Railroad Turnout Frog Profile Geometry and Elasticity Optimization
Using Revenue Service Wheel Profiles
Advisor: Professor J. Riley Edwards
Abstract
Railroad turnouts are essential track infrastructure elements facilitating train movements between
adjacent and diverging tracks. Most turnouts consist of three sections: the switch area, closure
area, and frog area. The turnout frog induces significant wheel impacts as the wheel traverses
through the turnout. These impacts are primarily attributed to both the frog profile geometry,
which includes a gap (i.e., flangeway) between the wing rail and the point, as well as the variation
in vertical track stiffness along the turnout. Given the high resiliency and reliability expectations
for heavy axle load (HAL) freight infrastructure in North America (N.A.), improvement of turnout
frog wear and impact resistance is crucial. My dissertation aims to optimize both the profile
geometry of the frog and the elasticity of the turnout, thereby reducing wear and damage, leading
to longer life cycles and fewer maintenance interventions.
Given that previous studies on turnout optimization predominantly relied on design wheel profiles
or a limited subset of wheels for wheel-rail interaction analysis, I developed and leveraged five
representative revenue service wheel profiles. These profiles were selected based on the severity
of hollow tread using a dataset of one million revenue service wheel profiles. In the geometry
optimization phase, static geometric interaction analyses were conducted on 30 unique frog
geometries. Wheel impacts during the wheel transition were quantified for each case using 400
randomly extracted revenue service wheel profiles. Among the geometries analyzed, the frog
design featuring a gradual point slope and lower wing rail height demonstrated an average 28%
reduction in wheel impacts compared to the existing frog design. To account for dynamic aspects,
finite element analysis (FEA) was conducted on three validated frog geometries: the existing
design, the geometry optimized through static analysis, and a version incorporating a longitudinal
wing slope. This research quantified contact forces between the wheel and frog across five wheel
profiles under three different train speeds. Results showed that the geometry with the longitudinal
wing slope provided an average wheel impact reduction of 46% compared to the existing frog
design. Finally, under tie pads (UTPs) were introduced to further reduce wheel impacts at the frog
point and minimize vertical track stiffness variations throughout the turnout. Laboratory
experiments were conducted to evaluate the performance of UTPs with varying material properties,
and the results were used to assess the impact of UTP characteristics and guide the selection of
appropriate UTP properties to optimize turnout elasticity. A 3D turnout model was developed
using the commercial multibody simulation (MBS) software VI-Rail, investigating four UTP
properties and three rail pad stiffness levels. The results indicated that UTP properties had a
negligible effect on wheel impacts. However, adopting soft rail pads reduced wheel impacts for
wheels in good condition but increased them for hollow worn wheels. Additionally, UTPs
improved track stiffness consistency by combining soft rail pads throughout the turnout with stiff
UTPs in the frog section. This configuration achieved consistent track stiffness along the turnout,
limiting displacement and corresponding stiffness variations to 2.3% and 6.9% for the switch and
frog sections, respectively.