Research On The Static And Dynamic Mechanical Characteristics Of Steel Fiber Reinforced Cellular Concrete Composites And Its Underwater Anti-explosion Protection Effects

In view of the seriousness of the accident consequences of hydraulic structures subjected to sudden extreme loads such as terrorist attacks or wars,the anti explosion fortification of high dam structures has attracted great attention from all over the world.The exploration of structural anti-explosion fortification can essentially be attributed to the study of new anti-explosion protection materials.In this paper,steel fiber reinforced cellular concrete（SFRCC）is proposed as the underwater anti-explosion protection material for high concrete dam for the first time.To fully understand the material characteristic of steel fiber reinforced cellular concrete and reveal its anti-explosion protection mechanism and anti-explosion protection effect,the SFRCC was prepared by the saturated super absorbent polymer（SAP）instead of traditional foam pores.For SFRCC materials,uniaxial compression and splitting tests under static loads and SHPB dynamic compression tests under high strain rates were carried out,and the modified HJC constitutive model for SFRCC was established based on the measured test results,and the effect of adding steel fiber reinforced cellular concrete protective layer on the anti-blasting ability of the protected roller compacted concrete slab under the condition of underwater explosion was studied.The main achievements of this paper are as follows:（1）The feeding sequence,molding method and the effective measures to control the floating of saturated SAP beads in the preparation process of SFRCC were systematically summarized,and the uniform SFRCC specimens with different steel fiber contents were prepared.The variation rules of compressive strength and splitting strength of SFRCC with different steel fiber contents were discussed,and the enhancement mechanism of steel fiber to its mechanical properties was revealed,and the suggestion that the steel fiber ratio in the SFRCC should not exceed 1.5%is given.In addition,an improved stress-strain curve model which can accurately describe the uniaxial compression behavior was established,and a new empirical formula for predicting the splitting strength of SFRCC was proposed.（2）The dynamic compression behavior of SFRCC with different fiber contents under high strain rate(76.0～289.89 s^-1)was studied by Split Hopkinson Pressure Bar（SHPB）.The results show that the SFRCC has obvious strain rate effect in the range of76.0～289.89 s^-1,and the more obvious the enhancement effect of dynamic compressive strength,peak strain and impact toughness with the higher the steel fiber content（V_f≤1.5%）.With the increase of strain rate,the failure state of steel fiber reinforced porous concrete samples gradually changes from bulk to small fragments under high strain rate,showing obvious"strain rate hardening effect";the higher the content of steel fiber,the smaller the damage degree of the specimen,and the breakage of the specimen under high strain rate will lead to the straightening or fracture of the hook end steel fibers,which shows that steel fiber can improve the concrete matrix strength and crack growth inhibition.For SFRCC,the dynamic reinforcement of steel fiber is mainly attributed to:1)at the beginning of loading,the steel fiber and the concrete pore wall structure jointly bear the impact pressure,and the steel fiber plays the role of strengthening the concrete skeleton structure;2)with the continuous increase of load,the weak area of the hole wall structure begins to crack,but the introduction of steel fiber can to a certain extent It can restrain the development of cracks,reduce the damage speed of concrete and improve the bearing capacity of concrete.（3）Based on the dynamic test results of steel fiber reinforced porous concrete,an empirical formula for predicting the dynamic growth factor DIF of steel fiber reinforced porous concrete under high strain rate is proposed,and the prediction results calculated by the formula are in good agreement with the test results,which verifies the effectiveness of the empirical formula.（4）A numerical calculation model of dynamic impact test is established,which can satisfy the assumption of one-dimensional stress and stress uniformity of SHPB test,and the developed modified HJC constitutive model is embedded into the finite element calculation.The dynamic response and damage evolution process of steel fiber concrete under high strain rate are reproduced by applying the loading method of half sine wave.The stress-strain curve and failure mode which are in good agreement with the SHPB test results are obtained,which is proved that the modified HJC constitutive model is effective in characterizing the dynamic mechanical behavior of SFRCC.In addition,the failure modes of SFRCC at different times under high strain rate and the influence of the parameters of modified HJC model on the simulation results are analyzed.（5）Taking Roller Compacted Concrete（RCC）Gravity Dam as the starting point for the blast-resistant fortification in front of the dam,the numerical simulation method is used to analyze the influence of different protection schemes on the blast resistance of the limited width roller compacted concrete slab under the condition of underwater explosion,revealing the wave suppression and energy absorption effects of SFRCC.And the methods of the failure volume rate and concrete damage classification evaluation method were used to comprehensively evaluate the anti-explosion protection effect of SFRCC protective layer,and it is proposed that the thicker SFRCC protective layer should be selected as far as possible when the construction and design conditions permit.