Civil Engineering Reference
In-Depth Information
5
Structural Analysis and
Design of Steel Railway
Bridges
5.1 INTRODUCTION
Elastic structural analysis procedures are used for steel railway bridge design based on
theASD methods of theAREMA (2008)
ManualforRailwayEngineering
.
∗
Strength
(yield, ultimate, and stability), fatigue and fracture, and serviceability (deflection
and vibration) criteria (or limit states) must be considered for safe and reliable steel
railway bridge design.
Fatigue, or the failure of steel at nominal cyclical stresses lower than yield stress, is
a phenomenon that occurs due to the cyclical nature of railway traffic and the presence
of stress concentrations in the superstructure. Fracture behavior is primarily related
to material (see Chapter 2) and fabricated detail characteristics. Therefore, it is not
directly affected by design methodology.
Ordinary steel railway superstructure design is often governed by deflection (stiff-
ness) and fatigue criteria. Since live load deflection and fatigue strength details are
evaluated at service loads, ASD is generally appropriate for steel railway super-
structures. Nevertheless, combined with the current state of knowledge concerning
material behavior, a better understanding of the railway live load spectrum may pre-
cipitateaprobabilisticreliability-basedapproachtofuturesteelrailwaysuperstructure
design. The design service life of railroad bridges is generally considered to be about
80 years.
∗
Recommended practices for the design of railroad bridges are developed and maintained by the Amer-
ican Railway Engineering and Maintenance-of-Way Association (AREMA, 2008). Chapter 15—Steel
Structures provides detailed recommendations for the design of steel railway bridges for spans up to
400 ft in length, standard gage track (56.5
), and North American freight and passenger equipment at
speeds up to 79 and 90 mph, respectively. The recommendations may be used for longer-span bridges
with supplemental requirements. Many railroad companies establish steel railway bridge design criteria
based on these recommended practices.
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