Experimental and numerical study of a pipe in pipe force limiting device (PPFLD)

The buckling behavior of compression member has a decisive role in the collapse behavior of a structure. The buckling and sudden capacity loss of the compression member can be prevented using a proposed PPFLD and the brittle post-buckling behavior of the compression member can be converted into ductility behavior. The PPFLD consists of two pipes, one of which is placed into the other pipe and the axial force applied to the inner pipe. Thus, the outer pipe operates as a casing for the inner pipe. The present study investigated a number of experimental specimens. Next, numerical analysis of these specimens has been done using finite element software. Further, the behavior of the PPFLD have been investigated under important parameters such as the gap between two pipes, the inner pipe slenderness coefficient, and the ratio of outer pipe length to inner pipe length, by studying more numerical specimens. The results indicate this PPFLD is an effective, simple and economical method to prevent the buckling of compression member and can lead to a favorable increase in the bearing and deformability capacity of the compression member. The bearing capacity of this PPFLD is inversely related to the size of the gap, and is directly related to the ratio of the outer pipe length to inner pipe length. The bearing capacity of the member will increase significantly, if the gap size is less than 43% of the inner pipe's gyration radius, and the the ratio of the outer pipe length to inner pipe length is greater than 55%. This is more sensible especially when the outer pipe covers the entire length of the inner pipe. The proposed PPFLD has the potential of eliminating the buckling of compression member and providing adequate and sufficient restraints to make yielding at compression member with different slenderness.