposals and proceeding through completion of construction, is 41 months. The recommended program delivery strategy is a conventional design build construction contract. The logic for the recommended design build delivery is that it provides the shortest overall duration from approval to proceed to project completion. The critical issues with Alternative #1 are the unknowns associated with retrofitting a significant portion of the existing viaduct. Foundation construction is always a risk concern. However, in this situation, extensive knowledge of the area has been developed from the ground support system construction for Washington State DOTs Alaska Way Tunnel, which is partially adjacent to the proposed park viaduct. Alternative #2, however, not only greatly reduces the cost, but it also reduces the retrofit risk. 7.2 Program Development Costs Public Information Workshops Conceptual Development Cost Preliminary Engineering Legal Expense Property clearance Property exchange existing facility Establishment of non profit for long term maintenance (if City requires) Agreement negotiations (scope of work) Surface reconstruction assumed to be part of City s Waterfront Rehabilitation Program Ballot cost if goes to public vote Contract documents (design/build project delivery strategy) Final design (included with design build procurement) Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 36

37 7.3 Suggested Project Delivery Strategy Competitive proposals on design build delivery strategy Design build delivery strategy benefit includes schedule reduction Program delivery costs need to be developed. The construction cost estimate does not include these costs. 7.4 Program Risks Escalation Conceptual construction cost estimate based upon 2015 costs Public opinion added to scope of work City requires portion of surface area costs to be included in this project Alternative funding concepts add to the cost Non profit concept for maintenance does not prove to be a viable alternative Washington State Department of Transportation adds to the scope of work Design issue a risk with Option #4 relative to expansive opening between the structural units, requiring development of an expansion joint Condition of existing concrete requires substantial repair 7.5 Program Opportunities Alternative #2 offers the opportunity for design improvement relative to span length, superstructure type selection details, and schedule improvements Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 37

38 8 Other considerations 8.1 Access and circulation for pedestrians and bikes (Figures and dimensions in this section to be confirmed subject to review) The design of the converted viaduct must place people at the heart of the design process, responding to their diversity and differences and provided access to the full range of opportunities provided within the scheme. The success of the design will be based around choice. For instance, while elevators may be provided for wheelchair users and ambulant disabled people, some people may prefer to use gradients provided for cyclists; some cyclists may prefer to carry their bikes on the stairs rather than use any gradients provided. Elevators should be sized to accommodate a mix of users including wheelchair users, cyclists as well as ambulant users. The key element will be to ensure that when people choose to use any aspect of the viaduct approaches, they can do so safely. It is recommended that consultation with disabled people informs the planning and design process, particularly since many disabled people (and particularly visually impaired people) feel ill-at-ease when using/sharing space with cyclists. Whether the danger is real or not, there is an over-riding perception that the combination of pedestrians and cyclists is hazardous. While there are some safety concerns relating to shared space for pedestrians and cyclists, these can be mitigated through segregation and appropriate design. The use of a consultative access group can have positive outcomes in defining what constitutes best practice. A recent successful example of this is the formation of a shared surface (pedestrian/cyclists) on the Greenway serving the Olympic Park in London, UK. This Greenway sought to minimize the amount of tactile paving used to delineate bike track from pedestrian walkway but to provide clear signals to both groups of users as to where to occupy the Greenway safely, and was planned using a collaborative approach driven by consultation. There is little data available at present, but anecdotal evidence suggests that the route is popular with both pedestrians and cyclists and there are no significant safety issues associated with use of a shared surface Surfaces Surfaces are to be firm, durable and slip resistant. Where there are different materials along an access route, they should have similar frictional characteristics. Visual contrast should be established to indicate level differences; it should not be used when it may confuse people with a visual impairment Graded routes A key consideration in addressing changes in level will be to ensure that choice remains with the user. It is the nature of a bridge used by pedestrians that the changes in levels may be beyond those that are normally accepted for buildings. Elements for the approach to the bridge, such as stairs and elevators should conform, at a minimum, to the provisions of relevant municipal building regulations. Key considerations for wheelchair users would be that gradients should be as shallow as possible and that sloped elements (e.g. less steep than 1:21) are preferable to ramps (steeper than 1:20). However, having shallow gradients comes at a cost, in that the flight lengths increase and the distances to traverse become difficult because of the added travel distances. In the case of this viaduct, the ramp would have to be over 1,000 feet long to achieve a 1:20 ratio. Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 38

39 There are opportunities elsewhere to connect to the existing roads without the need for long ramps. For instance the access from Union St is nearly level and the entire park is level. The bridge is likely to be a 5 story high structure. Changes in level generally cause problems for many people, whether they are disabled, parents with buggies/pushchairs or cyclists. Mobility ranges vary enormously between individuals with age and disability, while factors such as weather, gradients and obstacles can also affect mobility ranges. Where changes in level cannot be avoided and gradients are required, they should be designed to be as shallow as possible and have appropriate handrails and surfaces. If the graded approaches to the bridge are designed in the first instance to accommodate cyclists with gradients and path widths suitable for climb and descent, as well as switchbacks (zigzag) that allow for continuous flow, then an assessment can be made in regards to the provision and incorporation of suitable resting places which balance gradients and total rise against the length of flights. The following parameters in regards to the design of gradients need to be considered: Ramps for pedestrians, cyclists and equestrians shall not be steeper than 1 in 20 unless agreed otherwise with the Overseeing Organization. For reasons of keeping the access on the desire line, or to avoid long diversions, or to avoid damage to the environment, or for reasons of limitations of space, a steeper ramp may be used, preferably no steeper than 1 in 15. However, no ramp shall be steeper than 1 in 12. Where the ramp is steeper than 1 in 20, for safety reasons there should normally be a significant change either of direction (30 degrees or more) or in horizontal alignment (e.g. offset by at least one ramp width), at an intermediate landing at every 12 feet rise of the ramp. For ramps of gradient steeper than 1 in 20, successive sloping ramps in one line may be used in agreement with the Overseeing Organization where either no other arrangement of ramps is possible on the site or where it provides more encouragement to pedestrians to use the footbridge by shortening the walking distance. Some codes also establish the need for landings, although it must be noted that for gradients less steep than 1:20 intermediate landings are not necessarily required Stairs Access stairs to bridges used by pedestrians shall comply with the dimensional and safety requirements of US and federal standards. Commonly these are some of requirements for stairs: The number of risers in a single flight shall not be more than 13 A maximum of three successive flights may be used in line, provided any adjacent flight provide a change in direction of at least 30 degrees The risers and treads of each step degrees in a flight of stairs shall be uniform Risers shall not be variable in height over their width The riser shall be not more than 6 The tread width shall be not less than 12 and not greater than 14 Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 39

40 Landing lengths shall be not less than 6.5 feet measured along the center line of the stairs, or not less than the width of the stairs, whichever is the greater Elevators Elevators should be provided in pairs in order to ensure resilience. The provision of multiple elevators in external environments has not always been successful in city environments in terms of robustness as well as resilience. This should be addressed in the design and access statement and tracked throughout the design stages as they progress. Pedestrian and traffic flow will determine appropriate minimum elevator sizes. As an initial minimum recommendation, two (4.5 x 6.5 minimum) elevators should be used at both ends of the viaduct and one in the middle. This will need to be confirmed by further work. Elevators must be orientated so that they are wide and shallow so that they will suit most wheelchair users Segregation Shared facilities may be segregated or unsegregated. The form of segregation on the structure as determined locally shall be compatible with the segregation on the approaches. Where practical, and where agreed with the Overseeing Organization, differing surface textures on segregated footways to aid visually impaired users may be continued across the structure. Segregation can increase the sense of safety, user confidence and user comfort, and it might be required for a particular scheme to operate satisfactorily. Nevertheless, segregation is not without its disadvantages, and designers need to understand them to ensure they do not outweigh the benefits. Some forms of segregation are more effective than others. A rule of thumb is that as the effectiveness of segregation increases, so do the width requirements. Main circulation routes that are specifically intended for high levels of usage by both pedestrians and cyclists will be clearly demarcated in accordance with current good practice guidance. Demarcation helps give pedestrians (in particular people with a sensory impairment) confidence to use the circulation route as it helps remove the uncertainty of use. Pedestrian and cycle numbers will determine a segregation strategy and how it is to be implemented. It would be reasonable to assume that some form of segregation may be required which might include incorporation of separate cycle and foot paths. For instance, the incorporation of a curb will give people with visual impairments an indication of the limits of the footpath and cycle way; there may be other mechanisms that convey this information and will require exploration. Again, the importance of involvement and consultation with disabled people in arriving at a solution will be critical in the success of the scheme. Whether ramps are segregated or not, for long ramps consideration should be given by the Designer to providing chicane barriers to slow down mounted cyclists. This should be done in such a way that the passage of perambulators and wheelchairs or mobility and visually impaired users would not be hindered, and should preferably be located on level landings especially where ramp slopes are not steeper than 1 in 20. It is worth noting that the intention for this park is not a route for cyclists to travel at commuter speeds, it s a greenway for slow bicycle speeds that are compatible with crowded conditions and are safe for vulnerable users including children, the disabled and the elderly, perhaps similar to Green Lake Park in Seattle. Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 40

41 8.2 People and Bike Movement Levels of comfort (Figures and dimensions in this section to be confirmed subject to review) The following table gives the level of comfort for bridges users. Bridge widths and corresponding level of service Total Walkway Cycle path LoS Description width Minimum C+ The environment is becoming increasingly uncomfortable, with the majority of people experiencing conflict or closeness with others and bi-directional movement becoming difficult. Good B Good level of service. Enough space for normal speed with some conflicts. Comfortable A- The environment is very comfortable with plenty of space for people to move at the speed they choose. Note The Level of Service (LoS) values provided are obtained using international standards for pedestrian comfort; the same methodology, has also been broadly applied to cover the cycle ways. Level of Service A, the most comfortable environment, progresses through to LoS F, which is the most congested environment. These options assessed range from LoS A to C. 8.3 Design competition/outreach This report has completed the feasibility study and has given a clear set of parameters and constraints for further development of a viaduct design. It is understood that the next stage of the project could be a design competition which would encourage design innovation and produce a range of potential bridge designs. The parameters and constraints from this report can be used to form part of the competition brief. Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 41

42 9 Conclusion The aim of this project is to create a mile-long elevated park that preserves public access to the spectacular 360 degree view currently available from the upper deck of the Alaskan Way Viaduct. The team studied a number of options for the structure required to support the elevated park ranging from retrofitting the existing structure to constructing a new garden bridge. The options were: Option 1 Retrofit Double Deck Truss Frame Option 2 Retrofit Single Deck Truss Frame Option 3 Retrofit Moment Frame Option 4 New design - Single pier option (cast in place and precast) A further component has also been proposed, although a detail structural analysis of this option is outside the scope of this project: Option 5 retrofitting the existing structure consisting of straddle bents 60 to 55 An additional item of pedestrian/cycle from Union Street to the viaduct as also considered to improve accessibility. From a structural performance point of view option 3 (moment frame) and option 4 (new design) are preferred because: Option 3, among the three retrofit options, carries least risk. Option 4 is least reliant on the existing structure and minimizes the risk of redesign if the existing structure is weaker than expected. A detailed assessment of the cost for the above was varied out. Two alternates were presented: Alternative No. 1 Consisting of the following scope of work: Option #3 Existing structure retrofit as a single deck moment frame 1,600 lf Option #4 New structural design (cast in place concrete box girder) 3,000 lf Option #5 Bent 60 to 55 Optional Retrofit 400 lf Additional Item A Union Street Bridge 15,000 sf Total Conceptual Construction Cost for Alternate #1 $262m Alternative No. 2 Consisting of the following options: Option #4 New structural design (cast in place concrete box girder) 4,600 lf Option #5 Bent 60 to 55 Optional Retrofit 400 lf Additional Item A Union Street Bridge 15,000 sf Total Conceptual Construction Cost for Alternate #2 $165m Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved. Page 42

43 Appendix A Workshop in Seattle Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved.

44 Minutes Subject Park My Viaduct Alaskan Way Place Cascade Design Collaborative (911 Western Ave, Suite 210), Seattle, WA Present Kate Martin (Park My Viaduct) Job no UK ( US) Date 21 October 2014 Apologies - Distribution As above. Kate Ascher (BuroHappold) Davood Liaghat (BuroHappold) Donald Macdonald (Donald Macdonald Architects) Paul Silvestri (The National Constructors Group) Melissa Beams (KM s shadow) Objective of meeting: Park My Viaduct project team introduction, review of project and objectives, workshop and site visit. Item Action 1.0 Integration of cyclists within the approaches to the bridge and connection to the cycle network 1.1 Engage bike lobby and enlist their support 1.2 stations along the viaduct 1.3 Park is not going to be a commuter route. It will be for recreational use, be a trail and might be segregated by lanes/patterns 1.4 Bike stations (Pronto, park your bike) Minutes taken by: Davood Liaghat

45 1.5 Rumble strips 1.6 Access from Pike Market, Union St, each end of viaduct, use existing ramps possibly 1.7 Create concept of Ride the Viaduct 1.8 Requirement of 4 6 barrier for bike rider safety 2.0 Inclusive design & accessibility 2.1 Reference to Seattle natives 2.2 Political aspects, lobby senior citizens and disabled people 2.3 ADA requirement: flat ideally but 5% max plus rest areas, use of elevators 2.4 Potential use on and off ramps to viaduct 2.5 Emergency services access: Via Union street ramp reduced to 10 wide 2.6 Pedestrian barrier 3 6, 4 max spacing for horizontals and verticals Minutes taken by: Davood Liaghat

46 3.0 People movement & wayfinding 3.1 Min width of stairway to allow crowd flow to be respected 3.2 Safe ingress and egress form Century Link (Football/Soccer ~60,000 fans) & Safeco (Baseball ~60,000 fans) stadia events, fireworks, expect full crowd loading on event days 3.3 Require signage to and from the viaduct at strategic locations along the viaduct 3.4 Access to and from stadium, Pike Market, Union St via new bridge), Washington State Ferries 3.5 Viaduct Park to be closed at night for security reasons 4.0 Landscaping/plantation 4.1 Cascading waterfall on the east side? 4.2 Vegetation/ivy hanging from the vertical columns 4.3 Use recycled rain water for irrigation 4.4 Soil requirement: low plants 12 min, high plants 24 min 4.5 Water features? % plant coverage and 70 hard landscaping 4.7 Areas for seating/congregation/game areas 4.8 Paving patterns/signature memorable, low maintenance, reference to London 2012 Olympic Park 4.9 Crack repairs to existing upper deck essential and waterproofing 4.10 Public participation/design on surface patterns on the viaduct 4.11 Art exhibits 4.12 Food stalls and kiosks 4.13 Wind features? 4.14 Trash sites 5.0 Lighting 5.1 Feature/decorative: LED on handrails, under viaduct, on the vertical columns and bents, on the deck interspersed with paving Minutes taken by: Davood Liaghat

47 5.2 Functional/safety: facial recognition, required luminosity 5.3 Alternate power sources 6.0 Spatial constraints 6.1 Suggestion in some areas to keep middle tier and connect to top deck? 6.2 Blocking/building/real estate value: Marion St, South side opportunities 6.3 Seattle steam plant/public storage alongside the viaduct 7.0 Structural assessment: Frame analysis, static and seismic 7.1 Set of drawings (hard copy) of the viaduct from state highway was handed over to Davood Liaghat (BH) 7.2 Summarise pre-nisqually and post-nisqually reports of the viaduct 7.3 High level analysis to concentrate on failure of the structural frames and failure of the foundations. It was agreed the failure caused by mass movement of the liquefied soil surrounding the viaduct following the failure of the adjacent seawall is outside the scope of this feasibility study 7.4 Process for analysis: set up a 3D wireframe model of a standalone typical 3- bay structure of the viaduct 7.5 Carry out non-linear static analysis of the existing (benchmark) and the modified structure (see options to follow) 8.0 Superstructure strengthening solutions/options 8.1 Remove lower deck, replace with a system of rigid struts either in steel or concrete. Retain top deck or replace with a new steel structure. Strengthen Minutes taken by: Davood Liaghat

48 and retrofit existing columns and column to base connection 8.2 A new supporting structure, leaving the upper deck intact 9.0 Base/foundation solution/strengthening shaft and concrete connection on one side Minutes taken by: Davood Liaghat

49 10.0 Constructability & phasing Due to high structural stability risk, according to recent report, then sequencing of constructions is vital to minimise risk of collapse: 10.1 Tunnel or diversion first 10.2 Domino construction of components 10.3 Cut out and replace elements one by one 11.0 Cost estimation 11.1 Capital cost for both options: demolition in parts of the existing viaduct. New superstructure, foundations, retrofitting, repairs to concrete, waterproofing soft and hard landscaping 11.2 Maintenance cost 12.0 Bridge maintenance and durability 12.1 Regular maintenance: waterproofing, drainage, vegetation 13.0 Structural inspection 13.1 Drive-through on 17 th October 2014 (see separate report) BH 13.2 Walkover on 18 th October 2014 (see separate report) 14.0 Other Matters These were not discussed in any detail due to lack of time but are noted here for future reference: 14.1 Identification of underground services and utilities. Chartered surveys available, buried utility scans and mapping may be required for unchartered services 14.2 Cables and services within viaduct (lower deck): relocation is required 14.3 Plant irrigation and surface water collection and discharge, drinking fountains, public sanitation 14.4 Stakeholder consultation Minutes taken by: Davood Liaghat

50 14.5 Design competition/outreach, refer to published paper about good practice and process 14.6 EIA/mitigation analysis 14.7 Structures under viaduct 15.0 Program and way forward 15.1 October 2014 Project start - 1 st October 2014 Workshop and site visits on 17 th /18 th October 2014 Site visit report and minutes of meeting/workshop - 21 st October 2014 Development of structural options - ongoing Donald Macdonald to provide a few more hand sketches of two options in electronic format by 24 th October 2014 Structural analysis of options - ongoing Prepare headlines/placeholder of the feasibility report for agreement with Kate Martin w/c 27 th December 2014 Comments back from Kate Martin 31 st October November 2014 Skype workshop No. 1 - date to be confirmed, possibly w/c 10 th November TBC and organised by Kate Martin Discussion of outcome of analysis at Skype workshop Developed structural solutions to Paul Silvestri for costing - w/c 17 th November 2014 First run of cost estimates from Paul Silvestri 21 November 2014 Update feasibility report and share with Kate Martin w/c 24 th November 2014 Comments back from Kate Martin by 28 th November December 2014 Skype workshop No. 2 - date to be confirmed, possibly w/c 1 st December TBC and organised by Kate Martin Final analysis of structure w/c 1 st December 2014 Final cost estimate w/c 8 th December 2014 Review of draft of full report - w/c 8 th December 2014 Final version of feasibility report - w/c 19 th December 2014 Final approval of report by Kate Martin - by 19 th December 2014 All All BH All DMD BH BH KM All BH BH PS BH KM All BH PS All led by BH All led by BH KM The minutes detailed herein reflect the author s recollection of the discussions held during the meeting detailed above. If you feel that these minutes are inaccurate; proposed additions, corrections and/or comments must be submitted to the author in writing within five working days of the date of these minutes. If no written responses are received within this period, these minutes will be deemed the official record of the meeting. Minutes taken by: Davood Liaghat

52 Inspection Report Project Park My Viaduct Alaskan Way Subject Site Visit Project no UK ( US) Date 30 October 2014 Revision Description Issued by Date Approved (signature) 00 Report of field trip to Seattle and initial examination of Alaskan Way Viaduct DL 21 Oct 2014 KA 1 Introduction This report considers an initial examination and walkover of the existing Alaskan Way Viaduct on 17 th and 18 th October 2014 over a ¾ mile stretch of the structure from the stadia in Pioneer Square / SODO (south) to Pike Place Market (north). The Alaskan Way Viaduct is a concrete bridge / by-pass route (see Figure 1) in Seattle. It runs along the waterfront on the west side of Downtown Seattle as highlighted in red in the map of the city shown and in the aerial view shown in Figure 1. Figure 1 Alaskan Way Viaduct and its location in Seattle This report has been prepared for the sole benefit, use and information of Park My Viaduct for the purposes set out in the Design note or instructions commissioning it. The liability of BuroHappold Engineering in respect of the information contained in the report will not extend to any third party. All concepts and proposals are copyright February Issued in commercial confidence.

53 2 Existing Structure 2.1 Description The viaduct is approximately 47 wide and 55 high with a northbound upper deck and a southbound lower deck and was built in two phases in the early 1950s, see Figure Figure View of Alaskan Way Viaduct The Seattle Transportation Department built the north segment and the Washington State Transportation Department built the south segment a few years later. In the 1960s, downtown on and off ramps were added at Seneca St and Columbia St. The area of interest to this project is principally over the north section of the viaduct. The viaduct comprises a series of 3-bay double deck portals on the longitudinal direction and a single bay portal in the transverse structure (see Figure 2.1.2). It is a monolithic and integral concrete frame with no joints or bearings. Each 3-bay portal is independent of the adjacent portals. There are no expansion joints between consecutive structures, Figure Structural arrangement of a typical segment of the Alaskan Way Viaduct Page 2 of 16

54 3 Field trip 3.1 Visit on 17 th October 2014 (Drive-through) Present were: Kate Martin (Park My Viaduct) Kate Ascher (BuroHappold) Davood Liaghat (BuroHappold) Donald Macdonald (Donald Macdonald Architects) Paul Silvestri (The National Constructors Group) Weather: Overcast and rain at times. 3.2 Photographs Figure Side view of double deck structure looking west, note vehicle barriers Figure View of The Seattle Great Wheel from top deck level of viaduct Page 3 of 16

55 Figure View of the Seattle Downtown looking north, at the approximate starting point of south section of proposed park Figure View of the Seattle waterfront looking north, at the approximate location of bend of the viaduct Figure View of the underside of the lower deck of the viaduct, noting array of cables and services carried by lower deck and drainage pipes down columns and into ground Page 4 of 16

56 Figure View of the viaduct from Union Street at location of a proposed footbridge linking the two Figure Close proximity of the viaduct columns to existing buildings along Alaskan Way, note drainage pipes down columns and into ground Page 5 of 16

57 Figure View of the viaduct looking south at the approximate position of the start of north section of the proposed park Figure View from top deck level of viaduct looking north Figure View of the Seattle Steel Company from top deck level of viaduct Page 6 of 16

58 3.3 Visit on 18 th October 2014 (Walkover during road closure) Present were: Kate Martin (Park My Viaduct) Davood Liaghat (BuroHappold) Weather: Overcast. 3.4 Photographs Figure View from on ramp of viaduct at Columbia Street Figure View from on ramp of viaduct at Columbia Street, note extended portal legs at transition Page 7 of 16

59 Figure View of underside of the top deck of viaduct, note no services carried by the upper deck Figure View of underside of the top deck of viaduct at an atypical joint Page 8 of 16

60 Figure View of lower deck of viaduct at an atypical joint Figure View of underside of the top deck of viaduct at Columbia on-ramp, note CFRP beam strengthening (white) Page 9 of 16

61 Figure View of underside of the top deck of viaduct at a typical joint, note drainage pipes from top deck Page 10 of 16

62 Figure View of edge beam of the lower deck from Columbia on-ramp, note partial CFRP beam strengthening (white) Figure View of underside of the top deck of viaduct, note CFRP beam strengthening (white) Page 11 of 16

63 Figure View of underside of the top deck of viaduct, note damp patches through cracks Page 12 of 16

64 Figure View of underside of the top deck of viaduct, note presence of damp patch through cracks Figure View of cranes on the section of tunnel where Bertha tunnelling machine is stuck below ground Page 13 of 16

65 Figure View of viaduct at the location of Columbia on-ramp. Note change in viaduct section at transition Page 14 of 16

66 Figure View of viaduct column strengthened circa 2007 at the positon of the outside bend of viaduct Page 15 of 16

67 Figure View of viaduct column strengthened circa 2007 at the position of inside bend of viaduct Page 16 of 16

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74 FEASIBILITY STUDY: ENGINEERING & COSTS BUROHAPPOLD ENGINEERING - Donald MacDonald Architects - National Constructors Group ALTERNATIVE 1 OPTION 3 1,600 LF retrofit as a single deck moment frame $145.4 M OPTION 4 3,000 LF new single column garden bridge $92.3 M OPTION LF retrofit of historic segment $19.4 M ADDITIONAL ITEM A ped/bike bridge 500 LF Union Street Bridge $4.5 M ALTERNATIVE 1 TOTAL COST $ M OPTION 5 OPTION 3 PIKE PLACE MARKET OPTION 4 ADDITIONAL ITEM A CENTURY LINK FIELD ALTERNATIVE WATERFRONT VISION parkmyviaduct.org

75 FEASIBILITY STUDY: ENGINEERING & COSTS BUROHAPPOLD ENGINEERING - Donald MacDonald Architects - National Constructors Group ALTERNATIVE 2 OPTION 4 4,600 LF new single column garden bridge $141.3 M OPTION LF retrofit of historic segment $19.4 M ADDITIONAL ITEM A ped/bike bridge 500 LF Union Street Bridge $4.5 M ALTERNATIVE 2 TOTAL COST $ M OPTION 5 PIKE PLACE MARKET OPTION 4 ADDITIONAL ITEM A CENTURY LINK FIELD ALTERNATIVE WATERFRONT VISION parkmyviaduct.org

76 Appendix D Structural Analysis of Viaduct and Options Park My Viaduct: Alaskan Way Elevated Park Final Revision 00 Feasibility Study: Engineering & Cost Chapters 8 May 2015 Copyright BuroHappold Engineering. All Rights Reserved.

77 Design Note Project Park My Viaduct Alaskan way Subject Viaduct Analysis Project no Date 29 January 2015 Content 1. Introduction 2. Typical unit of existing structure 3. Option 1: Retrofit Double Deck Truss Frame 4. Option 2: Retrofit Single Deck Truss Frame 5. Option 3: Retrofit Moment Frame 6. Option 4: New Design Configuration /Single Pier option 7. Idealized Models of the Viaduct 8. Static analysis Retrofit Options 9. Static Analysis New Design (Option 4) 10. Modal analysis 11. Summary and Recommendations 1. Introduction Five structural analyses of a typical unit of the Alaskan Way Viaduct were carried out. Four models have been prepared: a. Basic un-strengthened unit (used as a benchmark) b. Option 1 Retrofit Double Deck Truss Frame c. Option 2 Retrofit Single Deck Truss Frame d. Option 3 Retrofit Moment Frame e. Option 4 New design - Single pier option A simple Finite Element frame model of the unit has been made using structural analysis program MIDAS employing beam and plate elements to model the beams, columns and the deck of the viaduct for the base model and options 1, 2, and 3. Structural program ROBOT was used for option 4. The models were analysed under static loading, wind loading and seismic in accordance with loadings from AASHTO. AASHTO load combinations were used in assessing the strengthening requirement of the viaduct. Modal analyses were also carried out to assess the pedestrian comfort and vibration levels. The assessment was done on the superstructure from an engineer s point of view only. Other important aspects such as foundation, construction program and cost have not been addressed yet. Stair/elevators are also excluded. A summary of the findings and recommendations are also presented at the end of this assessment. This report has been prepared for the sole benefit, use and information of Park My Viaduct for the purposes set out in the Design note or instructions commissioning it. The liability of BuroHappold Engineering in respect of the information contained in the report will not extend to any third party. All concepts and proposals are copyright February Issued in commercial confidence.

78 2. Typical unit of existing structure The typical unit consists of 3 bays with a total length of 184 made from reinforced concrete. The width is 45 7 ¼. The top deck is about 50 above ground. The deck is made up a five concrete beams in the longitudinal direction and with transverse beams spaced at about 14. The breakdown dimensions for each element are shown extracted from the drawings held by Washington State Department of Transportation. These dimensions are used to set up the base models and options 1, 2 and 3 models. Figure 1 Typical Unit Page 2 of 18

79 3. Option 1: Retrofit: Double Deck Truss Frame This option is similar to the Gray s retrofit proposal (July 2006) for upgrading the existing viaduct. The base unit is modified with new bracings in the lower deck. Figure 2 Option 1 Double Deck Truss Frame Retrofit Page 3 of 18

80 4. Option 2: Retrofit Single Deck Truss Frame The existing base unit is modified with new bracings in the upper deck. The lower deck is being removed. Figure 3 Option 2 - Single Deck Truss Frame Retrofit Page 4 of 18

81 5. Option 3: Retrofit Moment Frame In this option the existing frame is strengthened (picture framed) by installing HSS (Hollow Structural Sections) or I-shape beams. Figure 4 Option 3 Moment Frame Retrofit Page 5 of 18

82 6. Option 4: New Design Configuration The new design is assumed to consist of a single pier and a deck beam made entirely from reinforced concrete. The pier is a solid concrete column. The deck beam is a concrete box with internal diaphragms. The pier is spaced out at 100 and the deck is 56 6 above ground. Typical unit is shown in figure below. Figure 5 Option 4 New Design Page 6 of 18

83 7. Idealized Models of the Viaduct The idealized Finite Element model for the base model and the options are shown below. Figure 6 Base Model Figure 7 Option 1 - Double Deck Truss Frame Retrofit Page 7 of 18

84 Figure 8 Option 2 Single Deck Truss Frame Retrofit Figure 9 Option 3 Moment Frame Retrofit Page 8 of 18

85 Figure 10 Option 4 - New Design Page 9 of 18

86 8. Static analysis Retrofit Options Given the limited scope of this project the process taken for making a structural performance comparison between the base unit and the options are: a. Obtain the load effects for the beams, columns and deck under dead load, pedestrian live load, superimposed dead load, wind and seismic loads and the load combinations to AASHTO for the analysis. b. Compare options 1, 2 and 3 with the base unit and by considering the ratio for corresponding load effects and structural members determine vulnerable sections of the viaduct. An example of obtaining the bending moment in the top deck for base unit, options 1, 2 and 3 is shown in the diagrams below. Figure 11 Base Model Result Figure 12 Option 1 Result Page 10 of 18

87 Figure 13 Option 2 Result Figure 14 Option 3 Result The results are imported into a spreadsheet. Load effects for each of the options are compared by dividing the option figure over the base figure. Ratios greater than 1 are potential deterioration caused by the options. A screen shot of the spreadsheet is shown below. Page 11 of 18

88 Figure 15 Comparing Forces By comparing the ratios, a strengthening matrix for all the components of the viaduct as highlighted below was assessed. Note this comparison does not make any assumptions on strengthening required for the base model. Figure 16 Frame Member Groups Page 12 of 18

89 The output below shows the elements that require additional strengthening in options 1 and 2 when compared with the base model (current viaduct). Option 1 (Double Deck Truss Frame Retrofit): Option 2 (Single Deck Truss Frame Retrofit): This option for strengthening requires less strengthening of the viaduct components than the above option. Page 13 of 18

90 Option 3 (Moment Frame Retrofit): This option for strengthening seems to require less strengthening of the viaduct components than option 1 but more than option 2. Summary of number of areas which strengthening is required for the three options: Option 1 (Double Deck Truss Frame Retrofit) Upper Lower deck deck Option 2 (Single Deck Truss Frame Retrofit) Upper Deck Option 3 (Moment Frame Retrofit) Upper Deck Marginal required Require Not require Of the three options, option 3 repair can be targeted to areas that require strengthening while the other two only address the global repair and local repair is not assessed here. Since the degree of damage caused by past earthquake events is not known, there is a risk that the existing structure is beyond repair or strengthening associated with these options. Extensive investigation will be required ( beyond the scope of this study.) Page 14 of 18

91 9. Static Analysis New Design (Option 4) The design load effects for option 4 are obtained. The reinforcement content for the deck and pier are estimated using AASHTO design guidelines. They are 2.0% and 3.5% for the deck and pier respectively. Since this is new build, investigation of the existing structure is less critical than with the retrofit options. Nominal investigation is required for demolition purposes. 10. Modal analysis Since the retrofit and options for the bridge are primarily for pedestrian and cycle use, there needs to be an assessment made of the dynamics of the bridge for the intended use. The bridge has been designed for vehicles and the acceptable vibration and comfort criteria are different to that required by pedestrians. The first stage in this analysis is to calculate the natural frequency of the first few modes of vibration of the structure. The acceptable guidelines are shown in the following table. Mode Frequency (Hz) option 1 option 2 as built base model shape option 3 shape transverse 1.32 long long 1.35 transverse torsion 1.70 torsion deck 4.37 deck US criteria - sideway > 1.5Hz EU criteria - sideway > 1.5 Hz US criteria - deck > 3Hz EU criteria - deck > 5 Hz The only case that seems to be an issue is option 4 sideway mode. However, with the strengthening taken into account, it should have a sideway frequency over the guide line value. Then first 4 modes of vibration for the base model and options 1, 2 and 3 are demonstrated graphically in the following: Figure 17 As Built Mode Shapes Page 15 of 18

92 Figure 18 Option 1 Mode Shapes Figure 29 Option 2 Mode Shapes Figure 20 Option 3 Mode Shapes Page 16 of 18