Experimental Determination Of Concrete Thermal Stress

Through the concrete strain gauges and other observation instruments to monitor the stress state of the structure , has been an important tool to study the work state of the complex structure and verify the correctness of the calculation results , but also an primary method of the early warning and forecasting of the important project. However, the method of thermal stress analysis based on observations of the concrete gauges has not been resolved, so that a large number of observational data cannot be analyze reasonably ,and the observing instruments cannot play their due role in the online monitoring and early warning forecasting. The main purpose of this paper is to analyze the thermal stress based on the measured data of the concrete strain gauge preliminarily.The thermal stress of the concrete specimen with fixed and elastic restraints at both ends was measured by applying the temperature load on the specimen with an electric heater cable .The concrete specimen is a cylinder with 370mm in height and 105mm in diameter and fixed by the load distribution plates of the testing machine, a vibrating wire strain gauge and a temperature sensor were buried in the center of the specimen, the electric heater cable was wrapped on the lateral surface of the specimen, which was sealed with a layer of polyurethane foam with excellent heat insulating property. In the process of the experiments, the temperature rise was controlled by the temperature sensor, the thermal deformation of the specimen was measured by both embedded vibrating wire strain gauge and the dial gauges installed on the test machine, and the thermal stress was detected by the load sensor.The concrete specimens are heated in water or oil traditionally; In the test a heating cable program and an insulation system are designed, Which provide a more uniform temperature load and the easily use of restraint setup to meet the conditions of the simulation for concrete specimens.The results showed that:(1) The heating cable heating program designed can supply an uniform temperature load to the concrete specimens , a 70℃of the temperatures rise can be reached; (2) In the state of ends restraint, the thermal stress produced in the specimen is linearly dependent on the temperature rising, and the strain changes measured by the strain gauge is also linearly correlate to the thermal stress, but the measured values of the thermal stress are much smaller than theoretical ones.(3) In the state of ends restraint strongly and the temperature field changes uniformly, approximate results can be obtained by using the concrete strain gauge to measure the thermal stress.