F ARMING
February 1940
IN SOUTH AFRICA
The Spiral Method of Reinforcing Circular
Brick -Structures.
By J. J. O. Pazzi. Engineer. Transvaal Soil-Erosion Section.
HE designs of thin-walled reInforced brick structures described
and illustrated in various publications-e.g. Bulletin No. 79, "Reinforced Brick Reservoirs", by E. J. van
Meerten-issued by the Department of
T
the factor of safety in that portion of the
structure. If by mistake or neglect, a
number of such faulty joints are made
near e"ach other, excessive weakening of
the structure may result and cracks may
develop.
c.
AdvantaBes of Spiral Reinforoement.
Reproduced by Sabinet Gateway under licence granted by the Publisher (dated 2013)
The spiral method of reinforcing not
only obviates these difficulties and produces a job with an increased factor of
safety, but also expedites the work by the
elimination of the frequent cutting and
joining of wires.
The underlying
principle is best illustrated as follows:
Instead of the usual method of laying
Agriculture and :Forestry have rapidly
gained popularity. The demand for such
structures has increased as a result of
the facilities offered by the Department
under the soil erosion and silo schemes.
Hundreds have already been erected, and
the fact that only a few cases of failure
have been brought to the notice of the
Department is most encouraging. In
these cases the trouble was due entirely
to the use of unsuitable materials, such
as soft wire-instead of high-strain steel
wire-sandy or half-burned bricks, and
mortar mixtures weaker than those
specified. It is false economy to attempt
to erect such structures with materials
that do not conform to the prescribed
standards; faults are bound to develop
if inferior substances are used and if the
detailed instructions embodied in the
descriptive pamphl~ts are not rigidly
observed.
With the usual method of reinforcing,
difficulties are experienced in the placing
of the reinforcing wires. Since steel
wire, which must be used, is very stiff
and therefore awkward to manipulate, it
is difficult to make joints of individual
rings flat enough so that they do not
interfere with the regular thickness of
the layers of mortar, especially in cases
where a number of wires must be
embedded in one layer. If the joints of
the wires are pressed down when the
bricks are laid the mortar will be disturbed and may therefore lose its allround grip on the wire, thus decreasing
-
primarily on the type and the depth of
the stored material, and on the diameter
of the structure. Since the pressure of
the contents increases with the depth, it
follows that the resistance need not be of
uniform strength throughout the height
of the structure; consequen tly, the
maximum reinforcing to render such
maximum resistance must be at the
bottom, gradually decreasing towards the
top. In most instances, to resist the
lateral or bursting pressure effectively
the maximum number of wires is
required at the bottom of the structure,
the number proportionately diminishing
as the height increases; for instance, if
under certain conditions it is necessary to
insert 5, 4, 3 or '2 wires at the bottom,
the number of wires may gradually be
reduced by 1/., 1, ! and! respectively as
the brickwork ascends.
The three accompanying tables give
the required details for reservoirs, ensilage pit-silos and grain tower-silos. The
formulae on which the tables are based
are given at the end of this article, in
order that the required particulars for
exceptional cases may be computed.
--
- - -...=;-~<::::>c
~
•
" CJ "
n
wm( Fi..t=JP•
M£T
bricks in separate level rows, the bricks Since the rolls of wire are somewhat
are placed in a continuous and gradually . bulky it is advisable to cut the lengths
beforehand
to
facilitate
handling.
ascending spiral tier. In other words,
the layers of bricks will resemble a coil Naturally, when the required length
of wire that has been wound ronna the exceeds that of the available roll, it is
thread of a bolt. Both the brickwork not necessary to join another coil of wire
and the reinforcement follow this spiral to the coil which is being used, until the
pattern.
latter is almost finished. Plain highThe pressure which the walls of strain steel wire is obtainable in rolls of
storage structures have to resist, depends 50, 75 and 100 lb. (650, 1,050, and 1,450
51
Reproduced by Sabinet Gateway under licence granted by the Publisher (dated 2013)
February 1940
FARMING IN SOUTH AFRICA
yards respectively). The various brands
differ slightly in the length of wire per
standard of weight, but the foregoing
figures are representative enough for
estimating purposes.
Construction of the Base.
Figure 1 illustrates how the footing of
the spiral, which consits of 1: 3: 6
concrete is cast on top of the foundation
ring. Width does not matter as long as
it is at least 5 inches, which includes
an allowance for plastering. Point A in
Figure 1 is level with the foundation
ring, and the height of the conCtI'ete
spiral is progressively increased to 3
inches (thickness of brick, plus t inches
mortar joint) at the point B next to the
starting point A. To obtain an even
gradient, guide marks 1 inch and 2 inches
high are established in advance at points
respecti vely one-third and two-thirds of
the way round the circumference. It is
preferable to cast the footing of the
spiral and the foundation ring in one
piece at the same time, in order to eliminate a seam between tne two. (Fig. 1a.)
In that case the true level must be very
carefully determined beforehand and the
thickness of the foundation ring added
when the guide marks for the footing'
of the spiral are established. Approximately 10 feet before the foundation
spiral reaches its ultimate height of 3
inches, the ends of the required
reinforcing wires have to be embedded
(" C" in Fig. 1). The wire should
emerge almost flush with the surface
where the spiral was started. (For the
saJ\2 of clearness only two reinforcing
wires are shown as dotted lines in Figures
1 and la, whereas the number actually
required may be greater or less-vide
tables. )
After the required wires have been
inserted and the casting of the spiral
has been completed, brick-laying can be
started from the 3 inch step at point B
towards point A (Fig. 1). The first layer
of bricks ascends the inclined plane of
the foundation spiral, and the last brick
of the round should oye,rlap the first
brick laid by 4~ inches, i.e. half the
length of a brick, so that a good bond
may be obtained. This process continues
uniel the desired height of the structure
is reached. Ultimately the top of the
wall will have to be levelled off; this
can be done by masoning the lower parts
with chipped bricks and the remainder
with mortar in which small chips and
pebbles have been incorporated.
To
obtain a first-class finish and at the same
time level the top spiral, the wall should
be capped with concrete of a minimum
thickness of two inches, the maximum
thickness of the concrete at the lower end
of the last spiral being five inches.
The reader can imagine how the
number of wires diminishes steadily as
the work proceeds. Remember that the
rolls of wire must be unrolled in the
true sense of the word, otherwise the
wire will coil and twist. A little care
in this connexion will prevent much
trouble. When a wire terminates, the
end must be secured by twisting it back
a couple of feet, so that a gentle loop is
formed, as shown in Figure 2. This
loop farms an excellent bond in the
mortar joint. To join wires, the writer
prefers a plain twist without loops,
extended over a couple of yards as shown
in Figure 3, since such a joint is less
bulky than other types.
(2) Total length of spiral; or in other
total length of longest wire in yards.
Ll = D X H X 4·2.
(3) To obtain the individual lengths
remaining wires, ascertain the
N-1
N-2
N-3
X Lv
XLI'
X
Where more than 3 wires are specified
it will be worth while to make a few
templates for the purpose of keeping' the
strands of wire parallel and in position.
The templates may be made of flat iron
or hard wood and should have as lllally
holes in a single row as there are wires
to be guided. (Figure 4---" A ".) The
templates are shifted up the spiral as the
work proceeds and the wires immediately
ahead of the bricklayer are kept down
by loose bricks.
The total length of all wires is thusLl
L2
La
= Ll
---w+
N -
+
1
( ~ XLI
)
of the
values
.
L 1, IS
X L 1 , is reached.
+ ................
+
+ ......... + .......... , etc.
The following example illustrates: A reservoir 68 ft. in diameter and 7 ft. in height with
a wall 4t inches thick has to be constructed.
What reinforcement is required ?
DxH 68x7
.
(1) N =
= ---so=5 '95, that IS 6
-----so-
WIres.
When a decimal results the next highest
whole number must be taken.
(2) Ll=D X H X 4·2=68 X 7 X 4·2=
1,999'2; say 2,000 yards.
N-1
6-1
(3) L2 = -W- X Ll = -6- X 2,000 =
The particulars relative to the number
of wires, the lengths of the individual
wires, and the total length of wire
necessary for any uninterrupted round
brick-structure may be obtained by
using the following formulae:
1,666'6; say 1,670 yards.
(1) No. of wires for water reservoirs (N) =
Then La, L 4 , L5 and L6
Diameter in Feet X Height in Feet
80
(6 63); (6 64); (O~~)
=(6~2);
D : H
,0
=
---w-
~o on until the value ~
and
Formulae.
i.e. N
-w-
words
respectively XLI'
=(~); (~); (~);
The same formula can be used for grain silos
and ensilage pit-silos by changing the divisor
as follows:-
(i)
respectively X 2,000 = 1,340; 1,000; 670;
335 yards approximately.
Total Length.
(sum of Ll to L 6) = 7,015 yards.
Reinforcement required
allowances
7
rolls of 1,050 yards each.
X H £or gram
"1
N = D
~
SI as; an d
+
X H f or enSI'1 age plt-Sl
" 1 os.
N = D 240
Spiral Masoned Ensilage Pit-silos of Brick, 4t inches thick.
'tein/orcing wires and their lengths in yards.
Number
0/
I
1
INTERNAL DIAMETER
Depth of I
Struct'lre'l
OF
STRUCTURE. (Feet),
8
I
9
I
10
I 11
I 12
I 13
I 14
I 15
I-I-I-I-I-I-I-!
1
I
8 feet. .
280
313
346 1 380
41-i
448 I
481
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - - - 1 _ _ _ _ _10 feet..
No. of
'Vires.
1
349
391
433 I
474
5161
5591
600
1
16
18
20
- - - - - -I- - - - - - - - -
514
548
615
682
~~--767--- 850
1
-------------------------------------
419
12 feet ..
57()
520
469
620
670
- - ----- - - - - - - - - - - - -
14 feet ..
489
16 feet ..
559
18 feet ..
629
665
607
fJ.i8
724
782
720
770
820
920
840
898
957
1,074
537
1,094
1347
1,227
614
- . -. _ - -
------------------
759
694
626
827
---------
20 feet ..
6981-----;83
22 feet ..
17681861
I--
I
25 feet ..
8661949
873
1
978
1,043
953
I
I
854
780
705
I
1,187
594
1,082
541
I
I
I
52
930
I
-
1,136
568
1,192
596
--
---
894
960
1,027
1,006
1,080
540
1,156
578
1,362
681
---------
I
1,033
1,020
-
1,118
559
I
1,231
616
1,382
691
1,532
766
2
------------
1,200
600
1,284
642
1,368
684
1,535
768
1,702
851
1,688
844
I 1,872
936
------------------
1,230
1,412
1,505
1,320
615
660
706
753
---1---:--1,292
1,710
1,39611,500
1,606
646
698
750
803
855
1,920
960
2,130
1,426
713
3
Reproduced by Sabinet Gateway under licence granted by the Publisher (dated 2013)
F ARMING
February 1940
IN SOUTH AFRICA
Spiral Masoned Reservoirs of Briclc, 4~in. thick, standard Height 6 ft. Numbers
of reinforcing wires and their lengths in yards.
INTERNAL DIAMETER
20
25
30
I
35
40
45
OF
50
STRUCTURE (Feet).
55
60
65
II
70
75
80
6
6
6
--.--------------
Number of
Wires ......
Length of wires
in yards ....
Total length
(yards) ...
2
2
3
3
4
3
4
5
5
5
- -- -- -- -- -- -- -- -- -- -- -- -- 512
637
762
888
1,013
1,138
1,265
1,390
1,.~15
1,640
1,766
1,890
2,017
256
319
508
592
676
854
949
1,112
1,212
1,312
1,472
1,575
1,680
-
-
254
296
338
569
633
834
909
984
1,178
1,260
1,344
-
-
-
-
-
285
316
556
606
656
883
945
1,008
-
-
-
-
-
-
-
278
303
328
589
630
672
295
315
336
1~183
6,615
7,057
------'--1-----
~~~~ 2,027 2'8461~ 4,170
i 4,545
1 4 ,920
---------~--~----~--~--~--------~--~------~----~--~--------
Spiral Masoned Grain Silos of Brick, 4-k m. thicle.
N1lmbers
wires and their lengths in yards.
of
reinforcing
The Farming System.
HEIGHT OF STRUCTURE (Feet).
Internal N b
Diameter um er
-------,-------------c---------,----I-,----,--of
of
~~~~.
Wires. __1_0_
8 feet.
349
10 feet.
-----1--12 feet.
~i
419
2
489
- - - - ----724
362
1~':~
_2_4_+1_2_6----. __
28__ __
30_-.
,
559
280
---43-3- =:]20--60-7-1---69-4304
347
620
310
14 feet.
__l_4____1_6____1_8__
827
414
780
390
866
433
930
465
1,033
517
1,137
758
379
1,240
827
413
----- --------1-------4'------ - - - -----
840
420
960
480
1,080
720
360
1,200
800
400
1,320
880
440
1,440
960
480
1,560
1.040
520
1,680
1,260
840
420
- - - - - - - - -----1----1---1·---16 feet.
18 feet.
1,094
730
365
3
1,231
820
410
1,368
912
556
1,505
1,004
502
1,642
1,231
821
410
1,779
1,335
890
445
1,916
1,437
958
479
2,053
1,539
1,026
513
- - - - - - - - -----i-----..---!--- - - - - 2,154
2,308
1,691
1,845
1,382
1,.~35
2,000
1,724
1,845
1,269
1,383
922
1,500
1,024
1,293
1,384
461
512
846
922
1,000
862
923
500
423
461
431
461
- - - I - -_ _ _ _ _ _ I_ _ _ ~-----~---~---------20 feet.
2,552
2,212
2,382
I
1,702
1,872
2,042
1,769
1,904
2,041
1,561
1.276
1,404
1,428
1,531
1,327
4
851
936
1,040
1,020
885
952
425
468
520
510
442
476
,-,
1-
.0
Farm Manure for Sound
Farming.
IT is an incontrovertible fact that farm
manure constitutes the controlling factor
in successful farming in the South
Coastal Belt of the Cape Province.
Consequently the economical production
of crops is only possible for the farmer
who has an adequate supply of manure
at his disposal and who fertilizes his
lands thoroughly every 3 or 4 years. The
farmer who imagines that crops can be
successfully cultivated with the aid of
artificial fertilizers only, i.e. without
periodic applications of farm manure,
will most assuredly have his hopes dash
to the ground in the long run, since such
a system is impossible under practical
farming conditions.
Importance of Manure.
The chief reason why the applicatior;.
of farm manure is so very essential,
particularly in this area, is that the
soils, as a rule, are deficient in humus.
Humue may be regarded as the life and
53
soul of the soil; it also constitutes the
storeroom of nitrogenous plant food,
which is so vitally essential for vegeta. tion. The more frequently and intensively the soil in the area is tilled and
loosened, the faster the breaking up and
consumption of humus takes place and
the faster the soil becomes exhausted. A
deficiency in hu'mus exercises an injurious effect on the physical condition of
the soil, which manifests itself clearly in
the extent to which such soil compacts
after heavy rains and in the exhaustion
of the supply of plant food.
A notable characteristic of farming in
this area is the complete deficiency in
this most essential requirement, viz.
farm manure. The writer cannot think
of a single farm where there is an
adequate supply of manure for all the
lands, and consequently is convinced of
the fact that this deficiency constitutes
one of the chief reasons for the difficulty
which many farmers in this area are
experiencing nowadays in eking out a
satisfactory livelihood from farming.
This unhealthy condition compels one
to conclude that the farming system, as
applied, is too one-sided, inasmuch as
stock-breeding does not play a large
enough part in proportion to the comparatively large area which is cultivated
for the production of grain crops. Such
a one-sided system must necessarily lead
to overcropping and ultimately, in consequence of the gradual and systematic
destruction of the farm itself, to the
general weakening of the farmer's
economic position.
Thus a deficiency in farm manure is
beyond doubt the weak link in the farming system as it is at present being
applied in this area. Consequently it
is imperative that the farmer should
devote his attention to the necessity for
altering his system, in order that stockfarming may take its rightful place in
the farming concern. Not only is the
production of stock-farming products
more lucrative than that of grain products, but stock-farming is also very
necessary for the improvement and preservation of soil fertility, as it will
supplement the large deficiency in farm
manure.
ICI
Nurseries in Quarantine.
The following nurseries were in quarantine
on 1 January 1940:-Barclay Vale Nurseries, Rivulets, for red
scale in citrus (whole).
Wyngold Nursery (G. Green), Bathurst, for
red scale in citrus (whole).
Public Nursery, Vereeniging, for pernicious,
Ross and pustular oak scales in oaks, privets
and shrubs (part).
Municipal Nursery, Germiston, for pernicious, Ross and pectinatus scales in forest
and ornamental (part).
Alkmaar Estates, Alkmaar, for red scale in
citrus (whole).
Waterfall Nurseries
Johannesburg,
for
pernicious scale in deciduous fruit trees, hedge
and ornamental (part).
Subkleves Nurseries, Johannesburg, for oak
and pernicious scales in deciduous fruit trees,
hedge, forest and ornamental (part).