CERS - 2021

Permanent URI for this collectionhttp://192.248.9.226/handle/123/17780

Browse

Browsing CERS - 2021 by Author "Baskaran, K"

Filter results by typing the first few letters
Now showing 1 - 4 of 4
  • Thumbnail Image
    item: Conference-Abstract
    Performance of concrete-filled double-skin circular steel tubes in compression and its application in buildings in Sri Lanka
    (Department of Civil Engineering, University of Moratuwa, 2021-11) Vitharana, TVDVK; Baskaran, K; Hettiarachchi, P
    In this research, an attempt has been made to check the feasibility of using concrete-filled circular double skin steel tubes in buildings in Sri Lanka in terms of performance. Concrete-filled steel tubes (CFST) are becoming a new trend in the construction industry. CFST is a component with good performance resulting from the confinement effect of steel with concrete and design versatility. Concrete filled double steel tube is a composite construction component that consists of two steel layers embedding a concrete layer in between and the inner hollow steel section acts as formwork and reinforcement for the concrete. CFDST has many advantages such as high strength, high bending stiffness, good seismic and fire performance. Columns are designed to resist the majority of axial force by concrete alone can be further economized by the use of thin-walled steel tubes. The study about the behaviour and construction of CFDST columns is a prime need. Moreover, this type of structural member has not been used much in Sri Lankan conditions and hence it is vital to investigate further these sorts of structural elements. This research presents a detailed investigation on how CFDST columns behave under axial compression by experimenting on three concentrically loaded columns with three varying diameters. In terms of the failure, global buckling can be seen when the slenderness ratio is higher and the column with the least slenderness ratio demonstrated global buckling along with local buckling which was localized to the top end of the specimen. The test results were verified by analysing the structural element using ABAQUS finite element software and further validated by using a design standard. Finally, this research discusses the feasibility of using CFDST columns in buildings in terms of seismic performance.
  • Thumbnail Image
    item: Conference-Abstract
    Study on economical protective measures against concrete spalling
    (Department of Civil Engineering, University of Moratuwa, 2021-11) Senevirathne, WTL; Baskaran, K; Hettiarachchi, P
    Concrete spalling is a major problem in reinforced concrete structures, especially in public buildings, which were constructed some time ago. In Sri Lanka, many public buildings such as schools and hospitals exhibit this problem. Authorities prohibit the use of the building area, where there is potential for concrete spalling instead of immediately repairing, because the repairing work is expensive and time consuming. This research is to study economical protective measures to prevent falling of spalled cover concrete chunks until the proper repair is done. The research is conducted in two experimental series. Series one consisted of eight small scale concrete slab panels, which were installed with four different materials (plywood sheet, thin aluminium sheet, plastic mesh, and stainless steel wiremesh) by two installation methods (concrete wedge anchors and screws with wall plugs). Initially concrete slab panels were cast, and after 28 days the materials were installed with two distinct installation methods. Then the material installed structure was subjected to area load and failure loads were recorded. Second experimental series was performed with the same size concrete slab panels, three materials (stainless steel wire mesh, plastic sheet, and thin aluminium sheet) and one installation method (wedge anchors) which were used in first experiment. Initially slab panels were cast and kept to gain strength, then the selected three materials were fixed with the above installation method. After that, the material installed slab panels were subjected to cyclic wetting and drying using three percent sodium chloride solution by weight of water to create a spalling condition by the electrolysis process. Then the relevant observations of the material installed structure and concrete slab panels were made with the time. After 28 days, material installed structure was subjected to area load and failure loads were recorded as same as the first experiment. Stainless steel wire mesh installed with concrete wedge anchors showed the highest load carrying capacity.
  • Thumbnail Image
    item: Conference-Abstract
    Study on using bottom ash in manufacturing conventional cement blocks
    (Department of Civil Engineering, University of Moratuwa, 2021-11) Sritharan, D; Baskaran, K; Jayakody, JRUC; Hettiarachchi, P
    Bottom ash is a common by-product of thermal power plants or boilers. Due to the depletion of natural sources of fine aggregates, there is a need to encourage the use of alternative materials. In this study, coal bottom ash is used as replacement for fine aggregates. From an environmental and economical point of view, the use of coal bottom ash in cement mixtures is a beneficial application. The significance of the present study is maximizing the utilization of coal bottom ash by using it in the manufacturing process of conventional 300mm x 100mm x 150mm solid cement blocks and then checking its suitability to the construction industry against Sri Lankan standards. Finally, statistical models were developed between compressive strength, water absorption, density, and other input variables. The raw materials utilized in this experimental study were ordinary Portland cement, manufactured sand, bottom ash, and water. Bottom ash from Brandix Textile (Pvt) Ltd., Wayamba Industrial Zone, Makandura, Gonawilla, Sri Lanka was used to replace manufactured sand at different percentages by volume of sand. 1:6 cement: fine aggregate mix proportion was proposed for this experiment with the 0.5 consistent water/cement ratio. In this study, conventional vibrocompaction was used to mould the cement blocks. The blocks were cured by spraying water twice a day till the day of testing. Finally, the mechanical and durability properties of cement blocks were determined at the ages of 14th, 28th, and 56th days. The results showed that the density and compressive strength of cement blocks decreased, and water absorption increased with an increasing replacement level of bottom ash. From the analysis, it can be concluded that up to 45% of fine aggregate in the cement blocks can be replaced with sieved coal bottom ash in small and medium scale conventional cement block manufacturing using the mix proportions attempted in the present study.
  • Thumbnail Image
    item: Conference-Abstract
    Study on ways to minimize honeycombs in concrete construction
    (Department of Civil Engineering, University of Moratuwa, 2021-11) Manojh, N; Baskaran, K; Hettiarachchi, P
    During concrete construction, there may be some defects formed due to carelessness of humans. The defects formed include honeycombs, those due to poor formwork installation, shrinkage cracks, segregation, and exposed reinforcement to environment etc. These may have happened due to poor site experience, poor design, and carelessness of workers. One of the main defects is honeycombs. Honeycombs are porous volumes of coarse grain aggregates bonded together by cement. In practice, these defects are formed when the fresh concrete ingredients segregate e.g., due to granular convection effects. The presence of honeycombs causes loss of durability, loss of load bearing capacity and corrosion of reinforcement bars. So, there is a need to minimize the honeycombs in construction site to enhance the durability of concrete structures. Under this study, the causes, remedial measures, how to identify, and how to avoid were studied. The main objective of the present study is to find methods to identify the location of core honeycombs. Ultrasonic Pulse Velocity (UPV) test and measuring vibration levels using a vibrometer while striking the surface with a rubber mallet are the two approaches attempted in the present study. A questionnaire survey and an experimental analysis were done as part of research. Questionnaire survey was done among the batchmates on whether they have encountered honeycombs during their Industrial training. Experimental analysis was performed on six beams (600 mm x 250 mm x 150 mm) of Grade 30 concrete (with reinforcement three beams and without reinforcement three beams). The beams were cast with intentionally created honeycombs inside the beam in different depth using Polystyrene. Beams were cast with reinforcement of 4T12 bars and R6 stirrups at spacing 100 mm. On the faces of each beam a grid having lines at 100 mm interval in the horizontal direction and 50 mm interval in the vertical direction was made to carry out the UPV and Vibrometer testing. The experimental results show that by using UPV equipment it is possible to locate the core honeycombs precisely in the concrete panels with plaster and without plaster. However, accuracy of detecting honeycombs using Vibrometer in beams with or without plaster is less. In the plastered case, surface should be smoothened by Plaster of Paris for better results.