Monday, 1 March 2010

Constraints-Based Scheduling Of Precast Housing Project: A Case Study Of Preuksa Village III

In Thailand, housing projects have become highly competitive between local and overseas developers. The construction firms allocate bigger budget to get proper construction management software tools that can improve building processes, and which will give them higher profits.

Preuksa real estate public company limited, an outstanding firm in Thailand, acquired this newly developed and prefabricated technology from Germany. Preuksa Company tried to adjust the precast system suitable in Thailand and then investing in the precast manufacturing. As a result, Preuksa becomes the leader of the precast housing project.

However, the prefabricated technology from abroad cannot be used completely in Thailand because of the different criteria under consideration like the weather, site access, and resources available. Therefore, in the beginning, when this technology was being implemented in Thailand, many problems were faced. From that time onwards, continuous developing policies have been used. Therefore, this research work focused on how to improve the prefabricated system in Thailand, taking the Preuksa firm as the case study.

Mr. Prawat Tuptone proposed a study on the application of softwares based on the Line-of-Balance principle that is more efficient for real time productivity loss analysis, in preparation for future higher demand of precast housing. His study focused on four main objectives as follows:
1. To identify the constraints or problems on-site of precast housing project.
2. To rank the constraints in order of preference.
3. To minimize the construction productivity loss happening from the major constraints.
4. To analyze the results and make recommendations for improvement of prefabricated firms like Preuksa.

To acquire the knowledge and develop the precast method with necessary adjustments to implement in Thailand.


It is necessary for the project manager and concerned staff to measure and understand the productivity loss on-site for housing projects. And the value of construction productivity loss and disadvantage of delay should be measured. Such investigation is required for the prevention of the causes of delay and for their correction and recovery. The aim is to identify the priority of factors effecting the commencement of the project. The principle is to do the right thing at the right time. Also, the continuous development policy can be undertaken by the project manager through such practice.

Constraints Chosen by the Research
The constraints for precast housing project were identified through literature review and site survey. Ordinary constraints in housing projects have three categories:
1) External constraints including weather, economic environment, socio- political environment.
2) Management constraints including redoing work in case of prefabrication errors, safety at construction site, the delay (divided into contractors’ delay and owner’s delay) and financial concerns in payment to contractors and vendors.
3) Resources constraints including labor, materials and equipment and tools.

This study emphasized on major constraints that can cause construction productivity loss.

Ranking of constraints in Preuksa’s housing project

The seventeen construction productivity loss constraints were ranked from first to seventeenth. The top four constraints are 1) strict bank policy on loan, 2) higher construction materials prices, 3) higher fuel prices, 4) lack of skilled workers.

From the result, it can be observed that most of the top four constraints are financial constraints. This is due to the higher price of construction materials and higher fuel prices which strongly affect the firm’s income. Also, the Preuksa firm is implementing cost leadership policy, which means that a financial constraint is a very sensitive issue.

External constraints analysis by Easy Plan
Out of four external constraints, the only one chosen by the research is the impact of adverse weather constraint that can be measured as the loss of construction productivity. Information on this constraint was collected with the help of questions in the questionnaire that related seasonal productivity factors in perspective of project managers.

Seasonal Productivity Factors in perspective of Project Manager
Easy Plan program has the option to consider seasonal productivity factors as input. The effect of adverse weather is considered by this program. In fact, Thailand has three seasons which are the winter, the rainy season and the summer, so this factor has been taken into consideration as well. Spring was assumed to change to rainy season and fall to summer. The local weather factor was collected on-site. The input of productivities from the weather has the value between zero to one. The average value of productivities factors from the weather are 0.98 for the winter, 0.92 for the summer and 0.85 for the rainy season.

From the result of loss of construction productivity in case of adverse weather constraint, the project manager must realize that the value of time for manage the smooth-work at the good weather and try to avoid working at adverse weather.

Analysis of productivity loss for precast housing of type D by Easy Plan
The productivity loss analysis of precast housing focuses on constraints that affect construction productivity. Due to time limitation, the researcher has chosen three problems for consideration as follows:
1. Lack of skilled workers
2. Delay in delivery of construction materials
3. Rework

In addition, data has to be collected for making the assumptions of productivity loss, which is a very important point for consideration in each project.

Constraint-free Scheduling
The constraint-free method of calculation was considered as benchmark for comparing with other options such as labor shortage constraint, late delivery of construction materials constraint and rework constraints.

Combined with constraints
The results of analysis can be ranked by constraints affecting construction productivity. The constraint includes: 1) lack of skilled worker constraint, 2) delay in delivery of construction materials constraint, and 3) rework constraint. This approach is necessary to find out all values of actual productivity loss when all the constraints are combined together to affect the project.

Lack of skilled worker constraint
This analysis considered only two finishing works: wall plastering and ceramic tile. From the above discussion and interviews, lack of skilled workers is identified as an important constraint in the Thailand construction industry. Majority of the Preuksa firm’s worker has not gone through any proper training course and most of them are farmers from rural areas. Also their inefficient work performances might affect construction productivity. Therefore, in the aim to deal with this problem, top management should think about encouraging the unskilled workers to become skilled by arranging training programs for them.

Delay in delivery of construction materials constraint
Lack of construction materials management can affect construction duration because the contractor cannot finish the work in due time. For example, hollow core slabs of the first floor were not delivered all in the same time. Besides, it is also affected the contractors because of increased cost for renting the machines. Also, the factory did not deliver all the prefabricated panels that resulted in missing of sequences of work and time loss.

Rework constraints
While this constraint was considered, the analysis found that rework of prefabricated components can affect duration of structural work and finishing work. Otherwise the quality of prefabricated surface might lead to repairing which would cause delay in finishing the project. Estimation of such cost is complicated. For example, in the case of first floor panel installation, if the dowel steel is not in position with the hole underneath the panel, it will cause rework. Also, due to the problem of wrong dimension of dowel steel, a labor has to cut it off. The time for operation in this procedure can take around 50 percent of panel installation time. In addition, these can affect machine cost, labor, safety, and quality of work as well.

Recommendations for improvement

Lack of skilled worker constraint
Potential solutions are as follows:
- It is necessary to create a strategic plan to systematically deal with the issues causing the shortage of skilled workers. Employers, government, and trainers should work together to support the Training program.
- It is necessary to start a program to match young workers with experienced mentors.
- It is necessary to give certificates after testing formally and recognizing the competence of trainees and existing “skilled” personnel working in the construction industry and then to try to increase the number of certified skilled workers.

Delay in delivery of construction materials constraint
The solutions are as follows:

- Strict evaluation is used for suppliers is deemed necessary
- Use of modern technology in logistics to find the status of construction materials’ delivery is deemed necessary
- Planning and scheduling of materials’ delivery and regular update is deemed necessary

Rework constraints
The guiding solutions are as follows:

- Improvement in the process of prefabricated components and construction methods are necessary
- Project Managers should try to control the work by following the sequence of work
- Attempt to train the workers and emphasize on frequently occurring defects of work

In summary, to improve the situation, the firm should use the following approaches:
1. Enforcing liquidated damage and offering incentives for early completion.
2. Developing human resources in the construction industry through proper training and classifying of craftsmen. There is an urgent need for offering training courses in technical skills or finishing work such as wall plastering and ceramic tile installation.
3. Adopting a new approach to contract award procedure by giving less weight to prices and more weight to the capabilities and past performance of contractors.

His thesis abstract is copied and posted.


This thesis identifies and ranks the most important on-site constraints of precast housing project. A top management survey was conducted to identify the perceptions of project managers of Preuksa firm in relation to construction productivity. Construction labor productivity is of great interest to practitioners and researchers because it affects project cost and time overrun. This work evaluates and ranks the importance, frequency of project delay factors that affect the construction labor productivity for Preuksa village ΙΙΙ project.

The analysis revealed three most important financial constraints: 1) Strict bank policy on loan, 2) Higher construction materials prices, and 3) Higher fuel prices. The three major productivity loss constraints include: 1) Lack of skilled workers, 2) Delays in materials deliveries to site, and 3) Rework (prefabrication error). Comparing the total duration between constraint-free and other constraints, the productivity loss by 8 hours of work day found that in a single unit: lack of skilled workers loss is 0.7 percent, delays in materials deliveries to site loss is 1.6 percent and rework (prefabrication error) loss is 1.0 percent. The results showed that construction productivity loss of total time is small as compared with total cost because Easy Plan program can trade off time and cost. Therefore, the budget is spent more when the duration is reduced.
The inferences drawn from this study could be used by the project managers to take account of these factors at an early stage, hence minimizing the time and cost overrun. It is hoped that these findings and recommendations will guide efforts to improve the performance of the prefabricated firms.


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