Lovers don't save

S

sereze

New Member
I entered the supported length ratio (LTB) = 0.1 for the purlins. But it still didn't save. What adjustment do I need to make so that lateral buckling is not calculated for the lovers?
 
Hello there; You can remove the lovers from the analysis model. When you remove the analysis from the model, the purlins will be analyzed and the coating load, snow load and wind load will be distributed to the beams. In this case, the stiffness of the purlins will not be included in the system and the purlins will be solved separately. You can define and solve it as a simple supported single span element with the same loads, but the result will not change. The reason for the proportions of the purlins is the snow and wind load. If you enter a value such as LTB= 0.000001, the lateral buckling calculation you mentioned will be very low. However, there is no error in the lover accounts. It would not be correct to reduce the lateral adhesion ratio. The lovers already seem to be holding 0.333 in your model because of the tension rods. Apart from these, there is no element that holds them.
 
I would like to get the opinion of my fellow forum members. In all steel books, only the normal bending without lateral buckling is calculated for the purlins. It can be thought that the top screwed panel holds the purlin against lateral buckling. In addition, the tension rods we threw would reduce the length of the buckling, if we predict buckling, but they should also act as a support in the calculation in the weak direction and cause the moment to occur in the weak direction to be low. I guess it's not taken into account in this way at the moment.
 
Hello there; The purlins you modeled with İdeCAD Çelik were included in the analysis model. Therefore, in terms of the program, these elements are rod elements and their rigidity contributes to the whole system. So they are not checked for just normal bending as you mentioned. They are controlled in accordance with the internal force diagrams obtained as a result of the analysis results according to the load on them. In your model, it is seen that there is pressure on your purlins in your axial force diagram. Therefore, lateral buckling control should be performed. At this point, you have 2 options. Remove the lovers from the analysis model as I mentioned earlier. In the books you mentioned or in other programs that you analyze, lovers are not included in the system, they are also solved. After removing the analysis from the model, IdeCAD Çelik 8 will still calculate the lateral buckling. This is because the moment diagram will form in the opposite direction under the suction effect caused by wind loads, so the assumption that the pressure head is retained will not be correct. Therefore, as I mentioned before, you need to enter a value such as LTB= 0.0000001 in the lovers design inputs section. In case of a tension rod, if you model two tension rods rather than a single tension rod as in your model, your minor bending moment will decrease by 20%. However, as far as we can see in simple manual control, your lovers are not enough in this case. As a result of the loads on your purlins, if you manually check with simple beam calculation, you can see that your section is not sufficient in G+S loading. In fact, you mentioned a subject that is in program R&D work. As I said, it does not ensure that your sections are sufficient, including the falling moment diagrams. However, our lack exists regarding tension rods. The inclusion of tension rods in the mathematical model is a subject that is currently being studied. You can see the moment diagram you expect in future releases. Good work.
 
The bending moment capacities for UPN 140 were found to be 1.44-1.48 tm in the strong direction and 0.34 tm in the weak direction. In the strong direction, Sigma Safety x Moment of Strength = 1.4 x 86.5 = 121 tcm. = 1.21 tm Weak Side ............................................. ..... = 1.4 x 14.8 = 21 tcm. = 0.21 tm. shouldn't it be?
 
You calculated by considering the safety stress method, but AISC 360-10, like other modern regulations, is based on the bearing strength, namely plastic strength. Modern regulations do not limit the element to remain only within elastic limits. Steel is a material that exhibits elasto-plastic behavior. In this context, the capacity of the element will be determined by the yielding in the whole section. Let's go step by step according to AISC 360-10 (ASD). Capacity of the element = Yield stress * plastic strength moment / Safety factor For the material (S 235) and cross section (UPN 140) you choose: Fy = 24000 tf/m^2 Z3 = 103 cm^3 (strong direction plastic strength moment) Z2 = 28.4 cm^3 (weak plastic strength moment) S2 = 14.78 cm^3 (weak direction elastic strength moment) Omega = 1.67 (safety factor for bending) Strong direction bending capacity: Mn = Fy*Z3 Mn = 24000 * 103 * 1e- 6 = 2.472 tfm Mc = Mn/Omega = 2.47 / 1.67 = 1.48 tfm Weak flexural capacity: Mn = Fy*Z2 <= 1.6*Fy*S2 Mn = 24000 * 28.4 * 1e-6 = 0.68 tfm 1.6*24000*14.78 *1e-6 = 0.57 tfm 0.68 > 0.57 => Mn = 0.57 tfm Mc = 0.57 / 1.67 = 0.34 tfm The new Turkish Steel Structures Regulation, like other current regulations, is based on bearing strength and plastic strength. You can review the draft text from its file. It would be useful to update the resources you have and your current knowledge accordingly. ideCAD Steel has been developed based on current and international regulations.
 
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