structural health monitoring of the bridge of slovak ... · structural health monitoring of the...

TS 1 – Deformation Monitoring, Analysis and Interpretation

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Structural Health Monitoring of the Bridge of Slovak National Uprising using Automated System Alojz Kopáčik1, Imrich Lipták1, Ján Erdélyi1, Peter Kyrinovič1

1 Faculty of Civil Engineering, Slovak University of Technology in Bratislava, Radlinského 11, Bratislava, Slovak Republic, [email protected], [email protected], [email protected], [email protected]

Abstract. One of the main tasks associated with the safety of civil engineering structures is their deformation. Modern and often untypical shape of these objects generates requirements for the monitoring of structural deformations. A current approach in the automation of geodetic measurements allows the application of automated systems for structural monitoring. The paper presents a design of an automated measurement system developed for the permanent geodetic monitoring of the bridge structures over the river Danube in the capital city of the Slovak Republic, i.e., Bratislava. It describes the topology and preliminary experimental testing of the automated system on the actual bridge structure. The bases of the system are a geodetic total station, tilt sensors, accelerometers and complementary sensors such as a meteorological station and temperature sensors. The control of the measurement process is realized by the remote management and the data server via the mobile internet connection. The system is able to monitor long-term deformations and the dynamic behaviour of the bridge in real-time.

Keywords: accelerometer, automated monitoring system, bridge, deformation, natural frequency, structural health monitoring, tilt sensor, total station.

1. Introduction

The issue of the investigation, realization and implementation of new technologies in monitoring of civil engineering structures is generally discussed as Structural Health Monitoring (SHM). An important part of these activities is geodetic monitoring of bridges. Several operation restrictions in monitoring large bridge structures by classic geodetic technologies and methodologies and requirements on dynamic measurements, increase the number of installations of automated measurement systems on these structures.

Automated measurement systems have recently been implemented at large bridge structures around the world, mainly in Japan, China and USA [Hill & Sippel 2002], [Hsieh et al. 2006], [Yong & Spencer 2008], [Wenzel 2009] and [Ko & Ni 2005]. They significantly determine the approach in this research area,

SIG 2016 – International Symposium on Engineering Geodesy, 20–22 May 2016, Varaždin, Croatia

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especially in the area of sensors and monitoring of dynamic behaviour of bridge structures. In the countries referred to above the monitoring is focused on the seismic resistance of structures, due to many structures situated in areas affected by the increased seismic activity.

USA has implemented the program of long term monitoring of significant bridges supported by legislative frame as LTBP program (Long-Term Bridge Performance). This frame helped to implement several permanent long-term automated monitoring systems of bridges.

Automated systems on bridge structures are implemented especially at significant traffic corridors with high operation load. Several systems, focused on dynamic monitoring of the structures, have been implemented on highway bridges in Europe [Wenzel 2009], [Wenzel & Pichler 2005], [Enckell 2007] and [Geier 2009]. Measurement systems are based on terrestrial geodetic (total stations, GNSS) and non-geodetic measurement systems (accelerometers, strain gauges etc.). The most famous project in this area is the bridge crossing Oresund strait that connects Sweeden and Denmark [Peeters 2009].

Requirements on geodetic bridge monitoring in Slovak Republic are anchored by legislative frames and national technical standards. The realization of bridge monitoring is performed mostly by classic geodetic approach. The approach includes several disadvantages, such as requisition for some operation breaks, that cause traffic problems. This can be avoided by automated measurement systems of bridge structures.

The Department of Surveying at the Faculty of Civil Engineering of the Slovak University of Technology in Bratislava (FCE STU) has been monitoring the dynamic effects on civil engineering structures of different types and dimensions for a long time. Our recent research is focused on the automation of the monitoring process, the preparation of innovative geodetic technologies for multi-sensor fusion, with the aim of integrated automated structural health monitoring of large bridges in Slovakia. The focus of this paper is on recent research in the area of development of an integrated monitoring system of two Danube bridges in Bratislava – the Apollo Bridge and the Bridge of Slovak National Uprising.

2. Automated measurement system for bridge monitoring

Current geodetic monitoring of bridge structures is generally based on periodic measurements of selected parts of the bridge structure, that are realized when there is no traffic on the structure. According to these limitations, especially in the case of large bridges with significant operation load by traffic, arises the requirement regarding design and realization of an automated measurement system (AMS). AMS is able to monitor the bridge structure in arbitrary moment in time and frequency according to the requirements of the bridge management. This eliminates the requisites for the realization of the regular operation breaks, or minimizes the time of the operation breaks. It also brings significant logistic and economic advantages to the bridge management.


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The design of an AMS for long-term monitoring is focused on monitoring of behaviour of the bridge girders. These parts of the structures are extremely loaded under the influence of weather conditions and operation. AMS is designed for:

• a continuous and time unlimited monitoring of the bridge girder, • determining the dynamic and long-term deformation of the bridge girder, • providing information about the deformation in real time, • a remote access and management of the system. The designed AMS is divided into two separated and interconnected

subsystems [Figure 2.1]. Both subsystems are time synchronized. The subsystem of the sensors is designed for the installation on the bridge structure. It communicates with the master subsystem via the Internet connection, that is situated on the Department of Surveying of the FCE STU. Remote access to sensors is possible in real-time through the master subsystem.

Figure 2.1 Subsystems of the AMS

The subsystem on the bridge is built by several types of sensors and communication devices [Figure 2.2]:

• total station Leica TS30, • tilt sensors Leica Nivel220, • meteorological station Reinhardt DFT 1MV, • accelerometers HBM B12/200 and universal amplifier HBM Spider 8, • temperature sensors Pt1000/TG7 and data logger Comet MS6D, • local time server Mobatime LTS, • GPRS/EDGE/3G router Racom MG102.

Figure 2.2 Subsystem of sensors


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The base of the subsystem of sensors is the total station Leica TS30, used for measurement of the spatial long-term and dynamic deformations of the bridge girder. Tilt sensors measure longitudinal and transversal tilts of the bridge girder. These measurements are useful for monitoring of both, the vertical bending and the torsional deformation of the girder. Accelerometers are used for the measurement of vertical vibrations of the bridge deck. The sensor configuration is suitable for long-term continuous monitoring of changes as well as for the vibrations of the monitored structures. AMS is able to monitor changes in both, the structure and air temperature by contact resistive temperature sensors Pt1000.

The master subsystem is built by server located at the Department of Surveying. The server is running permanently, communicating with the subsystem of sensors by virtual private network (VPN). The advantage of this solution is a stable and safe access to the components of the system in real time and the possibility of the system configuration. Time synchronization of the system is realized through the local time server Mobatime LTS, that provides the time signal of the satellite navigation system NAVSTAR GPS. The accuracy of this synchronization is given by 0.05 second with evenly spaced actualization of the system time with frequency of 1 Hz.

The measurement and the registration process of most of the components is provided by proprietary software. Yet, for the dynamic measurements by total station, proprietary software solution does not exist. This was the reason to develop own software “Tracking TS30” using Leica GeoCoM protocol. This software is a unique solution for dynamic monitoring of engineering structures in real time, which is an important component of AMS [Lipták 2014].

3. Application of AMS at the Bridge of Slovak National Uprising in Bratislava

The developed AMS for a bridge structure stability control can be applicable at arbitrary bridge structure. In the case of the development of the system prototype, several versions of AMS installation at the cable-stayed steel bridge of Slovak National Uprising in Bratislava, were realized.

The reference network contains permanently stabilized points for controlling the stability of the total station using the spatial polar method. Spatial distribution of the objects in the bridge surrounding cause difficulties in the correct location and stabilization of the reference points. There is increased pedestrian and car traffic, which brings limitations for the permanent stabilization and operation of the total station. According to this the reference points at the bridge structure were located in non-standard position. There are 5 reference points stabilized for total station measurements [Figure 3.1].

The reference point VB1, with the total station [Figure 3.2], is built in the bridge abutment chamber at the right bank of the Danube (Petržalka). The position of this point provides a good protection and the visibility of each reference and measuring point at the bridge deck as well. The point is stabilized by


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cylindrical shaped and 1.20 m high steel pillar of the diameter of 300 mm and concrete filling. Tilt sensor Leica Nivel220 monitors horizontal stability of the pillar and the meteorological station Reinhardt DFT 1MV is situated near the pillar to monitor the weather conditions in the surroundings of the total station.

Figure 3.1 Stabilization of the reference points. Total station positioned at the reference

point VB1 (left). Longitudinal section of the bridge pillar and abutment (center). The position of the reference points inside the bridge abutment – situation (right)

Reference points VB2 – VB5 are used for control of the measured horizontal angles and for monitoring the stability of the total station. These are located in the thrust block and the bottom part of the bridge pylons. The position of the measuring points is given by typical points of the bridge deck where the deformation has the highest influence on the stability of the structure. The points are designed in three cross sections in the locations of the catenaries hanging [Figure 3.2]. In each cross section, at the outboard bottom flange, there are stabilized prisms Leica GPR1 [Figure 3.3 left]. In the chambers of catenaries hanging, tilt sensors Leica Nivel220, accelerometers HBM B12/200 and temperature sensors Pt1000 [Figure 3.3 right], are situated.

Figure 3.2 Measuring points configuration

Connection between sensors and data loggers is realized by UTP and FTP cables. UTP cables are used for the interconnection of tilt sensors, whereas FTP cables are used for the connection of accelerometers and temperature sensors. They are resistant to influence of external conditions and to non-stability of the electric voltage. This advantage reduces the risk of signal distortion. The measuring bus for power supply and communication interconnection of the sensor subsystem is installed in the thrust block of the bridge support near to the reference point VB1. The registration laptop and the universal amplifier HBM Spider8 are located in the chamber of the catenaries hanging No. 4.


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Communication of this part of the system with the measuring bus is realized by Wi-Fi working at 5 GHz frequency.

Figure 3.3 Stabilization of the measuring points

4. Long-term monitoring of the bridge

Application of the AMS enable us to monitor structural deformation in common time resolution and time range. The possibility of the continuous monitoring of the bridge dynamics is a significant advantage of the developed AMS. These measurements can be used for the analysis of long-term behaviour of the bridge dynamics, but can also perform useful data about the static deformation. Selected parts of the bridge monitoring using the developed AMS are described here.

4.1. Long-term monitoring of the bridge deck by total station

The long-term monitoring using total station enable us to monitor spatial displacements of the chosen part of the bridge structure, for example the bridge deck. The measurement was made by the total station Leica TS30, the measurement process was managed by Leica GeoMoS software. The results of realized experimental measurements indicate strong oscillation of the structure with dominant cyclical component at the level of 24 hours. Figure 4.1 brings the longitudinal bridge deck deformation during the experimental measurements realized from April 10, 2014 to April 15, 2014.

Figure 4.1 Longitudinal displacements of the bridge structure


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The results of the cross-spectral analysis of longitudinal displacements and the structure’s temperature underline a strong influence of the temperature variation at the bridge deck deformation. This fact was confirmed by high coherence (at level 0.95) between the structure’s temperature and the displacements at each measuring point. The analysis of the phase delay of time series describes structural response on temperature changes approximately in 1 to 1.5 hour. Average amplitudes of daily variations of displacements at points PBH01 and PBH02 are at level of 5.0 mm whereas at points PBH03 and PBH04 are at level of 10.0 mm. The highest amplitudes varies from 10.0 to 18.0 millimetres, at the control point PBH05.

The accuracy of the displacements determined in each direction was 1.2 millimetres. Monitoring the bridge deck deformation in real time and short time intervals provides high quality information about the structure health, like the temperature influence on the structure. The realized permanent measurements using the AMS have significant advantages against the classic long-term monitoring made in annual or longer intervals.

4.2. Long-term monitoring of the bridge by accelerometers

Accelerometers are stabilized at the typical parts of the bridge deck, where the dynamic response of the structure is the most significant. The aim of the dynamic deformation analysis is the determination of natural frequencies of vertical oscillation of the structure and the analysis of their variations. The important part of the dynamic bridge behaviour monitoring is the determination of relative vertical displacements of the bridge deck, as well. Deformations of the bridge deck of Bridge of Slovak National Uprising are described by Finite Element Method [Benčat et al. 2012], and characterized by vertical bending modes at significant frequencies at the level form 0.1 Hz to 5.0 Hz [Figure 4.2].

Figure 4.2 Spectral analysis of the accelerometer measurements

Determination of average daily vibration frequencies is realized in several steps. Continual measurements extracted into discrete 5 minutes long blocks are realized in the first step. In each block the trend component of the time series is also removed in the first step followed by then estimated frequencies of the structural deformation using spectral analysis. The calculated average daily frequencies of the structural deformation are in minimum different from the modelled frequencies, at level lower than 10%. This fact points to a very good


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compliance of the results from permanent measurements and the numeric model of the structure. The average vibration frequencies of the structural deformation determined by the accelerometers show minimal fluctuations at the level of each vibration modes. Figure 4.3 shows the changes of vibration frequencies during experimental measurements from April 10, 2010 to April 15, 2014.

Figure 4.3 Daily variations of the vibration frequencies

Differences reached the minimum values at the level 0.02 Hz. The highest fluctuations are at the 12th vibration mode at the frequency 2.48 Hz. The minimum changes are registered at the vibration mode with lower frequencies, where the daily variations are maximally 0.01 Hz. At each significant vibration mode frequency variations have a cyclical pattern with 24-hour long period. Results of cross-spectral analysis of the oscillation frequencies and structural temperature illustrate their significant coherence at level higher than 0.75. Phase delay of the changes in vibration frequencies and the temperature of the structure at the level around -150° shows the fact that the parallel with the increasing structure’s temperature is decreasing the vibration frequency with the time delay from 1.4 to 2.4 hours. The results of the realized measurements point to good use not only for the purpose of dynamic measurements but for long-term monitoring of the structure’s vibration, too.

5. Conclusion

The new development in the field of geodetic monitoring of engineering structures is closely connected with the innovations of the measurement and communication technologies, thus supporting the designing and application of the innovative methods and technological processes in the field of monitoring of complex structures. Automation of the measurement process and data processing increases the efficiency of the geodetic structural health monitoring. The paper is focused on the development of the integrated measurement system able- to monitor short time variations of spatial deformation of the bridge structures in fully automated mode. Data processing and analysis are based on mathematical models generally used for time series analysis. The designed system was installed and tested at the Bridge of the Slovak National Uprising in Bratislava. The system was tested by several experimental measurements, thus the results show wide possibilities of the system usage mainly in civil engineering and provide parallel


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large base for research in engineering surveying and in modal analysis in the field of structural engineering. The realized measurements show the good use of the applied technologies and measurements, as well as the developed methodology of data processing in this sphere. The development of the presented AMS prototype has not been finished yet. For the future, the extension of the system by another sensors is planned, parallel to the installation at all Danube bridges in Bratislava which are described in this paper. This approach will ensure the integrated measurement system for structural health monitoring of the busiest bridges in Slovak Republic, in the future.

Acknowledgement

„This work was supported by the Slovak Research and Development Agency under the contract No. APVV-0236-12“.

References

Benčat, J.; Stehlíková, M.; Papán, D. (2012). New Bridge crossing the Danube in Bratislava: Assessment, Measurement and Monitoring, At IX. International Scientific Conference of Faculty of Civil Engineering, Košice, Slovak Republic, May 22-25, 2012, Košice, Technical University in Košice

Enckell, M. (2007). Structural Health Monitoring of Bridges in Sweden, At the 3rd International conference on Structural Health Monitoring of Intelligent Infrastructure, Vancouver, British Columbia, Canada, November 13-16.

Geier, R. (2009). Recent Austrian Activities in Bridge Monitoring, In 5th Central European Congress on Concrete Engineering, Baden. Austria, VCE.

Hill, C. D.; Sippel, K.D. (2002). Modern Deformation Monitoring: A Multi Sensor Approach, In FIG XXII International Congress, Washington, D.C. USA, FIG, 2002.

Hsieh, K.H.; Halling, M.W.; Barr, P.J. (2006). Overview of Vibrational Structural Health Monitoring with Representative Case Studies, In Journal of Bridge Engineering, ASCE, Vol. 11, 6, 707-715.

Ko, J.M.; Ni, Y.Q. (2005). Technology Developments in Structural Health Monitoring of Large-Scale Bridges, In Engineering Structures, Elsevier, Vol. 27, 1715-1725.

Lipták, I. (2014). Automatisation of Deformation Measurements of Bridge Structures, Dissertation Thesis, Slovak University of Technology in Bratislava, Slovak Republic, Bratislava.

Peeters, B. (2009). Continuous Monitoring of the Øresund Bridge: Data Acquisition and Operational Modal Analysis, In Encyclopedia of Structural Health Monitoring.

Wenzel, H. (2009). Health Monitoring of Bridges, John Wiley & Sons, Ltd.


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Wenzel, H.; PichlerD. (2005). Ambient Vibration Monitoring, 1st edition, J. Wiley & Sons Ltd., Chichester.

Yong, G.; Spencer, B.F. (2008). Structural Health Monitoring Strategies for Smart Sensor Networks, Urbana-Champaign, University of Illinois at Urbana-Champaign.

Monitoring mosta Slovak National Uprising pomoću automatskog sustava Sažetak. Jedan od glavnih zadataka povezanih sa sigurnošću građevina je praćenje njihovih deformacija. Izgradnja modernih građevina netipičnih oblika zahtjeva monitoring pomaka i deformacija građevine. Trenutni pristup automatiziranih geodetskih mjerenja omogućuje primjenu automatskih mjernih sustava za monitoring građevina. U radu je prikazan dizajn automatskoga mjernog sustava razvijenog za potrebe kontinuiranoga geodetskog monitoringa mosta preko rijeke Dunav u glavnom gradu Slovačke Republike (Bratislava). Također je opisana topologija i preliminarno testiranje automatiziranoga mjernog sutava na mostu. Sustav se sastoji od geodetske mjerne stanice, senzora nagiba, akcelerometra i popratnih senzora kao što su meteorološka stanica i senzori za temperaturu. Kontrola mjernog procesa je ostvarena putem daljinskog upravljanja i servera podataka putem mobilne internet veze. Sustav omogućuje monitoring dugoperiodičnih pomak i deformacija i dinamičkog ponašanja mosta u realnom vremenu.

Ključne riječi: akcelerometar, automatski sustav za monitoring, deformacije, mjerna stanica, monitoring građevina, most, prirodna frekvencija, senzor nagiba.

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