- Email: [email protected]
DESCRIPTION OF Z24 BENCHMARK
Mechanical Systems and Signal Processing (2003) 17(1), 127–131 doi:10.1006/mssp.2002.1548, available online at http://www.idealibrary.com on
DESCRIPTION OF Z24 BENCHMARK J. Maeck and G. de Roeck Department of Civil Engineering, K.U. Leuven, Kasteelpark Arenberg 40, B-3001 Heverlee, Belgium. E-mail: [email protected]://www.kuleuven.ac.be/bwm/ (Received 1 October 2002, accepted after revisions 1 October 2002) Vibration monitoring is a useful evaluation tool in the development of a non-destructive damage-identification technique, and relies on the fact that occurrence of damage in a structural system leads to changes in its dynamic properties. It can give global information of a structure, and the location of the damage has not to be known in advance. Damageassessment techniques are validated on the progressively damaged prestressed concrete bridge Z24 in Switzerland, tested in the framework of the Brite Euram project SIMCES. A series of full modal surveys are carried out on the bridge before and after applying a number of damage scenarios. # 2003 Elsevier Science Ltd. All rights reserved.
1. INTRODUCTION
In the framework of Brite Euram project BE96-3157 system identification to monitor civil engineering structures (SIMCES), a series of damage scenarios were applied to a prestressed concrete bridge in Switzerland to detect, localise and quantify artificially applied damage. The test set-up and damage scenarios are described in this paper. Solution procedure and experimental validation results of direct stiffness calculation technique are reported and discussed in [1]. More can be found on http:// www.kuleuven.ac.be/bwm/SIMCES.htm.
2. TEST SET UP
2.1. BRIDGE DESCRIPTION The bridge used for validation is bridge Z24 in Canton Bern, Switzerland, connecting Koppigen and Utzenstorf. The bridge is a highway overpass of the A1, linking Bern and Zu. rich (Fig. 1). Z24 is a prestressed bridge, with three spans, two lanes and 60 m overall length. The geometry is plotted in Fig. 2. 2.2. DAMAGE SCENARIOS Within the SIMCES project, a series of progressive damage tests have been carried out during the summer of 1998. For a full description of all damage scenarios, instrumentation and safety considerations, refer to Kr.amer et al. [2]. The first eight scenarios are summarised in Table 1. The settlement is simulated by cutting the Koppigen pier and removing about 0.4 m of concrete. Lowering and lifting was done by six hydraulic jacks (Fig. 3). During the tests, the pier rested on steel sections with similar stiffness as the uncut concrete section. Other damage scenarios (spalling of concrete, landslide, cut of concrete hinges, failure of anchor heads, rupture of tendons) are not considered here as they caused no or a minor degradation of bending stiffness. 0888–3270/03/+$35.00/0
# 2003 Elsevier Science Ltd. All rights reserved.
128
J. MAECK AND G. DE ROECK
Figure 1. View of Z24 bridge.
Figure 2. Top view, cross-section, elevation [2].
129
Z24 BENCHMARK
2.3. SOLUTION PROCEDURE The experimental eigenfrequencies and standard deviations for the first five modes are summarised in Table 2 for the different reference measurements and damage scenarios. Processing of the measurements is done by the stochastic subspace identification method [3]. Comparison of identified eigenfrequencies and damping ratios from three excitation Table 1 Damage scenarios on Z24 #
Date
Scenario
1 2 3 4 5 6 7 8
04.08.98 09.08.98 10.08.98 12.08.98 17.08.98 18.08.98 19.08.98 20.08.98
First reference measurement Second reference measurement Settlement of pier, 20 mm Settlement of pier, 40 mm Settlement of pier, 80 mm Settlement of pier, 95 mm Tilt of foundation Third reference measurement
Figure 3. Settlement of pier scenario.
Table 2 Eigenfrequencies and standard deviation for bridge Z24 (PDT) No.
1 2 3 4 5 6 7 8
Mode 1
Mode 2
Mode 3
Mode 4
f
sf
f
sf
f
sf
f
3.92 3.89 3.87 3.86 3.76 3.67 3.84 3.86
0.02 0.03 0.01 0.01 0.01 0.02 0.01 0.01
5.12 5.02 5.06 4.93 5.01 4.95 4.67 4.90
0.02 0.04 0.02 0.04 0.03 0.03 0.02 0.03
9.93 9.80 9.80 9.74 9.37 9.21 9.69 9.73
0.02 0.03 0.04 0.03 0.04 0.04 0.05 0.06
10.52 10.30 10.33 10.25 9.90 9.69 10.14 10.30
sf 0.08 0.05 0.05 0.03 0.15 0.04 0.08 0.06
Mode 5 f
sf
12.69 12.67 12.77 12.48 12.18 12.03 12.11 12.43
0.12 0.16 0.15 0.08 0.10 0.08 0.15 0.22
130
J. MAECK AND G. DE ROECK
Figure 4. First five modeshapes of Z24 [5, 6].
sources, i.e. band-limited noise from shaker, impact from a drop weight and ambient sources, are reported in Peeters et al. [4]. Figure 4 shows the first five modes of Z24 for the second reference measurement. The first mode is a symmetric bending mode. The second mode is a lateral mode. The third and fourth modes are antisymmetric bending modes with torsion of the midspan. The fifth mode is a symmetrical bending mode with highest modal displacements at the side spans.
ACKNOWLEDGEMENTS
The research has been carried out in the framework of the BRITE-EURAM Program CT96 0277 SIMCES with a financial contribution by the Commission. Partners in the project are: * * *
*
* * *
K.U. Leuven (Department Civil Engineering, Division Structural Mechanics) Aalborg University (Insitut for Bygningsteknik) EMPA (Swiss Federal Laboratories for Materials Testing and Research, Section Concrete Structures) LMS (Leuven Measurements and Systems International N.V., Engineering and Modeling) WS Atkins Consultants Ltd. (Science and Technology) Sineco Spa (Ufficio Promozione e Sviluppo) Technische Universit.at Graz (Structural Concrete Institute)
Z24 BENCHMARK
131
REFERENCES 1. J. Maeck and G. de Roeck 2002 Mechanical Systems and Signal Processing, 17, 133–142. Damage assessment using vibration analysis on the Z24 bridge. 2. C. Krmer C. A. M. de Smet and G. de Roeck 1999 Proceedings of IMAC XVII, Kissimmee, Fl, USA, 1023–1029. Z24 bridge damage detection tests. 3. B. Peeters and G. de Roeck 1997 Proceedings of DAMAS 1997, Sheffield, UK, 377–386. The performance of time domain system identification methods applied to operational data. 4. B. Peeters, J. Maeck and G. de Roeck 2001 Smart Materials and Structures 10, 518–527. Vibration-based damage detection in civil engineering: excitation sources and temperature effects. 5. B. Peeters and G. de Roeck 1998 KUL, Leuven, Belgium. SIMCES Task B1 Internal Report. Stochastic subspace identification applied to progressive damage test vibration data from the Z24 bridge. 6. http://www.kuleuven.ac be/bwm/SIMCES.htm
DESCRIPTION OF Z24 BENCHMARK J. Maeck and G. de Roeck Department of Civil Engineering, K.U. Leuven, Kasteelpark Arenberg 40, B-3001 Heverlee, Belgium. E-mail: [email protected]://www.kuleuven.ac.be/bwm/ (Received 1 October 2002, accepted after revisions 1 October 2002) Vibration monitoring is a useful evaluation tool in the development of a non-destructive damage-identification technique, and relies on the fact that occurrence of damage in a structural system leads to changes in its dynamic properties. It can give global information of a structure, and the location of the damage has not to be known in advance. Damageassessment techniques are validated on the progressively damaged prestressed concrete bridge Z24 in Switzerland, tested in the framework of the Brite Euram project SIMCES. A series of full modal surveys are carried out on the bridge before and after applying a number of damage scenarios. # 2003 Elsevier Science Ltd. All rights reserved.
1. INTRODUCTION
In the framework of Brite Euram project BE96-3157 system identification to monitor civil engineering structures (SIMCES), a series of damage scenarios were applied to a prestressed concrete bridge in Switzerland to detect, localise and quantify artificially applied damage. The test set-up and damage scenarios are described in this paper. Solution procedure and experimental validation results of direct stiffness calculation technique are reported and discussed in [1]. More can be found on http:// www.kuleuven.ac.be/bwm/SIMCES.htm.
2. TEST SET UP
2.1. BRIDGE DESCRIPTION The bridge used for validation is bridge Z24 in Canton Bern, Switzerland, connecting Koppigen and Utzenstorf. The bridge is a highway overpass of the A1, linking Bern and Zu. rich (Fig. 1). Z24 is a prestressed bridge, with three spans, two lanes and 60 m overall length. The geometry is plotted in Fig. 2. 2.2. DAMAGE SCENARIOS Within the SIMCES project, a series of progressive damage tests have been carried out during the summer of 1998. For a full description of all damage scenarios, instrumentation and safety considerations, refer to Kr.amer et al. [2]. The first eight scenarios are summarised in Table 1. The settlement is simulated by cutting the Koppigen pier and removing about 0.4 m of concrete. Lowering and lifting was done by six hydraulic jacks (Fig. 3). During the tests, the pier rested on steel sections with similar stiffness as the uncut concrete section. Other damage scenarios (spalling of concrete, landslide, cut of concrete hinges, failure of anchor heads, rupture of tendons) are not considered here as they caused no or a minor degradation of bending stiffness. 0888–3270/03/+$35.00/0
# 2003 Elsevier Science Ltd. All rights reserved.
128
J. MAECK AND G. DE ROECK
Figure 1. View of Z24 bridge.
Figure 2. Top view, cross-section, elevation [2].
129
Z24 BENCHMARK
2.3. SOLUTION PROCEDURE The experimental eigenfrequencies and standard deviations for the first five modes are summarised in Table 2 for the different reference measurements and damage scenarios. Processing of the measurements is done by the stochastic subspace identification method [3]. Comparison of identified eigenfrequencies and damping ratios from three excitation Table 1 Damage scenarios on Z24 #
Date
Scenario
1 2 3 4 5 6 7 8
04.08.98 09.08.98 10.08.98 12.08.98 17.08.98 18.08.98 19.08.98 20.08.98
First reference measurement Second reference measurement Settlement of pier, 20 mm Settlement of pier, 40 mm Settlement of pier, 80 mm Settlement of pier, 95 mm Tilt of foundation Third reference measurement
Figure 3. Settlement of pier scenario.
Table 2 Eigenfrequencies and standard deviation for bridge Z24 (PDT) No.
1 2 3 4 5 6 7 8
Mode 1
Mode 2
Mode 3
Mode 4
f
sf
f
sf
f
sf
f
3.92 3.89 3.87 3.86 3.76 3.67 3.84 3.86
0.02 0.03 0.01 0.01 0.01 0.02 0.01 0.01
5.12 5.02 5.06 4.93 5.01 4.95 4.67 4.90
0.02 0.04 0.02 0.04 0.03 0.03 0.02 0.03
9.93 9.80 9.80 9.74 9.37 9.21 9.69 9.73
0.02 0.03 0.04 0.03 0.04 0.04 0.05 0.06
10.52 10.30 10.33 10.25 9.90 9.69 10.14 10.30
sf 0.08 0.05 0.05 0.03 0.15 0.04 0.08 0.06
Mode 5 f
sf
12.69 12.67 12.77 12.48 12.18 12.03 12.11 12.43
0.12 0.16 0.15 0.08 0.10 0.08 0.15 0.22
130
J. MAECK AND G. DE ROECK
Figure 4. First five modeshapes of Z24 [5, 6].
sources, i.e. band-limited noise from shaker, impact from a drop weight and ambient sources, are reported in Peeters et al. [4]. Figure 4 shows the first five modes of Z24 for the second reference measurement. The first mode is a symmetric bending mode. The second mode is a lateral mode. The third and fourth modes are antisymmetric bending modes with torsion of the midspan. The fifth mode is a symmetrical bending mode with highest modal displacements at the side spans.
ACKNOWLEDGEMENTS
The research has been carried out in the framework of the BRITE-EURAM Program CT96 0277 SIMCES with a financial contribution by the Commission. Partners in the project are: * * *
*
* * *
K.U. Leuven (Department Civil Engineering, Division Structural Mechanics) Aalborg University (Insitut for Bygningsteknik) EMPA (Swiss Federal Laboratories for Materials Testing and Research, Section Concrete Structures) LMS (Leuven Measurements and Systems International N.V., Engineering and Modeling) WS Atkins Consultants Ltd. (Science and Technology) Sineco Spa (Ufficio Promozione e Sviluppo) Technische Universit.at Graz (Structural Concrete Institute)
Z24 BENCHMARK
131
REFERENCES 1. J. Maeck and G. de Roeck 2002 Mechanical Systems and Signal Processing, 17, 133–142. Damage assessment using vibration analysis on the Z24 bridge. 2. C. Krmer C. A. M. de Smet and G. de Roeck 1999 Proceedings of IMAC XVII, Kissimmee, Fl, USA, 1023–1029. Z24 bridge damage detection tests. 3. B. Peeters and G. de Roeck 1997 Proceedings of DAMAS 1997, Sheffield, UK, 377–386. The performance of time domain system identification methods applied to operational data. 4. B. Peeters, J. Maeck and G. de Roeck 2001 Smart Materials and Structures 10, 518–527. Vibration-based damage detection in civil engineering: excitation sources and temperature effects. 5. B. Peeters and G. de Roeck 1998 KUL, Leuven, Belgium. SIMCES Task B1 Internal Report. Stochastic subspace identification applied to progressive damage test vibration data from the Z24 bridge. 6. http://www.kuleuven.ac be/bwm/SIMCES.htm