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we are going to discuss about the column splices and how to design the columnsplices. Basically when a joint is provided in the length of member is called splice. When thelength of column is more than the available length of steel section, in such cases we usesplice joint. So in many cases we have seen the available length of rolled steel section in themarket is less than the required length of the column, so in that case we need to joint thosetogether concentrically so that the load is transferred from one section to another section.Also in case of multi storey building where the columns are provided along its height wehave seen the columns section, size is required less because the load coming to the columnacross the height is gradually increasing towards the ground.Therefore we need to accommodate the column section size larger towards the ground level.And as a result we need to change the section size across the height and so that the economicdesign can be done, in such cases we have to provide splices between two floors to join twounequal sections. So basically if a compressive member is loaded concentrically we shouldnot provide any splice, means theoretically we do not need to provide any splice but load isnever axial and truly it is not axial and real column has to resist the bending due to theeccentricity of the load, therefore we have to provide the splice.
So now if we see the specification for design of splices we can see that when the ends of thecompression members are faced for complete bearing over the whole area, these should bespliced to hold the connected members accurately in position and to resist any tension whenbending is present. Say for example these two columns are joined by the spliced, so basicallyto hold the two members properly we need to connect these members through splice.And when such members are not faced for complete bearing, splices should be designed totransmit all forces to which these are subjected, means sometimes it may be faced completebearing or it may not be faced complete bearing. In case of complete bearing the whole area,then it should be spliced just for to transfer the load from upper storey to lower storey right.And spliced is designed just to connect the members accurately in position, so that in positionit may stay.But in case of incomplete bearing we have to transfer the load so the splice has to be designedin such a way the load transformation from one storey to another storey are done properly.And splices are basically designed as a short column.
Now if we draw a column flange having complete bearing we can see from the front viewthat two I sections are spliced. So here if load is concentrically acting then for completebearing the splice is provided just to hold the columns in position right. So we provide splicein two sides of the flange. Basically column flange are having complete bearing and the frontview would look like as shown in the figure. Now maybe we have to provide certain boltconnection here to connect the two section using splice.So it is spliced in this position and if it is connected by bolt then maybe we can connect twonumbers of bolt at each phase of each splice right. This will be looking as side view and ifweb has to be spliced for shear, then it should look like this (as in figure) if we splice the webalso then it will look like this (as in figure).Where splice will be provided for shear we can provide bolt at the flange to make a completebearing, and also at web we can provide splicing. So this is web splice for shear. So these arethe columns flanges having complete bearing.
Now let us see what are the steps we need to follow so that we can design the splice properly.Step-1:For axial compressive load the splice plates are provided on the flanges of the two columnsections to be spliced.If the column has machined ends, the splice is designed only to keep the columns in positionand to carry tension due to the bending moment to which it may be subjected. The spliceplate and the connection should be design to carry 50% of the axial load and tension.If the ends are not machined, the splice and connections are design to resist the total axialload and any tension, if present due to the bending moment.• The load for the design of splice and connection due to axial load,Pu1=Pu4 (For machined ends)Pu1=Pu2 (For non machined ends)Where, Pu is the axial factored load.• The load for the design of splice and connection due bending moment,Pu2=MuleverarmWhere, lever arm is the c/c distance of the two splice plates andMu is the factored bending moment.So then we will calculate total Pu on the splice plate, which will be Pu1 + Pu2.
Step-2:Splice plates are assumed to act as short columns (with zero slenderness ratio). So theseplates will be subjected to yield stress ( f y ).Step-3:The cross-sectional area of the splice plate is calculated by dividing the appropriate portion ofthe factored load coming over the splice by the yield stress.c/s area required ¿Pu1+Pu2f yStep-4:The width of splice plate is usually kept equal to the width of the column flange.Width of splice ¿bf (width of flange)The thickness of the splice plate can be found by dividing the c/s area of the plates with itswidth.Therefore the thickness of the splice plate can be found by dividing the cross sectional areawith its width. That means whatever area is coming area divided by width of flange will bethe thickness. So this is how we can find out the thickness of the splice plate.
Step-5:Nominal diameter of bolts for connection is assumed and the strength of the bolt is computed.Step-6:In case of bearing plate is to be designed between two column sections, the length and widthof the plate are kept equal to the size of lower-storey column and the thickness is computedby equating the ultimate moment due to the factored load to the moment of resistance of platesection.
So in case of bearing plate if it is to be designed between two column sections then we haveto consider these aspects. So these are the steps which we need to remember. Now followingthe steps we will go through this example and we will be able to understand how to design asplice.Example 5.12: A column ISHB 300 @ 576.8 N/m is to support a factored axial load of 500kN, shear force of 120 kN and bending moment of 40 kNm. Design the splice plate andconnection using 4.6 grade bolts. Use steel of grade Fe 410.So the example is like this a column of ISHB 300 at 576.8 Newton per metre is to support afactor load of 500 kN. So Pu that P total factor load is 500 kN and shear force 120 kN andbending moment 40 kN.So three type of forces are there right factor load P is 500 kN and shear force is given 120 kNand bending moment is coming 40 kN metre. Now design the splice plate connection using4.6 grade bolts and let us use steel of grade as Fe 410. So if we use this this data then we willsee how to design the splice plate, due to this axial load and shear force and bending moment.
So if we provide 6 number of bolts then we can find out the length of splice plate.Length of the splice plate 2×(2×60+2×35)=380 mmProvide a splice plate 380×250×6 mm on column flanges as shown in the figure.
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