There are a few minor issues regarding the calculation of the saddle
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The Zick method is used for saddle calculations, whether it is for domestic saddle calculations or the methods outlined in ASME Volume II. However, in the calculations for the saddles, no distinction is made between fixed ends and sliding ends. The axial forces and lateral shear forces required for the civil engineering structure take into account the sliding ends; for example, if both saddles of a device are sliding ends, the calculations for the axial and shear forces in PV do not make such a distinction. Yet, the civil engineering structure considers that only 30% of the mass acts on sliding saddles, so essentially the two approaches yield different values. I can understand that what we need to verify is the force on the saddle base in order to meet the requirements. The civil engineering team believes that only 30% of the equipment’s weight is transmitted to the foundation at the sliding end; therefore, this value needs to be calculated by the civil engineering team, not by us. Moreover, there is no corresponding option in PV that allows 30% of the weight to be taken into account in the calculations. Is there anyone who can tell me if my understanding is correct?
Your understanding is correct. In the saddle calculation (Zick method), there is indeed no clear distinction between fixed ends and sliding ends. Typically, the design and calculation processes are separate: the pressure vessel designer carries out calculations for the saddles, while the civil engineer independently calculates the design of the civil structure. In practical engineering applications, the results of these two parts are sometimes coordinated and integrated depending on specific circumstances. Based on your description, the civil engineering structure estimates that the force on the sliding saddle is only 30% of the mass; this value actually needs to be calculated by the civil engineering structure itself. The task of the pressure vessel designer is to verify the forces on the saddle base plate to meet the design requirements. The PV Elite software does not include parameter settings for the axial forces and lateral shear forces on the saddle base, so this aspect needs to be calculated by the civil structural engineer based on the actual conditions. In short, your understanding is correct: the design of pressure vessels and the design of civil structures need to be carried out separately, but it is also necessary to coordinate and integrate the results in actual engineering applications. In this process, the civil structure engineer should calculate the forces on the saddle base themselves, based on the type of saddle and the actual conditions of the project. .
This post was last edited by wanlirn on 2023-10-23 09:25. I’m not quite sure; the basic forces involved are two: one is the weight of the equipment, and the other is the horizontal force. Isn’t the horizontal force equal to the weight multiplied by the friction coefficient between the saddle base plate and the embedded components? For general steel-to-steel welding, 0.3 or 0.4 is fine. The 30% of the equipment weight you mentioned refers to the friction coefficient being set at 0.333….
The forces acting on the saddle include not only the weight of the equipment itself but also the load exerted by the pipe ends; in calculations, the engineering team responsible for the equipment sometimes fails to take into account the force generated by these pipe-end loads on the saddle. In addition to these two, there are also the forces exerted by earthquakes and wind loads. The coefficient of friction you mentioned is something different, right? For example, in the calculation of PV, wind loads and seismic loads are taken into account. For horizontal containers, seismic loads have a significant impact; these loads exert forces on the saddles in two directions: an axial force and a shear force. Typically, this force is compared with the friction force. My problem here is that the two saddles on my horizontal tank are both of the sliding type. According to the owner’s feedback, only 30% of the load is applied to these saddles, which will affect the final results. However, from an equipment engineering perspective, what I need to consider is the effect of the equipment on the saddles, rather than the interaction between the saddles and the foundation. Therefore, when checking the saddles, I don’t need to take into account whether 30% of the load is applied to the foundation; that should be something that the civil engineering team deals with.
Thank you for your reply. I think they used the data provided based on the equipment’s specifications, as well as the force exerted by the equipment on the saddle base plate, to carry out further calculations. According to their requirements, 30% of the mass should be taken into account to determine whether it meets the allowable values for the foundation. If this requirement is not met, then we will need to consider reducing certain parameters of our equipment, discuss with the pipeline department ways to reduce the load on the pipe connections, thereby decreasing the force exerted on the saddles due to those loads, or ensure that the seismic parameters are not overly conservative.
That’s why I didn’t understand what you were trying to say. For saddles and foundations themselves, in typical designs where the equipment weighs only a dozen or twenty tons, there’s no need to worry too much about them. Probably, with those huge structures weighing hundreds of tons, many factors have to be taken into consideration. Standards are not omnipotent either.