This lecture will be the continuation of previous lecture where we have gone through a designexample for designing of lacing system. So in last lecture we have discussed how to design alacing system, how to provide the length of the lacing, width of the lacing, thickness of thelacing. Then what will be the spacing between two lacings, what will be the angle ofinclination so all the details of lacing has been discussed.Today we will be going to discuss on the connection part, connection part means theconnection between the lacing and the main column. So as lacing is taking certain amount ofload, we need to design the lacing with the column in such a way that the connection betweenthese two can withstand the developed load, how to calculate developed load, we havealready discussed, today also we will calculate the developed load that means the transverseshear which is 2.5 percent of the compressive load which is acting on the main compressivemember.So from that we have to find out the value of the shear and then we can find out what will bethe connection details. Two type of connections are there, one is bolt connection another isweld connections. So for bolt connection how we will be designing the bolt and weld thosethings will be discussed today. So before going to do that first I will very quickly go throughthe previous days example so that we can remind our earlier calculations which will berequired for calculating the design strength of bolt and number of bolt or weld length.
Example: Design a laced column 10.5 m long to carry factored axial load of 1000 kN. Thecolumn is restrained in position but not in direction at both the ends. Provide single lacingsystem. Use 2 channel section placed as back to back. Assume steel of grade Fe 410 and boltsof grade 4.6.a) Design the lacing system with bolted connectionsb) Design the lacing system with site welded connectionsNow we will try to find out the design of the lacing system with bolted connections anddesign of the lacing system with welded connection where we will consider the weld as siteweld or shop weld, depending on that γmw value will be decided.
So if we remind the earlier lecture we can see that we got already the solution of this that isISMC 300 back to back we have provided with a spacing of 184 millimetre, right.
In every case I have told that if the criteria is not satisfying then we have to increase eitherthe thickness of the plate or the width of the plate means case to case we have to check.Sometimes we may have to reduce the length of the lacing plate by changing the angle ofinclination, so in this way we have to find out which dimensions and which orientation oflacing will be provided so that the design of the lacing will be safe.
Now we will come to now we will come to bolted connections. Now first is we are going toconsider the bolt connection when lacings are not overlapped each other.
a) Bolted connection (If lacings are not over lapped each other)Assuming that the 16 mm bolts of grade 4.6 are connecting both the lacing flats with thechannel at one point and that the shear plane will not pass through the threaded portion ofbolt.
b) Bolted connection (If lacings are over lapped each other)Assuming that the 16 mm bolts of grade 4.6 are connecting both the lacing flats with thechannel at one point and that the shear plane will not pass through the threaded portion ofbolt.
So in this lecture we have demonstrated the connection between lacing member and thecompression member, two types of connections, one is weld connection, another is boltconnection. Again for bolt connections we have shown that if the lacings are overlapped andif lacings are not overlapped then how to calculated the forces for overlapping lacing and fornot overlapping lacing and then how to provide the number of bolt because the strength of thebolt will be different for two cases.And also we have found the dimension of the tie plate, how to find the dimensions of tie platethat also has been demonstrated through the example and then again we have calculated thesame for weld connections like what will be the length of weld required we have calculatedand how to distribute also we have shown and how to calculate the length of weld based onthe size of the weld that also has been demonstrated, right. So I hope this example will makeyou clear about the connections between compression member and lacing member.
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