Wind-Induced Dynamic Responses of Structures with Outrigger Systems
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Analysis of high‐rise braced frames with outriggers
A graphical method of analysis for the preliminary design of tall building structures comprising braced frames with outrigger trusses subjected to horizontal loading is presented. For this method of analysis it is necessary to determine five stifnesses for the uniform structure: bending and racking shear stiffnesses of the braced frame and outriggers in addition to a stiffness parameter representing the axial lengthening and shortening of the exterior columns. The analysis allows a simple procedure for obtaining the optimum location of the outrigger up the height of the structure and a rapid assessment of the impact of the outrigger on the behaviour of the high‐rise structure. It is concluded that all five stiffnesses should be included in the preliminary analysis of a proposed tall building structure as the reductions in horizontal deflections and bending moments of the braced frame are influenced by all stiffness parameters. Copyright © 2003 John Wiley & Sons, Ltd.
Rubik's for cryptographers
Hard mathematical problems are at the core of security arguments in cryptography. In this paper, we study mathematical generalizations of the famous Rubik’s cube puzzle, namely the factorization, representation and balance problems in non-Abelian groups. These problems arise naturally when describing the security of Cayley hash functions, a class of cryptographic hash functions with very interesting properties. The factorization problem is also strongly related to a famous long-standing conjecture of Babai, at the intersection of group theory and graph theory. A constructive proof of Babai’s conjecture would make all Cayley hash functions insecure, but on the other hand it would have many positive applications in graph theory and computer science. In this paper, we classify existing attacks against Cayley hash functions and we review known results on Babai’s conjecture. Despite recent cryptanalytic progress on particular instances, we show that the factorization, representation and balance problems presumably remain good sources of cryptographic hard problems. Our study demonstrates that Cayley hash functions deserve further interest by the cryptography community.