Experimental Study On Thermo-mechanical Response Characteristics Of Prestressed High-strength Concrete Energy Pipe Pile

With the promotion of world economic integration,energy has gradually become the material basis of social development.Energy pile is a new building energy-saving technology which has double functions of ground source heat pump heat exchangers and supporting upper building loads,however,the energy pile combined with the prestressed high-strength concrete pipe pile has gradually been more and more widely used in engineering because of its advantages such as convenient construction,simple manufacture,and hole inside the pipe pile to facilitate the arrangement of heat exchange tubes.Based on the pile foundation project of the comprehensive gymnasium of Zhoukou Normal University,the thermo-mechanical response field tests of prestressed high-strength concrete energy pipe pile were carried out in this paper.The variation of the distribution of pile temperature,the coefficient of heat transfer performance(COP),the pile top load-displacement,the pile axial force,the pile side friction resistance and the additional temperature stress were emphatically studied.In this paper,by analyzing the experimental,the heat transfer performance of prestressed high-strength concrete energy pipe pile under cooling and heating conditions was studied,it is concluded that the heat transfer performance of energy pipe pile under cooling intermittent conditions is much higher than that under cyclic conditions,and the heat transfer performance under intermittent conditions decreased with the increase of the ratio of start to stop of the energy pipe pile system.In heating conditions,with the increase of the flow rate of the heat exchange liquid and cycle time,the COP value decreases gradually,but the change trend of heat transfer efficiency does not decrease linearly with the increase of flow rate.Besides,by analyzing the change of the pile top load-displacement,the pile side friction resistance and the pile additional temperature stress,it is concluded that the settlement displacement of the pile will be changed by the action of cooling and heating temperature load,the settlement of the pile will decrease under the action of heating load,but the change is small.The variation of the pile side friction resistance is different from that of conventional pile type,that the two ends of the pile are cold-shrinked generated the positive friction resistance in the upper part of the pile and the negative friction resistance in the lower part under the cooling condition,the distribution of the friction resistance is opposite under the heating condition.The neutral point is located at-8m of the pile,about 2/3 of the pile length,and the friction resistance is relatively small near the neutral point,with the increase of the loading level and the temperature variation of the pile,the cumulative effect of the thermal strain from the neutral point to the pile both ends increases,correspondingly,the value of the friction resistance increases gradually.The maximum additional tensile stress under the cooling condition is about 28.9% of the maximum additional compressive stress under the heating condition,therefore,the additional temperature stress caused by the change of the pile temperature will not damage the pile.Finally,in this paper,the theoretical analysis of the bearing characteristics and the calculation of the bearing capacity of prestressed high-strength concrete energy pipe pile are carried out,and the correctness and reliability of the theoretical calculation of the energy pipe pile bearing capacity are verified by combining the filed static load test results.In addition,the engineering application of energy pipe pile is prospected.