John C. (John Cresson) Trautwine.

Concrete online

. (page 20 of 23)
Online LibraryJohn C. (John Cresson) TrautwineConcrete → online text (page 20 of 23)
Font size
QR-code for this ebook


flange; O.

168. Portion, F, of width of slab, acting as flange.
t = thickness of slab ; L = span of beam or girder ;

b = breadth of beam or girder ; S = dist c to cbetw beams or girders.

F to be "determined by assuming that, in any hor-plane sec of the flange,
the stresses are distributed as the ordinates of a parabola, with its vertex
in the stress-stretch curve and with its axis in a longitudinal vert plane thru
the cen of the rib of the T." Said portion to be reinforced with bars near
the top, at right angles to the girder. Un.

169. F dependent upon hor shearing stress; F > 20 1, Ph; F > 10 b,
Mil.

170. F governed by shearing resistce betw slab and rib; F>*S(l y^J

> L/3, > % S. To be assumed as thus acting, slab must be cast at same
time with nb, Ch.

F > L/3, > -S, Ms ; > L/4, > 8 t + b, JC.

171. T'-beams to be reinfd against shear along plane of junction between
rib and flange, Un, Ph ; using stirrups thruout length of beam, Ph.

172. Ribs of girders and beams to be monolithic with floor slabs.
Un, Ph.

173. "Where reinfd cone girders carry reinfd cone beams, the portion of
the floor slab acting as flange to the girder must be reinfd with bars near



1200 CONCRETE.

For lists of Specifications for Concrete, see pp 1184, 1185.

the top, at right angles to the girder, to enable it to transmit local loads
directly to the girder and not thru the beams, thus avoiding an integration
of comp stresses due to simultaneous action as floor slab and girder flange."
Un, Ph.

Moment, M. See also 1H 178, 179.

174. W = load per sq ft; L = span, in ft. In freely supported slabs,
L = free opening + depth ; in continuous slabs, L = distance betw centers
of supports.

175. With concentrated or special loadings, calculate and provide for
moments and shears for critical condition of loading, Ch.

For dead load; M obtained from the actual dead loadl covering all
' live load, over supports; M obtained from the >- spans at

actual live load J same time.

between supports; M = max obtained from live load
covering 2 consecutive or 2 alternate spans at same time.
When all spans are equal, let M c = min live-load moment at middle of
span. Then,

W L 2
for intermediate spans, M c = r

117 T. 2

for end spans, M. =



10

TIT" j 2
Sum of live load moments over one support and at cen of span, < ^ ,

Hi.

Continuity. See also If 175.

176. Beams and girders considered as simply supported at ends ;

no allowance made for continuity, Un, Mh.

177. Beams, etc, calculated as simply supported, or as continuous,
according to the facts, Ch, Ms.

178. Continuous floor plates, reinfd at top over supports, may be
treated as continuous beams. Under uniformly distributed loads, mom, M,
taken at not less than 0.1 W L; 0.05 W L with square floor plates, reinfd
in both directions and supported on all sides, Un, Mh, Ph.

179. In floor sla^t>s adjoining walls: if slab is reinfd in one

-TTT J TT/ J

direction, M = ; if square and reinfd in both directions, M = ~Tf~',

Ph.

ISO. Floor slabs designed and reinfd as continuous over the supports.
If length of slab > 1.5 X its width, the entire load should be carried by
transverse reinfmt. "Square slabs may well be reinfd in both directions,"

181. For beams and slabs continuous for > 2 spans, bending moms at cen
and at support, for both live and dead loads, as follows:

In floor slabs and in interior spans of continuous beams, M = w L 2 /12;

in end spans of continuous beams, M = w L 2 /10,

w = load per unit of span; L = span, JO.

182. In continuous spans, provide, at supports, for

negative mom = 0.8 positive mom at cen of a simply supported span.
Pos mom, at cen of continuous span, may be taken = neg mom at support,
Ms.

Tests.

183. Bldg Commissioner may require tests of materials before or after
incorporated into bldg, Ms. Contractor must be prepared to make load
tests in any portion of bldg within a reasonable time after erection, and as
often as may be reqd by engineer, Ch, Ph, Mh, Un. Tests must show
that the constr will sustain loads as follows:



SPECIFICATIONS FOR SIDEWALKS. 1201

For abbreviations, symbols and references, see p 947 1.

load = 2 X sum of proposed dead and live loads, Ch ;

= 2 X proposed live load, Ph ;
' = 3 X proposed load, Mh.

184. Construction may be considered as part of the test load, Ch.

185. Each test load shall cover 2 or more panels, and remain in place
not less than 24 hrs, Ch.



186. Deflection of slabs not more than

oUU

Deflection of girders > -J X ratio of slab depth to girder depth, Ch.

oUU

187. Test, 45 days after completion.

Load = 1.5 X live load + 1.5 X dead load of finished area.
Deflection > 0.001 X length of member, Ci,b.

CONCRETE SIDEWALKS.

Abstract of Specification

Adopted by
National Association of Cement Users

Philadelphia, January, 1908.

1. Cement, Portland, to meet specification of A S T M, adopted Jan,
1906. See p 940.

2. Sand. To pass No. 4 screen. May contain > 5 % loam and clay,
if these do not coat the sand grains.

< 60 % of the sand to pass No 10 sieve, or

35 % to pass No 10 20 30 40 sieve,
and remain on No 20 30 40 50 " , respectively.
> 20 % of the sand to pass No 50 sieve, or

70 % to pass No 10 20 sieve,
and remain on No 40 50 " , respectively.

3. Screening's, from crushed stone as below, and meeting sand require-
ments, may be substituted for sand.

4. Aggregate. Stone, crushed from clean, sound, hard, durable
rock, screened dry thru %" mesh, retained on W mesh.

5. Gravel, clean, hard, ranging from that retained on M" mesh,
to that passing %" mesh.

6. Unscreened gravel, clean, hard. No particles larger than %".
Proportion of fine and coarse particles to conform to requirements below
for cone.

7. Water, "reasonably clean, free from oil, sulfuric acid and strong
alkalies."

Sub-base.

8. Sub-base to be thoroly rammed. Soft spots removed and
replaced by hard material.

9. Fills > 1 ft thick, to be thoroly compacted by flooding and tamping
in layers > 6" thick, "and shall have a slope of < 1 : 1.5." "The top of
all fills shall extend < 12" beyond the sidewalk."

10. "While compacting, the sub -base shall be thoroly wetted and
shall be maintained in that condition until the cone is deposited."

Base.

11. Voids. Cera must overfill voids in sand by < 5 %.

12. Mortar must overfill voids in agg by < 10 %. Proportions 1 : > 8
sand and agg.

13. When the voids are not determined, 1 : 3 sand or screenings : 5
stone or gravel. "A sack of cem, 94 Ibs, shall be considered to' have a
vol of 1 cu ft."

C12



1 202 CONCRETE.



14. Hand. Sand evenly spread on a level water-tight platform, cem
spread on sand. Mix dry to uniform color. Water sprayed and mass
turned until homogeneous and of uniform consistency. Drenched agg
added and all mixed until agg is thoroly coated with mortar.

15. Hand. With unscreened gra\ r el. Cem and gravel "mixed
dry until no streaks of cem are visible." Water sprayed and mixed.
Mortar must be equivalent to that specified above.

16. "Water may be added while mixing, but cone must be turned <
once immediately afterward.

17. "Machine mixing will be acceptable when a cone equivalent
in quality to that specified above is obtained."

18. Retemperiiig prohibited.

Orade.

19. Orade of sidewalk < sufficient for drainage, > M"/ft, "except
where such rise shall parallel the length of the walk. "

Form**.

20. Lumber, clean, free from warp, < 1%'' thick.

21. Upper edges to conform with finished grade of sidewalk.

22. Cross forms. "At each block division, cross forms shall be put
in the full width of the walk and at right angles to the side forms, " except
as in U 23.

23. Expansion joint. A metal parting strip ^" thick to replace a
cross form < once in 50 ft. "When the sidewalk has become sufficiently
hard, this parting strip shall be removed and the joint filled with suitable
material prior to opening the walk to traffic. Similar joints shall be pro-
vided where new sidewalks abut curbing or other artificial stone sidewalk."

24. "All forms shall be thoroly wetted before any material
is deposited against them."

25. Dimensions of blocks.

Size, feet ............... 6X6 5X5 4.5X4.5 4X4 3X3

Thickness, ins :

In business districts, 6 5.5 5 4 ...

In residence districts, 6 5 ... 4 3

In residence sidewalks, edges may be 25 % thinner than center; min = 3".

26. Separating tool > 6" wide, W thick. Groove cut thru into
sub-base; groove filled with dry sand before the top coat is spread; top
coat cut thru to the sand after floating and troweling, "and a jointer run
in the groove"; trowel then drawn thru groove again "so as to insure a
complete separation of the block."

Depositing.

27. Cone carried to forms in watertight wheelbarrows. Cone must not
slop over. Barrows must not be run over freshly laid cone.

28. Cone must be deposited within 1 hour after mixing, spread evenly,
and tamped until water flushes to the top.

Protection.

29. Workmen must not walk on freshly laid cone.

30. Sand or dust, collecting on the base, to be "carefully removed before
the wearing surface is applied."

Wearing surface.

31. Minimum thickness, %".

32. Mortar, 1 : 2 sand or screenings, mixed as for base, but wet enough
not to require tamping, and so as to be readily floated with a straight-edge.
"A thin coat of mortar shall be floated on to the base before spreading the
wearing surf." Mortar spread on base within 30 mins after mixing, and
floated within 50 mins after base cone is mixed.



CONCRETE BLOCKS. 1203

33. Marking. "After being worked to an approximately true surf,
the block markings shall be made directly over the joints in the base with a
tool which shall cut clear through to the base and completely separate the
wearing courses of adjacent blocks."

34. Surface edges rounded to a radius < W.

35. "When partially set, the surf shall be troweled smooth."

36. On grades > 5 %, surf to be roughened by a suitable tool "or
by working coarse sand or screenings into the surf."

37. Only mineral colors shall be used, and these shall be incor-
porated with the entire wearing surf.

Single coat work.

38. Proportions, 1 : 2 sand : 4 gravel or crushed stone. Blocks
separated as in two-coat work. Cone to be firmly compacted by tamp-
ing, and evenly struck off and smoothed to the top of the mold.
"Then, with a suitably grooved tool, the coarser particles of the cone tamped
to the necessary depth so as to finish the same as two-coat work."

Protection.

39. "When completed, the sidewalk shall be kept moist and pro-

tectecl from traffic and the elements for at least 3 days. The forms shall be
removed with great care, and upon their removal earth shall be banked

against the edges of the walk."

Grading adjacent to sidewalk.

40. On curb side, 1 J^" below sidewalk, slope < M"/ft. On property
side, "the ground should be graded back < 2 f t and not lower than the walk. "



CONCRETE BLOCKS.

1. Buffalo harbor. Blocks 6 ft long, abt 4 ft sq, 88.75 cu ft = 3.3 cu
yds, made in wooden molds. H bbl Port, 2.5 cu ft sand, 7.5 cu ft pebbles,
7.5 cu ft broken stone, made a layer of cone, in mold, about 6" thick. Faces,
6" thick, of blocks on lake-face of breakwater, of finer material. Face
placed first; backing placed before face had set. (Emile Low, A S C E,
Trans, June '04, Vol LII, p 96.)

2. Zeebrugge breakwater, Belgium. Blocks 25 m (82 ft) long,
9 m (29.5 ft) wide, 8.75 m (28.7 ft) high, 2000 cu m (2616 cu yds), 4500
tons each. Outer cone shell, with cutting lower edge, three compartments,
formed in iron framework and floated to place; placed between guides and
block last sunk; sunk by admission of water, and filled up with cone,
1 ceni: 2.5 sand : 6.1 broken porphyry, by means of skips of 10 cu m (13
cu yds). Top meter, rich in cem, placed above water at low tide. Seaward
toe immediately protected by rubble rip-rap.

Superstructure of 55-ton blocks, laid above water; these surmounted by
cone blocks, formed in place.

3. Molds for isolated monolithic sub-aqueous concrete
blocks, from 150 to 222 cu yds, forming pier of trapezoidal cross-
sec. The molds are bottomless boxes of trapezoidal cross-sec, composed
of two sides and two end pieces, held together by 1 %" turnbuckle tie-rods
acting on beams placed outside of the mold. The tie rods have, at each
end, eyes in which wedge-bolts are inserted at time of erection. To remove
the molds, the wedge-bolts are removed by turning up a nut on the rods
which form an integral part of the wedge-bolts. This pulls the wedge-bolt
from the eyes of the tie-rods and releases the walls of the molds, which
are then picked up by the mold traveller, and re-assembled on the traveller
ready for re-setting. Weight of mold, 40 tons. Time reqd for removing
mold from a block and re-assembling for re-setting, from 45 to 60 mins.
Buoyancy of timber overcome by cast iron ballast wts. Alternate blocks
placed first. For intermediate blocks only the two side pieces of a mold are
used. These are held in place and at their proper batter by six turnbuckle
tie-rods, each passing thru a hollow square box of one-inch plank, acting
as a strut. (South Pier at Superior Entry, Wisconsin. Report of Clarence
Coleman, Asst. Engr Report Chf Engr/U S A, 1904, Part IV, page 3781.)



1 204 CONCRETE.

4. " Lewis holes should be cast in the blocks where practicable"
and so "as not to bring excessive pres on the cone, particularly near the
mortar facing or near the arrises of the block." Lewises and dogs may
pull out of green blocks. Provide wooden blocks and rag cushions for use
in turning over the blocks, otherwise the corners may be damaged.

5. Casting 1 position. Blocks should be cast with the most important
face down, their showing faces as nearly vert as practicable, and the back
of the block on top, so that laitance, etc, rising to the surf, may appear there.

HOLLOW CONCRETE BUILDING BLOCKS.

Abstract of Specification

Adopted by
National Association of Cement Users,

Philadelphia, January, 1908.



1. Cement, Portland, to meet specification of A S T M, adopted Jan,
1906. See p 940.

2. Sand, silicious, clean, gritty, to pass Y^' mesh sieve.

3. Aggregate, clean broken stone, free from dust, or clean screened
gravel, passing %" mesh sieve, refused by W-

4. Unit of measurement for cem. Bbl = 380 Ibs net; cu ft >
100 Ibs. Cem either measd in original package, or weighed; not measd
loose in bulk.

5. Proportions. For exposed exterior or bearing walls.

(a) Machine-made. Semi-wet, 1 : > 3 sand : > 4 agg.

(b) Slush (or wet) cone (quaking or flowing), made in individual molds
and allowed to harden in them, 1 : > 3 sand : > 5 agg.

If stone is omitted, proportion of sand may be increased if tests show no
increase in voids or in absorption, and no loss of strength.

6. Water enough to perfect the crystallization of the cem.

7. Mixing. "Thoro and vigorous mixing is of the utmost importance."

(a) Hand. Cem and sand mixt dry. Water added slowly and workt in.
Moistened agg spread upon mortar, or mortar upon agg. Mix.

(b) Machine preferred. Cem and sand, or cem, sand and agg, mixt dry.
Water added and workt in. With wet cone, "this procedure may be varied
with the consent of the bureau, etc."

8. Molding. Top surf of tampt blocks, after striking off, to be "trow-
eled or otherwise finisht to secure density and a sharp and true arris."

9. Curing. After molding, blocks to be "carefully protected from
wind currents, sunlight, dry heat or freezing for at least 5 days," and sup-
plied with additional moisture during that time "and occasionally thereafter
until ready for use."

10. Minimum age before using. 1 : 3 sand, 3 weeks; 1 : 2 sand,
2 weeks "with the special consent of the bureau, etc"; special blocks, for
closures, 7 days "with the special consent of the bureau, etc."

11. Marking. All blocks to be markt with^ maker's name or brand,
day, month and year of mfr, and proportions, as "1 : 2 : 3," etc.

12. Mortar. "All walls, where blocks are used, shall be laid up with
Portland cem mortar."

13. Maximum load, including wt of wall, 8 tons per sq ft of area
of blocks.

14. Thicknesses of walls. Bearing walls "may be 10% less
than is reqd by law for brick walls." In curtain or partition walls same as
for hollow tile, terra cotta or plaster blocks.

15. Offsets. "Wherever walls are decreased in thickness, the top course
of the thicker wall shall afford a full solid bearing for the webs or walls of
the course of blocks above."

16. Under girders or joists, blocks to be made solid for < 8"
from inside face. If concentrated load, W, on block, > 2 tons, this applies
to the blocks supporting the girder, etc; if W > 5 tons, it applies to blocks
for < 3 courses below, and to a dist of < 18" each side of girder, etc.



SPECIFICATIONS FOR BLOCKS. 1205

17. In party walls, blocks must be filled solid.

18. Bond. "Where the walls are made entirely of cone blocks, but where
said blocks have not the same width as the wall, every 5th course shall
extend .thru the wall, forming a secure bond, when not otherwise sufficiently
bonded."

19. Block facing-, on brick backing, "must be strongly bonded to the
brick, either with headers projecting 4" into the brick work, every 4th course
being a header course, or with approved ties, no brick backing to be less
than 8"."

20. Thickness of web of block (in bearing walls) < 0.25 X ht of
block.

21. Hollow space. In bearing walls, min percentage of hollow space:
Buildings of 1st 2d 3d 4th 5th 6th story

1 & 2 stories 33 33

3 & 4 " 25 33 33 33

5 & 6 " 20 25 25 33 33 33

22. Sills and lintels to be "reinforced by iron or steel rods in a
manner satisfactory to the bureau, etc." When span > 54", lintel "shall
rest on block solid for < 8" from face next the opening and for < 3 courses
below bottom of lintel."

23. Prior to use, application must be filed with bureau or with
chief of proper department, giving "a description of the material and a
brief outline of its manufacture and proportions used," with "name of the
firm or corporation, and the responsible officers thereof," "and changes in
same thereafter promptly reported."

24. Certificate of approval to remain in force > 4 mos, "unless
there be filed with the bureau of building inspection, at least once every 4
mos following, a certificate from some reliable physical testing laboratory
showing that the av " of < 3 comp tests and < 3 transverse tests comply
with requirements; "the said samples to be selected by a building inspector
or by the laboratory from blocks actually going into construction work."

25. Preliminary test. Maker to submit product to tests required,
and file certificate, from a reliable testing laboratory, giving in detail the
results of the tests made. Results of all tests, satisfactory or otherwise, to be
filed in the bureau, open to inspection, but not necessarily for publication.

26. Additional tests. Maker or user or both "shall, at any and all
times, have made such tests of the cems used in making such blocks, or
such further tests of the completed blocks, or of each of these, at their own
expense and under the supervision of the bureau of building inspection, as
the chief of said bureau may require."

Failure to stand these tests involves immediate revocation of the certifi-
cate issued to maker.

27. Test requirements. Blocks must be subjected to transverse,
compression and absorption tests, "and may be subjected to the freezing
and fire tests." Freezing and fire tests not at cost of mfr.

28. Approval tests made at expense of applicant.

29. Sfot less than 12 samples to be selected by bureau, etc.

30. ' ' Samples must represent the ordinary commercial product,

of the regular size and shape used in construction. The samples may be
tested as soon as desired by applicant " but > 60 days after mfr.

31. Blocks, failing to stand tests, to be marked "condemned"
by mfr or user, and destroyed.

32. "Tests shall be made in series of at least 3, except that in the fire
tests a series of 2 (4 samples) are sufficient."

33. " Half samples may be used for the crushing, freezing and fire
tests. The remaining samples are kept in reserve, in case duplicate or con-
firmatory tests be reqd."



1206 CONCRETE.

34. "All samples must be marked for identification and com-
parison."

35. Transverse test. Sample (full size) placed flatwise on parallel
rounded knife-edge bearings, 7" apart. Load applied, midway between
supports, thru rounded knife-edge.

Modulus of rupture = ; where W = load, in Ibs; L = span = 7";

6 = breadth of block, ins; d = depth of block, ins. "No allowance should
be made. . . for the hollow spaces." At 28 days, modulus of rupture, av 150
Ibs/LT, min 100.

36. Compression test. "Samples must be cut from blocks, so as to
contain a full. web section. The sample must be carefully measd, then
bedded flatwise in plaster of paris, to secure a uniform bearing in the test-
ing machine, and crushed. The total breaking load is then divided by the
area in compression in sq ins, no deduction to be made for hollow spaces;
the area will be considered as the product of the width by the length."

37. Ultimate comp strength at 28 days, av 1000 Ibs/ D", min 700.

38. For bearing walls, min 1000 Ibs / D". No deduction to be
made for hollow spaces.

39. Absorption. Sample dried to cpnstant wt, at > 212 F.
Weighed; placed in water, face downward, immersed < 2". Weighed at
30 mins, 4 hours, 48 h, and replaced in water immediately after each weigh-
ing. At end of 48 h, comp strength of wet specimen to be determined as
in H 36.

,. wt of water absorbed

Absorption = . Av > 0.15; max, 0.22.

wt of dry block

40. Reduction of comp strength, by absorption, > %.*

41. Freezing test. Sample immersed, as in U 39, for < 4 h, and

weighed. Subjected to < 15 F for < 12 h. 1'h in water of < 150 F.
Operation repeated 10 times. Weigh while still wet from last thawing.
"Its crushing strength should then be determined" as in U 36.

42. Loss of weight, max 10%; loss of strength, max %.*

43. Fire test. Two samples placed in cold furnace. Temp gradually
raised to 1700 F. Maintained for < 30 mins. One sample plunged in
water of about 50 to 60 F. The other sample cooled gradually in air.
"The material must not disintegrate."

44. Cement brick, as substitute for clay brick. 1 : > 4 clean sharp
sand; or 1 : > 3 clean sharp sand : 3 broken stone or gravel passing Y 2 "
sieve and refused by W- In other respects, cem bricks to conform to specfns
for hollow cone blocks.

*" Except that, when the lower figure is still above 1000 Ibs / Q", the loss
in strength may be neglected."



COST. 1207



COST.

1. The following data respecting prices and costs are compiled from rec-
ords of actual construction as carried out by men presumably skilled in the
art, and employing labor at ab9ut the usual rates. They afford only approx
estimates of what may ordinarily be expected. The cost of materials, trans-
portation, and especially of labor, varies from time to time and from place
to place.

2. Not only does the rate per hour for labor vary; but the amt of work
turned out in a given time varies much more widely. A well matcht gang,
presided over by an efficient foreman, will produce usually from two to
four times the output of an indifferent gang. Even a well-meaning worker
will frequently let his efficiency drop to 75 % of what may reasonably be
expected; indifferent workers will produce only 30 or 20 %. The methods
of payment, the character of superintendence, and the way in which the
work is arranged and handled, are all very important; and a bungler, or
one unfamiliar with cone operations, would probably find difficulty in keep-
ing the total costs within double those given.

3. The principal items, making up the cost of cone (plain and reinfd)
may be classified as follows:

Materials; Gem, sand, gravel, stone, reinfmt.

Transportation to storage; Hauling, freight.

Storage.

Screening, washing.

Mixing ; Loading and transporting to mixer, mixing machine and power,
labor and depreciation connected with it, auxiliary apparatus as mixing
board, barrows, shovels, etc., and transporting cone to forms.

Forms; Erection, shifting, depreciation, material, labor.

Depositing; Dumping, spreading and ramming.

Finishing; plastering, brushing, etc.

Inspection and superintendence.

Plant (besides mixer and forms); Interest, depreciation, repairs, insurance.

Cost of Materials.


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 20 22 23

Online LibraryJohn C. (John Cresson) TrautwineConcrete → online text (page 20 of 23)