IABSE Conference Creativity and Collaboration
April 19-20 2017, Bath, United Kingdom
Developing an innovative lightweight concrete flooring system for
sustainable buildings
Will Hawkins, John Orr, Tim Ibell, Paul Shepherd
University of Bath, UK
Contact: w.j.hawkins@bath.ac.uk
Abstract
This project brings together modern developments in computational design, materials and
construction methods to propose a novel thin-shell concrete flooring system for multi-storey
buildings, aiming to create a low embodied energy and lightweight alternative to traditional
reinforced concrete flat slabs.
Keywords: Concrete shells, multi-storey buildings, innovative structural systems, form finding,
structural optimisation, textile reinforced concrete, sustainable design, finite element analysis.
1 Introduction
Recent developments in technology, legislation
and industrial practice are significantly improving
the operational energy efficiency of new buildings.
As a result, embodied materials are increasingly
the main contributor to the total lifecycle energy
[1]. The largest proportion of this typically comes
from the structural elements, with the floors
being the main contributor [2]. Concrete flat slabs
are commonly adopted for these, due to their
simple formwork, design flexibility and low
structural depth. However, their prismatic form
disregards the variable forces within the structure,
leading to large reinforcing steel requirements Figure 1. Structural efficiency through arching
and inefficient use of materials [3].
This paper discusses the ideas influencing the 2.2 Historical Examples
development of a novel, sustainable alternative The ability of concrete shells to cover large spans
structural system. efficiently was demonstrated by the famous shell
builders of the 20th century, including Eduardo
2 Inspiration & Guiding Principles Torroja, Felix Candela and Heinz Isler. Examples of
historical vaulted floors include traditional Catalan
2.1 Structural behaviour tile vaults, masonry barrel vaults and jack arches.
It has been shown that restraining flat slabs
laterally can increase their loading capacity by 2.3 Modern Technological Developments
almost three times due to an arching effect known More recently, renewed interest in concrete shells
as compressive membrane action [4]. This has been driven by advances in analysis,
supports the hypothesis that an alternative manufacturing and materials. For example, fabric
approach to slab design, using thin compression formwork enables concrete to be easily cast into
shells, could significantly improve material curved geometries [5]. Another development is
efficiency (Figure 1). textile reinforced concrete (TRC), which combines
1
IABSE Conference Creativity and Collaboration
April 19-20 2017, Bath, United Kingdom
a fibre reinforcing mesh with concrete in layers to
create a ductile composite material. TRC is well
suited to forming thin shell structures since there
are no minimum cover requirements.
3 Proposed Structural System
In the proposed system, thin pre-cast TRC shells
span between column supports to create a
vaulted ceiling (Figure 2). In order to create a
usable floor surface, a self-levelling fill of Figure 3. Example of preliminary analysis results
lightweight, low-strength concrete is then applied.
3.2 Future Work
Horizontal thrust is resisted by steel ties between
columns. By integrating the services within the A more detailed computational analysis model is
structural zone, the total depth is similar to an under development, which will be verified
equivalent flat slab. through prototyping and physical testing.
4 Conclusion
This project demonstrates how theoretical
understanding, historical inspiration and modern
technological developments can be combined to
develop innovative structural solutions.
This work is funded by the BRE Trust.
5 References
[1] Sturgis S, Roberts G. Redefining zero:
Figure 2. Proposed shell flooring system Carbon profiling as a solution to whole life
carbon emission measurement in buildings.
3.1 Preliminary Design Investigations London: RICS Research; 2010.
Initially, hand calculations were undertaken to [2] Foraboschi P, Mercanzin M, Trabucco D.
determine simple relationships between span, Sustainable structural design of tall
loading, compressive stress and lateral thrust. A buildings based on embodied energy.
parametric finite element analysis model was then Energy and Buildings. 2014; 68(Part A): 254-
created in order to quickly assess a number of 69.
design aspects in some detail (Figure 3), including: [3] Griffin CT, Reed B, Hsu S. Comparing the
Shell geometry embodied energy of structural systems in
Tie stiffness, prestress and height buildings. Proceedings of the 1st
International Conference on Structures and
Lateral and rotational restraint from
Architecture; 2010.
columns
Point and non-uniform live loading [4] Ockleston A. Arching action in reinforced
Differential column settlement concrete slabs. The Structural Engineer.
1958; 36(6): 197-201.
This allowed key design variables to be identified
and gave a fuller picture of the structural [5] Hawkins W, Herrmann M, Ibell T, Kromoser
performance, indicating a 47% reduction in self- B, Michalski A, Orr J, et al. Flexible
weight compared to a flat slab. formwork technologies - a state of the art
review. Structural Concrete. 2016; 17(6):
911 - 35.
