Stability and reinforcement analyses of high arch dams by considering deformation effects

The strict definition and logical description of the concept of structure stability and failure are presented. The criterion of structure stability is developed based on plastic complementary energy and its variation. It is presented that the principle of minimum plastic complementary energy is the combination of structure equilibrium, coordination condition of deformation and constitutive relationship. Based on the above arguments, the deformation reinforcement theory is developed. The structure global stability can be described by the relationship between the global degree of safety of structure and the plastic complementary energy. Correspondingly, the new idea is used in the evaluations of global stability, anchorage force of dam-toe, fracture of dam-heel and treatment of faults of high arch dams in China. The results show that the deformation reinforcement theory provides a uniform and practical theoretical framework and a valuable solution for the analysis of global stability, dam-heel cracking, dam-toe anchorage and reinforcement of faults of high arch dams and their foundations.

Automatic modal parameter identification of high arch dams:feasibility verification

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.

Parallel computation of seismic analysis of high arch dam

Parallel computation programs are developed for three-dimensional meso-mechanics analysis of fully-graded dam concrete and seismic response analysis of high arch dams （ADs）, based on the Parallel Finite Element Program Generator （PFEPG）. The computational algorithms of the numerical simulation of the meso-structure of concrete specimens were studied. Taking into account damage evolution, static preload, strain rate effect, and the heterogeneity of the meso-structure of dam concrete, the fracture processes of damage evolution and configuration of the cracks can be directly simulated. In the seismic response analysis of ADs, all the following factors are involved, such as the nonlinear contact due to the opening and slipping of the contraction joints, energy dispersion of the far-field foundation, dynamic interactions of the dam-foundation- reservoir system, and the combining effects of seismic action with all static loads. The correctness, reliability and efficiency of the two parallel computational programs are verified with practical illustrations.

Analysis of seismic disaster failure mechanism and dam-break simulation of high arch dam

Based on a Chinese national high arch dam located in a meizoseismal region, a nonlinear numerical analysis model of the damage and failure process of a dam-foundation system is established by employing a 3-D deformable distinct element code(3DEC) and its re-development functions. The proposed analysis model considers the dam-foundation-reservoir coupling effect, infl uence of nonlinear contact in the opening and closing of the dam seam surface and abutment rock joints during strong earthquakes, and radiation damping of far fi eld energy dissipation according to the actual workability state of an arch dam. A safety assessment method and safety evaluation criteria is developed to better understand the arch dam system disaster process from local damage to ultimate failure. The dynamic characteristics, disaster mechanism, limit bearing capacity and the entire failure process of a high arch dam under a strong earthquake are then analyzed. Further, the seismic safety of the arch dam is evaluated according to the proposed evaluation criteria and safety assessment method. As a result, some useful conclusions are obtained for some aspects of the disaster mechanism and failure process of an arch dam. The analysis method and conclusions may be useful in engineering practice.

FLOOD DISCHARGE AND ENERGY DISSIPATION BY JETS FROM OUTLETS IN HIGH ARCH DAM

In this thesis, the scale effect by an aerated water jet diffusing in the water upon the hydrodynamic pressure, the local riverbed scour by multiple layered jets and by those colliding in the vertical and the transverse directions, and the stability of the apron slab both in the inverted arch cushion pool and the flat bottom one by the large discharge and the high water head with 300m level are detailedly researched by means of model test and numerical simulation. A mathematic model simulating the destabilization of the flat bottomed slab is established to open out the mechanism of its stability. Both experimental researches both on the hydrodynamic pressure acted inside joints between the bedrock and the apron slab, and on forces at arch abutments in inverted arch cushion pool are carried out by using an advanced measurement and the imitation means to acquire the mechanism of the inverted arch pool to keep stability and its stability condition.

Transverse Joint Aperture Simulation of High Arch Dam Based on Measured Temperature in Construction Period

Transverse joint aperture is of certain reference value to ensure joint grouting quality and overall safety of high arch dam. A 3D isoparametric joint element model with spherical surface key grooves and finite thickness is used to simulate a transverse joint. A set of program is developed to simulate the transverse joint ap- erture of Dagangshan high arch dam. Combined with the measured temperatures, the whole developing process of Dagangshan arch dam＇s transverse joint aperture is simulated. The real work behav- ior of transverse joint, thermal and mechanical properties of con- crete, pouring process, joint grouting temperature and cantilever height of high arch dam are considered during the simulation. The simulation results show that the lower of the joint grouting tem- perature, the larger value of transverse joint aperture; the higher of cantilever height during the construction period, the smaller value of transverse joint aperture.