Part 2 (1/2)

In view of these considerations, it ive the steel reinforcement of columns some stiffness of its own by sufficiently connected lateral bracing The writer would suggest, further, that in beams where rods are used in compression a system of web members sufficiently connected should be provided, so that the strength of the combined structure would be determinate

To sum up briefly, columns and short deep beams, especially when the latter are doubly reinforced, should be designed as fraer connections than have been customary

JR WORCESTER, M AM SOC C E (by letter)--This paper is of value in calling attention to many of the bad practices to be found in reinforced concrete work, and also in that it gives an opportunity for discussing certain features of design, about which engineers do not agree A free discussion of these features will tend to unify methods

Several of the author's indicto by ood authorities; the ieneral use is unwarranted

The first criticisle, sthe curve, but in practice le It is undoubtedly true that in every instance a gradual curve is preferable

The author's second point, that a suitable anchorage is not provided for bent-up rods at the ends of a beam, may also be said to be a practice which is not recons

The third point, in reference to the counterforts of retaining walls, is certainly aimed at a very reprehensible practice which should not be countenanced by any engineer

The fourth, fifth, and sixth ite out the fact that undoubtedly there has been soners and authors on the subject of shear in the steel The author is wholly justified in criticising the use of the shearing stress in the steel ever being brought into play in reinforced concrete Referring to the report of the Special Committee on Concrete and Reinforced Concrete, on this point, it seeht have made the intention of the Committee somewhat clearer had the word, tensile, been inserted in connection with the stress in the shear reinforcing rods In considering a bea stresses are really diagonal, there is co that the metal must be inserted to resist the tensile portion of this stress, it is not essential that it should necessarily be wholly parallel to the tensile stress Vertical tensile onal tension, just as in a Howe truss all the tensile stresses due to shear are taken in a vertical direction, while the coonal direction by the wooden struts The author seems to overlook the fact, however, that the reinforced concrete beam differs from the Howe truss in that the concrete foronal compression members It is not necessary that a stirrup at one point should carry all the vertical tension, as this vertical tension is distributed by the concrete There is no doubt about the necessity of providing a suitable anchorage for the vertical stirrups, and such is definitely required in the recommendations of the Special Co necessary before the reinforcing ht into action, are just as likely to occur in the case of the bent-up rods with anchors at the end, advocated by him While his method may be a safe one, there is also no question that a suitable arrangement of vertical reinforcement may be all that is necessary to make substantial construction

With reference to the seventh point, naht be said that it is not generally considered good practice to reduce the positive moments at the center of a span to the amount allowable in a beaative moment over supports sufficient to develop the stresses involved in coin of safety, from the fact of the lack of possible fixedness of the beams at the supports The criticism is evidently aihth point, the necessary width of a beam in order to transfer, by horizontal shear, the stress delivered to the concrete froht be orth while for the author to take into consideration the fact that while the bonding stress is developed to its full extent near the ends of the beam, it very frequently happens that only a portion of the total nu been bent upward It may be that the width of a bea stress on the total number of rods near its center, and yet it th on the horizontal planes The custo the width of the bea stress will not be excessive, seeested by Mr Godfrey

Referring to the tenth and fourteenth points, it would be interesting to knohether the author proportions his steel to take the reation possible at the point where it is located, considering the neutral axis of the section under the combined stress Take, for instance, a chieneous material which will carry tension and compression equally well, and the neutral axis is found under the combined stresses, the extreenerally be a matter of 100 or 200 lb Evidently, if steel is inserted to replace the concrete in tension, the corresponding stress in the steel cannot be more than from 1,500 to 3,000 lb per sq in If sufficient steel is provided to keep the unit stress down to the proper figure, there can be little criticism of the method, but if it is worked to, say, 16,000 lb per sq in, it is evident that the result will be a different position for the neutral axis, invalidating the calculation and resulting in a greater stress in compression on the concrete

LJ MENSCH, M AM SOC C E (by letter)--Much of the poor practice in reinforced concrete design to which Mr Godfrey calls attention is due, in the writer's opinion, to inexperience on the part of the designer

It is true, however, that , who derided reinforced concrete only a few years ago, now pose as reinforced concrete experts, and probably the author has the mistakes of these men inago by a great many tests, h the theoretical side is not as easily answered; but it must be borne in mind that the stresses involved are mostly secondary, and, even in steel construction, these are difficult of solution The stresses in the web of a deep steel girder are not known, and the web is strengthened by a liberal nuure out to a nicety The ultith of built-up steel columns is not known, frequently not even within 30; still less is known of the strength of colus, or of the types used in the Quebec Bridge It seems to be impossible to solve the problener of that bridge known of the tests o, that accident probably would not have happened

Practice is always ahead of theory, and the writer claihly reliable tests made in the last 20 years, the man who is really infor the points brought out by Mr Godfrey

The author is right in conde rods

Experiencedthem, if only for the reason that such sharp bends are very expensive, and that there is great likelihood of breaking the rods, or at least weakening them Such sharp bends invite cracks

Neither is there any question in regard to the advantage of continuing the bent-up rods over the supports 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

The underside of continuous beams is in compression near the supports, yet no one will say that steel rods cannot take any stress there It is quite surprising to learn that there are engineers who still doubt the advisability of using bent-up bars in reinforced concrete bea the last 18 years in Europe, attention is called to the valuable tests on thirty beao, Milwaukee and St

Paul Railroad[H] All the beams were reinforced with about 3/4 of steel Those with only straight rods, whether they were plain or patented bars, gave an average shearing strength of 150 lb per sq in

Those which had one-third of the bars bent up gave an average shearing strength of 200 lb per sq in, and those which had nearly one-half of the rods bent up gave an average shearing strength of 225 lb per sq

in Where the bent bars were continued over the supports, higher ultimate values were obtained than where some of the rods were stopped off near the supports; but in every case bent-up bars showed a greater carrying capacity than straight rods The writer knows also of a number of tests with rods fastened to anchor-plates at the end, but the tests showed that they had only a slight increase of strength over straight rods, and certainlythan bent-up bars The use of such threaded bars would increase materially the cost of construction, as well as the time of erection

The writer confesses that he never saw or heard of such poor practices as mentioned in the author's third point On the other hand, the proposed design of counterforts in retaining walls would not only be very expensive and difficult to install, but would also be a decided step backward in mechanics This proposition recalls the trusses used before the introduction of the Fink truss, in which the load from the upper chord was transmitted by separateon the principle that the shortest way is the best There are in the United States ular water tanks Are these held by any such devices? And as they are not thus held, and inasmuch as there is no doubt that they must carry the stress when filled ater, it is clear that, as long as the rods froh to carry the tension and are bent with a liberal radius into the front wall and extended far enough to fore, the connection will not be broken The sa walls It would take up too much time to prove that the counterfort acts really as a bea on it are not as easily found as those in a common beam

The writer does not quite understand the author's reference to shear rods Possibly he itudinal reinforcement, which it seems is sometimes calculated to carry 10,000 lb per sq in in shear The writer never heard of such a practice

In regard to stirrups, Mr Godfrey seems to be in doubt They certainly do not act as the rivets of a plate girder, nor as the vertical rods of a Howe truss They are best compared with the dowel pins and bolts of a compound wooden beam The writer has seen tests made on compound concrete beams separated by copper plates and connected only by stirrups, and the strength of the combination was nearly the same as that of beams made in one piece