دانلود رایگان مقاله انگلیسی تحلیل محیطی فونداسیون های سطحی ساختمان: نوع شناسی و کدهای طراحی ساختاری - الزویر 2018

abstract

The design of building foundations has usually been based on tradition, local practice, experience, and structural design codes. Safety is invariably considered the main factor and environmental criteria (or, in general, sustainability) is seldom given due consideration. However, similar safety indicators can be achieved with different variables and a minimum safety factor must always be ensured. The main objective of this study is, from an environmental perspective, to assess the influence of the construction system (cast-in-situ or precast), foundation type (rigid or flexible), and structural code (EC-2 or EHE-08) in the case of a concrete shallow foundation (CSF), using Life Cycle Assessment (LCA). Applying this methodology, the materials (concrete and steel) yielded the highest impacts in all categories, at around 95% for cast-in-situ CSFs and at around 85% for precast CSFs, both in relation to global warming. Consequently, optimization of the amount of these materials is crucial when considering the particular variables selected in this study. The results showed that cast-in-situ and flexible CSFs at moderately shallow depths (and therefore with less steel reinforcement) and precast CSFs with considerable reductions in concrete volumes (due to sloped shapes) had lower environmental impacts. In addition, castin-situ CSFs constructed in accordance with the EHE-08 structural code showed lower impacts, while precast CSFs complying with the EC-2 code were environmentally preferable. However, a specific study might be required for specific factors in each case (loads, soil type, structural settlement, among others). Relevant environmental effects associated with the three variables should therefore be given specific consideration in the development of structural design codes and future constructions.

4. Conclusions

A structural analysis embedded within a Life Cycle Analysis (LCA) methodology has been used to assess the influence of certain key variables on the environmental impacts of the construction of concrete shallow foundations (CSFs). These variables were: built cast in situ or precast; rigid or flexible; and calculated with structural design code EC-2 or EHE-08.

One main conclusion drawn from the results is that decisionmakers should consider some key aspects of the traditional design and construction of CSFs, because they can significantly affect environmental performance. For instance, steel and concrete had the highest impacts in all impact categories, accounting for around 95% of GWP emissions for cast-in-situ CSFs and 85% for precast CSFs. In addition, careful selection of the variables in the study might vary all indicators of the environmental impacts of CSFs by 45e60%. The optimization of concrete and steel amounts, when considering the variables selected for this study, is therefore a crucial element to minimize the impacts.

Compared with the cast-in-situ CSFs, the precast CSFs resulted in increases of up to around 35% in all impact categories, when both types had the same volume of concrete but different amounts of steel. These higher impacts are partly due to the higher cement content of precast concrete. In addition, precast products require lengthier transport distances and the use of on-site mechanized installation, as well as tending to require more reinforcing steel for higher concrete strengths. In this regard, the different minimum quantities of steel established by each structural code (EC-2 and EHE-08) for precast CSFs might affect the environmental impacts with variations of up to 48%. Nevertheless, when precast concrete volumes are greatly reduced and steel reinforcement is not significantly increased, the findings make it clear that precast CSFs can achieve similar environmental impacts to cast-in-situ CSFs. For instance, the precast rigid sloped CSF calculated with EC-2 (PR-DEC2*) had impacts that were around 2% higher than the best option in the study (IF-S13-EHE). This observation is principally explained by the use of sloped shapes and because it was calculated with EC-2 that permits greater reductions of concrete than EHE-08, as the minimum depth of the CSF is not limited. This code-dependent variability comes from the different assumptions adopted in each one. These assumptions, deduced from specific behavioural models, are basically structural or related to durability.