Part 6 (1/2)

The ninth point raised by the author is well taken Too great en disclosed by an examination of many T-beams

Such ready concurrence, however, is not lent to the author's tenth point While it is true that, under all usual assumptions, except those made by the author, an extre moment of a reinforced concrete beam cannot be obtained, still his for even with approxie number of well-known experiments which have been published, that a little ymnastic ability on the part of the author and of other advocates of extreme simplicity would seem very necessary, and will produce structures which are far more economical and amply safe structurally, compared with those which would be produced in accordance with his recoard to the complex nature of the formulas for chimneys and other structures of a raphical methods developed by numerous German and Italian writers are recommended, as they are fully as simple as the rather crude method advocated by the author, and are in al analytical ard to the author's twelfth point, concerning deflection calculations, it would seem that they play such a sn, and are required so rarely, that any engineer who finds it necessary to ations of possible deflections would better use the most precise analysis at his command, rather than fall back on simpler but much more approximate devices such as the one advocated by the author

Much of the criticis the application of the elastic theory to the design of concrete arches, is justified, because designing engineers do not carry the theory to its logical conclusion nor take into account the actual stresses which es of span, settlee in the arch ring or ribs Where conditions indicate that such changes are likely to take place, as is alood rock and the arch ring has been concreted in relatively short sections, with ae; or unless the design is arranged and the structure erected so that hinges are provided at the abutes are afteredged or grouted so as to produce fixation of the arch ends--unless all these points are carefully considered in the design and erection, it is the speaker's opinion that the elastic theory is rarely properly applicable, and the use of the equilibriuon recommended by the author is much preferable and actually more accurate But there must be consistency in its use, as well, that is, consistency between n and erection

The author's fourteenth point--the determination of temperature stresses in a reinforced concrete arch--is to be considered in the sa points, but it see that the author should finally advocate a design of concrete arch which actually has no hinges, naid blocks, after he has condemned so heartily the use of the elastic theory

A careful analysis of the data already available with regard to the heat conductivity of concrete, applied to reinforced concrete structures like arches, da walls, etc, in accordance with the well-known but so the laws of heat conductivity and radiation so clearly enunciated by Fourier, has convinced the speaker that it is ithin the bounds of engineering practice to predict and care for the stresses which will be produced in structures of the simplest fores

The speaker concurs with the author in his criticisn of the steel reinforcement in columns and other compression members While there may be some question as to the falsity or truth of the theory underlying certain types of design, it is unquestioned that sons with dangerous properties The speaker has several times called attention to this point, in papers and discussions, and invariably in his own practice requires that the spacing of spirals, hoops, or ties be ulations and found in almost every concrete structure Morsch, in his ”Eisenbetonbau,” calls attention to the fact that very definite liitudinal rods as well as on theirof ties, where coluoes so far as to state that:

”It is seen from[the results obtained] that an increase in the area of longitudinal reinforceth to the extent which would be indicated by the forive rise to constructions which are not sufficiently safe”

Again, with regard to the spacing of spirals and the coitudinal rods, in connection with some tests carried out by Morsch, the conclusion is as follows:

”On the whole, the tests seeth, their pitch itudinal rods must be increased”

In the ether too large, and, from conversations with Considere, the speaker understands that to be the inventor's vieell

The speaker ard to the design of flat slabs supported on more than two sides (noted in the sixteenth point), na the area into strips, the moments of which are determined so as to produce co at right angles at each point of intersection This e amount of analytical work for any special case, and the speaker is mildly surprised that the author cannot recoeneral schen

If use is to be made at all of deflection observations, theories, and formulas, account should certainly be taken of the actual settlements and other deflections which invariably occur in Nature at points of support These changes of level, or slope, or both, actually alter very considerably the stresses as usually con work, should be considered

On the whole, the speaker believes that the author has put himself in the class with most iconoclasts, in that he has overshot his mark There seems to be a very important point, however, on which he has touched, naard to those items which most nearly correspond with the so-called ”details” of structural steel work, and are fully as important in reinforced concrete as in steel It is comparatively a small matter to proportion a simple reinforced concrete beaivenout of that ite road which should lead through the consideration of every detail, not the least important of which are such items as most of the sixteen points raised by the author

The author has done the profession a great service by raising these questions, and, while full concurrence is not had with him in all points, still the speaker desires to express his hearty thanks for starting what is hoped will be a co reinforced concrete design work

ALBIN H BEYER, ESQ--Mr Goodrich has brought out very clearly the efficiency of vertical stirrups As Mr Godfrey states that explanations of how stirrups act are conspicuous in the literature of reinforced concrete by their absence, the speaker will try to explain their action in a reinforced concrete beam

It is well known that the internal static conditions in reinforced concrete beae to some extent with the intensity of the direct or nor out his point, the speaker will trace, in such a beaes in the internal static conditions due to increasing vertical loads

[Illustration: FIG 8]

Let Fig 8 represent a beam reinforced by horizontal steel rods of such diameter that there is no possibility of failure from lack of adhesion of the concrete to the steel The beama] _P_ For low unit stresses in the concrete, the neutral surface, _n n_, is approximately in the ation of fro to tensile stresses in the steel of froe plain concrete would have reached its ultiation It is known, however, that reinforced concrete, ell ations; tests have shown that its ulti to tensions in steel of 30,000 lb per sq in

Reinforced concrete structures ordinarily show tensile cracks at very much lower unit stresses in the steel The main cause of these cracks is as follows: Reinforced concrete setting in dry air undergoes considerable shrinkage during the first few days, when it has very little resistance This tendency to shrink being opposed by the reinforcement at a tith or ductility, causes invisible cracks or planes of weakness in the concrete These cracks open and become visible at very low unit stresses in the steel

Increase the vertical loads, [Sigma] _P_, and the neutral surface will rise and small tensile cracks will appear in the concrete below the neutral surface (Fig 8) These cracks are most numerous in the central part of the span, where they are nearly vertical They decrease in nuhtly away from the perpendicular toward the center of the span The formation of these tensile cracks in the concrete relieves it at once of its highly stressed condition

It is impossible to predict the unit tension in the steel at which these cracks begin to forh not often visible, when the unit tensions in the steel are as low as from 10,000 to 16,000 lb per sq in As soon as the tensile cracks forh invisible, the neutral surface approaches the position in the beaned to it by the colected The internal static conditions in the beam are now modified to the extent that the concrete below the neutral surface is no longer continuous The coer be used to calculate the web stresses

To analyze the internal static conditions developed, the speaker will treat as a free body the shaded portion of the bea 8, which lies between two tensile cracks