QUALITY CONTROL Advanced Construction Management

WHAT IS DIFINITION OFQUALITY

Definition of Quality:

Quality is the totality of features and characteristics of a product or service that bear on its ability to satisfy stated or implied needs.

Some goals of quality programs include: Fitness for use. (Is the product or service capable of being used?) Fitness for purpose. (Does the product or service meet its

intended purpose?) Customer satisfaction. (Does the product or service meet the

customer's expectations?) Conformance to the requirements. (Does the product or service

conform to the requirements?)

Quality Management Processes

Quality Planning Quality Assurance Quality Control

Quality Planning

The process of identifying which quality standards are relevant to the project and determining and how to satisfy them.

Input includes: Quality policy, scope statement, product description, standards and regulations, and other process Output.

Methods used: benefit / cost analysis, benchmarking, flowcharting, and design of experiments

Output includes: Quality Management Plan, operational definitions, checklists, and Input to other processes.

Quality Assurance

The process of evaluating overall project performance on a regular basis to provide confidence that the project will satisfy the relevant quality standards.

Input includes: Quality Management Plan, results of

quality control measurements, and operational definitions.

Methods used: quality planning tools and techniques and quality audits.

Output includes: quality improvement.

Quality Assurance

Process of identifying or deciding all the quality requirements and guidelines or framework for a project

Documents: QA Documents Quality assurance includes all the activities related to

satisfying the relevant quality standards for a project Another goal of quality assurance is continuous quality

improvement Benchmarking can be used to generate ideas for quality

improvements Quality audits help identify lessons learned that can

improve performance on current or future projects

Quality Control

Tasks or activities performed in ground according to the quality guidelines or framework prescribed in the QA documents

monitoring specific project results to ensure that they comply with the relevant quality standards while identifying ways to improve overall quality

Quality Control

The main outputs of quality control are acceptance decisions rework process adjustments

Some tools and techniques include pareto analysis statistical sampling quality control charts testing

SOME TERMS

JUDGEMENT OF QUALITY

Was the project completed on time? Was the project completed within budget? Did the structure as well as the owner

expectation? Is it stable ?

Who will have responsible for quality and safety

common model :a group responsible for quality assurance and another group primarily responsible for safety

smaller projects, the project manager or an assistant might assume these and other responsibilities

ORGANIZING FOR QUALITY

Inspectors and quality assurance personal While the multitude of participants involved in the

construction process require the services of inspectors, it cannot be emphasized too strongly that inspectors are only a formal check on quality control. Quality control should be a primary objective for all the members of a project team

Work and Material Specifications

American Society for Testing and Materials (ASTM) American National Standards Institute (ANSI) SNI (Standard National Indonesia) American Welding Society Standard Specifications for Highway Bridges BINAMARGA (Indonesian Standard for Highway)

QUALITY OF WORK

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

Performance specifications

Traditional: specifications for asphalt pavement specified the composition of the asphalt material, the asphalt temperature during paving, and compacting procedures

a performance specification for asphalt would detail the desired performance of the pavement with respect to impermeability, strength, etc.

BINAMARGA

Performance specifications of concreteConcrete pavements of superior strength result in cost savings by

delaying the time at which repairs or re-construction is required. In contrast, concrete of lower quality will necessitate more frequent overlays or other repair proceduresBased on these life cycle cost considerations, a typical pay

schedule might beLoad Ratio Pay Factor

<0.500.50-0.690.70-0.890.90-1.091.10-1.291.30-1.49

>1.50

Reject0.900.951.001.051.101.12

Slump test

AGE

RATIO OF STRENGTH

3 0.45

7 0.65

14 0.88

21 0.95

28 1.00

90 1.20

365 1.35

EXCEPTION CONDITION

Unforeseen circumstances Incorrect design decisions or changed by owner Some design rely upon informed

aspects of quality control

insuring accurate and useful information is an important part of maintaining quality performance

document control (including changes during the construction process),

procurement, field inspection and testing, final checkout of the facility.

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

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

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

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.

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

An implicit assumption in these traditional quality control practices is the notion of an acceptable quality level which 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 productIn 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.

Total Quality Control

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.

TOTAL QUALITY CONTROL

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 circles in which groups of workers meet regularly to make suggestions for quality improvement.

Material suppliers are also required to insure zero defects in delivered goods. Initially, 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 tools of quality control# Name Where Purpose

01 Cause & Effect Diagram(Ishikawa, Fishbone)

Diagram showing an outcome and a list of potential causes (appears like a fish skeleton)

• To illustrate how various factors might be linked to potential problems or effects

• Used In Quality Planning (look forwards) and Quality Control (look backwards)

• Help stimulate thinking, organize thoughts, generate discussion

02 Control Charts Graphical representation mapping process variables within acceptable limits; upper and lower control limits contain normal/expected variations; uses Rule of Seven to identify non random patterns

• To determine whether or not a process is stable or has predictable performance

• Data gathering • Special Cause identification / assignable causes• Shows Process behaviour over time• Shows if the process is under control v out of control

03 Flowcharting Diagram showing activities, decision point and sequence from beginning to end and interrelation of various elements

• Can assist anticipation of problems and preventative action• Used In Quality Planning (look forwards) and Quality Control (look

backwards)

04 Histogram(Bar chart)

Bar Chart where Distribution of variables & height of column represent relative frequency.

• Helps Identify Cause of the problem by the shape and width of the distribution

05 Pareto Chart(80-20 chart)(Histogram)

Histogram order by frequency of occurrence, which shows how many defects regenerated by type or category of identified cause

• Identification of non-conformance• Addressing root cause of the most critical problems • Useful if there is little time available / prioritize• Separates critical few from the uncritical many

06 Run Chart Line Graph showing data points plotted in the order in which they occur

• Shows History and pattern of variation. Trend Analysis• Technical Performance (number of error/defects identified; number still

uncorrected)

07 Scatter Diagram Diagram showing the pattern of relationship between two variables

• The closer the points are to a diagonal line the more closely related they are; helps identify cause

Sample Fishbone or Ishikawa Diagram

PARETO DIAGRAM

Quality Control by Statistical Methods

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 lot or batch of materials or work products

Statically Sampling

There are two types of statistical sampling which are commonly used for the purpose of quality control in batches of work or materials:

1. The acceptance or rejection of a lot is based on the number of defective (bad) or no defective (good) items in the sample. This is referred to as sampling by attributes.

2. Instead of using defective and no defective 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 as sampling by variables.

Whatever sampling plan is used in testing, it is always assumed that the samples are representative of the entire population under consideration

Statistical Quality Control with Sampling by AttributesConsider a lot of finite number N, in which m items are defective (bad) and the remaining (N-m) items are non-defective (good). If a random sample of n items is taken from this lot, then we can determine the probability of having different numbers of defective items in the samplethe probability of having exactly x defective items in the sample is given by the ratio as the hyper geometric series

Suppose that the actual fraction of defectives in the lot is p and the actual fraction of no defectives is q

Statistical Quality Control with Sampling by Variables

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

In applying sampling by variables, an acceptable lot quality can be defined with respect to an upper limit U, a lower limit L

With both a lower and an upper limit on acceptable quality, the fraction defective would be the fraction of items greater than the upper limit or less than the lower limit

In the application of sampling by variables plans, the measured characteristic is virtually always assumed to be normally distributedThe normal distribution is likely to be a reasonably good assumption for many measured characteristics such as material density or degree of soil compaction.

The probability that the average value of a population is greater than a particular lower limit is calculated from the test statistic

which is t-distributed with n-1 degrees of freedom

With an upper limit, the calculations are similar, and the probability that the average value of a population is less than a particular upper limit can be calculated from the test statistic

The calculations to estimate the fraction of items above an upper limit or below a lower limit are very similar to those for the population average. The only difference is that the square root of the number of samples does not appear in the test statistic formulas: