2
J. Bujnak et al.
horizontal alignment, cant, gradients and vertical curves. Specific technology and
codes requirements should be applied in order to be taken into account rail-deck
interaction, dynamic impact of live loads, fatigue-resistance design, aerodynamic
effect, derailment or collisions.
Essential prerequisite for high speed corridor is to have control on the degradation
of track geometry, so as to keep various tolerances well within the specified limits.
Axle-load, speed, sub-grade characteristics and improvement of subgrade in poor
ground areas and bridges is recognized as one of the most significant factor. Therefore, track bed for high-speed lines is obviously much deeper than in the case of
conventional railways. With speed increasing, the noise problems appear. Its nature
changes with the speed increasing. Measures in the forms of screens, mounds of earth
should be taken to protect against noise, as well as possible modifications of the route
or the creation of artificial tunnels or covered sections and eventual modifications
to the rolling stock. Normally level crossing is not suitable for higher speed train
operation and hence road overpasses or road under bridges need to be constructed.
In addition, complete lines shall be screened to avoid interference of local people and
animals. Consequently, analyses of bridges for higher speed tracks present several
particularities.
1.1 Specific Railway Assessments
1.1.1 Traffic Actions on Bridge Structures
Besides assessments related to structures and materials, there are some specific
railway criteria to be checked. The characteristic vertical live load models LM 71
are given in EN 1991-2 [2]. A high speed train convoy can dynamically excite the
deformations of the bridge deck with the result of a resonant growth of the deflections. So, high speed load model HSLM should be along with taken into account
according to EN 1991-2 [2]. The authors of the documents [3] recommend similar
approaches to the standard procedure. Both loading shall be multiplied by a factor α
on lines carrying rail traffic which is heavier or lighter than normal rail traffic. When
multiplied by the factor α, the loads came to be classified vertical loads. The value
1.21 is normally recommended on lines for freight traffic and international lines. On
lines carrying rail traffic which is lighter, the factor α shall be 1.1.
Together with vertical actions, some horizontal forces due to rail traffic must be
taken into account. Traction and braking forces act at the top of the rails in the
longitudinal direction of the track. When the track is continuous at one or both ends
of the bridge, only a proportion of these acceleration and braking forces is transferred
through the deck to the bearings, the remainder of the forces are transmitted through
the track where it is resisted behind the abutments. The additional but transversal
centrifugal forces are considered fully transmitted through the deck to the bearings.
The nosing forces, also lateral ones, have generally only local effects. The centrifugal
and nosing forces, traction and braking actions shall be multiplied by the same factor
α. But, all calculations for fatigue are done with the LM 71 and the factor α = 1.0.
J. Bujnak et al.
horizontal alignment, cant, gradients and vertical curves. Specific technology and
codes requirements should be applied in order to be taken into account rail-deck
interaction, dynamic impact of live loads, fatigue-resistance design, aerodynamic
effect, derailment or collisions.
Essential prerequisite for high speed corridor is to have control on the degradation
of track geometry, so as to keep various tolerances well within the specified limits.
Axle-load, speed, sub-grade characteristics and improvement of subgrade in poor
ground areas and bridges is recognized as one of the most significant factor. Therefore, track bed for high-speed lines is obviously much deeper than in the case of
conventional railways. With speed increasing, the noise problems appear. Its nature
changes with the speed increasing. Measures in the forms of screens, mounds of earth
should be taken to protect against noise, as well as possible modifications of the route
or the creation of artificial tunnels or covered sections and eventual modifications
to the rolling stock. Normally level crossing is not suitable for higher speed train
operation and hence road overpasses or road under bridges need to be constructed.
In addition, complete lines shall be screened to avoid interference of local people and
animals. Consequently, analyses of bridges for higher speed tracks present several
particularities.
1.1 Specific Railway Assessments
1.1.1 Traffic Actions on Bridge Structures
Besides assessments related to structures and materials, there are some specific
railway criteria to be checked. The characteristic vertical live load models LM 71
are given in EN 1991-2 [2]. A high speed train convoy can dynamically excite the
deformations of the bridge deck with the result of a resonant growth of the deflections. So, high speed load model HSLM should be along with taken into account
according to EN 1991-2 [2]. The authors of the documents [3] recommend similar
approaches to the standard procedure. Both loading shall be multiplied by a factor α
on lines carrying rail traffic which is heavier or lighter than normal rail traffic. When
multiplied by the factor α, the loads came to be classified vertical loads. The value
1.21 is normally recommended on lines for freight traffic and international lines. On
lines carrying rail traffic which is lighter, the factor α shall be 1.1.
Together with vertical actions, some horizontal forces due to rail traffic must be
taken into account. Traction and braking forces act at the top of the rails in the
longitudinal direction of the track. When the track is continuous at one or both ends
of the bridge, only a proportion of these acceleration and braking forces is transferred
through the deck to the bearings, the remainder of the forces are transmitted through
the track where it is resisted behind the abutments. The additional but transversal
centrifugal forces are considered fully transmitted through the deck to the bearings.
The nosing forces, also lateral ones, have generally only local effects. The centrifugal
and nosing forces, traction and braking actions shall be multiplied by the same factor
α. But, all calculations for fatigue are done with the LM 71 and the factor α = 1.0.