Constructability in Construction and Issues at Design and Execution
The two main disciplines of construction, i.e. the design and the construction is separated by the tradition system of construction.
The design is carried out by the consultant (design engineer) and the construction is carried out by the contractor. It is rare to see a communication between both the parties before the start of the construction.
The designers who evolve the design do not have practical construction experiences. This does not let them know and bring up designs that are more compatible with the practical implications. This results in design complexity, high cost than estimates and more project duration.
Thus, there is the need of incorporating the construction knowledge in the design process. To assist the design engineer to understand the constructability of a selected design, the AI or the artificial intelligence or the expert system can be used.
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Importance of Constructability in Design Phase of Construction
The constructability is also called as buildability, which is a new term in construction industry. But the concept of buildability has existed from past.
The study of constructability showed that the traditional separation of construction and the design process have resulted in less efficient performance on the construction projects.
It also shows that good achievement of constructability depends on both the designer and the contractor in charge. This new term is achieving goof interest within the construction practitioners.
The planning in constructability facilitates the optimum integration of the construction knowledge and the experience with the engineer’s design. This helps in meeting overall project objectives. Still there are problems that are faced on how formally we can implement the constructability in practise.
Expert Systems for Constructability
In recent years the use of expert systems has become more prominent in the construction industry. These systems are developed as standalone modules or as an integrated system with algorithmic software systems.
These will perform the functions of:
- Cost Control
- Data management system
- Word processing
Constructability Assessment for a Design Detail System (CADDS)
This system involves integration of knowledge both from the design process and the construction. From a number of experienced design data and planning engineers, data are collected extensively and are gathered. These are structured and coded in carry out manipulation and processing with the CADDS.
This approach is based on well-defined principles and knowledge from experience in construction. These knowledge are gained from the literatures and the field surveys.
Design Details and Constructability
Important design considerations like methods to have easy construction of design and functionality have vital importance in the design stage of the project. The overall performance of a construction task is governed by both the functional and constructional aspects of the detailing.
Let us consider an example of exterior wall construction project activity. The basic requirements behind the same is the bring overall aesthetic beauty, energy, durable, fire resistant, acoustical and structural strength.
Along with the mentioned factors, the compatibility with the surrounding components, installation, cost and time are also considered important. We need to focus on construction related factors of feasibility, the impact on cost and schedule, other than the aspects of aesthetics and functionality.
The incorporation of constructability in the design process is often ignored. This will cause project disruption problems, during the project construction course. This might lead to legal disputes also. This will remind us to bring up easy facilities of construction with respect to the design details.
The importance of constructability is more focused on-site plan, project plan and for major construction projects. The requirement of constructability improvement demand data collection and its proper documentation.
The constructability factor is the major factor that helps in bringing a systematic approach to assess as well as catalogue the construction details. To capture and code the experiences from the field, computer technology can be employed.
Data Collection and Surveys in Constructability
This detail is based on a survey that is conducted by interviewing 26 contracting organizations and 30 consulting engineering practices in the construction industry of United Kingdom. Based on the survey the following view point were obtained.
View point of Contractor
From the interviews conducted with many of the contractors, it was found that most of the contractors have no complaints about the concept of the design. But have problem with the details that is incorporated in the design.
This is because of the design detail difficulties when implemented practically. The difficulties that are met are mentioned below:
1. Complex designs are bought which consume time and cost
2. The information provided may be of poor quality. The information includes the site investigation and the construction drawings.
3. The designs are put forward, without considering the practicality. The whole effect the design is going to provide is not considered.
4. Due to the complex shapes or the processes in construction, economic designs are costlier.
5. Poor sequencing of operations.
The difficulties that is faced in design are mentioned below:
Difficulties in Drawings:
The survey study conducted have a common note on the fact that most of the drawings are not suitable for the site operatives. The poor-quality drawing always receive criticism due to their lack of clarity and essential contents.
The issues are explained through certain examples:
1. Contradictory information is produced due to the lack of coordination as well as conflicting information. This information is received from different areas like from the Architects, the engineers, the mechanical and the electrical consultants.
2. The details are incomplete. The designer in charge completes some part of the design and leave the remaining to the contractor to finish it.
3. Some information is not sent and discussed in the site and the site in charge. But this is spread in the design office.
4. There might be situations where the dimensions are spread throughout the drawings. The dimensions provided by the architect won’t be always tied in.
5. No grid lines or datum levels are specified. This makes the setting out very difficult.
6. Essential minor details will be mixed up with unrelated details
7. The drawings that convey wrong bar bending schedules
8. Poor information causes difficulty in understanding how the job should be carried out.
The difficulties faced in the foundation design are
1. During the design stage, the contractor’s method of working is not considered. This is mainly in details related with the excavations like stripping the site. This is carried out in single operation to reach the reduced level, instead of excavation of individual areas in isolation.
2. Another issue is the use of small quantities of materials at the cost of extra plant time and labor. One such example is that the if the pad foundations are closely spaced it is not so cost saving to excavate each one separately. It is better to bring a strip foundation where it is excavated to the required reduced level in a single operation.
The difficulties in the design of structural Frames
1. There happens the mixing of trades within the structural elements and the poor sequence of operations.
2. No or a very little consideration is given to the speed of erection by the designers in the charge, while carrying the detail design of the structural frame. This include the design and erection of in situ staircase and bringing provisions for holes through the structural elements.
3. There are several issues faced when providing holes in the concrete walls. These include,
o The fixing of reinforcement will be less straightforward
o More time and cost is required to fix the box-out sections to the formwork
o Poor finish and difficulty in completion while undergoing the activity of concrete compaction under a square box-out.
The difficulties faced in reinforcement design
The need for using more prefabrication will bring in difficulties in the reinforcement design. Prefabrication is more preferred in the case of steel reinforcement for slab and beam floors.
The beam cages are placed in the ground level. This arrangement is then lifted and placed in the position required. It is very essential to provide generous cover mainly end covers while prefabricating the reinforcement. No good prefabricated cage is obtained without the provision of sufficient covers.
The difficulties that is faced in the Formwork design
1. The main difficulty faced is the reuse and repetitive use of formwork designs. Most of the lift shafts are designed by the designers as bracing. When considering a temporary work designer, it is critical during the construction of the floors. The shaft with four walls will form a box, but this is very difficult to build. This construction is very low and have less access for men and materials. Until this is completed the new floor cannot be constructed.
2. Another problem is that the design is not done for maximum use of mechanization. This measure can help in the reduction of labor costs.
3. More complex shapes are put forward. This is bought out with a fake belief that there is minimum amount of material is used and hence minimum cost. The practical difficulty is not taken into consideration.