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The bar which forms the band is bent close around each vertical bar in the concrete columns, and therefore assists in holding these bars in place. The bands for the rectangular concrete column b are made up of two separate bands for holding the bars in place in concrete beams and girders, have been successfully used. These spacers are made of heavy sheet iron. They are fastened to the stirrups by means of the loops in the spacers. The ends of the spacers which project out to the forms of the sides of the concrete beams should be made blunt or rounded. This will prevent the ends of the spacers being driven into the forms when the concrete is being tamped. The number of these spacers required will depend on the lengths of the concrete beams; usually 2 to 4 spacers are used in each concrete beam.

Among the patented methods of fastening the bars together for concrete beams and girders, is the Unit Girder Frame System. The loose bars are bent and made into a frame as shown in Fig. 183. All this work is done in a shop; and the frames are sent to where the building is being constructed, ready to be placed. The stirrups are made of round or flat bars, and are hot-shrunk on the longitudinal rods. The girder, concrete beam, or concrete column unit is shipped to the site of the building being constructed, bearing a tag numbered to correspond with a number on the plan showing the proper position of the reinforcement. The place and manner of making breaks or joints in concrete floor construction at the end of a day's work, is a subject that has been much discussed by engineers and construction companies. But there has not been any general agreement yet as to the best method and place of constructing these joints. Wherever joints are made, great care should be exercised to secure a bond between the new and the old concrete.

Fig. 184 shows a sectional view of one method of making a break at the end of the day's work, which has been used very extensively and successfully. The stirrups and concrete slab bars form the main bond between the old and the new work, if the break is left more than a few hours. Short bars in the top of the concrete slab will also assist in making a good bond; also, an additional number of stirrups should be used in the concrete beam where the break is to be made. Before the new concrete is placed, the old concrete should be well scraped, thoroughly soaked with clean water, and given a thin coat of neat cement grout. An objection to this method of forming a joint is that the shrinkage in the concrete may cause a separation of the concrete placed at the two different times, so that water will find a passage. The top coat that is generally placed later will greatly assist in overcoming this objection. Another method of forming stopping-places is by dividing the concrete beam vertically that is, making two L-concrete beams instead of one concrete T- beam.

This is a very good method, but practically it is found difficult to construct the forms dividing the concrete beam, as the steel is greatly in the way. The method of stopping the work at the center of the span of the concrete beams and parallel to the girders has been used to some extent. Fig. 186 illustrates this method. Theoretically the concrete slab is not weakened; and as the maximum bending moment occurs at this point, the shear is zero, and therefore the 326 concrete beams are not supposed to be weakened, except for the loss of concrete in tension, and this is not usually considered in the calculation. The bottoms of the concrete beams are tied together by the steel that is placed in the concrete beams to take the tensile stresses; and there should be some short bars placed in the top of these concrete beams, as well as in the top of the concrete slab, to tie them together.

The objection made in the description of the first method—in that any shrinkage in the concrete at the joint will permit water to pass through—is greater in the second and third methods than in the first. Fig. 187 shows the typical structural concrete floor plan, above the first concrete floor, of a building constructed for Buck at Fifth and Appletree Streets, Philadelphia. The architects were Ballinger & Perrot, and the building was constructed by Cramp & Company, Philadelphia. The building has a frontage of 90 feet on Fifth Street, and a depth of 61 feet on Appletree Street, and is seven stories high.

Are You in Westport Massachusetts? Do You Need Concrete Cutting?

We Are Your Local Concrete Cutter

Call 781-519-2456

We Service Westport MA and all surrounding Cities & Towns