Part 10 (1/2)
The following is another loose assertion by Mr Turner:
”Mr Godfrey appears to consider that the hooping and vertical reinforcement of columns is of little value He, however, presents for consideration nothing but his opinion of the matter, which appears to be based on an almost total lack of familiarity with such construction”
There is no excuse for statements like this If Mr Turner did not read the paper, he should not have attempted to criticize it What the writer presented for consideration was more than his opinion of the matter In fact, no opinion at all was presented What was presented was tests which prove absolutely that longitudinal rods without hoops th of a coluitudinal rods and ”hoops which are not close enough to stiffen the rods” th than a plain concrete column A properly hooped coluiven in the foregoing sentence The colu whatever on the paper, for they relate to columns with bands and close spirals Columns are sometimes built like these, but there is a vast a and bands are o spaced a foot or so apart
A steel colue part of its stiffness and ability to carry co, which should be of a strength commensurate with the size of the coluth The latticing er than necessary, but it would not add anything to the strength of the coluth of a colu with the size of the lattice If the lattice is weak, the column is simply deficient; so a formula for a hooped coluth of the column varies with the section of the hoops, and, on this account, the co, beyond a certain limit, and yet not an iota would be added to the coth of the colu before their full strength was brought into play Also, the hoops ht be too far apart to be of ht be too widely spaced There is no element of personal opinion in these th of a hooped coluitudinal steel, is dependent on the fact that thin discs of concrete are capable of carrying much more load than shafts or cubes The hoops divide the column into thin discs, if they are closely spaced; widely spaced hoops do not effect this Thin joints of lier than the same mortar in cubes Why, in the many books on the subject of reinforced concrete, is there no mention of this sinore the ith in columns? The trouble seems to be in the tendency to interpret concrete in terin to spread and flow, and a short coluth as a short block The action of concrete under compression is quite different, because of the weakness of concrete in tension The concrete spalls off or cracks apart and does not flow under coth of a shaft of concrete under compression has little relation to that of a flat block
Soo the writer pointed out that the weakness of cast-iron coluth or toughness in cast iron Compare 7,600 lb per sq in as the base of a column formula for cast iron with 100,000 lb per sq in as the coth of short blocks of cast iron Then compare 750 lb
per sq in, sometimes used in concrete coluth in blocks Ain co in tension with a ”safe” unit one-tenth as great! The greater tensile strength of richin coo, an investigator in this line reineers, that ”the failure of concrete in coth” This remark was considered of sufficient novelty and i periodical to ood illustration of the state of knowledge of the ele
Mr Turner states, ”Again, concrete is a e as a monolith, and, as such, the simple beam seems to be decidedly out of date to the experienced constructor” Sis could be said of steelwork, and with more force Riveted trusses are preferable to articulated ones for rigidity The stringers of a bridge could readily beof the ends to a floor-beae capacity to carry reverse e of at the end floor-bea the saer A sers would greatly increase this strength to resist reverse moments A steel truss span is ideally conditioned for continuity in the stringers, since the various supports are practically relatively i where each support may settle independently and entirely vitiate calculated continuous stresses Bridge engineers ignore continuity absolutely in calculating the stringers; they do not argue that a siineers would do vastly better work if they would do likewise, adding top reinforce only Failure could not occur in a systeative moments over the supports exceeded those for which the steel reinforcement was provided, for the reason that the deflection or curving over the supports can only be a small amount, and the simple-beam reinforcement will immediately come into play
Mr Turner speaks of the absurdity of anyato separate the construction into ele, of course, to the writer'sThe writer does not endeavor to ”separate the construction into ele the effect of cross-strips The ”separation” is analogous to that of considering the tension and co their size or reinforce their moment As stated in the paper, ”strips are taken across the slab and thethe limitations of the several strips in deflection iles therewith” It is a sound and rational assuh the middle of the slab, carries its half of the middle square foot of the slab load It is a necessary limitation that the other strips which intersect one of these critical strips across the middle of the slab, cannot carry half of the intercepted square foot, because the deflection of these other strips le Thus, the nearer the support a strip parallel to that support is located, the less load it can take, for the reason that it cannot deflect asslab the condition imposed is equal deflection of two strips of unequal span intersecting at the middle of the slab, as well as diminished deflection of the parallel strips
In this ular slab, the concrete in tension is not considered to be of any value, as is the case in all accepted o the writer tested a nu, with a load of 250 lb per sq ft These slabs were 3 in thick and had a clear span of 44 in between beams They were totally without reinforcee, the cracks running through theth of the beams They all carried this load without any apparent distress If these slabs had been reinforced with some special reinforceth which was ht have been ic properties could be thus conjured up for soetic proprietor could capitalize tension in concrete in this way and ”prove”
by tests his claiic properties of his reinforce to do with the reinforceth of concrete as having a positive value in the bottom of that slab It means to reinforce for the stretch in the concrete and not for the tensile stress If the tensile strength of concrete is not accepted as an ele one-way reinforce reinforceth of concrete in a slab of any kind is of course real, when the slab is without cracks; it has a large influence in the deflection; but what about a slab that is cracked froes the issue in thethat they were not correctly placed in the tests made at the University of Illinois He cites the Hennebique system as a correct sample This system, as the writer finds it, has some rods bent up toward the support and anchored over it to some extent, or run into the next span Then stirrups are added There could be no objection to stirrups if, apart from them, the construction were made adequate, except that expense is added thereby Mr Turner cannot deny that stirrups are very commonly used just as they were placed in the tests made at the University of Illinois It is the coic in the literature of the subject which the writer condemns
Mr Thacher says of the first point:
”At the point where the first rod is bent up, the stress in this rod runs out The other rods are sufficient to take the horizontal stress, and the bent-up portion provides only for the vertical and diagonal shearing stresses in the concrete”
If the stress runs out, by what does that rod, in the bent portion, take shear? Could it be severed at the bend, and still perform its office?
The writer can conceive of an inclined rod taking the shear of a beah sorip in the concrete from the centroid of compression up and from the center of the steel down This latter is a practical impossibility A rod curved up from the bottom reinforcement and curved to a horizontal position and run to the support with anchorage, would take the shear of a bea out of a rod at the point where it is bent up, this will hardly stand the test of analysis in the majority of cases On account of the parabolic variation of stress in a bearip of a rod in the space from the center to the end of a bearip, the whole span should then be not less than four times 50, or 200 diameters of the rod For the same reason the rod between these bends should be at least 200 dia rods are equal to or more than one-two-hundredth of the span in diarip
Mr Thacher states that Rod 3 provides for the shear He fails to answer the argument that this rod is not anchored over the support to take the shear Would he, in a queen-post truss, attach the hog-rod to the beam so and shear back into the very bea and shear? Yet this is just what Rod 3 would do, if it were long enough to be anchored for the shear, which it seldom is; hence it cannot even perforive it back to the concrete beam from the point of its full usefulness to the support
Mr Thacher would not say of a steel truss that the diagonal bars would take the shear, if these bars, in a deck truss, were attached to the top chord several feet away froood for only a fraction of the stress in the bars Why does he not apply the sa the third point, Mr Thacher ic in reinforced concrete literature, which does not bother with preh the coe” If the rods have sufficient anchorage, what is the nature of that anchorage? It ought to be possible to analyze it, and it is due to the seeker after truth to produce so is there to anchor these rods? The writer has shown by analysis that they are not anchored sufficiently In e Mr Thacher matic statement that they are anchored There is a faint hint of a reason in his statement that they run into the compression part of the concrete
Does he rip the rod like a vise? How does this comport with his contention farther on that the beams are continuous? This would mean tension in the upper part of the beam In any beareatest, is s
In this sa the third point and the case of the retaining wall that is given as an example, ”In a counterfort, the inclined rods are sufficient to take the overturning stress” Mr Thacher does notstress” He see to pull the counterfort loose froht of the earth fill over this slab is the force against which the vertical and inclined rods of Fig
2, at _a_, must act Does Mr Thacherthis slab, with its heavy load of earth fill, on the short projecting ends of a few rods? Would he hang a floor slab on a few rods which project froirder? He says, ”The proposed2, at _b_, where an angle is provided as a shelf on which this slab rests The angle is supported, with thread and nut, on rods which reach up to the front slab, fro about the toe of the wall as a fulcru force on the slab There is positively no way in which this wall could fail (as far as the counterfort is concerned) but by the pulling apart of the rods or the tearing out of this anchoring angle Co out of a few ends of rods, in the design which Mr
Thacher says is just as effective This is another exaht into requisition in order to justify absurd systeovern in a bridge pin where there is a wide bar or bolster or a similar condition The writer takes issue with hi need not be taken to find the bendingelement There is no reason why a wide bar or a wide bolster should take a smaller pin than a narrow one, siive too large a pin Bending can be taken in this, as in other cases, with a reasonable assu depth in the wide bar or bolster The rest of Mr
Thacher's comment on the fourth point avoids the issue What does he mean by ”stress” in a shear rod? Is it shear or tension? Mr Thacher's statement, that the ”stress” in the shear rods is less than that in the botto that it is shear, as the shearing unit in steel is less than the tensile unit This vague way of referring to the ”stress” in a shearwhether this ”stress” is shear or tension, as was done in the Joint Committee Report, is, in itself, a confession of the i the ”stress” in thesetension or shear, both of which are absurd in the ordinary h, as a rule, to state that these rods are in shear, and yet their writings are so indefinite as to allow this very interpretation
Mr Thacher criticises the fifth point as follows:
”Vertical stirrups are designed to act like the vertical rods in a Howe truss Special literature is not required on the subject; it is known that the ood results, and that is sufficient”
This is another exan--another dogmatic statement If these stirrups act like the verticals in a Howe truss, why is it not possible by analysis to show that they do? Of course there is no need of special literature on the subject, if it is the intention to perpetuate this senseless n No amount of literature can prove that these stirrups act as the verticals of a Howe truss, for the simple reason that it can be easily proven that they do not