Doctor of Philosophy (Ph.D.)http://dl.lib.uom.lk/handle/123/124292024-03-29T14:34:07Z2024-03-29T14:34:07ZDevelopment and validation of a novel CFRP/steel hybrid crack repairing technique for the steel structuresAbeygunasekara Shttp://dl.lib.uom.lk/handle/123/222052024-02-08T22:07:28Z2023-01-01T00:00:00ZDevelopment and validation of a novel CFRP/steel hybrid crack repairing technique for the steel structures
Abeygunasekara S
Steel structures such as steel bridges greatly contribute to the socio economic development of
the world. The current traffic demand has exhausted the service life of steel bridges paving the
way for failures without prior warning due to fatigue. In fact, fatigue contributes to change the
microstructure of a material which fails below the yield point. Therefore, fatigue could be
considered as an issue related to materials, even though it is linked to the area of engineering.
Interestingly, several unavoidable stress types on structures occur on steel bridges due to
various reasons. As a result, avoiding fatigue on structures has become impossible during their
service life. The result of stress fluctuation has caused crack initiation on steel structures while
the initial stage is at a micro scale level and not visible to the naked eye. Thus, it should be
controlled at the initial stage avoiding adverse effects later. Although the conventional crack
repair techniques have extended service lives of structures they have led to numerous
drawbacks too.
The crack stop hole technique could be considered as an emergency repairing technique to
extend the fatigue life of a cracked steel structures that is quick, simple and economic. This
technique was successfully applied in the aerospace industry primarily, however there had
been irregularities due to the size of the hole with re-cracking appearing due to continuous
service loads. Carbon fiber reinforce polymer (CFRP) materials have become popular as it has
potential to replace the conventional repairing techniques with recent research focused on
CFRP materials due to its light weight, corrosion resistivity, damping characteristics, fatigue
resistivity and high tensile features. Therefore, this study proposes a crack stop hole (CSH)
technique combined with a CFRP strengthening method to acquire the lost capacity due to
fatigue in old structures with delaying re-cracking by further continue their services by steel
bridges in the road and railway network operate at present.
An experimental test program carried out to determine the behavior of strengthened and nonstrengthened
CSH
in
steel
members
subjected
to
low
cycle
flexural
fatigue. Overall, the test
program was focused on estimating yield strength losses and yield strength gained by CFRP.
Interestingly, various types of fatigue testing apparatus are available in the open market for a
relatively high cost which is not affordable in a university laboratory, thus a hydro-electric
controlling fatigue loading apparatus was designed and fabricated as an initiation to this
research study to fulfill this vacuum. In this development process, machine operation, and
development technique with finite element analysis on the test frame was investigated.
In the next phase of this research, a numerical model was developed using an advanced finite
element model (FEM) and results were validated using the laboratory test results. The
proposed numerical model was based on the cyclic J-integral method under the detect cyclic
mode. The test results agreed with the model results consisting nine key parameters affecting
the final results. This CFRP strengthened CSH technique is significantly enhanced fatigue life
of the structural members. This investigation reported the yield strength losses; which are in
the range of 13.4 % to 25.2 % compared to the non-conditioned and yield strength gains with
CFRP; which is in the range of 32.2 % to 45.3 % compared to the non-strengthened CSH with
the diameter varies from 4 mm to 25 mm. A considerable amount of strain controlled were
recorded by CFRP with respect to non-strengthened CSH. When considering the critical
parameter effects, the test results recorded a yield strength gain with respect to off-set distance;
which was in the range of 36 % to 131 % compared to the CSH at the midpoint. The yield
strength variation recorded due to the length of CFRP layer was in the range of 89 % to 223
% compared to the least length considered. This investigation recommended by CFRP
strengthened technique has significantly enhanced fatigue bearing capacity of structural
members with CSH. Design guidelines are developed for practical implementations.
2023-01-01T00:00:00ZA Dynamic, clay double wall system for indoor coolingPadmaja RAMhttp://dl.lib.uom.lk/handle/123/211872023-10-13T02:32:59Z2022-01-01T00:00:00ZA Dynamic, clay double wall system for indoor cooling
Padmaja RAM
Truly, sustainable development promises environmental, social, economic, yet
personal meaningfulness, beyond increasing financial wealth. The usage of clay in
construction is proven sustainable in all three aspects since its usage from the very
beginning of human civilization. However, the chauvinism toward clay as a
nonmodern material is detrimental, and therefore novel innovations of clay, are
required to fasten with modern architecture for a whole new perspective. The usage of
clay for primary, heavy walling is common in hot arid climates, yet fewer studies
incorporate clay for interiors and double walling in the tropics.
This gap was addressed by developing a Dynamic, Clay Double Walling (DCDW)
solution for heat reduction with easy maintenance and favorable aesthetics. The
cooling effect of these structures can be attributed to the resistance of heat flux to the
building due to the porosity of the structure, heat absorption, and thus decline of
thermal conductivity.
The research thus investigates improvements in internal porosity and air permeability
of clay, for improved mechanical and chemical properties, and thermal stability upon
firing. Patterns and characteristics for best indoor air temperature reduction were
identified on the material mix, mix composition, firing configurations, thermal
conductivity, shrinkage, panel thickness, etc.
The practicality and application potentials of the invention were tested on-site,
potential improvements were tested virtually (with building simulations) for their
effectiveness, and in completion, the long-term sustainability, and profitability of the
DCDW system were investigated by identifying the LCC.
The innovation suggests an energy-efficient, low-cost, low maintenance and
lightweight, sustainable, double walling solution for high-end to low-end, yet new
construction to retrofitting for tropical interiors.
2022-01-01T00:00:00ZIntegration of double skin green wall as a sustainable design approach in tropical contextRupasinghe HThttp://dl.lib.uom.lk/handle/123/211932023-10-13T02:33:53Z2022-01-01T00:00:00ZIntegration of double skin green wall as a sustainable design approach in tropical context
Rupasinghe HT
Global warming and energy crisis are two of the biggest issues the world faces today which
require immediate mitigatory actions. Building sector plays a major role in contributing to
these issues due to the high energy consumption and carbon emissions. Highly dense
urbanities directly contribute in urban heat island effect thus local warming. Therefore,
researchers have given considerable interest on the building envelop design with the concerns
for energy efficiency, aesthetic appearance and sustainability. As a result, integration of
green facades with buildings has rapidly evolved due to the aesthetic appeal and sustainable
benefits such as uplifting the urban environmental conditions by promoting air quality,
reducing heat island effect and etc. However, adaptation of vertical greenery is still at an
initial stage in Sri Lanka.
The research was initiated to introduce vertical greenery to a broader context and to develop
an innovative modular green wall system for building facades as a sustainable building
envelop in Sri Lankan context. Field studies were conducted in identifying the potential of
introducing a vertical greening system and benefits of existing vertical greening systems in
tropical Sri Lankan context. Modular panel and green wall system development was
conducted as on-site experiments and the thermal performance evaluation and long-term
benefits of the proposed modular panel vertical greening system was conducted as on-site
investigations combined with software simulations.
Results of the field investigations on the perception on vertical greening in local context
demonstrated that general public, building occupants and the building designers are willing
to accept the vertical greening as a sustainable approach for buildings. Yet, lack of knowledge
on the vertical greening systems, maintenance methods and their benefits and misconceptions
on related costs have impeded the popularization of vertical greening. Identified existing
vertical greening types in local context; living walls, indirect and direct green facades are
beneficial in reducing the surface temperature of buildings where living walls recorded the
highest temperature reduction of 10.15
o
C. Internal air temperature reduction was recorded to
be 2.21
o
C, 1.82
o
C and 0.66
o
C by living wall, indirect green façade and direct green façade.
Pilot and extended field investigations on plant selection for the proposed vertical greening
system resulted in shortlisting two species, from which Axonopus compressus was selected as
the best plant species where a maximum 10.08
o
C external wall surface temperature reduction
and 3.15
o
C internal surface temperature reduction was recorded. The experimental studies on
finalizing growth media resulted 1:1/2:1/2: 1/4 coir: sand: compost: soil ratio as the growth
media with the best compaction and the permeability for the plant growth in the proposed
vertical greening system. Proposed system is advantageous as it can be easily introduced to
existing structures and as the panels can be handled separately allowing easy installation and
easy replacement with minimum technical support. Size of the modular panel was finalized as
600mm (width) x 900mm (height) for easy handling and the fiber was selected as the material
due to strength and durability.
Developed walling system recorded a surface temperature reduction of 17.26
C in
external wall and internal wall surface and a temperature reduction of 2.89
C of internal air
temperature. Simulation studies conducted in building scale and urban scale resulted significant
indoor air temperature reduction, cooling load reduction and urban air temperature reduction
when integrating the proposed modular panel green wall whereas the quantifiable long-term
benefits are achievable in terms of savings from energy consumption and façade maintenance
and numerous un-quantifiable benefits related to sustainability and health.
2022-01-01T00:00:00ZCoconut fiber reinforced polymer composite for non-load bearing panel wallsDharmaratne P Dhttp://dl.lib.uom.lk/handle/123/211842023-10-13T02:33:51Z2022-01-01T00:00:00ZCoconut fiber reinforced polymer composite for non-load bearing panel walls
Dharmaratne P D
The study's main aim was to develop a lightweight walling panel for apartment buildings by
employing coconut [coir] fiber with waste polyethylene. In this study, the flexural performance
of coconut fiber reinforced polymer [CFRP] sandwich panels with different core
configurations has studied experimentally and numerically. The numerical investigation was
carried out using finite element analysis software “ANSYS 17.2”. The coconut fiber
reinforced polymer sandwich panel was developed with thin CFRP sheets for the outer faces
and cell arrangement for the internal core structure which was made by the same CFRP sheets.
The sequences of cells with different core structures were considered to determine the
optimum solution for flexural behavior. The first part of this study was the investigation of
coconut fiber's physical, mechanical, and chemical properties by using an experimental
investigation and a literature review. The next step was to develop the CFRP composites. In
this study, the coir fiber was used as reinforced material, and the waste polyethylene was
utilized as a matrix material. Composite was developed using hand-layup techniques by
varying the coir length and coir weight fractions. This composite material was analyzed using
ASTM standards for tensile and bending performance. The sample which optimum results
obtained relevant to the coir length and weight fraction were used to develop a composite
sandwich panel of 400mm x 400mm in size. The most suitable manufacturing conditions were
also studied. The flexural properties of this panel were inspected using experimental and
numerical methods. The three-point bending test was carried out to investigate the maximum
failure stresses for the panel sample. The next part of this study is to develop the numerical
models for the three-point bend test using finite element software. Then, the experimental
results obtained from the three-point bend test and numerical outcomes are compared and
validated. In the end, the numerical analysis is expanded to examine the sample panel's flexural
performance of different cell arrangements. Finally, the failure stresses and the volume at
minimum failure stress were identified for each cell configuration. This result concluded that
the best cell configuration with minimum weight for wall panels was the result. The proposed
wall panel should be durable and low-cost. Therefore, service characteristics and production
costs were analyzed. Further, to extend this research, the proposed wall system's life cycle cost
and embodied energy were analyzed to identify the long-term benefits of the proposed walling
system.
2022-01-01T00:00:00Z