- 2 days ago
Learn how to model a steel truss in STAAD.Pro with clear step-by-step guidance. This video covers member creation, load application, and detailed discussion of structural concepts—perfect for civil engineering students and professionals.
#STAADPro #SteelTruss #StructuralEngineering #TrussDesign #CivilEngineering
#STAADPro #SteelTruss #StructuralEngineering #TrussDesign #CivilEngineering
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00:00now in this lecture we shall learn that how we can design the trusses that we
00:05have to you know design in our day-to-day basis so many times we do get
00:10a problem that where we have to design the structural steel trusses for a
00:13project now before designing you know we must have done this n number of times
00:19in your we can say college or undergraduate studies the thing is that
00:23the concepts are different when you know we are designing the theoretical trusses
00:27and the concept is completely different when you are designing the practical
00:32trusses in your structural engineering practice now the first thing that you
00:37do need to understand here is that the first concept for the truss is that the
00:42supporting conditions now you must have read about the supporting conditions in
00:46your we can say college lecture also so the ideal condition is that at one point
00:52it has to be ruler and at the other point it has to be either you know
00:57we can say restrained along both the axis that only for the we can say vertical
01:04loads and the later loads not for the we can say bending moment so as a simple you
01:10know the first concept for the trusses is that on the edges there should not be like
01:15we are transferring the bending moment here so the ideal condition here is that we
01:20do have to like let us say if you are designing this particular truss in the
01:24start software so in the start what you need to do here is that we do need to
01:29assign a ruler support here and at this particular point unlike in your college
01:34studies you do only have we you know the vertical and one degree of lateral
01:40restraint but in start in addition to being the vertical here also obviously
01:44ruler means the vertical restraint you do have to provide the restraint along you know
01:51the this particular direction so for this particular direction whatever you know the
01:57lateral force is coming it has to be restrained by this particular direction but the thing is
02:04that in the case where you are designing multiple number of trusses and joining them also so in
02:12that case it is not that you can provide only one lateral restraint along this axis you have to provide the
02:19later restraint along this axis also and for this particular case also restraint has to be provided along in this
02:26particular direction that is out of the plane or we can say along the perpendicular to the plane of this particular
02:33truss so that is the you know mistake that most of the structural engineers that I have seen do you know when they
02:41design the practical structures many times in my practice what I have done seen here is that many engineers what they do
02:49they do assign a fixed support here so there is no such harm in doing that obviously we can design a truss for the
02:57fixity at this particular base but again instead of this what we can do if you want to assign a fixed support here
03:05then instead of the truss you can have a beam here so that shall become simply a portal frame so there is no as such logic in
03:16selecting the fixity for a truss section it is always recommended that we do have to play with the
03:23behavior of the truss what is the behavior of the truss the behavior of the truss are majority of the axial
03:29forces only we don't talk about any kind of bending moment when we are talking about the truss design
03:38there is one more thing that you do need to understand you know when you are designing the
03:43space truss in real let us say a space truss is there in front of you can you say that not even a 0.1 kn
03:52meter bending moment shall be there obviously 0.1.2 kn meter bending moment shall be there but again that
04:00shall not be because of the we have to you know provide that that shall be because there may be a little bit of
04:06eccentricity there may be a little bit of we can say minor bending moment getting developed because of
04:12either eccentricity in the supporting condition eccentricity in the fixing condition or we can say out of the
04:18plane wind load also let us say this truss is there in the open so when wind shall be striking on this
04:24particular member there shall be bending moment along the minor axis so it may bend but the thing here again is
04:31that we do have to ensure that whatever you know supporting conditions are there whatever actual site
04:38conditions are there regarding the loadings on the basis of that we have to stimulate the type of the
04:44truss support and the type of the fixing members now again you know when we are talking about designing the
04:51truss either in STAT or we can say ETABS or we can say SAP 2000 the principal concept here is that you can do
05:03the 2D analysis also and you can do the 3D analysis also so either we can proceed with 2D or we can proceed
05:10with the 3D analysis so ideally what I recommend here is that you know the correct practice here is that we can design the
05:20truss as a 2D truss correct or we can say it gives us better efficient results efficient in the terms of the
05:29economy if you design a truss in the 2D analysis that shall be lighter as compared to when you should design
05:38a truss in the 3D analysis so both the options we can do that is up to you and it shall be a little bit heavier
05:46I can I must say if you are designing the truss in the 3D analysis because ultimately a member whatever member
05:54that we are providing that has to you know resist the forces along all the three axes so that is why
06:02ideal condition we can proceed with this but if you think that the truss is an open or we can say there are a lot of eccentricities
06:12or you are not sure about whether you know the construction quality shall be that great you can proceed to the 3D analysis
06:19so now the coming back to the start as I said what we shall do here is that we shall do the 2D analysis
06:26now principally start gives us three option either we can proceed with the space or we can proceed with the frame
06:33or we can proceed with the truss the good thing about truss is that when you are doing the truss stard analysis that is you are telling the stard that this is a truss
06:47in that case there shall be zero bending moment there shall not be even a 0.1 0.2 kn meter bending moment but if you tell the stard that it is a space it shall simply get converted into 3D analysis in that there may be a little bit of 0.1
07:020.2 or 0.2 or 0.5 or 1 kn meter bending moment depending on the loading conditions that you are providing in all of these trusses members
07:09so before here one more thing that you do need to understand if you are providing that we can say truss here you do need to you know confirm that we have to provide the pearl and salts on the top
07:29so these are the usually the C pearl lens that you must have studied in your we can say college or undergraduate studies also
07:36so in that what we usually do is that this spacing becomes important that is the distance between these two pearl lens usually it is in the range of 1200 mm to 1700 mm
07:51it may you know be any of these numbers ideally you know wherever we can say that wind load is quite high in that case we can proceed with 1200 mm
08:05or like in pre-engineered building structures the one that you must be seeing in all around India like majority of the warehouses in that case what they usually do is that they take the spacing between the two pearl lens
08:20as 1600 mm to 1750 mm also but on the condition that they do provide the tie rods here
08:27so these tie rods they are like a solid rods of either we can say 12 mm dia or 16 mm dia depending again on the wind loads
08:38so what basically happens is that in like in majority of the pre-engineered building structures that you are seeing across India
08:44they do assign the pearl lens they do assign the pearl lens as a cold form C pearl lens that also we shall you know design in a separate lecture
08:51so they take this as a either as a Z pearl lens or C pearl in itself
08:59so these are the cold form members their their thickness is in the range of we can say 1.6 mm or 2 mm or in the cases where the wind load is quite less in that case the thickness may becomes
09:131.2 mm also so that is the case with the we can say Z pearl lens or C pearl lens
09:20now why we are discussing here is that this spacing here that is the planning of these members that is dependent on the spacing of these pearl lens
09:28so what we shall do is that in our case let us assume that this stress span is in the range of let us say 20 meters and this height now again this slope this slope has like two values either you know we can proceed with 1.4.5 or we can proceed with 1.6 it is not that you can not go with any other number you can go for 1.6
09:57you can go for 1.7 also 1.8 also and in like in pre-engineered building structures the slope that they usually take that is 1.10 so if you have an interview in any of the we can say pre-engineered building organizations this is the number that you do need to remember that the slope of the pre-engineered building structures that is usually taken as 1.10 so it means that let us say this span is 30 meters
10:26so it means that height here at the apex point this height shall be 3 meters that is 3 divided by 30 or we can say 1 is to 10 similarly in this case let us say here we are talking about 1 is to let us say we take the slope as 1 is to 5 in between value we are free to take any kind of you know slope
10:48so in that case so in that case uh sorry uh it should be 1.5 meter my part because you know the distance here it should be uh l by 2 so uh 1.5 divided by 15 uh i'm sorry for this mistake
11:06the thing here is that it should be uh 1.5 divided by 15 or we can say 1 is to 10 so height here it should be 1.5 meter
11:19uh the height of the uh pb remember here similarly here if we are talking about let us say 1 is to 5
11:27so the distance here is 10 meters so if we take 1 is to 5 the height here it should be 2 meters so
11:35according to that you know we can we shall proceed with the stat so that uh we shall make uh this span here
11:43is 20 meters and this height here is 2 meters considering that the slope of our process 1 is to 5
11:51and the spacing we can take it as 1500 mm center to center so we can open the start software here
11:59now the thing that you do need to understand here is that we are working on the latest uh start version
12:06so if you have an old version that you can uh you know check for my other uh courses that are using the
12:16uh older versions of the start uh but keeping the course updated i am referring to the latest
12:23start version here so here we can refer to the first of all we do need to tell the uh start the
12:29we can say of units so in here you know if you are not getting this editor option you can click on this
12:36option and here you can switch on the command file analysis output it shall save a lot of time
12:41of you so uh opening that we can say this particular start editor option here the first thing that we
12:49do need to tell the start is the units so we can enter the units as meter and kilonewton let me just
12:59zoom in the screen so in here we can enter the joint coordinates so my approach here is that i always
13:07prefer to open the editor first enter the units enter the uh you know or we can say model the
13:17node at the origin and then start replicating as per the our requirement so we can go to the select
13:25and node cursor here we can press shift and k shift and k option on a keyboard so here is the
13:33node that we have modeled and that is at origin that is zero zero and zero and the span of the
13:39truss that we have selected is 20 meters so we can select or we can enter x here is 20 and we can go to
13:48the geometry and add beam option here so we can model the beam from this point to this point we can go to
13:54the select beam cursor select this beam right click here insert node add midpoint left click on ok
14:02now we know that the slope of the truss that we have selected was one is to five so the height of
14:09this truss that has to be two meters so we can again go to the geometry add beam option here
14:16here we can enter this uh you know trust from this point to this point now the main question comes that
14:23you know we have to consider the purlins here so one of the option here is that you can you know
14:29model the truss in the autocad software and on the basis of that you can you know measure the
14:35distances in the autocad and then model them in the start software second option is that
14:41we can just right click here left click on insert node here we know that the length of the beam is
14:4810.198 so if we want around we can say 1.5 meters so we can try entering at ns 7 points so here the
14:57distance become 1.2748 we can click on remove so instead of 7 we can enter 6 points here so distance
15:05is in the range of we can say 1.5 meter so this distance become approximately 1.45 meter here
15:11so we can left click on ok here and we can go to the geometry add beam by perpendicular intersection
15:18we can drop the intersections here we can go to the view front view here we can drop the
15:26intersections here by modeling the beam from this point to this point here now the same exercise we
15:35can repeat on the left side also but there is a shortcut for that what we shall do is that we can we can
15:41again go to geometry add beam and here we can enter the diagonal or we can say 45 degree truss members here
15:53so now we have modeled the particular truss now there is two approaches there are two approaches one
15:59approach here is that we can again replicate the same process here or what we can do we can just
16:04simply delete this let click on ok delete these nodes yes and we can select this particular address
16:13go to geometry and here we do get an option of having a mirror so mirror plane we can keep it as yz here
16:20we can see yz plane node on plane we can select this particular node and we can click on copy here
16:28so we have simply saved a lot of time of us just by you know replicating that in the or we can say taking
16:35a mirror as a model so we can go to the beam tools and here we can select merge beams so with that we can
16:43simply remove this particular node so now we have modeled the truss here and we can check the distance
16:51by going to utilities node tools and node to node distance and we can like select from this point to
16:58this point this span is 20 meters and this height here obviously uh that is in the range of we can say
17:05uh two meters itself so that is well understood that how we can model the truss members in the star
17:13software now the second thing obviously we can select the properties here also
17:18now in india you know we do have two options either we can proceed with the box sections
17:25or we can proceed with the angle sections now if we are proceeding with the box section we can either
17:31proceed with the rectangular hollow sections or square hollow sections or we can proceed with the
17:38circular hollow sections also but that is not recommended because fabrication or circular hollow
17:43sections is is a little bit difficult so for that what we can do we can you know uh proceed with
17:49either first of all we shall uh model the and analyze and design with the angle sections
17:57theoretically that is the first that you do need to understand after that we shall you know model
18:02the same truss with the uh rectangular and square hollow sections also so first of all we can go to
18:09the legacy sections here this is the thing that you know that has been updated in the latest chart
18:16earlier there was the section database option but that has been simply replaced with the legacy
18:22or there is you know we can click on the standard option also here so if we click on the standard
18:29obviously the graphical user interface of this option is a little bit better as compared to the
18:34legacy option so in here we can select the india and after that we can select angle equal and in
18:42here we can select let us say we proceed with 75 by 75 by 6. there is one more thing that you do need to
18:49understand it is not that all the sections that you can see here are available that also i have seen
18:56many engineers doing that what they usually do is that they select 50 by 50 by 7 but that member itself
19:03is not available in the market so we don't need to make a structure which is fabrication friendly
19:10so first of all we can proceed with the 50 by 50 by 6 section here and we can left click on add
19:19similarly we can select 75 by 75 by 6. first of all the section that is available in the market is 25
19:25by 25 then 40 by 40 then 50 by 50 then 65 by 65 and then 75 by 75 so we can proceed with 75 by 75 by 8
19:35section also and if required we can add 100 by 100 by 10 section also so we can left click on 100 by 100
19:44by 8 section also so uh first option is single section second option is that we can take the double
19:51section also that is this kind of section so usually the outer members that we can see here on the outer
19:57periphery usually they taken as double angle only so uh as per you know preliminary assessment what we
20:04can see here is that 75 by 75 by 8 long leg back to back double angle material we can take it as steel
20:11spacing we can take it as 0.01 because we do have to fix the plate inside so we can left click on add here
20:20so what we shall do is that we shall select the outer periphery members as double member rest of the
20:25members we can assign it as per our requirement so uh we shall you know uh i hope the concept is clear
20:32to you so in the next lecture we shall learn that how we can assign the properties assign the loading
20:37and accordingly how we can design the trust sections
20:47you
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