The Experts below are selected from a list of 204 Experts worldwide ranked by ideXlab platform
Dan M Frangopol - One of the best experts on this subject based on the ideXlab platform.
-
improved assessment of Mass Concrete dams using acoustic travel time tomography part ii application
Construction and Building Materials, 2000Co-Authors: William F Kepler, Leonard J Bond, Dan M FrangopolAbstract:Abstract The aging of key elements of our civil infrastructure, including dams, is presenting new challenges for the development of methodology that will adequately predict remaining safe life, and identify those structures where remedial action is required. To meet this need, a new approach for non-destructive testing of large Concrete dams has been developed. It combines aspects of ultrasonic non-destructive testing and seismic surveying in a new methodology ‘Acoustic Travel Time Tomography’ (ATTT). This is the second part of an investigation on improved assessment of Mass Concrete dams using ATTT. A companion paper [Bond LJ, Kepler WF, Frangopol, DM. Improved assessment of Mass Concrete dams using acoustic travel time tomography. Part I — Theory. Constr Build Mater 2000 Vol. 14, No. 3, pp. 133–146] focused on the background of the physics of ATTT. ATTT was tested in the laboratory, modified for large-scale testing, then evaluated for reliability. This study reports the application of the methodology, instrumentation, and data analysis techniques developed during the study. The research demonstrates that ATTT can locate and characterize cracks, voids and other anomalies deep within a Mass Concrete dam. The results at each stage of the study have shown that ATTT is a potentially highly accurate testing procedure, and that it is uniquely suited to the evaluation of large Concrete dams.
-
improved assessment of Mass Concrete dams using acoustic travel time tomography part i theory
Construction and Building Materials, 2000Co-Authors: Leonard J Bond, William F Kepler, Dan M FrangopolAbstract:Abstract This is the first part of an investigation on improved assessment of Mass Concrete dams using Acoustic Travel Time Tomography (ATTT). It presents the concept and basic science for ATTT. ATTT combines aspects of ultrasonic measurements previously used for material characterization, ultrasonic methods applied to test Concrete and features of methods used in shallow seismic surveys. This science/technology is integrated into a system that records travel time data and applies tomography software. The resulting tomographs have the potential to provide cross-sectional images of the structure that can be used to locate cracks, identify regions of structural damage, and other anomalies deep inside a Massive Concrete structure. Results from initial laboratory and field studies obtained with a system that embodies the approach presented in this paper and which provides proof-of-concept data, are presented in a companion paper (Kepler WF, Bond LJ, Frangopol DM. Improved assessment of Mass Concrete dams using acoustic travel time tomography. Part II — applications. Constr Build Mater, 2000; vol. 14, No. 3, pp. 147–156).
Yi Dua - One of the best experts on this subject based on the ideXlab platform.
-
precise simulation analysis of the thermal field in Mass Concrete with a pipe water cooling system
Applied Thermal Engineering, 2015Co-Authors: Xinghong Liu, Chao Zhang, Xiaoli Chang, Wei Zhou, Yonggang Cheng, Yi DuaAbstract:Abstract Thermal analysis is one of the main components in the design and construction of Mass Concrete structures. A procedure for a heat-fluid coupling model (HFCM) is presented to simulate the thermal field of Mass Concrete with a pipe cooling system, which can accurately reflect the temperature gradient near the pipe and the temperature rise along the pipe. Additionally, to make it suitable for the simulation of forced-convection during pipe cooling, a modified particle swarm optimization (MPSO) method, based on particle migration is adopted for parameter identification of the Dittus–Boelter equation used by the heat-fluid coupling model, according to field tests. To verify the accuracy and computation efficiency of the method, a simplified 3D model is simulated and compared to other numerical models. Subsequently, the model is applied to the analysis of a monolith of the Dagangshan high arch Concrete dam in the construction period. The actual climatic conditions, cooling pipe system, cooling schedule and thermal properties of the materials are considered in the analysis. The simulation results indicate that the proposed method can effectively simulate the cooling pipe state, water temperature rise along the flow, and directional changes of the flow in the thermal field of Mass Concrete. Moreover, the temperatures determined by the numerical simulation are in good agreement with the monitoring values. Findings in this research show that the proposed HFCM is feasible and has attractive advantages in the simulation of the thermal field in practical complex Mass Concrete engineering projects with cooling pipe systems.
Michael Ergi - One of the best experts on this subject based on the ideXlab platform.
-
determination of required insulation for preventing early age cracking in Mass Concrete footings
Transportation Research Record, 2014Co-Authors: Adria M Lawrence, Mang Tia, Michael ErgiAbstract:One of the methods for controlling the heat of hydration of Mass Concrete structures is to insulate the poured Concrete. Currently, no method can provide adequate insulation to prevent early-age cracking for Mass Concrete footings. This study developed a method for determining the required insulation for rectangular footings. The study included isothermal calorimetry testing of cementitious materials, field monitoring of temperature in footings, and finite element modeling. A fully insulated bridge pier footing constructed in the field in Florida was monitored for temperature development and for assessing the efficiency of the insulation used. A parametric study consisting of 63 finite element analyses was conducted on three footing shape—cubic footing, 4:4:1 footing (length-width-depth ratio of 4:4:1), and 4:2:1 footing (length-width-depth ratio of 4:2:1)—to determine the required insulation for footings with a volume-to-surface area ratio ranging from 1.1 to 13.1 ft. The obtained results suggest that th...
-
importance of insulation at the bottom of Mass Concrete placed on soil with high groundwater
Transportation Research Record, 2013Co-Authors: Adria M Lawrence, Mang Tia, Michael ErgiAbstract:Frequently, when Mass Concrete is placed directly on top of a soil layer, an insulation layer is not used at the bottom of the Concrete. The rationale for this practice is that the soil on which the Concrete is placed is already an insulating material. This study investigated the question of whether the absence of an insulating layer between the Mass Concrete and the soil may cause a problem with cracking of the Concrete at an early age. A three-dimensional finite element model was used for this investigation. The typical soil condition in Florida, where the groundwater level is high, was considered. The soil layer beneath the Concrete was modeled to simulate realistic heat transfer between the Concrete and the soil. To validate the developed model, temperature development in a bridge pier footing constructed in the field in Florida was compared with the computed temperature distribution from the finite element model. The results showed that the temperatures predicted by the model closely agreed with thos...
-
effect of early age strength on cracking in Mass Concrete containing different supplementary cementitious materials experimental and finite element investigation
Journal of Materials in Civil Engineering, 2012Co-Authors: Adria M Lawrence, Mang Tia, Christophe C Ferraro, Michael ErgiAbstract:AbstractThis paper presents the findings of an investigation using the finite-element method to predict the distribution of temperatures within a hydrating Massive Concrete element. The temperature distribution produced by the finite-element thermal analysis of the model is used in the finite-element structural analysis to quantify the maximum allowable internal temperature difference before cracking will initiate in the Concrete. To verify the results obtained in the finite-element model, four different mixes of Concrete, typical for use in Mass Concrete applications in Florida, were produced and each mix was used to make two large-scale 1.07 m×1.07 m×1.07 m (3.5 ft×3.5 ft×3.5 ft) Concrete blocks. The mechanical and thermal properties of early age Concrete used values obtained experimentally from the Concrete used to construct the four sets of blocks. The temperature distributions produced by the model were shown to be very similar to those measured in the experimental blocks. Results suggest that ...
Leonard J Bond - One of the best experts on this subject based on the ideXlab platform.
-
improved assessment of Mass Concrete dams using acoustic travel time tomography part ii application
Construction and Building Materials, 2000Co-Authors: William F Kepler, Leonard J Bond, Dan M FrangopolAbstract:Abstract The aging of key elements of our civil infrastructure, including dams, is presenting new challenges for the development of methodology that will adequately predict remaining safe life, and identify those structures where remedial action is required. To meet this need, a new approach for non-destructive testing of large Concrete dams has been developed. It combines aspects of ultrasonic non-destructive testing and seismic surveying in a new methodology ‘Acoustic Travel Time Tomography’ (ATTT). This is the second part of an investigation on improved assessment of Mass Concrete dams using ATTT. A companion paper [Bond LJ, Kepler WF, Frangopol, DM. Improved assessment of Mass Concrete dams using acoustic travel time tomography. Part I — Theory. Constr Build Mater 2000 Vol. 14, No. 3, pp. 133–146] focused on the background of the physics of ATTT. ATTT was tested in the laboratory, modified for large-scale testing, then evaluated for reliability. This study reports the application of the methodology, instrumentation, and data analysis techniques developed during the study. The research demonstrates that ATTT can locate and characterize cracks, voids and other anomalies deep within a Mass Concrete dam. The results at each stage of the study have shown that ATTT is a potentially highly accurate testing procedure, and that it is uniquely suited to the evaluation of large Concrete dams.
-
improved assessment of Mass Concrete dams using acoustic travel time tomography part i theory
Construction and Building Materials, 2000Co-Authors: Leonard J Bond, William F Kepler, Dan M FrangopolAbstract:Abstract This is the first part of an investigation on improved assessment of Mass Concrete dams using Acoustic Travel Time Tomography (ATTT). It presents the concept and basic science for ATTT. ATTT combines aspects of ultrasonic measurements previously used for material characterization, ultrasonic methods applied to test Concrete and features of methods used in shallow seismic surveys. This science/technology is integrated into a system that records travel time data and applies tomography software. The resulting tomographs have the potential to provide cross-sectional images of the structure that can be used to locate cracks, identify regions of structural damage, and other anomalies deep inside a Massive Concrete structure. Results from initial laboratory and field studies obtained with a system that embodies the approach presented in this paper and which provides proof-of-concept data, are presented in a companion paper (Kepler WF, Bond LJ, Frangopol DM. Improved assessment of Mass Concrete dams using acoustic travel time tomography. Part II — applications. Constr Build Mater, 2000; vol. 14, No. 3, pp. 147–156).
Vahid Lotfi - One of the best experts on this subject based on the ideXlab platform.
-
seismic plastic damage analysis of Mass Concrete blocks in arch dams including contraction and peripheral joints
Soil Dynamics and Earthquake Engineering, 2017Co-Authors: Omid Omidi, Vahid LotfiAbstract:Abstract Seismic nonlinear analysis of Concrete arch dams is a topic having been extensively studied in the last two decades. Due to the existence of different joints within the body of arch dams, the discrete crack (DC) approach utilizing interface elements for the joints is the most realistic method. In fact, it could be the first step to assess the seismic safety of an arch dam. Furthermore, since the Mass Concrete blocks may crack due to severe ground excitations, a plastic–damage (PD) model well capturing stiffness degradation and permanent deformation due to tensile cracking and compressive crushing might be needed. In this study, a special finite element program called SNACS is developed based on the combined discrete crack and plastic–damage (DC–PD) technique. The dam–reservoir interaction as an important factor affecting the seismic response of arch dams is also treated by the Lagrangian–Eulerian formulation. The joints modeling strategy adopted herein is addressed first and then, a brief review of the plastic–damage model proposed by Lee and Fenves and extended herein to 3-D space is presented. Afterwards, the nonlinear seismic analysis of a typical thin arch dam is performed based on the combined approach and the response is compared with the results of each method. It is emphasized that employing the combined DC and PD models gives more reliable and consistent response in comparison with using DC or PD approaches applied alone. Therefore, the DC–PD technique could be considered as a major step toward a more accurate seismic safety evaluation of Concrete arch dams.
-
comparison of non orthogonal smeared crack and plasticity models for dynamic analysis of Concrete arch dams
Computers & Structures, 2003Co-Authors: Radin Espandar, Vahid LotfiAbstract:Abstract A special three-dimensional finite element program is developed to study the seismic response of Concrete arch dams. Two types of continuum mechanics non-linear techniques are incorporated in the program, i.e. non-orthogonal smeared crack and elasto-plastic models. The formulation is presented initially and accuracy of the models and their correct implementations are verified by analyzing a notched beam and comparing its results with available experimental data. Following the satisfactory results of the beam analysis, the program is applied to a practical problem, viz. the non-linear behavior of the 130 m high Shahid Rajaee arch dam in Iran, subjected to the Friuli–Tolmezzo earthquake. Two cases of non-orthogonal smeared crack model are implemented for the dam, namely, ordinary and fictitious approaches. Meanwhile, an elastic–perfectly plastic model for Mass Concrete is also applied. The results are compared with those obtained from a linear elastic analysis under the same excitation. Based on the results, it is concluded that the non-orthogonal smeared crack approach can redistribute the state of stresses and produces a more realistic profile of stresses in the dam. Further, the elasto-plastic model could reduce significantly the high amount of overstressing noticed in the linear analysis. However, the elasto-plastic model is not perceptibly activated in the compressive state of stresses. It is also observed that a drift in the crest displacements is the prominent consequence of cracking or plasticity of the dam.