About roof cross and purlin problems.

F

Fatihcelal

New Member
Hello; I would appreciate if you could help with the following issues; 1. Should we leave some space between the roof crosses and the purlins in truss roof systems. Is there a load on the crosses due to the deflection of the purlin? (Is it like 1 cm without touching the cross and the purlin, or 3-4 cm according to the highest deflection of the purlin) In 2 cases, the results of the crosses It turns out very different 2. In scissor systems, we pull back the ridge and brook purlin by 10-15 cm. While forming the roof diagonal, we place them according to the nodal points of the scissors. When we pull back 10-15 cm to align the end points of the crosses with the purlins (cross end node points, When we bring the purlin to the nodal points) a very high rate of axial force is formed in the purlins. Should it be obeyed to the scissor joint or to the purlins? 3. Is it true that in the same loading combination of X-shaped roof braces, all elements are tensioned or all elements are pressurized? 4. The design report of the combination made by combining the 2 cross ends and the scissor upper head while making the Cross End joint is not formed. When we combine the cross ends and the scissor head one by one, the report is formed. In 2 cases, the operation of the scissors changes. Is there a deficiency here? 5. In scissor systems, when the purlins are continuous, the deflection and capacity calculations of the ridge and brook purlin are made incorrectly, there is no problem in the other intermediate purlins. (Calculations are made for the entire continuous purlin length, such as 15m-30 m). We do cross placement in the last range. Would it be wrong if we skip the first and last range and place the second range? What are the benefits of cross placement to the first range. 7. How should we choose the R coefficient and the ductility coefficient when the braces do not continue in the vertical plane when only the diagonal is used on the roof. Thank you in advance for your interest.
 
Hello there; 1- For scissors, purlins and crosses, you need to check the nodes from the analysis model There is no connection between the deflection of the lover and the crosses. Check your analysis model as I mentioned. If you have problems, send your project. 2- It is more appropriate to act in accordance with the scissors node points. To avoid additional effects on the scissors. 3- Since the tension and compression conditions depend on your combination and your loads, your model should be discussed. 4- To get the joint report, save your model as a different model and model the cross-end joint one by one. However, there cannot be a significant difference between the two models in terms of analysis and design. It is normal to have a minimal difference. Make sure you have created your model correctly. 5- In your model, the first and last purlins are not divided, arrange the purlins by giving offset distance, divide the purlins again. 6- Cross configuration is the choice of the engineer. 7- If you work with a normal ductility level, we recommend that you choose a coefficient considering that only the frame system will meet the earthquake effect, since there are no braces that act as curtains against vertical earthquake loads. Good work.
 
Hello there; There is no problem in your roof diagonals. Since your scissor head is under the pressure effect, it is quite normal for the crosses to come out under the pressure effect as a result of the loads transferred to the crosses. If you wish, you can compare the analysis results by transferring them to Sap2000. In the sample project, the red colored braces were created with the steel beam command. When the results of the analysis are examined, it is seen that it is only under the pressure effect. You can test it this way too.
 
You must log in or register to reply here.
Back
Top