Part 9 (1/2)

_Point 11_--The writer has never designed a reinforced concrete chimney, but if he ever has to do so, he will surely not use any formula that is dependent on the modulus of elasticity of concrete

_Points 12, 13, and 14_--The writer has never had to consider these points to any extent in his oork, and will leave discussion to those better qualified

_Point 15_--There is ard to reinforced concrete columns; but the matter is hardly disposed of as easily as indicated by the author Other engineers draw different conclusions from the tests cited by the author, and from some to which he does not refer

To the writer it appears that here is a proble solution on a really satisfactory basis It seems incredible that the author would use plain concrete in columns, yet that seems to be the inference

The tests see and longitudinal reinforce should not be integral with the coluh results obtained by M Considere in testing small specimens cannot be depended on in practice, but that the reinforcereat value, nevertheless The writer believes that when load-carrying capacity, stresses due to eccentricity, and fire-resisting qualities are all given due consideration, a type of coluitudinal reinforcement provided with shear members, will finally be developed, which will more than justify itself

_Point 16_--The writer has not gone as deeply into this question, from a theoretical point of view, as he would like; but he has had one experience that is pertinent Soo, he built a plain slab floor supported by brick walls The span was about 16 ft The diles to the reinforcement was 100 ft or more

Plain round bars, 1/2 in in diales to the reinforce to lessen cracks

The reinforce from wall to wall

The rounds were laid on top of the Kahn bars The concrete was frozen and undeniably daed, but the floors stood up, without noticeable deflection, after the removal of the forms The concrete was so soft, however, that a test was decided on An area about 4 ft wide, and extending to within about 1 ft of each bearing wall, was loaded with bricks piled in small piers not in contact with each other, so as to constitute practically a uniformly distributed load When the total load a load for the 4-ft strip, considerable deflection had developed As the load increased, the deflection increased, and extended for probably 15 or 20 ft on either side of the loaded area Finally, under about three-fourths of the desired breaking load for the 4-ft strip, it became evident that collapse would soon occur The load was left undisturbed and, in 3 or 4 min, an area about 16 ft square tore loose from the remainder of the floor and fell The first noticeable deflection in the above test extended for 8 or 10 ft on either side of the loaded strip It would see power in the round rods, although they were not counted as reinforce purposes at all The concrete was extremely poor, and none of the steel was stressed beyond the elastic lihter reinforcement for the short way of the slab, it at least indicates a very real value for some reinforcement in the other direction It would seeht steel ht resist a small amount of shear The slab in this case was about 6 in thick

SANFORD E THOMPSON, M AM SOC C E (by letter)--Mr Godfrey's sweeping condemnation of reinforced concrete columns, referred to in his fifteenth point, should not be passed over without serious criticis, as he states, are the most vital portion of the structure, and for this very reason their design should be governed by theoretical and practical considerations based on the most comprehensive tests available

The quotation by Mr Godfrey from a writer on hooped columns is certainly ineers, but the best practice in column reinforcement, as recommended by the Joint Committee on Concrete and Reinforced Concrete, which assu stress in accordance with the ratio of elasticity of steel to concrete, and that the hooping serves to increase the toughness of the column, is founded on thethe second edition of ”Concrete, Plain and Reinforced,” the writer examined critically the various tests of concrete columns in order to establish a definite basis for his conclusions Referring more particularly to columns reinforced with vertical steel bars, an examination of all the tests of full-sized columns made in the United States appears to bear out the fact very clearly that longitudinal steel bars eth of the coluth of the combination of steel and concrete may be coe columns have been made at the Watertown arsenal, the Massachusetts Institute of Technology, the University of Illinois, by the City of Minneapolis, and at the University of Wisconsin The results of these various tests were recently summarized by the writer in a paper presented at the January, 1910,of the National association of Cement Users[O] Reference may be es of the tests of each series are worth repeating here

In coes of reinforced coluned to increase the strength, or with horizontal reinforce of the concrete, are oiven are made up from fair representative tests on selected proportions of concrete, given in detail in the paper referred to, while in other cases all the corresponding speciiven in Table 1

The comparison of these tests must be made, of course, independently in each series, because the materials and proportions of the concrete and the amounts of reinforceiven si out the point, very definitely and distinctly, that longitudinally reinforced coluer than columns of plain concrete

A more careful analysis of the tests shows that the reinforced coluth due to the reinforce a ratio of elasticity of 15, would predicate

Certain of the results given are diametrically opposed to Mr Godfrey's conclusions from the sae 69), to a plain column tested at the University of Illinois, which crushed at 2,001 lb per sq in, while a reinforced column of similar size crushed at 1,557 lb per sq in,[P] and the author suggests that ”This is not an isolated case, but appears to be the rule” Examination of this series of tests shows that it is somewhat more erratic than most of those made at the University of Illinois, but, even fro his ht be reached, for if, instead of selecting, as he has done, the weakest reinforced coluest plain coluth of the plain column would have been stated as 1,079 lb per sq in and that of the reinforced column as 3,335 lb per sq in If extremes are to be selected at all, the weakest reinforced column should be coest reinforced coluest plain column; and the results would show that while an occasional reinforced coluth, an occasional plain column will be still lower, so that the reinforcee in increasing strength

In such cases, however, coth of the reinforced coluiven in Table 1, is considerably higher than that of the plain columns

TABLE 1--AVERAGE RESULTS OF TESTS OF PLAIN _vs_ LONGITUDINALLY REINFORCED COLUMNS

--------------+--------+--------------+--------------------------------- | | Average | |Average | strength of | Location |strength|longitudinally| Reference

of test |of plain| reinforced | |columns| columns | --------------+--------+--------------+--------------------------------- Watertown | 1,781 | 2,992 |Taylor and Thompson's arsenal | | |”Concrete, Plain and Reinforced”

| | |(2nd edition), p 493

--------------+--------+--------------+--------------------------------- Massachusetts| 1,750 | 2,370 |_Transactions_, Institute of | | |Ay | | | --------------+--------+--------------+--------------------------------- University of| 1,550 | 1,750 |_Bulletin No 10_ Illinois | | |University of Illinois, 1907

--------------+--------+--------------+--------------------------------- City of | 2,020 | 2,300 |_Engineering News_, Minneapolis| | |Dec 3d, 1908, p 608

--------------+--------+--------------+--------------------------------- University of| 2,033 | 2,438 |_Proceedings_, Wisconsin | | |A Materials, | | |Vol IX, 1909, p 477

In referring, in the next paragraph, to Mr Withey's tests at the University of Wisconsin, Mr Godfrey selects for his coroups of concrete which are not co the tests, refers to two groups of plain concrete columns, _A1_ to _A4_, and _W1_ to _W3_ He speaks of the uniforroup, theonly 2, but states, with reference to columns, _W1_ to _W3_, that:

”As these 3 columns were made of a concrete much superior to that in any of the other columns made from 1:2:4 or 1:2:3-1/2 mix, they cannot satisfactorily be compared with them Failures of all plain colu”

Now, Mr Godfrey, instead of taking columns _A1_ to _A3_, selects for his comparison _W1_ to _W3_, made, as Mr Withey distinctly states, with an especially superior concrete Taking columns, _A1_ to _A3_, for comparison with the reinforced colue of 2,033 for the plain colu the third series of tests referred to by Mr Godfrey, those at Minneapolis, Minn, it is to be noticed that he selects for his criticism a colu at center (bad batch of concrete at this point)” Furthermore, the column is only 9 by 9 in, and square, and the stress referred to is calculated on the full section of the coluh the latter eneral practice in a hooped column The inaccuracy of this is shown by the fact that, with this small size of square colu and never taken into account in theoretical coitudinal reinforcement is concerned, is always between the two plain columns and the six columns, _E_, _D_, and _F_ The results are so instructive that a letter[Q] by the writer is quoted in full as follows: