Using analytic hierarchy process as a decision-making tool in the design process of building elements: A case study on a portable dwelling unit

The environment itself is a dynamic phenomenon, thus dwelling - as the primary source of human existence - should be adaptable to such ever-changing and evolving environmental factors. The style and standards of living, mentality, and habits of today's society demand an architecture that provides unrestrained, fluid, and more practical and immediate solutions to the eventual problems and needs. Within this study, an introductory project scenario has been developed primarily for the design of a dwelling unit that is mobile and easily assembled/disassembled with abilities to be adapted in different environmental conditions of shifting climatic patterns and varying topographic settings. As a projection to the changing world order, dwelling - the most fundamental architectural solution to common human problems - is desired to yield itself open to sustained adjustments and configurations to satisfy the indefinite demands. In designing of such dwelling unit, the determination of the performance criteria for the architectural product to be designed are of primary importance as they shall be articulated as essential parameters to the design process. Based on the scenario adopted, a portable dwelling unit with capability of complying with the changing parameters of design has been aimed for; yet, it has been diagnosed that the preferred notions of 'adaptability' and 'moveability' demand much complex measures. Therefore, in the identification of certain performance requirements to be met by the dwelling unit at issue, supplementary criteria such as adaptability, mobility, and integration have been introduced, in addition to the 'generic' performances of structural strength and stability, durability, fire endurance, continuity of performances, thermal considerations, water and moisture impermeability, natural ventilation, natural lighting, acoustics, maintenance, and sustainability. Within the context of this study, the concept of architectural adaptability has been considered as the tolerance towards modifications; therefore, the physical architectural components are to be recognized in regards to their ability to adopt the change, especially on site. As for mobility, the notion has been addressed in regards to the dimensional and weight-related limits of the physical components, elements, or the entirety of the unit. Integration, referring to construction and installation of the architectural product, covers the issues of assembly and disassembly along with the skills of integrating with other sub-systems. Varying factors affecting the design, which are to be confronted with the physical dwelling, have revealed the emergence of outnumbering criteria to be considered; in addition to being design inputs, such factors also constitute the physical conditions that must be managed and regulated by the physical architectural components of the design. Building elements, together with the structural members, compose the physical components referred in this study; they have primary functions to serve within the building system, and design decisions regarding these particular sub-systems are recognized to affect and alter the conceptual design studies performed beforehand. Therefore, it has been observed that the process of realizing an accurate dwelling unit design in accordance with the study objective has become increasingly complex due to a large number of performances to be delivered and a vast number of alternatives to choose from. Further, it has been desired that the design of the dwelling unit, rather than being a personal and arbitrary interpretation of the designer, should be resolved by an analytical and mathematical method to transfer subjective evaluations into objective judgments. The concern of designing properly functioning physical components for the dwelling unit and difficulties in decision-making towards an optimized solution on the basis of building sub-systems to be designed have resulted in a need for a support tool in the processes of evaluation and decision-making. Decision-making is the process of making an evaluation and comparative selection among the alternatives according to the criteria established with respect to the objectives and goals of the decision problem. The process of architectural decision-making is often attempted with experience and intuitive means, which may lead to unreliable results depending on the knowledge and experience level of the designer, or decision maker. The design problem addressed in this study is a simple dwelling unit design to satisfy the minimum requirements, yet the process includes a myriad of design inputs to deal with, a large number of performances to be met, many physical components and building elements to be designed, and a vast variety of alternatives to choose from, all of which makes the design decision a much complex problem. In addition, each physical component possesses its own design sub-processes, creating an incrementally growing and interdependent decision sequence. Therefore, the study has built its question on how to manage such a wide range of variables all at once in search of an optimized solution. In order to systemize the sequential decision-making processes within the study, a tool has been demanded in translating a subjective judgment into an objective decision with evaluations of performances contradictory to each other and assessment of alternatives with respect to the prioritized criteria. As identified through literature review, there are several systematic decision-making tools to be used for decision problems faced in many disciplines such as management, engineering, design, and architecture. The aim of this study is to investigate the systematic methods that can be used in the evaluation and decision-making processes which have an important share in designing of the building elements and to present an implementation of an existing method as a design decision support tool in various sub-processes of the building element design. Within the scope of this study, primarily, the building subject has been investigated in consideration of systems approach; the physical components and building elements constituting the building, the relevant classifications, and the performance criteria affecting the design of these building elements have been examined, and eventually, a decision-making tool for implementation has been selected following the analysis on the act of decision-making and identification of the available decision-making tools. Subsequent to the brief examinations on the existing building element design approaches, the application scheme of the decision support tool which is desired to be used in the design process is created. On the basis of these investigations, a design process has been established as a flow diagram based on the Analytic Hierarchy Process (AHP), developed by Thomas L. Saaty, due to its easy-to-understand content, clarity in application, and prevalence in decision-making problems in architecture and other disciplines; thus, the usability and feasibility of the tool has been demonstrated and examined through the design process of the physical components for a portable dwelling unit. In regards to the project scenario adopted in this study, the portable dwelling to be designed has been assessed with regards to the physical components and building elements it shall possess and a different set of pairwise comparison matrices have been established for each with changing performance criteria and various alternatives. The physical components of the dwelling unit to be designed using the AHP have been identified as structural system, footing system, external walls, floors, roof, windows and doors, and stairs. The application of the selected tool has served the purpose of evaluating the performance priorities and to determine their relative importance over each other separately for each physical component to be designed. Having collected all the pairwise comparison data, the priorities can be computed and priority vector for each rated object can be obtained. This process step can also be described as the subjective scoring and influence factor calculation of each building performance requirement, defining their relative importance with respect to a higher goal, that is being the design of a portable dwelling unit. Once the alternatives of the sub-systems to be designed are identified, they are compared according to the each governing criterion in the next higher level, in a similar manner through pairwise comparison matrices; the dominance of the element assessed is being indicated as a numeric information.