tailieunhanh - Introduction to Elasticity Part 3

Tham khảo tài liệu 'introduction to elasticity part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | TRUSSES David Roylance Department of Materials Science and Engineering Massachusetts Institute of Technology Cambridge MA 02139 June 8 2000 Introduction A truss is an assemblage of long slender structural elements that are connected at their ends. Trusses find substantial use in modern construction for instance as towers see Fig. 1 bridges scaffolding etc. In addition to their practical importance as useful structures truss elements have a dimensional simplicity that will help us extend further the concepts of mechanics introduced in the modules dealing with uniaxial response. This module will also use trusses to introduce important concepts in statics and numerical analysis that will be extended in later modules to more general problems. Figure 1 Truss tower supporting the NASA wind turbine generator at Oahu Hawaii. Example 1 Trusses are often used to stiffen structures and most people are familiar with the often very elaborate systems of cross-bracing used in bridges. The truss bracing used to stiffen the towers of suspension bridges against buckling are hard to miss but not everyone notices the vertical truss panels on most such bridges that serve to stiffen the deck against flexural and torsional deformation. Many readers will have seen the very famous movie taken on November 7 1940 by Barney Elliott of The Camera Shop in Tacoma Washington. The wind was gusting up to 42 mph that day and induced a 1 sequence of spectacular undulations and eventual collapse of the Tacoma Narrows bridge1. This bridge was built using relatively short I-beams for deck stiffening rather than truss panels reportedly for aesthetic reasons bridge designs of the period favored increasingly slender and graceful-appearing structures. Even during construction the bridge became well known for its alarming tendency to sway in the wind earning it the local nickname Galloping Gertie. Truss stiffeners were used when the bridge was rebuilt in 1950 and the new bridge was free of the oscillations .