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PLANS AND SPECIFICATIONS FOR CONCRETE FENCE
T. E. Rust, Chairman;
O. H. Sessions, ARTHUR ANDERSON, Vice-Chairman; W. C. SWARTOUT, L. B. Curtis,
The Sub-Committee to which was assigned the preparation of plans and specifications for concrete fence posts has prepared and submits herewith plans of round and square concrete line posts and specifications sufficiently general to cover concrete fence posts of any size. The SubCommittee recommends that these plans and specifications be submitted to the Association for information and criticism. Plans for concrete end and corner posts have not yet been prepared.
SPECIFICATIONS.—The specifications herewith submitted follow, in general, the Tentative Specifications for Concrete and Reinforced Concrete of the Joint Committee of this Association, the American Society of Civil Engineers, the American Society for Testing Materials, the American Concrete Institute and the Portland Cement Association, which specifications were submitted to the constituent organizations on June 4, 1921. A great deal of matter not considered applicable to concrete fence posts has been omitted and other things have been added, but the spirit of these Tentative Specifications has been followed quite closely. The reason for following these Tentative Specifications rather than the specifications heretofore adopted by this Association is that the former presumably reflect the latest developments in the art of making concrete. We also considered that it was probable that this Association would, as soon as the Joint Committee submits its final report, adopt specifications very closely following such tentative specifications. The Sub-Committee does not believe that this Association should adopt any specifications for concrete posts at this time and perhaps not until revised specifications for concrete and reinforced concrete have been adopted. The accompanying specifications are submitted for information and for criticism as to their scope, arrangement and special features, so that the Association will have, when such revised specifications for concrete are adopted, a set of specifications for concrete fence posts which will require only minor revision.
Plans.—The plans and specifications for concrete fence posts must be considered as a unit. The plans herewith submitted were drawn with the assumption that the materials used and methods employed would be in accordance with the specifications. For this reason the Sub-Committee asks that the plans be not adopted separately, as they are, like the specifica. tions, submitted for information and criticism.
Some information regarding the posts shown on the plans is given in the following table:
Square Post Round Post Average sectional area of post 7 ft. long.....13,915 sq. in. 14,333 sq. in. Sectional area of steel, wire reinforcing. .0984 sq. in. .1232 sq. in. Sectional area of steel, bar reinforcing. .1104 sq. in. .1656 sq. in. Volume of post 7 ft. long...
.676 cu. ft. .697 cu. ft. Approximate weight of post 7 ft. long. 101 1b.
104 1b. Weight of steel, wire reinforcing..
.2.34 lb. 2.94 lb. Weight of steel, bar reinforcing.
.2.63 1b. 3.94 1b. Approximate ultimate strength of post, wire reinforcing
192 1h. Approximate ultimate strength of post, bar reinforcing
224 lb. The "ultimate strength” shown above is the load which, applied at the small end of the post would cause the post to fail as a cantilever beam, the point of support being 60" from the load. The breaking load is calculated by the ordinary formulae for beams reinforced top and bottom, the ultimate strength of cold drawn steel wire being assumed to be 90,000 lb. per sq. in., and of hard steel bars 80,000 lb. per sq. in. In 1917 the Association adopted the conclusion that, “it is not economical to make posts that will have the strength to resist a force of over 200 lb. when the post is tested in the manner above described.” The use of the next smallest commercial size of reinforcing in the posts shown on the plans would reduce the force which the posts could resist to considerably less than 200 lb. and is not advocated. As to the reasonableness of the ultimate strengths of steel referred to above it may be stated that the average ultimate strength of the wire reinforcing in posts tested by Committee IX in 1914 was about 100,000 lb. per sq. in. At that time three round posts 12" larger in diameter than the post shown on the plans and reinforced with six No. 8 wires were tested and the average strength found to be considerably in excess of that given above, allowance being made for the difference in size.
In deciding on the size of posts and amount of reinforcing, as shown on the accompanying plans, the Sub-committee was guided by the conclusions already adopted by the Association, the tests made in 1914, theoretical calculations made this year as to the strength of posts of various sizes, and, more particularly, the record of posts now in service. There are nearly a half million round posts in use by railroads, of the size shown on the Committee's plans and reinforced with six No. 8 or No. 9 wires, which are giving satisfaction and the Committee could not justify the use of a larger section or heavier reinforcing. The size and reinforcing decided upon for square posts is such as to give them a strength substantially the same as that of the round posts. The Committee suggests that it might be well, during the coming season, to test posts made in accordance with the plans and specifications herewith submitted and using rods and wires whose ultimate strength and elastic limit have been previously tested. Possibly such tests might result in more definite specifications as to proportions of ingredients and amount of water used in mixing as well as confirming the theoretical calculations as to strength.
The Committee repeats its former conclusions as to the relative merits of round and square posts. Viewed as a beam the square section seems obviously superior. The above table shows a saving in both concrete and steel by the use of square posts. On the other hand the round post is perhaps superior in resisting fire and disintegration. The methods used in the manufacture of round posts have probably been better than those usually employed in the manufacture of square posts, but the Committee can see no reason why the same methods could not just as well be employed in both cases.
The Committee also believes that "U" shaped posts, if properly made and reinforced, will be entirely satisfactory. This type of post has lost favor with railroads more because of improper reinforcing than on account of any defect in the shape of the post, which differs very little from that of a square post. Most of these posts have been reinforced with flat bars, a shape which seems to cause longitudinal cracks in the concrete and which, also, does not give as good adhesion as a round or square bar.
The Sub-Committee is not yet prepared to submit plans for corner, end or gate posts, or methods of bracing end and corner panels. A few examples of such posts and methods of bracing are submitted for information. No two roads, apparently, use the same size of end posts or the same style of bracing.
RECOMMENDED SPECIFICATIONS FOR CONCRETE FENCE
(1) MATERIALS 1. Intent. The intent of these specifications and the plans of which they form a part is to produce concrete fence posts having a uniform and sufficient strength and durability at a minimum of cost. On account of the thinness of the section, this can only be accomplished by intelligent and constant attention to securing proper proportions of all ingredients.
2. Cement. Cement shall conform to the present Stanlard Specifications and Tests for Portland Cement of the American Railway Engineering Association and subsequent revisions thereof.
3. Fine Aggregate. Fine aggregate shall consist of sand, stone screenings, or a combination thereof, having clean, hard, strong, durable, uncoated grains, and free from injurious amounts of dust, lumps, soft or Alaky particles, shale, alkali, organic matter, loam or other deleterious substances. It shall range in size from fine to coarse, preferably within the following limits : Passing through a No. 4 sieve
.not less than 95% Passing through a No. 50 sieve
..not more than 30% Weight removed by decantation
..not more than 3%
4. Coarse Aggregate. Coarse aggregate shall consist of crushed stone, gravel, or combination thereof, having clean, hard, strong, durable, uncoated particles free from injurious amounts of soft, friable, thin, elongated or laminated pieces, organic or other deleterious matter. It shall range in size from fine to coarse within the following limits : Passing a 1/2" screen.
.not less than 95% Passing a No. 4 screen.
.not more than 15% Passing a No. 8 screen
...not more than 5% 5. Bank Gravel. Natural combinations of fine and coarse aggregate, in the form of bank gravel, may be used providing its particles meet all the requirements in paragraphs 2 and 3 above, and provided such particles are properly graded from fine to coarse within the following limits : Passing a 1/2" screen...
not less than 95% Passing a 14"
..from 35% to 55% Passing a No. 50 screen.
not more than 15% Weight removed by decantation...
.. not more than 172% 6. Water. Water for concrete shall be clean and free from oil, acid, alkali, organic or other deleterious substance.
7. Metal Reinforcement. Steel reinforcement shall be hard steel and shall conform to the present Standard Specifications for Steel Reinforcement of the American Railway Engineering Association or, if wire is used, to the present Tentative Specifications for Cold-Drawn Steel Wire of the American Society for Testing Materials, or to such modifications of either of such specifications as may hereafter be adopted by the American Railway Engineering Association. Reinforcement shall be in the form of round or square bars, preferably deformed, or steel wires. Crimped, stranded or flat reinforcing shall not be used. Reinforcing, before being placed in the molds, shall be thoroughly cleaned of mill and rust scale, and of coating that will destroy or reduce the bond.
(II) PROPORTIONING AND Mixing CONCRETE 8. Proportioning. The unit of measure shall be the cubic foot, One bag of Portland cement shall be considered as one cubic foot. Each of the constituent materials shall be measured separately by volume, using a method whịch will secure the specified proportions. The water shall be measured by an automatic device that will secure the same quantity in successive batches.
9. Strength. The proportions of cement, water and aggregate shall be such as to produce a concrete having a compressive strength at 28 days of 2,000 lb. per sq. in. The proportions of fine and coarse aggregate to produce such a concrete shall be determined by making a screen analysis of the available aggregates and using such a mixture as will secure a maximum density. To such a mixture sufficient cement shall then be added to produce concrete of the desired strength. If bank gravel is used it shall be screened and remixed, if necessary in order to produce