Cross section insufficiency of roof purlins, pressure build up problem

[Fatihcelal]

Hello; In the project in the attached link, there is a very high pressure for the roof purlins to the creek and ridge purlin and the sections do not save. again the problem has not changed.

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[nurgulkaya]

Re: Cross section insufficiency of roof purlins, pressure formation question Hello; It is true that the crosses that are primarily related to modeling are modeled first. However, you have advanced systematically in cross modeling. The general method is to create the first and last partitions crosswise, if one partition is full, one is empty, or if your structure is not very long. Your structure is arranged like this. As for the problem with the lovers: 1) You should remove all the lovers from the analysis. When the purlins are removed from the analysis, they are designed in-house with the coating loads on them and transfer the load to the shears as a purlin reaction. You do not need to include the purlins in the analysis as we use cross on the roof. Crosses provide lateral stiffness, it is appropriate to exclude purlins from the analysis in order to be more economical. 2) If you divide the purlins from all intersections, each truss is analyzed as a simple supported rod element resting on it. In this way, you can examine the shear force and bending moment diagrams in the purlin results. If you do not divide the lovers, it will be suitable for the gerber beam logic, you can see this situation when you examine the diagrams. The Gerber beam gives economic results in 3-4 spans, the positive effect of the reverse moment in the support area is eliminated in the spans above it. Therefore, either divide at all intersections or model by staggering the purlins by dividing them at 3-4 intervals. 3) When you divide by all intersections, there will still be a shortage of lovers. The reason is that our roof slope is as high as 25%. The solution is actually general system optimization. While the ridge area of your trusses is 200 cm, the ends should be 15 cm, and the diagonals should be as close to 45 degrees as possible for the performance of the truss beam systems to be high. In short, obtaining grid in the shear provides economy. We recommend that you lower your scissors height to both reduce your scissor sections and make your purlins sufficient. 4) If you think the above steps are not suitable for your project, you should increase the purlin cross section or decrease the column axis distances. In the appendix you can find the crosses and purlins of your project arranged. Good work.

 

[Fatihcelal]

Re: Cross section insufficiency of roof purlins, pressure formation question Hello, Ms. Nurgül; Thank you for your return. When all purlins are included in the analysis system in the system, no cross is used on the roof. When I examine the reports, the program does not give any errors and the sections are sufficient. What are your thoughts on this subject? The capacity of the braces used on the roof saves, but the slenderness ratios do not. What can be done for this situation. Thank you.

 

[nurgulkaya]

Re: Cross section insufficiency of roof purlins, pressure formation question Hello; Including purlins in the analysis and using them to provide lateral rather than diagonal grip and stability is an engineering assumption. There are also drawbacks. Most engineers do not include lovers in the system at all. It is recommended to align the crosses at the beginning, middle and end of the cross to include purlins in the analysis. For this, you can examine the trainings given by the instructors at IMO together with the new steel structures regulation. It is the engineering approach in the two cases mentioned above. It depends on your interpretation. For the slenderness problem of the diagonals, you should either increase the cross section or change their length by increasing the number of diagonals. If you search the forum on this subject as a slenderness problem, you can find a lot of detailed entries. Good work.