Strength and Axial Behavior of Cellular Lightweight Concrete-Filled Steel Rectangular Tube Columns under Axial Compression

This paper presents the experimental results on the strength and axial behavior of rectangular steel tube columns filled with cellular lightweight concrete (CLC) under axial compression. A total of 24 specimens, including 6 reinforced cellular lightweight concrete (RCLC) columns and 18 cellular lightweight concrete-filled steel tube (CLCFT) columns are investigated. The nominal dimension of the rectangular columns are 150×75 mm in cross-section and 750 mm in height. The parameter used in all tests are the ultimate compressive strengths of the CLC, which are 15 MPa, 20 MPa and 25 MPa, and the wall thicknesses of steel tubes, which are 3.0 mm, 4.5 mm and 6.0 mm. All specimens are prepared and loaded concentrically in axial compression to failure. The results of these tests demonstrated that the CLCFT columns have a linear behavior up to the approximately 80-90% of their maximum compressive load. Then, the behavior of the columns is nonlinear. The nonlinear behaviors are due to the crushing of the concrete core and local wall buckling of the steel hollow tube. In addition, it is found that the CLCFT columns have high axial deformability at the failure when compared to the reference RCLC columns. Finally, by comparing the maximum compressive load of the test results with those obtained from the ACI composite design equation, the comparison results show that calculation formula in ACI code can be applied to compute the axial capacity of CLCFT columns under axial compression.

Analytical and Computational Models for Investigations of Local Buckling in Honeycomb Sandwiches

This work highlights and solves problems with the prediction of the compressive strength, limited by local instabilities, of sandwich material compounds based on honeycomb cores and very thin facesheets. Analytical methods in conjunction with periodic finite element unit cell models are utilized for this task. The finite element models are found to be well suited for all kinds of buckling predictions. Different uni- and bi-axial loadings are considered as well as influences of core height, core material, core geometry, and facesheet thickness are investigated. Finally, a new analytical approach is introduced for the treatment of the rather unexpected core cell wall buckling under in-plane compression of the sandwich, which predicts the critical load very accurately.

Locomotion Through the Intestine by Means of Rolling Stents

Colonoscopy is a standard medical procedure in which a long and flexible endoscope is inserted into the rectum for inspection of the large intestine and for simple interventions. Pushing the endoscope tip from behind via a long and flexible tube leads easily to buckling when the tip comes in contact with sharp curves in the intestinal wall. Buckling is accompanied by painful cramps and makes it difficult to complete the procedure. A way to avoid buckling is not to push the tip from behind, but to use the friction with the intestinal wall to pull the tip forward. This paper describes the state-of-the-art in research on intestinal locomotion methods and presents a new locomotion method based on a rolling donut that is positioned around the endoscope tip. The donut functions like a circular caterpillar and is constructed from three stents that generate high friction with the intestinal wall. The diameter of the donut can be changed and the stents can be driven independently to reduce slip in intestinal curves. The resulting Rolling-Stent Endoscope contains a new steerable mechanism by which the tip can be bent in all directions over a very large angle. The Rolling-Stent Endoscope was applied for a patent and a prototype is under development for evaluation in the intestine of a pig.