Life cycle analysis of structural systems of residential housing units in the Philippines (2013)
ARCILLA, Nicolas Ryan
ONG, Janelle Kathryn
-In designing a house, or any structure, there are three things commonly considered by the structural engineer; these are represented in the safety–serviceability–cost triangle. Safety and serviceability ensure that the structure can fulfill its intended purpose by satisfying code requirements on strength, ductility, and deflections. Addressing economy, on the other hand, requires value engineering to produce an optimum design with reasonable cost. However, the triangle is increasingly found to be incomplete. There is the question of environmental impacts the structure may bear on society. But what parameter may be used to guide structural designers to make their structures “greener”? This paper proposes the use of a “Structural Sustainability Index (SSI)”, a single-score based on the Life Cycle Assessment (LCA) framework. The SSI was derived from five environmental impacts, whose respective weights were determined from a survey of Civil engineering professionals. The impacts and their weights are: Global Warming Potential (36%), Ocean Acidification (10%), Human Toxicity (12%), Abiotic Materal Depletion (16%), and Energy Use (26%). The concept was applied to low-cost housing units in the Philippines. Four models with approximately 60 sq.m. floor area were investigated. structural systems of these houses are conventional reinforced concrete, modular block system, I beam, and modified system. Among the four, the I beam house incurred the lowest SSI of 0.682 while the conventional had the greatest at 0.986. The I beam, however, was found to have the largest contribution in abiotic material depletion due to heavy steel usage. This could be lessened through recycling of steel, as the manufacturing stage was found to contribute the most damage. Significant improvements were made in all impact categories when converting from a conventional to a modified system using T-joists and wall stiffeners, for a total of 9.87% decrease in SSI. Costs likewise decreased. With the SSI and LCA framework, sustainability concerns can be quantified by structural engineers and significant improvements can be made in designing.
Dr. Andres Winston C. Oreta