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Structural Engineering and Mechanics
  Volume 5, Number 4, July 1997 , pages 415-431

Stability and minimum bracing for stepped columns with semirigid connections: Classical elastic approach
AristizabalOchoa JD

    Stability equations that evaluate the elastic critical axial load of stepped columns under extreme and intermediate concentrated axial loads in any type of construction with sidesway totally inhibited, partially inhibited and uninhibited are derived in a classical manner. These equations can be utilized in the stability analysis of framed structures (totally braced partially braced and unbraced) with stepped columns with rigid semirigid and simple connetions. The proposed column classification and the corresponding stability equations overcome the limitations of current methods which are based on a classification of braced and unbraced columns. The proposed stability equations include the effects of: 1) semirigid connections; 2) step variation in the column cross section at the point of application of the intermediate axial load; and 3) lateral and rotational restraints at the intermediate connection and at the column ends. The proposed method consists in determining the eigenvalue of a 2X2 matrix for a braced column at the two ends and of a 3X3 matrix for a partially braced or unbraced column. The stability analysis can be carried out directly with the help of a pocket calculator. The proposed method is general and can be extended to multi-stepped columns. Various examples are inclued to demonstrate the effectiveness of the proposed method and to verify that the calculated results are exact. Definite minimum bracing criteria for single stepped columns is also presented.
Key Words
    buckling, bracing, building codes, columns, construction type, computer application, frames, loads, stability

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