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Bridge Strength and Life Extension - Missouri river crossing, Sioux Falls, SD
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The railroad bridge that crosses the Missouri river at Pierre, SD consists of a 446' truss (swing span), 4-350'
trusses, and 3 deck plate girder (45', 64' and 53') approach spans. The truss spans were built during the early part
of the 20th century. The spans were inspected visually to evaluate existing conditions, and then rated (Normal &
Maximum rating) to determine their capacity to carry heavy axle loads (315,000 lb traffic). Subsequently, a fatigue
analysis was conducted on the truss spans to evaluate remaining life. Rating and fatigue analysis determined that
only the floor systems of the trusses were slightly deficient, and that by strengthening only the floor system, the
useful life of the entire bridge could be extended by many years.
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Bridge strength and life estimation for heavy axle load operations, Indian Railways
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Indian Railways has permitted the operation of increased axle load wagons (CC+8+2) on selected routes in India
as part of a pilot project. While 22.82 t axle loads have been introduced initially, 25 t
axle loads in the near future are contemplated. These heavier axle loads, in combination with heavier, hi-adhesion locomotives, induce
increased vertical and longitudinal loads onto track and bridges. Given that many bridges on the system are 75 to 100
years old, there is a critical need to better understand the impact of these loads on the structural performance of bridges.
Detailed numerical models of the various bridges were developed to identify critical members and appropriate gage locations. The bridges were instrumented using the appropriate sensors to measure and monitor stresses (strains, deflections,
accelerations, and tilt were monitored at key locations). Data was collected under a variety of conditions including
low speed trains, high speed trains, acceleration and braking events, and revenue service traffic.
The residual life of steel bridges is being evaluated through analysis of traffic data from railway records and counting
of stress cycles under such traffic. Material samples were tested to establish the strength properties of the bridge members.
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Inspection and Remaining life analysis, Pemberton, Canada
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Four steel bridges (2 deck girders, 1 through truss and 1 pony girder) on a Canadian railroad from North Vancouver
to Pemberton were analyzed to determine their capacities and remaining life. The bridges were inspected to evaluate their
existing conditions, including corrosion levels in the superstructure. Metal thickness losses were evaluated by using an
ultrasonic thickness gage. Section losses were evaluated based on these measurements and subsequently, ratings were
calculated.
Traffic history on the structures was developed from railroad provided data for the purpose of remaining
life analysis. Based on the traffic history, expected traffic, and condition of the structures,
the remaining lives of the bridges were evaluated.
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Remaining Life Assessment of Multi span steel girder bridge, Ford City, IL
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The double track, ballasted deck, multi-span structure (700 ft) on a commuter rail line was inspected and analyzed
to estimate its remaining life. The structure, built in the early 1900s, is located on a curve and is composed of a series
of deck girder and through girder spans. Losses in metal thickness due to corrosion were measured during inspection and
section losses due to corrosion were estimated. Remaining life analysis was conducted as per AREMA recommendations. Traffic history on the bridge was estimated using available records from the railroad and information about the types
of trains run during various time periods. Based on the results of the analysis, the railroad was able to decide between
the various replacement and rehabilitation options available, and also plan its capital expenditure requirements.
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Axle Load Monitoring System
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The intent of this project was to develop and implement an unattended train/wheel load monitoring system to monitor
load activity and thus gauge the load environment experienced by railroads.
The selected site for the load station is in Miller, Indiana (a few miles east of Gary, Indiana) on tangent, and
well-maintained, single-track territory with continuously welded rail. Traffic on the line includes passenger/commuter
traffic as well as freight traffic (shared right-of-way), especially from steel mills and scrap yards.
Load sensors were applied and calibrated at four locations on each rail for a total of eight cribs. Sensor cables
from the cribs lead into a weatherproof bungalow that houses the data acquisition and communications equipment.
Load data measured through instrumented rail and car identification data read through an Automatic Equipment
Identification (AEI) tag reader are processed locally and then transferred to remote (off-site) servers, which
provide user data access through the Internet, additional processing and data repository services.
The system development process considered all necessary aspects including robustness, reliability, accuracy, speed,
ease of integration, ease of maintenance, and self-monitoring capabilities. The field computers have mechanisms to
monitor themselves and take appropriate action if they are not functioning as expected. Hardware 'watchdog' devices
are incorporated in each of the machines in the field, in order to handle unexpected system hang-ups.
The load monitoring system is now functional and the load data collected is made available to appropriate users through
a web portal.
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Railway Bridge Safety Monitoring Systems
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Potentially dangerous bridge conditions leading to derailments or damaging bridge force
levels can result from on-track bridge activity or from external activity. An effective Railway
Bridge Monitoring System (RBMS) can warn bridge engineering personnel and/or train crews
about such conditions. The life saving potential of such systems is considerable, especially
in passenger service.
The objective of this project was to identify various techniques that can be used to effectively
monitor railroad bridge systems, and to establish the feasibilities of the identified techniques. An additional objective was to conceptually develop a system that is capable of unmanned
operation and could monitor the structure on either a continuous or a periodic basis as
designed. Such an automatic monitoring system, would ‘keep an eye' on railroad bridges at
all times, and give an early warning of impending problems.
The feasibility of the proposed approaches was established through analytical modeling of
the bridge and vehicle systems. Two different dynamic models were developed to study
bridge-vehicle dynamics under various conditions of bridge distress. The first was a 3-
dimensional beam model of a bridge, created and analyzed using the SAP-90 program. The
second was a model of the bridge (using plate elements) and a vehicle (using springs,
dampers, & masses) modeled using LS-DYNA, an explicit finite element solver. Based on the analyses,
the applicability of various detection techniques/algorithms for different defect scenarios were studied
for both the bridge resident & mobile systems.
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Bridge Management Databases – Software Development
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SA has designed and developed a database to help railroads, with their bridge infrastructure inventory,
inspections and maintenance needs.
The database allows bridge specific details of individual bridges and bridge inspections to be maintained and retrieved
on an as-needed basis. The condition of various bridge components is easily quantified using special condition indices
that allow for easy tracking. The GUI allows the bridge engineer to search through the database and find bridges that
meet specific sets of conditions or capacity criteria.
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Load Testing of Railway Bridges
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SA was requested by one of the Class I railroads for load testing one of their truss bridges to evaluate the
capacity of the bridge and to evaluate the performance of a retrofit on one of the bridge's members. The bridge in
question consisted of three 160' Pratt truss spans, with steel beam approach spans at both ends. The work scope
included instrumentation, testing, theoretical modeling and fatigue life estimation of the bridge structure.
The project revealed that the bridge was subjected to lower stress levels and
fewer load cycles than previously assumed. Based on these test results, the
railroad was able to extend the inspection intervals on the structure and permit
occasional heavier loads.
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Damage Tolerance Analysis of Railroad Bridge
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This project covered the inspection, capacity calculations, and damage tolerance
analysis of a steel bridge on Alaska Railroad. The bridge is a single 60 ft. open
deck through plate girder span. The intent of the project was to evaluate the
capacity of the bridge to carry 32t axle load traffic and to establish
inspection intervals for the bridge.
The bridge was visually inspected to determine condition, corrosion levels, and other signs of distress. The capacities
of the bridge was evaluated based on application of the appropriate structural engineering principles and applicable
sections of the AREMA Manual of Recommended Practices. Due to concern with some of the connection details on one of
the bridges, crack growth analysis was conducted to evaluate the rate at which an initial crack would grow under railroad
usage. This analysis offers the railroad, the opportunity to detect cracks
during annual inspections, and take corrective action if a problem is detected.
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