Contraction Joints Research Articles

Simple models for simulating shear key arrangement in nonlinear seismic analysis of arch dams

Shear keys are commonly designed on contraction joints to limit joint slipping and improve the overall seismic behavior of arch dams. However, shear keys are usually over-simplified in the current nonlinear seismic analysis. This paper proposes a geometric simplification method for simulating shear key arrangement. Actual shear keys on a contraction joint are simplified into the combination of large oblique-type shear keys along the cantilever direction and horizontal direction. Key geometric features and progressive failure of shear keys can be naturally considered using the contact boundary model and the plastic-damage model. Nonlinear seismic analysis of the Xulong arch dam is implemented with different shear key models for verification and comparison. The proposed method is firstly verified by analyzing seismic responses of the dam with geometrically-simplified shear keys and fine shear keys, respectively. Furthermore, seismic responses of the dam with geometrically-simplified shear keys, free-slipping plane joints (ignoring shear keys but considering surface friction), and non-slipping plane joints (modeling perfect shear keys) are compared to investigate the effects of shear key modeling methods. Ignoring shear keys and modeling perfect shear keys underestimate and overestimate the seismic capacity of the dam, respectively. The nonlinear dynamic behavior of shear keys can be more reasonably represented with the proposed method without much increasing modeling efforts.

Coupled arch dam-reservoir-massed foundation problem under different earthquake input mechanisms

The aim of the present study is to investigate a coupled arch dam-reservoir-massed foundation problem under two earthquake input mechanisms. The problem nonlinearity originates from opening/slipping of the vertical contraction joints of the dam body. The reservoir-structure interaction is taken into account assuming compressible reservoir. Also, the meshing approach (structured mesh vs. unstructured one) in the foundation medium is investigated. The Karoun-I double curvature arch dam is selected as a case study. Three components of the 1994 Northridge earthquake are selected as the free-field ground motion. A deconvolution analysis in 3D space is conducted to adjust the amplitude and frequency contents of the earthquake ground motion applied to the bottom of the massed foundation to determine the desired acceleration response at various points on the dam-foundation interface taking into account the coupling between the foundation and the structure. It is found that in the deconvolved earthquake input models, the maximum tensile and the compressive stresses increase by 19% and 12%, respectively in comparison with those of the free-field input models. In addition, modeling foundation using the unstructured mesh decreases the maximum compressive stresses within the dam body by about 20% in comparison with that obtained using the structured mesh model. In the same way, the maximum crest displacements in the horizontal direction decreases by about 30%.

Performance of AC overlays using geogrids on PCC contraction joints

It is widely known that vertical displacements and strains occur on the joints and these cause defects on the asphalt concrete (AC) overlays on existing Portland cement concrete (PCC) pavements. Various approaches were introduced to minimize these defects. In this study, the effect of joint support formed using the geogrid material with grout mortar on the vertical displacement of PCC and the strain at the bottom of the AC layer. Produced layers were exposed to 1,186,000 Equivalent Single Axle Load (ESAL) in an APT (Accelerated Pavement Test) facility and the results were monitored. According to the obtained results, the use of AC overlay reduces vertical displacement in the PCC by 75%. When geogrid reinforced AC overlay was used, an additional reduction in displacement by 41.2% was achieved. Geogrid reinforcement reduced strain values formed at the bottom of the AC layer from 29.5% to 92.5%. The use of geogrid at joints instead of increasing the thickness of the AC layer from 50 to 80 mm resulted a more significant reduction in both strain and displacement. Besides, the usage of a geogrid interlayer instead of increasing the thickness of the AC layer also provided a significant cost reduction of 57.9% in overall cost.

Evaluation of trigger temperature for concrete pavement growth based on joint movement data

The failure of concrete pavement as a result of pavement growth has become a serious concern as it causes blow-up distress and damages the adjoining structures, such as bridge abutments and decks. This further adversely impacts the road user, and the roads thus require costly maintenance and reparations. Pavement growth is caused by pressure generated from rising temperature and moisture content in the concrete pavement. The trigger temperature for pavement growth (TTPG) is the temperature at which all transverse cracks and contraction joints between the expansion joints begin contacting and generating an axial compressive force in the pavement section. This is a critical factor affecting pavement growth. However, the evaluation of TTPG has not been documented yet. TTPG is affected by the accumulation of concrete slab expansion resulting from the alkali-silica reaction, amount of incompressible material infiltrated in the joint or cracking. The rate of this accumulation depends on the environmental conditions, pavement age, pavement configuration, and pavement materials. Therefore, this study examines the factors affecting TTPG of in-service pavements, using the Long-Term Pavement Performance Seasonal Monitoring Program database. According to the results, TTPG is significantly affected by pavement age, precipitation, and joint spacing. The paper further presents an empirical equation to estimate the TTPG of concrete pavement under the given conditions based on the generalized linear modeling regression method.

Modification of direct-FE method for nonlinear seismic analysis of arch dam-reservoir-foundation system considering spatially varying ground motion

The present paper aims to modify an existing direct finite element method for nonlinear seismic analysis of high arch dam-reservoir-massed foundation systems to consider the effects of spatially varying ground motion at the bottom of the foundation rock with the non-stationary frequency characteristics. Viscous-damper boundaries are used to model the semi-unbounded foundation rock and the reservoir domains. In the existing direct finite element method, it is assumed that incident waves propagate vertically upwards from beneath the foundation rock towards the ground surface, and the effective seismic forces starting from the control motion on the foundation surface are applied to the bottom and the side vertical boundaries of the foundation rock. Three components of the motion recorded at Parkfield fault zone 16 during the 1983 Coalinga earthquake are selected as the free-field control motion at the surface of the foundation rock. On the other hand, in the modified direct FE method, fully non-stationary spectrum-compatible ground motion time histories, including both wave passage and incoherency effects, are simulated at a number of locations at the foundation bottom. Then the generated ground motions are used as multiple input incident motions to compute effective seismic forces applied to the bottom and the side boundaries of the foundation rock in the dam-reservoir-massed foundation system. Step-by-step procedures for computing the effective earthquake forces in the existing and the modified direct FE methods are presented. The nonlinearity originates from opening/sliding of the vertical contraction joints within the dam body. The reservoir–structure interaction is accounted for via the finite element method assuming compressible reservoir. The Karoun-I, a double curvature high arch dam, is selected as a case study. Several numerical validation models are conducted and compared with the benchmark solutions to indicate the accuracy of the existing direct FE method. It was seen that applying effective earthquake forces determined from the modified direct finite element method increases the nonlinear seismic response of the dam-reservoir-massed foundation system in terms of the crest displacements and stress levels.

Evaluation of structural safety reduction due to water penetration into a major structural crack in a large concrete project

Structural damage to an arch dam is often of major concern and must be evaluated for probable rehabilitation to ensure safe, regular, normal operation. This evaluation is crucial to prevent any catastrophic or failure consequences for the life time of the dam. If specific major damage such as a large crack occurs to the dam body, the assessments will be necessary to determine the current level of safety and predict the resistance of the structure to various future loading such as earthquakes, etc. This study investigates the behavior of an arch dam cracked due to water pressure. Safety factors (SFs), of shear and compressive tractions were calculated at the surfaces of the contraction joints and the cracks. The results indicated that for cracking with an extension depth of half the thickness of the dam body, for both cases of penetration and non-penetration of water load into the cracks, SFs only slightly reduces. However, in case of increasing the depth of crack extension into the entire thickness of the dam body, the friction angle of the cracked surface is crucial; however, if it reduces, the normal loading SFs of stresses and joints tractions reduce significantly.

Parametric Investigation of Canyon Shape Effects on the Seismic Response of 3D Concrete Gravity Dam Model

In this study, the three-dimensional seismic response of Pine Flat concrete gravity dam is investigated. For this purpose, two- and three-dimensional nonlinear analyses are carried out based on the finite element method. The effects of canyon shape variation on the seismic response of the dam are evaluated, and different components of a seismic record are considered to assess the dominance of each earthquake component on the structural behavior. Two sources of nonlinearity are taken into account including material and geometric nonlinearities. As geometric nonlinearity, vertical contraction joints are considered within the dam body, and the results are compared with integrated models. It is concluded that stream component of earthquake record plays an important role on the crest displacement. Assuming two- and three-dimensional dam-reservoir-foundation coupled system may lead to partly different results. It is finally observed that, although utilizing contraction joints increases the amount of compressive stresses in the allowable range, but the tensile damages imposed to the dam body may encounter a significant decrease.

Noncontact Ultrasonic and Computer Vision Assessment for Sawcut Initiation Time

AbstractSawcut timing of contraction joints in concrete pavements is affected by interactions between the time-dependent concrete properties, notch depth, base friction, climate, and type of saw. E...

Effect of Contraction Joints on Structural Behavior of Double Curvature Concrete Dam Subject to Dynamic Loading

A double curvature arch dam considers as complex mega structure built for the hydropower or agriculture national goals. Arch dam cost effective is less compared to other types of dams, construction a safe and stable of arch dam depending on intelligent formation of dam layouts. This work conducted to explore the structural behavior of the double curvature arch concrete dam under the variation effect of the distance in between the contraction joints. The dam blocks divided and distributed as seven intervals of the distance between the blocks of the dam as 15,17.5,20,22.5,25, 27.5, and 30 m. Stresses analysis of arch dam conducted to study the effects of these intervals on the structural behavior of double curvature concrete dam when the water in the reservoir at the operation level. Arch dam data input considered the Nonlinearity in both of dam shape and concrete materials properties to evaluate the maximum and minimum principal stresses at the top of the crown cantilever, and the maximum principal stresses along the crest path of the upstream face. Finite element and building information modeling tools (Revit – Abaqus6.13) were considered during the modeling and analysis process. The results show that the dam must be simulated for a specific interval of distance between each two contraction joints are 20 to 22.5 meter and the optimum selection to this interval of contractions joints leads to increase the structural stability status of the arch dam.

Rapid detection of concrete joint activation using normalized shear wave transmission energy

ABSTRACT A rapid and reliable method to detect the activation of contraction joint cracks is needed to assess the effectiveness of sawcut depth and timing on new concrete pavements and for forensic investigation. A one-sided ultrasonic measurement technique is presented that detects the existence of a contraction joint crack, which is not visible from the concrete slab surface. A multi-sensor ultrasonic array device is used to generate and receive ultrasonic shear waves (S-wave) across the inspected joint. The acquired time-domain signals are used to calculate a newly defined feature, called normalised transmission energy (NTE), across the joint. A laboratory experiment investigated the proposed technique on three 500 × 500 × 150 mm3 concrete specimens with 38 mm notch depth, the first without a propagated crack, the second with a narrow width crack, and the third specimen with a full-depth open crack. The laboratory results demonstrate that the NTE technique can identify the existence or not of a crack beneath the notch. Finally, the NTE technique coupled with a 2D decision boundary equation was field validated on 152 concrete pavement contraction joints with various slab thickness (e.g. 102 to 152 mm) and notch depths (less than 38 mm) from multiple projects in Illinois and Iowa (USA).

Seismic Damage Indexes of a High Arch Dam Based on the Monolith

To assess safety of a dam in an earthquake, establishing the performance evaluation index of the arch dam is significant. The finite-element model based on the 289 m-high Baihetan Dam in Southwest China is taken as a case for seismic response analysis, in which the radiation damping of infinite foundation and opening of contraction joints are taken into consideration. Using the incremental dynamic analysis (IDA) approach, a three-component earthquake scaled to 12 increasing intensity levels is applied to the model, and the seismic response of the model is analysed. In this paper, it is proposed to study the damage based on the monolith, so the monolith damage volume ratio and monolith damage area ratio are suggested to determine the most severe part of the dam. Meanwhile, to help identifying the damage of the dam, the response results of contraction joints are extracted to analyse the potential relationship between the proposed indexes, providing a reference for exploring new detection indexes and damage evaluation indexes. In order to explore the possibility of the simplified layout of dam damage monitoring, the dam body is partitioned according to the results of monolith damage development.

The Effect of Shear Sliding of Vertical Contraction Joints on Seismic Response of High Arch Dams with Fine Finite Element Model

The contraction joints of arch dams with and without shear keys are simplified to be with no‐slip condition and with relative sliding condition, respectively. Based on the Lagrange multiplier method, a contact model considering the manner of independent cantilever dead load type with no‐slip condition and relative sliding condition is proposed to model the nonlinearities of vertical contraction joins, which is special to the nonlinear analysis of arch dams considering the manner of dead load type. Different from the conventional Gauss iterative method, the strategy of the alternating iterative solution of normal force and tangential force is employed. The parallelization based on overlapping domain decomposition method (ODDM) and explicit message passing using distributed memory parallel computers is employed to improve the computational efficiency. An existing high arch dam with fine finite element model is analyzed to investigate the effect of shear sliding of vertical joints on seismic response of the arch dam. The result shows that the values of maximum principal tensile stress under relative sliding condition are significantly greater than those under no‐slip condition.

Effect of abutment movements on nonlinear seismic response of an arch dam

Abutment movement that induces a reduction of the valley width in the periods of initial impoundment has been observed in a few high arch dams. In this article, the effect of the abutment movement on the nonlinear dynamic response of arch dams subjected to strong earthquakes is studied. The 285.5 m high Xiluodu arch dam is analysed. The results show that the abutment movement of 65–110 mm after initial impoundment leads to upstream displacements and a significant increase in compression stress in the arch dam under static conditions. When subjected to strong earthquake, the abutment movement results in a much larger opening of contraction joints in the middle part of the dam and prevention of opening of the other joints on both sides. Additional damage cracking is likely to occur in the surface outlets and the mid-level orifices. The damage cracking on the dam–foundation interface appears to propagate from the upstream face towards downstream, especially near the abutments where it extends one fourth thickness of the interface and is possible to damage the grout curtain.

Seismic damage investigation of arch dams under different water levels based on massively parallel computation

Parallelization based on the overlapping domain decomposition method (ODDM) is adopted to increase the computation speed of large-scale nonlinear dynamic analysis. A comprehensive system of arch dam-reservoir-foundation is established considering the foundation radiation damping and the nonlinearity of joint opening and concrete damage. A planned 240 m-high arch dam including approximately 3.5 million degrees of freedom and 34 contraction joints is selected as a case study. In particular, to the best of the authors' knowledge, such large-scale seismic damage analysis of an arch dam-reservoir-foundation is unique and can help in understanding damage to an arch dam under an earthquake. The influence of water level on the seismic safety of the arch dam is evaluated based on the damage. New findings are revealed through sophisticated simulation. Under strong earthquake, although free blocks form under low water level conditions, there seems to be no risk of a catastrophic release of the reservoir.

Numerical Investigation into Underwater Explosion–Resistant Performance of an Arch Dam Considering Its Transverse Contraction and Control Joints

Arch dams appear vulnerable to underwater-explosion (UNDEX) shock loadings due to their relatively thin bodies. Many seismic analyses have highlighted the significant nonlinear joint contact behavior in dynamic responses of arch dams. This paper examines the effects of the transverse contraction and control joints, particularly the combination of the two joint types, on the UNDEX-resistant performance of arch dams. The investigation takes the form of a numerical case study of a 141-m-high arch dam subjected to an UNDEX using ABAQUS/Explicit. A surface-interaction-based approach that can consider damage initiation, evolution, and ultimate failure of the shear keys was employed for the joint modeling. The results show that the shear keys undergo considerable shearing damage under a 50-kg trinitrotoluene-equivalent UNDEX, which is mainly distributed at the upper halves of the joint interfaces. The radial displacement of and tensile damage to the dam in the basic case are not strictly enveloped by those in the two extreme cases. The damage-preventing effect of the control-joint implementation seems somewhat less pronounced than expected. This study has identified the significant role of transverse joints in UNDEX-induced responses of arch dams. Extreme approaches to the joint modeling in arch dams do not necessarily produce extreme results for the UNDEX-resistant performance evaluation. The control-joint implementation should be reviewed on a case-by-case basis in design practices. The surface-interaction-based approach could probably be usefully and easily employed in engineering practices.

Seismic analysis of arch dams using anisotropic damage-plastic model for concrete with coupled adhesive-frictional joints response

A finite element model for seismic analysis of concrete arch dams is proposed. Material inelasticity as well as joints nonlinearity is considered. A damage-plastic formulation governs nonlinear behavior of concrete. Degeneration occurring during nonlinear behavior of concrete induces anisotropy into its microstructure. This anisotropy becomes more complex in seismic simulations, in which the state of stress expeditiously changes with time. Thus, anisotropic formulation is preferred over classical isotropic models. Utilizing rate-dependent anisotropic damage-plastic model, irreversible deformations, stiffness degeneration, induced anisotropy, closing/reopening of cracks, and viscous response of concrete are attained. Non-penetration condition, frictional behavior, and adhesion resulted by grouting of contraction and peripheral joints are also modeled in a coupled and rate-dependent manner. Different combinations of material and joints nonlinearities are used to model a system of dam-foundation-reservoir. The system is excited using three components of an earthquake, and effect of different sources of nonlinearities is investigated through comparison between results. In addition, capability of the anisotropic damage-plastic model is compared against an available isotropic formulation. A sensitivity analysis is also performed to investigate the effect of properties of joints on responses. Owing to high convergence rate of material and joints constitutive models, implicit time integration is employed, which leads to stable and accurate solutions.

Seismic Stability Sensitivity and Uncertainty Analysis of a High Arch Dam-Foundation System

Parameter uncertainty associated with concrete arch dams always arises from modeling assumptions and the lack of knowledge or information of the engineering geological situations, especially in the seismic stability analysis of arch dams. In this research, a high arch dam is selected as a case study for probabilistic analysis of the seismic stability performance. The arch dam abutment and the dam are coupled as a system. A comprehensive approach considering contraction joints, boundaries of the probable sliding rock mass and the dam-foundation interface is presented. The contact nonlinearity is solved by using the dynamic contact model with Lagrange multiplier method. The main parameters of the probable sliding block are considered as random variables containing the friction coefficients and cohesions. Both the slippage and sliding area ratio are chosen as the engineering demand parameters (EDP). The sensitivity analysis is performed to reveal the relative influence of each parameter separately by the approximate incremental dynamic analysis (IDA) method. The friction coefficients are shown to be more crucial than the cohesions on the dam’s resistance to seismic instability. The sliding area ratio can be better used for unveiling the sliding process of the arch dam of concern, while the slippage is useful for one to judging the stability of the arch dam under seismic hazards. The Latin hypercube sampling (LHS) with approximate moment estimation is used to investigate the parameter uncertainty to the seismic stability performance of the high arch dam. The results provide a useful reference for using the median/mean-parameter model to accurately estimate the median/mean response of the dam.

A Comparative Study of Cantilever- and Integral-Type Dead Loads on the Seismic Responses of High Arch Dams

The actual dead load of an arch dam should be applied gradually through staged construction and sequenced grouting. However, the cantilever- and integral-type dead loads commonly used in the analysis of arch dams represent simplified versions of the actual loading. In this paper, these two types of dead loads, i.e. cantilever and integral types, are presented based on the Lagrange multiplier method considering the nonlinear behaviors of contraction joints. Based on the finite element method and an appropriate contact model together with artificial viscoelastic boundary conditions, a dynamic analysis model of a dam–foundation–reservoir system is established in consideration of the interactions between the arch dam and foundation, the opening and closing of contraction joints, and the radiation damping effect of the far-field boundary. Taking a 300 m high arch dam in the strong earthquake area of West China as an example, a fine mesh finite element model with a total of approximately 3.5 million degrees of freedom is established. The separate effects of the cantilever and integral dead loads on the static and dynamic responses of the dam are studied. The results demonstrate that the distribution and magnitude of the contraction joint opening width and maximum tensile stress are different under the two different dead load simplifications.

SA2USING GENETIC INSTRUMENTS TO ASSESS CAUSAL PATHWAYS TO EDUCATIONAL ATTAINMENT IN ADHD AND AUTISM: EVIDENCE FROM A TWO SAMPLE MENDELIAN RANDOMISATION STUDY

Fluid–structure interaction formulated in the Lagrangian–Eulerian approach with pressure-based fluid elements, which inherently results in non-symmetric matrices, is commonly treated by either direct un-symmetric solvers or staggered solution methods. Developing an in-house finite element code called SNACS, we implement the pressure-based Eulerian formulation so that a usual symmetric solver can be employed for dam–reservoir interaction analyses. The equilibrium equations of motion for such a coupled system are directly integrated herein by the HHT time marching algorithm in an incremental–iterative solution procedure to tackle a highly nonlinear dynamic analysis of jointed arch dams. The HHT time integration scheme is able to damp out high-frequency noises resulting from sudden changes in the stiffness due to opening/closing of pre-existing joints during an earthquake. First, a Pseudo-Symmetric technique is proposed to store the total matrices and solve the coupled non-symmetric equations in a symmetric manner. Then, the interface element formulation and stress update procedures of two discrete crack constitutive models suitable for contraction and peripheral joints of arch dams are detailed. Afterwards, results of the analysis on a typical arch dam are compared with the case in which the interaction is approximately represented by added masses as a widely-used method in dam engineering practice to illustrate the effects of water compressibility and reservoir bottom absorption. Besides, the straightforward implementation of pressure-based fluid–structure interaction utilizing a symmetric solution strategy is validated herein to be efficient for a 3-D large scale practical usage in other finite element codes even the commercial ones to avoid using un-symmetric solvers. Employing this symmetric implementation for the dam–water interaction drastically reduces the computational effort, particularly when an iterative scheme is required to solve such a highly nonlinear system.

Seismic design of Xiluodu ultra-high arch dam

The 285.5 m-high Xiluodu Arch Dam is located in a seismic region along the Jinsha River in China, where the horizontal components of peak ground accelerations for design and checking earthquakes have been estimated to be 0.355g and 0.423g, respectively (g is the gravitational acceleration). The ground motion parameters of design and checking earthquakes are defined by exceedance probabilities of 2% over 100 years and 1% over 100 years, respectively. The dam shape was first selected and optimized through static analysis of the basic load combinations, and then adjusted after taking into account the seismic loads. The dam should be operational during and after the design earthquake with or without minor repairs, and maintain local and global stabilities during an extreme earthquake. Both linear elastic dynamic analysis and nonlinear dynamic analysis considering radiation damping, contraction joints, and material nonlinearity were conducted to assess the stress in the arch dam. The dynamic analysis shows that the maximum dynamic compressive stresses are less than the allowable levels, while the area with tensile stress over the limit is less than 15% of the dam surface and the maximum contraction openings range from 10 mm to 25 mm. The arch dam has sufficient earthquake-resistance capacity and meets the safety requirements. Nevertheless, steel reinforcement has been provided at the dam toe and in the zones of high tensile stress on the dam surface out of extra precaution.