Pseudo-cyclic loading

Fig. 4A3 Stress versus strain for pseudo-cyclic loading of two materials at nominal strain-rate 0.03 s". PUl and PU2 are both based on MDI and PEA but differ in their chain extender. PUl has slight crystallinity (4%) while PU2 is amorphous [135]...

Similar observations were made by us when PUs were cycled to increasing extension [175]. A further series of mechanical tests was designed to compare inelasticity of the various materials under cycling to increasing extension. Thus each specimen was subject to a continuous pseudo-cyclic straining sequence, such that on the nth cycle it was cycled between a maximum nominal strain s ax = n and zero load. The magnitude of extension rate was the same as in the previous experiments. 

Phase 2 consisted of a series of load-unload cycles conducted at the same rate as in Phase 1, but taken to progressively higher nominal strains Cmax on each cycle 1,2, 3. Between 3 and 5 cycles were possible before failure with most materials. These may be described as pseudo-cyclic experiments, to distinguish them from those in Phase 1 where the maximum strain was constant. As in Phase 1, for each... 

In order to determine the lateral displacement and load bearing capacity of the strengthened system, a displacement control reversed cyclic loading up to 66 mm of top displacement was applied to the specimen after the pseudo-dynamic tests. Figure 10.8 shows the reverse cyclic displacement protocol for the top story of the test frame. The cyclic displacement histories applied to the first and second stories were consistent with the first modal shape of the test frame. They were determined using the method proposed by Molina et al. (1999) and Maia and Silva (1997) by taking the top story displacement protocol into consideration. 

At the end of the pseudo-dynamic tests, a reversed cyclic loading was applied on the test specimen in order to investigate the residual lateral load carrying capacity and the displacement capacity of the enhanced frame. 

MSWs are complex mechanical systems and this complexity is compounded when the structures are subjected to transient dynamic loading due to earthquake. Pseudo-static and displacement methods may be sufficient for simple structures, for stable ground conditimis and MSWs in low seismic risk areas, and/or for preliminary design. Otherwise, more sophisticated analyses may be warranted using advanced dynamic finite element model or finite difference computer programs. Today commercially available computer programs offer the user a suite of constitutive models for the component materials and in some cases allow the user to implement their own constitutive models. In order to accurately model the soil in a MSW, it may be necessary to use nonlinear cyclic stress-strain models. The equivalent-linear... 

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