Steel roof capacity ratios are very high

M

Mesut Turan

New Member
Good day hello; I just bought İdecad 10.5 Reinforced Concrete + Steel program. Since my steel roof model is not very complex and regular, I drew the purlins myself on the 3d screen instead of the ready-made purlin modeling part. When I looked at the analysis results, the capacity ratios were very high due to the modeling, 1- I checked the geometry and no problem was detected. 2- Steel projects do not always come in simple form, so we may have to draw purlins ourselves because we cannot benefit from the ready-made purlin modeling section. If the program divides the lover into two in the account model, it should also divide in the account details. There is an inconsistency here. 3- When we want to see the steel joint calculation results, what is the reason why the results do not appear and appear gray (a general purpose question) My maximum purlin span is around 360 cm M= ql2 /8 = 70kg/mx ( 3.6 )^2 / 8 = 113.4 kg m = 11340 kg cm Stress in the element: M / W 3-3 = 11340 kgcm / 17.8cm^3 = 637 kg/cm2 D/C = 637kg/cm2 / 1440 kg/cm2 = 0.442 purlin results should be obtained. Good work .
 
According to AISC 360-10, box section elements under torsion, bending, shear and axial load are controlled by the interaction equation in the picture. He has already used this equation in the program. So it's not enough just to check for tilt. Moreover, you checked your inclined purlin element for bending in only one direction. You have neglected axial thrust, torsional and shear forces. In this respect, I do not think that the program made a mistake. You can design the lovers as the 2nd carrier that will only try to bend. In this case you will need to change your static model. I wish you good work.
 
1- As can be seen, my lovers do not sit on the support at an angle (the lovers cannot sit vertically and inclined, the angled purlins you mentioned occur in horizontally thrown purlins). For this reason, the biggest factor affecting the capacity ratio of the element will be the bending in the 3-3 strong axis. The stresses caused by the axial load on the purlins are negligible because they are not very effective;( For 200kg axial load, 40x80x4 profile A : 8.9cm2 corresponds to a funny stress like 200kg/8.9cm2 = 22kg/cm2. Its contribution to the capacity ratio is as follows 22kg/cm2 / 2400x09 kg/cm22 (Safety stress, LRFD) = 0.01 The axial load is too high in the program, I couldn't understand it. In the application of the purlins in the field, the purlins are not added end to end, either they are placed side by side, or there is a distance between them. The force should only occur a small amount due to bending? Stress from the Weak Side(M22) (For a 3.5 m purlin, it will not affect the capacity, if you have a 6 m purlin, it is okay to apply a tensioner to reduce the weak stress) Attention to the formula If you do, the shear and torsion ratios are squared, so the effect is very low, and in which purlin design that does not sit at an angle on the support, the capacity ratio is high due to the axial load. did you see Capacity ratio affecting the formula due to Shear Den Ex. Even if it is 0.2, (0.2)^2 = 0.04, the effect is very small. THE CAUSE OF INCONSISTENCE IN THE ACCOUNT IS DUE TO THE SIZE OF THE ELEMENTS DIVIDED WHEN LOOKING IN 3D IN THE CALCULATION MODEL, BUT THE PROGRAM DOESN'T REMEMBER THAT THE LOVERS ARE DIVIDED IN THE ACCOUNT DETAILS. SUGGESTION : IF WE CAN CREATE A NODGE POINT BY DIVING THE RODS IN THE ANALYSIS MODEL, I WOULD DIRECTLY RESPECT THE LENGTH OF THE LOVERS WERE TAKEN WRONG. If the program divides the lover into two in the account model, it should also divide in the account details. There is an inconsistency here. ? I just talked about it .... I just bought the idecad program, it's been 2 weeks I guess, so I'm trying to learn the logic of modeling, my aim is not to criticize the program. After all , I prefer it to other programs ... Mr. Ismail , the project size is too large , so I sent it to the support mail , I would be very happy if you are interested . Thanks
 
Mr. Mesut, you can criticize the program, I think it's okay. I am just a user like you. Your axial load is 6096 kg, not 200 kg. Compression force is coming, not tension, so you cannot calculate the stress by dividing the force by the cross-sectional area. Dividing the element does not mean that you are dividing the calculation length, or drawing the element as a full piece does not mean that the calculation length is not divided. For example, you have a 8 meter column in Sap2000. You modeled this column in one piece and you can get a cantilever crane from 6 meters. In the design of Sap2000, when calculating the non-retained length of this column, it perceives it as being held from where the crane gusset is. However, the cantilever gusset does not affect the retention length of the colon. That's why it gives the opportunity to interfere with such design data in other programs, including Idecad. If you think the program is using incorrect design parameters, you can intervene manually. Regards, good work.
 
Mr. Mesut; If you upload your project, I can make a detailed explanation on your project. If the project size is large, you can upload it with the help of the wetransfer site. Best regards...
 
1- I didn't say that there is a load of 200kg on my employee, I see that it is 6096 kg :) I found it strange that my lovers have such an axial load, I can understand if it is 200kg. 2- You said that pressure is coming, not pulling?? The essence of the event is as follows: The lovers you see are the bending element; that is, TENSILE stresses occur in the region above the influence line of the element and in the region below the PRESSURE. Broken fibers are at the top of the material. If we consider the worst case and talk about the fiber at the top of the material, which is compressive stress. The stresses that tensile and compressive forces will create in the element are as follows. You can make P/A in the tension element. In the pressure element, we punish the element a little and multiply it by the buckling coefficient and increase the stress Wx P / A. I am aware of this, you can be sure. But in a purlin (40x80x4) with a real bending length of 3.5m (60-70kg/m), be sure that buckling does not occur. As a designer, I am in the practical part of the job. 3- You said that dividing the staff does not mean that you are dividing the account length; Answer : I did not divide the element, the program perceived the profile that touches the bottom and bottom as a support and divided it from that part, and I can see it when I look at the 3d calculation model. If in the account model, can I explain why I am questioning it in split accounts? After all, why is there a 3d account model display? I am expressing this issue, which I consider important, again; SUGGESTION : IF WE CAN CREATE A NODGE POINT BY DIVING THE RODS IN THE ANALYSIS MODEL, I WOULD DIRECTLY RESPECT THE LENGTH OF THE LOVERS WERE TAKEN WRONG. The more we, as program users, scrutinize, the better it will be for the future of the program if there are feedbacks. Mr. Ismail. (I sent the project to SUPPORT e-mail). Best regards.
 
Hello Mesut, I have reviewed your project and your questions. First of all, as you mentioned above, in order to calculate M = q*l2/8, the element must be a simple beam with hinged ends. Since the elements in the roof you modeled are rigidly connected to each other, the moment diagram appears as if there is no joint in the beam on which the purlin sits. If you do not want this situation to occur, and you can make a suitable calculation for the simple beam with hinged two ends you mentioned above, you can follow these ways. First of all, the program does not automatically divide the individual elements that pass through each other (this can be column, beam, single purlin, single cross) from the supports they sit or pass through, and connects the contacting elements with a joint point. As a result of this situation, the moment diagram above is formed. You can split an element into multiple parts when you use the "split" command in the program to split the beams and set the start and end distances. Or you can create snap points on the main beam with the command "create snap points on object" from the right-click menu. You can then identify the lovers using these snap points. There are also two ways to define a joint. If you connect suitable simple joins to the ends of the elements, the program will automatically identify the joint. If you want to analyze without defining a join, double-click the element to open the element properties window. You can then give the M2 and M3 freedoms from the "freedoms" tab. When you apply these operations, you will find values close to your account. Regarding element sizing and design results; Element dimensions are made under the effect of axial force and biaxial bending. If your element has more axial force, then the design ratio will increase. However, the axial force in roof purlins is generally caused by earthquake effects. Therefore, the axial load assumption you calculated above may not always work. It may be necessary to check the values from the analysis results. However, when you look at the dimensions and proportions in the project, there is a very serious difference. This difference may be due to wall loads. Wall loads remain defined on all beams in your project. You can avoid this situation in your other projects if you use the templates from version 10 of these wall loads. On the other hand, since you have a console distance of 3 m, you may need to enlarge the dimensions of the main elements that will carry the console. At the same time, in the design results of the purlins, the Lfactor value of some elements was around 1.5. You can correct the Lfactor value by extending the column a little to take into account the retained size from the column. Best regards...
 
Thanks a lot, as I said, I'm new to the idecad program, I was using a ready-made template of a friend of mine, it turns out that there is a serious wall load defined on steel beams :) I understood what you said. Thank you for your sensible answers. Best regards.
 
The outer contours are not consoles, I want to support those parts, but I could not find them, they will be anchored to the reinforced concrete part. 1- How do I assign a manual support 2- How can I change the built-in support on the existing columns to a fixed support 3- In some cases, I don't want seismic combinations to interfere with the analysis, so there are steel roofs that I want to do linear static analysis only, where can I choose this? Best regards
 
"Mesut Turan":3b8hmmwz" said:
1- I didn't say that there is a 200kg load on my employee, I see it as 6096 kg :) I found it strange that my lovers have that much axial load, even if it is 200kg. In fact, the purlins you see are bending elements, that is, the region above the influence line of the element, TENSILE stresses occur in the region below the PRESSURE and the region below the PRESSURE, the fractured fibers are at the top of the material. You can do P/A in the tension element in the stresses that the compressive force will create on the element.We will punish the element a little and increase the stress by multiplying it with the buckling coefficient Wx P / A I am sure of this.But in a purlin with a real bending length of 3.5m (60-70kg/m) ( 40x80x4 ) make sure that sprains do not occur for me as a designer, the practical part of the job I'm in. 3- You said that dividing the staff does not mean that you are dividing the account length; Answer : I did not divide the element, the program perceived the profile that touches the bottom and bottom as a support and divided it from that part, and I can see it when I look at the 3d calculation model. If in the account model, can I explain why I am questioning it in split accounts? After all, why is there a 3d account model display? I am expressing this issue, which I consider important, again; SUGGESTION : IF WE CAN CREATE A NODGE POINT BY DIVING THE RODS IN THE ANALYSIS MODEL, I WOULD DIRECTLY RESPECT THE LENGTH OF THE LOVERS WERE TAKEN WRONG. The more we, as program users, scrutinize, the better it will be for the future of the program if there are feedbacks. Mr. Ismail. (I sent the project to SUPPORT e-mail). Best regards.
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Mesut Bey, that's what I meant anyway. If you want to run the purlins as bending elements, you have to tell the program about it. When it is done with a macro, the program does this automatically. However, since you drew it like a manual beam, the program accepted both ends as rigid and designed it that way. Oğuzcan Bey has already stated this. I wish you good work.
 
Hello there; As seen in the picture above, in order to add a new support, go to the analysis model from the right-click menu and open the node numbers. Then, hover over the node where you will define the support and use the "add new support" command from the right-click menu and select the freedoms you want to keep. (For example, if you tick all the boxes, it will be a fixed support.) Similarly, if you hover over the built-in supports and use the add new support command and release the rotations, you will define a simple support. The point you need to pay attention to here is which node points are selected. After defining the support for the nodal points you have selected, check if they are selected. ideCAD Statik v10 defines design combinations according to TBDY 2018 and Steel structures Design, Calculation and Construction Principles regulations. You can check these combinations in "Structure tree -> Analysis -> Design combinations" and define combinations yourself. However, we do not recommend removing combinations with earthquakes. Because in this case you are skipping some parts of the regulation. We organize free trainings for ideCAD Statik v10 every month at the Istanbul office. You can register for the training
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. You can also watch modeling and interface online training videos on our youtube channel
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. There are also videos for steel element designs where all calculations are made manually and compared with the program results (
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). If you examine the design videos of the steel structure elements in the link you added, you can learn the calculation principles of ideCAD Static software and make comparisons. You may need to pay attention to a few details while making a project. First of all, if you make occasional analysis while modeling and examine the results for that situation (such as cross-section effects, deformations, design results), you can see the wrong models in the program and intervene more easily. At the same time, you can easily prevent user-defined errors in your projects by getting help from technical support. Best regards...
 
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