| Concrete is the most widely used material in civil engineering structures. Apartfrom dead load and live load, it may suffer from accidental load in its service time, suchas explosion and impact. If the impact energy is severe enough, it can lead to collapse orfailure of structures. In many cases, the impact energy is not so severe to cause collapse,the structure would not be completely destroyed, but its bearing capacity will decreaseand its dynamic characteristics will change. In such situation, it is necessary to find outan appropriate method to evaluate the damage degree of concrete structures, which willhelp determine the residential capacity of concrete structure and propose a reasonablestrengthening scheme.A series of impact experiments was carried out with the drop hammer machine inHarbin Institute of Technology.24short concrete columns of3strength grades wereapplied with different impact load, thus causing different degrees of damage. Thedamage was detected with an ultrasonic instrument and the mechanical property ofconcrete gained with the5000kN press machine. In addition, finite element programABAQUS was used to simulate the impact process. This article deals with the followingitems:(1) Axial impact load was applied to24concrete short columns with the drophammer machine. The impact force and strain of concrete columns were measured, andthe procedure of impact was recorded by a high-speed camera.(2) An ultrasonic instrument was used to test the concrete columns before and afterimpact so that we can find out the variation of acoustic parameters in damaged concrete.A damage variable D based on ultrasonic velocity was proposed to describe the damagedegree of concrete.(3) The stress strain curve of damaged concrete was gained to find out the changeof mechanical parameters (including elastic modulus, compressive strength and ultimatecompressive strain) in damaged concrete.(4) Finite element analysis software ABAQUS/Explicit was used to simulate theimpact process. |
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