Diseño y orientación de la vivienda

Technology is another tool that is available to today’s construction managers. Research has shown that several new technologies have been developed that improve project performance in terms of schedule and acceleration. One such technology is the development of four-dimensional (4D) visualization of construction scheduling. This technology helps optimize construction operations, ultimately aiming at minimizing time and cost of the overall project.

One of the first applications of 4D occurred at Virginia Tech in 1990. A system that combined scheduling networks with three-dimensional (3D) computer models was created to form a Visual Scheduling Simulation (VSS), aiming at enhancing traditional planning and scheduling

techniques through the use of CAD technologies. The system generated a visual simulation of construction activities so that construction processes could be viewed over specific periods of time (Skolnick et al. 1990). This initiative introduced a new use of CAD technologies in the construction phase. Today, 3D and 4D animation tools are extendedly used with effective applications in the design and construction phases of projects.

4D planning models integrate 3D geometrical models with the fourth dimension of time by incorporating the associated project activity schedule. The result is a program that enables users, and particularly project and construction managers, the visualization of prospective scenarios where alternative construction sequences can be tested at any time. By visualizing different scenarios, logistics problems can be identified and therefore eliminated before they happen. In addition, 3D models linked to the schedule allow the analysis of resource requirements for each activity, material layout planning, and cost breakdown. 4D graphical visualization can also be used by construction managers for fast and efficient decision making or short term replanning. 4D technologies can be used as well by designers and engineers during design for checking constructability and improving construction performance through design. Thus, 4D visualization models represent an efficient tool to improve overall management and planning during design and construction. (Chau et al 2004).

b. Implementation

4D models are composed of different tools that enable the interchange of data and allow the integration between the 3D geometrical model and the project schedule. Generally, this type of models employ AutoCad as the graphics tool and typical project scheduling programs such as Microsoft Project or Primavera as the scheduling tool. A data warehouse is also used to store the large amounts of data and information that the graphics tools and the scheduling program

retrieve.

The 3D design model is developed in AutoCad following regular design procedures. Design components are introduced in the program, and they are categorized according to the function they have in the actual construction. Typically, components can be divided in three categories: structural elements, operational objects, and temporary facilities. Structural elements can be further classified under subclasses of building elements such as floor, beam, column, slab, wall, and so on. The second component, operational objectives, allows the graphical representation of construction activities that are in progress for a particular structural component. These can be formwork erection, falsework installation, steel work and concrete work. Each of these is represented in the 3D model. Other features such as temporary facilities can also be included

because they occupy space even though they are not part of the permanent structure under construction (Chau et al. 2004).

The schedule is developed in the adopted project scheduling program. Basic scheduling

information is sufficient to develop the schedule and link it with the 3D model. Basic scheduling information includes activity durations, start dates and finish dates for each activity, and activity sequencing.

The data warehouse stores the data generated by the 3D model and the schedule. It also enables a bi-directional flow of information between both features.

Once the 3D model and the schedule have been completed, they are linked to generate the 4D representation. Through the 4D model, the user can specify different planning actions and view the output results from the system. For example, the user can play with the sequence of activities for a given construction planning stage, alter the duration of activities, add new scheduling data, and so on, and the system returns a visual representation of the product of the changes.

Depending on the level of sophistication of the model, some may automatically add temporary facilities to the layout plan if needed. The results generated by the system follow a series of knowledge modules stored in a knowledge database that works under certain heuristic rules on construction technology. The 4D visualization model can also be altered directly. However, these modifications usually have to be again manually introduced in the schedule because most models do not automatically translate changes from the 4D model into the schedule. Research is still underway to improve this interface.

c.

Advantages

4D is a tool that has the potential to improve project performance through its application in the different stages of project development in different ways.

During project design, 4D models can be used as a tool to improve design and construction performance. Construction visualization at this stage provides designers with a tool to analyze different alternatives for design and assess how each of these may affect construction. 4D representations can also be used to check and improve construction constructability.

In the construction stages of the project, the construction manager can specify different planning actions and view the output results of the different tested alternatives through the 4D model. Thus, 4D provides construction managers with a tool to improve construction management decision-making as it facilitates the performance of what if scenarios on specific sections of construction.

4D representations also allow the development of improved construction sequences to reduce project durations. Problems associated with construction sequencing, temporary facility interferences and congestion can also be identified before they happen and properly addressed. As a result the schedule becomes a more accurate and achievable instrument, and the confidence among all teams and employees increases.

Site management is also improved through the use of 4D visualization models in different ways. 4D generates different site facility layouts which permits the analysis of production flow and workspace utilization. 4D models visually integrate building elements, construction methods and trade space occupation requirements which provide the construction manager with the means to

improve sequencing and coordination of construction trades (Tan et al. 2005). 4D applications also allow the evaluation of site access such as access for the installation and use of large equipment and construction items. Further benefits to site management can be obtained by sharing the 4D representations of the project with subcontractors and particularly suppliers. Through the visualization of site layout, subcontractors and suppliers can plan better their work accounting for actual site access and availability of workspace. Through efficient

communication and integration between the construction manager and subcontractors and suppliers along with the use of the 4D model, coordination problems can be eliminated resulting in fewer interruptions, enhancing thereby schedule performance.

Assessment and better planning of situations that can be physically hazardous is another advantage of graphically visualizing the site. Other management tasks are also improved including operations and maintenance planning, and construction progress control and monitoring (Chau et al. 2004).

The scheduling feature of the model along with the 4D technology enhance typical management functions such as the analysis of resource requirements for the activities under each different scenario including labor, material and equipment requirements. Estimation of quantities of construction materials can also be calculated as well as the estimation of costs. Thus, the model can assist the construction manager in the planning process by reducing waste costs.

Under unexpected circumstances, site planning visualization enables the making of construction management decisions faster and more efficiently, resulting in better short-term planning or replanning. Additionally, visualization enhances communication and understanding among all parties involved.

Consequently, planning visualization combined with construction scheduling tools enables improved planning and optimization of construction operations, which ultimately results in overall reduction of project delivery time and costs.

d. Key elements to ensure a high degree of success

The development of 3D and 4D applications require extensive knowledge and expertise. In order to develop the 3D model and link it to the time feature, technical knowledge in the use of

AutoCAD or the selected graphic tool is indispensable. Designers and contractors normally have the essential levels of familiarity in the application of 3D technologies, however, further training may be required to effectively link and make use of the 4D design.

In addition, high levels of knowledge in 3D and 4D are also expected at the management level. Management’s involvement with the 4D representation is imperative to successfully take advantage of its features. Therefore, training has to be implemented at the management level as well.

3D and 4D technologies are tools that have no use if they are not properly communicated to all the parties involved in the project team. Constant and efficient communication is crucial to allow all parties under the different disciplines that comprise the construction process understand and take advantage of the 4D model. As mentioned before, 4D’s use can be further exploited when project’s 4D layouts are shared with subcontractors and suppliers, as it improves overall site coordination and management, leading ultimately to improved construction performance.

e.

Disadvantages

4D is a technology tool that offers construction managers vast opportunities for construction and site management improvements; nevertheless, its application is associated with high

implementation costs. In addition, the development of 4D models is a process that requires user’s knowledge and expertise. The use of 4D technologies without the proper knowledge and tools can turn into a time-consuming and eventually unfeasible venture.

f.

Applicability and use

In the past years, 4D techniques have been adopted in construction projects mostly as pilot models for experiencing its use and potential benefits. However, the construction community has begun to recognize the attainable improvements that 4D visualization allows in design and construction performance. The use of this technology within the industry is fairly increasing, particularly for improving the design and construction of large-sized and complex projects like the development of nuclear plants and such. Nonetheless, the high investments involved with its implementation have limited 4D’s adoption in medium or small-sized projects. It appears that the benefits offered by 4D and similar technologies are maximized when implemented in large projects where the inversion in the 4D tool and the potential benefits can be offset by the usual incurred costs associated to projects of this complexity and size. In addition, the development of large and complex projects typically involves, by nature, other high technologies and resources with experience and knowledge in high technologies which enhances 4D’s adoption success.

J. Overlapping sequential construction activities based on concurrent