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Yonjung Bridge is a hybrid multispan bridge that is designed to transport high-speed trains (HEMU-430X) with maximum operating speed of 430 km/h. The bridge consists of simply supported prestressed concrete (PSC) and composite steel girders to carry double railway tracks. The structural health monitoring system (SHM) is designed and installed to investigate and assess the performance of the bridge in terms of acceleration and deformation measurements under different speeds of the passing train. The SHM measurements are investigated in both time and frequency domains; in addition, several identification models are examined to assess the performance of the bridge. The drawn conclusions show that the maximum deflection and acceleration of the bridge are within the design limits that are specified by the Korean and European codes. The parameters evaluation of the model identification depicts the quasistatic and dynamic deformations of PSC and steel girders to be different and less correlated when higher speeds of the passing trains are considered. Finally, the variation of the frequency content of the dynamic deformations of the girders is negligible when high speeds are considered.

The Republic of Korea (South Korea) launched the Korea Train eXpress (KTX) in 2004 and High-Speed Electric Multiple Unit (HEMU-430X) in 2013, becoming the fifth nation to launch high-speed rail service [

Routes used and strategy plan railway for the high-speed trains in South Korea [

In 2012, KTX trains carried nearly 53 million passengers, compared with the Southwest Airlines’ 112 million enplanements for fiscal year 2012 [

SHM is used to detect the behavior and performance of structures based on designing a reliable measurement system. The main purposes of the recorded measurements are assessing, evaluating, and predicting the performance of the structures under consideration in time and frequency domains. To assess the dynamic performance of different structures, the acceleration and displacement are common measurements that can be investigated. Many studies have conducted SHM techniques for the high-speed railway bridges. Previous studies and their concluded results are briefly introduced in the following sections.

Both theoretical and experimental studies have been continuously carried out on PSC box girder bridges, which account for the majority of the bridges along the high-speed railway system [

In this paper, the quasistatic and dynamic characteristic of the Yonjung Bridge deformations is investigated. The performance assessment of two types of girders, that is, prestressed concrete and composite steel box girders of the bridge, is conducted. Moreover, the performance evaluation is considered including the identification model parameters and frequency content analysis for the quasistatic and dynamic deformations of the girders. Comparing the various deformation results under different speeds of two types of trains (HEMU and KTX) is investigated. In addition, the results are compared with the standard dynamic behavior requirements set by Eurocode and Korean High-Speed Railway. Finally, through interpretative analysis, a quantitative comparison between the prestressed concrete and steel girder is achieved.

The Yonjung Bridge is a multispan hybrid bridge constructed in South Korea. It connects Iksan and Jungeup cities. The bridge consists of several PSC box girders with various spans (25 m and 40 m) and a composite steel box girder with span 50 m as illustrated in Figure

PSC and steel girders of Yonjung Bridge.

Axial spacing and loads of HEMU-430X train (a) and KTX-2 train (b).

Various sensors are applied to detect the static and dynamic deformations of the two girders of the bridge. Accelerometers denoted as (A), LVDT sensors, and ring gauges denoted as (R) are installed at different locations of the two girders. LVDT (CDP-10) strain transducers are used. The ring gauge (OU-30) with capacity of 30 mm was attached to the strain gauge to detect the direct displacement of the girder. The installed sensors in the PSC girder and the composite steel girder are depicted in Figure

Sensors types and location at the different types of girders.

PSC box girder

Composite steel box girder

The field measurement evaluation of the Yonjung Bridge is conducted to assess the static and dynamic performance of the bridge under the high-speed train passage. Two spans of the bridge, that is, PSC box girder (40 m span) and steel composite girder (50 m span), are evaluated. A set of experimental tests were performed during the operation of KTX and HEMU high-speed trains, and a number of accelerometers, LVDTs, and ring-type displacement transducer are utilized for measurement of the two main responses of the bridge (vertical acceleration and deflection). The time and frequency domains are analyzed and presented in this section. In addition, the Eurocode [

The deflection and acceleration measurements for two train types KTX with speed 169 km/h and HEMU with speed 399 km/h are shown in Figure

Vertical acceleration and deflection for the bridge girders for the (a) KTX (169 km/h) and (b) HEMU (399 km/h).

From Figure

Maximum acceleration and deflection measurements.

Train speed | Direction | PSC girder | Steel girder | |||||
---|---|---|---|---|---|---|---|---|

Peak Acc. (g) | Def. (mm) | Peak Acc. (g) | Def. (mm) | |||||

Pas. | Ops. | Pas. | Ops. | 0.33 | 0.5 | |||

KTX-165 | Iksan to Jungeup | 0.680 | 0.622 | 1.01 | 0.342 | 0.283 | 2.66 | 3.19 |

KTX-169 | Iksan to Jungeup | 0.562 | 0.560 | 1.00 | 0.279 | 0.248 | 2.53 | 3.04 |

HEMU-376 | Jungeup to Iksan | 0.257 | 0.164 | 1.06 | 0.193 | 0.134 | 1.84 | 2.21 |

HEMU-399 | Jungeup to Iksan | 0.320 | 0.223 | 0.90 | 0.211 | 0.126 | 1.68 | 2.02 |

HEMU-403 | Jungeup to Iksan | 0.343 | 0.260 | 0.90 | 0.209 | 0.091 | 1.67 | 2.00 |

The variations of maximum passage direction acceleration and midspan deflection are shown by 50% and 68%, respectively, between PSC and steel girders, as shown in Table

The acceleration and deflection of the PSC and steel girders decrease when increasing the train speed, whereas the dynamic wheel weight decreases during the upward movement. Furthermore, the difference between the maximum acceleration variations between passage and opposite direction for the PSC girder is shown to be higher than the variation for the steel girder. In addition, the maximum deflection under different train speeds is within the design criteria of the Korea Rail Network Authority. However, the results obtained from the maximum vertical acceleration differed significantly from the vertical deflection results. In other words, responses exceeding the criteria were observed in the PSC box girder with KTX trains. This is because the rigidity of PSC section of this type of bridge and the number of cars for the KTX train type or higher noise may have occurred. Therefore, Figure

Histogram of measured acceleration (a) KTX and (b) HEMU.

In addition, Figure

To assess the long-period (quasistatic) deformation, the signal filtration is applied to remove the measurement noises for the LVDT sensor. Figure

Static performance of bridge (a) moving average filter effective, (b) quasistatic deflection with train speeds.

The extracted long-period displacement after filtration at the deck level of the steel and PSC girders are very small. In addition, it can be seen that the deflection change for the PSC and steel decks by 9.6% and 33.3%, respectively, due to train speed changes from 169 to 399 km/h, which implies that the deflection of the PSC girder is smaller than the steel girder.

Basically, the process of parameter identification is an optimization process with the aim of reducing a previously or futurity-defined objective function to a minimum. Although it is considered simple at the first glance, the procedure can become costly in terms of computational time when the set of variables increases. Herein, for the output models, the time series model identification is one of the statistical analyses of measurements techniques. The model identification philosophy is presented in Figure

Parameter identification philosophy.

The model identification applications to evaluate structures are presented and discussed in Sohn et al. [

Therefore, in this section, the ARMA model based on GARCH process will be applied to estimate the parameters for the filtered displacement and acceleration measurements for the PSC and steel girders during KTX and HEMU train passage. It should be mentioned that the estimation of parameters of ARMA model and GARCH process usually requires a more complicated iteration procedure. However, firstly the model parameters are defined to estimate the proper model parameters to be used. Therefore, two criteria are applied to define the best model parameters and order can be used. The first criterion to find a suitable model is to use the Akaike Information Criterion (AIC), where smaller AIC means better quality of models parameters numbers can be used. The AIC for model estimation can be calculated as follows [

AIC for the displacement and acceleration measurements for the steel girder models.

Model | ARMA | |||||
---|---|---|---|---|---|---|

| | | | | | |

AIC-Disp | | | | | | |

AIC-Acc | | | | | | |

AF with 95% confidence intervals of the residuals for the (a) displacement and (b) acceleration.

From Table

AF with 95% confidence intervals of the residuals for the (a) GARCH

Therefore, the parameters of models using ARMA

Models parameters and evaluation for the displacement and acceleration measurements.

Train | Parameter | PSC girder | Steel girder | ||||
---|---|---|---|---|---|---|---|

Value | St. error (%) | | Value | St. error (%) | | ||

Displacement models | |||||||

| |||||||

KTX | | | 0.001 | | 0.383 | | 86.547 |

| 0.964 | 0.010 | 92.920 | 0.933 | 0.011 | 84.223 | |

| | | 1.577 | | | 2.887 | |

| 0.293 | 0.097 | 3.023 | 0.256 | 0.055 | 4.655 | |

| 0.716 | 0.231 | 3.097 | 0.739 | 0.187 | 3.959 | |

| | 0.250 | | 0.009 | 0.231 | 0.037 | |

| |||||||

HEMU | | | | | | 0.002 | |

| 0.846 | 0.015 | 55.562 | 0.971 | 0.010 | 100.448 | |

| | | 8.139 | | | 1.410 | |

| 0.000 | | 0.000 | 0.279 | 0.096 | 2.897 | |

| 0.867 | 0.206 | 4.202 | 0.733 | 0.227 | 3.226 | |

| 0.145 | 0.256 | 0.566 | | 0.273 | | |

| |||||||

Acceleration models | |||||||

| |||||||

KTX | | | | 0.301 | | | |

| 0.536 | 0.022 | 23.874 | 0.366 | 0.020 | 18.041 | |

| | | 2.188 | | | 5.770 | |

| 0.814 | 0.012 | 67.968 | 0.785 | 0.009 | 86.207 | |

| 0.172 | 0.020 | 8.676 | 0.275 | 0.019 | 14.720 | |

| 0.028 | 0.027 | 1.008 | | 0.018 | | |

| |||||||

HEMU | | | | 1.888 | | | 0.599 |

| 0.623 | 0.020 | 31.644 | 0.199 | 0.026 | 7.521 | |

| | | 3.847 | | | 3.055 | |

| 0.744 | 0.015 | 48.710 | 0.847 | 0.013 | 65.742 | |

| 0.225 | 0.026 | 8.776 | 0.159 | 0.021 | 7.733 | |

| 0.062 | 0.037 | 1.659 | | 0.025 | |

Comparison of the histogram of model error with the probability density function of Gaussian distribution with the same mean value and standard deviation for the displacement (a) and acceleration (b) considering HEMU.

Our first indication that the model is good is based on the

Moreover, the standard errors for the parameters are acceptable in the two cases of measurements and girders types. Furthermore, the

The displacement parameters changes between the two models of PSC and steel girders are shown to be 3.2, 12.6, and 3.2% for the

The change of the frequency content is one of the mode shape analyses in the frequency domain of structures [

Acceleration frequency contents for the (a) KTX and (b) HEMU trains.

The KTX dynamic frequency content shows that the frequency modes for the steel girder are 4.4, 36.6, 45.4, and 50.3 Hz, while they are 4.9, 31.7, 36.1, 45.4, and 50.3 Hz for the PSC girder. The maximum PSD for the steel and PSC girders are

In other way, the low frequency content (static frequency change) for the bridge girders is shown in Figure

Displacement frequency contents for the (a) KTX and (b) HEMU.

It is known that once the fatigue crack appears, extensive fatigue cracking may occur and will cause severe consequences [

The

Weibull parameters for the displacement measurements.

Train | Parameters | PSC girder | Steel girder |
---|---|---|---|

KTX | | 0.116 | 0.251 |

| 0.581 | 0.516 | |

HEMU | | 0.229 | 0.297 |

| 0.790 | 0.612 |

Cumulative distribution function (CDF) of the bridge girders displacement: (a) original data and Weibull calculation; (b) different girders displacement measurements.

Figure

From Table

This study investigates the performance of the Yonjung Bridge that is designed to transport high-speed trains (HEMU-430X) with maximum operating speed of 430 km/h. The performance of the bridge is assessed in terms of analyzing the recorded deformations and accelerations in time and frequency domains. Two types of bridge girders are considered: prestressed reinforced concrete and composite steel box girders. These girders are investigated under different speeds of the passing train. Two various types of high-speed trains are used in this study: KTX and HEMU trains. The identification model parameters and the frequency contents are proposed and calculated.

The acceleration and quasistatic deformations of the PSC and steel girders decreased when considering higher train speeds. Furthermore, the difference between the maximum acceleration variations between passage and opposite direction for the PSC girder is shown to be higher than the variation for steel girder. The maximum deflection and acceleration were within the design criteria of the Korea Rail Network Authority.

The ARMA

The dominant frequency change for the PSC girder is significantly smaller than for the steel girder, which referred to the rigidity of PSC girder. Furthermore, the dynamic performance did not suffer major changes when increasing the train speed, while at low speeds the frequency content of the dynamic deformation considerably changed. Finally, no low frequency modes occurred with the KTX train, while low frequency modes were easily observed with HEMU train especially when considering the steel girder, which explained the convergence of the quasistatic (low frequency) deformations for the two girders.

Finally, the measurements assessment shows that the failure rate of the bridge is in an early-life failure stage, while the failure rate for the steel girder is observed to be less than that for PSC girder. Moreover, the steel girder is shown to be more stable than the PSC girder under the train speed change. Nevertheless, it can be concluded that the bridge is safe under the different high-speed trains.

The authors declare that there is no conflict of interests regarding the publication of this paper.

This work was supported by a 2016 Incheon National University (INU) Research Grant. The authors gratefully acknowledge these supports.