University of Twente Student Theses


Determining Load Capacity of Upright Profiles Subject to Pinching due to Diagonal Bolts

Schuurman, F. (2015) Determining Load Capacity of Upright Profiles Subject to Pinching due to Diagonal Bolts.

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Abstract:During the past three months I carried out an internship for the final Bachelor thesis. I participated in a research project at the company NEDCON in the city of Doetinchem, the Netherlands. NEDCON produces and develops storage racking for large warehouses. Storage racks are build out of beams and frames. Frames consist of two uprights with diagonals in between. This research will focus on the uprights. Production tolerances in the upright profiles are expressed in the opening of the upright which can be 3 to 4 mm larger than required, see also the red line in Figure 1. At the stage of assembly a diagonal spacer is inserted between the upright opening and a bolt should serve as a fastener. When an upright opening is substantial larger than the spacer, tightening the bolt will cause an initial imperfection in the upright due to the pinching. The objective of this research is to find out what the effect is towards the bearing capacity of the uprights profiles. In general, there are three groups of potential buckling modes most common in NEDCON’s upright profiles. These groups are the global, distortional and local buckling modes. In global buckling, the cross sectional geometry will not deform while the profile is bending out or rotating globally. In distortional buckling, the cross section deforms over a large part of the upright’s length. Distortional buckling can occur in symmetric and A-symmetric shapes. The other buckling mechanism is local buckling, where the profile deforms locally. It is assumed that the pinching effect will mostly affect the distortional and local buckling modes due to the deformation in the cross section. A series of tests was carried out to catch the effect of pinching experimentally. Two types of profiles were selected from standard range dimensions, one lipped and the other non-lipped. The extra lip at the ends near the upright opening are expected to have significant influence on bearing capacity. The first type of test setup was the Stub column test. The idea of the Stub test is to find the compressive strength of a column which is sufficiently short to only trigger the local failure mechanism. This test pointed out that local buckling effects are not significantly affected by pinching effects. A complete frame test setup is used to assess the pinch effect on the distortional buckling mode. The distortional buckling tested showed potentially significant influence in buckling capacity after pinch. There are two ways of modelling stability problems in open thin walled profiles. The first one is the Finite Strip Method and the second the Finite Element Method. The Finite Strip Method is fast in computational time, but lacks the ability of having any changes in geometry or boundary conditions along the length of the profile. The method is suitable for quick estimation of modal behaviour of profiles without spacers and can be useful for finding lengths of the upright with least resistance against buckling. The Finite Element Method should be employed to take into account various amounts of pinching. On first sight, both models seem to be rather good at estimating failure mode shapes. However, estimating actual failure load is difficult and results are inaccurate. The combination of models can be used to fin the ‘worst case’ scenario, in which the length applied in the construction leads to the weakest resistance in combination with substantial sensitivity to buckling effects. This research resulted in a development of a new frame test setup. Numerical simulation can be used as a tool to find the ‘worst case’ scenario which can be tested to find the critical load after pinching
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering BSc (56952)
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