NOTES - 02
EQUIPMENT MANAGEMENT
TIPS FOR THE CONSTRUCTION ENGINEERS
AND PLANT &
MACHINERY ENGINEERS
AN INTRODUCTION TO
CONSTRUCTION PLANT AND EQUIPMENT
EQUIPMENT MANAGEMENT
TIPS
APPLICATION OF
KNOWLEDGE AND EXPERIENCE
I. INTRODUCTION
When
the prospective owner of a project under consideration recognizes a need for
the project, he usually employs an engineer/consultant to make a study to
determine whether the project is justified and this exercise is known as
feasibility study. If the study indicates that it is justified an
engineer/consultant will be engaged to prepare the plans and specifications and
usually to supervise the construction of the project. It is the function and
duty of the engineer to design the project which will most nearly satisfy the needs
of the owner at the lowest practical cost. The Engineer should study every
major item to determine if it is possible to reduce the cost without unduly
reducing the service which the project will furnish. It may be possible to
change the design, modify the requirements for construction or revise portions
of the specifications in such manner that the cost of the project will be
reduced without sacrificing its essential value. An engineer/consultant who
practices the philosophy is rendering a real service to his client. Thus it is
evident that an engineer/consultant should be reasonably familiar with
construction methods and costs if he is to design a project that is to be
constructed at the lowest practical cost. Construction is an age old
profession. The construction activity could be traced to be the first
transformation of a 'caveman' to a different standard of living and the need to
have a different shelter over his head. There is evidence however, that the
development and the construction industry in the country like several other
industrial fields were rather slow and unsystematic till the nineteenth
century. It is mainly during the current century that the induction of large
scale mechanization has brought about rapid changes in building practices and
in the management and construction jobs. It is practically during the last few
decades however, that India has resorted to considerable systematization and
mechanization in the industry when it had to deal, for the first time, with
massive construction programs of irrigation, power, steel, cement, paper,
defense and other industrial development projects.
As
regards the construction techniques and management of the construction
operations in different countries, depending upon their stage of development and
material environment there has to be considerable difference in the state of
development of the industry. In developed countries, for example, there is
large scale mechanization and industrialization in construction and the
management lies around the optimum utilization of resources such as the limited
number of man, construction equipments and materials. In India though we have
also introduced considerable mechanization particularly during the last 25 to
30 years, there is still a major element of manual labor to be taken care of,
in actual construction activity and management.
Statistics
show that the construction industry contributes annually about 8-10 per cent to
the gross national product of both the developing and developed countries. It
is also well known and established fact that the construction industry accounts
for the largest single element in national development expenditure. The
investment in developing countries may range anywhere from 45 to 55 per cent of
budget. In fact in the successive five years plan in India the investment on
construction projects has been assessed at not less than 50 per cent of the
total national plan budget. There is also no doubt that to a large extent the
projects of the country as a whole will depend on success of new national
development programs.
II. NEED FOR EQUIPMENT
- MECHANISATION OF CONSTRUCTION
With
the sudden advancement in technology and rapid increase in the labor rates
there is an increasing trend of mechanization, industrial pre-fabrication,
pre-casting and industrialized methods of construction in the industry all over
the world. In developed countries, due to acute shortage of manpower it has
become obligatory to go for mechanization to the highest possible extent to
keep pace with the demands of industrialization. In India though we claim to
have resorted to high mechanization particularly in some of our irrigation and
industrial projects, still full scale mechanization is rare. The time is
however, not far off when a contractor who does not keep himself abreast of new
construction equipment and methods of planning and construction may discover
that he is out of business.
A
problem which frequently confronts, contractor as he plans to construct a
project is the selection of most suitable equipment. He should consider the
money spent for equipment as an investment which he can expect to recover with
a profit during the useful life of equipment. A contractor does not pay for
construction equipment; the equipment must pay for itself by earning for the
contractor more money than its cost. Unless it can be established in advance
that a unit of equipment will earn more than the cost it should not be
purchased.
A
contractor can never afford to own all types or sizes of equipment, which might
be used for the kind of work he does. It may be possible to determine which
kind and size of equipment seems to be most suitable for a given project but
this information alone will not necessarily justify the purchase of equipment.
Perhaps the project under consideration is not large enough to justify the
purchase because the cost cannot be recovered within the completion period of
the project and it may not be possible to dispose-off the equipment at the
completion of the project at a reasonable price. A contractor may own any type
of equipment, but, considering the probable heavy depreciation for the proposed
equipment and the uncertainty whether it can be used on future projects, the
apparently ideal equipment may prove to be more expensive than the equipment
now owned by the contractor.
Any
time, a unit of equipment will pay for itself on work that is certain to be
done; it is good business to purchase it. For example if a unit of equipment
costing Rs.5 lakhs will give Rs.10 lakhs on a project, a contractor is
justified in purchasing it regardless of the prospects of using it on
additional projects or the prospects of selling it at a favorable/justifiable
price on completion of the project. Under these conditions, one of the largest
single elements of investment of the contractor would be on owning and
operating of plant and equipment. The capital investment on the purchase and/or
rentals/lease and operation of the plant and equipment being generally high, it
has to be managed so as to ensure minimum operational, maintenance and repair
costs, maximum productivity and returns on the investment made. Proper and
efficient management of this important resource therefore, is essential for the
success of a construction company.
The
foremost important decision is to select the most suitable plant and equipment
which can pay for itself and determine the number and type, essentially
required for the newly acquired job. A good deal of information and the
specifications, production capacities, capital costs and costs of operation and
maintenance are available in the suppliers' manuals for various types of
equipment. A well experienced equipment engineer/planner comes handy in the
decision making.
III. TYPES OF
EQUIPMENT
There
is no clear definition of standard equipment. Equipment that is standard for one
contract may be special equipment for another. It depends on the extent to
which a contractor will use it in his construction operations. Another method
which is sometimes used to distinguish between standard and special equipment
is the extent to which it is commonly manufactured and available to prospective
purchasers. Thus a 1 cu.yd. diesel powered crawler mounted power shovel is a
standard equipment, whereas a 30 cu.yd. shovel is classified as special
equipment. The larger shovel is manufactured for a specific purchaser.
Contractor
should continue their purchases of standard equipment unless a project
justifies the purchase of special equipment. Delivery of standard equipment may
be obtained more quickly. Standard equipment can be used economically on more
than one project. Repairs for the standard equipment may be obtained more
quickly and economically than for special equipment. If a contractor no longer
needs a unit of standard equipment he can usually dispose of it more easily and
at a more favorable price.
IV. SPECIAL EQUIPMENT
One
definition of special equipment is equipment that manufactured for use on a
single project or for a special type of operation. Such equipment may not be
suitable or economical for use on another project. An example of special
equipment is a 30 cu.yd power shovel used to remove the overburdening in open
cast mining of coal. Another example is the hydraulic dredge which was
constructed primarily for use in building of the Bhakra Nangal Dam Project.
Another special type of equipment is the Canal trimmer. This equipment is used
for the trimming of the bottom and sides of an earthen canal prior to placing
of watertight membrane such as concrete or asphalt surfacing. However, as this
type of equipment is becoming more common in canal construction it might now be
considered as standard equipment. Although belt conveyer systems are sometimes
used to transport aggregates for several miles in construction of dams, such
installation probably should be considered as special equipment.
In
developed world the construction industry is more or less fully mechanized,
right from stage of excavation, compaction, binding and placement of
reinforcement, fixing of frame work, batching, mixing and pouring of concrete,
use of concrete pump, tower cranes and other material handling and conveyance
systems and building implements up-to the finishing stage, suited to the job.
Some of the equipments most frequently and commonly used in a high degree of
mechanization on a project could be as follows:-
A. TRACTORS
Tractors
have many uses as construction equipment. Use of this, primarily may be to pull
or push goods, they are also used as mounts for many types of accessories such
as front end shovels, rippers, bulldozers, side brooms, hoes, trenchers and others.
There are sizes and types to fit almost any job for which they are usable.
Tractors may be divided into two major types:
-
Crawler Type Tractor
-
Wheel Type Tractor
B. EXCAVATION
Bulldozers
- the term bulldozer may be used in a broad sense to include both a bulldozer
and an angle dozer. These machines may be further divided on the basis of their
mountings, into crawler tractor or wheel tractor mounted. Based on the method
of raising and lowering the blade a bulldozer may be classified as cable controlled
or as hydraulically controlled. Each type of equipment has a place in the
construction industry. For some projects one type will be satisfactory while
for other projects some other type will be suitable. Bulldozers are versatile
machines on many construction projects where they may be used from the start to
the finish of such operations as:
-
cleaning land and timber and stumps
-
operating up pilot roads through mountains and rough terrains
-
Moving earth for haul distances up-to 300' (@100M)
-
helping load tractor pull scrapers
-
Spreading earth fill
-
cleaning construction sites to debris
-
Maintenance of haul roads
-
cleaning the floors of borrows and quarry pits
Bulldozers
are mounted with blades perpendicular to the direction of shovel while angle dozers
are mounted with blades at an angle with the direction of travel. The former
push the earth forward while the latter push it forward and to one side. Some
blades may be adjusted to permit their use of bulldozers or angle dozers.
The
size of a bulldozer is indicated by length and height of the blade, plates may
be installed at the ends of the blades to reduce the spillage when a machine is
used for moving earth.
C. SCRAPERS
Tractor
pulled scrapers has established an important position in the earth moving
field. As they are self operating to the extent that they can load, haul and
discharge material they are not dependent on other equipment. If one of them
experiences a temporary breakdown it is not necessary to stop the job as would
be the case of machine which is used exclusively for loading earth into hauling
units for if the loader breaks down the entire job must stop until repairs can
be made. The self loading scrapers are available with capacities upto 50 cu.yd.
or more.
These
machines are the result of a compromise between the best loading and best
hauling machines and as must be expected with any composite machines they are
not superior to other equipment in both loading and hauling. Power shovels,
draglines and belt loaders usually will surpass them in loading only while
trucks may surpass them in hauling only especially when long-haul is there.
However, their ability to load and haul earth gives them a definite advantage
on many projects. The development of high-speed wheel type tractors has increased
the economic haul distance speed for the type of equipment up-to 1/2 to 2 km.
or more in many projects.
The
ability of these machines to deposit their load in uniform thick layers will
facilitate the succeeding spreading operation on the return trips to borrow
pits. The cutting blades of scrapers may be lowered enough to remove high
spots, thereby assisting in maintaining the haul roads.
D. OTHER EXCAVATING
EQUIPMENT
Following
equipments are used to excavate earth and related materials and to lift them frequently
in construction operations.
The
equipment includes the following machines:
-
Power Shovels
-
Backhoes
-
Draglines
-
Clamshells and Cranes
-
Trenching Machines
-
Wheel Mounted Belt Loaders
-
Power Shovels are used for excavation and loading into hauling units
-
Backhoes are used in excavation on natural surface. These are more rigid than
draglines and advantageously used on close range work.
-
Draglines are advantageously used in canal trench excavation and excavation
under water.
-
Clamshells are used mainly for lifting vertically and handling loose materials
such as sand, crushed stones in dams, pier foundation and sheet piling etc.
-
Trenching machines are either wheel or crawler type
-
Wheel excavators can cut weathered or broken rock.
E. MATERIAL HANDLING
-
Trucks and wagons in handling earth, aggregates, rock ore, coal and other
materials serve one purpose. They are hauling units which because of their high
speeds when operating on suitable roads have high capacities and provide
relatively low hauling costs. They provide a high degree of flexibility and the
number of services may be increased or decreased to permit modifications in the
total hauling capacity of a fleet. Most trucks may be operated over any haul
road for which the surface is sufficiently firm and smooth and on which the
grades are not excessively steep.
Some
units now in use are designated as off highway trucks because their sizes and
total loads are larger than are permitted on highways. These trucks are used
for hauling materials on large projects where the size and costs are justified.
Trucks
may be classified according to many factors including the following:
-
Size and type of engine - gasoline, diesel, butane, propane
-
Number of gears
-
Kind of drive - two wheels, four wheels, six wheels etc.
-
Number of wheels and axles and arrangement of driving wheels
-
Method of dumping the load - rear dump, side dump
-
Class of material hauled - earth, rock, coal, ore etc.
-
Capacity in tones or cubic yards method of dumping the load for rear dumps
-
Hydraulic or cable
If
trucks are to be purchased for general materials hauling, the purchaser should
select units that are adaptable to the purposes for which they will be used.
However if trucks are to be used on a given project for a given purpose the
purchaser should select trucks that most nearly fit the requirements of the
project.
F. BELT CONVEYERS
Belt
conveyers systems are used extensively in the field of construction where they
frequently provide the most satisfactory and economical method of handling and
transporting materials such as earth, sand, gravel, crushed stone, ores,
cement, concrete etc. Because of the continuous load of material at relatively
high speeds, belt conveyers have high capacities.
The
essential parts of the belt conveyer system includes a continuous belt, idlers,
a driving unit, driving and tail pulleys, take up equipment and a supporting
structure.
A
conveyer for transporting materials a short distance may be portable unit or a
fixed installation. One of the first questions that arise in considering the
use of a belt conveyer is whether this method of transportation is the most
dependable and economical when compared with other methods. The way to answer
to the question is to estimate the cost of transporting the material by each
method under consideration. Assume that a belt conveyer is to be compared with
trucks for hauling aggregates for a large construction project.
The
net total cost of the conveyer system will include the installed cost of the
system, on access road for installing and servicing the system, maintenance,
replacements and repairs, fuel or electrical energy, the labor, less the net
salvage value of the system under completion of its use. Interest on
investment, taxes and insurance, if they apply should be included. Likewise any
cost of obtaining a right way for the system should be included. The unit cost
of moving the materials per ton or cubic yard may be obtained by dividing the
net total cost of the system by the numbers of units to be transported.
The
cost of transporting the materials by truck will include cost of constructing
and maintaining a road, plus the cost of operating the trucks. The unit cost of
moving the materials may be obtained by dividing the net total cost by the
number of units to be transported.
If
either method requires additional hauling costs at the source or at the
destination these costs should be included prior to determining the unit cost
of moving the materials.
G. CRUSHERS
The
production of crushed stone aggregate involves drilling, blasting, loading,
transporting, crushing, screening, handling and storing the aggregate. In
operating a quarry and a crushing plant, the drilling pattern, the amount of
explosive, the size of power shovel to handle stone, and the size of the
primary crusher should be so coordinated to assure that all stones from quarry
can pass through the opening of the crusher. It is also desirable for the
loading capacity of the shovel and capacity of the crushing plant to be
approximately equal.
Types
of Crushers
Crushers
may be classified according to the stage of crushing which they accomplish,
such as primary, secondary, tertiary etc. A primary crusher receives the stone
directly from quarry and produces the first reduction in size. The output of
the primary crusher is fed to a secondary crusher who further reduces the size.
Some of these stones may pass through four or more crushers before it is
reduced to the necessary fineness. While there is no rigid classification of
crusher, the following is representative of common crushers:
i.
Primary crushers
-
jaw
-
gyratory
-
hammer mill
ii
Secondary crushers
-
cone
-
roll
-
hammer mill
iii.
Tertiary crushers
-
roll
-
rod mill
-
ball mill
As
stone passes through a crusher, it undergoes a reduction in size which may be
expressed as a ratio of reduction. The ratio of reduction is the ratio of the
distance between the fixed and moving faces at the top divided by the distance
at the bottom of a crusher. Thus if the distance between the two faces of a jaw
crusher at the top is 16" and at the bottom is 4" the ratio of
reduction is 4.
H. BATCHING AND MIXING
PLANT, TRANSIT MIXERS ETC.
Concrete
is basically a mix of cement, aggregate and water which have been mixed
together deposited and permitted to solidify. In order to produce concrete
having the required properties, it is necessary to control the quantity of each
material that goes into a batch. This is referred to as batching the materials.
Although batching may be done by volume or by weight the former method is so
unreliable that it should not be used on any job where properties of concrete
are of importance. Weigh batching is much more dependable and more commonly
used than volume batching.
Concrete
mixers
Concrete
mixers may be classified as
-
Construction mixers
-
paving mixers
-
transit mixers
The
old practice of specifying the size of a mixer as one bag, two bags etc. is
being well abandoned in favor of specifying the size by the nominal volume of
concrete that can be mixed in a batch, expressed in cubic feet for construction
and paving mixers and in cu.yd./cu.m. for transit mixers.
For
construction mixers with a single compartment drum the standard sizes are 3S,
1/2S, 6S, 11S, 16S, 28S, 56S, 84S and 112S. The number indicates the normal
volume of mixed concrete in cu.ft. while the letter 'S' designates that the
equipment is a construction mixer. These mixers must be capable of mixing 10
per cent more of the rated capacities when they are operating in a level
position. The output of a concrete mixer generally is expressed in cu.yd./cu.m.
per hour of concrete mixed. Obviously, the output will vary with the size of a
mixer and the conditions under which it is operated. For any given mixer and
job conditions the output will be the product of the volume per batch in times
and the number of batches per hour.
Concrete
mixing (batching) plant
A
concrete mixing plant may be installed to mix concrete for a large structure
such as a dam or for sale to the public. Such a plant includes equipment for
handling and storing aggregate and cement batches and construction concrete
mixer. The mixed concrete may be discharged into buckets, agitators or dump
trucks.
Paving
mixers
Paving
mixers are used primarily to mix and place concrete for highways, streets and
airport runways. They are mounted on crawler trucks in order that they may move
along with placing of concrete.
I.
TRANSIT MIXER AND AGITATOR TRUCKS
A
transit mixer or agitator truck is a truck on which a concrete mixer is
mounted. If the aggregate including the cement is charged into the mixer at a
central batching plant, with mixing to be done en-route on the job, the unit is
called a mixer. If the unit is used to have mixed concrete which required
agitation en-route to the project to prevent it from segregating, the unit is called
an agitator. The transit mixers are available in capacities varying from 1 to
7.5 cu. yds.
J.
PLACING OF CONCRETE
Concrete
may be handled and transported by several methods such as buggies, buckets,
handled by crane, hoisting towers or cables, chutes, belt conveyers, trucks,
transit mixers or dump trucks, pumps and pipelines. Each method which has
advantages and disadvantages is suitable for use under certain conditions. The
method selected should permit use of concrete having the required properties:
-
hand buggies or carts equipped with pneumatic tyre which are available in sizes
of 6 to 11 cu.ft. are suitable for use on many projects.
-
Power driven buggies: Within recent years power buggies have been used at
increasing rates to haul concrete. They have capacities of 1/3 to 1/2 cu.yd.
and speeds upto 15 mph can make a 180 degree turn on about 4 ft. and can climb
grades upto about 20 per cent when loaded. Power buggies may pay for themselves
in 1 to 6 months by economies which they can affect compared with the cost of
transporting concrete with hand buggies.
-
Buckets: Buckets may be divided into two parts- those used with material towers
and those used with power cranes, cables etc. The former which are referred to
as tower buckets, vary in size from 8 to 36 cu.ft. while the latter which are
referred to as concrete buckets vary in size from about 0.5 to 8 cu.ft.
Concrete
buckets have bottom gates which may be opened in such a manner that concrete
will flow vertically downward. The gates on the smaller buckets are operated
manually while the gates on the larger buckets are operated by compressed air
or by some mechanical method. Gates should be designed so that they may be
opened or closed at will to regulate the flow of the concrete.
Concrete
pumps
A
wide variety of pumps are available for placing concrete. These pumps can
handle all kinds of mixes and can pump upto 125 cu.yd. per hr. Recommended
pumping discharges vary from 250 to 2000 ft. horizontally and from 75 to 400
ft. vertically. These pumps may be mounted on truck's trailers or skids.
The
truck mounted pump and boom combination is effective in saving labor and
eliminating pipeline handling and set up time and costs. Hydraulically operated
and articulated, the booms come in various lengths up-to nearly 100 ft. Pumps
are sometimes also classified by way of their functioning.
-
piston
-
pneumatic
-
squeeze type
K. COMPRESSORS
These
are available as stationary, portable, rotary or reciprocating types and used
for drilling of rocks, pile driving and for pneumatic vibration, concrete
lining of tunnels etc.
L. PILE DRIVING
EQUIPMENT
Pile
hammers are classified as drop single action steam, double action steam,
differential acting steam or diesel.
M. CRANES
Because
cranes are used to hoist and move loads from one location to another it is
necessary to know the lifting capacity and working range of a crane selected to
perform a given service.
Cranes
on the building site offer three possible advantages:
a.
They can lift heavier loads and thus provide an opportunity for alterations in
building techniques.
b.
They can often save money by handling materials more cheaply, but this depends
on how intensively they are used.
c.
Since they can move loads, both horizontally and vertically, they can usually
handle materials faster, this can sometimes obviate 'bottle necks' in supply.
V. SOME USEFUL
BUILDING CRANES
1.
Derricks - Derricks are simple, inexpensive fixed cranes for handling heavy
loads. They are made in a wide range of sizes but the capacities normally used
are 5 to 10 tones, with jibs about 30 m long. They can be mounted at ground
level or on the building under construction and are much used for erecting
steel frames. They are usually hand operated or electrically powered.
2.
Mobile cranes - Mobile cranes have unimpeded full circle slewing and a powered
traveling motion. Normally jibs are up-to 5 m long and capacities from 1 to 5
tones. These cranes are mainly used for low building work - erecting factory
frames or prefabricated houses. Mobility is limited by ground conditions and
type of under - carriage used, but they will travel up slopes of 1 in 5 and
work on slopes of 1 in 40. Long jibs up-to 36 m may be fitted but load may be
severely restricted at long reaches.
3.
Tower crane - Tower crane is perhaps the most generally useful crane for
building. It is the only type of crane designed specifically for building, and
the only type capable of distributing materials over the whole plan area of a
tall building. In the popular models which are mostly of continental origin,
jibs are from 12 to 30 m long from 500 kg to 1500 kg can be handled at extreme
reach.
4.
Climbing cranes - some of the smaller types of tower cranes with fixed, short,
non-slewing towers, can be mounted in such a way that they are wholly supported
by the building and can be made to climb up as it grows.
Some
other miscellaneous equipment which are extensively used at construction sites
are summarized below:
-
Block making machines
-
Cutting and bending reinforcement machines
-
Pumps
-
Tile polishing machines
-
Vibrators
-
Material hoists
-
Centering, shuttering and scaffolding equipments
-
Jack hammer
-
Rock drills
-
Water bowzers of various capacities
-
Joint cutters & miscellaneous tools and tackles etc.
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