Modal parameters, including fundamental frequencies, damping ratios, and mode shapes, could be used to evaluate the health condition of structures. Automatic modal parameter identification, which plays an essential ro...Modal parameters, including fundamental frequencies, damping ratios, and mode shapes, could be used to evaluate the health condition of structures. Automatic modal parameter identification, which plays an essential role in realtime structural health monitoring, has become a popular topic in recent years. In this study, an automatic modal parameter identification procedure for high arch dams is proposed. The proposed procedure is implemented by combining the densitybased spatial clustering of applications with noise(DBSCAN) algorithm and the stochastic subspace identification(SSI). The 210-m-high Dagangshan Dam is investigated as an example to verify the feasibility of the procedure. The results show that the DBSCAN algorithm is robust enough to interpret the stabilization diagram from SSI and may avoid outline modes. This leads to the proposed procedure obtaining a better performance than the partitioned clustering and hierarchical clustering algorithms. In addition, the errors of the identified frequencies of the arch dam are within 4%, and the identified mode shapes are in agreement with those obtained from the finite element model, which implies that the proposed procedure is accurate enough to use in modal parameter identification. The procedure is feasible for online modal parameter identification and modal tracking of arch dams.展开更多
A seismic stability assessment of arch dam-foundation systems is presented using a comprehensive approach,in which the main factors that significantly influence the seismic response of an arch dam-foundation system ar...A seismic stability assessment of arch dam-foundation systems is presented using a comprehensive approach,in which the main factors that significantly influence the seismic response of an arch dam-foundation system are considered.A large scale finite element model with over 1 million degrees of freedom is constructed for the Baihetan arch dam(289 m high),which is under construction in the Southwest of China.In particular,the complicated geological conditions with faults intersecting interlayer shear weakness zones at the dam base and the dam abutment resisting force body is modeled in the analysis.Three performance indices are adopted to assess the seismic stability of the arch dam.The results demonstrate that the opening of the joints of the Baihetan arch dam is small and the water stop installed between the joints would not be torn during a design earthquake.The yielding formed in the interface between the dam and foundation does not reach the grouting curtain that would remain in an elastic state after an earthquake.The yielding zones occurring on the upper portion of the dam faces extend 1/8 thickness of block section into the dam body and thus cantilever blocks need not be concerned with sliding stability.The faults and interlayer shear weakness zones in the near field foundation exhibit severe yielding,and a potential sliding surface is penetrated.Although the factor of safety against sliding of the surface fluctuates with a decreased trend during an earthquake,the minimum instantaneous value reaches 1.02 and is still larger than 1.0.Therefore,a conclusion is drawn that the Baihetan arch dam-foundation system will remain stable under the design earthquake.展开更多
A chemo-damage model for cracking analysis of concrete dams affected by alkali-aggregate reaction (AAR) is proposed, which combines the plastic-damage model for concrete with the AAR kinetics law. The chemo-damage mod...A chemo-damage model for cracking analysis of concrete dams affected by alkali-aggregate reaction (AAR) is proposed, which combines the plastic-damage model for concrete with the AAR kinetics law. The chemo-damage model is first verified by a stress-free AAR expansion test. The expansion deformation obtained from the simulation is in good agreement with the measurement, demonstrating that the proposed model has a sufficient accuracy to predict the expansion of AAR-affected concrete. Subsequently, the expansion deformation and cracking process of the AAR-affected Fontana gravity dam is analyzed. It shows that permanent displacements in the upstream direction and the vertical direction are gradually increased during the long-term operation period, and that their maximal values reach 1.6 and 3.6 cm, respectively. A crack is observed on the wall in the foundation drainage gallery, and extends towards the downstream face of the dam. With the further development of AAR, another crack forms on the downstream face, and then intersects with the gallery crack to penetrate the downstream side profile of the dam. The third crack occurs in the upstream side wall of the gallery and propagates a short distance towards the upstream face of the dam. The simulated cracking pattern in the dam due to AAR is similar to the in situ observation.展开更多
基金National Natural Science Foundation of China under Grant Nos. 51725901 and 51639006。
文摘Modal parameters, including fundamental frequencies, damping ratios, and mode shapes, could be used to evaluate the health condition of structures. Automatic modal parameter identification, which plays an essential role in realtime structural health monitoring, has become a popular topic in recent years. In this study, an automatic modal parameter identification procedure for high arch dams is proposed. The proposed procedure is implemented by combining the densitybased spatial clustering of applications with noise(DBSCAN) algorithm and the stochastic subspace identification(SSI). The 210-m-high Dagangshan Dam is investigated as an example to verify the feasibility of the procedure. The results show that the DBSCAN algorithm is robust enough to interpret the stabilization diagram from SSI and may avoid outline modes. This leads to the proposed procedure obtaining a better performance than the partitioned clustering and hierarchical clustering algorithms. In addition, the errors of the identified frequencies of the arch dam are within 4%, and the identified mode shapes are in agreement with those obtained from the finite element model, which implies that the proposed procedure is accurate enough to use in modal parameter identification. The procedure is feasible for online modal parameter identification and modal tracking of arch dams.
基金National Natural Science Foundation of China under Grant Nos.51209120,51579133 and 51323014the Tsinghua University Initiative Scientifi c Research Program under Grant No.20131089285
文摘A seismic stability assessment of arch dam-foundation systems is presented using a comprehensive approach,in which the main factors that significantly influence the seismic response of an arch dam-foundation system are considered.A large scale finite element model with over 1 million degrees of freedom is constructed for the Baihetan arch dam(289 m high),which is under construction in the Southwest of China.In particular,the complicated geological conditions with faults intersecting interlayer shear weakness zones at the dam base and the dam abutment resisting force body is modeled in the analysis.Three performance indices are adopted to assess the seismic stability of the arch dam.The results demonstrate that the opening of the joints of the Baihetan arch dam is small and the water stop installed between the joints would not be torn during a design earthquake.The yielding formed in the interface between the dam and foundation does not reach the grouting curtain that would remain in an elastic state after an earthquake.The yielding zones occurring on the upper portion of the dam faces extend 1/8 thickness of block section into the dam body and thus cantilever blocks need not be concerned with sliding stability.The faults and interlayer shear weakness zones in the near field foundation exhibit severe yielding,and a potential sliding surface is penetrated.Although the factor of safety against sliding of the surface fluctuates with a decreased trend during an earthquake,the minimum instantaneous value reaches 1.02 and is still larger than 1.0.Therefore,a conclusion is drawn that the Baihetan arch dam-foundation system will remain stable under the design earthquake.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51209120, 41274106 and 40974063)
文摘A chemo-damage model for cracking analysis of concrete dams affected by alkali-aggregate reaction (AAR) is proposed, which combines the plastic-damage model for concrete with the AAR kinetics law. The chemo-damage model is first verified by a stress-free AAR expansion test. The expansion deformation obtained from the simulation is in good agreement with the measurement, demonstrating that the proposed model has a sufficient accuracy to predict the expansion of AAR-affected concrete. Subsequently, the expansion deformation and cracking process of the AAR-affected Fontana gravity dam is analyzed. It shows that permanent displacements in the upstream direction and the vertical direction are gradually increased during the long-term operation period, and that their maximal values reach 1.6 and 3.6 cm, respectively. A crack is observed on the wall in the foundation drainage gallery, and extends towards the downstream face of the dam. With the further development of AAR, another crack forms on the downstream face, and then intersects with the gallery crack to penetrate the downstream side profile of the dam. The third crack occurs in the upstream side wall of the gallery and propagates a short distance towards the upstream face of the dam. The simulated cracking pattern in the dam due to AAR is similar to the in situ observation.
