hello everyone is that really required to prepare a 3D St model for a simple vrow type of a structure or a simple PB frame is it da required before moving to the video If you new here I am par Jan a structural engineer software developer and your steel design guy I post regular videos on Structural Engineering steel design a I and stuffff and finally the automations please do subscribe to the channel and give a thumbs up it really motivates me to create more such free content okay now coming back to the video in order to understand a 3D behavior of a steel portal frame here I have a simple 2D frame so like which is 30 m in width and and around 8 m height okay yeah it that's fine for this preliminary model I have just applied dead load roof life Lo collateral and the wind loads okay so all the loads are applied in the horizontal and vertical Direction a steel portal frame by concept is intended to take only the horizontal and vertical loads it will not take any of the longitude itudinal forces once it encounters a longitudinal Force which means the force which is perpendicular to the frame Direction then this particular frame will collapse in order to see that in an action let is go and provide a very small load here say for example I'm creating a no load and there's a direction say 1 K yeah it is okay so let me add that load here upon analyzing this Frame should completely collapse it should not take any of the forces right yeah if you see the deflected shape it is totally flat so I'm checking the summary here it is around like 2.3 into 10^ 12 in the Z Direction so the frame is completely flat upon applying a very min longitudinal Force what do we infer from here yeah since it is a 2d frame it is not taking any longitudinal forces if you do it as a 3D whether it will take it's a big question mark right now let us go to a 3D frame and see how it behaves and you will be getting more ideas on the behavior of a frame when we move on to 3D for this exercise I have created created a simple 3D frame from the 2D model which we have seen okay yeah here it is I just copied that frame and added strut tubes uh provided a member specification of trust to the strut tubes and added a property for those things okay so similar to the previous one I'm applying same 1 Kon load here as well so since it is a 3D what do you think whether this Frame will withstand that Force or this two will collapse let us go to the deflection here it is collapsing as well the frame is not even standing it is totally flat the deflection is coming around 2.2 78 there it is 2.3 into 10^2 here it is 2278 into 10^2 so mostly the same kind of behavior so either a 2d or 3D a steel portal frame is not inter Ed to take any of the longitudinal forces then here comes a question how does this longitudinal force or with standard by structure that is where bracings comes to action so we would have seen several building failures similar to this one in the video the complete structure collapsing down because of the poor erection process where they missed the bracings right so prings and struct tubes will take care of these longitudinal forces and pass it on to the supports let us see that in an action okay so let me quickly create bracing to this particular frame okay yeah the beam is added let me create a property for a solid round 24 then for the specification I'm going to provide member tension okay that's fine let me check whether material steel is provided to all the member yes it is provided okay now let us see how the building is going to behave if we go to post processing now there is no much of a deflection here it is just 641 mm so once the bracings were installed the total longitudinal deflection is being absorbed so whatever forces which we provide on the longitudinal direction is taken care by these bracing forces you can ask whether these forces since these bracings are connected to our rafs whether we won't be having any forces on the Rafters there will be a very minimum forces say for example let us compare the internal forces of this 2D and 3D frame for the 2D frame before that let me remove that additional load okay so I'm deleting it let me analyze this Frame now yeah is done if we go and check the frame it is having a moment of 73 around 74 and 150 compression if you come here check the this particular column it is 714 and 151 comparision which is nearly equal next 714 and 94 which is 73 again 74 and 96 if we get to see the rich piece 294 119 this is 290 and 118 yeah the results were very much similar the only thing is like we are having a very minute here in a 3D we will be having a very minute minor axis moment other than that the internal forces are same with this we can come to a conclusion that comparing 2D and 3D there is no much of a variation in terms of internal forces nor the deflection say here if we check for the serviceability cases the deflection is 42 and 119 there we got 42 and 117 so it is slightly varying but not much of a deviation so if you are designing a simple vrow kind of structure without any much of a longitude component say for example a huge Meine a very high fascia like that if those things were not there and you are going to design a simple frame then it is 100% good to go with a 2d design itself it will save lot of time considering you know how to calculate the bracing forces in toi and don't worry if you don't know how to calculate the bracing forces I have made a specific video on this top iic I will be providing you the video on the cards above and you can check the same in the description as well so upon going through that video we will get a clearcut picture of how to calculate the bracing forces manually for our 2D design assumptions right so in order to conclude this session either 2D or 3D both are giving a nearly same kind of result so unless and until the longitudinal force is more or like it is very hard to predict the force path of this longitudinal force moving to a 3D analysis design is not required a 2d is more than sufficient it saves a lot of time and this video is a proof for that with this said I will catch you guys in the next video please you stay till this end please give a thumbs up and comment out your views on this particular video