Compressive Behavior Of Reinforced Concrete Piers Under Freeze-Thaw Cycles

In recent decades,China has made great efforts to develop infrastructure construction projects,in which concrete structure-based bridge engineering more and more,and China’s vast territory,north China,northeast,northwest and other regions in winter temperature is lower,so that many buildings have occurred freeze-thaw damage.So in the cold regions of the building,the frost resistance of concrete is very important,while the frost resistance of concrete is also a very important aspect of its durability;early years,domestic and foreign experts and scholars usually through the concrete frost performance as a standard to evaluate the durability of concrete,and some even through the concrete freeze-thaw test as its durability test.In this paper,the frost resistance of piers and the compressive performance of piers after freezing and thawing are studied.The freeze-thaw cycles of 20,40,60,100 and 120 times of reinforced concrete piers are carried out.And the compressive strength of the reinforced concrete piers was analyzed by ABAQUS finite element analysis software.The temperature field and thermal stress of the reinforced concrete piers were analyzed by thermo-mechanical coupling.Based on these two tests,The stress-strain curve obtained in the experiment is used to study the compressive behavior of damaged pier columns by using the plastic damage constitutive model of concrete.Finally,on this basis,the influence factors of concrete thermal stress under freeze-thaw cycle are analyzed And the influence of slenderness ratio on the compressive behavior of damaged pier columns.The main conclusions are as follows:(1)With the increase of the number of freeze-thaw cycles,the thermal stress and strain of the structure increase gradually.When the number of freeze-thaw cycles increased to 120 times,the thermal stress of the components increased by 50.5% and the thermal strain increased by 86.0%.It was found that with the increase of the number of freezing-thawing cycles,the damage of components was accumulated.(2)When the number of freezing and thawing cycles reaches 120,the maximum thermal stress of the inner and outer components is 0.8Mpa and 2.5Mpa respectively.The stress on the outer surface of the component is 3 times of the center of the component,which shows that the damage degree of the concrete surface is relatively large.(3)In the early stage of freezing and thawing,the thermal stress of rebar is the fastest,and when it reaches 60 times,the temperature stress of steel bar reaches the peak value of 0.65 Mpa.With the increase of the number of freeze-thaw cycles,the temperature stress gradually decreases linearly.At the same time,compared with concrete,the existence of reinforced concrete damage is still relatively large,when up to 120 times,the peak stress of concrete than reinforced concrete stress decreased by 14%;It can be seen with the freezing and thawing times,The influence of rebars on the internal damage of concrete is becoming more and more serious.(4)With the increase of freezing and thawing cycles,the peak stress of the damaged pier has a tendency of decreasing linearly.After 100 cycles of freeze-thaw cycles,the peak displacement is 2.27 times of the freezing-thawing cycle,The original displacement increased by 127.2%.Indicating that the stiffness of the component is getting smaller and smaller,the ductility is more and more.(5)When the flexibility coefficient is relatively large,the compressive strength of the pier column decreases with the different boundary conditions,compressive strength of the maximum and minimum values corresponding to the boundary conditions are fixed at one end and fixed at one end of the free end of the case,both ends of the case of fixed-end compression than the fixed end of the free end of the pier The compressive strength of the column is 13.2% higher.(6)After 120 times of freezing and thawing,the thermal stress of the relatively large water-cement component is 0.28 Mpa,which is 10.7% higher than that of the water-cement.When the cooling rate is accelerated,the temperature stress of concrete is obviously higher than that of normal cooling,which is 16% higher than that of normal cooling.When the low temperature of the outermost environment is-5 ℃,the freezing-thawing frequency has no effect on the temperature stress,and the stress is basically constant.The temperature of the component is increased with the decrease of the minimum temperature.