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A few months ago, I bought your wire rope programme and undertook some preliminary designs for a project. The input and output data is shown below: Please can you advise where I might be going wrong. Many thanks for your comprehensive and extremely helpful answer. For our application it also precisely the answer we were hoping for. |
The attached image shows the construction of a typical 6x19 → 7x19 As you know, the wire rope calculator allows for just one filament size, so you need to work out an equivalent diameter for bending stiffness (EI) and the average axial stiffness (EA) to find the expected bend radius and axial growth. The Young’s modulus of the material of the two filaments are assumed to be the same, so I can ignore 'E'. Given that I have estimated the filament diameters from a photograph (attached) and I don’t know the lay angle, I may be a little out. |
User-friendliness issues |
As a result of one of our customer's problems disseminating the output data in the wire rope calculator, we have decided to rewrite it with a view to making it easier to use. This calculator was reissued (version 1.1) on |
1) I don’t see anywhere in the calculator where I can change the geometry of the cable beyond OD of cable, dia of filament and number of filaments. In short I can’t seem to create constructions beyond a generic cluster. 2) My original question is that when I change the value of E (or Ef as the software calls it) by, say, even three order of magnitude the value of EI does not budge implying that the value of “E” in EI is being pulled from somewhere else. |
1) The properties of a wire rope are defined by the filament diameter, strength and packing density (wire rope diameter), not the construction 'type'. The packing density is only achievable with particular construction types. Therefore the construction types are unnecessary to define the loaded wire rope. 2) The bending stiffness provided is for a wire rope with 50% breaking load applied. Under such conditions the filament Young's modulus has negligible effect on the bending stiffness of the steelcord. However, as your customer is the second person to raise this question I have modified the calculator to provide [include] bending stiffness and radius for the wire rope in unloaded condition. |
I have purchased the Wire Rope calculator, and would like a description of how the bending stiffness calculation is made. I'm ... trying to understand which modeling approach is used to generate the results. Is it possible to have the methodology described? I see no such explanation in the technical area of your website. |
The Wire Rope calculator includes no 'modelling' in its truest sense. Over many years dealing with multi-strand wire I have generated numerous models for the properties of various wire rope constructions (steelcord, hosecord, tyrecord, OTR, structural, etc.) in an attempt to find an all-encompassing model that can be successfully applied across the board. I am afraid that to-date I have not yet discovered one. In doing so, however, I have been able to establish a set of factors that provide an acceptable level of accuracy for most constructions in most applications and that require minimal input data. It is these factors that have been used in the Wire Rope calculator. The Wire Rope calculator is not a ‘right-or-wrong’ facility in the same way that most of CalQlata’s other products are, in that they provide one mathematically correct result. If I was to provide a mathematically correct model capable of extreme accuracy for any steelcord construction, the input data necessary to ensure an accurate result would need to be extensive and in some cases difficult to acquire as the information is copyright protected by the manufacturer. It would also only apply to that piece of cord, the same properties of another section of cord extracted from the same length would most probably not be so accurately predicted using the same model. By way of assistance; structural wire ropes such as hosecord, mooring, lifting and bridge building constructions are normally (but not always) relatively consistent in their properties and generally work well with the Wire Rope calculator. Tyrecord is also fairly predictable but OTR can be wildly variable if manufactured with ‘less-than-best’ quality and even my ‘universal’ constants would struggle to predict the properties of some of these cords within an acceptable degree of accuracy. That said most of the complex models I have generated in the past would also have failed to produce reliable results for many OTR constructions. Note: When I have required accurate data in the past I always tested the wire rope concerned, but frequently discovered that even the properties of pieces that were cut from the same manufactured lengths varied in some cases by more than the accuracy I would expect from my ‘universal’ factors. |
Dear Sirs; I just purchased wire rope CalQlata and the results I got for my example is a bit strange, I used the following as input data |
Dear Sir Postscript: |
I just downloaded your Wire Rope Calculator application. I want it to use it for wire axial stiffness calculations. |
Wire rope is not as predictable as homogeneous metals, that much everybody understands. The problem is that not only are its properties non-linear but vary in every plane.The most unpredictable and non-linear of all these properties is axial tension. You can take a single length of wire 100m long from a drum of exactly the same specification from all the manufacturers of steelcord and cut them all up into 1m lengths. When you test them all, you will find that the axial properties of every piece will be different from every other piece. The variation can be as much as 35%. It is for this reason that we do not calculate EA in the wire rope calculator; i.e. it is outside CalQlata’s definition of acceptable error margins. Your customer is very observant in his suggestion that friction is taken into account in our calculation of E in the calculator, albeit not exactly: Whilst the above may not be much comfort, I can recommend a rule of thumb for his calculation, which appears to work at relatively low tensions (note: E for wire rope increases with tension), i.e. less than 50% breaking load: It has been my experience that EA for most wire ropes (not OTR as this will be noticeably less) will be about 10% that expected for a solid piece of the filament wire material the same diameter of the wire rope. But the above calculation is more accurate. However, your customer’s cable configuration has only one strand and very large filament diameters, so I would expect his EA value to be nearer to 25% than 10% E for torsional calculation of stiffness will be different for both directions of twist and will vary similarly to the values for E in EA but the angle you use in the calculation will be different. Moreover, I must admit I have never studied the behaviour of Titanium in wire rope. It has a much lower tensile modulus that steel but if the filaments are kept within their elastic deformation range the calculations should work reasonably well. My only word of caution is that under significant compression (e.g. between two adjacent filaments) the coefficient of friction will be different, resulting in [slightly] higher EI values. I suggest that these should be increased by 5% for titanium over those predicted in the wire rope calculator. All of that said, your customer has quite rightly pointed out that the technical help web page for this calculator does not make this sufficiently clear. |