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From the end of 1990s it became evident that Sargon required a post-processor dedicated to steel connections (or joints). However, an investigation of the problem showed how difficult it was to address the subject; on the other hand it was rather clear that the solution suggested by some of the program’s users, that is, putting in place specific routines for the calculation of typical joints, would not result in a product that was adequate to meet the actual needs of the specialists, the practitioners who comprise the principal market for both Sargon and CSE.

Given that the problem was not only difficult but also exceptionally interesting, it was decided to address it in the most general way possible, within a broad class among all possible classes, aware that the work on the project would probably take several years. Among other things, the requirements of other work commitments made it impossible to carry out this project uninterruptedly, nor was funding from other institutions or associations in fields related to such problems forthcoming: generally speaking, either the products that are sold in Italy are created by specialists in other countries (any nation or country, no matter how far away or exotic “sounds” better in our technical and scientific arenas, in spite of the glorious Italian tradition that includes Galileo, Castigliano, Ricci and Piola among others, and the fact that there are excellent Italian scholars working in the field today), or the projects that do manage to find funding prove to be futile, resulting in the waste of public funds (there are innumerable examples). Research in the true sense of the term, which requires years before producing results and innovations, is extremely difficult to carry out in Italy, even more so if the researcher has no “patron saint”, and thus requires a degree of courage and perseverance that few can maintain. The CSE project was carried out in intervals of one or two months a year over the course of about ten years.

Connections Study Environment Software Program: research

Image: notes on the research in the analytics of jnodes.

The first attempts to define the problem date back to 1999. A specific terminology was introduced that included new terms such as “unito” ("joined"), “unitore” ("joiner" or "connector"), “tramite” ("through"), “matrice di trasferimento” ("transfer matrix"), “jnodo” ("jnode"), “renodo” ("renode"). This was also the period of the first thoughts about how to describe the joint in the most general way possible. Arduous problems soon arose that could be initially described but not resolved.

In the meantime (2000, 2001) work began on writing the general parts of CSE, those which in any case had to be addressed independent of problems related to calculation: the graphic representation in 3D, hidden surfaces, the cataloguing of the nodes. In rendering hidden surfaces, CSE does not make use of raster algorithms, but rather of vector algorithms: this makes it possible to create borders that much more easily readable than those produced in many other programs that use pre-set routines using raster algorithms. This results in images that are clear and readable, much more so that those of other programs that use shadows and various hues of colours to represent the shape of the objects.

Chronologically, the first specific problem addressed was that of how to convert a FEM model into a model of the members. It became clear (this was in 1999-2000) that additional information had to be included in the FEM model, and the program was adjusted so that it was able to extract a model of the members from a FEM model.

The next problem addressed was the thorny one of how to recognize equal jnodes. It was clear that there had to be a way to distinguish jnodes from renodes. The routine for the recognition of equal jnodes was the first extremely important success in the development of the program. Even at that early phase of development there was no other program that could accomplish anything similar.

This goal was reached thanks to jnode analytics, a study which explained the logic of the most frequent connections. So CSE was able to recognize them automatically. Today CSE equal-jnodes recognition is a single command, and it lasts some seconds, but years were necessary to completely deepen the issue.

 This brought the work to the early years of the 2000s, and the program was marketed with these somewhat limited (but innovative and useful) capabilities of analysis. At the time it was generally believed that the calculation of joints could only have been accomplished by means of “instructions” given to a program by the user, given the lack of general rules for calculation. Therefore, the program began to be equipped with a substantial set of functions aimed at encompassing the rules of calculation. Thus appeared the pre-defined variables associated with the components (e.g.,, P1.A, etc.), the possibility of adding new variables (e.g., sigmaN=m1.N/m1.A), and the addition of conditions, or relations (generally inequalities) expressed as a function of the pre-defined variables and those introduced by the user, capable of describing the checks to be performed (e.g., m2.N < m2.fu* (m2.A - B1.n * B1.dh *

Meanwhile, much effort had been dedicated to the construction of the renode, that is, to all those commands intended to ensure that the user was able to work in an environment that was perfectly 3D when adding components and processing them. You might say that the aim was to create a virtual LEGO™. This part of the project was quite complex and took a long time to develop. It required creating commands for positioning and manipulating the objects, not only by means of rigid-body transformations (rotations, translations) but also by means of additional and indispensable processing. This environment is typical of programs that allow 3D modelling, whose capabilities, however, are usually “limited” to drawing or “rendering” the objects once they are created. In the environment of the CSE project, such functions could in some way be considered preliminary, since the fundamental object was calculating the joints and not drawing them. The problem was to calculate, and to check.

Connections Study Environment Software Program: research
Image: notes on the topology of the elementary renodes.

Work on the problem slowed from 2005 to 2007, in part because large projects and commissions made it very difficult to work on research. While it was already possible to recognise equal (j)nodes, construct the scene by positioning the components, recognise the joints solely on the basis of their geometric positioning, and add many other useful functions, the problem of calculation was still unresolved. Could it be true that the user had to explain to the program how the joint was to be calculated? Was there no other way? The idea (which remains such today) is that the user could explain to the program what checks to make, and that the program would then apply them automatically, memorizing the typologies of nodes in order to call them up at a later moment. Although general and useful, this approach still required a certain degree of effort on the part of the user: we would have to specify typical nodes and then the user could go forward from there.

Between the end of 2007 and the spring of 2008, a window of several months’ time dedicated to in-depth study finally made it possible to arrive at a solution to the main problem, that is, the automatic calculation of freestanding joints. Concepts such as hyper-connectivity were defined, and from there it was finally possible to understand how to describe the problem of calculation in a unitary way by means of a model with finite elements that was clean, reliable, balanced and coherent. In the space of a month the program was adjusted so that it could calculate, on its own, using hypotheses that were broadly general and normally verifiable, with no need of instructions on the part of the user, the stresses acting on the joiners, as well as bearing checks, checks that were written and tested during the spring and summer of 2008. A document containing information about the program and a manual for validation to demonstrate both the validity and the reliability of the calculation were written. The class of the problem was notably broadened through the introduction of anchors, friction bolts and bolts only in shear.

There still remained problems to address and functions to add, but the main road had been paved.

Knowing the stresses on the connectors opens the way for checking the throughs and the members. The problem was addressed starting in autumn 2008, by first introducing the bolt layout with bearing surface (e.g. base-plate), and then the checking of the net-sections of the members, and finally the simplified checking of the throughs. At the beginning of 2009 the fundamental characteristic was added, which consisted in the automatic creation of the fem models of the components, subject to forces that were known because they were calculated during the first, fundamental analysis. This opens a completely new vista: the automatic creation of FEM models (throughs, members, stiffened or not) leads to checks that are much more rigorous of both the throughs and of the members themselves than those performed manually.

During spring 2009 the hypertext help manual and the guide were updated and it was decided that, although the program was still in full-blown development, it was now time to make it available to the community of experts, not least because this was a valuable source of funding for the project, and one that derived from the project itself.

As of May 2009, the road ahead is clear, and although it is certainly complex, and it will require more time to complete, there don’t appear to be any more dilemmas such as those that were faced in past years. All of the steps still to be taken are understood, partly because the functions that CSE is still lacking (specifying the parameters of typical joints, specifying the joints, further amplification of the range of applications of the program in order to better manage certain problems such as complete penetration welding or hollow sections), these are functions that appear not to present any particular conceptual problems: the program will eventually arrive where other programs arrive today (at the steel structure drawings or at the calculation of only typical joints) but from a completely different point of departure, since by now the problem of calculating the joints of steel structures has been solved in a way that is very general and reliable from an engineering standpoint.

Milan, 17 May 2009 – some ten years after the CSE project began

From May 2009 until November 2011, many new functionalities and features have been added, leading CSE project to a full development stage. An incomplete list includes the following improvements:

  • Dozens of new standard components and new typical structures have been added to simplify component and (j)node geometry description.
  • Automatic FEM checks have been improved, now every component can be automatically meshed and solved, also including non linear (elastic-plastic) analyses. The program Sargon Reader has been added to CSE as standard sub-component, in order to look at the FEM results, and to study FEM analyses.
  • Block shear checks, punching shear checks and partial or full penetration weld layouts have been added.
  • The program has now English interface and documentation (guide, in PDF, HTML or CHM formats, has more than 650 pages). Checks according to Indian Standards IS and USA AISC standards have been added.
  • A universal exchange file format has been set up (.SR3) to easily allow for more FEM programs to interface .
  • Internal actions of members can now be defined also by user by pasting Excel tables, so that CSE is fully stand alone (does not need FEM programs).
  • Parametric Real Nodes (PRenodes) are now managed by the program. Families of similar Real Nodes can be stored and described parametrically by using formulae for the sizing and placing of components, no matter how complex they are. This is a very powerful feature, which places CSE at the forefront of innovation in this field.
  • An archive of parametric real nodes has been prepared (and is currently extended) which also the user can upgrade by adding his/her new prenodes (170 prenodes available at November 2011).
  • A PRenode can now be applied to an empty real node, to automatically and immediately construct the final 3D Real Node with all components and work processes ready to use.
  • LIGHT versions of the program, dealing with pre-defined connection families have been set up.
  • Interfaces to STRAP, STAAD PRO and a new text file format named SR4 have been added.
  • BS 5950 standards have been added.

Milan, December, 19, 2012 (upgraded to version  4.90)

From December 2012 to July 2013, several important improvements have been added to the program:

  • CSE is now able to create on request the Finite Element Models (FEM) of aggregates of components, or also of the whole node (see press release).
  • CSE has been equipped with a buckling analysis solver, which, starting from the results got for the FEM model at hand, does compute critical load multipliers for all combinations.
  • New interfaces, to MIDAS and to RISA3D, have been added.
  • The number of PRenodes has been increased up to 395.
  • Prying forces factor has been added to bolt layout computation.


Milan, July 5, 2013 (upgraded to version 5.50)

CSE has been sold in many Countries (Europe, Asia, America), all around the world. During the time span from July 2013 to May 2015 the program has been improved and got stroger, also keeping into account users' hints & requests. Here some of the most important improvements are listed:

  • The russian standards have been added (SNiP).
  • FEM analyses can now be run also adding geometric non linearity and contact non linearity, not only material non linearity.
  • The parameterized node collection has been incremented from 395 to 786 units.
  • The "Universal Nodery" concept and functionalities have been added.
  • It is now possible to copy and paste components, and also the whole node, from one node to another or from one file to another.
  • Load displacement curves of key nodes are now stored and can be analyzed to allow a better understanding of non linear behavior.
  • The bolt holes can now be explicitly added to automatically createed FEM models.
  • The "assistant pane" has been added to interface to guide during modelling phases.
  • Many commands have been improved and made more powerful, many new functionalities have been added, also considering users' feedbacks.

Milan, May 12 2015 (upgraded to version 6.30)

During the time span from April 2016 to May 2017, Paolo Rugarli has written the book Steel Connection Analysis which explains the theoretical background of CSE. The book will be soon available, published by John Wiley & Sons.

With this book, the long research & development path begun at the end of the 90s arrives to a major goal. The book, unique in the existing publishing panorama referring to connection analysis, tackles the problem of checking connections with a general approach, able to allow the solution of every type of connection.

In the last two years, as always, much work has been done to widen the program range and to improve its functionalities. In particular, it has been done much work in order to generalize the modeling of connectors (welds and bolts) both in linear and in non linear range, and assigning specific working mode flags like no-shear, shear-only, longitudinal-shear only, to single bolts or to single weld seams.

Milan, September 1, 2017 (upgraded to version 8.00)