Farewell Bend Bridge Final Assessment and Recommendations

February 29, 2016

October 2015 │ Project No. 297-7414-001

DRAFT

Farewell Bend Park

Type, Size, and Location Report

Farewell Bend Bridge

Prepared for

Bend Parks & Recreation Dist.

799 SW Columbia St

Bend, OR 97702

Prepared by

Parametrix

595 SW Bluff Drive, Suite B

Bend, OR 97702

T. 541.508.7710 F. 1.855.542.6353

CITATION

Parametrix. 2015. DRAFT

Farewell Bend Park

Type, Size, and Location Report

Farewell Bend Bridge.

Prepared by Parametrix, Bend, Oregon. October 2015.

DRAFT

Farewell Bend Park

Type, Size, and Location Report

Farewell Bend Bridge Bend Parks & Recreation Dist.

October 2015 │ Project No. 297-7414-001

CERTIFICATION

The technical material and data contained in this document were prepared under the supervision and

direction of the undersigned, whose seal, as a professional engineer licensed to practice as such, is

affixed below.

____________________________________________

Prepared by Daniel J. McIntier, PE

____________________________________________

Checked by Barry Johnson, PE

____________________________________________

Approved by Daniel J. McIntier, PE

DRAFT

Farewell Bend Park

Type, Size, and Location Report

Farewell Bend Bridge Bend Parks & Recreation Dist.

October 2015 │ Project No. 297-7414-001 i

TABLE OF CONTENTS

1. BACKGROUND ..................................................................................................................... 1

1.1 INTRODUCTION ........................................................................................................................ 1

1.2 PROJECT DESCRIPTION ............................................................................................................. 1

1.3 LOCATION ................................................................................................................................ 1

1.4 RIGHT-OF-WAY RESTRICTIONS................................................................................................. 1

1.5 EXISTING CONDITIONS ............................................................................................................. 1

1.6 UTILITY CONFLICTS OR RESTRICTIONS ..................................................................................... 1

1.7 DESIGN CRITERIA AND SPECIFICATIONS .................................................................................. 2

2. ENVIRONMENTAL ................................................................................................................ 2

3. DESIGN CONCEPTS RATIONALE ............................................................................................. 2

3.1 ALTERNATIVE DISCUSSIONS ..................................................................................................... 2

3.2 COST ESTIMATES ...................................................................................................................... 4

3.3 ALTERNATIVE SELECTION ......................................................................................................... 4

4. GEOMETRY AND LAYOUT ..................................................................................................... 5

4.1 STRUCTURE LENGTH ................................................................................................................ 5

4.2 PLAN AND PROFILE .................................................................................................................. 5

5. FOUNDATIONS ..................................................................................................................... 5

6 CONCLUSIONS AND RECOMMENDATIONS ............................................................................ 5

LIST OF TABLES

3-1 Superstructure Evaluation .................................................................................................... 3

3-2 Superstructure Alternative Selection ................................................................................... 4

3-2 Superstructure Cost Estimates .............................................................................................. 4

FIGURES

Figure 1. Vicinity Map

DRAFT

Farewell Bend Park

Type, Size, and Location Report

Farewell Bend Bridge Bend Parks & Recreation Dist.

TABLE OF CONTENTS (CONTINUED)

ii October 2015 │ Project No. 297-7414-001

APPENDICES

A Existing Trail Plan and Profile

B Preliminary Bridge Plan & Elevation Drawing

C Detailed Cost Estimates

DRAFT

Farewell Bend Park

Type, Size, and Location Report

Farewell Bend Bridge Bend Parks & Recreation Dist.

October 2015 │ Project No. 297-7414-001 iii

ACRONYMS PARKS Bend Park & Recreation District

LRFD load resistance factor design

AASHTO American Association of State Highway and Transportation Officials

ODOT Oregon Department of Transportation

TS&L Type, Size, and Location

ROW right-of-way

1. BACKGROUND

1.1 Introduction

This report documents the decisions for determining the appropriate structure type, size, and location

for replacing the existing Farewell Bend Bridge with a longer clear span structure.

1.2 Project Description

The bridge is a vital part of the Park’s trail network in Deschutes County (County). It serves as a primary

pedestrian route for the parks on each side of the Deschutes River, recreation and event uses.

The original Farewell Bridge was built in 1940s with an out-to-out width of 15 feet. The existing longest

span is 81 feet with a bridge length of 136 feet. The river is near perpendicular to the pedestrian bridge

and the bridge is oriented on a north-south axis.

The river active channel width is defined at 136 feet requiring a new bridge span of 155 feet. The

Ordinary High Water Mark (OHWM) is at Elevation 3604.19. The 50-year flow elevation is XXXX.XX feet.

1.3 Location

The project site is in central Bend in the Old Mill District, where the Deschutes River transects Farewell

Bend Park and Riverbend Park The bridge is at latitude N44°02'31", longitude W121°19'30" in Township

18S, Range 12E, Section 6, west side, Willamette Meridian. See Figure 1 – Vicinity Map.

1.4 Right-of-Way Restrictions

There are no anticipated right-of-way restrictions for the project. The replacement bridge will be on the

same alignment as the existing bridge.

1.5 Existing Conditions The northern portion of the area is located within Riverbend Park and includes a rocky shoreline lined

with riprap. The northern terminus of the area is delineated by a paved bike/pedestrian trail (which

historically was used as a logging road) and a rock cliff.

The southern portion is located within an area that was historically used as a log deck before being

converted to Farewell Bend Park. This area consists of an artificial shoreline constructed of fill and riprap

and a paved bike/pedestrian trail.

The Deschutes River within the area is highly regulated by dams upstream and downstream. Also, the

river is regulated to flow higher during the summer and lower during the winter draw-down period.

1.6 Utility Conflicts or Restrictions

Presently, there are no overhead or underground utilities within the bridge footprint. A relocation plan,

as required, will be developed during final design. The proposed bridge can allow for attachment of

utilities such as irrigation lines or conduits for future use.

1.7 Design Criteria and Specifications

Preliminary designs have been developed in accordance with the AASHTO LRFD Guide Specification for

the Design of Pedestrian Bridges, December 2009.

Assumptions and design criteria used to establish this Type, Size, and Location (TS&L) study are:

• Plans, specifications and cost estimates will be prepared in English units.

• Design Live Load shall be 90 psf (pedestrian) and a H10 Vehicular Live Load.

• Unit costs for estimates are based on ODOT unit bid prices and previous pedestrian bridge

projects.

• Minimum clearance from the water will be 7’ with a desired minimum of over 8’.

• Bridge grades will be set to allow for accessible grades on the approaches as well as the bridge.

Bridge railing height follows the AASHTO Guide for the Development of Bicycle Facilities, 2012, 4th

edition and is planned at 48 inches in height utilizing vertical pickets to deter climbing and jumping.

Additional railing treatment may include stainless steel cables above and/or outside the hand railing to

further deter jumping.

The proposed bridges shall be designed for a 75 year life with maintenance on an as needed basis for

bridge elements that wear with use, ie. timber decking and bearing pads.

2. ENVIRONMENTAL

It is understood that there are several environmentally sensitive areas located in the proximity of the

structure. However, it is assumed that environmental concerns will not influence the type, size, or

location of the proposed structure.

3. DESIGN CONCEPTS RATIONALE

3.1 Alternative Discussions

The Farewell Bend Bridge is a vital part of the trail network in Bend. Based on a review of the existing

trail corridor, maintaining the existing alignment is proposed in order to minimize environmental and

length of span impacts. Therefore, differences between each alternative where evaluated on cost,

constructability, construction schedule, and aesthetics.

Four superstructure types were evaluated for span capacity, availability, and cost. The girder types are

shown in Appendix D-1. The girder types evaluated were:

1. Pre-engineered truss bridge – Constant depth Pratt through truss with timber deck. The bottom

chord of the truss is about 3 feet below the deck with a majority of the truss above the deck. This

alternative increases clearance from the river and maintains or lowers the trail profile. Readily

available in the Pacific Northwest.

2. Pre-engineered bowstring arch truss bridge- Bowstring arch through truss with timber deck. The

bottom straight chord is about 2 feet below the deck with the arch shape above the deck. This

alternative increases clearance from river and maintains or lowers the trail profile. Readily available

in the Pacific Northwest.

3. Prestressed Bulb Tee Girders with concrete composite deck – BT84 prestressed girders with a cast in

place concrete deck 9 inches thick. The girder is below the deck with the bottom flange about 8 feet

below. Structure mass will require larger footing/piling. This alternative either reduces the vertical

clearance or requires more extensive modifications to the approach trail slopes. Girders may come

from Harrisburg, Oregon or Caldwell Idaho.

4. Steel plate girders with concrete composite deck – Steel plate girders were evaluated for

completeness. Steel girders are typically not desirable due to the higher costs, higher maintenance,

and availability. The steel beams would be made composite using a formed cast-in-place concrete

deck a minimum of 9 inches thick. The bottom flange is about 10 feet below the deck. This also

reduces the vertical clearance or requires more extensive modifications to the approach trail slopes.

Structure mass will require larger footing/piling. Steel girders can be fabricated in Portland,

Oregon, Deer Park, Washington or Salt Lake City, Utah.

Each girder has construction and design issues as shown in Table 3-1.

Table 3-1. Superstructure Evaluation

The following selection matrix, Table 3-2, rates each alternative by category by ranking from 4 to 1. A 4

is the highest rank (most favorable) and a 1 the lowest (least favorable). In the event of an equal

comparison each alternative is given the same rank. The values are summed with the highest score

being most favorable. To clarify the criteria, the following provides a short explanation of decision

factors.

• Issues –effort in preparing a design for alternative.

• Efficiency –structural capacity versus mass of alternative.

• Availability –fabricator location and shipping to site

• Spliceable –being delivered in shorter sections and assembled on site.

• Shipping –difficulty in delivering, storing, and erecting.

• Schedule –amount of time to erect alternative (impact to users).

• Equipment –type and size of erection equipment.

• Cost –estimated cost of structure not including any other cost.

Girders Deck

Stay in

Place Form Construction Issues Design Issues

Pratt Truss Timber N/A Splicing Jump

deterrent

Bowstring Arch

Truss

Timber N/A Splicing Jump

deterrent

PS girders Concrete No Weight Cost Delivery Depth Max Span Aesthetics

Steel girders Concrete No Weight Cost Splicing Depth Maintenance Aesthetics

• Site –work zone footprint needed to complete the structure.

• Jumping –deterrent to jumping from the bridge, climbing the bridge, etc.

• Trail –impact to existing trail plan and profile.

• View from –the amount of visual obstructions of the river from the bridge.

Table 3-2 Superstructure Alternative Selection

Selection Criteria

Design Construction Impacts

Superstructure Issues Efficiency Availability Spliceable Shipping Schedule Equipment Cost Site Jumping Trail View

Pratt Truss 4 4 4 Yes 4 4 4 4 4 3 4 4

Bowstring Truss 4 3 4 Yes 4 4 3 3 4 4 4 3

PS Girder 2 2 3 No 1 2 1 4 2 1 1 4

Steel Girder 1 1 3 Yes 2 2 2 1 2 1 1 4

The Pratt Truss and the Bowstring Truss are nearly equal in rankings with scores of 43 and 40

respectively. The PS girder and steel girder bridges total 23 and 20, respectively.

3.2 Cost Estimates

The tables below provide a preliminary construction cost estimate for each of the alternatives based on

the bid item unit cost per ODOT unit bid tabulations based on 3 low bids through December 2014 and

historic project costs for pedestrian bridges. These are summarized in the Table as cost per square foot.

The cost estimate does not include costs of trail work, environmental or erosion control, preliminary

and final design, or construction engineering.

This is a preliminary estimate for comparison of superstructure types and, therefore, has a 15 percent

contingency added to the estimated quantities. A detailed estimate is in Appendix C. A summary of

costs is shown in Table 3-3.

Table 3-3

Superstructure Bridge Cost

Range

Approx.

Cost/SF

Remarks

Pratt Truss $495k – 545k $257 Recommended

Bowstring Truss $570k – 625k $298

PS Girder $505k – 555k $263 Does not include cost to raise trail

Steel Girder $810k – 890k $423 Does not include cost to raise trail

3.3 Alternative Selection

From a cost perspective, Alternatives 1 through 3 are about equal cost per square foot if you add in the

cost of raising the trail for Alternative 3 knowing that raising the trail may impact the ADA allowable

slopes. In comparison, the pre-engineered truss alternatives will require smaller cranes and less time for

construction than the bridge girder alternatives. See Appendix B for preliminary Plan and Elevation

drawing.

4. GEOMETRY AND LAYOUT

4.1 Structure Length

The river’s active channel width is 136 feet. Typically, a single span bridge length is determined by the

active channel width multiplied by 1.5. This would require a span length of 200 feet. There is a steep

rocky outcrop near the river on the north side and a steep bank to an elevated fill on the south side. In

addition, due to the significant control of flows through upstream dams, the variation in maximum flows

is relatively minor. A reduction in total span length is appropriate. Therefore, the estimated span length

is 160 feet.

4.2 Plan and Profile

The bridge will be located to match to the existing trail plan and profile.

5. FOUNDATIONS

A geotechnical investigation is being performed for the TS&L by Wallace Group. It is anticipated that the

foundation system would be small-diameter pipe piles. With the long span, seat abutments using

elastomeric bearings for thermal displacements are anticipated. Approach slabs are not anticipated.

The backfill at the abutments will have geotextiles placed at each lift to minimize approach settlement.

The final foundation and abutment fixity will be determined during final design. For estimating

purposes, it is assumed the piling will be 80 feet in length.

6. CONCLUSIONS AND RECOMMENDATIONS

The increased bridge span and location of the bridge in the trail alignment have resulted in some ideal

bridge geometry with minimal impact to the environment. The bridge is on a tangent with a crest curve

vertical profile. The long span minimizes impacts to the Deschutes and eliminates timber piling or any

other structures in the river. The pre-engineered truss is commonly used for pedestrian bridges and

can be found in use near this site. There are several customizations that can be accommodated by the

fabricators for aesthetics and user safety.

Based on the assessment and rankings, the prefabricated truss options are relatively equal. The

following is a list of comparisons between the two truss options.

Description Pratt Truss Bowstring Truss

Cost Most Economical About 15% more than Pratt

Stiffness (Bounce) Most noticeable movement Stiffer than Pratt but not as stiff as

girder bridges

Jump Deterrence Can be modified to add extensions to

rail that angle away. Will be more

pronounced than Bowstring Truss

Can be accommodated with addition

of cables between structural

members. No “appendages” needed

Aesthetics Simple structure that has the least

visual obstruction

Bowstring truss style was used in

many of the old mill buildings. Is

more interesting and open.

View From Bridge No obstruction above eye height.

Has a large structural member (about

12” x 12”) at top of railing

Structural member varies in height

across the length with the bottom of

member about 9’ above the deck at

mid-span. Varies from about 7.5’ to

9’ over main channel.

Either truss option meets the design criteria identified. The importance of the various factors shown

above will dictate the preferred alternative.

EXISTING BRIDGE

PRATT TRUSS