Study On Temperature Field And Temperature Stress Of Single-cell Box Girder Curing With Electric Heater

During the process of precasting box girder,the partial size of single-cell box girder relatively large,which leads to the great temperature difference and influences the quality of the box girder production.Under winter construction,concrete strength of box girder develops very slowly.In order not to extend or even shorten construction period,the fast prefabricated construction methods of box girder are need to be researched.Based on the engineering project of the Chong Qing West Railway Station,pick the 26.58 meters long single-box single-cell box girder as the object of study.In the construction site,the strength test of concrete samples under the same condition was conducted,and the single chamber box girder in the electric heating under the heat curing process,so was the temperature monitoring test on the single-cell box girder curing with electric heater.First the maintenance method of box girder was designed,and insulation measure was studied.Then the theoretical model of box girder temperature field and thermal parameters were discussed.Using the finite element analysis software ABAQUS to calculate the box girder temperature field under this curing condition,and it was compared with the results of the temperature monitoring test.At last,to calculate the stress field of box girder further.Analyze the winter maintenance process with the feedback.The main conclusions are as follows:(1)In the early stages of the development and change of the box girder temperature field,the main factors affecting the first is the heat of hydration of box girder itself.The high performance concrete box girder of the bridge use heat quantity is big,the early exothermic rapidly,box girder temperature rise rapidly.Box girders of maximum temperature difference of time 78 h after casting,the box girder flange end temperature gradient is remarkable.Box girder is the highest temperature can reach 42.3 ?,in the joint of roof and web of core,because the heat is not lost.Box girder roof and web have obvious temperature-rise,constant temperature,cooling three stages,while the flange end after the peak temperature began to slow cooling.(2)The theoretical value and measured value of roof and web error is always present,maximum error is about 7%,the simulation calculation results are in good agreement with the test result.The established finite element model can well simulate the actual single-hole box girder temperature field under the condition of the maintenance.(3)After concrete pouring early compressive stress appeared in the higher temperature of local area.And the outer surface of the low temperature and low end constraint strong areas appear tensile stress area.As the growth of the age,the tensile stress increases obviously,the growth of the compressive stress is not obvious.Finally formed within a circle hole room surface compressive stress of concrete,and the entire box girder of peripheral zone is under tensile stress.Is the location of the maximum stress appears on the flange end,time corresponds to 78 h,a time is also the largest temperature difference.(4)Box girder under the condition of the electric heater heat preservation of maintenance under the finite element analysis simulation is safe and effective,does not produce early cracks because of the temperature change.In the practical engineering application,also not observed cracks on the beam body.In this paper,the innovation points are: this article has the following innovation points:(1)proposed the single room box girder using electric heater to heat insulation curing method;(2)the in-situ monitoring and study method of the finite element software simulation results contrast;(3)using the production activities provide research data,the results of the study to improve the actual production of the two-way feedback mechanism.