Stress Test In The Core Area Of FRP Confined Concrete Short Column Under Axial Load By Using Sensor

Fiber Reinforced Polymer (FRP) is a new type of structure material, which has obtainedthe fast development in domestic over the last ten years. Because of its advantages of lightweight, high strength, convenient construction, easy maintenance and good durability, manyscholars have made it in-depth research in the field of applications in civil engineering, and ithas developed into a new type of reinforcement technology. Study on the change of the internalstress of structural under the effect of external conditions and made pertinence reinforcement isa very meaningful topic.As to FRP confined rectangular cross section concrete short columns under axial loads,because of the non-uniformity of FRP constraint stress caused by volume expansion at the fourcorners and four sides of concrete, the concrete stress calculated according to theoreticalderivation formula under the state of complicated stress are limited, the problem can besolved after cement-based piezoelectric sensor embedded in the column and measure thestress directly. The practical application of cement-based piezoelectric sensor in the field ofcivil engineering is mainly in material characteristics and the feasibility of application, andthe combination with actual civil engineering structures are few.In this paper, cement-based piezoelectric sensors are embedded in the core area ofconcrete short columns and stresses are tested directly in the core area of FRP confined shortconcrete columns under axial loads. And the combination between cement-based piezoelectricsensors and civil engineering are described, including the following several aspects:（1）This test made6square cross section concrete short columns, cement-basedpiezoelectric sensors are embedded into the core area of concrete columns, and conductdynamic fatigue load test on the columns before and after FRP reinforced. The results showthat: There is an obvious linear relation between cement-base piezoelectric sensor outputsignal and test input load. The load-sensor signal curve slope of the concrete short columnafter reinforced by FRP is larger than the one of the concrete short column. Sensor signal andstress are linear dependence, the sensor signals are increased with the increase of the loadingfrequency when loading frequency is less than5Hz. The change of loading frequency isalmost no effect on the increasing extent of the stress in the core area of the concrete short column and the CFRP confined concrete short column. The stresses can be significantlyimproved after the columns reinforced by CFRP, the results show that the stress incrementpercentages are in the range of5%~20%.（2）This paper presents a new method of direct stress test in the core area of FRPconfined concrete short column by using cement-based piezoelectric sensor. The shortcolumn’s numerical model between sensor signal and concrete stress is built on the basis ofthe dynamic fatigue load test of concrete short columns, verifying the rationality of thenumerical model according to the dynamic fatigue load test of FRP confined concrete shortcolumns, the results show that the stress calculated according to numerical model basicallytallies with the theoretical ones. The new method is proved to be feasible for direct stress testin the core area of FRP confined concrete short column under axial load by usingcement-based piezoelectric sensor.（3）Analysis the advantages and disadvantages of cement-based piezoelectric sensorwhen the sensor is applied in concrete structure test and engineering application, explore thefeasibility of new methods applied in construction method and test method in the field of civilengineering, the results show that cement-based piezoelectric sensor can be applied in civilengineering structure effectively: According to the numerical model between the outputsensor signal and the temperature stress, the process of cement hydration can be real-timemonitored. According to the output sensor signal, the internal structure damage of concretecan be real-time monitored. According to the numerical model between the output sensorsignal and the vehicle load, whether the vehicle is overloaded can be real-time monitored.According to the numerical model between the output sensor signal and the vehicle speed,whether the vehicle is overspeed can be real-time monitored. According to the alternatingoutput sensor signal, the vehicle’s berth of large parking can be real-time monitored.According to the most suitable reinforcement ratio of reinforced concrete frame structuremodel, the technical basis can be provided for the reinforcement of the required sections ofreinforced concrete frame structure applied in practical engineering.