Railway Bridges Up-to-Date - Purdue University

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Railway Bridges Up-to-Date

Stephen Dick, PhD, SE Senior Research Engineer

Bowen Laboratory Lyle School of Civil Engineering

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Railway Bridges Up To Date

• Railroad system in general • Railroad environment • Bridge design philosophy • Bridge types • Steel and fatigue • New technologies

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United States Railway System

• US rail network is 137,000 route miles • Indiana 3,786 route miles

• 200,000 employees (rr’s only) • Three tiers of railroad (revenue)

• Class I – $447,621,226 7 (+Amtrak) • Class II – $35,809,698 21 • Class III – everything else 510

Network -- NS

-- All 01fler Rail -- KCS

BNSF C

-- UP -- CP

- CSXT

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US Railway System

from ResearchGate

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Class 1 Business Statistics – 2018

• Total revenue – $76.2 billion

• 26,000 locomotives (40,000 for all railroads)

• 1.67 million freight cars (total)

• Total reported asset base – $253.5 billion

• Capital Expenditures – $12.4 billion

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Regulatory Environment

• Two main federal agencies • Surface Transportation Board (STB)

• Financial and corporate regulation

• Federal Railroad Administration (FRA)

• Operations, maintenance, and safety enforcement

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Regulatory Environment (2)

• Federal Railroad Administration (FRA)

• Regulation of railroad bridges

• Title 49 CFR Part 237 requires: • a Bridge Management Plan • a Load Rating for all bridges • annual bridge inspections

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Self-Regulatory Environment

• Association of American Railroads (AAR)

• Regulates the design and construction of freight railcars

• Regulates some maintenance issues on railcars

• Regulates and provides accounting services for interchange and other billings between railroads

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Self-Regulatory Environment (2)

• Association of American Railroads (AAR)

• Regulates the maximum axle weights and total railcar weights for the railroad system

• Maintains minimum length and axle spacing requirements for railcars

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Regulatory Environment (3)

• Federal Railroad Administration

• Regulation of railroad bridges

• Title 49 CFR Part 237 requires: • a Bridge Management Plan • a Load Rating for all bridges • annual bridge inspections

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' 45,000,000 I

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1915 1930 1945 1960 1975 1990 2005 2020

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Historical Operating Data

Tonnage (thousands)

2,000,000 , .... .4 " I \ A

1,750,000 / u, ~-

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500,000

1915 1930 1945 1960 1975 1990 2005 2020

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Historical Operating Data (2)

Cars per Freight Train

80.0

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Historical Operating Data (3)

Freight Car Capacity

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105 .0

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1915 1930 1945 1960 1975 1990 2005 2020

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Historical Operating Data (4)

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70

60

so

40

30

20

1915

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1930

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1945

Average Tons per Carload

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Historical Operating Data (5)

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Railroad Train Loadings

• CURRENT CONDITIONS: • Heavy train conditions ≥ 50 trains per day

• Train lengths – up to 10,000 feet are common • Increases in lengths are planned for some railroads

• Train weights – 15,000 to 20,000 tons for bulk commodity trains, “light passenger trains” 500 -1,000 tons

• Number of cars – unit trains 60 – 200 cars manifest (mixed) trains 100 – 150 cars

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Railroad Train Loadings (2) • Design Loading – Cooper E Loading system

• Maximum 80,000 lb. axle loads (current E-80)

• Actual Loads: • Maximum car weight of 286,000 lbs. on four axles (interchange)

• Up to 315,000 lbs and higher by special movements

• Railcars designed to load to maximum weights • Railcar lengths from 42 – 95 feet

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The Specialized Loads

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And a Bad Day at the Office

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Bridge Design Philosophy • Highway Bridges

• LRFD for all bridge designs • Specifications published by AASHTO • Integral abutments and other modern design details

• Railway Bridges • ASD for steel bridge designs • LFD or ASD for concrete bridge designs • Recommendations published by AREMA • Discrete construction without modern appurtenances installed

WHY?

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Bridge Design Philosophy (2)

• LRFD – Highway Bridges • Advantageous in continuous spans • Dead load simple/live load continuous spans • Deflection to resist the loads on the bridge

• ASD – Railway Bridges • Simple spans • Deflection controls track surface requirements, not load • Deflection requirements are more stringent than load requirements

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Bridge Design Philosophy (3) • LRFD – Highway Bridges

• LRFD provides sufficient strength but deflection must be checked • LRFD provides a safety margin for extreme events

• ASD – Railway Bridges • Stringent deflection requirements drive the section size with stresses from

live loads easily handled • No advantage to using LRFD for simple spans • Railroad trains loading the bridge are the extreme event

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Bridge Design Philosophy (4)

• Highway Bridges • Economy of section with continuous spans • Different measures for protection of bridge elements

• i.e., we don’t intentionally salt railway bridges anymore

• Railway Bridges • Simple spans are easier and faster to maintain and replace • Reduction of maintenance and construction time “Time is money.” • Exposed elements easier to inspect • Accelerated bridge construction a fact of life for railroads to keep the track

open for running trains.

7

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Railroad Bridge Design Loads

• Live Load – Cooper E Load • Span Lengths 0 – 400 feet (130m)

• Cooper E80 Load

8

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51 61 51

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Railroad Bridge Design Loads (2)

• Live Load – Alternate Load (Steel Bridges Only)

• Axle load 25% greater than Cooper E80 • Useful for short spans, floor systems • Creates maximum design moment up to 50 feet • Better representation of actual loadings

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TC TC

s s s S 2

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AAR Railcar Minimum Requirements

Gross Rail Load - 220,000 lbs Gross Rail Load - 286,000 lbs

Overall Length 35 ft 0-1/2 in Overall Length 41 ft 10-1/2 in Truck Centers 20 ft 6 in Truck Centers 27 ft 4 in Truck Wheelbase 5 ft 8 in Truck Wheelbase 5 ft 10 in

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AREA/AREMA Bridge Design Levels

Time Period Design Level (Cooper)

Impact Equation (Year)

Allowable Stress (ksi)

1906-1919 E40 1906 16 1920-1934 E60 1920 16 1935-1947 E72 1935 18 1948-1967 E72 1948 18

1968- present E80 1968 20

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60

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ow

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Span L ngth,. ft

Steel Bridge Design Impact

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16,000

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C 12,000 .. V') :, :, 10,000

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0 0 80 90 1 0 110

Span Length, . ft

219 35 E 219 8

EBO 1968

120 1 0 1 l 0

Girder Section Modulus Requirements

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Bridge Population

Concrete ~25%

Steel ~55%

Timber ~20% Approximately 1600 miles of bridge

On the Class 1 system

Estimated 1/3 of all bridges are steel riveted deck girders

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Timber Bridges

• Timber trestles are the vast majority of the timber bridges still in inventory

• Population is declining due to multiple factors • Lack of quality timber • Loading increases makes wood insufficient to handle

the required loads and stresses • Creosote treatment is a hazardous material

• Eventually will be gone from Class I railroads

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Timber Bridges

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Timber Bridges (2)

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Sometimes a fire problem exists

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Did I mention that they burn?

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Concrete Railway Bridges

• Currently, the main use of concrete for railway bridges is: • Specialty cast-in-place structures

• Prestressed concrete beams for superstructure • Precast concrete elements for substructure • Timber trestle replacements also as a standard

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Concrete Railway Bridges (2)

• Prestressed superstructure elements: • Slab beams for trestle replacement • Double-voided box beams for trestle replacement • AASHTO section I-beams for longer spans • Tall Tee beams for the longest spans • Maximum practical span length for Cooper E80 is about 100 feet for Tee Beams

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Concrete Railway Bridges (3)

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Concrete Railway Bridges (4)

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Concrete Railway Bridges (5)

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Concrete Railway Bridges (6)

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Concrete Railway Bridges (7)

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Steel Railway Bridges

• The largest part of the bridge inventory • Used for beams, girders, and trusses • Riveted deck girders are the main type • Eyebar-Pin trusses are still great in number

• Built mainly before World War I • Load capacity could be an issue

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Steel Girder Bridges

Deck Girder

Through Girder

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1885 1905 1925 1945 1965 1985 2005

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Steel Girder Construction

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Steel Girder Rule of 75’s

• Approximately 75% are 75 years old or older • Approximately 50% are 100 years old or older • Most are riveted (Fatigue Category D)

• Approximately 1/3 of all railway bridges are steel deck girders

• Typically two girders per track for older spans

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Modern Steel Girders – 200 feet long

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Modern Steel Girders – 200 feet long (2)

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Modern Steel Girders – 200 feet long (3)

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Modern Steel Girders

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Hillman Composite Beam (HCB®)

•A new technology • A tied concrete arch inside a box • Box is fiberglass • Prestressing strand used to tie the arch • Proprietary technology

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Hillman Composite Beam (HCB®)

•Light weight alternative •Requires only one crane for lift •Replaces three trestle spans versus two for prestressed concrete

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Hillman Composite Beam (HCB®)

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Hillman Composite Beam (HCB®) (2)

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• Total revenue – $76.2 billion

Hillman Composite Beam (HCB®)

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Hillman Composite Beam (HCB®)

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Thank You!