Browsing by Author "Somaratna, N"

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Open Access
Correlation of tensile strength of blended cement concrete with specimen dimensions and aggregate size: A practical test review
(SLIIT, Faculty of Engineering, 2025-02) Amarasinghe, N; Somaratna, N
Test specimen dimensions affect most strength properties of concrete. The existing empirical relationships in this regard are predominantly based on concrete samples made by using Ordinary Portland cement (OPC). An important recent trend in Sri Lanka has been the increasing use of blended cements. This makes it necessary to examine whether the relationships hold for blended cements as well. In this study, split cylinder tensile strength tests were conducted to determine whether the specimen size and the tensile strength of concrete prepared using a blended cement (Portland Composite Cement (PCC)) display relationships similar to OPC. Tests were conducted on specimens using two cement types – OPC and PCC - and three concrete mix ratios and a range of specimen dimensions to study the effect of the specimen length (L), diameter (D), and aggregate size (a) on the split cylinder tensile strength (T). The data was examined using dimensional analysis based on Buckingham's π theorem. A slight increasing trend was observed in the ratio of split cylinder tensile strength to mean a compressive strength (T/fc,mean) with an increasing L/D ratio. As for the ratio of the aggregate size to the specimen diameter (a/D), the analysis showed an increasing trend in T/fc,mean values with an increasing a/D ratio, indicating a significant correlation between T/fc,mean and a/D. A nonlinear regression analysis was used in an attempt to determine a functional relationship among the non-dimensional parameters T/fc,mean, L/D, and a/D. But the differences in the derived relationships for different concrete mixes were too large for reaching a common relationship. Perhaps this was due to the small number of data points available. It was seen that relationships established for OPC may hold true for PCC too. However, the data used was limited in range and more comprehensive further tests should be conducted to confirm these findings.
Open Access
Structural Behavior of Two Major Concrete Dams in Sri Lanka Under Earthquake Loads
(SLIIT, 2022-02-11) Chandrasena, A; Weerasekara, K; Somaratna, N
Dams are built for a variety of purposes including hydropower generation, irrigation, water supply, and flood mitigation. Concrete and earth dams are common types of dams in Sri Lanka. Concrete dams can be categorized as Gravity dams and Arch dams. Gravity dams are most common in Sri Lanka. Dams can also pose safety hazards. Failure of a dam can cause serious damages to both people and property downstream. One of the major threats to dams is earthquakes. They can have significant impacts on the stresses within the dams. In extreme cases this can cause even failures of dams. These possibilities can be investigated using finite element analysis. In this study Rantambe and Moragahakanda concrete gravity dams were selected for 2-D finite element analysis under the action of suitable earthquakes. For each case linear time history analysis was performed using SAP2000 software. The stresses were examined for potential failures. Important considerations in this process were selection of dams, selection of suitable earthquake records, and identification of an appropriate failure criterion. The selection of earthquake records was based on proximity and geological conditions. Koyna earthquake was used to develop suitable earthquake loadings. Peak ground acceleration was varied from 0.05g to 0.15g. Westergaard method was used to assign hydrodynamic loads. Coulomb-Mohr criterion was employed to investigate potential failures in concrete. Stresses in dam models during the earthquakes was scrutinized for potential failures. Significant stress increases were observed in some areas of the dams. These critical areas and corresponding values of earthquake parameters were identified. It was concluded that the dams were unlikely to suffer material failures under earthquake loads even with a peak ground acceleration of 0.1g (which is the value recommended for use for critical structures in the areas concerned).