construction & quality

8/10/2019 Construction & Quality

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Construction & QualityCivil Works

Introduction

Many building and construction techniques that we use today have not changed much since

Egyptian or Indus valley times. The construction process still uses the raw materials of varyingsorts that are now available around the world with ease of transportation and shipping. However

the advanced technologies that we use today require extensive amount of labor to manufacture

erect and deliver the finished product (building). With the introduction of globalization and

privatization in Indian economy, the growth of technology in India has grown very rapidly in the

field of mechanization and information technology in construction industry. Building

construction which is considered to be the highest stake holder in terms of financial turnover,

market growth and field requirement, is advancing rapidly with advances in chemical

technology, application of physics and mechanical engineering without compromising on the

environmental aspects. Some of the latest advances technology related to building construction

are discussed here. However the technology that is discussed here is rapidly changing and may

become obsolete within of days completion of this programme.

Pre-engineered Buildings (PEB)

Pre-engineered building is designed by a PEB supplier or PEB manufacturer, to be fabricated

using best suited inventory of raw materials available from all sources and manufacturing

methods that can efficiently satisfy a wide range of structural and aesthetic design requirements.

Within some geographic industry sectors these buildings are also called Pre-Engineered Metal

Buildings (PEMB) or, as is becoming increasingly common due to the reduced amount of pre-

engineering involved in custom computer-aided designs, simply Engineered Metal Buildings(EMB).

Typically, primary frames are 2D type frames (i.e. may be analyzed using two-dimensional

techniques). Advances in computer-aided design technology, materials and manufacturing

capabilities have assisted a growth in alternate forms of pre-engineered building such as

thetension fabric buildingand more sophisticated analysis (e.g. three-dimensional) as is required

by some building codes.

Cold formed Z- and C-shaped members may be used as secondary structural elements to fasten

and support the external cladding. Roll-formed profiled steel sheet, wood, tensioned fabric,

precast concrete, masonry block, glass curtain wall or other materials may be used for the

external cladding of the building.

In order to accurately design a pre-engineered building, engineers consider the clear span

between bearing points, bay spacing, roof slope, live loads, dead loads, collateral loads, wind

uplift, deflection criteria, internal crane system and maximum practical size and weight of

fabricated members. Historically, pre-engineered building manufacturers have developed pre-
http://en.wikipedia.org/wiki/Tension_fabric_buildinghttp://en.wikipedia.org/wiki/Tension_fabric_buildinghttp://en.wikipedia.org/wiki/Tension_fabric_buildinghttp://en.wikipedia.org/wiki/Tension_fabric_building


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calculated tables for different structural elements in order to allow designers to select the most

efficient I beams size for their projects. However, the table selection procedures are becoming

rare with the evolution in computer-aided custom designs.

While pre-engineered buildings can be adapted to suit a wide variety of structural applications,

the greatest economy will be realized when utilizing standard details. An efficiently designedpre-engineered building can be lighter than the conventional steel buildings by up to 30%.

Lighter weight equates to less steel and a potential price savings in structural framework. Details

of typical PEB are presented below. The main advantage of this technology is faster rate of

construction that improved construction efficiency with lesser ambiguity in construction process.

Typical section of Pre Engineered Building

Structural sections for PEB


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and primarily resist vertical seismic shear forces. Horizontal joints connect the horizontal faces

of the adjoining wall and floor panels and resist both gravity and seismic loads. Depending on

the construction method, these joints can be classified as wet and dry.

Wet joints are constructed with cast-in-place concrete poured between the precast panels. To

ensure structural continuity, protruding reinforcing bars from the panels (dowels) are welded,looped, or otherwise connected in the joint region before the concrete is placed. Dry joints are

constructed by bolting or welding together steel plates or other steel inserts cast into the ends of

the precast panels for this purpose. Wet joints more closely approximate cast-in-place

construction, whereas the force transfer in structures with dry joints is accomplished at discrete

points. Panel connections represent the key structural components in these systems. Based on

their location within a building, these connections can be classified into vertical and horizontal

joints. Vertical joints connect the vertical faces of adjoining wall panels and primarily resist

vertical seismic shear forces.

Horizontal joints connect the horizontal faces of the adjoining wall and floor panels and resistboth gravity and seismic loads. Depending on the construction method, these joints can be

classified as wet and dry. Wet joints are constructed with cast-in-place concrete poured between

the precast panels. To ensure structural continuity, protruding reinforcing bars from the panels

(dowels) are welded, looped, or otherwise connected in the joint region before the concrete is

placed. Dry joints are constructed by bolting or welding together steel plates or other steel inserts

cast into the ends of the precast panels for this purpose. Wet joints more closely approximate

cast-in-place construction, whereas the force transfer in structures with dry joints is

accomplished at discrete points.

Frame Systems

Precast frames can be constructed using either linear elements or spatial beam-column

subassemblies. Precast beam-column subassemblies have the advantage that the connecting faces

between the subassemblies can be placed away from the critical frame regions; however, linear

elements are generally preferred because of the difficulties associated with forming, handling,

and erecting spatial elements. The use of linear elements generally means placing the connecting

faces at the beam-column junctions. The beams can be seated on corbels at the columns, for ease

of construction and to aid the shear transfer from the beam to the column. The beam-column

joints accomplished in this way are hinged. However, rigid beam-column connections are used in

some cases, when the continuity of longitudinal reinforcement through the beam-column jointneeds to be ensured.

Precast reinforced concrete frame with cruciform and linear beam elements (Seria 106) is an

example of a frame system with precast beam-column sub assemblages. The system was

developed in Kyrgyzstan in 1975. The load-bearing structure consists of a precast reinforced

concrete space frame and precast floor slabs. The space frame is constructed using two main


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modular elements: a cruciform element and a linear beam element. The cruciform element

consists of the transverse frame joint with half of the adjacent beam and column lengths. The

longitudinal frames are constructed by installing the precast beam elements in between the

transverse frame joints. The precast elements are joined by welding the projected reinforcement

bars (dowels) and casting the concrete in place. Joints between the cruciform elements are

located at the mid-span of beams and columns, whereas the longitudinal precast beam-column

connections are located close to the columns. Hollow-core precast slabs are commonly used for

floor and roof structures in this type of construction.

Slab-Column Systems with Shear Wal ls

These systems rely on shear walls to sustain lateral load effects, whereas the slab-column

structure resists mainly gravity loads. There are two main systems in this category:

Lift-slab system with walls

Prestressed slab-column system

This type of precast construction is known as Seria KUB. The load-bearing structure consists

of precast reinforced concrete columns and slabs. Precast columns are usually two stories high.

All precast structural elements are assembled by means of special joints. Reinforced concrete

slabs are poured on the ground in forms, one on top of the other. Precast concrete floor slabs are

lifted from the ground up to the final height by lifting cranes. The slab panels are lifted to the top

of the column and then moved downwards to the final position. Temporary supports are used to

keep the slabs in the position until the connection with the columns has been achieved. In the

connections, the steel bars (dowels) that project from the edges of the slabs are welded to the

dowels of the adjacent components and transverse reinforcement bars are installed in place. Theconnections are then filled with concrete that is poured at the site.

Most buildings of this type have some kind of lateral load-resisting elements, mainly consisting

of cast-in-place or precast shear walls, etc. In case lateral load-resisting elements (shear walls,

etc.) are not present, the lateral load path depends on the ability of the slab-column connections

to transfer bending moments. When the connections have been poorly constructed, this is not

possible, and the lateral load path may be incomplete. However, properly constructed slab-

column joints are capable of transferring moments.

Another type of precast system is a slab-column system that uses horizontal prestressing in two

orthogonal directions to achieve continuity. The precast concrete column elements are 1 to 3

stories high. The reinforced concrete floor slabs fit the clear span between columns. After

erecting the slabs and columns of a story, the columns and floor slabs are prestressed by means

of prestressing tendons that pass through ducts in the columns at the floor level and along the

gaps left between adjacent slabs. After prestressing, the gaps between the slabs are filled with in

situ concrete and the tendons then become bonded with the spans. Seismic loads are resisted


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mainly by the shear walls (precast or cast-in-place) positioned between the columns at

appropriate locations.

Rapid Wall

Rapid wall panels based on construction manual prepared by IIT Madras to suit Indian situation.FACT & RCF, two fertilizer giants under public sector are together setting up Rapid wall and

plaster products manufacturing plant at Ambalamugal using Rapid wall technologies of Australia

called FACT RCF Building products Ltd. (FRBL). FACT has about 7 million tons of

industrial by product gypsum. By setting up Rapid wall & Plaster products plant, they intend to

produce 1.4 million sqm or 15 million sq ft panel per year and about 50000 tons of superior

quality wall plaster and wall putty.

Rapid wall panel is worlds largest load bearing lightweight panels. The panels are

manufactured with size 12 m lengths, 3m height and 124 mm thickness. Each panel has 48

modular cavities of 230 mm x 94 mm x 3m dimension. The weight of one panel is 1440 kg or 40

kg/sqm. The density is 1.14g/cm3, being only 10-12% of the weight of comparable concrete

/brick masonry. The physical and material properties of panels are as follows.

o Weight- light weight 40 Kg/ sqm

o Axial load capacity 160 kN/m{ 16 tons/ m}

o Compressive strength 73.2 Kg/cm2

o

Unit Shear strength 50.90 kN/m

o Flexural strength 21.25 kg/cm2

o Tensile Strength 35 KN/ m

o Ductility 4

o Fire resistance 4 hr rating withstood 700-10000 C

o Thermal Resistance R 0.36 K/W

o Thermal conductivity 0.617

o Elastic Modulus 3000-6000Mpa

o Sound transmission{STC} 40

o Water absorption < 5%

The vertical and lateral load capability of Rapid wall Panel can be increased many fold by infill

of concrete after placing reinforcement rods vertically. As per structural requirement, cavities of

wall panel can be filled in various combinations (See Fig.1.)


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Wall to wall L, T, + angle joints and horizontal wall joints are made by cutting of inner or outer

flanges or web appropriately and infill of concrete with vertical reinforcement with stirrups for

anchorage. Various construction joints are illustrated in Fig.2.

Fig.1: RCC infill to increase load capability

Fig.2 various construction joints

Rapid wall Panel can also be used for intermediary floor slab / roof slab in combination with

embedded RCC micro-beams and RCC screed concrete (Fig.3).


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Fig.3 GFRG embedded with RCC micro beams and RCC screed concrete

For Rapid wall buildings/ Housing a conventional foundation like spread footing, RCC column

footing, raft or pile foundation is used as per the soil condition and load factors. All around the

building RCC plinth beam is provided at basement plinth level. For erection of panel as wall, 12

mm dia vertical reinforcement of 0.75m long of which 0.45m protrudes up and remaining portion

with 0.15m angle is placed into the RCC plinth beams before casting. Starts up rods are at 1m

centre to centre.

RAPIDWALL FOR RAPID CONSTRUCTION

Rapid wall enables fast track method of construction. Conventional building construction

involves various cumbersome and time consuming processes, like i) masonry wall construction

ii) cement plastering requiring curing, iii) casting of RCC slabs requiring centering and

scaffolding and curing iv) removal of centering and scaffolding and v) plastering of ceilings and

so on. It also contributes to pollution and environmental degradation due to debris left on the site.In contrast, Rapid wall construction is much faster and easier. There will be no debris left at site.

Construction time is minimized to 15-20%. Instead of brick by brick construction, Rapid wall

enables wall by wall construction. Rapid wall also does not require cement plastering as both

surfaces are smooth and even and ready for application of special primer and finishing coat of

paint.

RAPID CONSTRUCTION METHOD

As per the building plan, each wall panel will be cut at the factory with millimeter precision

using an automated cutting saw. Door/window/ventilator, openings for AC unit etc will also be

cut and panels for every floor is marked relating to building drawing. Panels are vertically loaded

at the factory on stillages for transport to the construction sites on trucks. Each stillage holds 5 or

8 pre-cut panels. The stillages are placed at the construction site close to the foundation for

erection using vehicle mounted crane or other type of crane with required boom length for


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construction of low, medium and high rise buildings. Special lifting jaws suitable to lift the pane

are used by inserting into the cavities and pierced into webs, so that lifting/handling of panels

will be safe. Panels are erected over the RCC plinth beam and concrete is infilled from top.

Protruded starts up rods go inside cavities as can be seen from. All the panels are erected as per

the building plan by following the notation. Each panel is erected level and plumb and will be

supported by lateral props to keep the panel in level, plumb and secure in position. Once wall

panels erected, door and window frames are fixed in position using conventional clamps with

concrete infill of cavities on either side. Embedded RCC lintels are to be provided wherever

required by cutting open external flange. Reinforcement for lintels and RCC sunshades can be

provided with required shuttering and support.

After inserting vertical reinforcement rods as per the structural design and clamps for wall

corners are in place to keep the wall panels in perfect position, concrete of 12 mm size aggregate

will be poured from top into the cavities using a small hose to go down at least 1.5 to 2 m into

the cavities for directly pumping the concrete from ready mix concrete truck. For small building

construction, concrete can be poured manually using a funnel. Filling the panels with concrete is

to be done in three layers of 1m height with an interval of 1 hr between each layer. There is no

need to use vibrator because gravitational pressure acts to self compact the concrete inside the

water tight cavities.

An embedded RCC tie beam to floor slab is to be provided at each floor slab level, as an

essential requirement of national building code against earth quakes. For this, web portion to

required beam depth at top is to be cut and removed for placing horizontal reinforcement with

stirrups and concreted.

Rapid wall for floor/roof slab will also be cut to required size and marked with notation. First the

wall joints and other cavities and horizontal RCC tie beams are infilled with concrete ; then

wooden plank of 0.3 to 0.45 m wide is provided to room span between the walls with support

wherever embedded micro beams are there; finally roof panels will be lifted by crane using

strong sling tied at mid-diagonal point, so that panel will float perfectly horizontal


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Each roof panel is placed over the wall in such a way that there will be at least a gap of 40 mm.

This is to enable vertical rods to be placed continuously from floor to floor and provide

monolithic RCC frame within Rapid wall. Wherever embedded micro-beams are there, top

flanges of roof panel are cut leaving at least 25mm projection.

Reinforcement for micro-beams is placed and weld mesh as reinforcement is placed. Concrete is

poured for micro-beams and RCC slab. These results in the embedded RCC micro beams and 50

mm thickness screed concrete become a series of T beams.

The following day, erection of wall panels for the upper floor can be arranged. Vertical

reinforcement of floor below is provided with extra length so as to protrude to 0.45 m to serve as

start up rods and lap length for upper floor. Once the wall panels are erected on the upper floor,

vertical reinforcement rods are provided, door/window frames fixed and RCC lintel cast. Then

concrete is filled where required and joints are filled. Then RCC tie beam all around is concreted.

Roof panel for upper floor is repeated same as ground floor. For every upper floor the same

method is repeated.

Fig: Erection of upper floor panel

Once concreting of ground floor roof slab is completed, on the 4th day, wooden planks with

support props in ground floor can be removed. Finishing of internal wall corners and ceiling

corners etc can be done using wall putty or special plaster by experienced POP plasterers.

Simultaneously, electrical work, water supply and sanitary work, floor tiling, mosaic or marble

works, staircase work etc can also be carried out. Every upper floor can be finished in the same

way.

Other recent advances in Buil ding Construction


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In addition to these advances in building construction, the constraints of fund availability and

time required for construction are leading to advances in innovative technologies in building

construction. The technologies viz. Composite construction, automation and robotics in

construction, advances in form work technologies will be discussed in the lecture sessions. Even

though these technologies are less used in Indian construction sites, it is slowly penetrating into

the industry due to its efficiency and effectiveness in life cycle cost and reduction in energy

consumption.

Quality and Safety Concerns in Construction

Quality control and safety represent increasingly important concerns for project managers.

Defects or failures in constructed facilities can result in very large costs. Even with minor

defects, re-construction may be required and facility operations impaired. Increased costs and

delays are the result. In the worst case, failures may cause personal injuries or fatalities.

Accidents during the construction process can similarly result in personal injuries and large

costs. Indirect costs of insurance, inspection and regulation are increasing rapidly due to these

increased direct costs. Good project managers try to ensure that the job is done right the first time

and that no major accidents occur on the project.

As with cost control, the most important decisions regarding the quality of a completed facility

are made during the design and planning stages rather than during construction. It is during these

preliminary stages that component configurations, material specifications and functional

performance are decided. Quality control during construction consists largely of

insuring conformanceto this original design and planning decisions.

While conformance to existing design decisions is the primary focus of quality control, there are

exceptions to this rule. First, unforeseen circumstances, incorrect design decisions or changes

desired by an owner in the facility function may require re-evaluation of design decisions during

the course of construction. While these changes may be motivated by the concern for quality,

they represent occasions for re-design with all the attendant objectives and constraints. As a

second case, some designs rely upon informed and appropriate decision making during the

construction process itself. For example, some tunneling methods make decisions about the

amount of shoring required at different locations based upon observation of soil conditions

during the tunneling process. Since such decisions are based on better information concerning


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facility. Typically, this documentation includes any special provisions of the facility design as

well as references to generally accepted specifications to be used during construction.

General specifications of work quality are available in numerous fields and are issued in

publications of organizations such as the American Society for Testing and Materials (ASTM),

the American National Standards Institute (ANSI), or the Construction Specifications Institute

(CSI). Distinct specifications are formalized for particular types of construction activities, such

as welding standards issued by the American Welding Society, or for particular facility types,

such as the Standard Specifications for Highway Bridgesissued by the American Association of

State Highway and Transportation Officials. These general specifications must be modified to

reflect local conditions, policies, available materials, local regulations and other special

circumstances.

Construction specifications normally consist of a series of instructions or prohibitions for

specific operations. For example, the following passage illustrates a typical specification, in this

case for excavation for structures:

Conform to elevations and dimensions shown on plan within a tolerance of plus or minus 0.10

foot, and extending a sufficient distance from footings and foundations to permit placing and

removal of concrete formwork, installation of services, other construction, and for inspection. In

excavating for footings and foundations, take care not to disturb bottom of excavation. Excavate

by hand to final grade just before concrete reinforcement is placed. Trim bottoms to required

lines and grades to leave solid base to receive concrete.

This set of specifications requires judgment in application since some items are not precisely

specified. For example, excavation must extend a "sufficient" distance to permit inspection and

other activities. Obviously, the term "sufficient" in this case may be subject to varying

interpretations. In contrast, a specification that tolerances are within plus or minus a tenth of a

foot is subject to direct measurement. However, specific requirements of the facility or

characteristics of the site may make the standard tolerance of a tenth of a foot inappropriate.

Writing specifications typically requires a trade-off between assuming reasonable behavior on

the part of all the parties concerned in interpreting words such as "sufficient" versus the effort

and possible inaccuracy in pre-specifying all operations.

In recent years,performance specificationshave been developed for many construction

operations. Rather than specifying the required constructionprocess,these specifications refer to


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the required performance or quality of the finished facility. The exact method by which this

performance is obtained is left to the construction contractor. For example, traditional

specifications for asphalt pavement specified the composition of the asphalt material, the asphalt

temperature during paving, and compacting procedures. In contrast, a performance specification

for asphalt would detail the desired performance of the pavement with respect to impermeability,

strength, etc. How the desired performance level was attained would be up to the paving

contractor. In some cases, the payment for asphalt paving might increase with better quality of

asphalt beyond some minimum level of performance.

Total Quality Control

Quality control in construction typically involves insuring compliance with minimum standards

of material and workmanship in order to insure the performance of the facility according to the

design. These minimum standards are contained in the specifications described in the previous

section. For the purpose of insuring compliance, random samples and statistical methods are

commonly used as the basis for accepting or rejecting work completed and batches of materials.

Rejection of a batch is based on non-conformance or violation of the relevant design

specifications. Procedures for this quality control practice are described in the following sections.

An implicit assumption in these traditional quality control practices is the notion of

an acceptable quality levelwhich is a allowable fraction of defective items. Materials obtained

from suppliers or work performed by an organization is inspected and passed as acceptable if the

estimated defective percentage is within the acceptable quality level. Problems with materials or

goods are corrected after delivery of the product.

In contrast to this traditional approach of quality control is the goal of total quality control. In

this system, no defective items are allowed anywhere in the construction process. While the zero

defects goal can never be permanently obtained, it provides a goal so that an organization is

never satisfied with its quality control program even if defects are reduced by substantial

amounts year after year. This concept and approach to quality control was first developed in

manufacturing firms in Japan and Europe, but has since spread to many construction companies.

The best known formal certification for quality improvement is the International Organization

for Standardization's ISO 9000 standard. ISO 9000 emphasizes good documentation, quality

goals and a series of cycles of planning, implementation and review.


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Total quality control is a commitment to quality expressed in all parts of an organization and

typically involves many elements. Design reviews to insure safe and effective construction

procedures are a major element. Other elements include extensive training for personnel, shifting

the responsibility for detecting defects from quality control inspectors to workers, and

continually maintaining equipment. Worker involvement in improved quality control is often

formalized in quality circlesin which groups of workers meet regularly to make suggestions for

quality improvement. Material suppliers are also required to insure zero defects in delivered

goods. Initally, all materials from a supplier are inspected and batches of goods with any

defective items are returned. Suppliers with good records can be certified and not subject to

complete inspection subsequently.

The traditional microeconomic view of quality control is that there is an "optimum" proportion

of defective items. Trying to achieve greater quality than this optimum would substantially

increase costs of inspection and reduce worker productivity. However, many companies have

found that commitment to total quality control has substantial economic benefits that had been

unappreciated in traditional approaches. Expenses associated with inventory, rework, scrap and

warranties were reduced. Worker enthusiasm and commitment improved. Customers often

appreciated higher quality work and would pay a premium for good quality. As a result,

improved quality control became a competitive advantage.

Of course, total quality control is difficult to apply, particular in construction. The unique nature

of each facility, the variability in the workforce, the multitude of subcontractors and the cost of

making necessary investments in education and procedures make programs of total quality

control in construction difficult. Nevertheless, a commitment to improved quality even without

endorsing the goal of zero defects can pay real dividends to organizations.

Experience with Quality Circles

Quality circles represent a group of five to fifteen workers who meet on a frequent basis to

identify, discuss and solve productivity and quality problems. A circle leader acts as liason

between the workers in the group and upper levels of management. Appearing below are some

examples of reported quality circle accomplishments in construction

1. On a highway project under construction by Taisei Corporation, it was found that the loss

rate of ready-mixed concrete was too high. A quality circle composed of cement masons


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found out that the most important reason for this was due to an inaccurate checking

method. By applying the circle's recommendations, the loss rate was reduced by 11.4%.

2. In a building project by Shimizu Construction Company, may cases of faulty reinforced

concrete work were reported. The iron workers quality circle examined their work

thoroughly and soon the faulty workmanship disappeared. A 10% increase in productivity

was also achieved.

Quality Control by Statistical Methods

An ideal quality control program might test all materials and work on a particular facility. For

example, non-destructive techniques such as x-ray inspection of welds can be used throughout a

facility. An on-site inspector can witness the appropriateness and adequacy of construction

methods at all times. Even better, individual craftsmen can perform continuing inspection of

materials and their own work. Exhaustive or 100% testing of all materials and work by

inspectors can be exceedingly expensive, however. In many instances, testing requires the

destruction of a material sample, so exhaustive testing is not even possible. As a result, small

samples are used to establish the basis of accepting or rejecting a particular work item or

shipment of materials. Statistical methods are used to interpret the results of test on a small

sample to reach a conclusion concerning the acceptability of an entire lotor batch of materials or

work products.

The use of statistics is essential in interpreting the results of testing on a small sample. Without

adequate interpretation, small sample testing results can be quite misleading. As an example,

suppose that there are ten defective pieces of material in a lot of one hundred. In taking a sample

of five pieces, the inspector might not find anydefective pieces or might have allsample pieces

defective. Drawing a direct inference that none or all pieces in the population are defective on

the basis of these samples would be incorrect. Due to this random nature of the sample selection

process, testing results can vary substantially. It is only with statistical methods that issues such

as the chance of different levels of defective items in the full lot can be fully analyzed from a

small sample test.

There are two types of statistical sampling which are commonly used for the purpose of quality

control in batches of work or materials:


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1. The acceptance or rejection of a lot is based on the number of defective (bad) or

nondefective (good) items in the sample. This is referred to assampling by attributes.

2. Instead of using defective and nondefective classifications for an item, a quantitative

quality measure or the value of a measured variable is used as a quality indicator. This

testing procedure is referred to assampling by variables.

Whatever sampling plan is used in testing, it is always assumed that the samples are

representative of the entire population under consideration. Samples are expected to be chosen

randomly so that each member of the population is equally likely to be chosen. Convenient

sampling plans such as sampling every twentieth piece, choosing a sample every two hours, or

picking the top piece on a delivery truck may be adequate to insure a random sample if pieces are

randomly mixed in a stack or in use. However, some convenient sampling plans can be

inappropriate. For example, checking only easily accessible joints in a building component is

inappropriate since joints that are hard to reach may be more likely to have erection or

fabrication problems.

Another assumption implicit in statistical quality control procedures is that the quality of

materials or work is expected to vary from one piece to another. This is certainly true in the field

of construction. While a designer may assume that all concrete is exactly the same in a building,

the variations in material properties, manufacturing, handling, pouring, and temperature during

setting insure that concrete is actually heterogeneous in quality. Reducing such variations to a

minimum is one aspect of quality construction. Insuring that the materials actually placed

achieve some minimum quality level with respect to average properties or fraction of defectives

is the task of quality control.

Statistical Quality Control with Sampling by Variables

As described in the previous section, sampling by attributes is based on a classification of items

asgoodor defective. Many work and material attributes possess continuous properties, such as

strength, density or length. With the sampling by attributes procedure, a particular level of a

variable quantity must be defined as acceptable quality. More generally, two items classified

asgoodmight have quite different strengths or other attributes. Intuitively, it seems reasonable

that some "credit" should be provided for exceptionally good items in a sample. Sampling by

variables was developed for application to continuously measurable quantities of this type. The


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procedure uses measured values of an attribute in a sample to determine the overall acceptability

of a batch or lot. Sampling by variables has the advantage of using more information from tests

since it is based on actual measured values rather than a simple classification. As a result,

acceptance sampling by variables can be more efficient than sampling by attributes in the sense

that fewer samples are required to obtain a desired level of quality control.

Reference:

Richard Lambek, John Eschemuller (2009) Urban Construction Project Management, McGraw

Hill Construction

http://en.wikipedia.org/wiki/Pre-engineered_building referred on 17/10/2014

http://en.wikipedia.org/wiki/Prefabricated_buildingreferred on 17/10/2014

Mansi Jain (2012) Economic Aspects of Construction Waste Materials in terms of cost savings

A case of Indian construction Industry International Journal of Scientific and Research

Publications

Hakam, Z, H. R. (2000) Retrofit of Hollow Concrete Masonry Infilled Steel Frames Using

Glass Fiber Reinforced Plastic Laminates Ph.D. thesis, Civil & Architectural Engineering

Department, Drexel University, Philadelphia, June, pp. 517

NCMA TEK 3-12 Load bearing Concrete Block in High Rise Buildings National Concrete

Masonry Association, 1998.

CSIRO Australia, Division of Building, Construction and Engineering, Rapid Building Systems

(ed.) (1999): Fire Resistance of Rapid wall, Adelaide 1999.

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