A Study On Static/dynamic Mechanical Properties And Anti-Explosion And Anti-Penetration Mechanism Of Steel Fiber Reinforced Self-Compacting Concrete

Benefiting from the accelerating development of economics and military,domestic construction of reinforced concrete structures with dense steel bars in super high-rise buildings and protection engineering will increase significantly in the future,which will greatly increase the demand for steel fiber reinforced self-compacting concrete(SFRSCC),especially SFRSCC with reinforced strength and impact resistance,because SFRSCC does not require vibration.In this paper,firstly a new type of SFRSCC was developed,including design of the mix ratio,study on its working performance,experiments on its quasi-static tensile and compression properties.Then,various types of test specimens of this type of SFRSCC were prepared,and dynamic tensile experiments,dynamic compression experiments,anti-explosion experiments,and anti-penetration experiments were carried out.The main contents and innovations of this article include:Two types of self-compacting concrete with different strength grades of C40 and C60 were designed,and four different volume fractions of steel fibers were added:0.5%,1.0%,1.5%and 2.0%.A total of 8 types of SFRSCC samples were prepared.Quasi-static mechanical performance experiments were performed on these samples.A special fixture was designed to carry out the uniaxial tensile test,and the quasi-static uniaxial tensile strengths of C60 SFRSCCs was obtained,and the relationship between the uniaxial tensile strength and the steel fiber volume fraction was obtained by data fitting,which is linear.Compared with ordinary self-compacting concrete,when the steel fiber volume fraction increases from 0.5%to 2%,the tensile strength increases from 7%to 18%.Split tensile experiments were carried out.For C40 SFRSCCs,when the steel fiber volume fraction increases from 0.5%to 2%,the splitting tensile strength increases by approximately 36%.For C60 SFRSCCs,except for samples with 1%fiber volume fraction,the overall trend of splitting tensile strength is the same as that of C40 SFRSCCs,but the change range is smaller.The SHPB dynamic compression experiment results show that the C40 and C60 SFRSCCs both have significant strain rate effect,but for the C40 SFRSCC,the strain rate sensitivity is higher than that of plain concrete,and the C60 SFRSCC is close to plain concrete.Dynamic tensile tests were carried out on SFRSCC using modified SHPB device.The results show that the tensile strength of SFRSCC is mainly determined by the compressive strength of the corresponding SCC and the fiber volume fraction.The greater the compressive strength,the greater the tensile strength.The higher the fiber volume fraction,the greater the tensile strength.An empirical formula was proposed to describe the relationship of SFRSCC’s dynamic tensile strength,quasi-static compressive strength and fiber volume fraction.Combining the concept of "equivalent micro voids system" and "nucleation growth model",a compression-shear coupled damage evolution model is proposed.By fitting the stress-strain curve of SHPB dynamic compression tests of SFRSCC,the parameters of compression-shear coupled damage evolution equation are obtained.Circular slabs(Φ400 mm×60 mm)of SFRSCC with different strength levels and different steel fiber volume fractions was fabricated,and water bath explosion experiments were carried out on them.The experimental results show that when the steel fiber content exceeds 1.5%,there is almost no damage and cracks on the front of the SFRSCC slabs.The strength level of concrete has little effect on the blast resistance of the SFRSCC slab.When the steel fiber content is the same,the failure and deformation of the C40 and C60 SFRSCC slabs are similar.Loading method also has a great influence on the failure form of the SFRSCC slab.Under the contact explosion,the explosion pressure is directly transmitted to the slab,and the center of the slab is penetrated as a whole.While under water bath explosion,the explosive pressure propagates to the slab surface through the water,the slab is more uniformly loaded,the target slab is not penetrated locally,and the blast crater on the front and the spalling area on the back are also smaller.The FEM-SPH coupling algorithm was used to carry out the numerical simulation of SFRSCC slab anti-explosion experiment.The numerical simulation can clearly reproduce the explosion process,the deformation and failure of the concrete slabs.The calculated concrete damage distribution is in good agreement with the experiment,indicating that the model can accurately predict the damage distribution of the concrete slab under the water bath explosion.Block targets(350mm×350mm×200 mm)of SFRSCC were produced,and penetration resistance tests were conducted on them using long rod projectiles.The results show that SFRSCC with steel fiber content of 1.5%has better penetration resistance than that of 0.5%,but when the steel fiber content increases to 2.0%,the penetration resistance decreases.Based on the existing concrete penetration model,considering the influence of steel fiber,the empirical formula for predicting the penetration depth of SFRSCC target was proposed,and the relevant parameters were modified according to the test results.The calculated results are in good agreement with the test data,indicating that the formula can accurately predict the penetration depth of the projectile to the SFRSCC target.