Part 11 (1/2)
Professor Clifford has informed the writer that the tests on bent rods to which he refers were made on 3/4-in rounds, embedded for 12 in in concrete and bent sharply, the bent portion being 4 in long The 12-in
portion was greased The average maximum load necessary to pull the rods out was 16,000 lb It see or crushi+ng of the concrete before a very large part of this load was applied The load at slipping would be a more useful determination than the ultimate, for the reason that repeated application of such loads ear out a structure In this connection three sets of tests described in Bulletin No 29 of the University of Illinois, are instructive They were made on beae of steel The results were as follows:
Beams 5111, 5112, 5121, 5122: The bars were bent up at third points
Average breaking load, 18,600 lb All failed by slipping of the bars
Beaiven a sharp right-angle turn over the supports Average breaking load, 16,500 lb The beaside the bar toward the end
Beams 5142, 5143: The bars were bent up at third points and had anchoring nuts and washers at the ends over the supports Average breaking load, 22,800 lb These failed by tension in the steel
By these tests it is seen that, in a beaer in their hold on the concrete by an average of 13 than those with hooks Each test of the group of straight bars showed that they were stronger than either of those with hooked bars Bars anchored over the support in the er than hooked bars and 20 stronger than straight bars These percentages, furtheres of anchored bars The nificance A failure by tension in the steel is an ideal failure, because it is easiest to provide against Failures by slipping of bars, and by cracking and disintegrating of the concrete beam near the support, as exhibited by the other tests, indicate danger, and deer factors of safety
Professor Clifford, in criticizing the statement that a member which cannot act until failure has started is not a proper elen, refers to another statement by the writer, namely, ”The steel in the tension side of the bea all the tension” He states that this cannot take place until the concrete has failed in tension at this point The tension side of a beam will stretch out aout of the bealy minute, if no cracks occurred in the beam
Mr Mensch says that ”the stresses involved are mostly secondary” He coirder, which can scarcely be called secondary Furthermore, those stresses are carefully worked out and abundantly provided for in any good design To give an exairders have rivets in the flanges, spaced 6 in apart near the supports, that is, girders designed with no regard to good practice These girders, perhaps, need twice as ood and acceptable practice, which is also rational practice The girders stand up and perform their office It is doubtful whether they would fail in these rivet lines in a test to destruction; but a reasonable analysis shows that these rivets are needed, and no good engineer would ignore this rule of design or claiirders do their work anyway There are ineer who has exa supervision can testify, which are bad, but not quite bad enough to be cause for condeo the writer ordered reinforceineers in the United States, because the floor-beales This is not a secondaryrods are not a secondary matter No ae angles will perfor else must be overstressed, and herein is a violation of the principles of sound engineering
Mr Mensch e as an exath of steel coner of that bridge had known of certain tests o, that accident probably would not have happened It has never been proven that the designer of that bridge was responsible for the accident or for anything e which would have been weak in service The testi the chords, is, ”We have no evidence to show that they would have actually failed under working conditions had they been axially loaded and not subject to transverse stresses arising fro in the big erection gantry would have saved the bridge, for every feature of the wreck shows that the lateral collapse of that gantry caused the failure Here are sonored
It is when practice runs ”ahead of theory” that it needs to be brought up with a sharp turn It is the general practice to design da that which works into horizontal seams and below the foundation, and exerts a heavy uplift
Da force which is proven to exist by theory
Mr Mensch says:
”The author isrods can only receive their increments of stress when the concrete is in tension Generally, the contrary happens In the ordinary adhesion test, the block of concrete is held by the jaws of the machine and the rod is pulled out; the concrete is clearly in compression”
This is not a case of increiven to it by the grips of the testing machine Furthermore, it is not a bea the writer'srod in a concrete bearip of the concrete, but these increments can only be imparted where the tendency of the concrete is to stretch”
This has no reference to an adhesion test
Mr Mensch's next paragraph does not show a careful perusal of the paper The writer does not ”doubt the advisability of using bent-up bars in reinforced concrete bea up the bars with a sharp bend and ending them nowhere When they are curved up, run to the support, and are anchored over the support or run into the next span, they are excellent In the tests mentioned by Mr Mensch, the beams which had the rods bent up and ”continued over the supports” gave the highest ”ultimate values” This is exactly the construction which is pointed out as being the most rational, if the rods do not have the sharp bends which Mr Mensch hi the tests mentioned by him, in which the rods were fastened to anchor-plates at the end and had ”slight increase of strength over straight rods, and certainlythan bent-up bars,”
the writer asked Mr Mensch by letter whether these bars were curved up toward the supports He has not answered the communication, so the writer cannot comment on the tests It is not necessary to use threaded bars, except in the end beams, as the curved-up bars can be run into the next beam and act as top reinforcee
Mr Mensch's state wall reinforced as shown at _a_, Fig 2, is astounding He ”confesses that he never saw or heard of such poor practices” If he will exa periodical of recent years, he will have no trouble at all in finding several examples of these identical practices In the books by Messrs Reid, Maurer and Turneaure, and Taylor and Tho walls illustrated, which are al 2 at _a_ Mr Mensch says that the proposed design of a retaining ould be difficult and expensive to install The harp-like reinforceround, and raised to place and held with a couple of braces Compare this with the difficulty, expense and uncertainty of placing and holding in place 20 or 30 separate rods The Fink truss analogy given by Mr Mensch is a weak one If he werea cantilever bracket to support a slab by tension from the top, the bracket to be tied into a wall, would he use an indiscriminate lot of little vertical and horizontal rods, or would he tie the slab directly into the wall by diagonal ties? This is exactly the case of this retaining wall, the horizontal slab has a load of earth, and the counterfort is a bracket in tension; the vertical wall resists that tension and derives its ability to resist from the horizontal pressure of the earth
Mr Mensch states that ”it would take up too much time to prove that the counterfort acts really as a beam” The writer proposes to show in a very short time that it is not a bea strains caused by transverse loading This will do as a working definition The concrete of the counterfort shown at _b_, Fig
2, could be entirely eliht into the anchoring angle and were connected with little cast skewbacks through slotted holes There would be absolutely no bending in the rods and no transverse load Add the concrete to protect the rods; the function of the rods is not changed in the least MS Ketchum, M
Am Soc C E,[U] calculates the counterfort as a beaonally do not even run into the front slab He states that the vertical and horizontal rods are to ”take the horizontal and vertical shear”
Mr Mensch says of rectangular water tanks that they are not held (presumably at the corners) by any such devices, and that there is no doubt that they must carry the stress when filled ater A water tank,[V] designed by the writer in 1905, was held by just such devices
In a tank[W] not held by any such devices, the corner broke, and it is now held by reinforcing devices not shown in the original plans