Crack propagation processes in specially prepared concrete discs and rectangular specimens containing a single cylindrical hole or multiple holes of varying diameters have been studied both experimentally and numerica...Crack propagation processes in specially prepared concrete discs and rectangular specimens containing a single cylindrical hole or multiple holes of varying diameters have been studied both experimentally and numerically. In this research, the cracks coalescence paths in Brazilian disc and rectangular specimens made from rock-like material containing multi-holes are investigated. These concrete specimens are specially prepared from an appropriate mixture of Portland Pozzolana Cement （PPC）, fine sands, and water. The pre-holed Brazilian discs and rectangular specimens are experimentally tested under compression. The breakage load in the ring type disc specimens containing an axial hole with varying diameters is measured and the distribution of the induced lateral stress is obtained. The mechanism of cracks propagation in the wall of the ring type specimens is also stud- ied. In the case of multi-hole Brazilian disc and rectangular specimens, the cracks propagation and cracks coalescence are also investigated. These experiments are numerically modeled by a modified higher order displacement discontinuity method. It has been shown that the corresponding experimental and numerical results are in good agreement with each other. The results presented in this research vali date the accuracy and applicability of these crack analyses procedures.展开更多
The use of coral aggregate concrete(CAC)as a novel construction material has attracted significant attention for the construction of reef engineering structures.To investigate the static splitting-tensile behaviors of...The use of coral aggregate concrete(CAC)as a novel construction material has attracted significant attention for the construction of reef engineering structures.To investigate the static splitting-tensile behaviors of CAC under the influence of two factors,namely specimen geometry and bearing strip size,a three-dimensional(3D)mesoscale modeling approach with consideration for aggregate randomness in shape and distribution was adopted in this study.We established 12 different specimen models with two specimen shapes(i.e.,a cube with an edge length of 150 mm and a cylinder with dimensions ofφ150 mm×300 mm)and six strip widths(i.e.,6,9,12,15,18,and 20 mm)for calculation.The effects of specimen geometry and strip width on the splitting-tensile properties of CAC,such as failure processes,final failure patterns,and splitting-tensile strength(fst),are analyzed and discussed systematically.The results indicate the high reliability of the developed mesoscale modeling approach and reveal the optimal computational parameters for simulating and predicting the splitting-tensile properties of CAC.The fstvalues of CAC are associated with both the specimen geometry and width of the bearing strip.The fstvalues of the cube model are slightly higher than those of the cylinder model for the same bearing strip size,representing geometry effects that can be explained by differences in fracture area.Additionally,the fstvalue of CAC gradually increases with the relative width of the bearing strip ranging from 0.04 to 0.13.Based on the elastic solution theory,the variation area of CAC fstvalues with the relative width of the bearing strip was determined preliminarily,which has great significance for studying the tensile performance of CAC.展开更多
In order to provide parameters for numerical analyses of the huge Three-Gorge concrete dam (2309 m long by 175 m height), complete tensile stress-deformation curves for large-size plain concrete specimens were measure...In order to provide parameters for numerical analyses of the huge Three-Gorge concrete dam (2309 m long by 175 m height), complete tensile stress-deformation curves for large-size plain concrete specimens were measured and studied by per-forming uniaxial tensile tests on large-size unnotched specimens (250 mm×250 mm×1400 mm). The specimens were prepared with the three-graded-aggregate materials provided by the client of the Three-Gorge project. To prevent a failure occurring near the ends of the unnotched specimens, both the ends of each specimen (450 mm in length) were cast using a higher-strength concrete than the middle part (i.e., active part). Tensile tests were completed on a specially-designed tensile testing machine, which can be easily re-assembled to accommodate different-size specimens. To make the specimens fail stably, a cyclic loading scheme was adopted after the peak strength was reached. Four of five tests in this study were successful, and four complete tensile stress-deformation curves were obtained. It was found that the post-peak curve of the large-size specimens used in this study is more gradual than those for the small-size specimens reported in the literature.展开更多
A new "conceptual" design named "double pull" specimen was proposed in order to measure the bond-slip(δ-τ) relationship of fiber reinforced polymer(FRP)-to-concrete interface more accurately.A fi...A new "conceptual" design named "double pull" specimen was proposed in order to measure the bond-slip(δ-τ) relationship of fiber reinforced polymer(FRP)-to-concrete interface more accurately.A finite element analysis(FEA) was performed for preliminarily evaluating the suitability of the proposed conceptual double pull specimen.Through the FEA,it was indicated that the FRP-to-concrete interface of the proposed conceptual specimen might subject to a much higher load level than that of the most commonly used simple shear specimen,showing a great potential for measuring δ-τ relationship more accurately.In the light of the conceptual specimen,a kind of "practical" double pull specimen was developed and proved to be more suitable for measuring δ-τ relationship through an exploratory experimental study with 20 specimens.Consequently,an experimental program with 10 double pull specimens was performed for measuring the ultimate slip δu which was difficult to capture by using the existing specimens.It is shown that the range of δu is 0.31-0.52 mm based on the test results.The suggestion for improving the measure method is also put forward.展开更多
基金sponsored by Iran’s National Elites Foundation (INEF)
文摘Crack propagation processes in specially prepared concrete discs and rectangular specimens containing a single cylindrical hole or multiple holes of varying diameters have been studied both experimentally and numerically. In this research, the cracks coalescence paths in Brazilian disc and rectangular specimens made from rock-like material containing multi-holes are investigated. These concrete specimens are specially prepared from an appropriate mixture of Portland Pozzolana Cement （PPC）, fine sands, and water. The pre-holed Brazilian discs and rectangular specimens are experimentally tested under compression. The breakage load in the ring type disc specimens containing an axial hole with varying diameters is measured and the distribution of the induced lateral stress is obtained. The mechanism of cracks propagation in the wall of the ring type specimens is also stud- ied. In the case of multi-hole Brazilian disc and rectangular specimens, the cracks propagation and cracks coalescence are also investigated. These experiments are numerically modeled by a modified higher order displacement discontinuity method. It has been shown that the corresponding experimental and numerical results are in good agreement with each other. The results presented in this research vali date the accuracy and applicability of these crack analyses procedures.
基金financial support from the National Natural Science Foundation of China(52178190,51878350,11832013,51678304,and 52078250)the Science and Technology on Near-Surface Detection Laboratory pre-research Fund(6142414200505)+1 种基金the Interdisciplinary Innovation Foundation for Graduates,Nanjing University of Aeronautics and Astronautics(NUAA)Grant(KXKCXJJ202005)The support provided by the China Scholarship Council(202006830096)during a visit of Zhangyu Wu to University College London is also sincerely acknowledged。
文摘The use of coral aggregate concrete(CAC)as a novel construction material has attracted significant attention for the construction of reef engineering structures.To investigate the static splitting-tensile behaviors of CAC under the influence of two factors,namely specimen geometry and bearing strip size,a three-dimensional(3D)mesoscale modeling approach with consideration for aggregate randomness in shape and distribution was adopted in this study.We established 12 different specimen models with two specimen shapes(i.e.,a cube with an edge length of 150 mm and a cylinder with dimensions ofφ150 mm×300 mm)and six strip widths(i.e.,6,9,12,15,18,and 20 mm)for calculation.The effects of specimen geometry and strip width on the splitting-tensile properties of CAC,such as failure processes,final failure patterns,and splitting-tensile strength(fst),are analyzed and discussed systematically.The results indicate the high reliability of the developed mesoscale modeling approach and reveal the optimal computational parameters for simulating and predicting the splitting-tensile properties of CAC.The fstvalues of CAC are associated with both the specimen geometry and width of the bearing strip.The fstvalues of the cube model are slightly higher than those of the cylinder model for the same bearing strip size,representing geometry effects that can be explained by differences in fracture area.Additionally,the fstvalue of CAC gradually increases with the relative width of the bearing strip ranging from 0.04 to 0.13.Based on the elastic solution theory,the variation area of CAC fstvalues with the relative width of the bearing strip was determined preliminarily,which has great significance for studying the tensile performance of CAC.
文摘In order to provide parameters for numerical analyses of the huge Three-Gorge concrete dam (2309 m long by 175 m height), complete tensile stress-deformation curves for large-size plain concrete specimens were measured and studied by per-forming uniaxial tensile tests on large-size unnotched specimens (250 mm×250 mm×1400 mm). The specimens were prepared with the three-graded-aggregate materials provided by the client of the Three-Gorge project. To prevent a failure occurring near the ends of the unnotched specimens, both the ends of each specimen (450 mm in length) were cast using a higher-strength concrete than the middle part (i.e., active part). Tensile tests were completed on a specially-designed tensile testing machine, which can be easily re-assembled to accommodate different-size specimens. To make the specimens fail stably, a cyclic loading scheme was adopted after the peak strength was reached. Four of five tests in this study were successful, and four complete tensile stress-deformation curves were obtained. It was found that the post-peak curve of the large-size specimens used in this study is more gradual than those for the small-size specimens reported in the literature.
基金Project(2006BAJ03A07) supported by the National Key Technologies R & D Program of ChinaProject(5008283) supported by the Natural Science Foundation of Guangdong Province, China
文摘A new "conceptual" design named "double pull" specimen was proposed in order to measure the bond-slip(δ-τ) relationship of fiber reinforced polymer(FRP)-to-concrete interface more accurately.A finite element analysis(FEA) was performed for preliminarily evaluating the suitability of the proposed conceptual double pull specimen.Through the FEA,it was indicated that the FRP-to-concrete interface of the proposed conceptual specimen might subject to a much higher load level than that of the most commonly used simple shear specimen,showing a great potential for measuring δ-τ relationship more accurately.In the light of the conceptual specimen,a kind of "practical" double pull specimen was developed and proved to be more suitable for measuring δ-τ relationship through an exploratory experimental study with 20 specimens.Consequently,an experimental program with 10 double pull specimens was performed for measuring the ultimate slip δu which was difficult to capture by using the existing specimens.It is shown that the range of δu is 0.31-0.52 mm based on the test results.The suggestion for improving the measure method is also put forward.
