พฤติกรรมแบบเหนียวของโครงสร้างคานเหล็กรูปพรรณแบบกล่องสี่เหลี่ยมกรอกคอนกรีตต้านทานแรงกระแทก

Abstract

This research studies the behavior of simple beams subjected with impact loading and static loading under three-point bending load. The impact load was established with dropped hammer weight 160 kg. from 70 cm to the mid-span at the first time and with different heights at another times. For static loading test, the point load was generated at mid-span and increased gently until failure. The specimens included 3 groups : reinforced concrete beams, concrete filled steel tube beam, and hollow steel beam. The clear span was 1.2 m. in all samples. For each group, the number of sample under impact loading was 8 samples and under static loading was 4 samples. The shear strength and flexural strength of reinforced concrete beam samples were designed equal to the concrete filled steel tube beam samples. Furthermore, the section of concrete filled steel tube beam samples and hollow steel beam samples were same dimension. From the impact loading test, in early stage, the input impact energy was absorbed and dissipated with the energy absorption, inertia force. For reinforced concrete beams had higher impact load comparing with the concrete filled steel tube beams but they had lower energy absorption. A large flexural crack was also found in the center of the beam after impact loading. For concrete filled steel tube beams showed very little damage from the first impact load. For hollow steel tube beams, a large local buckling was founded after impact load, resulting in a loss of loading resistance. For the static loading, it was found that The bending strength of the reinforced concrete beam and the concrete filled steel tube beam were similar as designed. the failure mode of reinforced concrete beams were flexural failure with flexural cracks distributed along span of beams. It was shown that the impact resulted in a change in the characteristic of the crack of the reinforced concrete beam specimens. The concrete filled steel tube beams caused a little lateral local buckling, Hollow steel tube beams caused a large lateral local buckling. And the stiffness of the reinforced concrete beams was the highest. From the test results, it can be concluded that the concrete filled steel tube beams are more suitable for impact load than other types of specimens. It is because it produced less Impact force and less damage than other types of specimens. Also, when the specimen is repeatedly impacted, the specimen is still able to withstand the impact well.