Browsing by Author "Dilrukshi, KGS"

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item: Conference-Full-text
Contribution to numerical modelling of concrete- masonry interface In concrete framed structures with masonry infill
(2013-12-01) Induprabha, SAD; Dilrukshi, KGS
Masonry infills have long been used as interior partitions and exterior walls in buildings. They are usually treated as non-structural elements, and their interaction with the bounding frame is often ignored in design. Nevertheless, infill contributes strength to a structure and will interact with the bounding frame when the structure is subjected to strong lateral seismic loads, when the infill is stressed due to movements of an overlying slab or any other case of in-plane or out of plane lateral loading. This interaction may or may not be beneficial to the performance of the structure, however, and it has been a topic of much debate in the last few decades. The interaction of the infill is governed by the relative stiffness and strength characteristics of each individual component and most importantly the interface characteristics that decide the degree of composite action. An interface is a special contact plane on which nonlinear relations between stresses and displacement discontinuities are present. Very often initiation and propagation of cracks along these interfaces are the cause of failure of the relevant structures. Similarly, in the case of concrete framed masonry assemblages, the bond between the masonry and the concrete frame is a weak link, through which failure is possible. Therefore to simulate this behaviour, interface elements with a suitable constitutive model can be utilized. This paper explores finite element models developed to simulate the behaviour of concrete- masonry interface of masonry infill. In this study, brick-concrete couplets were mathematically modelled, using commercially available software ANSYS. The adopted numerical strategy consists of simplifying the concrete-masonry-mortar interface to a zero thick interface, modelling the brick units and the concrete units with three dimensional solid brick elements and modelling the bond using zero thickness interface elements with a cohesive-zone model (CZM) for mixed-mode fracture based on damage mechanics introduced by Alfano and Crisfield(2001).
item: Conference-Extended-Abstract
Cracks in masonry walls due to thermal movements of overlying slab
(2006) Dilrukshi, KGS; Dias, WPS
Concrete slabs exposed to direct sunlight experiences temperature related horizontal movements. In addition, temperatures on the top surface will be higher than those on the underside of the slab, causing an upward movement of the slab during heating. In a typical building, masonry and concrete structural elements restrain each other at their respective interfaces. Therefore, significant movements may be generated on the masonry walls, due to movement on roof slab. These movements can result in overstressing and cracking in masonry.
item: Conference-Full-text
Determination of suitability of the limestone aggregates as coarse aggregate for concrete
(Department of Civil Engineering, University of Moratuwa, 2014-03) Perera, MUD; Dilrukshi, KGS; Hettiarachchi, MTP
The use of limestone in the construction industry has been increasing due to its potential as aggregate. Some of the benefits of limestone include good strength, low possibility of alkali-silica reaction and the decrease in drying shrinkage in concrete. In the northern part of the Sri Lanka, limestone is used as aggregate in concrete due to its availability'. The aim of this research is to observe, evaluate, compare and discuss general characteristics of the limestone aggregate in the northern part of Sri Lanka and check the suitability of the limestone as coarse aggregates in concrete. There are two different kinds of limestone there, namely Red limestone and white limestone. Then experiments are conducted for both kinds of limestone together with the normal coarse aggregates. The properties of density, water absorption, particle size distribution, Flakiness Index, Los Angeles Abrasion Value, Aggregate Impact Value, Aggregate Crushing Value and Soundness of the aggregate are observed. The results are compared with the properties of the coarse aggregates and then suitability of limestone aggregates is evaluated.
item: Conference-Full-text
Determination Of Suitability Of The Limestone Aggregates As Coarse Aggregate For Concrete
(2014-06-10) Perera, MUD; Dilrukshi, KGS
The use of limestone in the construction industry has been increasing due to its potential as aggregate. Some of the benefits of limestone include good strength, low possibility of alkali-silica reaction and the decrease in drying shrinkage in concrete. In the northern part of the Sri Lanka, limestone is used as aggregate in concrete due to its availability. The aim of this research is to observe, evaluate, compare and discuss general characteristics of the limestone aggregate in the northern part of Sri Lanka and check the suitability of the limestone as coarse aggregates in concrete. There are two different kinds of limestone there, namely Red limestone and white limestone. Then experiments are conducted for both kinds of limestone together with the normal coarse aggregates. The properties of density, water absorption, particle size distribution, Flakiness Index, Los Angeles Abrasion Value, Aggregate Impact Value, Aggregate Crushing Value and Soundness of the aggregate are observed. The results are compared with the properties of the coarse aggregates and then suitability of limestone aggregates is evaluated.
item: Conference-Full-text
Experimental approach to investigate concrete-masonry interface
(Department of Civil Engineering, University of Moratuwa, Sri Lanka., 2011-12) Premadasa, PKS; Liyanage, SK; Ariyarathna, HDAR; Induprabha, SAD; Dilrukshi, KGS; Ratnayake, N
A masonry infill wall is a common cell in a concrete framed building. More importantly the bond between concrete and masonry has considerable effect to the performance of infill masonry walls and hence to the frame structure itself. Therefore, understanding of the element interaction between concrete and masonry become very important and has become a topic of considerable researchinterest in the past few decades. Many researchers have tried to represent this interaction numerically. However, reliable numerical analysis can be achieved only with the correct mechanical properties which are obtained experimentally. This paper presents the results of a series of experimental studies carried out to determine the tensile and shear behaviour of concrete masonry interface relevant to the Sri Lankan brick masonry. Tests were carried out in accordance with ASTM standards. In this study, the effect of the mortar designation and the joint thickness on the bond was also investigated. From the results, it can be concluded that properties of the bond is significantly affected by the roughness of the brick used and workmanship apart from the mortar designation and joint thickness. Also it can be recommended to use 10 mm mortar joints in construction, since both shear and tensile strength of the joints get reducedwhen the joints become thicker, irrespective of the mortar designation.
item: Article-Abstract
Field survey and numerical modelling of cracking in masonry walls due to thermal movements of an overlying slab**
Dilrukshi, KGS; Dias, WPS
Concrete slabs exposed to direct sunlight experience temperature related horizontal movements. In addition, temperatures on the top surface will be higher than those on the underside of the slab, causing an upward deflection of the slab during heating. In a typical building, masonry and concrete elements are connected to each other at their respective interfaces. Therefore, significant movements may be generated on the masonry walls due to the movement of the roof slab. These movements can result in overstressing and cracking in masonry. These cracks may not be structurally serious, but may lead to ingress of moisture and in any case are not acceptable especially where good finish is desired. In this study, the behaviour of these cracks was predicted based on surveys of buildings where cracks have formed. Also, typical structural arrangements were mathematically modelled using 3D brick finite element models, with link elements between the masonry and concrete elements in order to model interfaces. The objective of the study was to investigate the stresses developing on the wall due to the movement of the roof slab. Locations and directions where cracking would occur were identified using the principal stresses developed in the finite element model and a failure criterion developed based on the modified Von-Mises theory. Also, using these numerical models, the effect of wall length and structural form of the wall (i.e. load bearing walls and reinforced concrete framed walls) on the formation of these cracks was studied. These results were compared with the information obtained from the survey.
item: Conference-Full-text
Investigation of the effect of using isotropic and anisotropic modelling techniques to study the cracking in masonry walls due to thermal movements of an overlying slab
(2013-12-01) Haadi, MSB; Dilrukshi, KGS
Use of roof slabs in Sri Lankan buildings is getting popular especially in commercial buildings and hotels, and even in some residential buildings. In a tropical country like Sri Lanka, roof slabs are exposed to direct solar radiation over more than eight hours per a day. Concrete slabs exposed to direct sunlight experience thermal movements. These movements can result in over stressing and cracking in underlying masonry walls. Due to the presence of vast range of geometrical and structural configurations, use of physical models to investigate the behaviour of masonry is a costly and a difficult exercise. As a solution, finite element modelling is widely used in investigation of masonry. Masonry is a composite material that exhibits distinct directional properties due to the presence of mortar joints. Therefore, it is important to study the effect of the presence of these joints considering masonry as an anisotropic material rather than an isotropic material in numerical studies. This paper describes a numerical modelling exercise employed to understand the above effect related to the modeling of cracking in masonry walls due to thermal movements of an overlying slab. Further, models were used to study the effect of the aspect ratio, structural form and presence of other geometrical features such as openings and lintels on the above phenomenon. Also, the results were used to propose remedial measures to the problem. It was found that the pattern (type and location) of cracking depends significantly on the structural and geometric features of the wall and anisotropic approach can predict better results when structural and geometric features become complicated.
item: Conference-Full-text
Investigation Of The Properties Of Limestone Concrete
(2014-06-10) Hemadasa, MBC; Dilrukshi, KGS
More than seventy percent of the volume of concrete is occupied by aggregates. Aggregates with undesirable qualities will have an adverse effect on durability and structural performance of concrete. Though gneiss is normally used as coarse aggregates in production of concrete, due to their unavailability in the region, limestone is used as coarse aggregate for production of concrete in Northern Sri Lanka, without appropriate investigations. In this study, impact of limestone aggregates on concrete properties such as slump, initial setting time compressive strength, flexural strength, etc. were investigated under laboratory conditions and the results were compared with the concrete made with normal aggregates. Two types of limestone aggregates were used for this purpose, red limestone which was collected from Walikamam west, Jaffna and white limestone, which was collected from Chavakachcheri area. It was found that water absorption of limestone aggregates is 50% higher than that of the normal aggregates. Also, workability and compaction ability in limestone concrete are significantly lower for a given w/c ratio compared to normal aggregate concrete. However, compressive strength and flexural strength are found to be the same as the normal aggregates. Also, results indicate that red limestone aggregates have better performance than the white limestone aggregates
item: Conference-Full-text
Investigation of the properties of limestone concrete
(Department of Civil Engineering, University of Moratuwa, 2014-03) Hemadasa, MBC; Dilrukshi, KGS; Hettiarachchi, MTP
More than seventy percent of the volume of concrete is occupied by aggregates. AggreSates w^h undesirable qualities will have an adverse effect on durability and structural performance of concrete. Though gneiss is normally used as coarse aggregates in production of concrete, due to their unavailability in the region, limestone is used as coarse aggregate for production of concrete in Northern Sri Lanka, without appropriate investigations. In this study, impact of limestone aggregates on concrete properties such as slump, initial setting time compressive strength, flexural strength, etc. were investigated under laboratory conditions and the results were compared with the concrete made with normal aggregates. Two types of limestone aggregates were used for this purpose, red limestone which was collected from YValikamam west, Jaffna and white limestone, which was collected from Chavakachcheri area. Abstract: It was found that water absorption of limestone aggregates is 50% higher than that of the normal aggregates. Also, workability and compaction ability in limestone concrete are significantly lower for a given w/c ratio compared to normal aggregate concrete. However, compressive strength and flexural strength are found to be the same as the normal aggregates. Also, results indicate that red limestone aggregates have better performance than the white limestone aggregates.
item: Thesis-Abstract
Numerical and physical modelling of cracks in masonry walls due to thermal movements of an overlying slab
Dilrukshi, KGS; Dias, WPS
Concrete slabs exposed to direct sunlight experience temperature related horizontal movements. In addition, temperatures on the top surface will be higher than those on the underside of the slab, causing an upward deflection of the slab during heating. In a typical building, masonry and concrete elements are connected to each other at their common interfaces. Therefore, significant movements may be generated on the masonry walls due to the movement of the roof slab. These movements can result in overstressing and cracking in masonry. These cracks may not be structurally serious, but may lead to ingress of moisture and in any case are not acceptable especially where good finish is desired. In this study, the behaviour of these cracks was studied based on surveys of buildings where such cracks have formed. Also typical structural arrangements were numerically modelled to investigate the stresses developing in walls due to the movement of the overlying slab and consequent cracking. Using these numerical models, the effect of the aspect ratio of the wall, structural form of the wall and presence of other structural features such as openings and lintels on the formation of these cracks was studied. These results were compared with the information obtained from the field survey and also with a few physical models which were constructed to the scale of 1/3 of the prototype. The formation of cracks was observed and the strains generated on walls and the temperature variations of the assemblies were monitored. These observations enabled qualitative validation of the numerical models. Numerical modelling was initially done as a linear elastic un-coupled analysis. A commercially available structural analysis software SAP2000 was used for the study. Locations and directions where cracking would occur were identified using the principal stresses developed in the finite element model and a failure criterion developed based on modified Von-Mises theory. Using detailed numerical modelling (i.e. non-linear structural-thermal coupled analysis), the development of cracks in walls under the time varying thermal load was studied. Modelling was done using a commercially available finite element code ANSYS 11.0. The model was also used to study the effectiveness of various remedial measures for the problem of thermal cracks in concrete framed walls. It was found that concrete framed walls could exhibit horizontal cracking under the beam and inclined cracking (at 45° to the horizontal) near the ends of walls. For load bearing walls the inclined cracking at wall ends had an inclination to the horizontal of around 60°, while vertical cracking near the wall mid length was also a possibility. Linear elastic analysis will give a reasonably good idea of crack locations in solid walls. However non-linear analysis would be required for predicting crack locations in walls with openings. The results of detailed numerical modelling illustrate that the use of a lintel in a concrete framed wall is not an effective solution to the problem of thermal cracking in walls. However, separating the wall from the concrete frame at the wall-beam interface and wall-column interface (for a depth of 1/3 of the wall height from the beam soffit level) seems to be an effective solution
item: Conference-Extended-Abstract
Numerical modelling of cracking of masonry walls due to thermal movements of an overlying slab
(2010) Haadi, MSB; Gunasekera, DN; Rathnasekara, KSK; Dilrukshi, KGS
Concrete slabs exposed to direct sunlight experience temperature related horizontal movements. In addition, temperature of the top surface of the slab reaches higher temperature than the bottom, causing an upward deflection of the slab during heating. In a typical building, masonry and concrete elements restrain each other at their respective interface. Therefore significant movement would be generated on the masonry walls, due to movement of the roof slab. These movements can result in overstressing and cracking in masonry. Therefore in the buildings with roof slabs, cracking of walls which are located immediately under the roof slab has become a considerable problem. In this study stresses indicated on the masonry walls due the thermal movement of the roof slab were investigated using three dimensional finite element models. Location and direction of possible cracks were identified using a failure criterion developed based on principal stresses. Using the finite element models, the effect of the aspects ratio of wall, structural form (i.e. load bearing and reinforced concrete framed walls), and presence of other geometrical features such as opening and lintels on the above phenomena were identified. In addition, the effect of modeling masonry as an anisotropic material rather than as isotropic material was investigated.
item: Article-Abstract
Numerical modelling of cracks in masonry walls due to thermal movements in an overlying slab
Dilrukshi, KGS; Dias, WPS; Rajapakse, RKND
This paper describes a numerical modelling exercise employed to understand the propagation of cracks in masonry walls under a time varying thermal load in an overlying roof slab. A structural thermal coupled non-linear analysis was used to predict locations, directions and propagation of cracks. A commercially available finite element code ANSYS was used to construct the model. It is shown that masonry walls under a concrete slab that is exposed to solar radiation can experience cracking, and that this cracking can be predicted based on the features of the wall i.e. whether the wall is load bearing or framed and the presence of openings and lintels. The results were compared with the information obtained from a survey of buildings having cracks and also with a few physical models. It was found that the pattern (orientation and location) of cracking depends significantly on whether the wall is load bearing or framed by the reinforced concrete elements. Cracking around openings is very likely, irrespective of the structural form of the wall. The use of a continuous lintel will not be able to remedy this cracking, but a limited separation of the wall from the frame at roof level will.
item: Conference-Full-text
Study Of Torsional Buckling Behavior Of Carbon Nanotubes Using Molecular Dynamics Simulations
(2014-06-10) Dodangoda, MT; Dilrukshi, KGS
An accurate study of mechanical behavior of CNTs is vital to understand their response under mechanical loading in their applications. Much experimental and analytical work has been done to quantify the mechanical properties of CNTs over the past two decades. However, limited studies have been reported related to torsional behavior and estimation of shear modulus. The reported values of shear modulus of CNTs in the literature also shows considerable variations revealing the effects of the method used in the predictions. This paper reports the study carried out to investigate the effect of different parameters in estimating shear modulus and torsional buckling behavior of CNTs using molecular dynamic (MD) simulation method. MD simulator called large-scale atomic/molecular massively parallel simulator (LAMMPS) is used in this regards. The effects of potential function (REBO and AIREBO) used to define atomic interaction and ratios of the CNT considered in simulation were studied with respect to Armchair and Zigzag CNTs with different diameters. The results of the studyrevealed that the effect of the CNT aspect ratio for estimating the shear modulus can be eliminated by using the CNTs with aspect ratio above 12. However, potential function use for the simulations has considerable impact on the results.
item: Conference-Full-text
Study of torsional buckling behavior of carbon nanotubes using molecular dynamics simulations
(Department of Civil Engineering, University of Moratuwa, 2014-03) Dodangoda, MT; Dilrukshi, KGS; Hettiarachchi, MTP
An accurate study of mechanical behavior of CNTs is vital to understand their response under mechanical loading in their applications. Much experimental and analytical work has been done to quantify the mechanical properties of CNTs over the past two decades. However, limited studies have been reported related to torsional behavior and estimation of shear modulus. The reported values of shear modulus of CNTs in the literature also shows considerable variations revealing the effects of the method used in the predictions. This paper reports the study carried out to investigate the effect of different parameters in estimating shear modulus and torsional buckling behavior of CNTs using molecular dynamic (MD) simulation method. MD simulator called largescale atomic/molecular massively parallel simulator (LAMMPS) is used in this regards. The effects of potential function (REBO and AIREBO) used to define atomic interaction and ratios of the CNT considered in simulation were studied with respect to Armchair and Zigzag CNTs with different diameters. The results of the studyrevealed that the effect of the CNT aspect ratio for estimating the shear modulus can be eliminated by using the CNTs with aspect ratio above 12. However, potential function use for the simulations has considerable impact on the results.