 Study Reminders Support
Text Version

We will email you at these times to remind you to study.
• Monday

Tuesday

Wednesday

Thursday

Friday

Saturday

Sunday

Video 1
Now I am going to discuss about certain steps which we should follow in case of design oftension member. So in last few lectures we have seen that how to calculate the designstrength of the tension member and we have seen that tension member may fail due to itsgross yielding, it may fail due to rupture of the net section, also it may fail due to block shear.So these three aspects we have to see as well as one another thing we have to that is theslenderness ratio means radius of gyration and allowable slenderness ratio.The member which we are going to consider whether it is exceeding its limiting value or notthat is necessary from serviceability criteria point of view. Therefore these four aspects wehave to keep in mind while designing the things. So if we can develop methodologymethodology means the steps that what are the steps we will follow whether we first calculatethe slenderness ratio and we will try to find out the section or we will calculate the designstrength due to block shear, then we will find out the section that we have to decide, right.So in today’s lecture I will give an overview of the steps to be followed and then I will cometo the some flow chart that how if I write a program then how flow chart can be developedand how algorithm we can develop at our own, so that we can make a program and we canmake it useful we can make it useful in the sense that we have seen that design calculationTds we have to calculate lot of things, lot of complicated expressions are there.So when we are going to design means it is a repetitive process repetitive process means wecan start with certain angle section or certain other section but that may fail or may beoverdesigned. So we may have to reiterate again, right. So doing all the things for everymember it is Tds job. So if we can develop a program at our own in an customized mannerthen it will be useful and easier and helpful for us for designing a tension member in aneconomic way and in a short time, right.
So if we come to the steps we will see that first step is we have to find out the gross areabecause the design because the load acting on the member is given that is Tu the ultimateload means the factor load that is given if the factor load is given then how do I decide themember, right. For a particular member if some factor load is given then how to start that canbe started with the use of gross yielding of the section from that we can find out aapproximate area because in our experience we have seen you can see in the previousexample also we have seen that the least strength comes generally due to yielding.So first we will try with yielding, we will try to find out the gross area then we will choose asection and then we will go for other sent criteria we will see whether it is fulfilling thecriteria of not if it is not fulfilling then we have to go for higher section otherwise we canmake use of it, right.So first we will find out the gross area to carry given factor load Tu considering the strengthin yielding from the following expression that is we know Tu is the means Tdg is the Agfy bygamma m0. So from that equation I can write that Ag is equal to Tu into gamma m0 by fy,right here Tu is the factor load that load coming in the member with certain factor.Then from this Ag the gross area we can find out the suitable shape of section means first wehave to design whether we are going for angle section, or channel section, or some othersection, right. So depending on the shape of section we will go to the IS handbook and thenwe will find out what is the gross area available for a particular section, right.
So first we will find out the shape of the section whether it is I section, or channel section, orangle section then we will find out what should be the section size, right. So that section sizecan be found from this gross area if we know the gross area then we will go to correspondingarea of that angle section or other section and then we will choose a section whose gross areais slightly more than the gross area obtained in step 1, right.So member what we will be choosing its gross area will be more than the gross area obtainedin step 1, because it has to satisfy this criteria, right and I mentioned already that usually ifminimum edge and pitch distance is maintained, strength in yielding gives least value, right.So design will be safe if gross area provided is greater than the gross area required so heregross area required is this and we will provide slightly higher gross area and accordingly wewill choose a particular section depending on the requirement, right.Then what we will do one section is chosen section is chosen means two things we arechoosing one is shape and its size, shape means whether it is angle section or channel section,or some built up section this is one thing and then size what should be the size, size of thesection should be in such a way its area should be more than this area required area, requiredgross area, right.And then we can find out the number of bolts or the welding length required and we canarrange the bolts.
So what we will do next that we can find out a particular bolt means we can choose adiameter of bolt and then we can find out the pitch, edge distance, right and then we can findout what is the shear strength of this bolt Vdsb shear strength of the bolt, then bearingstrength of the bolt Vdpb, right.So from this we can find out the bolt strength and then we can go to find the number of boltrequired, right and this number of bolt we can find out from the total load coming that Tu bythe shear strength, ok. So shear strength oh sorry strength of the bolt so say Vb, so if Vb is thestrength of the bolt and Tu is the factor load then I can find out the number of bolt if we aregoing to use bolt connection.And if we are going to use weld connection then also we have to find out the weld lengthassuming size of the weld, we can assume certain size of the weld depending on the platethickness or angle thickness we can assume certain size of the weld and according to the sizeof the weld we can find out the strength depending on the material properties of the weld weare using. And then we can find out the length required to withstand that much tensile loadthat is Tu, ok.So in second step what we can do sorry in third step what we can do we can find out thenumber of bolts and its positions that means how we are going to make it whether it is chainbolting or zig-zag bolting, so those things we will see and what will be its pitch distance,what will be edge distance, so all these things we will fix or if we go for weld connectionwhat will be the weld length distribution in top and bottom and what will be the size of weld,what will be the length of weld so everything will be decided, right.So in step three we have to do that because if we do not do that we will not be able tocalculate Anc value and Ago value, net area of the connected leg and gross area of theoutstanding length also we cannot find out the shear lag width unless we know shear lagwidth we cannot find out the factor beta then we cannot find out the strength due to rapturethat is Tdn, also later we cannot find out the block shear strength.
So to find those things we have to make detail of the connections, right. So once we do that instep 3 we can go further to step 4 that is in step 4 we can find out the yielding of the grosssection that means Tdg, then rapture at critical section we can calculate this also, thenstrength in block shear, right. So these three we will consider and we have to see the Tu valuethe load acting on the member the tensile load that should be less than these three, this Tdg,Tdn, and Tdb, ok this has to be less.That means so it has to be less if it is not less then what we will do we have to increase thesize of the section, right. So if any of the above strength become less than the factored tensileforce so so if if any of the strength become less than the factored shear force Tu then we haveto increase the size of the section, right if it is more than the Tu then find that means if designstrength is more than the applied load then it is fine otherwise we have to increase the size ofthe section and we have to repeat 3 step 3 we have to repeat, that means step 3 we will doagain and again we will go for step 4, right.So what we could see here that we have to find out the yielding of gross section, rapture ofcritical section and strength in block shear and these three strength should be greater than theTu otherwise we have to increase the section size and we have to repeat the steps so that thisthis criteria is fulfilled.
Next what we can do in step 6, that if we see the if the design strength that means minimumof these three in step 4, is too high compare to factored load then also we can decrease thesection size suitably and repeat from step 3. That means if we see the design strength is quitehigher than the applied load applied load means the Tu the axial tension if the design strengthis quite high design strength means least of Tdg, Tdn and Tdb that is the design strength, ifdesign strength is quite high then the Tu value that applied load then it will be a conservativedesign that means it will be uneconomic whatever section is required we have consider biggersection.So what we can do we have to means we can go with this one or if we make if we want tomake economic design then we have to reduce section size and again we have to follow fromstep 3, right.And once it is over we can check the slenderness ratio of the member and the limiting valueis given in table 3 of IS: 800-2007. Now if the value of slenderness ratio exceeds the value ofgiven in the code, then this is not ok that means what we have to do then we have to increasethe size of the section and redesign redesign means again we have to go to step 3 and we haveto check all the things, right. So these are the steps which we have to follow for designing atension member.
Video 2
Next I will show uhh the flow chart diagram of the of the developed algorithm and I willshow some screenshot of the developed code and one program I will run and I will show howthe things are means outputs are coming and how we can make it useful, right. So it has beendeveloped in MATLAB program and also it is graphical user interface based program, so as itis GUI based so it will be user friendly means user can easily make useful of this programand they can find out the intended section due to a particular load.
So in flow chart if we see the flow of the program will be like this this is basically based onthe steps whatever I have discussed in earlier slides that is first what we will do is thecalculation of cross section require that is from the gross yielding we can find out what is thegross area require that is Ag once that is find out then what we can do we can decide meanswe can we have to decide whether we are going for bolt connection or weld connection.So from gross area we can find out the smallest angle with cross section area greater than thecross section area calculated or taken before and thickness of length of connected leg largerthan taken before, ok.So as per the requirement with there we are going for bolt connections or for weld connectionthe program will flow accordingly if we go for (weld) bolt connection then we have to seewhether length connected leg is bigger enough to fit the bolt if not then we have to go and wehave to again increase the section size otherwise we can go for calculation of number of bolt,ok.So after that we will go for calculation of design strength of angle due to net section rapture.So (net) rapture of net section we can calculate the design strength in other way also we canstart with welding. So from that we can find out the minimum weld length require and welddistribution also we have to do then we will find out the rapture strength. That means oncethe section is selected either we will go for weld connections or we will go for boltconnections accordingly number of bolts and its distribution can be decided and then rapturestrength can be calculated or if we use weld connection then also we can distribute therequirement of weld length properly and then we can find out rapture strength.So as per the necessity we will follow the path, that means when we will right the programwe will right in such a way that as per the choice of the user it will flow the path.
Next is we will calculate that is angle safe in next section of rapture that means the rapturestrength we calculated in earlier step. Now if rapture strength is less than the applied forceapplied tensile force then we have to go to the earlier step to increase the section size, right. Ifit is not less than we will go for either welding or bolting as we have decided, that means if itis bolt then what we will do that we will find out the gauge distance and other things to findout the block shear so we will calculate the block shear.And then if block shear due to block shear it is going to fail then what we can do we canchange the gauge distance and we can redesign it, right means without changing the size ofthe section otherwise if it is not going to fail then we will go next step. Similarly here also incase of welding we check for block shear then if angle is safe then fine if not then either wewill increase the length of the weld and then we will recheck or we will go for higher sectionwhatever we feel we can do and if it is safe then we will go to next step next step means forbolt case also we will go to next step, for weld also we can go to next step.
So in next step so what we have seen that the strength due to block shear, strength due torapture is more than the the applied load, if it is so then it has come to this step, if it is no thenit has gone to the earlier step to increase the section size, so once it is over the strengthcalculation is over we will go for check for slenderness ratio. So the slenderness ratio limitwe know from the codal provisions and if the slenderness ratio is less than the allowable thenit is fine if it is no then we have to go for increase of the section size, so that the slendernessratio is becoming more, right.And if slenderness ratio is less than allowable then we can say that angle is ok. So in this wayone can flow its program so that he can write the program and find out the intendedcalculations.
Video 3
Now I will show some snapshot of the developed program as I told that develop program wasdone using MATLAB and in MATLAB you have options so this programs were developed bysome of my students during summer summer intensive course. So in fact you can develop inother way means according to your requirement in the industry or in your case, so you candecide what should be the GUI and what are the options you want, right. Here we have givencertain options like if you see option is that one is single angle section with bolt connectionsand single angle section with weld connections that means according to our option chosen wecan find out the design calculation, so one is the single angle section with bolt connections orsingle angle section with weld connections.Another option is two angle sections placed back to back on the same side of gusset plate,right and two angle sections placed back to back on the opposite side of gusset plate. So theseare four options at that time we have considered you can choose any other type also like hereonly we have considered the angle sections, you can consider channel sections and you canfind out its design strength also, you can consider any other sections also as you wish, just fordemonstration purpose we have used this and then once you choose a particular type then youclick on this give input values. So once if you click then you can go to next one, right.
So here another snapshots I have shown that is if you choose this one that is that is if youchoose two angle sections placed back to back, so it will be like this on the same side ofgusset plate. Again if the angle sections are chosen on the opposite side of gusset plate it willbe like this. So for different options different pictures have been given, so that the user canunderstand properly.