NUI Galway – UL Alliance First Annual ENGINEERING AND - ARAN ...

Analysis of Shear Transfer in Void-Formed Flat Slab Systems, Including In-
Situ Measurements from a Building
David Byrne 1 , Jamie Goggins 2 , Eamonn Cannon 3
College of Engineering and Informatics, National University of Ireland, Galway
1)david.byrne@nuigalway.ie, 2) jamie.goggins@nuigalway.ie, 3)eamonn.cannon@nuigalway.ie
Abstract
This research primarily focuses on the analysis
of shear transfer in void formed flat slab units. It also
incorporates the instrumentation of the New
Engineering Building (NEB) at NUI Galway and its
development as an interactive teaching tool. The project
itself is jointly funded by IRCSET and Arup Consulting
Engineers.
1. Introduction
Void from flat slab systems are an innovative
and novel form of flat slab system. They consist of
spherical void-formers, positioned in the middle of the
concrete cross section to reduce the overall self weight
of the slab, while maintaining the full flexural strength
allowing a two-way or bi-axial load transfer. The
reduction in self-weight, up to 35%, allows for savings
in overall materials and permits longer spans. Void
form flat slabs can be constructed by two methods;
traditional in-situ or in combination with pre-cast
elements. This research focuses on the use of semiprecast
elements and how two-way action in the bottom
steel is restricted. To ensure that two-way action is
achieved between the different slab panels a series of
reinforcement or ‘stitching’ bars are provided. These
‘stitching’ bars are centred on the joint between the precast
elements. The assumption is that these will provide
sufficient bond between the slab panels to ensure
transfer of load across the slab joints rendering the
joints irrelevant to the completed structural
performance. One of the primary aims of this project is
to analyse this load transfer.
2. Aims of the Project
The project forms part of the overall
instrumentation of the NEB and its development as an
interactive teaching and learning tool. The NEB will be
a ‘living laboratory’ for engineering, where live data
sets from numerous types of sensors will be provided
for use in illustrating structural engineering and
building performance concepts in undergraduate
teaching, and in the development of full-scale research
in structural engineering and energy. As such a central
aim of the project is to oversee the instrumentation of
the NEB from a structural engineering point of view. To
date almost 260 gauges have been installed in various
structural elements throughout the building.
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The project will also offer an independent
investigation into, and contribute an original idea in, the
design of void form flat slab systems. At present there
are very few publications in relation to this unique slab
system and their design is not specifically included
within the provision of Eurocode 2. As such the project
aims to highlight a set of procedures which could be
incorporated within the codes. The extent to which
shear transfer is achieved through the use of ‘stitching’
bars in void form flat slabs will be examined and to
determine if there is a better and more efficient method
of achieving shear transfer. Any design issues in
relation to void form flat systems will also need to be
clarified along with investigating what areas of the slab
are susceptible to failure and the failure mechanisms
involved.
3. Methodology
Central to the project will be data gained from
the instrumentation of the void form flat slab system
used in the NEB. The NEB was the first building to
incorporate the use of flat slab systems in Ireland. Over
160 gauges have been installed in the slab element and
these are continuously monitoring the temperatures and
strains within the slab. This data from site will allow a
detailed understanding of exactly how void form flat
slabs react during the various stages of a buildings
construction and also during its lifetime.The overall
research strategy will combine numerical simulation
using finite element models and field measurements.
The finite element models of the instrumented slab
system will be validated by comparison and continual
updating of data obtained from measurements on site.
Furthermore to augment the data collected on site a
range of experiments and testing will be carried out in
the laboratory. Aspects which contribute to shear
transfer include the adhesion and bonding of concrete,
shear friction between the pre-cast and in-situ elements
and the dowel action of the reinforcement bars across
the precast joints. All aspects will need to be analysed
and the manner in which they contribute to the overall
shear transfer in the slab system. Time dependant
effects of concrete such as creep, shrinkage and
temperature effects also need to be taken into account.
Each has an effect on the stresses and strains
experienced within the slab element and thus have an
impact on the data received from site.