A Comparative Study of Façade Samples in Residential Buildings of Tehran by Analytical Hierarchy Process (AHP)

Nowadays، there is a rapid growth in residential construction in Tehran. Part of the growth is related to providing housing for citizen and reconstruction of old urban fabrics. Yet many difficulties and barriers may arise in the future due to the relative paucity of technical standards. The façade skin is considered as one of the most effective ways in aesthetic elements of the urban landscape. The facade plays a vital role in the distinction between interior and exterior spaces. Additionally، it is one of the most vulnerable elements of structures، when they are subjected to earthquakes. Tehran is placed in the one of the world’s most active seismic belts and has sustained repeated considerabledamages due to high magnitude earthquake activitieshappening in some 150 year cycle. Already 182 years have passed since the last one in 1830. It is feared that a major earthquake in Tehran، a megalopolis of over 8 million inhabitants، situated on among active faults، could well lead to substantial loss of life at some 380،000 in the worst case scenario and considerable financial damages particularly due to rapid urbanization started in the 1950s. The main objective of this research is to determine the most appropriate facade system for residential buildings in Tehran. Two types of double-skin facades (twin wall or incorporated shuttering wall and lightweight 3D sandwich panel) and single-skin facades (insulating concrete form and fiber cement board facade) have been selected based on the available studies of facade systems. Data was gathered through Delphi technique. The Delphi technique is an approach used to gain consensus among a panel of experts. This is normally achieved through a series of rounds where information is fed back to panel members using questionnaires. Fourcriteria were selected in the research. Thesecriteria are as follows: earthquake resistance، cost and speed of performance، heat insulation and architectural aesthetics. Weights of them were analyzed by analytical hierarchy process (AHP) method and the systems are compared. An AHP hierarchy is a structured means of modeling the decision at hand. It consists of an overall goal، a group of options or alternatives for reaching the goal، and a group of factors or criteria that relate the alternatives to the goal. Sincepairwisecomparisons are the keystone of these decision-making processes، correctly quantifying them is the most decisivestep inmulti-criteria decision-making methods which use qualitative data. Pairwise comparisons are quantified by using a scale. Such a scale is an one–to-one mapping between the set of discrete linguistic choices available to the decision maker and a discrete set of numbers which indicate the importance، or weightof the previous linguistic choices. In the final step of the process، numerical priorities are calculated for each of the decision alternatives. These numbers represent the alternatives’ relative ability to attain the decision goal، so they allow a straightforward consideration of the various courses of action. Accordingly، lightweight 3D sandwich panel is suggested as the most appropriate for residential buildings in the earthquakeprone areas of Tehran.