Study On Bending Mechanical Properties Of Reinforced Concrete Beams Which Are Strengthened By HPFL After Fire On Secondary Load

High performance ferrocement laminate(HPFL)is a practical method of structural reinforcement with good performance in repairing RC beams after fire.Analysis and tests on bending mechanical properties of reinforced concrete beams which are strengthened by HPFL after fire on second load are put forward.The main contents and conclusions are as follows:1.Thermal parameters and material properties after fire of concrete and steel at home and abroad were summarized,such as strength,elastic modulus,stress-strain curve and bonding strength between steel and concrete.The thermal properties of concrete were affected by temperature.As the temperature increasing,the strength and elastic modulus decreased much and the residual amount would less than 20%after temperature exceeded 800'C.At the same time,stress-strain curve gradually slowed and the peak point moved down and right.The temperature effect on steel was smaller than on concrete.Reduction coefficient of strength and elastic modulus was not over 0.8 when the temperature didn't exceeded 800?.Decreasing slope of steel stress-strain curve,increasing plastic deformation and elongation were also showed.These thermal properties were not recovered obviously after materials cooled.Bond strength between steel and concrete went down with increasing temperature.2.The basic theory about ANSYS simulating RC beams reinforced by HPFL after fire was introduced.Through simulating the two-dimensional section temperature field of RC beams,it found fire duration and sectional dimension were the most important influence factors and also presented pictures about section temperature field at different sectional dimension under different fire duration.Material properties were described in detail during establishing the three-dimensional model,and flexural bending capacity and stiffness were also showed at last.3.On the basis of existing experiments,stress plain section assumption and internal forces balance,mechanical equations were created.It put forward a series of theoretical analysis on residual flexural capacity of RC beams after fire and flexural strengthening of RC beams with ferrocement,such as failure modes.The formulas of initial strain of strengthened elements were obtained,as well as the formulas of flexural capacity.It gets a good matching between theoretical values and experimental values when the calculated results were compared with trial values.4.Combined with project,residual stiffness of RC beams after fire was researched,as well as RC beams reinforced by HPFL.The test shows HPFL reinforcement technique can repair cracks and appearance for RC beams,and also improve their bending stiffness and anti-cracking property.The theoretical analysis about short-term stiffness of RC beams after fire with ferrocemen was introduced through stiffness analytic method.It put forward formulas and discussed the variables in them.The result shows that deflection of RC beam meet norm requirement.