This paper presents a new attempt for geometric nonlinear and postbuckling analysis of structures using only elastic stiffness. This can be achieved not without reasons. Aside from a correct updating of the structural geometry in the incremental sense, there are two concerns for iterations: (i) The local strategy is that the element forces recovered in each iteration should not violate the rigid body rule, in order not to induce any fictitious forces. (ii) The global strategy is that the path-tracing scheme should be able to deal with multi critical points, such as limit and snap-back points. Both strategies will be explained via the mechanism of iterations, which seems not new, but can shed some new lights. The results obtained using only the elastic stiffness will be compared with the normal case including the geometric stiffness, with the level of approximation assessed by the general stiffness parameter (GSP). Through the study of a number of trusses, beams and shell structures, it is confirmed that the elastic stiffness alone can be used to solve the nonlinear and postbuckling responses of a wide range of structures, with only an increase in the number of iterations. This paper represents a limit application of the elastic stiffness to nonlinear structural analysis.
[Aims] The saline soil in continuous silting tidal areas will become a crucial reserved land resource in China. A prominent problem is controlling soil salinization for improving agricultural water and land resources’ productivity in coastal areas. [Methods] An experiment was conducted to study the effects of different mulching and tillage measures on soil salt-water status and maize growth. There were four treatments: (1) film mulching (FM), by only setting a transparent plastic film (with a thickness of 6 μm) on the surface soil; (2) straw deep-burying (SDB), in which only straw was buried as a layer at a soil depth of 30 cm; (3) combining film mulch with deep-buried straw (F+S), in which a straw layer was buried at a soil depth of 30 cm with plastic film mulching on the soil surface; and (4) control (CK), by simulating standard local practice. [Results] The results showed that the soil water storage (SWS) under FM and F+S was significantly higher than others, and F+S showed the best role in soil water conservation. The film mulching had a reasonable effect on soil salinity regulation during the whole maize growth stage; the soil salt content at 0–30 cm was decreased by 1 g/kg and 0.74 g/kg under F+S and FM, respectively. Compared to CK, the plant height, LAI, SPAD value, and yield were all improved under mulching and tillage. The growth process of maize and water-use efficiency (WUE) under F+S was more significantly improved than those under other treatments. [Conclusions] Overall, the F+S can be recommended as a suitable strategy for regulating soil salt and moisture, and thus improving crop productivity in coastal tidal areas.
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