Punch shear tests have been widely used to determine rock shear mechanical properties but without a standard sample geometric dimension suggestion.To investigate the impacts of sample geometric dimensions on shear beh...Punch shear tests have been widely used to determine rock shear mechanical properties but without a standard sample geometric dimension suggestion.To investigate the impacts of sample geometric dimensions on shear behaviors in a punch shear test,simulations using Particle Flow Code were carried out.The effects of three geometric dimensions(i.e.,disk diameter,ratio of shear surface diameter to disk diameter,and ratio of disk height to shear surface diameter)were discussed.Variations of shear strength,shear stiffness,and shear dilatancy angles were studied,and the fracture processes and patterns of samples were investigated.Then,normal stress on the shear surface during test was analyzed and a suggested disk geometric dimension was given.Simulation results show that when the ratio of the shear surface diameter to the disk diameter and the ratio of disk height to the shear surface diameter is small enough,the shear strength,shear stiffness,and shear dilatancy angles are extremely sensitive to the three geometric parameters.If the ratio of surface diameter to disk diameter is too large or the ratio of disk height to surface diameter is too small,a part of the sample within the shear surface will fail due to macro tensile cracks,which is characterized by break off.Samples with a greater ratio of disk height to shear surface diameter,namely when the sample is relatively thick,crack from one end to the other while others crack from both ends towards the middle.During test,the actual normal stress on the shear surface is greater than the target value because of the extra compressive stress from the part of sample outside shear surface.展开更多
This paper present an experimental study on the RC slab-column connections with nonrectangular columns, namely cross-shaped column, T-shaped column and L-shaped column. The punching shear deformation and strength char...This paper present an experimental study on the RC slab-column connections with nonrectangular columns, namely cross-shaped column, T-shaped column and L-shaped column. The punching shear deformation and strength characteristics of slab-column connections with nonrectangular columns under punching shear load are investigated. Nine specimens with the three kinds of nonrectangular columns and two reference specimens with square columns are tested. The tested ultimate loads, deformations, and failure modes of specimens are presented and discussed. Test results reveal that the punching shear strength and ductility of the connections with nonrectangular columns are higher than those of the corresponding connections with square columns, and also prove that the application of nonrectangular columns to flat-plate structure was feasible. Based on the test results, one method of calculating punching shear strength of connections with nonrectangular columns is proposed, which conforms with the current design practice of China. The test results on the punching shear strength are compared with the predictions of the formulas proposed by codes of several different countrie; and the predictions given by ACI code and China code are found to be conservative as the reinforcement ratio is increased.展开更多
Punching shear failure of flat concrete slabs is a complex phenomenon with brittle failure mode, meaning sudden structural failure and rapid decrease of load carrying capacity. Due to these reasons, the application of...Punching shear failure of flat concrete slabs is a complex phenomenon with brittle failure mode, meaning sudden structural failure and rapid decrease of load carrying capacity. Due to these reasons, the application of appropriate punching shear reinforcement in the slabs could be essential. To obtain the required structural strength and performance in slab-column junctions, the effect of the shear reinforcement type on the punching resistance must be known. For this purpose, numerous nonlinear finite element simulations were carried out to determine the behavior and punching shear strength of flat concrete slabs with different punching shear reinforcement types. The efficiency of different reinforcement types was also determined and compared. Accuracy of the numerical simulations was verified by experimental results. Based on the comparison of numerical results,?the partial factor for the design formula used in Eurocode 2 was calculated and was found to be higher than the actual one.展开更多
This paper presents an investigation on energy absorption characteristics of nano-reinforced panels, laminated face sheets and sandwich composites in high velocity ballistic and low velocity punch-shear experiments. T...This paper presents an investigation on energy absorption characteristics of nano-reinforced panels, laminated face sheets and sandwich composites in high velocity ballistic and low velocity punch-shear experiments. The vinyl ester panels were reinforced with 1.25 and 2.5 wt. percent nanoclay and exfoliated graphite platelets. Three different face sheets were manufactured with E-glass, Owens Corning HP ShieldStrand? glass and T-700 Carbon woven fabric in vinyl ester;and one with the E-glass and graphite platelets impregnated vinyl ester matrix. The sandwich composites were fabricated with balsa, PVC foam, 3D-fiber reinforced Tycor? and fire resistant fly-ash based Eco-Core? cores in between E-glass/vinyl ester face sheets. Ballistic tests were conducted according to NIJ level III using a universal receiver equipped with a barrel to launch 0.308 caliber M80 ball round projectile at about 890 m/s. Low velocity punch-shear tests were performed at around 3 m/s according to ASTM D3763 Standard using a drop-weight impact test system. The tortuosity of the fractured surface in nanocomposite specimens has been investigated using digital microscope. In ballistic tests, the 3-D fiber reinforced Tycor? core provided the most resistance when projectile strikes at the web-flange interface region. The 2.5 wt. pct. graphite platelet reinforced nanocomposite, HP ShieldStrand? glass vinyl ester face sheets, and E-glass/Eco-Core? sandwich composite showed the best energy absorption under low velocity punch-shear.展开更多
Reinforced concrete(RC)flat slabs,a popular choice in construction due to their flexibility,are susceptible to sudden and brittle punching shear failure.Existing design methods often exhibit significant bias and varia...Reinforced concrete(RC)flat slabs,a popular choice in construction due to their flexibility,are susceptible to sudden and brittle punching shear failure.Existing design methods often exhibit significant bias and variability.Accurate estimation of punching shear strength in RC flat slabs is crucial for effective concrete structure design and management.This study introduces a novel computation method,the jellyfish-least square support vector machine(JS-LSSVR)hybrid model,to predict punching shear strength.By combining machine learning(LSSVR)with jellyfish swarm(JS)intelligence,this hybrid model ensures precise and reliable predictions.The model’s development utilizes a real-world experimental data set.Comparison with seven established optimizers,including artificial bee colony(ABC),differential evolution(DE),genetic algorithm(GA),and others,as well as existing machine learning(ML)-based models and design codes,validates the superiority of the JS-LSSVR hybrid model.This innovative approach significantly enhances prediction accuracy,providing valuable support for civil engineers in estimating RC flat slab punching shear strength.展开更多
基金supported by the Fundamental Research Funds for the Central Universities,CHD(Nos.300102210307,300102210308)the National Natural Science Foundation of China(Nos.51708040,41831286,51678063,51978065).
文摘Punch shear tests have been widely used to determine rock shear mechanical properties but without a standard sample geometric dimension suggestion.To investigate the impacts of sample geometric dimensions on shear behaviors in a punch shear test,simulations using Particle Flow Code were carried out.The effects of three geometric dimensions(i.e.,disk diameter,ratio of shear surface diameter to disk diameter,and ratio of disk height to shear surface diameter)were discussed.Variations of shear strength,shear stiffness,and shear dilatancy angles were studied,and the fracture processes and patterns of samples were investigated.Then,normal stress on the shear surface during test was analyzed and a suggested disk geometric dimension was given.Simulation results show that when the ratio of the shear surface diameter to the disk diameter and the ratio of disk height to the shear surface diameter is small enough,the shear strength,shear stiffness,and shear dilatancy angles are extremely sensitive to the three geometric parameters.If the ratio of surface diameter to disk diameter is too large or the ratio of disk height to surface diameter is too small,a part of the sample within the shear surface will fail due to macro tensile cracks,which is characterized by break off.Samples with a greater ratio of disk height to shear surface diameter,namely when the sample is relatively thick,crack from one end to the other while others crack from both ends towards the middle.During test,the actual normal stress on the shear surface is greater than the target value because of the extra compressive stress from the part of sample outside shear surface.
文摘This paper present an experimental study on the RC slab-column connections with nonrectangular columns, namely cross-shaped column, T-shaped column and L-shaped column. The punching shear deformation and strength characteristics of slab-column connections with nonrectangular columns under punching shear load are investigated. Nine specimens with the three kinds of nonrectangular columns and two reference specimens with square columns are tested. The tested ultimate loads, deformations, and failure modes of specimens are presented and discussed. Test results reveal that the punching shear strength and ductility of the connections with nonrectangular columns are higher than those of the corresponding connections with square columns, and also prove that the application of nonrectangular columns to flat-plate structure was feasible. Based on the test results, one method of calculating punching shear strength of connections with nonrectangular columns is proposed, which conforms with the current design practice of China. The test results on the punching shear strength are compared with the predictions of the formulas proposed by codes of several different countrie; and the predictions given by ACI code and China code are found to be conservative as the reinforcement ratio is increased.
文摘Punching shear failure of flat concrete slabs is a complex phenomenon with brittle failure mode, meaning sudden structural failure and rapid decrease of load carrying capacity. Due to these reasons, the application of appropriate punching shear reinforcement in the slabs could be essential. To obtain the required structural strength and performance in slab-column junctions, the effect of the shear reinforcement type on the punching resistance must be known. For this purpose, numerous nonlinear finite element simulations were carried out to determine the behavior and punching shear strength of flat concrete slabs with different punching shear reinforcement types. The efficiency of different reinforcement types was also determined and compared. Accuracy of the numerical simulations was verified by experimental results. Based on the comparison of numerical results,?the partial factor for the design formula used in Eurocode 2 was calculated and was found to be higher than the actual one.
文摘This paper presents an investigation on energy absorption characteristics of nano-reinforced panels, laminated face sheets and sandwich composites in high velocity ballistic and low velocity punch-shear experiments. The vinyl ester panels were reinforced with 1.25 and 2.5 wt. percent nanoclay and exfoliated graphite platelets. Three different face sheets were manufactured with E-glass, Owens Corning HP ShieldStrand? glass and T-700 Carbon woven fabric in vinyl ester;and one with the E-glass and graphite platelets impregnated vinyl ester matrix. The sandwich composites were fabricated with balsa, PVC foam, 3D-fiber reinforced Tycor? and fire resistant fly-ash based Eco-Core? cores in between E-glass/vinyl ester face sheets. Ballistic tests were conducted according to NIJ level III using a universal receiver equipped with a barrel to launch 0.308 caliber M80 ball round projectile at about 890 m/s. Low velocity punch-shear tests were performed at around 3 m/s according to ASTM D3763 Standard using a drop-weight impact test system. The tortuosity of the fractured surface in nanocomposite specimens has been investigated using digital microscope. In ballistic tests, the 3-D fiber reinforced Tycor? core provided the most resistance when projectile strikes at the web-flange interface region. The 2.5 wt. pct. graphite platelet reinforced nanocomposite, HP ShieldStrand? glass vinyl ester face sheets, and E-glass/Eco-Core? sandwich composite showed the best energy absorption under low velocity punch-shear.
基金Acknowledgements This research was supported by the Research Program funded by Seoul National University of Science and Technology(SeoulTech).
文摘Reinforced concrete(RC)flat slabs,a popular choice in construction due to their flexibility,are susceptible to sudden and brittle punching shear failure.Existing design methods often exhibit significant bias and variability.Accurate estimation of punching shear strength in RC flat slabs is crucial for effective concrete structure design and management.This study introduces a novel computation method,the jellyfish-least square support vector machine(JS-LSSVR)hybrid model,to predict punching shear strength.By combining machine learning(LSSVR)with jellyfish swarm(JS)intelligence,this hybrid model ensures precise and reliable predictions.The model’s development utilizes a real-world experimental data set.Comparison with seven established optimizers,including artificial bee colony(ABC),differential evolution(DE),genetic algorithm(GA),and others,as well as existing machine learning(ML)-based models and design codes,validates the superiority of the JS-LSSVR hybrid model.This innovative approach significantly enhances prediction accuracy,providing valuable support for civil engineers in estimating RC flat slab punching shear strength.