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Transcript
A BUILDING EXTENSION: H and W CANOPIES
Technical details:
Frame:
Small purlins:
Posts:
Frame brackets:
Roof:
Gutter:
Scandinavian redwood – cut to size and planed. All conform to British Standard
CP112.
Main beam over the post:
2” x 6” (5.1 cm x 15.2 cm)
Wall plate and cross-members: 1 ½ “x 6“ (3.8 cm x 15.2 cm)
1 ½” x 2 ¼” (3.8 cm x 5.7 cm)
Galvanised steel tube 1 ¾” (4.4 cm) in diameter conforming to BS 1775.
Steel “U” clips are welded across the top of each tube.
Posts should be set 1 ft (30 cm) into the ground.
Maximum headroom 10 ft (3 metres).
“U” clips in galvanised steel.
All metal parts are coated in white polyurethane.
Corrugated PVC sheets in clear, green or yellow: 2’6” (76 cm) wide.
Grey PVC gutter and down-pipe supplied.
All screws and bolts (zinc-coated) are supplied.
ONLY SIMPLE TOOLS NEEDED
D.I.Y. or ERECTED FOR YOU
NO STANDARD SIZES – YOU TELL US DIMENSIONS AND WE´LL MAKE IT
Label the following:
post
u-clip
PVC sheet
screw
main beam
down-pipe
wall
bolt
wall-plate
cross member
gutter
purlin
Here is a description of H and W canopy, but a number of facts are wrong. Correct the
description.
The H and W canopy comes in a range of standard sizes up to 15 feet wide and 12 feet high. You
can put it up yourself, but some specialised tools are required for this. The canopy structure is
made entirely of wood (Canadian pine) and conforms to British Standards. The wall plate and
main beam are 2” x 6” and all other wooden members are 11/2” x 5”.
The upright posts are bolted to the ground with steel U-clips. The 2” diameter posts and the
frames brackets are zinc-coated and finished in grey polyurethane. The roof is also coated in
clear, green or yellow polyurethane sheets, 21/2ft wide.
CONCRETE
Concrete is the only major building material that can be delivered to the job site in a plastic state
and molded to virtually any form or shape. Concrete can be used to construct a wide variety of
structures, such as highways and streets, bridges, dams, large buildings, airport runways,
irrigation structures, breakwaters, piers and docks, sidewalks, silos and farm buildings, homes,
and even barges and ships. Other desirable qualities of concrete as a building material are its
strength, economy, and durability. The tensile strength of concrete is much lower, but by using
properly designed steel reinforcing, structural members can be made that are as strong in tension
as they are in compression.
The two major components of concrete are a cement paste and inert materials. The cement paste
consists of Portland cement, water, and some air. The inert materials are usually composed of
fine aggregate, which is a material such as sand, and coarse aggregate (as gravel, crushed
stone, or slag). Under normal conditions, concrete grows stronger as it grows older. The chemical
reactions between cement and water that cause the paste to harden and bind the aggregates
together require time. The reactions take place very rapidly at first and then more slowly over a
long period of time. In the presence of moisture, concrete continues to gain strength for years.
Depending on the applications, the proportions of the ingredients in the concrete can be altered to
produce specific changes in its properties, particularly strength and durability. In general, the
more water in a concrete mix, the easier it is to work with, but the weaker the hardened concrete
becomes. Concrete can be made to have any degree of watertightness. It can be made to hold
water and resist the penetration of wind-driven rains. On the other hand, for purposes such as
constructing filter beds, concrete can be made porous and highly permeable. Concrete can also
be given a polished surface that is as smooth as glass. By using heavy aggregates, including
steel fragments, dense concrete mixtures can be made that weigh 4005 or more kg/cu m.
Concrete that weighs only 481 kg/cu m can be made by using special lightweight aggregates and
foaming techniques. Forms consisting of such lightweight aggregates can be floated on water,
sawed into pieces, or nailed to another surface.
Reinforced concrete. Concrete used in most construction work is reinforced with steel in the form
of a mesh, or roughened or twisted bars. When concrete structural members must resist extreme
tensile stresses, steel supplies the necessary strength.
Prestressed concrete. The basic function of prestressing is to greatly reduce the tensile stresses
to which crucial areas of concrete structures are subjected.
CEMENT
In engineering and building construction the term cement usually refers to a finely powdered,
manufactured substance consisting of gypsum plaster or Portland cement that hardens and
adheres after being mixed with water.
PORTLAND CEMENT
Portland cement is manufactured from lime-bearing materials, usually limestone, together with
clays, shales, or blast-furnace slag containing alumina and silica. In the manufacture of cement
the raw materials are ground together, the mixture is heated until it fuses into a clinker, and the
clinker is ground into a fine powder. The heating is usually accomplished in rotary kilns. The
material takes approximately 6 hours to pass from one end of the kiln to the other. After it leaves
the kiln, the clinker is cooled quickly and ground, and then conveyed by a blower to packing
machinery or storage silos. The amount thus produced is so fine in texture that 90 percent or
more of its particles will pass through a sieve with 6200 openings per sq cm.
A number of tests are used to check the quality of the cement. A common one is to use a mortar
specimen of one part of cement and three parts of sand and measure its tensile strength after a
week in air and underwater. A good cement will show a tensile strength of 19.4 kg per sq cm
under these conditions.
SPECIAL CEMENTS
By varying the percentage of its normal components or adding others, Portland cement can be
given various desirable characteristics, such as rapid hardening, low heat during hydration, and
resistance to alkalis. Rapid-hardening cements, sometimes called high-early-strength cements,
are made by increasing the proportion of tricalcium silicate or by finer grinding Some of these
cements will harden as much in a day as ordinary cement does in a month. They produce much
heat during hydration, however, which makes them unsuitable for large structures where such
heat may cause cracks. Special low-heat cements, which usually have a large proportion of
dicalcium silicate, are generally used for massive pourings. Where concrete work must be
exposed to alkaline conditions, which attack concretes made with ordinary Portland cement,
resistant cements with a low aluminum content are generally employed. Cements for use under
salt water may contain as much as 5 percent iron oxide, and those with as much as 40 percent
aluminum oxide are used to resist the action of sulfate-bearing waters.
FACTORS AFFECTING THE HOUSE
A house in this country needs protection against the elements, the environment and a number of
other risks. Of course, the location of the house is an important factor. However, some types of
protection are important for both city and country houses. Other types of protection will depend on
whether the house is in a city or the country. In addition, although protection is important, it is
certainly not required against everything. In fact, it would be impossible to give a house total
protection. So we must look at each factor and decide how important protection is in each case.
The first factor is solar radiation. As we live in a temperate climate, it is unlikely that a house will
need protection against it. However, in hot climates this type of protection is often provided by
means of external wooden shutters or internal blinds. But I think that in Britain houses are unlikely
to get too much sun.
The next factor is high winds. Here I think we need to distinguish between city and country
houses. A country in an exposed location may need protection. But I think that in a city a house is
unlikely to be so exposed, and therefore unlikely to need protection against high winds.
The fourth factor is noise from outside. A normal brick structure, perhaps with double-glazed
windows provides sufficient protection. But a house located in a noisy area may need more
protection against outside noise.
Now I’d like to move on to the next factor – noise from inside. Here we need to consider how to
insulate one room against noise coming from another room. For this purpose interior brick walls
are recommended.
I’ve already mentioned rain, but there is also damp from underground or rising damp. In addition,
it is likely that both city and country house will need protection against it. Good foundations and a
solid stone floor are ideal for this type of protection.
All houses will certainly need protection against the risk of fire from outside. There is also the
danger of fire from inside. In this case we need to consider the type of heating used, as well as
other factors. In my opinion, all houses may require this type of protection.
The next point is heat loss. Although we live in a temperate climate, the British winters are
typically cold and very damp. Thick walls and well-fitted doors and windows prevent that loss.
Finally, there is a question of heavy snow. Heavy snow is not normal in most parts of Britain and
therefore a house definitely won’t need this type of protection.
GEOLOGICAL EXPLORATION
Geological exploration may be preliminary or detailed; the former determines the general type of
the soil, the latter must result in a minute report containing all the important particulars. Some
geological explorations are supplemented with the examination of the soil by means of sounding.
Geophysical methods are often used in determining the presence, level, fluctuation and general
behaviour of underground water. This exploration is especially important near wells, ponds and
streams. Another work that must not be neglected is a chemical analysis of underground water
that determines whether the water is aggressive by any chance. An accurate surveyor's plan,
which is naturally essential for a project to be perfect, enables all types of work to be done
properly and the individual objects to be spaced according to schedule.
WORK ON THE SITE
After the building site has been measured and mapped by surveyors and all other
investigations have been completed, the proper work can be started. The next and sometimes the
most complicated stage of the whole construction is earthmoving.
Today nearly all kinds of excavating and grading have been transferred to modern
earthmoving machinery. Excavators, bulldozers, scrapers and dump trucks are the most
important among them. Only narrow trenches and some digging on limited space are dug even
now by men once called "navvies".
All sites require the availability of electric power supply and water supply and good access
to the road network to enable safety and fluent transportation of people, building materials and
components. Sites on remote locations should be provided with canteens, temporary buildings
serving as changing rooms and shower baths for the workmen and with offices for the staff of
engineers.
The whole process of construction should be properly planned and accomplished
according to schedule. The site manager is responsible for keeping to the plan. The man who
checks the quality of work is the general foreman. He must be an experienced man who had
been working on several building sites as a tradesman and as a foreman.
Tradesmen in civil engineering is the name given to bricklayers, carpenters, concreters,
mechanical fitters and other skilled labour who do special kind of work. For example, plumbing is
done by plumbers and gasfitters, wiring by electricians, painting the walls and woodwork by
decorators.
On large sites we cannot do without cranes lifting various components, panels and other
heavy materials. There are many types of cranes as erecting cranes, full-gantry portal cranes,
travelling cranes and many other special-purpose cranes. The choice of a crane depends on the
construction requirements and kind of handling.
GEOLOGY AND THE CIVIL ENGINEER
Geology is the study of the solid earth and it includes the investigation of the rocks and
soils that form the earth. The civil engineer needs to understand the composition and the
structure of the rocks and soils because this governs their behaviour and because he is always
making use of them in one way or another.
For example, we build on them and so we need to know about the properties of the rocks, and in
this context particularly their load-bearing capacity.
We also excavate rocks, perhaps to create a reservoir site, or road cuttings, or railway cuttings.
We need to dig rocks and soils out of the way in order to be able to lay pipelines or cables or
perhaps even to dig canals to convey water from one place to another, and in this context we are
concerned with slope stability, the capacity of the soil to hold itself in place.
We also sometimes tunnel through the rocks. So we need to know whether or not the rock can
support itself or whether we need to put up some artificial support to prevent the roof of the tunnel
from collapsing.
We also quarry or mine rocks for their own value. Some rocks make very good building materials,
for example. Certain rocks are traditionally used for building stones. Other rocks make good
aggregates, (in other words, we break them up into small fragments) and these aggregates form
the basis for concrete or road stone and a number of other uses. Other materials are economic in
themselves; they have a high value, because they contain minerals such as gold, iron ore,
copper, etc.
Another use or application of geology is due to the fact that rocks contain water or perhaps oil or
other fluids which may be, again, economically worthwhile exploiting. These are the reservoir
rocks, and the engineer is involved in drilling into these rocks to extract the fluids.
Therefore, most engineering projects involve some excavation or some loading of the earth by
actually building on it, and I'm sure you can all think of lots more ways, lots more situations when
the earth materials play an important part in the design or construction of an engineering project.
It is important that the engineer can recognize common rocks and geological structures, and in
reading reports or studying geological maps he must understand the meaning of geological terms
and grasp geological concepts and arguments.
SOIL MECHANICS
I.
Every large civil engineering job starts with a soil mechanics survey in its early stages. The soil
samples and the laboratory results obtained from triaxial compression tests and shear tests show
at what depth the soil is likely to be strong enough to take the required load. The apparatus
generally used for measuring the shear strength of soil is the triaxial compression apparatus.
The strength of a soil generally increases with depth but it can happen that it becomes weaker
with depth. In choosing the foundation pressure for this sort of soil, a knowledge of soil
mechanics is therefore essential since it will give us an idea of the likely settlement.
There are, however, several other causes of settlement apart from consolidation due to load.
These include frost action, chemical changes in the soil, underground erosion by flowing water,
reduction of the ground water level, nearby construction in the form of tunnels, open cuts or
structures, or vibrating machinery such as vehicles.
II.
The shear strength can also be obtained from in-situ tests using a variety of methods. Two of
these give the shear strength directly; the in-situ box test carried out on the exposed surface and
generally used in overconsolidated clays, and the vane test carried out below the base of a
borehole or by direct penetration and used in normally consolidated or lightly consolidated clays.
Soil mechanics is based on the grain size, since it is the grain size that decides whether a soil is
frictional or cohesive, a sand or a clay.
Starting with the largest sizes boulders are larger than 10 cm, cobbles are from about 5 to 10 cm,
gravel or ballast is from 5 cm to 5 mm, grit is from about 5 mm to 2 mm, sand is from 2 mm to
0.06 mm. All these soils are frictional; being coarse and thus non-cohesive, their stability depends
on their internal friction. For the cohesive or non-frictional soils the two main internationally
accepted size limits are: silt from 00.2 mm, and clay for all finer materials. There are of course
many silty clays and clayey silts.
CONCRETE CONSTRUCTION TECHNIQUES
Concrete is poured into place in a number of ways. For the footings of small buildings, the wet
concrete is poured directly into trenches dug into the earth below frost level. Concrete for
foundations and certain types of walls is placed between supporting wood or metal forms, which
are removed after the concrete has hardened. In lift-slab construction, floors and roof slabs are
cast at ground level and then raised by hydraulic jacks and fastened to columns at the desired
elevation. Slip forms are used to produce vertical shafts for silos and the cores of buildings. They
are moved upward at a rate of 15 to 38 cm per hour while concrete and reinforcements are put in
place. The tilt-up method of construction is frequently used for one- and two-story buildings. Walls
are cast in place on the ground or on the previously laid concrete floor and tilted into position by
cranes. The walls are joined at the corners or between panels with cast-in-place concrete
columns. To pave a highway or road with concrete, a slip-form paver is used. For certain
applications, such as the construction of swimming pools, canal linings, and curved surfaces,
concrete may be applied by the shotcrete method. Often the use of shotcrete eliminates the need
for formwork and permits placement of concrete in confined areas where conventional forms
would be difficult or impossible to construct. Air-entrained concrete is concrete in which minute air
bubbles are intentionally trapped by the addition of an admixture to the cement. In freshly mixed
concrete, entrained air acts as a lubricant, improving the workability of the mix, thereby reducing
the amount of water that needs to be added. Entrained air also reduces the need for fine material
(sand). Entrained air in hardened concrete dramatically reduces the scaling that might otherwise
result from the use of chemicals to melt ice on roads and streets. It also prevents damage to
pavements caused by freezing and thawing. The air bubbles function as minute safety valves by
providing room for the free water in concrete to expand harmlessly as freezing occurs.
CONCRETE MASONRY is block and brick building units molded of concrete and used in all types
of masonry construction. Concrete masonry is used for load-bearing and nonload-bearing walls;
piers; partitions; fire walls; backup for walls of brick, stone, and stucco facing materials;
fireproofing over steel structural members; firesafe walls around stairwells, elevators, and other
enclosures; retaining walls and garden walls; chimneys and fireplaces; concrete floors; and many
other purposes. About 60 percent of all concrete masonry units, such as cinder blocks, are made
with lightweight aggregates. Masonry units are laid horizontally, and are cored to reduce weight
and to provide an insulating air space within the block. New types of concrete masonry, such as
split and slump block, are being used as facing in homes, commercial buildings, schools,
churches, and municipal facilities.
THE SCOPE OF CIVIL ENGINEERING
It was not until the middle of eighteenth century that precise scientific principles were applied to
civil engineering construction. Although the strength of materials such as wood and iron had been
measured and tabulated, practically nothing had been done to calculate the stresses in structures
in order to design them scientifically.
The foundations of the profession were laid by a soldier, Sebastian le Prestre de Vauban. He took
every possible opportunity of carrying out important public works of great value for peaceful
commercial use. He appreciated the value of controlling rivers and building canals, to help in the
defence of his country during wartime, and to stimulate trade in peace. His work was noteworthy
for the careful methods which he applied to it, a model which the young designer of today would
be well advised to follow.
Tremendous activity centres round such works as roads, motorways, railways, ports, factories,
large buildings, and power stations. These great schemes could never be completed within
reasonable time if it were not for widespread mechanisation. This has reduced costs and
surmounted labour shortage.
As a result of this, an immense variety of plant and equipment is now employed in civil
engineering work. Thus the construction of roads and airfields demands a fleet of tractors and soil
scrapers, excavators, and dumpers. Mobile concrete mixing and placing machinery, or central
concrete mixing plant, in addition to concrete spreading machines vibrators and handling
equipment, asphalt spreading machines, and road rollers are also necessary.
Work on heavy foundations requires excavators, heavy cranes, piling equipment,
compressed air plant, pumps and portable generation units. Concrete mixing and vibrating
equipment are also necessary. For undertaking hydro-electric and water supply schemes, heavy
earth moving plant, rock tunnelling plant, heavy cranes and cableways are all necessary. Where
large quantities of concrete have to be placed, crushing and screening plant is required for
producing aggregates. In tunnelling operations, the plant used largely depends upon the nature of
the ground. Rock drills, tunnelling shields, and compressed air equipment will generally be
required. Diesel or electric locomotives, rolling stock and track, together with pit winding gear and
cranes will also be necessary for moving excavated material and for placing concrete. Building
construction has become increasingly mechanised, and requires a tremendous variety of lifting
tackle. Machines include hoists, light derrick cranes, tower cranes, concrete mixers, dumpers,
and a very wide range of power hand-tools for finishing work.
From all this we can see that in modern civil engineering construction the best use of plant
combined with efficient maintenance is essential for success. A very wide range of work is
covered on large civil engineering projects, with the result that many specialists are employed.
Their work must be co-ordinated and carefully dovetailed into the overall construction
programme.
BRICKS
Bricks are one of man’s oldest permanent building materials. They were first used 5,000 years
ago. Building bricks are masonry units made of clay and hardened by heat or chemical action.
Sun-dried, or adobe, bricks are a mixture of clay and vegetable fibres; kiln-burnt bricks are made
from clays and are formed in a mould and fired in a kiln to hardness. Sand-lime bricks are a
mixture of sand and lime that has been hardened under steam pressure. Concrete bricks are
composed of Portland cement and aggregate. The most commonly used type is kiln-burnt brick.
Bricks are made chiefly from clay and shale. Clay is a mineral substance composed of very small
rock particles and is found over most of the Earth’s surface. Clay becomes slippery and plastic
when it is wet, when it dries it becomes hard. When clay is heated to a high temperature (about
450o C), it changes chemically so that it no longer becomes plastic when wet. This means that
bricks of baked clay will not soften and lose their shape when they become wet. Good bricks
should be thoroughly burnt in kilns at temperatures 870 to 1,200 o C, which makes them hard and
durable. This is the quality of lasting for a long time without disintegrating. The green bricks turn
red at about 535o C and the colour becomes darker as the temperature increases. Generally the
bricks should be true to size and shape, with straight edges and even surfaces which facilitates
laying them in position. Good, common bricks should be free from cracks, chips and large
particles of lime. Inferior bricks are generally underburnt and as a consequence easily broken and
very porous. Hollow bricks are much lighter than solid bricks.
Most brick produced in the United States is made by the stiff-mud process, using mixtures of
surface clays and shales. In the soft-mud process, a much wetter clay is pressed into moulds or
extruded, rather than sliced from a brick-sized column of clay. In the dry-press process high
pressure is used to compress a fairly dry clay in a mould and is then used to manufacture
refractory masonry, such as firebrick.
A firebrick is a brick that is capable of withstanding high temperatures without melting or
disintegrating. Firebricks for use in fireplaces, chimneys, flues, and common industrial furnaces,
where temperatures are less than 1,855oC (3,000oF), are made from clays containing alumina or
silica. For industrial processes requiring even higher temperatures - for example, steelmaking or
glassmaking - firebricks of magnesite or chrome or, less commonly, bauxite or silicon carbide are
used. The bricks are fired in tunnel kilns at temperatures of more than 1,292.5 oC.
Modern kilns are permanent enclosures with the heat usually generated by external ovens. The
heated air is circulated through the bricks stacked in the kiln to produce a fairly uniform masonry
unit. Kilns are classed as intermittent or continuous. In the intermittent kiln, the brick must be
piled, fired, cooled, and the bricks removed before new dried brick is piled to be fired. The
continuous, or tunnel, kiln consists of a tunnel with several zones in which the temperature is
carefully controlled. The moist clay formed by machines is loaded onto special cars that are
drawn through the kiln at a constant rate of speed. The bricks are successively shaped, dried,
fired, and cooled to produce a uniform product.