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Module 1: Design of Tension Members and Connectors

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Design of Splices in Tension Members

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Video 1
Now I am going to discuss about splices with respect to tension member, in fact splices areused if the available length is less than the required length of a tension member. When thesingle pitch of tension member of requisite length is not available then we may have toconnect with another pitch of member with the use of splices.So different type of tension members we have, so when we are joining those tensions memberwith the use of splices we may face different type of problem like if we do not join two sidesproperly then eccentricity of the joint will come into picture and because of eccentricitymoment will come into picture.
So we have to design the splices such a way that no eccentricity is developed, say forexample if we consider a member, we need to join this member with another member, right.So if we want to join these two members, now if I provide a splice here, then it will not besymmetric. So transfer of the load through splice to another member will not be doneproperly means eccentricity will develop.So to avoid that we always try to provide another splice in this direction, so that thesymmetricity is maintained, this is what we need to do. However this is a problem when oneangle is to be joined with another angle, right. So if we have unsymmetrical joint like thisthen the forces will develop here and because of that eccentricity will come into picture, sowe have to keep in mind that eccentricity does not take place that how can we do, say for thisangle section say angle is like this right so if we see.Now we can join a splice here in two section, right and to make the system concentric whatwe can do, we can join a splice here and we can join another splice here. So this is the way ifwe do then the problem can be avoided. So while making splice design we have to try tomake joint in such a way that eccentricity does not occur.Another case can happen if two members of different thickness are joined. So in such caseswhat we can do we can make a splice in this place but here we have to provide a packingplate. So we have to provide a packing plate to fill up the gap and then we can provide asplice like this.
So what I discussing let me tell in short once again that the strength of splice plate and thebolt which are joining them should be able to develop strength equal to design load. Thatmeans the strength of the plate whatever we are joining should be same to the strength of thisplate and this plate, right.Then when tension members of dissimilar thickness are to be connected, packing or fillerplates are introduced what I discussed earlier that if thickness are different then we have touse packing plate or filler plate. Now the design shear capacity of bolts carrying shearthrough a packing or filler plate in excess of 6 mm shall be decreased by a factor as given byβpkg = 1 – 0.0125tpkWhere, tpk = thickness of the packing plate in mmAnother thing is, as per IS specification, the splice connection should be designed for a forceof atleast 0.3 times the member design capacity in tension or design action whichever ismore.
Video 2
Example: Design a tension splice to connect two tension member plates of size 200  10and 220  12. The member is subjected to a factored tensile force of 280 kN. Use M20grade 4.6 ordinary bolts for the connection.Splice will be provided in both sides of the tension members. Therefore, bolt value needs tobe calculated for double shear.Shear strength of M20 bolts in double shear
Now it is interesting to note that the splice plate is provided in such a way that it is becomingsymmetric, so we are maintaining the symmetric of the section so that the eccentricity doesnot develop in the member.So this is all about the design of splice plate as well as I am completing today the design oftension member. In case of tension member we have seen how to find out the design tensilestrength from different criteria like yielding of gross section, rupture of net section, blockshear failure. So from those three points of view we have to design the member, also we haveto consider the slenderness ratio value so that the it does not exceed the limiting value of theslenderness ratio.Also we have seen that when the required length is not available in case of tension memberthen we have to join 2 members with the use of splice that also we have discussed today andalso we have discussed about the lug angle, how to provide lug angle that also we havediscussed. So with this I would like to conclude the tension member design, thank you.