Thursday, 22 November 2018

FAQ: Utilization linearization method behind the plastic interaction formulas

The possibility of tracking back the results of the utilizations of the design checks to the actual Eurocode formulas is a very legitimate requirement from our users, and we are constantly putting great effort into each development to provide it.

On the other hand, the end result the optimization process, is of course the utilization of each structural element. Based on it, we make section changes, or structural modifications, until we reach the adequate state, below 100% utilization. The scale of our changes on the model strongly depends on the given utilization of our structure. Is a simple section change enough? Should we rethink the mechanical model of the structure?

And here where the problem comes. If we check on the plastic interaction formulas, it is clear, that the result of it is not a utilization, but a statement if the section is adequate or not. By definition, utilization shows that how far from the 100% we are, how much reserve do we have or not have. For this, the result of the formula can not be used.

To resolve this issue, ConSteel uses the Newton-Raphson iterative method to solve the nonlinear equation of the plastic interaction formulas, evaluates the load level which satisfies the equality, and compares it with the actual load level to obtain a practically useful utilization value.

Section: SHS 120x4 section
Dominant check is Plastic interaction - Biaxial bending (acc. to 6.41 formula of EC1993-1-1)
N= 565,2 kN
My= -10,2 kNm
Mz= -1,1 kNm

If we would calculate the formula with the common approach, and try to determine a utilization it seems, that we are facing with quite a big structural problem. It is clear, that the value can not be used as a utilization of the section:

So ConSteel evaluates the load level of the N-My-Mz internal forces - considering conservative one parameter loading – satisfying this formula for equality and uses it to evaluate the final utilization. 

If we make our modifications considering the 116% utilization, it turns out, that a simple section change from SHS120x4 to SHS140x is enough to go below 100%. 

This formula is being applied on all of the plastic interaction checks:
  • Major axis shear + Torsion, acc. to EC3-1-1 6.2.7
  • Minor axis shear + Torsion, acc. to EC3-1-1 6.2.7
  • Bending around major axis + Shear, acc. to EC3-1-1 6.2.8
  • Bending around minor axis + Shear, acc. to EC3-1-1 6.2.8
  • Bending around major axis + Axial force, acc. to EC3-1-1
  • Bending around minor axis + Axial force, acc. to EC3-1-1
  • Biaxial bending + Axial force, acc. to EC3-1-1

Friday, 3 August 2018

Global buckling analysis

Stability is one of the most important, but also the most complicated design situation. Design standards are covering the most conventional structural designs, but what can you do in case of complex buckling problems that are not covered by code rules?

To automatically calculate the complex global stability failures (flexural buckling, torsional buckling, lateral-torsional buckling and any interactions of these) ConSteel introduced 7 degrees-of-finite element (7 DOF) for steel members.

The 7DOF element is specially developed for thin-walled members where the warping of the cross-section is of high importance in the behavior, this effect is considered by the 7th DOF. In the following figure the considered nodal displacements are illustrated:

The first 6 DOF are the conventional displacements (Ux, Uy, Uz) and rotations (Φx, Φy, Φz), but 7th DOF needs more explanation. Mechanically it represents the warping of the section which is straight consequence of torsion on thin-walled members. The next figure illustrates the warping effect of I shaped cross-section when the flanges step out of the original plane of the section.

In this case, the warping DOF can be considered as a dual and opposite rotation of the flanges about the axis perpendicular to their width.

Based on the advanced 7 DOF finite element and global buckling analysis, ConSteel is able to automatical perform the stability design for the global model, including the irregular structural members such as tapered members, haunched members, and built up members.

Friday, 29 June 2018

Tips & Tricks: Copy-paste unique load combination data from Excel

Even if all of the load combination generation formulas are implemented in ConSteel for the automatic generation of combinations, standard formulas may not cover every necessary combination cases. 

Of course, in this case, it is possible to define the missing combinations manually, but it is very likely, that the missing combinations are available, probably in a table form.

It is good to know, that ConSteel is capable to receive combination data, by the good old CTRL+C & CTRL+V method. If you have the factors for load combinations stored in table form, stored for example in Excel, just copy the data of the factors to the clipboard by CTRL+C, and then CTRL+V paste them into ConSteels's load combination table:

Of course, it works in the other way too, combination data can be copied to the clipboard from ConSteel by pressing CTRL+C and pasting it into spreadsheets by CTRL+V!

Friday, 22 June 2018

Tips & Tricks: Custom envelop figure

As you may already know, you can check the max, min and min-max envelop diagrams for (first and second order) analysis results are available in ConSteel. By default, the envelop figures can be requested for SLS and ULS combinations. These default options will use the results of all of the calculated ULS or SLS loadcombinations:

But did you know, that you can create your own envelop figures, with a wide variety of custom settings?

If you choose the Define envelope figure... option from the load combinations dropdown menu of the analysis tab, you will get the User defined envelope dialogue:

You are able to create as many envelope figures as you desire, while the setup options for them are the following:

  • Create envelope figures based on the selected load combinations

In this case, you have to choose with the checkboxes from the calculated ULS and/or SLS combinations, that which of them should be used for your custom envelope figure

  • Create envelope figures based on the selected load cases

  • In this case, you have to choose with the checkboxes of each load case, that which ones do you want to use to generate your custom envelop figure

  • Create envelope figures from load combinations based on selected load cases

  • In this case, at the left side of the dialogue you are choosing load cases, and on the right side those load combinations will be listed, which are generated based on the selected loadcases. These combinations will be used to generate your envelope diagram. 
    After you click apply, the custom envelope diagram will be created, and it will be available below the default envelop figures from the dropdown menu:

    Try it for free, by downloading the ConSteel INSTALL PACKAGE now!

      Wednesday, 20 June 2018

      Customer Project - Targu-Jiu Stadium

      Architects Dico si tiganas
      Structural Engineering Plan 31 RO
      OptimART Project
      Location Targu-Jiu, Romania
      Built in 2015-2019
      Size 37.500 seats
      Material S235, S355 and C30/37

      The dated Targu-Jiu Stadium is to be completely demolished and rebuilt. The new multipurpose arena will offer outstanding comfort for athletes, spectators and journalists.

      Seat capacity will grow from 9.200 to 37.500.

      Our partner, OpimArt Project, used ConSteel software to carry out the high-level structural analysis, design and optimization of the steel roof. To have an overview of the global behaviour of the whole structure, not just the steel, but the concrete structural parts were modelled.

      Global stability analysis was carried out on the full 3D structural model.

      Wednesday, 13 June 2018

      Word export - Create your own style for your documentation

      In ConSteel, you are able to export your documentation into an editable Word format with the same style as it was in ConSteel. But did you know, that you can create your own template with custom styling?

      The Word export function -debuted in ConSteel 12-, can be found in the file menu of your generated ConSteel documentation.
      The function uses Microsoft's .dotx file format, which can be used to store styling settings, sofor it is ideal for templates. In the INSTALL PACKAGE of ConSteel, we have already packed you a template in dotx format, which is filled up with the same styling settings, what ConSteel uses for documentation generation. This file by default can be found in the installation folder of your ConSteel, by the name of Consteel.dotx:
      C:\Program Files\ConSteel 12\Data\Export\Consteel.dotx

      To create a custom template with your style, simply copy this file

      After the copy is made, open the copied file, and start to customize the style of it, by bringing up the styles dialogue, and modifying any of the objects:
      After all of the style changes were performed, the template can be saved. Next time when exporting a documentation to word, the template has to be browsed on the Document export dialogue:
      By pressing the OK button, export process will be initiated, and the docx file will be created according to the custom styling settings in the template file:

      Friday, 11 May 2018

      Monday, 7 May 2018

      ConSteel 12: Improved fired design for steel members

      The new version introduces complete EuroCode fire design of steel members.

      Improved fire design covering not just the cross-section checks, but the complete stability design in fire design situation as well.
      In case of fire design situation, ConSteel applies the proper cross-section classification and buckling curve according to the EN 1993-1-2.

      ConSteel 12 is coming! Stay tuned to get the very first glimpses in the upcoming weeks.

      Wednesday, 25 April 2018

      ConSteel 12: Automatic use of swaying modes as imperfection

      To apply the swaying modes as imperfection is crucial, but in case of complex, 3d structures it is a tough issue which is not covered by the books.

      ConSteel 12 provides a completely new approach, that can identify the proper direction of buckling mode based imperfection in each of the load combinations and able to calculate the appropriate amplitudes.

      The new analysis results show not just the combined effects with imperfection, but engineers are able to see the displacements, inner forces etc. caused by each of the imperfection cases.

      Tuesday, 17 April 2018

      ConSteel 12: Reinforced concrete beam and column design

      In ConSteel 12, not just the steel and composite member design can be carry out effectively, but reinforced concrete beams and columns also.

      Calculation of concrete parts are fully integreted part of the ConSteel design process, therefore the entire multi-material building can be designed and optimized in one seamless process.

      ConSteel 12 is coming! Stay tuned to get the very first glimpses in the upcoming weeks.

      Wednesday, 11 April 2018

      ConSteel 12: csPI automatic code check and debugging

      The parametric model build is very powerful and effective, but without an automatic, continuously running code check and an effective debugging function it could be very struggling.

      In ConSteel 12, csPI programming interface was improved with these mandatory functionalities to speed up your model build.

      ConSteel 12 is coming! Stay tuned to get the very first glimpses in the upcoming weeks.

      Wednesday, 21 February 2018

      Customer Project - Stainless steel slide

      Structural Engineering MŰÉP Ltd.
      George Keller+Co. Ingenieurgesellschaft mbh.
      Location Sindelfingen, Germany
      Built in 2017
      Size Length 10.0 m.; height 7.0 m
      Material Stainless steel

      A 7-meter high and 10 meters long, stainless steel slide's analysis and design were carried out with ConSteel software.

      Support legs are made of 219,1 and 80 mm diameter cold formed tube with 3mm thickness. In general, the wall thickness of the slide is 2.5mm, but around the connection points of the support legs, it is increased to 10.5mm.

      Buckling analysis

      3D model was created in the structural engineering software ConSteel. The slide was modelled as a surface element, support legs were modelled as beam elements. Connections between the legs and the thin wall were entered with rigid link elements.
      The elastic buckling behaviour of the model was analyzed by linear eigenvalue solution.

      Local buckling of the slide's wall was checked by the reduced stress method of EuroCode.

      Friday, 16 February 2018

      This is what happens with the cross sections of your model under the hood - The Unified cross section model

      Advanced steel structural analysis softwares prefers the finite element method based on 3D thin-walled beam-column elements. This method requires the analysis-oriented modeling of cross-section problems. 
      On the other hand, the integrated design modules based on modern design standards (like Eurocode 3) need the design-oriented approach. 
      The design of class 3 shapes is based on the linear elastic properties used in analysis, while the design of class 1 and 2 cross-sections requires the plastic properties. Moreover, the design of class 4 shapes uses the effective cross-section model to take the local buckling into consideration. 

      It is concluded that the integration of the analysis and standard design needs an approach that covers both areas.

      In ConSteel, a unique model-oriented approach has been developed for the integrated analysis of cross-sections that satisfies the requirements of both the advanced beam-column analysis and the automatic standard design procedure. 

      During the integrated analysis-design procedure the different program components require different cross-section properties computed on different basic conditions. The elastic analysis used commonly in the standard design needs the nominal properties that are computed on the basic model. The geometric non-linear analysis requires a refined model to compute the stress-dependent Wagner coefficient. The design of class 4 shapes needs the effective cross-sections. However, all the relevant computational models can be derived from the fundamental model. This fact has emerged the object-oriented approach of the problem. Each procedure can be based on the fundamental geometric model and on the nominal properties related to this model.

      When a cross section is defined, ConSteel automatically generates the two parallel fundamental cross sections:
      • General Solid Section GSS: Compute the elastic cross-sectional properties for any kind of elastic cross-sections as accurate as possible
      • Elastic Plate Segment EPS: Able to serve specific cross-sectional properties for the standard design procedures

      Papp F, Iványi M, Jármai K.Unified object-oriented definition of thin-walled steel beam-column cross-sections. COMPUTERS & STRUCTURES 79: pp. 839-852. (2001) (Abstract)

      Friday, 2 February 2018

      Tips & Tricks: Ever wondered how to check the GLOBAL and LOCAL stability behaviour on the same model?

      When you want to check the global buckling behaviour of your structure, it is very straightforward, that first, you will perform a buckling analysis. The results of the analysis are the actual stability loss forms of the structure, and the load levels, on which these stability losses will happen (so called elastic critical load factors). The elastic critical load factors are calculated for each load combination, and they are being used at the global checks to determine the slenderness and the reduction factors each member. Reducing the cross section resistances with the reduction factors will result the global stability resistance of the structure.

      But what can you do, if you want to get a picture about the local buckling behaviour of a single member of your structure, which is sensitive for local buckling?

      The answer is the convert members to plate function of ConSteel.

      Here is a nice example how to check local buckling problems:

      1. The initial model is a frame, with segmented tapered members, built from welded I sections, with a relatively high web at the corner regions:

      2. Checking the global buckling behaviour of the structure, with a buckling analysis

      It seems, that the dominant part of the frame is the corner region. It may worth to see this region how it behaves for local buckling.

      The critical load level for the buckling shape is 4,25

      3. Use the Convert members-to-plates function on the beam at the corner region:

      All eccentricities, supports, and member parameters are kept during the transformation. Good to know, that at the end of the converted members, so called rigid bodies are automatically created. The rigid bodies provides the proper load transfer process between the bar members, and the plates:

      4. Check the local buckling behaviour of this part, along with the whole structure, by performing a buckling analysis on this model:
      The critical load factor for this local buckling mode is 2,73 (!)

      5. Perform some modification on the plate, by adding some stiffeners to the region:

      6. And finally, perform a buckling analysis again to see the difference in local buckling behaviour after the changes:

      The critical load factor for this local buckling mode is 3,52

      7. Repeat the iteration until the desired load factor is reached...

      Tuesday, 30 January 2018

      csPI - Introducing the for loop

      The for loop, or the cycle, is the heart of the parametric model creation. With the use of it, repeating operations can be executed, such as variable definitions, any kind of commands like object creations, if-else statements, or even more cycles!

      Just make sure not to end up in an endless cycle!

      Tuesday, 9 January 2018

      Complete model exchange and change management between ConSteel & Tekla Structures

      The advanced BIM link of ConSteel with Tekla Structures provides smooth transition between the participants of the design and detailing process in a clash free, time saving and efficient way through it's workflow. 
      The BIM functions between ConSteel & Tekla Structures are:
      • Model export to Tekla from ConSteel
      • Model import from Tekla to ConSteel
      • Model update between Tekla & ConSteel
      • Export of structural joints from ConSteel to Tekla Structures as macros