Analysis Of Vertical Shear Bearing Capacity Of Steel-ECC Composite Beams After High Temperature

The steel concrete composite beam bridge is a bridge structure formed by combining steel members and concrete slabs with shear keys.Its outstanding advantages include high strength,strong spanning ability,and fast construction speed.However,steel-concrete composite beam bridges also have the problem of concrete bridge deck cracking under tension,and the bridge may be exposed to fire during operation,threatening structural safety.ECC(Engineered Cementitious Composite)is a high-performance material with multiple crack and strain hardening behaviors.Applying ECC materials to steel concrete composite beam bridges can improve the safety and durability of structures.In this paper,the vertical shear resistance of steel ECC composite beams after high temperature is studied.The research contents and conclusions are as follows:1.The mechanical properties of ECC and steel under different cooling methods after high temperture were experimentally studied.The microstructure of ECC after high temperature was observed by scanning electron microscopy and the damage mechanism was analyzed.The results show that:(1)The compressive strength and tensile strength of ECC generally decrease with increasing temperature;(2)The compression and tensile strength of ECC are significantly reduced by water spray cooling The melting of PVA fibers,the weakening or loss of the "bridging effect" between the fibers and the substrate,and the state of hydration products are the main reasons for the significant differences in the strength of ECC under different high temperatures and different cooling methods;(4)Within 400 ℃,temperature has a small impact on the strength of steel.2.High temperature tests and static tests after high temperature were conducted on each test beam,,and the results showed that:(1)Both the composite beam at room temperature and after high temperature were subjected to the failure of ECC wing plate through oblique cracks;(2)As temperature increases,the bearing capacity,stiffness,and ductility of steel ECC composite beams deteriorate The effect of internal cooling at 200 ℃ on the shear bearing capacity is small,and the shear bearing capacity of composite beams after wet water cooling at200 ℃ decreases significantly.After wet water cooling,the initial shear stiffness of steel ECC composite beams increases,while after natural cooling,it decreases.3.The ABAQUS software is used to establish a thermal analysis model for steel ECC composite beams,The results show that:(1)The finite element simulation results agree well with the experimental results,and the heating under the bridge is more unfavorable for the steel ECC composite beam;(2)Applying fire retardant coating on steel beams can significantly improve the fire resistance of steel ECC composite beams,reduce the sensitivity of steel beams to temperature,and effectively reduce the damage degree of composite beams caused by fire under the bridge.4.ABAQUS was used to analyze the impact of shear parameters on steel ECC composite beams at room temperature and after high temperature.The results show that:(1)The yield strength of steel beam and the thickness of steel beam web are the main influencing factors,followed by the thickness of ECC flange plates and ECC strength,and the diameter of steel bars has a small impact on the mechanical properties of steel ECC composite beams;(2)Compared with natural cooling,the increase in shear capacity of steel ECC composite beams after wet water cooling with flange thickness is smaller.5.The calculation formula of vertical shear bearing capacity of steel-ECC composite beam after high temperature is proposed,and the calculated value of the prediction formula is in good agreement with the experimental value.