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Cracked Columns. Deceitful and Correct Remedies. Columns are often cracked in cooling or in shipping. Dishonest foundry men will sometimes fill in the cracks with paint. Cracked columns are discovered by sounding with a hammer.

Some times part of a flange or lug may be broken off in setting, as in Fig. 26a. Such defects may be remedied by sawing off the broken lug at the root, and by providing a steel knee angle in place of the original lug. This angle may be bolted to the body of the column by means of 3/4 in. tap bolts, and one or two through bolts as shown in Fig. 26b, will prevent the steel angle from pulling away from the col

umn.

In the case of column to column connections where cast iron columns are used, the Building Code requires not less than four 3/4 in. bolts in each column connection. Where a flange is chipped off so that a portion containing a bolt hole is missing, and when no injury to the main column body has been caused, a heavy steel angle about 6x4x1⁄2 in. can be bolted with two 34 in. tap bolts as in Fig. 27. The steel angle has a 13/16 hole in the outstanding leg for a 3/4 in. bolt.

One more instance of cracked columns will be mentioned. A cast iron column was being lowered in the cellar, in order to rest it on top of a cast iron base. During the lowering of the column, the cog that controlled the drum of a hand derrick slipped out, and let the column strike the base a powerful blow. The flange of the column broke. Where such things are liable to happen, both column and base should be carefully inspected for cracks, by striking a few good blows with a sledge hammer.

3. Honeycomb. Columns that are badly honeycombed and all columns that have blowholes or other imperfections which reduce the cross-section of the column at any point by more than 10% should be rejected according to the Code. Dishonest foundrymen will sometimes fill in the column in such spots with molten lead. This is a very low and dangerous practice and cannot be sufficiently condemned. Careful tapping with a hammer will generally locate such spots by a difference in the sound.

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4. Sand Holes are often bored, tapped and plugged with a headless steel bolt, which is left in the column. many cases a piece of wrought iron is heated to a white heat and hammered over or into the sand This is more commonly met with in cast iron bases. Sandholes and blowholes give a dull sound on tapping. Test holes should be drilled in doubtful spots.

5. Milling. Use of Shims. All cast iron columns must have their ends milled to bear and at right angles to the length of the column. Where this is not the case, shims should be used. Good specifications prohibit the use of shims, because shims concentrate the load at points, and occasionally crack the flange; but mostly because shims cause eccentric loading on the column below.

In a 12 story structure where only cast iron columns were used the specifications prohibited the use of shims. As the workmanship of the foundry was inferior, many columns could not be made plumb, due to the incorrect milling, and some that were kept plumb by iron floor beams bolted to such columns, would only touch the lower column on edge. See Fig. 28. This brought the whole load eccentrically on the lower column, causing excessive bending. Wedges were ordered to be put in at the high end, although contrary to specifications, but just to cause less eccentricity at the low end, and to make the load of the column above come nearer the centre of the lower column.

Where shims have to be used, they should not be nails, but steel plates or wedges. Steel plates 1/16 in. thick, four to six inches wide and of a length nearly equal to the diameter of the flange may be found suitable. Two or more such plates can be used together, one on top of the other, when necessary.

6. Painting. In good jobs the ends of cast iron columns after being milled, are treated with white lead and tallow. Otherwise all cast iron work must be delivered unpainted and must not be painted until inspected and approved by the Building Department. The inspector may order any cast iron work that was painted before approval, to be washed with kerosene, benzine or other dissolvent, for the purpose of removing the paint and uncovering the metal for inspection. After inspection, all iron work must receive at least one field coat. This is usually done in cast iron work after the columns are in place.

7. Bolting. Cast iron structures are generally inferior to steel structures mainly on account of having bolted connections. These connections do not possess the rigidity offered by riveted connections in steel work. As it is, however, unusual attention must be given to bolting in cast iron work. All bolts must be of sufficient length to grip the full dept of the nut.

All bolts must be tight.

All bolts in column flanges must be 3/4 in. diameter; and no bolts should be less than 34 in. diameter when used in 13/16 in. holes.

No bolts should be omitted. Where holes do not match, a drift pin cannot be used as it may crack the cast iron. The hole should, therefore, be reamed out with a hand or a compressed air reamer or drill.

8. Plumbing Up. All columns should be made plumb and kept plumb by means of guy ropes with turn-buckles. These guy ropes running transversely from wall columns to interior columns, will also strengthen the structure during construction against wind pressure.

As an additional measure of precaution, the brick walls and floor arches should be carried up as quickly as possible. The guy ropes may be removed from floors where the masonry has been completed, and has set sufficiently.

STEEL COLUMNS.

1. Lengths. These are generally made in two and three story lengths. The three story columns are mostly used as the last sections near the top of the buildings. While such columns save some splices and field riveting and give a stronger job, they would be too heavy and too difficult to handle, if used in the lower stories.

2. Temporary Bolts. All steel columns are set approximately plumb; temporary bolts are next provided in the column splices. It is customary to demand not less than 50% of temporary bolts in connections which are to be riveted. These temporary bolts:

(1) Increase the resistance of the structure against wind pressure and are therefore more necessary in long columns and in tall, narrow structures.

(2) They make field connections to match and to come fair before riveting.

3. Erection and Temporary Bracing. Whenever practicable columns are erected in panels of four, and the beams in between are set in place to tie them together. In addition columns in outside panels are tied with diagonal steel ropes to the first or second floor immediately below. These ropes are provided with turn-buckles and are used to draw the columns into a plumb position. Such ropes greatly increase the resistance of the structure against wind pressure. For this reason more diagonal braces are required in taller and narrower buildings.

The columns are next made plumb and then the splices are riveted. To insure plenty of work on hand for the riveters, the iron superintendent will often have several splices. temporarily bolted, along any vertical line of columns, thus

keeping the erectors considerably ahead of the riveters. When the number of unriveted or open splices becomes too large the structure may be endangered through lack of rigidity; in fact it may be blown out of plumb. To avoid such accidents it is customary to allow not more than three open splices along any column, in structures that are well tied with longitudinal steel ropes.

4. Riveting. Riveting splices may proceed from any column; some engineers, however, will start with the outside columns. Column splices are usually riveted in all tall buildings, while beam connections are either bolted or riveted.

It is interesting to note, that there is nothing in the building code compelling an architect to specify the use of rivets, when he desires to use bolts, except that about 20% more bolts are required for field work by making the allowable unit stresses for bolts smaller than for rivets. Now bolting column splices is half as expensive as riveting, and in the case of a new twelve story loft all column splices as well as beam connections were bolted. The iron contractor had his choice between bolting and riveting; hence he preferred bolting which was much cheaper. This however is not good practice and the usual specifications should state that all column splices as well as beam connections within three feet from a column should be riveted; other connections may be either bolted or riveted.

In a twelve story building intended to be used as a printing establishment, all connections have been riveted.

5. Splice Plates. Before riveting column splices, it is very important that the splice plates should be straight and that all holes should match. Bent splices prevent the formation of tight rivets. This is due to a spring action in the steel plate when bent. Plates slightly bent through handling, or while in transit, may be straightened out before riveting by means of a few blows with a heavy sledge hammer.

6. Milling. According to the Building Code all columns must be milled at their ends at right angles to their axes. Milling can be performed with wonderful accuracy and up to 1/500 of an inch if necessary. Where milling is not carefully performed, columns will bear on one edge only (see Fig. 29), causing dangerous eccentric loads and additional bending in the columns below.

7. Incorrect Lengths and Remedies for Same. Another case of a similar nature results where a column is cut too short (see Fig. 30), or where the field holes in the splice plates are punched too high. In such cases the upper column

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