Bridge Alternate Study

Railroad Grade Separation Case Study

So Why do a Structure Type Study? Present Alternatives Set Goals & Criteria Make Comparisons Explain Differences Document Selection

Structure Type Study Basis for Comparison: Initial Construction

Roadway pay items Bridge pay items Right-of-way costs Engineering costs

Classic Parameters

10-year EL = 1028.0

100-year EL = 1029.6

Exist Span = 90 ft (+/-)

Proposed Span ~ 120 ft

STRUCTURE DEPTH

OHW EL = 1024.0

Normal EL = 1020.0

Basis for Comparison: Initial Construction Structure Depth Profile Grade Impacted Footprint

Structure Type Study Basis for Comparison: Constructability &

Permitting Equipment Required Access & Delivery Staging Areas Crane Pads & Causeways Environmental Permits

Structure Type Study

Lower Level (Adjacent) Upper Level (Approach Roadway)

Crane Size & Position

Permitting

Railroad Permitting Environmental Permitting

RR Force Account & SWPPP Maintenance

Basis for Comparison Basis for Comparison: Life Cycle Costs

Initial cost to construct Annual work activities, maintenance and

inspections Repair and Preservation Activities (10 years) Minor rehabilitation projects (20 years) Major rehabilitation projects (50 years) Residual Values Net Present Value (NPV)

Design Life Timeline

Recondition./Deck Replace.

Life Cycle Costs: Net Present Values

Cost basis = Year of Bid Tabulation Data Design Life Term = 75 years Interval timeline = 10 years; 20 years; 50 years Discount rate = 2.7% per year

n

NPV = Σ RCFt / (1+i)t t=0

where: RCFt

i

n

= = =

Real Cash Flow Annual Discount Rate term

to calculate NPV:

Life Cycle Costs: Net Present Values

Calculations Microsoft Office Excel Function

Structure Type Study Reference Papers

Purpose of the Papers To give local infrastructure managers a guide

and reference to use when scoping and evaluating a site for a bridge project.

Ensures all costs and factors are considered, including life cycle costs.

Real world sites and examples.

Case Study – Rail Grade Separation Structure Type Study

Narrative (19 Pages) Alternate Descriptions Life Cycle Cost Analysis Evaluation Matrix Evaluation of Alternatives Evaluation of NPV of

Alternatives Conclusion & Summary 4 Appendices with

drawings, cost estimates, etc.

• Low structural rating• Single lane

• Blind curves on approach roadway

Ezell Road (Before)

2009 and 2011 aerials provided by USDA NCRS

Ezell Road Alignment (Before & After)

Early Feasibility Decisions One track & two tracks considered along with

One Span and Three Span bridges. Crane Location & Lifting Method

?

future trackhere?

or here?

cran

e?

cran

e?

cran

e?

Span Arrangements – Ezell RoadNumber of

SpansSingle or Double

TrackMain Spanover Track(29˚ Skew)

TotalBridge Length

Three Single* 45 feet 113 feet

Three Double 62 feet 154 feet

One Single* 112.5 feet 112.5 feet

One Double* 112.5 feet 112.5 feet

*CSXT requested that the bridge span two tracks in the future, although it was not planned, in terms of which side the track would be added, or if the tracks would be realigned, symmetrically along the centerline. It was therefore permitted to assume that the future project would construct retaining walls using soil nailing or tie backs to accommodate the required area.

Lifting Method – Ezell RoadLifting Method

Temporary Haul Road & Staging Area

Crane Size & Crane Pads

Railroad Impacts

Track Side

• Haul road envisioned down the side slopes of the railroad cut

• Limited storage area at track level

• Lighter Cranes

• Smaller Pads

• More Force Account Work and Flagman Controls

• Slow Progress

• Diminished Safety

Approach Roadway

• No haul road

• Simpler staging

• Heavier Cranes

• Larger Pads

• Less Force Account Work

• Faster Progress

Alternatives – Ezell Road Final Alternates:

Alt. 1 – Single Span P/S AASHTO Girders Alt. 2 – Single Span Steel Plate Girders Alt. 3 – Single Span Steel Pony Truss Girders

Level of Engineering

Compare Depths & Weights

Four - AASHTO IV (54”) Girders Indiv. Girder Weight = 91,130 lbs. Superstructure Members: $101,250 Grade Raised by 6.5 ft.

Four - 55 3/16” Plate Girders Indiv. Girder Weight = 27,705 lbs. Superstructure Members: $112,720 Grade Raised by 5.0 ft.

W30x108 Floor Beam Indiv. Truss Girder Weight = 35,060 lbs. Superstructure Members: $200,000 Grade Raised by 3.6 ft

Results - Ezell RoadComparisons Alternate 1

(Single-Span P/S Girders)

Alternate 2(Single-Span

Steel Plate Girders)

Alternate 3 (Single-Span Steel

Truss Girders)

Initial Project Cost (+/- % Min.)

$1,039,609(+31.2%)

$1,033,157(+30.4%)

$792,142(0.0%)

Life Cycle Cost (+/- % Min.)

$1,402,9417(+29.7%)

$1,388,823(+28.4%)

$1,082,055(0.0%)

Disturbed Area 1.3 Acres 1.1 Acres 0.9 Acres

Right of Way 0.30 Acres 0.28 Acres 0.2 Acres

Profile Grade/ Structure Depth

Raised by 6.5 ftTtotal 5.72 ft

Raised by 5.0 ftTtotal 4.60 ft

Raised by 3.6 ftTtotal 3.56 ft

Foundation

- Pile caps (43’x3.5’)- Six HP 14x73 /abut- Pile Wt. = 42,415 lbs- Retaining walls

- Pile caps (43’x3.0’)- Four HP 14x73 /abut- Pile Wt. = 28,035 lbs

- Pile caps (41’x3.0’)- Eight HP12x53 /abut- Pile Wt. = 40,600 lbs

Savings of $241,000

Grade change reduction of 2.90 ft.

Results – Ezell RoadComparisons

Alternate 1(Single-Span P/S Girders)

Alternate 2(Single-Span

Steel Plate Girders)

Alternate 3 (Single-Span Steel

Truss Girders)

EnvironmentalImpact

• SWPPP req’d for disturbance over 1 acre

• Add’l permitting & const- ruction inspections

• SWPPP req’d for disturbance over 1 acre

• Add’l permitting & const- ruction inspections

• Land disturbance less than one acre

ConstructionMethod

• Long beams are difficult to transport

• Heavy crane and track-levelstaging area req’d for lifting beams (91 kips)

• Long beams are difficult to transport

•Medium crane and track- level staging are req’d for lifting beam pairs (28 kips)

• Trusses transported in sections with

bolted conn.’s

• Medium crane and small staging area from the approach roadway (35 kips)

ConstructionSchedule

• Estimated 10 weeks in the railroad red zone

• Add’l time for grading activities and

construction of retaining walls

• Estimated between 2 and 10 weeks in the railroad red zone

• Shop welding is labor QC intensive

• Estimated 2 weeks in the railroad red zone

• Trusses are prefabricated

Conclusions – Ezell Road A single span alternative was selected as a

prudent way to minimize current construction costs while providing for expansion to two tracks in the future.

Alternate 3 (steel truss) had the least impacts to the project footprint in terms of raised grade, disturbed area and right-of-way acquisition.

Alternate 3 (steel truss) was the least cost alternative of the final superstructure alternates saving the client $241,000.

Alternate 3 (steel truss) has the 2nd lightest foundation and 2nd lightest crane lifts among the alternatives.

What Have We Learned Comprehensive costs are important to

evaluate. In the case of smaller bridge projects, changes

in profile grade have a great affect on the overall project costs.

Costs embedded in items such as “Mobilization”, “Cofferdams-/Cribbing/Sheeting”, or permitting can also affect the overall costs and should be evaluated appropriately.

For certain span lengths and certain sites, steel truss bridges provide a way to shorten the length that a controlling member must span and therefore they provide a way to reduce the project’s profile impacts.

Construction Sequence

Staging Area in Approach Roadway

Field Segments Spliced Together

Lift First Truss Girder

First Truss in Position and Secured

Rail Traffic During Construction

Erecting Second Truss Girder

Erecting First Floor Beam

Erecting Remaining Floor Beams

Framed with Stringer Beams

Setting Forms

Open for Traffic

Thank you