Civil Engineering Reference
In-Depth Information
7
Global critical load ratio
A number of publications and guidelines are available for the elastic stability
analysis of the
elements
of complex systems. The choice is much more limited
when the stability of the
whole
system is investigated. The practical significance
of the elastic global critical load has been recognized but research in this direction
has concentrated mainly on framed structures [Dulácska and Kollár, 1960; Kollár,
1972; Council…, 1978a and 1978b; Stevens, 1983]. Theoretical research and recent
developments in computer modelling of structures show that it is essential to
understand whole building behaviour as an analysis based on global approach
can lead to safer and more economical structures. Dowrick [1976] drew attention to
the importance of the overall stability of structures but national and international
codes have been slow to incorporate global approaches. Halldorsson and Wang
[1968] suggested that a 'general safety factor' should be used for building structures
as its importance is comparable to that of the 'overturning safety factor' used in
the design of dams. Chwalla [1959] recommended some forty years ago the
introduction of the factor. The reason for not taking the 'general safety factor' on
board was probably the lack of simple and clear methods for the determination of
the global critical load at that time.
National [BS5950, 1990; DIN 18800, 1990; MSZ series, 1986] and European
[Eurocode 1, 1995; Eurocode 2, 1992; Eurocode 3, 1992] codes do not use a consistent
approach to sway instability and do not address torsional instability although the
importance of these phenomena and their direct link with global safety are well
known [Council…, 1978a and 1978b; CEB, 1983; ISE, 1988].
It is shown in this chapter that, based on the global critical load introduced in
Chapter 3
, the global critical load ratio can be easily produced and effectively used
for assessing the safety and the performance of the bracing system.
