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Since high-speed railway bridges are subjected to cyclic
loading by the continuous wheel loads traveling at high speed and regular
spacing, their dynamic behavior is of extreme importance and has significant
influence on the riding safety of the trains. To secure the
riding safety of the trains, advanced railway countries have limited the
vertical acceleration of the bridge slab below critical values at specific
frequency domains. Since these limitations of the vertical acceleration
constitute the most important factors in securing the dynamic safety of the
bridges, these countries have opted for a conservative approach. However, the
Korean specifications limit only the size of the peak acceleration without
considering the frequency domain, which impede significantly rational
evaluation of the high-speed railway bridges in Korea. In addition, the
evaluation of the acceleration without consideration of the frequency domain is
the cause of disagreement between the dynamic analysis and measurement results.
This study conducts field monitoring and dynamic analysis on high-speed railway
bridges to gather the acceleration signals and compare them. Significant
difference in the size of the vertical acceleration was observed between the
measured and dynamic analysis accelerations when discarding the frequency
domain as done in the current specifications. The comparison of the
accelerations considering only low frequencies below 30 Hz showed that the
dynamic analysis reflected accurately the measured vertical acceleration.
The design live load of
railway is divided into common railway and high-speed railway separately inKorea.
Accordingly, the Korean design specification of railway specifies the impact
factor for common railway and high-speed railway respectively. The impact
factor for high-speed railway is based on Eurocode. Since the impact factor
criteria inKoreawere established by adopting those of the Eurocode and without dedicated
investigation relying on research results reflecting the domestic
circumstances, thorough examination should be implemented on these criteria.
Therefore the evaluation of impact factor based on field tests is required.
Both dynamic and static vertical displacements are necessary to compute the
impact factor. The dynamic response can be obtained from the measurement of
deflection of the bridge slab crossed by the firstKoreahigh-speed train (KTX, Korea
Train eXpress) running at high-speed. The main difficulties encountered are in
obtaining static response because static response corresponds to the response
of the bridge when the train remains immobile on the bridge or crosses the
bridge at speed slower than5 km/hr. This study
introduces the static response derived by applying the moving average method on
the dynamic response signal. To that goal, field measurements was conducted
under train speeds of5 km/hr and ranging
from100 km/hr to300 km/hr
on Yeonjae Bridge located in the trial section of the Gyeonbu High-Speed
Railway Line before its opening. The validity of the application of the moving
average method is verified from comparison of measured static response and
derived static response by moving average method. Moreover, evaluation is
conducted on the impact factor computed for a bridge crossed by the KTX train
running at operational speed.
This paper presents the results of fatigue performance
tests performed up to 10 million cycles on a load-measuring pot bearing with
built-in load cell to verify its field applicability and proposes an empirical
temperature correction formula. In Part I of this work, various measurement
performances of the load-measuring pot bearing were evaluated through static
and dynamic loading tests. Bridge bearings are subjected to the effect of
fatigue caused by the repeated application of moving loads and exposed to harsh
site conditions including cold and hot weathers differently to laboratory conditions.
Accordingly, the durability of the load-measuring pot bearing with built-in
load cell shall be secured and the environmental effects like temperature shall
be minimized for its application on field. This study conducted fatigue tests
up to 10 million cycles on a load-measuring pot bearing with the capacity of 1000
kN to examine eventual degradation of the measurement accuracy with respect to
the number of fatigue loading cycles. In addition, the experimental temperature
correction procedure is proposed to obtain the temperature correction formula
enabling to correct the effect of temperature on the load measurement.
This paper presents the underlying principle and the
results of various performance evaluations for a load-measuring pot bearing
with built-in load cell. The pot bearing composed of a pot made of steel in
which an elastomer disk is inserted is a bearing supporting larger loads than
the elastomeric bearing and accommodating rotational movement. Owing to a
Poisson’s ratio close to 0.5, elastomer withstands hydrostatic pressure when
confined in a rigid body. Accounting for this principle, the vertical load
applied on the pot bearing can be obtained by converting the pressure acting on
the elastomer. Therefore, a load-measuring pot bearing is developed in this
study by embedding a load cell exhibiting remarkable durability in
the base plate of the bearing. The details for the insertion of the load cell
in the base plate of the pot were improved through finite element analysis to
secure sufficient measurement accuracy. The evaluation of the static
performance of the pot bearing applying these improved details verified that
the bearing exhibited sufficient accuracy for the intended measurement purpose.
The dynamic performance evaluation results indicated that accurate measurement of
the dynamic load was also achieved without time lag.