Study On Crack Control Of The Underground Prestressed Flat Slab Under The Construction And Service Loads

The empirical coefficient method,the equivalent frame method,the finite element method calculation and the distribution law of the internal forces under the vertical loading of the flat slab was studied.The method of load equilibrium was used to estimate the amount of prestressed reinforcement,and nominal tensile stress method was used for anti-crack calculation.Secondly,the slab of the underground building of Hefei Railway Station were simulated and monitored to verify the rationality of the anti-crack design.The conclusions are as follows:Flat slab can be divided into column strip and middle strip.The negative moment of column strip the at the bearing section is 2 to 3 times that of the middle strip,and the sagging moment of the column strip at the middle section is 1.1 to 1.4 times that of the middle strip.The absolute value of the line moment at the slab-column joint is the largest.Thus,it is necessary to strengthen the design of the slab-column joints.The method of load equilibrium was used to estimate 27 and 9 prestressed tendons are arranged on the X-direction column and middle strip.When the concrete reaches the design strength,the scaffolding could be removed before prestressing.In the usage stage,the tensile stress at the bottom of the corner of the slab is large and the design needs to be strengthened.In the simulation of the underground flat slab,the slab meets the requirements of the crack control design under the construction loads.When the concrete reaches the design strength,the scaffolding could be removed before prestressing.Under the service loads most area of the slab meets the requirements of crack control design,and the plate and column joints and some corner plates need to be reinforced to meet the crack control requirements.In the monitoring of the underground flat slab,the covering soil provides the thermal insulation effect for the structure,the total strain without stress was small,and the factors such as temperature and shrinkage have little influence on the concrete strain.During construction to service,the minimum sensor strain value was negative,and the maximum value was positive.Both were less than the concrete ultimate tensile strain.Slab cracks width at monitoring sites meet specification requirements.