In order to study the calculation methods of bending behavior of Chinese reinforced concrete beams from 1912 to 1949, tests on the mechanical performance of 66 rebars from different modem Chinese concrete buildings, t...In order to study the calculation methods of bending behavior of Chinese reinforced concrete beams from 1912 to 1949, tests on the mechanical performance of 66 rebars from different modem Chinese concrete buildings, the concrete compressive strength of 12 modem Chinese concrete buildings, and the concrete cover thickness of 9 modem Chinese concrete buildings are carried out; and the actual material properties and structural conformations of modem Chinese concrete buildings are obtained. Then, the comparison on calculation methods of bending behavior including the original Chinese calculation method, the present Chinese calculation method, the present American calculation method and the present European calculation method is studied. The results show that the original Chinese calculation method of bending behavior is based on the allowable stress calculation method, and the design safety factors are 3.55 to 4. 0. In term of the calculation area of longitudinal rebars of reinforced concrete beams, without considering earthquake action, the original Chinese structural calculation method is safer than the present Chinese structural calculation method, the present European structural calculation method, and the present American structural calculation method. The results can provide support for the structural safety assessments of modem Chinese reinforced concrete buildings.展开更多
Although several experimental and numerical studies have been carried out on the shear capacity of RC beams retrofitted by carbon or glass fibre-reinforced polymers, there has been little work on hybrid FRP sheet appl...Although several experimental and numerical studies have been carried out on the shear capacity of RC beams retrofitted by carbon or glass fibre-reinforced polymers, there has been little work on hybrid FRP sheet applications, particularly under cyclic loading. In the present research, five RC beams were constructed, and four of which were retrofitted using various schemes of FRP sheets. All beams were subjected to quasi-static cyclic loading in an attempt to represent the effect repetitive loading. The ultimate load, and deflection response at mid-span of the beams were measured and compared with predictions of a computational model based on finite element analysis. Experimental results demonstrated that hybrid applications of FRP sheets can improve the shear performance of retrofitted RC beams and increase the ultimate strain of the FRP sheets at failure. The results of the computational model were in reasonable agreement with the corresponding experimental results.展开更多
This paper evaluates two methods of diagnosing damage, Natural frequency and Stiffness-Frequency change-Based damage detection method in reinforced concrete beams under load using vibration characteristics such as nat...This paper evaluates two methods of diagnosing damage, Natural frequency and Stiffness-Frequency change-Based damage detection method in reinforced concrete beams under load using vibration characteristics such as natural frequency and mode shape. The research uses finite element method with crack damage instead of deleting or reducing the bearing capacity of the element like in previous studies. First, a theory of the damage diagnosis method based on the change of natural frequency and mode shape is presented. Next, the simulation results of reinforced concrete beams using ANSYS will be compared with the experiment. Particularly, the investigated damage cases are cracks in reinforced concrete beams under loads. Finally, we will evaluate the accuracy of the damage diagnosis methods and suggest the location of the vibration data and specify the failure threshold of the methods.展开更多
混凝土是由砂浆和骨料构成的非均质材料。在细观层面上评估混凝土的断裂过程有助于阐明混凝土的材料特性。采用C++编制的梁-粒子模型求解器(Beam Particle Model Solver,简称BPMS)对砂浆和混凝土进行二维数值分析。为了模拟混凝土的断裂...混凝土是由砂浆和骨料构成的非均质材料。在细观层面上评估混凝土的断裂过程有助于阐明混凝土的材料特性。采用C++编制的梁-粒子模型求解器(Beam Particle Model Solver,简称BPMS)对砂浆和混凝土进行二维数值分析。为了模拟混凝土的断裂,采用点阵法高效快速地建立细观尺度的颗粒模型。数值研究较好地呈现了砂浆和混凝土在单轴压缩条件下的破坏行为以及混凝土三点弯在冲击条件下的断裂过程,从而证实了BPMS的强健性及稳定性。展开更多
Many studies have focused on reinforced concrete(RC)slender beams,while there is a paucity of studies on deep beams.Furthermore,there is a lack of studies on the impact performance of FRP-reinforced concrete beams.In ...Many studies have focused on reinforced concrete(RC)slender beams,while there is a paucity of studies on deep beams.Furthermore,there is a lack of studies on the impact performance of FRP-reinforced concrete beams.In this study,a 3-D numerical model was established to explore the impact behavior of the basalt fiber reinforced polymer(BFRP)and steelreinforced concrete beams with different span-to-depth ratios(l0/h).The effects of impact mass and tension reinforcement ratio were analyzed and discussed.It is determined that the impact behavior of the shortest beam with l0/h=1.5 corresponds to punching shear failure,which is distinctive from the other deep beam.When l0/h exceeds 3.0,the failure mode gradually changes from shear dominant to flexural dominant.The increase in the impact mass leads to a linear increase in the max midspan deflection,the duration of the contact between the hammer and member,and the duration of the dynamic reaction force.The max midspan deflection has a negative correlation with the reinforcement ratio.The max reaction force increases with an increase in the reinforcement ratio,which is more evident for higher l0/h.The failure mode of the BFRP-reinforced concrete beam is similar to that of the steel-reinforced beam.Under the impact condition,in this study,part of the steel bars yield,whereas BFRP bars exhibit no signs of fracture because of their higher tensile strength and better deformability.A simplified calculational method based on energy is proposed in this study,and the method accurately predicts the residual deflection of the concrete beams with different l0/h.Furthermore,it is established that it is difficult to reproduce the impact response of the deep beams via the singledegree-of-freedom(SDOF)model,which is based on the assumption of the same deflection shape as that of slender beams.Hence,a more rational simplified model for deep beams under impact loads is still required.展开更多
基金The National Natural Science Foundation of China(No.51138002)the Foundation for the Author of National Excellent Doctoral Dissertation of PR China(No.201452)the Open Fund of Shanghai Key Laboratory of Engineering Structure Safety(No.2015-KF06)
文摘In order to study the calculation methods of bending behavior of Chinese reinforced concrete beams from 1912 to 1949, tests on the mechanical performance of 66 rebars from different modem Chinese concrete buildings, the concrete compressive strength of 12 modem Chinese concrete buildings, and the concrete cover thickness of 9 modem Chinese concrete buildings are carried out; and the actual material properties and structural conformations of modem Chinese concrete buildings are obtained. Then, the comparison on calculation methods of bending behavior including the original Chinese calculation method, the present Chinese calculation method, the present American calculation method and the present European calculation method is studied. The results show that the original Chinese calculation method of bending behavior is based on the allowable stress calculation method, and the design safety factors are 3.55 to 4. 0. In term of the calculation area of longitudinal rebars of reinforced concrete beams, without considering earthquake action, the original Chinese structural calculation method is safer than the present Chinese structural calculation method, the present European structural calculation method, and the present American structural calculation method. The results can provide support for the structural safety assessments of modem Chinese reinforced concrete buildings.
文摘Although several experimental and numerical studies have been carried out on the shear capacity of RC beams retrofitted by carbon or glass fibre-reinforced polymers, there has been little work on hybrid FRP sheet applications, particularly under cyclic loading. In the present research, five RC beams were constructed, and four of which were retrofitted using various schemes of FRP sheets. All beams were subjected to quasi-static cyclic loading in an attempt to represent the effect repetitive loading. The ultimate load, and deflection response at mid-span of the beams were measured and compared with predictions of a computational model based on finite element analysis. Experimental results demonstrated that hybrid applications of FRP sheets can improve the shear performance of retrofitted RC beams and increase the ultimate strain of the FRP sheets at failure. The results of the computational model were in reasonable agreement with the corresponding experimental results.
文摘This paper evaluates two methods of diagnosing damage, Natural frequency and Stiffness-Frequency change-Based damage detection method in reinforced concrete beams under load using vibration characteristics such as natural frequency and mode shape. The research uses finite element method with crack damage instead of deleting or reducing the bearing capacity of the element like in previous studies. First, a theory of the damage diagnosis method based on the change of natural frequency and mode shape is presented. Next, the simulation results of reinforced concrete beams using ANSYS will be compared with the experiment. Particularly, the investigated damage cases are cracks in reinforced concrete beams under loads. Finally, we will evaluate the accuracy of the damage diagnosis methods and suggest the location of the vibration data and specify the failure threshold of the methods.
文摘混凝土是由砂浆和骨料构成的非均质材料。在细观层面上评估混凝土的断裂过程有助于阐明混凝土的材料特性。采用C++编制的梁-粒子模型求解器(Beam Particle Model Solver,简称BPMS)对砂浆和混凝土进行二维数值分析。为了模拟混凝土的断裂,采用点阵法高效快速地建立细观尺度的颗粒模型。数值研究较好地呈现了砂浆和混凝土在单轴压缩条件下的破坏行为以及混凝土三点弯在冲击条件下的断裂过程,从而证实了BPMS的强健性及稳定性。
基金supported by the National Natural Science Foundation of China (Grant Nos.51822801,51978022)。
文摘Many studies have focused on reinforced concrete(RC)slender beams,while there is a paucity of studies on deep beams.Furthermore,there is a lack of studies on the impact performance of FRP-reinforced concrete beams.In this study,a 3-D numerical model was established to explore the impact behavior of the basalt fiber reinforced polymer(BFRP)and steelreinforced concrete beams with different span-to-depth ratios(l0/h).The effects of impact mass and tension reinforcement ratio were analyzed and discussed.It is determined that the impact behavior of the shortest beam with l0/h=1.5 corresponds to punching shear failure,which is distinctive from the other deep beam.When l0/h exceeds 3.0,the failure mode gradually changes from shear dominant to flexural dominant.The increase in the impact mass leads to a linear increase in the max midspan deflection,the duration of the contact between the hammer and member,and the duration of the dynamic reaction force.The max midspan deflection has a negative correlation with the reinforcement ratio.The max reaction force increases with an increase in the reinforcement ratio,which is more evident for higher l0/h.The failure mode of the BFRP-reinforced concrete beam is similar to that of the steel-reinforced beam.Under the impact condition,in this study,part of the steel bars yield,whereas BFRP bars exhibit no signs of fracture because of their higher tensile strength and better deformability.A simplified calculational method based on energy is proposed in this study,and the method accurately predicts the residual deflection of the concrete beams with different l0/h.Furthermore,it is established that it is difficult to reproduce the impact response of the deep beams via the singledegree-of-freedom(SDOF)model,which is based on the assumption of the same deflection shape as that of slender beams.Hence,a more rational simplified model for deep beams under impact loads is still required.
