Stability Design

M

miralay

New Member
Does the program make a calculation about the stability design mentioned in chapter 6 of the steel code? Or does it leave this part to the user?
 
Hello there; P-Large delta and P-Small delta analysis are performed with the v10 version to take into account the second-order effects. In the buckling length method, B2=1 is assumed and the process is performed. General analysis (Direct Analysis Method of Design) method is still in the writing stage. Good work.
 
Hi, where does it say B2=1 can be accepted? As far as I know, B2=1 is the minimum value, but it can be in systems with lateral displacement prevented. In systems where lateral translation is not prevented, using this value will be on the unsafe side.
 
Hello there; It is obligatory to trade with B2=1, the phrase is not mentioned anywhere. The program operates as 1 by default. The user must define the combination and use the B2 parameter himself in the combination. The article is written for informational purposes only. P-large delta and P-small delta analyzes already give the actual results of Second Order Effects, which are tried to be taken into account with coefficients B1 and B2. Therefore, you can consider direct effects instead of the approximate coefficients B1 and B2. If you want to use B1 and B2, user intervention is required through combinations as I mentioned. Good work.
 
In order to perform direct analysis from P-delta, analysis must be done with the general analysis method. The program cannot do this for the moment. For the analysis with the buckling length, the B2 coefficient should be calculated and should be less than 1.5. The user has to calculate the coefficient and verify that it is less than 1.50. For the approximate second order analysis, the coefficients B1 and B2 must already be calculated. The user needs to calculate the coefficient and enter it into the program. This is what I understood from your answer. Therefore, if the program analyzes with the buckling length, it makes more sense to first set the default value of 1.5, which is the upper limit, with the understanding of safety. In summary, in stability design, as in every program and design, the control and calculation of the engineer has priority.
 
The B2 coefficient, which is the ratio of the second-order relative storey drifts to the first-order relative storey drifts, consisting of YDKT load combinations to be calculated for all floors or loadings equal to 1.6 times the GKT load combinations, is likely to be less than 1.5 in many simple/ordinary steel structures, but still calculated by the user, control and evaluation will be correct. Non-vertical columns (buckling length method cannot be applied anyway in such structures), long columns, large cantilevers, high torsional irregularity etc. The B2 coefficients must be checked by the user in order to apply the buckling length method in special types of steel structures containing elements such as:
 
In fact, for direct analysis from P-delta, nonlinear analysis can be made not only with the general analysis method, but also with the buckling length method. In the application of the buckling length method, nonlinear analysis in which P-delta (large + small) effects are taken into account within the scope of second order theory, B1 and B2 values can be made as 1.0 (the attached stability design image will be summative). However, the point to be noted here is that if the general analysis method or if any of the buckling length methods meet the application conditions, when the P-delta (large + small) effects are also taken into account, the loads cannot be superpositioned for load combinations as in the first order analysis. It is necessary to solve the geometric pre-defects by directly modeling each load combination individually and in the combinations specified by the regulation or by considering horizontal fictitious loads.
 
Is the program currently using method #4? If it uses it, it calculates B2, but because it uses this method, it accepts B2=1. I'm asking you because I couldn't download the demo from the site and try it.
 
Hello there; With B1 and B2=1, the program is designing stability. As Tolga mentioned, if you use non-linear analysis methods, you can see that the program takes B1 and B2 values appropriately. With ideCAD Static IDS v10, you can determine P - Delta (large+small) effects. You can have comprehensive information on the subject in future training programs about the new version possibilities. You can register for the trainings at the link
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. For information specifically on P-delta and nonlinear analysis, Chapter 5 - Design by Shapeshifting training will answer some of your questions. Good work.
 
At the top of the algorithm sent by Mr. Tolga, it is written that the B2 coefficient, that is, the ratio of the second-order relative storey drifts to the first-order relative storey drifts, must be less than 1.5 in order to use the method number 4. My question is, does the program calculate B2 and verify that it is less than 1.5, and then use the analysis method number 4?
 
The program evaluates the second order effects within the scope of TBDY 4.9.2. Accordingly, it calculates the second order indicator value (theta) for each floor according to TBDY (4.35). It finds the largest of the calculated values for all floors and compares it with the limit value calculated with TBDY (4.36). If this value is lower than the limit value, second-order effects in the structure can be neglected. In this case, if the designer wishes, considers the second-order effects according to ÇYTHYEDY. The program makes the stability design for steel structures according to ÇYTHYE 6.4 Buckling Length Method. In this method, the required strengths are obtained by using nonlinear P-delta analysis or linear approximate second order analysis without considering stiffness reduction. The program uses linear calculus and approximate second order analysis (3rd method in Tolga Bey's table) but does not calculate B2, it accepts 1.0 (This is among our missing notes). If you check and limit the second order effects according to the carrier system you have chosen from the report as I mentioned in the paragraph above, the B2 coefficient calculated by ÇYTHYE 6.5 Approximate second order analysis will be 1.0 or close to 1.0.
 
Then, should we follow a path like the following for design? We will construct a model for gravitational and wind loads and consider second-order effects. Then we will create a second model for earthquake loading, check equation 4.35 without considering second order effects and continue. We will use the adverb of the results from these two. Otherwise, doesn't this article in the earthquake code nullify the stability design in the steel code?
 
You don't need to create two separate models. 1. If there are wind loads acting on the structure, you can calculate the B2 coefficient according to ÇYTHYE 6.5. You can only increase the axial force and bending moment in the columns due to the wind effect with this coefficient. You use these increased values for load combinations with wind effect. 2. It is sufficient to check from the report that the maximum second order indicator value for the earthquake effect is less than the limit value. The stability design mentioned in ÇYTHYE obliges to consider not only the earthquake effect but also the second meter effects that will occur from other loads (vertical loads, wind loads). As you know, the part in the earthquake regulation is for the second order effects that will occur under the effect of earthquake and is independent of the reinforced concrete or steel carrier system.
 
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