ON THE DEVELOPMENT OF A ROBUST ELEMENT FOR 2ND-ORDER NONLINEAR INTEGRATED DESIGN AND ANALYSIS (NIDA)

This paper describes and applies a theory for practical second-order a nalysis and design of steel frames. The practicality, convenience and high precision of the method of 'Non-linear Integrated Analysis and De sign (NIDA)' that allows for the second-order effects for design of st eel frames and trusses is demonstrated. The need for using two or more elements per member to accurately simulate the axial load effect on t he element stiffness and to locate the maximum moment along an element is eliminated. Unlike previous work for 'Advanced Analysis' which is difficult to use in practice as it ignores many important practical fe atures such as element imperfection, the proposed method meets the cur rent design code requirements and is based on the first-plastic-hinge concept which is currently adopted by engineers. Further more, the ele ment by itself can predict the beam-column load carrying capacity usin g a single element per member to model the P-delta effect and, therefo re, it can be used for simultaneous analysis and design. The use of se veral elements per member still possesses an error of idealising a phy sically smoothly curved member by a series of segments of straight ele ments. Conceptualy, the suggested method designs a structure by modell ing accurately its true behaviour, instead of making use of empirical formulae for individual member checks. It is readily available for des ign application of realistic structures and it is envisaged that the N IDA will initiate a revolution in the practical design of steel struct ures. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.