Strategy
Segmental arch compared to others types of arches and vaults
10.35m span segmental vault at Deepanam School, Auroville
Segmental arch compared to others types of arches and vaults
Inspiration
Throughout history, structures have been designed and constructed by analysing the form which can perform most efficiently. Great examples can be seen from bridges designed and constructed in the past centuries and other large buildings.
Designing with major considerations of structural form was imperative due to the relative weakness of earlier building materials and in older cases the lack of reinforcing steel technology with regard to concrete structures.
Today these early techniques could be used to augment and revolutionise reinforced concrete technology to help produce highly efficient structures which use lesser materials, and thus aligning designs with the vision of sustainable development.
Material optimisations for traditional slabs, steel vs. concrete
Cost optimisation for traditional slabs, steel vs. concrete
Form-Active Slab Mid-Span Stress Distribution
Material optimisations for traditional slabs, steel vs. concrete
Introduction
The design of concrete structures through manipulation of structural form can help reduce the concrete volumes that would otherwise be needed. These types of designs can be observed from many large structures and bridges throughout history. The structures designed to carry their loads through their structural forms are called form-active structures, and this thesis looked at focussing the technique on concrete roof and floor slabs in residential and small commercial buildings.
Background
The design and results of form-active concrete floor slabs needs to be put in contrast to the traditional solid slab. The traditional solid slab design is a tried and tested design procedure that is both safe and predictable if done properly. However, the design process has a built in assumption that adds a substantial inefficiency in the slabs; this assumption is that the concrete in the tension zone is ignored. These slabs can nonetheless still be enhanced according to mass reduction techniques or more lightly, material and/or cost optimisation, and with that a precise comparison could be made against well-designed traditional solid slabs and form-active slabs. The comparison was mainly of structural efficiency which was taken as the ratio of load carrying capacity of a structural element to its self-weight.
FEA Deflection Analysis
Deflections are greatly minimised due to the cambered shape of the form-active slab, moreover internal stresses are also reduces by almost half
Results​​
As expected the form-active slabs were found to be structurally superior to traditional solid slabs, to be exact ca. two times more efficient. The concrete used in form-active slabs can go up to 65% less than in traditional solid slabs and the steel needed can be reduced by up to 70%. However, serviceability restrictions apply to form-active slabs, floors need to be flat on top, unless they are roof slabs, and these types of restrictions can be overcome by providing solutions like wooden decks on the top faces of the slabs.
FEA models were created with similar concrete material properties, i.e. Young’s Modulus and Poisson’s ratio, these slabs were loaded and compared to further shed light on the calculated results. The models showed that stress distributions in form-active slabs produce lesser internal forces and as expected, mostly compression forces, hence the reduced need of reinforcing steel, for this reason changes to concrete crushing strengths are much more effective in form-active slabs.
NB: FEA - Finite Element Analysis, see deflection results below.