(2) The dead load is to include the estimated weight of the structure and all other fixed loads and forces acting upon the structure.

(3) The live load is to include all variable and moving loads or forces acting upon the structure in any direction.

(4) As the working stresses herein recommended are for static loads, the dynamic effect of moving loads is to be added to the live load stresses.

(5) The span length for beams and slabs is to be taken as the distance from centre to centre of the supports, but not to exceed the clear span plus the depth of beam or slab. (6) The internal stresses are to be calculated upon the basis of the following assumptions:

(a) A plane section before bending remains plane after bending.

(b) The distribution of compressive stresses in members subject to bending is rectilinear.

(c) The ratio of the moduli of elasticity of steel and concrete is 12.*

(d) The tensile stresses in the concrete are neglected in calculating the moment of resistance of beams.

(e) The initial stress in the reinforcement due to contraction or expansion in the concrete is neglected.

(The depth of a beam is the distance from the compressive face to the centroid of the tension reinforcement.

(g) The effective depth of a beam at any section is the distance from the centroid of the compressive stresses to the centroid of the tension reinforcement.

(h) The maximum shearing unit stress in beams is the total shear at the section divided by the product of the width of the section and the effective depth at the section considered. This maximum shearing unit stress is to be used in place of the diagonal tension stress in calculations for web stresses.

(i) The bond unit stress is equal to the vertical shear divided by the product of the total perimeter of the reinforcement in the tension side of the beam and the effective depth at the section considered.

(k) In concrete columns the concrete to a depth of 1 in. is to be considered as a protective covering and is not to be included in the effective section.

(7) When the maximum shearing stresses exceed the value allowed for the concrete alone, web reinforcement must be provided to aid in carrying the diagonal tension stresses. This web reinforcement may consist of bent bars, or inclined or vertical members, attached to or looped about the horizontal reinforcement. Where inclined members are used, the connection to the horizontal reinforcement shall be such as to insure against slip.

"In the calculation of web reinforcement when the concrete alone is insufficient to take the diagonal tension, the concrete may be counted upon as carrying one-third of the shear. The remainder is to be provided for by means of metal reinforcement consisting of bent bars or stirrups, but preferably both. The requisite amount of such reinforcement may be estimated on the assumption that the entire shear on a section, less the amount assumed to be carried by the concrete, is carried by the reinforcement in a length of beam equal to its depth."

(8) The following recommended working stresses, in pounds per square inch of section, are for use in concrete of such quality as to be capable of developing an average

* The unit stresses as recommended in the report were higher than these values, which have been reduced in conformity with the fibre stresses employed in other portions of the chapter.

compressive strength of at least 2,000 lbs. per square inch, when tested in cylinders 8 in. in diameter and 16 in. long, and 28 days old, under laboratory conditions of manufacture and storage, the mixture being of the same consistency as is used in the field.

Structural steel in tension..

High carbon steel in tension...

† Steel in compression, 12 times the compressive stress in the surrounding con

crete

Concrete in bearing where the surface is at least twice the loaded area........ † Concrete in direct compression, without reinforcement on lengths not exceeding twelve times the least width

† Concrete in direct compression with not less than 1 per cent, nor over 4 per cent longitudinal reinforcement on lengths not exceeding twelve times the least width......

† Concrete in compression, on extreme fibre in cross bending.

† Concrete in shear, where the shearing stress is used as the measure of web

stress

NOTE. The limit of shearing stresses in the concrete, even when thoroughly reinforced for shear and diagonal tension, should not exceed....

† Bond for plain bars...

† Bond for drawn wire..

† Bond for deformed bars, depending upon form

14,000

17,000

700

350

350

500

30

120

50

30

80-120

NOTE: Chapters XVII and XVIII differ, in that, the former chapter is applicable only to the column and to the special case of the simple horizontal beam carrying a uniformly distributed load, while, in the latter chapter, the methods are general and applicable to beams loaded in any manner. The methods of design are, however, identical in both chapters, and in order to render each one complete in itself, a certain amount of matter has been repeated. It is thought that the reading of this chapter will be rendered easier by first showing the application of the theory of design to a simple case, as was done in Chapter XVII.

†The unit stresses as recommended in the report were in general higher than these values, which have been reduced in conformity with the fibre stresses employed in other portions of the chapter.

CHAPTER XIX

SYSTEMS OF REINFORCEMENT EMPLOYED

Systems of Reinforcement Employed.-Different Forms of Rods and Bars.-Special Fabrics and Types of Reinforcement.

REINFORCEMENT is used in a variety of shapes and combinations, nearly all of them patented, and some of them forming the basis for so-called systems.

All these systems of reinforcement have been developed principally during the last decade, each one of them having its adherents and all of them giving substantial structures if intelligently employed. The selection of the type for any particular case will depend upon the nature of the structure, the local conditions, the experience of the designer, and often upon the argument of the salesman. The illustrations will serve to bring out the essential features of the different systems.

Specifications for Reinforcing Steel.-The quality of steel to be used for reinforced concrete work has received a great deal of attention from engineers and steel-makers and the rules given below represent the latest practice in this respect:

SPECIFICATIONS FOR STEEL REINFORCEMENT *

1. Steel shall be made by the open-hearth process. Rerolled material will not be accepted.

2. Plates and shapes used for reinforcement shall be of structural steel only. Bars and wire may be of structural steel or high carbon steel.

* From the report of the Committee on Masonry at the annual convention of the American Railway Engineering and Maintenance of Way Association, Chicago, March 16, 1910.

3. The chemical and physical properties shall conform to the following limits:

4. The yield point for bars and wire, as indicated by the drop of the beam, shall be not less than 60 per cent of the ultimate tensile strength.

5. If the ultimate strength varies more than 4,000 lbs. for structural steel or 6,000 lbs. for high carbon steel, a retest shall be made on the same gauge, which, to be acceptable, shall be within 5,000 lbs. for structural steel, or 8,000 lbs. for high carbon steel, of the desired ultimate.

6. Chemical determinations of the percentages of carbon, phosphorus, sulphur, and manganese shall be made by the manufacturer from a test ingot taken at the time of the pouring of each melt of steel, and a correct copy of such analysis shall be furnished to the engineer or his inspector. Check analyses shall be made from finished material, if called for by the railroad company, in which case an excess of 25 per cent above the required limits will be allowed.

7. Plates, Shapes, and Bars.-Specimens for tensile and bending tests for plates and shapes shall be made by cutting coupons from the finished product, which shall have both faces rolled and both edges milled to the form of a standard test specimen; or with both edges parallel; or they may be turned to a diameter of inch with enlarged ends.

* See paragraphs 11 and 12. †"d = 4t" signifies “around a pin whose diameter is four times the thickness of the specimen."

8. Bars shall be tested in their finished form.

9. At least one tensile and one bending test shall be made from each melt of steel as rolled. In case steel differing 3/8 in. and more in thickness is rolled from one melt, a test shall be made from the thickest and thinnest material rolled.

10. For material less than 5/16 in. and more than 3/4 in. in thickness the following modifications will be allowed in the requirements for elongation:

(a) For each 1/16 in. in thickness below 5/16 in., a deduction of 2 1/2 will be allowed from the specified percentage.

(b) For each 1/8 in. in thickness above 3/4 in., a deduction of I will be allowed from the specified percentage.

II. Bending tests may be made by pressure or by blows. Shapes and bars less than one inch thick shall bend as called for in paragraph 3.

12. Test specimens one inch thick and over shall bend cold 180° around a pin, the diameter of which, for structural steel, is twice the thickness of the specimen, and for high carbon steel is six times the thickness of the specimen, without fracture on the outside of the bend.

13. Finished material shall be free from injurious seams, flaws, cracks, defective edges, or other defects, and have a smooth, uniform, and workmanlike finish.

14. Every finished piece of steel shall have the melt number and the name of the manufacturer stamped or rolled upon it, except that bar steel and other small parts may be bundled with the above marks on an attached metal tag.

15. Material, which, subsequent to the above tests at the mills, and its acceptance there, develops weak spots, brittleness, cracks or other imperfections, or is found to have injurious defects, will be rejected and shall be replaced by the manufacturer at his own cost.

16. All reinforcing steel shall be free from excessive rust, loose scale, or other coatings of any character, which would reduce or destroy the bond.

Types of Reinforcement.-The reinforcement consists of steel in one or more of the following forms:

1. Round or square rods.

2. Twisted or deformed rods.