Abstract
Progressive deformation (ratcheting) can occur as a response to variable loads as soon as the elastic limit is exceeded. If this is the case, strains and displacements accumulate in the event of cyclic loading in each load cycle. Widely known as triggers for ratcheting and already being considered in some design codes are configurations, in which a structure is subjected to at least two different types of load, namely a constant load (the primary load) and a superimposed cyclic load. In this paper, another mechanism that generates ratcheting is introduced. It can be attributed solely to the effect of a single load. In the simplest case, this can be explained by the successive activation of (an infinite number of) plastic hinges if a load of constant magnitude is moved in space. The increments of strains and displacements can decrease or increase from cycle to cycle, when the material is hardening, or if elastic foundation is present, or if the equilibrium condition is formulated for the deformed system (second-order theory) or if “large” rotations are taken into account (third-order theory).
Highlights
If a structure is operated beyond the elastic limit, inevitably present variable portions of the load, even when of low intensity, that is to say even in ‘‘predominantly staticRatcheting can trigger different failure mechanisms
It can be attributed solely to the effect of a single load. This can be explained by the successive activation of plastic hinges if a load of constant magnitude is moved in space
For example, the continuous beam treated in ‘‘Force moving to the right’’ adopting the theory of plastic hinges is subjected to an additional axial compression force of 1608 kN, the displacement increments increase continuously from one cycle to the when applying the secondorder theory (Fig. 24) until the system becomes unstable after a series of load cycles
Summary
If a structure is operated beyond the elastic limit, inevitably present variable portions of the load, even when of low intensity, that is to say even in ‘‘predominantly staticRatcheting can trigger different failure mechanisms. Structural ratcheting can be explained by the development of several plastic hinges, which are only alternately active in the different states of a variable load (Hubel 2016).
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