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Aluminium Design and Construction - Chapter 5

Tài liệu tham khảo giáo trình nhôm trong thiết kế xây dựng - Chương 5 Limit state design and limiting stresses British Standard BS.8118 follows steel practice in employing the limit state approach to structural design, in place of the former elastic (‘allowable stress’) method [14]. Limit state design is now accepted practice in most countries, the notable exception being the USA. | CHAPTER 5 Limit state design and limiting stresses British Standard BS.8118 follows steel practice in employing the limit state approach to structural design in place of the former elastic allowable stress method 14 . Limit state design is now accepted practice in most countries the notable exception being the USA. In this chapter we start by explaining the BS.8118 use of the limit state method and then go on to show how the required limiting stresses are obtained. 5.1 LIMIT STATE DESIGN 5.1.1 General description In checking whether a component i.e. a member or a joint is structurally acceptable there are three possible limit states to consider Limit state of static strength Serviceability limit state Limit state of fatigue. Static strength is usually the governing requirement and must always be checked. Serviceability elastic deflection tends to be important in beam designs the low modulus E of aluminium causes it to be more of a factor than in steel. Fatigue which must be considered for all cases of repeated loading is also more critical than for steel. In the USA when limit state design is mentioned it is given the logical title Load and Resistance Factor Design LRFD . 5.1.2 Definitions Some confusion exists because different codes employ different names for the various quantities that arise in limit state design. Here we consistently use the terminology adopted in BS.8118 as below. Copyright 1999 by Taylor Francis Group. All Rights Reserved. Nominal loading. Nominal loads are the same as working loads . They are those which a structure may be reasonably expected to carry in normal service and can comprise dead loads self-weight of structure and permanently attached items imposed loads other than wind wind loads forces due to thermal expansion and contraction forces due to dynamic effects. It is beyond the scope of this book to provide specific data on loading. Realistic imposed loads may be found from particular codes covering buildings bridges cranes etc. Wind