Study On Crack Resistance Of Roof Slab Under Large Temperature Difference During Construction

Concrete is a very widely used material nowadays.Crack is often accompanied by concrete material problems,cracks will not only reduce the structural strength,but also on the psychological impact of users,according to incomplete statistics,every year due to the roof slab,floor cracks after the problem of complaints,accounted for 90% of the total contradictions between the owners and developers,construction enterprises.In the process of the generation and development of cracks,the proportion of non-structural cracks is large,and the concrete performance changes dramatically during the construction period,and the cracking sensitivity is strong.Therefore,it is of great significance to study the cracking of roof slab under the condition of large temperature difference during the construction period.Based on the relevant thermodynamics theory of concrete,this paper takes ABAQUS as the research platform,based on the concepts of hydration degree and equivalent age,and considering the changes of thermal conductivity,specific heat and thermal expansion coefficient with age,the temperature field and temperature stress subroutine of concrete roofing slab is compiled,and the rationality of the subroutine is verified.The results show that in the simulation of adiabatic temperature rise,the temperature field constructed by the subroutine is consistent with the theoretical temperature field.In the simulation of average temperature,the average temperature of the panel under the subroutine is consistent with the rule of theoretical solution and the error is small.On the fitting of the experimental temperature field,the temperature field of the program is consistent with the law of the experimental data,and the numerical error is small.In the simulation of stress field,the stress level of roof slab and steel bar fits well with the theoretical solution,and the program is reasonable.Through programmed to one project roofing board on the temperature field and stress field numerical simulation and analysis,to explore the influence of the constraint effect,through the variable constraint conditions,three different constraint conditions of concrete roof slab temperature stress analysis,the results showed that the constraint is decided early age concrete roof slab stress distribution and stress level of the important reasons.After that,several common factors that may affect the temperature stress of early age concrete roofing slab,such as reinforcement ratio,steel bar spacing and wind speed,are studied.The results show that the increase of reinforcement ratio has a certain inhibitory effect on the temperature rise of roofing slab.In the case of steel bar spacing,the effect of steel bar spacing on the temperature stress itself is not obvious.The influence of wind speed on the temperature stress of early age concrete roofing slab is very strong.The reduction of wind speed of 2m/s brings benefits equivalent to the reinforcement ratio of 0.6%,which is more economical.In the aspect of anti-cracking,a method to reduce the stress in the high-stress area of early age concrete roofing slab is put forward,and the concrete effect is simulated numerically.Based on the XFEM method,the crack development of concrete roofing slab under three kinds of constraint conditions is simulated,and the results show that the crack distribution form is basically consistent with the stress expression form,the shear wall structure has the highest crack sensitivity,and the frame structure has a good crack resistance performance.The study of this paper can provide reference for anti-cracking measures of concrete roofing slab in early age.