Experimental Studies On Dynamic Response And Residual Strength Of Thin-walled Sandy Pebble Filled Square Steel Tube Columns Under Lateral Impact

Sandy pebble filled square thin-walled steel tube columns take full advantage of the characteristics of the steel and the sandy pebble, which could not only enhance the stability of empty thin-walled steel column, but also make up for the shortage of concrete filled steel tubular column that is difficult to save energy and protect environment and recycle after a certain number of years. In recent years, with the increasing emphasis on this type of composite columns, it would inevitably suffer from a variety of unexpected impact loads as main load-bearing structure columns during installation and service structure. There would be different degrees of damage under impact load, even causing serious collapse of the whole structure, both of which inevitably lead to the capacity decline and even loss of carrying capacity. Therefore, it is of great significance for carrying the studies on the basic mechanical properties and its residual strength of sandy pebble filled square thin-walled steel tube columns under lateral impact load in order to further promote engineer applications timely, which have very important applications for deformation, damage and residual strength in the background. This paper has studied response process and residual strength of sandy pebble filled square thin-walled steel tube columns under impact load. The main work and results are as follows:1. Analyzing qualitatively the impact and failure modes among thin-walled empty square tubular columns, sandy pebble filled square thin-walled steel tube columns and thin-walled steel concrete columns, the platform values of which in turn increase under impact load, and the platform values of thin-walled steel concrete columns are 3 to 4 times of the thin-walled empty steel columns and 2 to 3 times of sandy pebble filled square thin-walled steel tube columns. Failure modes of thin-walled empty square tubular column are mainly local failure, accompanied by certain degree of overall bending deformation, and sandy pebble filled square thin-walled steel tube columns have produced locally deformed in the impact area, which have within 2mm of overall maximum deflection values, however, thin-walled steel concrete columns produce only a small deformation and cannot substantially affect the overall force structure.2. In order to study on the properties of sandy pebble filled square thin-walled steel tube columns under impact load by using self-designed simple drop hammer to test 24 specimens with compaction coefficient(0, 81%, 86%, 92%) and slenderness ratio(14.5,29.1,38.8,43.6,58.2) as the main parameter changes. The experiment crucially records history curves of impact and observes degree of deformation, which show that the more compaction coefficient increases, the greater the value of the impact force platform, the more obvious the overall deformation restraint effect, and the less plastic hinges that consume less energy, thereby filling the sand and gravel within the energy consumed, but the role of time is reduced, ductility is relatively weakened. Slenderness ratio on the extent of damage to the specimen form larger than the compaction factor, long column shape deformation damage mainly local deformation and overall deformation coupling under impact load. In addition, the influence of the slenderness ratio parameters on the peak value of the impact force, the platform value and the action time of the specimens is significantly different. The larger the slenderness ratio, the smaller the value of the platform, the greater the action time, but the change is not obvious in the slenderness ratio over 43.6.3. The paper have completed the vertical static load test to 24 root damage specimens after impacting and 16 root contrast intact specimens(intact original specimen). The experiment records the value of the load and the axial displacement, the lateral displacement of mid-span and 1/6 and strain values, besides, the experiment also observes failure modes of the specimen. The failure modes of all the intact specimens are local buckling, and the failure modes of the damaged specimens are local and overall buckling. Based on the size of the residual strength of specimens, to determine the degree of damage to define the degree of injury under the impact load. With the increase of compaction coefficient and the slenderness ratio, the degree of damage showed a trend that first increase and then decrease,and found that in addition slenderness ratio of 29.1 specimens is a serious injury member, the other members are moderate injury.