| Steel core-fiber composite bars(SFCB)consists of a high-strength steel core wrapped with continuous carbon fiber layers,with the inner core reinforcement improving the overall elastic modulus and the outer fiber providing additional strength and durability.At the same time,SFCB coral concrete offers cost advantages over FRP reinforced coral concrete.The current research on the impact resistance of SFCB coral concrete members is still involved,for this reason,this paper takes SFCB coral concrete beams as the main research object,and compares the impact resistance of composite reinforcement and single reinforcement coral concrete beams by conducting drop hammer impact tests on the test beams,the main findings are as follows:1.The damage morphology of SFCB beams under impact loading is more complex than that of steel and CFRP reinforced beams.At low impact heights,the damage morphology is similar to the static load action and shows flexural damage.With the increase of impact height,the damage morphology becomes diversified.Under low reinforcement ratio,the concrete crush zone appears at the top of the span and gradually expands to the bottom of the beam,and the failure section is usually located near the middle of the span,and the damage morphology has the characteristics of flexural damage,and the anchorage failure of the main tensile longitudinal reinforcement often occurs.Under high reinforcement rate,the failure section shifts to the bending shear section,and the area of large concrete collapse also occurs in the bending shear section,and the overall exhibits the characteristics of shear damage.2.Due to the inertia effect and strain rate effect,the specimen bearing capacity is higher than the static load effect.In general,the bearing capacity increases with the increase of impact height,but when the impact energy input threshold of the specimen is exceeded,the impact bearing capacity will no longer increase and the trend of decrease appears.In addition,affected by the stress wave propagation effect,each data signal is excited in turn according to the loading point far and near,and there is a relative lag in the triggering moment,and according to the lag time of the triggering moment of the longitudinal bar strain measurement point,the stress wave propagation speed in the coral concrete beam is calculated to be approximately1700 m/s3.In general,with the increase of impact height,the peak impact force and support reaction force of the test beam increase,and the lag time of support reaction force relative to the impact force is about 1.8ms.Since the peak impact force is significantly affected by the flexural stiffness,the peak impact force of SFCB beams with high reinforcement is larger than that of SFCB beams with low reinforcement,and the peak impact force of steel reinforced beams is larger than that of SFCB beams and CFRP reinforced beams.In addition,the impact time duration of SFCB beams is smaller than that of steel and CFRP beams,and the low reinforcement SFCB beams are prone to anchorage damage during impact,which makes the impact time duration shorten with the increase of impact height.4.During the impact,the peak deflection of SFCB beams is less than that of steel and CFRP beams,while the residual deflection is much lower than that of steel beams and similar to that of CFRP beams.The frequency and magnitude of fluctuations in the deflection time range of SFCB beams during the descending phase are much less than those of CFRP beams.This shows that the deformation performance and damping effect of SFCB is better than that of single reinforcement,and it has better impact resistance than single reinforcement when used in protection structures.In addition,with the increase of the impact height,the shape of the support reaction-deflection hysteresis curve gradually changes from quadrilateral to triangular,and in general,the energy dissipation capacity of SFCB beams increases with the increase of the impact height. |
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