This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
Taking one rib and the base half way on each side between the next rib would give a section at the box, which may be taken as the fixed end, similar to Fig. 222. Calculate then the position of the neutral axis and figure the moment of inertia of the section about this axis. Having determined the bending moment for the width between the ribs, the fiber stress in tension and compression can be found by the formulas used in calculation of beams. f= My/I where M is the bending moment in inch pounds, y the distance from the neutral axis to the extreme fiber, and I the amount of inertia.
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A section must of course be assumed at the outset and it may be necessary to modify this to come within the requirements. It is necessary also to calculate the stresses at the most unfavorable sec-tion, and to see that there is sufficient metal across the corners to prevent cracking diagonally between the foot of the ribs on adjacent sides.
Different sections of columns require, as previously stated, different sections of box under the column, and this would affect the arrangement of the ribs more or less. These ribs in general should be at an angle of 45 or GO degrees. In some cases lower bases can be used, but these are of course subject to greater bending strains.
1. Given a 12-in., 31 1/2 Mb. beam framed to a column at each end, the distance between faces being 12 ft. 2 1/2 in. The beam has two 7-in., 15-lb. I-beams framed on one side and opposite these in each case is a 12-in., 31 1/2-lb. I-beam. The distance from center of connections to the face of the column at each end is 3 ft. of in. Make a shop detail of the 12-in. girder, all beams being flush on top.
2. In the above problem, if the 7-in. beams frame at the other end to a 12-in., 31 1/2-lb. beam along a wall, both being flush on top. and it is 11 ft. center to center of girders, make shop details covering both 7-in. beams.
3. Given a 15-in., 33-lb. channel framed to a column at each end, the distance being 16 ft. 5 1/4 in. between faces, and the channel having a 3 1/2 X2 1/2 x 1/4-in. angle on the back side, with the long leg vertical and 1 3/4 in. from the bottom. A 10-in., 25-lb. beam frames flush with bottom of the channel 5 ft. 4 1/4 in. from face of each column. Make detail of above.
Hill Building Columns. Fig. 223 gives the detail of the columns shown in Fig. 186, Part II, and by the plate on the preceding page. This is a latticed channel column. Each flange is double laced, that is, it has two systems of lattice bars. In many cases such columns have only one system across each flange; in such cases the bars on one flange would cross those on the opposite flange; just as if one system shown by Fig. 186 was on one flange and the other on the other flange.
This column has a bracket for a crane track girder with a diaphragm bracing the crane girder to the column. The roof column, as shown by Fig. 186, is a plate and angle column and sets down between the channels, as the web runs at right angles to the web of the channels. It is always better to avoid re-entrant angles in a plate if possible. In a case like this where a bracket plate comes into the lines of the column at the top and there is a plate the width of the flanges above this point, it is better to make this a separate plate. If this plate is necessary for the effective area of the column the joint can be faced. The bracket and shelf angles on the plate are for a beam framed between columns.
Figs. 229, 230, 231.
The student should be able to follow this detail and understand all the points without further explanation.
Fig. 224 shows another type of column made of a web plate and four angles with channels across the flange angles, the flanges being turned in.
There are various reasons for turning the channels with flanges in; here it is desirable to have a 10-in. arch for stiffness, and the thickness of the wall in which this column comes makes it necessary to turn the flanges in; this also allows the column to set flush with the inside face of the wall and gives a smooth surface. Then again, this gives good connection for the cranes girder bracket and for the wind strut below, at N and O.
The top of this column receives a heavy floor girder and another column; the latter column is made of a smaller web so as to provide a seat over the main column members for the girder. Fig. 225 gives a detail of the wind strut which frames between the columns.
In columns of the type shown in Fig. 224, the dimensions must be such as to give room between the flanges of channels, and between the flanges and web, to rivet up the different members.
For light building construction columns are sometimes made of hollow iron pipe fitted with a cast iron cap and base. The dimensions, weights, etc., of standard steam, gas, and water pipe, as manufactured by the American Tube and Iron Co., will be found on page 344, Cambria Handbook. Fig. 234 gives a diagram giving the "strength of wrought iron pipe in compression" according to the formula;