FAQ: Design

  • How is it designed a node?
    • The node is decomposed into elementary joints and these are designed separately. Then, after the node is completed, it is re-checked as a whole: indeed, in the complete node the forces flowing to the components might change, due to the mutual interaction between the joints. If a node passes all the checks it can be adopted. If the design-mode is “take first design OK“, the first design passing all the checks is kept. If the design mode is not this, then among all the designs that pass all the checks, the one implying the minimum cost is chosen.
  • But how can the program choose?
    • Every joint has a given number of parameters, that vary within intervals, for the most part specified in the design criteria. A design is a particular combination of these parameters. It is considered acceptable if all the checks are passed.
    • As a huge work has been done in order to reduce the computational time, the program can examine hundreds designs in a few seconds.
  • What checks are made?
    • The checks are all in “closed form”, that is they are formulae that are listed in the report and that therefore are clearly readable and understandable. Indexes, subscripts, greek letters, square roots, sinuses and cosinuses, all is readable in a very clear way thanks to LateX.
    • In general the typical checks that are executed are:
      • Bolt resistance to shear, traction and combined effects.
      • Weld resistance, both of fillet welds and penetration welds.
      • Bolt spacing.
      • Edge distances.
      • Weld seams size.
      • Bolt bearing.
      • Block shear.
      • Net cross-sections and gross cross-sections checks.
      • Whitmore section.
      • Buckling of stiffeners, or web-panel, or gusset plates.
      • T-stub.
      • Other special checks whenever required.
  • How are the forces flowing into the connectors computed, starting from the member forces?
    • In the most part of the cases they are computed thanks to a specific simplified finite element model (chapt. 9 Steel Connection Analysis). This model assures the balance of the forces and moments for every geometrical configuration.
    • The program is able to find the algebraic relations that bind the first to the second, and it writes these in the report.
    • In other cases, the choice of the forces to be considered (for instance seated plus fin connections), is directly made to assign certain proportions that are on the safe side, to this or to that component.
  • Can we say that traditional approaches are used?
    • Yes, basically the design is made by traditional approach. This implies that:
      • You can consider disjointly the effects on the master member.
      • The simplified closed formulae of a traditional approach can be applied.
  • But, which is the advantage in using traditional approach?
    • Given that Castalia is well aware of the limits of traditional approaches, as writtten in the book Steel Connection Analysis and as testified by the fact that CSE itself, before any other software in the world, has made automatic the creation of plate-shell FEM models of nodes, it must be said that traditional approaches still have several merits.
    • First the results are controllable by everyone because there are formulae. Not so the total FEM results, that risk to be a black box.
    • Second, the design time is quite short, whereas with a full fem design it would not be possible to design thousands nodes in a reasonable amount of time.
    • Third, the traditional approach do not exclude the use also of the FEM approach: for some nodes, particularly complex or important, after the automatic design is made a further full FEM check can be applied, with the very same software program.
  • And if, for a given node, a more refined analysis is required?
    • Just ask. CSE is able to automatically prepare the FULL FEM model both in linear and in not-linear range (geometric NL, material NL, contact NL).
  • How should the automatic design made by the Service be considered?
    • The program “designs” meaning that it chooses the sizing that pass all the checks that have been listed in the prameterized nodes, for many different joint typologies. Infinite possible solutions are possible (several infinities) and the program finds one, starting from joints of the simpler types and moving progressively toward the more complex ones.
    • The design criteria are set by the user. Also, if discard or consider some joint typologies.
    • The member forces are set by the user.
    • The metric of cost, if minimum-cost design-mode is asked for, is set by the user.
    • We have created the parameterizations and listed the checks needed according to our judgment.
    • The Service is meant to be a design in this sense.
    • However, no program will ever replace the designer. Therefore, the user must however check what the program has done, and whenever this is considered proper, deepen with more in-depth analysis, also using more refined analysis methods (CSE is also able to prepare full FEM models, in linear or not-linear range).
    • Our experience is that in many cases, the great most part, the design made by the program can be accepted with no further modifications, but the user must control and the final responsability of the design is his/hers.
    • The cost of the service consider all this. You do not buy a software, but a pre-design service that will then have to be judged by the user.
  • But which are the advantages of this service?
    • We believe the advantages are these:
      • All the nodes, or the great most part, can be really checked, while now many nodes are indeed left with no real check, as the computational burden is too high.
      • The time needed dramatically diminishes. This itself is an enormous advantage and has quite important economic consequences. We can design 1,400 nodes in two or three hours.
      • A more in-depth analysis can address the most important, most frequent (for the cost) or most complex nodes. There, the designer can better act, by using more sophisticated analyses, as the node is already prepared for the FULL FEM CSE evaluation.
      • Thanks to CSE Reader the nodes can all be considered in a very short time and the expert judgement of the designer will immediately understand where is necessary to deepen the analysis.
      • The cost of the service avoids a sea of computations, allowing quickly to understand how and where to refine. The service greately reduces the amount of work to be done.
      • The costs of our service have been thought imagining that our user is going to recharge them to his/her client, increasing them for the part referring to his/her fundamental control/deepening/integration.