bridge alternate type study - railroad grade separation (04-17-14)
TRANSCRIPT
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
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)
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:
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.
Early Feasibility Decisions One track & two tracks considered along with
One Span and Three Span bridges. Crane Location & Lifting Method
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
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.