we will be discussing about the double lacing system andwe will see how to design the double lacing system. The design procedure will be more orless similar like single lacing system except the certain configuration of the lacing like whatwill be the spacing of the lacing. Double lacing system is used when we need less spacingbetween two lacing systems and it is required when the main compression members are weakin a certain direction means from radius of gyration point of view.So if the slenderness ratio of a certain member is very weak in a direction then sometimes weneed to provide very fine spacing between two lacing systems and in that case we go fordouble lacing system with lighter member. And in case of double lacing system also we canuse flat plate bar, angle sections, light channel section and tubular section.Now first I will go through one example today with the basis of this double lacing systemwhere we will see that if the angle sections say four angle sections are connected, then how tofind out the sectional area of the angle, how to make the spacing of the angle and then thelacing systems. So let us go through the example.
Example: Design a built-up double laced column with four angles to support an axial load of800 kN. The column is 14 m long and both ends are fixed. Assume Fe 410 grade of steel.
Here we have to provide four column four equal angle section to make the built-up sectionand this built-up sections has been shown here which will be making as a box section.Now for designing first we have to know what should be the angle section size and whatshould be the spacing between the two angles.
Now I will go to the connecting system, so in first part what we have seen that we could findthe section size of the angle and then the spacing between two members and two angles in zdirection and y direction and spacing has been made in such a way that moment of inertia inboth the direction becomes same so that the equal resistance of the column can be achievedand the spacing has been made in such a way that the strength of the member becomes morethan the actual one.
Connecting system:Let us provide a double lacing system with the lacing flats inclined at 45°. Both areprovided at the centre of the leg of angle.
So in this lecture we have understood how to find out the appropriate section of the angle towithstand that given load then how to find out the distance between two angle that is spacingin both the direction to withstand that much load and then how to design a lacing systemusing double lacing. So this is all about the lacing system in next class we will discuss aboutthe batten system, thank you.
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