This paper presents an analysis of the stiffness of bars and simple bar structures. Stiffness values were determined in a rigorous, analytical manner. Examples of a single bar with various boundary conditions were analyzed, taking into account imperfections, bar geometry, and load application imperfections for loads within the elastic range. The stiffness of a portal frame with rigidly fixed vertical bars was also analyzed. The analysis shows that the stiffness of a structure is a variable quantity that decreases as it is loaded. It reaches its minimum stiffness, to which it asymptotically tends, at a load close to the critical load.The paper utilizes analytical solutions for the deformed axis of bars and simple systems available in the literature. By knowing the equations of the deformed axis, the longitudinal (axial) stiffness of these structures was determined. A dimensionless quantity K, called the stiffness function, and the ratio m=P/PKR representing the external load were introduced.
The results of the analyzed examples are presented in K=K(m) charts.
2. EXAMPLES
2.1. Example 1 (…)
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Source: Logistyka Magazine