Research On The Influence Of Spatial Distribution Of Fractured Stirrups On The Shear Behavior Of RC Beams

The durability of reinforced(RC)concrete structure is widely concerned around the world.In recent years,The fracture of stirrups in the bending end caused by alkali aggregate reaction(ASR)has been found in many investigation reports.Due to the uneven distribution of reaction material,diverse service environment and different boundary condition,the fracture location of reinforcement caused by ASR is random and irregular in structures.For the RC structures located in the marine environment,the severe corrosion caused by chloride ingression will cause the fracture of stirrups in the bending end,which may also result in the severe degradation of bond strength near the fractured position.Stirrups plays an important role in shear resistance for RC beams,and thus the deterioration phenomenon mentioned above certainly decreases the shear capacity of RC beams and leads to unexpected brittle failure.However,few researches are conducted to investigate the effect of stirrups fracture on the shear behavior of RC beams.This paper focuses on the RC beams deteriorated by ASR and severe chloride corrosion,and experimental investigation and finite element analysis are conducted to investigate the influence of spatial distribution of stirrup fracture on the shear behavior of RC beams.The effect of bond deterioration around fractured position on shear behavior is also taken into consideration."U" type stirrups are used to simulate the fracture caused by alkali aggregate reaction and "U" type stirrups packaged with cellophane and duabed with oil are used to simulate the corroded fracture caused by severe corrosion.The parameters of this experiment are as follows:spatial distribution of fractured stirrups,length of bond lose in fractured stirrups and shear span to effective depth.Fourteen experimental beams were cast and three-point loading test were conducted to investigate the influence of spatial distribution of stirrups fracture on the shear behavior of reinforced concrete beams.Based on the experimental results,finite element analysis by DIANA software was also conducted and the result of numerical analysis agrees well with experimental results.The conclusions of this paper are as follow:(1)Comparing with the sound specimen,no matter the fracture of stirrups appears locally or overall within the shear pan,the fracture of stirrups decreases the shear capacity of reinforced concrete beams,and the reductions of shear capacity is related to the spatial distribution of fracture stirrups and shear-span-to-effective-depth(a/d).When the fractured stirrups appear within the whole shear span,it shows an obvious decline in shear capacity.Especially,when the fracture of stirrups appear in the bottom bending end near the supporting point and in the top bending end near the loading point simultaneously,it will lead to the lowest shear capacity among the specimens without bonding loss.(2)For RC beams with long a/d,it is more adverse that the fractured stirrups appear near the supporting position than near the loading position.When the fractured stirrups appear near the supporting position,it can't restrict the appearance and the development of bond cracks along the longitudinal direction,which finally weakenes the "arch action" and results in a notable decline in shear capacity.When the fractured stirrups appear near the loading position,even though the shear resistance by "truss action" decreases,the "arch action" is still sound and consequently the shear capacity descends slightly.(3)For RC beams with short a/d,it is more dangerous that the fractured stirrups appear near the loading position than near the supporting position.The "arch action"is easy to come into being while the "truss action" becomes the key factor of shear resistance.When the fractured stirrups appear near the loading position,the stirrups yield barely and the "truss action" is damaged,which finally lead to an obvious decline in shear capacity.Otherwise,though the fractured stirrups near the supporting position weaken the "arch action",the "truss action" is still sound and the final shear capacity has little change.(4)Both in long a/d specimens and short a/d specimens,when the stirrups fracture within all the shear span and lose bond with the certain length,RC beams shows further decline in shear resistance.The longer the length of bond lose is,the more significant the decline of shear capacity is.For RC beams with 10d length bond lose in fractured stirrups,the bigger the shear span to effective depth is,the more obvious the decline of shear capacity is,a linear relationship is confirmed in between.(5)Either in long a/d beams or in short a/d beams,the fracture of stirrups appear in local position has little influence on the stiffness of reinforced concrete beams,but when it appear in all the shear span,the obvious decrease in stiffness is found.Especially,when the fracture of stirrups appear near the bottom bending end and the top bending end simultaneously,it will lead to the lowest stiffness in all beams without bonding loss.(6)Baseing on the bond-slip obtained from finite element analysis,the father the distance between the end of fractured stirrups and the intersecting point of the main inclined crack and stirrup is,the fewer the bond-slip around the fractured end is.It means that the length of this distance affects the anchorage effect of the stirrup,the stirrup can even come into yielded when the bonding length is sufficient.