Jianwen Pan

Seismic performance assessment of arch dams using incremental nonlinear dynamic analysis

In this paper, an approximately incremental dynamic analysis (IDA) is presented for seismic performance assessment of arch dams. The nonlinear seismic analysis of arch dams involves the effects of contraction joint opening, cracking of concrete and foundation radiation damping. Three damage measures, i.e. the maximum joint opening, the cracking depth on the dam–foundation interface and the extent of cracking in the upper portion of the dam, associated with the IDA curves are suggested to identify the performance levels of arch dams. The Dagangshan arch dam (210 m high) under construction in China is used as the case study. Although there is slight cracking on the dam–foundation interface during earthquake with the peak ground acceleration (PGA) up to .30 g, the dam exhibits nearly linear behaviour with contraction joints closing and can be approximately considered to have serviceability performance. The dam suffers severe damage on the dam–foundation interface and in the upper portion, and it is repairable under the design earthquake (PGA = .56 g) or the check earthquake (PGA = .66 g). The collapse prevention performance of the dam is achieved when the PGA reaches 1.10 g, in which case, the horizontal cracking in the upper portion penetrates the dam blocks and generates partially free cantilevers that control the dynamic stability of the structure.

Numerical prediction of swelling in concrete arch dams affected by alkali-aggregate reaction

A chemo-damage model is presented for anisotropic swelling analysis of concrete arch dams affected by alkali-aggregate reaction (AAR). The model combines the AAR kinetics and the plastic-damage model, and the chemical and mechanical phases are coupled. A redistributing weight function, determined by the applied stresses in the concrete, is introduced to control the AAR-induced anisotropic expansion of the concrete. Creep strain is also included in the approach using the Kelvin–Voigt model. Accelerated tests, in which the specimens are confined with steel rings and subjected to axial loads, are first analyzed using the proposed model. The computed strains of the specimens are in good agreement with the experimental measured strains. The application to the AAR-affected Kariba dam is then carried out. The radial and vertical displacements of the dam due to AAR are reproduced with sufficient accuracy. The stresses within the dam are significantly redistributed during the AAR process. Severe cracking and damage appear to occur in the dam heel and the downstream face on both sides of the dam-foundation interface. It demonstrates Kariba dam is facing an increased risk of collapse associated with the increasing compressive stresses within the dam and developing cracks on both sides of the downstream face during the development of AAR.

Comparison of different fracture modelling approaches to gravity dam failure

Purpose – There is not a unified modelling approach to finite element failure analysis of concrete dams. Different behaviours of a dam predicted by different fracture methods with various material constitutive models may significantly influence on the dam safety evaluation. The purpose of this paper is to present a general comparative investigation to examine whether the nonlinear responses of concrete dams obtained from different fracture modelling approaches are comparable in terms of crack propagation and failure modes. Design/methodology/approach – Three fracture modelling approaches, including the extended finite element method with a cohesive law (XFEM-COH), the crack band finite element method with a plastic-damage relation (FEPD), and the Drucker-Prager (DP) elasto-plastic model, are chosen to analyse damage and cracking behaviour of concrete gravity dams under overloading conditions. The failure process and loading capacity of a dam are compared. Findings – The numerical results indicate that the...

Seismic stability assessment of an arch dam-foundation system

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.

Chapter 11 – Influence of Seismic Input Mechanisms and Radiation Damping on Arch Dam Response1

Two earthquake input models are introduced: the massless foundation model and the viscous-spring boundary model considering radiation damping. Linear elastic and nonlinear contraction joint opening analyses of the 210 m high Dagangshan arch dam are performed using the two models. The responses of the three-dimensional canyon without the dam are analyzed with massless-truncated foundation and viscous-spring boundary; then, linear and nonlinear analyses of the dam–foundation system are performed and compared using the two models. Hydrodynamic effects are considered using finite element discretization for incompressible reservoir fluid. Stresses, displacements and contraction joint opening in the dam are significantly reduced in linear and nonlinear analyses using the viscous-spring boundary model. In linear analysis, the massless foundation model with a high damping ratio of 10% leads to a similar response to that using the viscous-spring boundary model. Maximum tensile stresses from nonlinear analysis are 10–25% larger than those from linear analysis owing to a partial release of the arch action.

Seismic Safety Evaluation of High Concrete Dams: Part 2: Earthquake Behavior of Arch Dams – Case Study

Key issues for the seismic safety evaluation of high concrete dams are reviewed. The earthquake input mechanism and foundation modeling are important in this regard. Engineering applications to high arch dams are demonstrated. A case study on the Dagangshan arch dam to resist the design earthquake using state-of-the-art techniques is performed considering different input mechanisms, nonlinearity of contraction joint opening, damage fracture behavior, involving tensile stresses in cantilevers, and measures to strengthen the dam. Although sophisticated numerical methods for earthquake analysis of large concrete dams are available, realistic earthquake behavior and damage mechanisms of large dams are yet to be elucidated.

Chapter 13 – A Comparative Study of the Different Procedures for Seismic Cracking Analysis of Concrete Dams1

Different procedures are compared for the three-dimensional seismic cracking analysis of gravity and arch dams during strong earthquakes. The fracture procedures include the extended finite element (FE) method with cohesive constitutive relations, crack band FE method with plastic-damage relations and the FE Drucker–Prager elastoplastic model. These procedures are used to analyze the nonlinear dynamic response of Koyna dam to the 1967 Koyna earthquake and the seismic cracking of the Dagangshan arch dam subjected to design earthquakes. The cracking process and profiles of the two dams using the three different procedures are compared. The applicability and suitability of the three procedures for seismic cracking analysis of gravity and arch dams are discussed.

Chapter 19 – Comparative Study Procedure for the Safety Evaluation of High Arch Dams1

A set of factors for the safety evaluation of the dam heel crack and ultimate bearing capacity of high arch dams is presented: the curtain safety factor k1, the structural mutation safety factor k2 and the ultimate safety factor k3. The factor k1 reflects the curtain safety at the dam heel, k2 describes the structural mutation stage for the adjustment of the multiple arch–cantilever system and k3 reflects the ultimate bearing capacity of the entire dam structure. A comparative study on the performance and ultimate bearing capacity of dams is performed to give a more reasonable evaluation criterion of safety factors.

Chapter 12 – Seismic Damage-Cracking Analysis of Arch Dams Using Different Earthquake Input Mechanisms1

A nonlinear model is presented for analysis of damage-cracking behavior in arch dams during strong earthquakes using different seismic input mechanisms. The nonlinear system includes a plastic-damage model for cyclic loading of concrete considering strain softening and a contact boundary model of contraction joint opening. Two earthquake input mechanisms are used: a massless foundation input model and a viscous-spring boundary model considering radiation damping due to infinite canyon. The results show significant effects of seismic input mechanism and radiation damping on nonlinear response and damage-cracking of the dam. Compared with the results using the massless foundation input model, the damage-cracking region and contraction joint opening are substantially reduced using the viscous-spring boundary model taking into account radiation damping. If the damping ratio of the dam is artificially increased to ∼10–15% for the massless foundation input model, the joint opening and damage-cracking of the dam are comparable to results obtained from the viscous-spring boundary model.