9. Member design verifications according to Eurocode 3
The module INSTANT steel – Member Design allows the design of hot – rolled section members according to Eurocode 3 norm. The module performs various verifications and can issue comprehensive reports for all their results.
The module provides the options to create a stand – alone project, or one linked to an existing solution. In the first case, the user must fully define the members to be designed, from geometry and section to the internal forces data. The latter will use geometry and section information from the structural model and internal forces from the analysis results. The program implements the following design criteria and assumptions:Note: In INSTANT steel a specified member can be designed either according to ENV 1993-1-1:1992 or according to EN 1993-1-1:2005.
The design rules for the members and sections of a steel structure according to EC-3 (EN 1993-1-1:2005) are incorporated in INSTANT steel through the menu option “EC3 Members”. Sections are classified in classes 1,2,3,4 according to the chapter 6. All sections of all classes are covered, except those of angles, channels and hollow beams of class 4. Through the menu option “EC3 Members” the following checks are performed per section type:
(*) From the menu option “EC3 Members”, in the case of hot rolled or welded cross-sections Ι or Η, when necessary, web buckling is covered as per §6.2.6(6) according to the simple post-critical method §5.6.3.
(*) The automatic calculation of the buckling length according to annex E of ENV 1993-1-1:1992 is included.
(*) The verification tests of single angle cross-sections are performed using the characteristic values of their main axes.
(*) The elastic critical moment in lateral-torsional buckling is calculated according to formula F.2 of annex F of ENV 1993-1-1:1992.
(*) The C1, C2 & C3 factors in lateral-torsional buckling are taken by the program as: C1=1, C2=0, C3=0.
(*) Interaction factors kyy, kyz, kzz, kzy are calculated automatically per loading case according to Table A1 of EC3.
(*) The equivalent uniform moment factors for flexural buckling (Cmo.y, Cmo.z) per loading case are automatically calculated according to Table A2 of EC-3. The value δx is taken equal to 0.
(*) For the verification test for bending and axial tension §5.5.3 a computation of the lateral-torsional buckling resistance §5.5.2 takes place, with the member support conditions under consideration.
B. Member design procedure
We start the member design procedure from the general window INSTANT steel – Linear 3D, by selecting: Design Checks > EC3 Hot – rolled Members as shown below.
After the completion of the above selection a new window will open called “INSTANT steel”. Select the “New” icon and from the “New” dialog window that will open select “Member design project”.
Then, the “INSTANT steel – MemberDesignDoc” window will open as shown below:
We give a “Project name” in the specified above field, select the appropriate “Regulation” – EN 1993-1-1:2005 – that will take place in the member design process and also click on the “Link to job” field. The last selection will result in opening a selection box button with three (3) bullets.
By clicking on the 3 bullets button the dialog window “Selection of results file” will appear. There the user finds the results file that is located in the INSTANT steel 2013 > Projects > “Name of the saved INSTANT steel job”.ajf.
After, the conclusion of the above selections the “INSTANT steel – MemberDesignDoc” window will load the topology and the analysis data from the specified “Projects” folder.
On the left hand-side of the “INSTANT steel – MemberDesignDoc” window there are some “Automatic member definition options”. There the user makes some pre-selections that will apply for all the future member definition that will take place in this particular example. Select the steel grade quality according to EN10025 equal to S275.
Then we continue to the Tab called “Members”.
In this particular Tab the user defines the members that he wishes to design according to EN regulation. More specifically, we define all the column members that were derived in the previous chapter were we observed the summary of column internal forces.
Let us consider, for this Member design example, that the column with the worst design ratios is the one (3rd from the left hand-side) with the maximum compressive force. The definition of the column is made on the right hand-side of the above screen, by selecting the start and end node of the corresponding column. After the completion of the described selection the “Members” tab will be as following:
On the top left hand-side we can observe the length of the specified member, the Section definition and also the steel quality (S275). In addition, there are some “Members data”, where the user can alter some of the pre-selections, such as the steel quality or even the steel section. We can also observe the internal forces along the length of the specified member and for a particular loading case or combination, e.g “Self weight”.
At this point we can save our member design project by clicking the appropriate “Save” icon as shown below.
This selection will initiate the following window.
Here, the user defines the member design file name and also the folder that the file will be saved.Note: The program preselects the Save filename destination. It is advised to save the member design files in the following path: INSTANT steel 2013 > Projects > “Job Filename”.ajf > MDEC3.
Then, we continue by selecting the “Buckling XY” tab. In this tab the user defines the “List of constraints” for the specified member. In this particular column member, we select “Fixed” conditions for the start node of the column and “Pinned” for the end node, as shown below (N51 constraint rotation – N52 constraint translation).
The above selection will have as an effect to reduce the buckling length by a factor “K” equal to 0.7. As a result the calculated buckling length for the XY plane is equal to 4199.267 mm.Note: The user can easily alter the buckling length of a member either by altering the “k” factor value or by altering the “Buckling length” simply by clicking on the specified field and setting out the desired values.
We are using the same procedure as described above in order to derive the buckling length of the member in the XZ buckling plane. There we choose “Pinned” conditions for both start and end node of the column member, as shown below.
In addition to the above selections, choose that there is a constraint in XZ plane at the positions where run the purlins. This will result in reducing the original XZ buckling length to 1500mm, as shown above.Note: More info regarding the buckling constraints is given in the Member Design EC3 Help Contents file.
Then continue with the “Lateral – Torsional Buckling” constraints definition. Select for the start node that there is a translation constraint for the calculation of “K” and “Kw” factors. Also, for the end node select that there is a rotation constraint for the calculation of “K” and “Kw” factors as shown below.
After all the above steps are finished we are now ready to proceed with the analysis by selecting the “Analysis” tab.
In this tab the user makes a number of selections simply by clicking on the relative fields. In the particular example, select that in the Analysis the partial safety factors that are going to be used are according to EN1993-1-1:2005 norm. In addition, the report language is set to “English”, simply by clicking on the “Report language” field and changing the initial value from “Greek” to “English”.Note: There are three (3) available “Report language” options, such as: Greek, English and Romanian.
In the “Reports” field there are a numerous of options. More specifically the user can select among the following options: • None (this will activate the “Results” tab where the user can observe the worst ratios for the worst loading case) • Detailed (this will open a detailed results report either in a Text or Word format) • Table (this will open a table results report)
By selecting the options described below in the “Analysis” tab we have the following results:
By altering our selection in the “Analysis” tab and selecting in the field “Reports” > Table we have the following after pressing the “Member Design” button:
As shown above, the user by selecting the “Table” option can quickly observe the ratios that appear for the specified member / members during the design according to the specified by the user norm. Starting from the left, the table lists the member being verified, the loading case index number for which the verification found the worst ratios, the section classification class, the ratio in combined axial, bending and shear (N+M+V(y,z)) as well as in Shear Y and Z axis. Next are the member stability results as described in the specified norm. Ratios below 1.0 verify that the member design is satisfactory.Note: In the “Analysis” tab there is an option called “Section Design”. This selection will result in performing a section design of all beam members that are presented in the linked topology.
Using the same procedure the user can ask to have a detailed report for specific member or members, for a specific loading case or a number of loading cases and finally a detailed report for the worst loading case among the selected from the user loading cases.
A detailed report for the worst loading case for the specified column member is shown below:
In case where some of the ratios are greater than 1.0, we can alter in the “INSTANT steel – MemberDesignDoc” the section of the specified column member by clicking on the “Section” tab as shown below. This selection will result in opening the “CCS Section database” dialog. There the user can select another section from the initial section that was derived from the topology and run again the member design check. This will give him a rough idea on the appropriate section that he should use for the specified member.
The procedure described above is repeated for all the member categories that exist in a structure, e.g rafters, purlins, rails etc.