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Construction costing and contracts assignment 1

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Table of contents

Introduction …………………………………………………………………………………………………………

Systems thinking ……………………………………………………………………………………………………

o Setting out ……………………………………………………………………………………………………

o Construction of the base ……………………………………………………………………………………

o Construction of columns and beams ……………………………………………………………………

o Curing ………………………………………………………………………………………………………

o Environmental protection …………………………………………………………………………………

Systems to control the appropriate level of strength and accuracy of concrete ………………………………

Health and safety hazards ………………………………………………………………………………………

Reference ……………………………………………………………………………………………………………

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Conversion

process Inputs

Opportunities

/ Constraints

Output

Mechanisms

Introduction

A system is an organized collection of parts or subsystems that are highly integrated to accomplish an

overall goal. The system has various inputs, mechanisms and certain processes to produce outputs,

which together, accomplish the overall desired goal for the system. This system is subject to constraints

and offers opportunities. The current goal is to design a system for the water tank construction process.

1.0. Systems thinking

Systems thinking is defined as an approach to problem solving, by viewing "problems" as parts of an

overall system, rather than reacting to specific part, outcomes or events. One of the best ways of solving

problems using system thinking is to model a problematic scenario into simple input-output system. The

input-output system consists of;

Input – things to be converted by the conversion process

Output – things produced or created as a result of the

conversion process

Constraints – elements that limit the conversion process

Opportunities – sub product of conversion process

which benefits another process

Mechanisms – personnel, equipment and technology

used in conversion process

Conversion process- is an activity which uses a mechanism to

convert an input into an output under certain constraints while

offering opportunities for other conversion process.

Setting out

This is the construction process by which the specific locations of structures to be constructed are

located in the site. The input of this process is the bare land and the output will be the location of the

structural elements to be constructed such as columns. The mechanisms used in this process are skills

of surveyors and surveying equipment. The main constraints of this process are the difficulty to locate

points due to possible weather conditions and uneven topology of the construction site.

Construction of the base

This is the construction process by which the foundation for the water tank is constructed. The inputs for

this process are the bare lands with marking of perimeter of foundation and construction materials. The

outputs will be the foundation of the water tank. The mechanisms used in the process are the skills of

labour, excavating machinery, steel bar bending machines and concrete mixer. The main constraints will

be unforeseeable adverse weather conditions and unexpected ground conditions and the opportunities

are the fact that the workshop setup to make concrete and bend reinforcement steel can be used for

other construction process like construction of columns and beams.

Construction of columns and beams

This is the construction process by which columns and beams for the water tank is constructed. The

inputs for this process are construction materials and the output is the columns and beams of the water

tank. The mechanisms used in the process are the skilled labour, steel bending machines and concrete

mixer. The constraints are unexpected adverse weather conditions and the fact that there are many

mistakes that can be made in the dimensions of structures and when mixing of concrete.

Figure 1 - Input-Output Model

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Curing

This is the process by which the concrete is protected from loss of moisture and kept within a reasonable

temperature range so that the concrete can reach it complete strength. The inputs for this process are

water and concrete and the output is fully cured concrete structure. The mechanisms used in the

process are the curing techniques like ponding and spraying. The constraints are the fact that hot

weather can decrease moisture content of concrete due to evaporation and the fact that the process

must be continued for 7 days hence there is a possibility to miss curing of at certain places

Environmental Protection

This is the process by which harm caused to the surrounding environment due to the construction

process is reduces to appropriate levels or eliminated altogether. Input for this process is the

surrounding environment and the output is the surrounding environment with minimum change due to

the construction. The mechanisms used are environmental protection techniques such as recycling

waste materials and proper disposal of construction waste. The constraints are the extra costs that occur

for proper environmental protection and this can delay construction too. Opportunities are the fact that

cleaner environment paves way for a more sustainable future and recycling construction waste can

reduce the overall cost of construction.

2.0. Systems to control the appropriate level of strength and accuracy of concrete

During the construction process there are three main places where the strength and the accuracy of the

concrete is decided; during manufacturing of cement and admixtures, during mixing of concrete and

during curing of concrete.

Manufacturing of cement and admixtures is not a part of the actual construction process therefore

there is a possibility the materials bought is of low quality.

The construction process is fairly large hence it requires many batches of concrete with different

composition of aggregates and admixtures which can lead to mistakes in mixing of concrete

which in turn can affect the strength of the concrete.

After the laying of the concrete its moisture level must be controlled to make sure the concrete

reaches its maximum strength. If the moisture level is not properly controlled the concrete

strength will reduces and form cracks and also its permeability will increase which can affect the

long-term strength of reinforced concrete structures

Different concrete testing methods and quality control mechanisms can be used in a systematic way to

ensure that appropriate levels of strength and accuracy of concrete is achieved at each stage of

construction. The system of quality control can be made chronologically and using feedback loop system

so that mistakes at each level can be detected and rectified.

Cube test – this is used before construction to find the compressive strength of concrete. This

has to be performed 7 days before construction using the cement bought for concreting. This

should be carried according to BS EN 12390-1:2012

Slump test – this is used to test the workability and stability of concrete and to ensure uniformity

between different batches of similar concrete. This should be carried out according to BS EN

12350-2:2009

Windsor probe test – this is a penetration test used to find the strength of concrete after

construction. This should be carried according to BS 1881-207:1992.

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Concrete curing – ponding and regular spraying of water are methods of concrete curing which is

used to make sure concrete is cured properly

3.0. Health and Safety hazards

During the construction process the workers are exposed to many health and safety hazards therefore

there is significant need for a safe work system to identify and to reduce the risk to an acceptable level or

to eliminate it altogether. Below are some of the possible health and safety hazards pertaining to this

construction process and their Risk rating;

Impact magnitude

No injuries 1

Negligible injuries 2

Minor injuries 3

Major injuries 4

Single fatality 5

Multiple fatalities 6

Likelihood magnitude

Within the bounds of possibility, but 1

A rare occurrence 2

Not very likely 3

A 50/50 risk 4

Very likely 5

Expected 6

Hazard Impact Likelihood Risk rating

Falling objects from above 4 4 16

Collapse of form work and false work 4 4 16

Excavation collapse 5 3 15

Trips and falls 3 4 12

Electric shocks 5 2 10

Injuries from hand tools 3 3 9

Exposure to hazardous chemicals 4 1 4

Exposure to high vibration 1 3 3

Inhalation of dust 1 2 2

Cube test

Slump test for every batch

Check moisture levels in curing

method regularly

Windsor probe test

Appropriate level of strenght of concrete

reached

Fail Fail

Return materials

to manufacturer

Discard cement

batch

Increase moisture

level by adding water

Build extra supporting structure or destroy current structure and

reconstruct

Construction

materials received Pass Pass

Pass

Pass

Fail

Fail

Figure 2 - System for quality control of cement

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Risk assessment is the determination of quantitative or qualitative value of risk related to a concrete situation and a recognized hazard. A risk assessment involves identifying the hazards present in any undertaking and then evaluating the extent of the risks involved, taking into account existing precautions

According to ICTAD Conditions of Contract major contracts clause 17.1 and clause 17.2 the contractor is responsible for any injury or sickness of any person whatsoever arising out of or in the course of the construction process. The possible hazards, the construction stage likely to occur in and their prevention methods are listed below;

It is the responsibility of the contractor to employ a health and safety representative who will look into the

hazards pertaining this construction and implement suitable prevention method. Also according to ICTAD

Conditions of contract major contracts clause 18.3, the contractor is responsible for insuring all

personnel against injury.

By following the ICTAD condition and by implementing suitable prevention methods for each health and

safety hazard it is possible to create a proper safe work system so that the risks can be reduced to a

appropriate level or eliminated altogether.

Hazards Construction stage Prevention methods

Falling objects from above

During construction of superstructure

Prevented by wearing hard hats and steel toe boots

Collapse of formwork and falsework

Likely in all stages of construction

A competent engineer with adequate training and experience in designing false work and form work should be appointed.

Excavation collapse

During excavation for base

Vehicles and heavy machinery shouldn’t be kept near the excavation. Fix retaining walls during deep excavation.

Trips and falls Likely in all stages of construction

Can be prevented by labeling trenches, pits or any other surface that can cause workers and to slip or trip

Electric shocks Likely in all stages of construction

Avoid using electrical equipment in damp conditions unless they are specially designed for those conditions. make sure that the wires of equipment are not damaged

Injuries from hand tools

Likely in all stages of construction

Prevented by making sure the worker has enough training to use the tool and by making sure the tool is maintained properly and is in mint condition.

Exposure to hazardous chemicals (e.g. Cement and admixtures)

Likely in all stages of construction

If skin contact with these substances is inevitable, suitable protective clothing and gloves should be worn. Washing of hands after work and skin care are essential to prevent dermatitis. However, solvents should never be used to clean hands or other body parts

Exposure to high vibration

Most likely during excavation for base

Where possible, low vibration tools should be used. They should also be properly maintained so that they are balanced and have no loose parts. Wearing anti-vibration gloves can also reduce the harmful effect of vibration.

Inhalation of dust

Likely in all stages of construction

By the use of dustproof masks.

Risk rating = Impact x Likelihood of risk

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Reference

http://books.google.lk/books?id=eqbGoz7cAUcC&pg=PA26&lpg=PA26&dq=input+conversion+process+

output+constraints+mechanisms&source=bl&ots=DvazW1eKxF&sig=ruWCsOU2yEasiRBuCmP247DMr-

4&hl=en&sa=X&ei=GppnVICYHdG0uASh0YHYDA&ved=0CBwQ6AEwAA#v=onepage&q=input%20con

version%20process%20output%20constraints%20mechanisms&f=false

http://books.google.lk/books?id=cubDyC7zsPwC&pg=PA363&lpg=PA363&dq=input+conversion+proces

s+output+constraints+mechanisms&source=bl&ots=X3GVmIteDS&sig=B5lGNQE1zocf62nHT3SaKpymn

VI&hl=en&sa=X&ei=GppnVICYHdG0uASh0YHYDA&ved=0CCcQ6AEwAw#v=onepage&q=input%20con

version%20process%20output%20constraints%20mechanisms&f=false