THESIS
2020
xiv, 144 pages : illustrations (some color) ; 30 cm
Abstract
Basement walls in tall buildings are generally designed as Water Retaining Structures (WRS)
that are usually constructed using steel reinforced concrete (R/C). In contrast to conventional
R/C structures, the design of WRS needs to satisfy additional criteria to ensure sufficient crack
control for water-tightness. To ensure acceptably low crack widths at Serviceability Limit State
(SLS), a higher amount of reinforcement than that required for Ultimate Limit State (ULS), is
usually needed. This results in high reinforcement ratios and congestion which make concrete
placement and compaction difficult. This may lead to construction defects that compromise
structural integrity, whereby water often seeps in through flaws or cracks in the concrete. This
issue is particularly severe fo...[
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Basement walls in tall buildings are generally designed as Water Retaining Structures (WRS)
that are usually constructed using steel reinforced concrete (R/C). In contrast to conventional
R/C structures, the design of WRS needs to satisfy additional criteria to ensure sufficient crack
control for water-tightness. To ensure acceptably low crack widths at Serviceability Limit State
(SLS), a higher amount of reinforcement than that required for Ultimate Limit State (ULS), is
usually needed. This results in high reinforcement ratios and congestion which make concrete
placement and compaction difficult. This may lead to construction defects that compromise
structural integrity, whereby water often seeps in through flaws or cracks in the concrete. This
issue is particularly severe for a basement wall as it needs to restrict water under high pressure
from seeping into the interior space of the structure.
Strain-Hardening Cementitious Composites (SHCC) have intrinsic crack control properties.
Using this material in place of conventional concrete would eliminate the extra steel required
to limit crack width in a reliable manner. Conversely, the wall section can be reduced to provide
more usable space. SHCCs have been developed based on the theory of micromechanics to
ensure tensile strain-hardening, multiple micro-cracking and durability through tight crack
control. It has also been shown that concrete cracks which are sufficiently small can be sealed
by autogenous healing under appropriate conditions. However, the high material cost associated
with the fibres used in SHCCs and its low elastic modulus, compared to concrete, have
hampered their wider usage as a construction material in real life structural applications.
This study focuses on comprehensive design and development of a cost-effective SHCC to be
used in place of concrete in the construction of WRS using a performance driven design approach. The key structural performance parameters in the design of the basement wall such
as the flexural moment capacity of the section, shear strength, crack width, etc. are identified.
The same are linked to the material properties such as tensile strength, strain capacity, elastic
modulus and compressive strength. Finally, these material properties are achieved by judicious
selection of matrix and fibre combination under specified processing conditions. Locally
available conventional construction materials along with a lower cost alternative PVA fibre and
a novel PVA coated PET fibre are used to produce a SHCC at a lower cost that meets the
material property requirements derived from the structural performance criteria. The
mechanical properties as well as the self-healing ability of the developed SHCC are evaluated.
In addition, a design approach for flexural members in its ULS and SLS using reinforced SHCC
is also proposed and verified by testing flexural elements of different scales.
With the superior tensile properties of the developed SHCC, it is shown that there can be a
reduction of reinforcement or member thickness compared to the R/C design. Hence, even
though material cost of SHCC is still higher than ordinary concrete, the overall cost for the
member can still be comparable. In addition, the reduction of reinforcement congestion
facilitates concrete placement, labour cost saving and elimination of defects. In brief, this study
highlights the feasibility of using reinforced SHCC in place of R/C in the construction of water
retaining structures using basement wall as an example of a practical application.
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