Beside the point of whether the country is developed or underdeveloped, energy crisis is a common scene all over the world. In order to balance energy supply and demand, either one has to increase the supply or decrease the demand. The latter seems to be the better choice since we have limited sources of energy. About 20% - 40% of energy produced by a country is being consumed by HVACs in buildings. Hence much e ort is towards energy conservation in buildings. Around 30% of the building energy consumption in India is due to cooling load. Previous studies have shown that around 60% of the heat due to solar radiation enters through the roof of the building. The present work aims to reduce the heat load entering through the roof by coming up with a better roofing technique for moderate climatic regions. In the present work, enclosures with the side walls and the floor (bottom slab) insulated has been studied both numerically and experimentally. Heat transfer between the ambient and enclosure is only through the roof (top slab). Six common roofing types have been studied in this thesis. Reinforced cement concrete (RCC) roof Mangalore tile roof Thatched roof GI Sheet roof and Concrete roof with lawn (green roof) Concrete roof with a layer of wet sand The experimental studies have been carried out to understand heat transfer through these roofs. A comparative study of all six types of roofs has been done. Apart from this, the effect of a shade net on room models with bare RCC roof and GI sheet roof is also studied and presented in this thesis. Each enclosure has a height of 0.3m and the sides are 1m in size. Mangalore tile and thatched roofs are inclined to the horizontal. To understand the heat flow process, the temperature variations of different surfaces and enclosure air, and, air temperatures near the top and bottom slabs were recorded. In addition, weather conditions such as solar radiation, ambient air temperature, and wind speed are recorded. The details of the experimental set up are given in chapter 3. In chapter 2, a mathematical model to determine the temperature variations in the enclosure is given. All the three modes of heat transfer (conduction, convection and radiation) are present and the system is unsteady. The objective is to find the temperatures of the walls and the enclosure air temperature. Heat flows either from surroundings to the enclosure or from enclosure to the surroundings through the walls of the enclosure. As the solar radiation data is known for a given location, un-steady heat conduction equation is solved for the walls of the enclosure with heat flux boundary conditions to solve for the temperatures. Standard correlations have been used for calculating the convective heat transfer to the ambient and in the enclosure. Most importantly, the experiments conducted were field experiments. The main objective of the study had been to understand the effect of roof on thermal comfort conditions inside the scaled model rooms under five different weather conditions which are commonly observed in warm tropics: (1)summer, (2)winter, (3)cloudy, (4)unsteady, and, (5)rainy. The details of weather conditions have been discussed in chapter 4. In the present analysis, various issues were looked upon such as, temperature values, time lag, thermo-physical properties of the roof material, weather conditions, average over a 24 hours cycle etc. For the comparative analysis, bare RCC roof has been assumed to the base case as most of the buildings are built with RCC roof (for example, in India, around 29% of the buildings have RCC roof, as per 2011 census). On one side we have passive cooling techniques (lawn over RCC roof and wet sand over RCC roof), and, on the other side we have breathing roofs (Mangalore tile roof and thatched roof). Apart from these, the GI sheet roof is commonly used for small scale industries and residential houses. It has been observed that the concrete roof with lawn (hereafter called as lawn over RCC roof ) being the best one among the considered six roofs. Having lawn over RCC roof could result reduction in both solar gain and the diurnal variation of enclosure inside temperatures. The range of temperature variation was least disturbed due to change in weather conditions. In the case of wet sand over RCC roof, the diurnal variations of enclosure inside temperatures were relatively higher as compared with those in the lawn over RCC roof case. As far as breathing roofs are concerned, the two were found to be better than bare RCC roof with thermal comfort as point of view. On the other hand, breathing effects are found to be better in case of Mangalore tile roof than in case of thatched roof. GI sheet roof was found to be the worst among considered for thermal comfort. The effect of using shade net over RCC and GI sheet roof proves to have good potential to reduce cooling load with negligible adverse effects during night time. Detailed discussion of results has been done in chapter 4. Numerical simulations have been carried out for the case of model room with bare RCC roof. A comparative analysis of both experimental and numerical results has been discussed in chapter 5. The important conclusions are discussed in chapter 6.

Reinforced cement concrete (RCC) structures have become an important aspect in most of the buildings in our society around the world. Most of the multistoried reinforced concrete buildings house important institutions such as hospitals, schools, government establishments, defense establishments, business centers, sports stadiums, super markets and nuclear power plants. The cost of construction of such multistoried RCC structures is very high, and these structures need to be maintained and restored based on their functionality and importance using repair and retrofit strategies when these structures undergo damage. The steps involved in restoring RCC structures that have damages using repair / retrofit measures consists of identifying the source or cause of damage, assessment of the degree or extent of damage that has taken place using nondestructive techniques. Based on the assessment of degree of damage suitable repair / retrofit strategy using the appropriate repair material is applied to achieve the required load carrying capacity or strength. The present work involves assessing the efficacy of carbon fibre reinforced polymer (CFRP) based system applied on pre-damaged structural members to restore the member’s strength and stiffness through experimental investigations and finite element predictions. To validate the macrolevel properties of predamaged concrete micromechanical analysis, microscale studies and analytical investigations have been conducted. Plain and reinforced concrete test specimens: cylinders, square prisms and rectangular prisms having 25MPa and 35MPa cylinder compressive strengths pre-damaged due to mechanical (monotonic and cyclic loading) and thermal loading (exposure to different temperature and time durations) with applications of CFRP repair subjected to compression is investigated to study the behavior and enhancement in the compressive strength and stiffness after application of repair. Non destructive testing of thermally damaged concrete (exposed to different temperature and exposure time) is conducted using ultrasonic pulse velocity and tomography methods to understand the degradation in the strength and stiffness of thermally damaged concrete. The results of the non destructive testing helps in assessing the amount of repair that can be applied. To validate the macro scale behavior of thermally damaged concrete micro scale studies was performed adopting micro indentation, petrography, Raman spectroscopy, scanning electron miscroscopy (SEM) and Electron probe micro analysis (EPMA). During the event of a fire in RC structures which have been retrofitted. The high temperature caused due to fire tends to make the concrete to deteriorate and the repair material to delaminate. Loss of strength/ stiffness in concrete and delamination of the repair material in a retrofitted structural component in a structure causes instability which results in partial collapse or complete collapse of the structure. Thermal insulation of concrete and the repair material (CFRP) using geo-polymer mortar and simwool thermal fibre blanket exposed to high temperature and different exposure time are experimentally investigated. This is to evaluate the effectiveness of the thermal insulation in protecting epoxy based structural repair material(CFRP) from thermal damage and to minimize the delamination of the repair material when exposed to high temperatures. Slender columns when loaded eccentrically fail at a load much lesser than their actual load carrying capacity. In RC buildings where additional floors need to be added, in those situations slender columns which are already eccentrically loaded tend to get damaged or fail due to additional load which act on them. Therefore to restore such columns experimental and finite element investigations on reinforced concrete slender columns having 25MPa cylinder compressive strength subjected to eccentric monotonic compressive loading with applications of CFRP repair is studied to understand the behavior and the enhancement in load carrying capacity after application of repair. Experimental investigations are conducted to study fracture and fatigue properties of thermally damaged concrete geometrically similar notched plain and reinforced concrete beams having 25MPa cylinder compressive strength exposed to different combinations of temperature and durations with application of repair (CFRP). Nonlinear fracture parameters of thermally damaged concrete is computed which help in understanding the fracture behavior of thermally damaged concrete and application of repair. Effectiveness of CFRP repair and failure behaviour of these beams are studied when these thermally damaged notch concrete beams are subjected to monotonic and cyclic (fatigue) loading. Reinforced concrete slender beams when subjected to unexpected loads such as earthquakes get damaged. The increase in load carrying capacity and fatigue life of reinforced concrete slender beams having 25MPa cylinder compressive strength in flexure subjected to monotonic and cyclic loading with applications of CFRP repair is investigated using experimental and finite element investigations. Finite element analysis of concrete specimens pre-damaged due to mechanical (monotonic and cyclic loading) / thermal loading (exposure to different temperature and time durations) with applications of CFRP repair and assessment of amount of repair required is investigated. Analytical (empirical) models are developed to assess the mechanical properties of concrete (elastic moduli, compressive strength and split tensile strength) exposed to different temperatures and time durations. Nonlinear fracture parameters of geometrically similar plain concrete notch beams exposed to different temperature and time durations are determined. Fracture parameters (stress intensity factor) of thermally damaged plain and reinforced concrete notched beams with application of CFRP have been determined. Effect of size and shape of thermally damaged plain concrete compression members with application of CFRP wrap have been studied. Crack mouth opening displacements (CMOD), strains and crack lengths of thermally damaged plain concrete (PC) notched beams using digital image correlation has also been determined.