N End Widening 2012-256 - Responsive - 11

7/30/2019 N End Widening 2012-256 - Responsive - 11

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Obtained by Bob Mackin via Freedom of Information

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Report

City of Vancouver

Burrard Street BridgeNorth End WideningFeasibility Study

July 2012


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REPORT

iP:\20112789\00_Burrard_Rehab_Des\Engineering\03.02_Conceptual_Feasibility_Report\NorthEndWidening\RPT_06July2012\rpt_van_northendwide_20120706_sc.doc

Table of Contents

SECTION PAGE NO.

Table of Contents i

1 General Information 1

2 Assumptions and Constraints 1

3 Proposed North End Widening 3

3.1 Alternative 1: Sidewalk Widening - Widen the Deck at Sidewalk Level 3

3.2 Alternative 2: Roadway Widening - Widen the Deck at Roadway Level 5

3.3 Lighting Requirements 6

3.4 Heritage Impact 6

4 Comparison and Evaluation 6

5 Conclusion 8

6 Closure 8

Appendix A - North End Widening Sketches

Appendix B - Heritage Evaluation Tables for North End Widening Alternatives


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1 General Information

Associated Engineering (AE) was retained by the City of Vancouverto complete the retrofit and

rehabilitation design of the Burrard Street Bridge. As part of that assignment, we have completed

a feasibility study for widening the north end of the concrete approach spans to accommodate a

north bound bike lane on the bridge deck plus a traffic queue due to turning traffic.

The Burrard Street Bridge, shown in Figure 1-1, consists of steel truss main spans and concrete

approach spans.

Figure 1-1

Burrard Street Bridge

The bridge deck has a roadway net width of 18.3 m and currently carries two traffic lanes and a

bike lane in the south bound direction and three traffic lanes north bound. The City is considering

relocating the north bound cycle lane onto the bridge deck and restricting the north bound traffic to

two lanes. Currently, north bound traffic exiting east onto Pacific frequently backs up onto the

bridge deck restricting the capacity of through traffic to two lanes. To avoid a significant loss of

capacity, third northbound traffic lane towards the north end will need to be maintained if one traffic

lane is replaced by a bike lane. This study will present feasible alternatives, which not only meet

the structural requirements, but also consider architectural objectives and the heritage character of

the bridge.

2 Assumptions and Constraints

This study assumed that the traffic flow is acceptable with four traffic lanes across most of the

bridge. Starting from the north end of the bridge, there are concrete approach spans from the

North Abutment to Pier No. 6 and deck truss spans from Pier Nos. 6 to 4. Structurally, it is feasible

to widen the deck truss spans by extending the floor beam cantilevers and adding a new sidewalk

facility.


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However, we do not recommend widening the deck truss spans for the following reasons:

Negative visual impact on usage underneath the span.

Negative visual impact on adjacent property.

Increased heritage impact.

High construction costs.

The concrete approach span widening is structurally feasible by extending the existing cantilever

floor beams and strengthening the existing cross beams. No new substructure is required. Pier

No.6 is the critical point which separates the deck truss spans from the concrete approach spans.

We recommend that Pier No. 6 be used as the introduction point for the additional north end traffic

lane. We evaluated the existing concrete approach structure and determined that 3 m of deck

widening is feasible between Pier No. 6 and the North Abutment as shown in Figure 2-1. The total

length of the widening is about 120 m, which should provide sufficient traffic storage capacity.

Figure 2-1


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Burrard Street BridgeNorth End Widening

Feasibility Study


3 Proposed North End Widening

3.1 Alternative 1: Sidewalk Widening - Widen the Deck at Sidewalk Level

The sidewalk widening, as shown in Figure 3-1, will extend the current sidewalk for another 3 m

outside the current walkway fence while maintaining the existing deck, sidewalk and walkway fence

unchanged. The existing pedestrian fence will remain in its current location, i.e., this character-

defining element will be maintained and a visual symmetry of the bridge will be preserved along the

roadway. The existing fence line will be suitably gapped north of Pier No. 6 to allow the sidewalk to

transition to the outside. A lightweight pedestrian fence will be installed along the new sidewalk

outer edge, to distinguish the new fence from the existing.

Figure 3-1Deck Cross Section of Alternative 1 - Sidewalk Widening

The existing cantilever beams will be modified and extended to support the widened walkway

loads. A new concrete beam will be wrapped around the cantilever beam, as shown in Section C

in Figure 3-2. The cross section of the cantilever beam will be increased in both width and depth to

carry the additional loads. The overall shape of the new extension and modified portion of the

cantilever beams will have a similar elevation profile as the existing cantilever beams and will be

related to each other. This will give the impression that the beams were intended to be there rather

than having been added awkwardly.

As shown in Figure 3-1, a new concrete undelay will be constructed to increase the capacity of the

cross beams between the facial girder and the center girder adjacent to the widening side. The

cross section of the cross beam shown in Section B in Figure 3-2 will be thickened at the bottom

and two concrete blister blocks will be constructed to anchor the new top reinforcing bars from the

strengthened cantilever beams.


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Figure 3-2

Cross Beams of Alternative 1 - Sidewalk Widening

The new lightweight fence will be designed to match the height and characteristics of the existing

fence but using steel rather than concrete. One railing design in Figure 3-3 shows a steel frame

mirroring the openings in the concrete fence, while the other shows a solid plate. The design

details will be developed further as part of detail design.

Figure 3-3

If the suicide barrier is implemented, the north end fence design could be adapted as follows:


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Figure 3-4

3.2 Alternative 2: Roadway Widening - Widen the Deck at Roadway Level

The roadway widening, as shown in Figure 3-5, will provide an additional 3 m of roadway and

extend the current walkway by 3 m. This widening strategy will relocate the current walkway fence.

As a result, a heritage character-defining element will be displaced and roadway symmetry will not

be preserved. However; the advantage of this option is the bike lane, which will always be at the

same level of the roadway. To carry the new deck width, the cantilever beams and cross beams

will be modified in a similar fashion to Alternative 1.

Figure 3-5

Deck Cross Section of Alternative 2 - Roadway Widening


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3.3 Lighting Requirements

The proposed street lighting is symmetrically located on the outside of the concrete fences. For the

North End Widening, the current lighting will need to be modified to meet the new lightingrequirements. Under Alternative 1, a pedestrian luminaire will be mounted on the street light pole

towards the widening side to illuminate the new sidewalk.

Under Alternative 2, shown in Figure 3-5, the light pole for the roadway widening will be located on

the outside of the new sidewalk. As a result, either more powerful LED lights or an extra light pole

with a longer arm pole will be required to achieve the same lighting capability for both vehicular and

pedestrian traffic. The light poles will be asymmetric for this solution.

3.4 Heritage Impact

The following changes applying to both alternatives will have a minimum heritage impact:

x The cantilever beam extensions and cross beam underlays.

x The exterior girder strengthening.

Because the existing concrete fences are considered to be character-defining elements, any

change to the fence and symmetry of the bridge will be assessed as high heritage impact. We

believe that Alternative 1 has low heritage impact by maintaining the existing concrete fence

location and maintaining fence and street light symmetry. In contrast, under Alternative 2 the

existing fence is relocated and symmetry of the fence and light poles is lost. We consider that

Alternative 2 has high heritage impact.

s.13(1) and s.17(1)(c), (d), & (f)


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s.13(1) and s.17(1)(c), (d), & (f)


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Appendix A - North End Widening Sketches


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Appendix B - Heritage Evaluation Tables for NorthEnd Widening Alternatives

Table B-1

Conservation Standard Impact Evaluation

North End Widening Alternative 1 Alternative 2

Description Sidewalk Widening Roadway Widening

Sketches

1) Conserve the heritage value of a

historic place. Do not remove, replace,

or substantially alter its intact or

repairable character--defining elements.

Low High

2) Conserve changes to a historicplace, which over time, have become

character-defining elements in their own

right.

N/A N/A

3) Conserve heritage value by adopting

an approach calling for minimal

intervention.

medium High

4) Recognize each historic place as a

physical record of its time, place and

use. Do not create a false sense of

historical development by adding

elements from other historic places orother properties or by combining

features of the same property that never

co-existed.

medium High

5) Find a use for a historic place that

requires minimal or no change to its

character-defining elements.

low High


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6) Protect and, if necessary, stabilize a

historic place until any subsequent

intervention is undertaken.

N/A N/A

7) Evaluate the existing condition of

character-defining elements to

determine the appropriate intervention

needed. Use the gentlest means

possible for any intervention. Respect

heritage value when undertaking an

intervention.

Low Medium

8) Maintain character-defining

elements on an ongoing basis. Repair

character-defining elements by

reinforcing their materials using

recognized conservation methods.

Replace in kind any extensively

deteriorated or missing parts of

character-defining elements, where

there are surviving prototypes.

Low (railing replaced in-kind) Medium (railing replaced but

relocated)

9) Make any intervention needed to

preserve character-defining elements

physically and visually compatible with

the historic place and identifiable upon

close inspection. Document any

intervention for future reference.

Low Medium

10) Repair rather than replace

character-defining elements. Where

character-defining elements are too

severely deteriorated to repair, and

where sufficient physical evidence

exists, replace them with new elements

that match the forms, materials and

detailing of sound versions of the sameelements. Where there is insufficient

physical evidence, make the form,

material and detailing of the new

elements compatible with the character

of the historic place.

Low Low


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11) Conserve the heritage value and

character-defining elements when

creating any new additions to an historic

place and any related new construction.

Make the new work physically and

visually compatible with, subordinate to

and distinguishable from the historic

place.

Low Medium

12) Create any new additions or related

new construction so that the essential

form and integrity of an historic place

will not be impaired if the new work is

removed in the future.

Low Low

13) Repair rather than replace

character-defining elements from the

restoration period. Where character-

defining elements are too severely

deteriorated to repair and where

sufficient physical evidence exists,

replace them with new elements that

match the forms, materials and detailing

of sound versions of the same

elements.

N/A N/A

14) Replace missing features from the

restoration period with new features

whose forms, materials and detailing

are based on sufficient physical,

documentary and/or oral evidence.

N/A N/A

OVERALL IMPACT Low Medium-High


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Table B-2

Heritage Impact Ranking and Heritage Expression



Sketches

Road Gate Parti: Primary Character-Defining ElementsPylons and Brazier Lights Medium High

Concrete Piers N/A N/A

Concrete Fences Low High

Curved Retaining Walls N/A N/A

Flanking Staircases N/A N/A

Suspended Galleries N/A N/A

Sculptural Program N/A N/A

Tile Roofs N/A N/A

Central Steel Truss N/A N/A

Perceived Width of Roadway Low HighOriginal Plaque N/A N/A

Wrought Iron Grilles N/A N/A

View from the Bridge Low High

Sea Gate Part: Primary Character-Defining Elements

Concrete Piers N/A N/A

Steel Trusses of Centre Span N/A N/A

Concrete Fences Low High

Gradual Sweep of Rising Roadbed Low Medium

Views of the Bridge Low Medium

Road Gate Parti: Secondary Character-Defining ElementsConcrete Abutments and Columns N/A N/A

Steel Trusses under Bridge N/A N/A

Interior Staircase, Pier One N/A N/A

OVERALL IMPACT Low Medium

Documents

N End Widening 2012-256 - Responsive - 11