Alternative formwork systems to build concrete shells

• Grant number: 19/06234-0
• Support Opportunities: Scholarships abroad - Research
• Start date: September 01, 2019
• End date: August 31, 2020
• Field of knowledge: Engineering - Civil Engineering - Structural Engineering
• Principal Investigator: Leila Cristina Meneghetti Valverdes
• Grantee: Leila Cristina Meneghetti Valverdes
• Host Investigator: Bhavna Sharma
• Host Institution: Escola Politécnica (EP). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Institution abroad: University of Bath, England

Abstract

Concrete is the world's second most consumed man-made material, and is responsible for up to 7% of total greenhouse gas emissions. Considering the planetary need to reduce global warming and microplastic littering in nature, the search for novel sustainable and renewable construction solutions is paramount. Shell structures are well-known as structurally efficient elements, with pleasing architectural and aesthetic appeal in view of their wavy shapes. With their membrane-like behavior (plane stresses only) and reduced bending and shear stresses, they need to be but a few centimeters-thick to manage large spans. In contrast to this structural efficiency, the traditional timber and ply formwork system is highly complex in such cases (in order to reach the shape of the elements), highly labor-intensive and therefore, very costly. This complexity of construction and the empiricism in form finding processes prevalent in the 1960 and 1970s, the heyday of shell-like structures, has finally sidelined them in favour of the traditional slab-beam-columns system. However, current advances in modeling techniques and the advent of computers with ever more powerful data processing capabilities, together with marked progress in material technology (concrete), have again opened up the possibility of employing shells as innovative structural elements. If, on the one hand, modeling techniques allow definition of structurally highly efficient shapes, construction systems must accompany this trend in order to contribute with a more ecologically-oriented, less energy-consuming system. Flexible formwork systems have been invented in late-19th century Germany, combining the use of natural fibre fabrics (hessian fabrics) or paper with a wire reinforcing net. Only after 1960 has this type of system awakened architectural interest, culminating in today's architects' and research engineers' desire to optimize structural elements' shapes. With this aim, the present research project proposes the development of alternatives for shell construction systems, employing natural fibre-reinforced composites. Brazil is the world's largest producer and exporter of sisal fibre, with an annual production of around 140.000 tons. It is chiefly used in handicraft items and rugs, while mainly used abroad for tying hay, being a renewable, eco-friendly material that can be safely left in the fields with no injury to animal health if ingested. As a construction material, it can be used as a cementicious matrix composite or as a resin. This project intends to assess the potential of sisal fibre fabric and plant resin composites to form the first hardening layer in building pneumatically formwork shells. The second alternative to be researched is the formation of a textile concrete, equally to function as a hardening layer, but contributing also to the shell strength capacity. In the case of cementicious matrices, will be used cements with pozzolanic admixtures in such amount as to eliminate the free calcium hydroxide in the matrix and ensure sisal's durability against the cement alkaline attack. The viability of employing such alternative composites will be verified through tests in reduced scale shell models. Parameters found in such essays, together with mechanical properties characterization data, will serve for calibrating numerical models foreseeing the structural behavior of shells with various curvatures and for definition of the composite necessary thickness. The main results envisaged are the development of an innovative and optimized construction system in terms of project (topology), with low carbon emission - low ecological footprint. From a social standpoint, this research contributes to diversification of sisal use and the development of Brazilian northeastern rural communities who depend on sisal for survival. (AU)