Browsing by Author "Herath, HMST"

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item: Conference-Abstract
Adoption of precast hollow core panels for external walls of multi-storey buildings
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Subakaran, R; Jayasinghe, MTR; Herath, HMST; Mallikarachchi, C
Precast hollow core wall panels have gained popularity for their efficient use as load-bearing and non-load-bearing wall elements. ICC ACOTEC hollow core wall panels are manufactured locally and intended to be used as internal partition wall panels in multi-storey buildings. Partition walls in general are not load-bearing elements, thus they do not undergo significant deformations. This research study focuses on verifying the usability of such precast panels as external wall panels in multi-story buildings, where their load resistance is investigated under lateral wind loads and vertical deformations due to column shortening effects. In addition, using the shape optimisation technique in-built into ABAQUS/CAE advanced finite element software and parametric optimisation study, a better layout for the precast wall is also proposed and its performance is compared with the current standard layout under similar loading and boundary conditions. The numerical model was validated using experimental test results and the optimised panel has a 16% lower net volume than the original hollow panel. Meanwhile, the optimised panel did not show any reduction in strength properties and does not pose any challenges in manufacturing. Using shape-optimised panel sections, panel assemblies are simulated to investigate the panel assembly response under wind loads. Further, recommendations are given on the maximum number of wall panels that could be installed as a single assembly under different wind load intensities at various heights of multi-story buildings. Considering practical aspects, these recommendations are integrated with proposals on connection mechanisms between panel assemblies. Due to the nature of the scope of this research study, long-term effects such as creep and fatigue were not incorporated, and it is recommended to conduct experimental tests for the proposed panel assemblies before practical usage.
item: Conference-Full-text
A comparative study on the mechanical properties of concrete by substituting cement with sugarcane bagasse ash
(IEEE, 2023-12-09) Sankeeth, S; Kumara, BS; Damruwan, HGH; Herath, HMST; Lewangamage, CS; Koswattage, KR; Abeysooriya, R; Adikariwattage, V; Hemachandra, K
This research study compares the mechanical properties of concrete by substituting Sugarcane Bagasse Ash (SCBA) at various weight ratios for Ordinary Portland Cement (OPC) and Portland Composite Cement (PCC). The study was mainly concerned with determining the consistency, setting time, workability, compressive strength, and split tensile strength of concrete mixes containing different percentages of SCBA. Three replacement scenarios were considered into account: 0% SCBA (control sample), 5% SCBA, and 10% SCBA, which would have replaced both OPC and PCC. Various tests were conducted according to relevant standards to evaluate the performance of the concrete mixes. The results revealed that replacing 10% of OPC with SCBA performed better than replacing PCC and the control samples. Higher compressive strength and split tensile strength were among the improved mechanical characteristics of the concrete mixtures with 10% SCBA. These results show the possibility of using SCBA as a partial cement substitute to enhance the overall performance of concrete, especially when replacing OPC. This research offers important insights into sustainable construction practices by identifying SCBA as a feasible cementitious material with favorable economic and environmental effects. The results may assist researchers and concrete experts in optimizing the use of SCBA in concrete mix designs to achieve desired mechanical properties and enhance sustainability in the construction industry.
item: Conference-Full-text
A Comparative Study to Assess the Sustainability of Bamboo Reinforced Concrete over Conventional Steel Reinforced Concrete
(2022-08-23) Vitharana, TVDVK; Bandaranayake, SS; Jayasinghe, MTR; Herath, HMST; Mallikarachchi, HMYC
Amongst various sustainable building materials, bamboo reinforced concrete has come into concern as a potential substitute for steel-reinforced concrete. This has drawn attention due to some major drawbacks of steel in reinforced concrete including elevated cost, high energy consumption, increased emission of carbon, etc. Bamboo is a rapidly renewable material that has displayed outstanding mechanical properties which are adequate to replace steel in reinforced concrete. In the present context, in addition to its structural performance, it is of vital importance to evaluate the sustainability of bamboo reinforced concrete over conventional reinforced concrete. In this work, the structural capacity of replacing steel with bamboo in different structural elements was analytically determined. Subsequently, a comprehensive work study-based analysis was executed to compare the sustainability of a bamboo reinforced concrete beam element with a conventional steel-reinforced concrete beam element in terms of their embodied carbon and cost. Results of this study justify the possibility of promoting bamboo as a potentially sustainable alternative to steel in reinforced concrete as bamboo reinforced concrete displays drastically reduced sustainability indices for embodied carbon, and cost while maintaining adequate structural capacities.
item: Conference-Abstract
Design optimisation of a steel bridge bracket
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Liyanagunawardhana, SK; Herath, HMST; Mallikarachchi, C
Steel brackets have a renowned potential of being used in bridge constructions as a load-bearing element. Due to the higher consumption of steel in bridge constructions, the emission of Carbon Dioxide (CO2) gas is increased when manufacturing steel components. CO2 is one of the main greenhouse gases prompting the increase in global warming. Moreover, excessive material usage in bracket manufacturing will lead to expensive constructions and increased embodied energy consumption. Another concern is that, though the material usage is to be reduced, the strength, stiffness and stability of the structure should be preserved. Hence, engineers have identified that structural optimisation is the best solution to address this global problem, and they have been practising structural optimisation principles on the structural components recently to achieve sustainability during the service life. In other words, their ultimate target is to apply sustainable concepts to the construction principles. Although many researchers have studied various structural optimisation tools and presented novel designs, applications of those designs in the construction industry are still limited due to the complex geometries of the optimised designs. Nevertheless, the advantages of optimised designs are more powerful than the manufacturing challenges. The recent developments in additive manufacturing extend higher flexibility and efficiency to the fabrication of these structures by overcoming the manufacturing challenges. However. nowadays, these novel and eco-friendly techniques are getting more attention all over the world because of their merits in the ever-evolving field of Civil Engineering. To circumvent the above-mentioned challenges, this research demonstrates a novel approach for producing an optimum and sustainable steel bracket for a pedestrian bridge construction. Among several structural optimisation methods, topology optimisation is used as the tool of choice in this work, which has a proven record of arriving at the highest stiffness to weight ratio. This study uses an existing steel bridge bracket in Castleford Foot Bridge, England as a study case. The bracket is optimised under several volume fractions and ultimately, the optimum design is selected based on both simulation results and practical considerations. According to the results, the optimised model with a 30% volume constraint is selected as the optimum design which leads to the manufacturing of cost-effective and sustainable structure. Considering the manufacturing possibilities, the optimised model from the finite element software is converted into a manufacturable parametric Computer-Aided Design (CAD) model using the Rhinoceros software package for further post-processing and analysis. The modified CAD model is re-analysed using finite element software and its structural performance is verified. It is shown that a considerable amount of material could be saved without sacrificing the strength and stiffness requirement of the bridge bracket. Similarly, further optimisation could be performed in terms of the shape of the geometry which is identified as a potential future work that stems from this study.
item: Conference-Abstract
Design-informed optimization of 2D skeletal structures using convolutional neural networks
(Department of Civil Engineering, University of Moratuwa, 2024) Jayaweera, JANN; Herath, HMST; Pasindu, HR; Damruwan, H; Weerasinghe, P; Fernando, L; Rajapakse, C
Structural optimization aims to find the most efficient material distribution within a design domain by minimizing material usage, self-weight, and strain energy, while maximizing strength. Optimization approaches often use compliance as the objective function and volume as a constraint, which can result in designs that may not fully meet the practical requirements of civil and structural engineering due to potential inadequacies in structural integrity. To address this issue, design-informed optimization integrates structural optimization with design codes such as EN 1993-1-1, ensuring that optimized designs comply with structural integrity requirements and real-world applicability. Existing design-informed optimization algorithms typically rely on iterative schemes, which are computationally intensive and require specialized expertise. To overcome these challenges, this study introduces a novel computer vision-based framework that predicts design-informed optimized frames and accurately identifies member sizes using image processing techniques coupled with probabilistic section classifiers. This framework utilizes input parameters such as span, height, and load to predict the topology, size, and layout of optimized frames that satisfy structural adequacy criteria. It is particularly beneficial for assembly-based manufacturing, where precise member section prediction is crucial for construction efficiency and material optimization. The framework consists of three stages. In Stage 1, the CNN64 model generates a low-resolution layout of the optimized frame using input parameters such as span, height of the design domain, and load. In Stage 2, the CNN512 model refines this layout to produce a high-resolution image of the optimized frame, where section sizes are assigned. These models are trained on varying parameters including fixity, design domain, and load conditions. Stage 3 involves a member section identification algorithm that classifies the optimal structural section sizes through image processing techniques. The efficacy of the framework was validated using simply supported and cantilever beam datasets, achieving pixel accuracies of 94.6% and 91.8%, respectively. Post-calibration, the section identification algorithm, which accounts for unavoidable errors such as generator residuals and section identification errors, achieved near 100% accuracy, demonstrating the robustness of the probabilistic section classifier. Compared to alternative architectures, the CNN64+CNN512 framework consistently outperformed others in metrics such as pixel accuracy, true positive rate, and binary cross-entropy in both datasets. It also demonstrated a significant reduction in computational loss, further confirming its computational efficiency. Overall, the analysis reveals that the CNN64+CNN512 model not only provides superior performance in prediction accuracy but also strikes an effective balance between computational efficiency and model complexity.
item: Conference-Abstract
Design-informed structural optimisation
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Amarasinghe, IT; Herath, HMST; Mallikarachchi, HMYC; Mallikarachchi, C
Structural optimisation has become an important tool in the field of Civil Engineering, but there is limited research done on structural optimisation of specific structures and components, especially for large construction machinery. By optimising construction machinery components, it is possible to reduce the material usage and decrease the cost of the machine, without compromising its strength. This research study looks at a case study of optimising a wheel loader arm. Initially, the critical load calculation and the static force analysis of the wheel loader arm were conducted and the forces and reactions acting on the arm were obtained. Then a finite element analysis was conducted by assigning the relevant loads and boundary conditions and the results obtained deemed that the stresses and displacements of the arm were within the acceptable limits. The Solid Isotropic Microstructure with Penalisation (SIMP) for intermediate densities method is used for the topology optimisation process considering the minimum compliance as the objective function and the volume fraction as the constraint. Using the Abaqus FEA software, topology optimisation models were obtained for different volume fractions and the most optimum geometry comparing maximum von Mises stress, displacement, and mass with the original design. After the completion of the topology optimisation process, Computer-Aided Design models are generated by exporting the mesh into SOLIDWORKS. Subsequently, shape optimisation is conducted considering the different manufacturing constraints. The final optimised model has a 20.3% reduction of mass compared to the original structure, while stresses, displacement and strains are kept within the allowable limits in accordance with codes of practice. This case study demonstrates on how structural optimisation can be integrated into the designs of different structures and components. By using a similar method, it is possible to optimise different components of the wheel loader arm and other construction machinery components. These optimisations will reduce the weight and material usage of these components, which can help reduce the overall cost of the machines significantly.
item: Conference-Full-text
Distributed intelligence as an information retrieval system
(2013) Jayathilake, DSP; Herath, HMST; Wimalasooriya, RDDP; Karunarathne, SDJ; Weerawardhane, S
The traditional knowledge based approach is not a feasible choice to be utilized in information retrieval in domains such as Geographic Information Systems (GIS), because accurate information of geographic data is spatially distributed and vast in volume. The challenge is to improve the process of information retrieval, which can be applied to varying contexts such as GIS, going beyond the limits imposed by the knowledge base centric approaches. Social networks possess a vast amount of unstructured knowledge in its user base, which can be used in drawing interesting patterns, if analyzed in a systematic approach. 1n this paper, we emphasize on an approach for information search and retrieval, by combining the social network of human intelligence and knowledge bases of information. Users of the system can present natural language queries, and questions can be directed to relevant experts within the social network. Distributed information retrieval and information fusion is applied to optimize the process of single answer generation. The feasibility of our proposed architecture is investigated by implementing a QA(Question Answering) system on a social network as a proof of concept. The Question Answering System is based on geographic queries which will be directed to relevant users within the network to gather answers. Varying methods of information fusion and Natural Language Processing have been researched and discussed to discover the suitable approaches for answer generation. With the wide acceptance of the social networking paradigm and sharing of information, this approach can - be extended to other domains as well.
item: Conference-Full-text
Distributed intelligence as anlnformation retrievalsystem
(The Engineering Research Unit, University of Moratuwa, 2013-02) Jayathilake, DSP; Herath, HMST; Wimalasooriya, RDDP; Karunarathne, SDJ; Weerawardhane, S; Rodrigo, R
such as Geographic Information Systems (CIS), because accurate information of geographic data a spat,ally distributed and vast in volume. The challenge is to improve the process of information retrieval, which can be applied to varying contexts such as GIS, going beyond the limits imposed by the knowledge base centric approaches. Social networks possess a vast amount of unstructured knowledge in its user base, which can be use in a awing interesting patterns, if analyzed in a systematic approach. In this paper, we emphasize on an approach for information search and retrieval, bv combining the social network of human intelligence and knowledge bases of information. Users of the system can present natural language queries, and questions be directed to relevant experts within the social network. Distributed information retrieval and information fusion is applied to optimize the process oj single answer generation. The feasibility of our proposed architecture is investigated by implementing a QA(Question Answering) system on a social network as a proof of concept. The Question Answering System is based on geogi aphic queries which will be directed to relevant users within the network to gather answers. Varying methods of information fusion and Natural Language Processing have been researched and discussed to discover the suitable approaches for generation. With the wide acceptance of the social networking paradigm and sharing of information, this approach be extended to other domains as well.
item: Conference-Abstract
Effect of preloading and endplate imperfections in bolted connections: Moment-rotation characteristics through explainable artificial intelligence
(Department of Civil Engineering, University of Moratuwa, 2024) Dharmawansha, DAST; Herath, HMST; Pasindu, HR; Damruwan, H; Weerasinghe, P; Fernando, L; Rajapakse, C
Stainless-steel is a popular engineering material due to its durability, high resistance to corrosion, aesthetic appeal, ease of construction and maintenance, recyclability, and ductility. It is often used in a wide range of structural engineering applications such as frames, buildings and bridges. Across these diverse applications, steel connections are a crucial component as they ensure the unified performance of the structure. This study investigated the effect of bolt preloading, endplate imperfections, and geometric parameters on the connection moment rotation response of extended endplate bolted connections. This study employed a validated numerical model against experimental results from the structural testing laboratory of the University of Moratuwa, further validated against experimental results available in the literature. The validated numerical model was then used to investigate the impact of varying levels of bolt preloading and imperfections on rotational stiffness. The results showed that rotational stiffness increases by 134% with ultimate preloading. Residual deformation from welding causes initial imperfections in bolted endplate connections, with V-shape, C-shape, and W-shape imperfections identified in the literature. This study examines the impact of C-shape and V-shape imperfections on rotational stiffness. The results indicate that V-shape imperfections have minimal influence if the level of imperfection is limited to the criterion of (endplate depth)/300, while C-shape imperfections significantly affect rotational stiffness, even within acceptable limits. A novel explainable machine learning approach was utilized to investigate the influence of geometric parameters on the moment-rotation response of connections. A comprehensive numerical modelling approach (validated using related work) was used to generate data for various input features, such as endplate thickness, bolt diameter, overall section width, overall depth, web thickness, flange thickness, vertical bolt spacing, and horizontal bolt spacing. An artificial neural network (ANN), extreme gradient boosting (XGB), random forest (RF), and k-nearest neighbours (KNN) were employed alongside Shapley additive explanations (SHAP) to interpret the trained models. Analysis shows that endplate thickness strongly governs the moment-rotation behaviour of the bolted endplate connections. Moreover, SHAP explanations align with the generally accepted behaviour of steel extended endplate bolted connections according to EN 1993-1-8.
item: Conference-Abstract
The effectiveness of different structural forms for mediumrise apartment buildings
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Wijekoon, KMSR; Jayasinghe, MTR; Herath, HMST; Mallikarachchi, C
To fulfil the housing requirements of the ever-growing population with the scarcity of valuable land, the best solution is to come up with high-rise or medium-rise apartment buildings. The effect of lateral forces (wind and seismic) on those structures is significant to be studied because they govern the structural design. The selected structural system should be optimal in the aspects of associated cost, structural efficiency and maximum usable floor area. Therefore, once the structural form of the lateral load-resisting system of a building is defined, the optimal element sizes should be derived while satisfying all serviceability lateral stiffness and practical sizing requirements. This comparative study evaluates the effectiveness of six different structural forms of 20-story RC (Reinforced Concrete) structures under the effect of wind and seismic loadings including a moment-resisting frame as the base model, four wall frame structures, and a frame-tube structure. Maximum top story displacement, inter-story drift ratios, member forces and moments utilisation, associated cost, and human perception level for windinduced lateral acceleration were considered as the parameters to carry out the comparison. The main objectives of this study are to assess and compare the wind-induced lateral behaviours and behaviours against earthquake loadings of rigid-frame,wall-frame, and frame-tube medium-rise structures and to determine the most effective structural system for medium-rise apartment buildings based on established parameters. The methodology which was followed, 1. Establish the parameters/ design criteria that need to be satisfied. 2. Study the wind load and seismic load effect on typical medium-rise structures. 3. Select six different structural forms including a moment-resisting frame as the base model, four wall frame structures, and a frame-tube structure for the case study. 4. Develop FEM models and do the comparison based on established parameters. 5. Optimisation and cost analysis. The major findings can be identified as followings. The lateral stiffness of bare frame structures can be increased considerably by increasing the depth of beams rather than increasing the size of columns. As well as in bare frame structures, the columns which are in line with the shear walls along the windward direction are subjected to high axial forces when the structure is subjected to wind effects. Also, with the addition of a sufficient amount of shear walls at lucrative positions, the required axial forces and bending moment capacities in both columns and beams can be reduced drastically. Even though the frame-tube structure shows better performances in lateral stiffness, the columns and beams are subjected to high axial forces and bending moments because the overall lateral stiffness is provided by columns and beamcolumn rigid joints.
item: Conference-Abstract
Euro-code compliant adaptive layout optimisation of twodimensional steel trusses
(Department of Civil Engineering, 2023-09-27) Denuwanthi, GMD; Herath, HMST; Mallikarachchi, C; Hettiarachchi, P; Herath, S; Fernando, L
Truss optimisation plays a vital role in the design and analysis of various engineering structures, ranging from bridges to aerospace applications. Over the years, researchers have proposed numerous numerical methods to achieve optimal truss configurations, considering factors such as weight minimisation, stiffness maximisation, and cost efficiency. However, despite the significant progress in the field, the absence of universally accepted standards for determining the optimum truss solution remains a challenge. This paper presents a novel methodology for optimising steel trusses using Euro-code standards as a reference framework specifically focusing on pin-jointed truss systems. The proposed methodology aims to combine numerical optimisation algorithms with the relevant design provisions outlined in Euro-code, ensuring compliance with structural integrity and safety criteria. The process involves a Python script for convex optimisation and the numerical optimisation algorithm employs an adaptive member-adding solution scheme which provides a computationally efficient means of generating near-optimum trusses for the problems. The objective function of the optimisation algorithm is to minimise the total structural volume of the truss and the process satisfies the force equilibrium at each node of the truss as well as limiting stress criteria as defined in the Euro-code. The research provides a thorough overview of the relevant Eurocode provisions that pertain to steel trusses. Initially, the optimisation studies employ a method to handle layout and geometry optimisation simultaneously to determine the optimal layout of the truss structures, taking into account practical and manufacturing constraints. Then, the methodology progresses to size optimisation which involves optimising the member cross-sections to enhance their stiffness and overall structural performance. Finally, the use of commercially available steel sections for the construction of optimised trusses is assessed to avoid financial challenges due to the high costs associated with additive manufacturing technologies within the context of Sri Lanka. To ensure the scientific robustness and practical applicability of the proposed methodology, rigorous examinations are conducted using practical examples.
item: Conference-Abstract
Feasibility of using 3D point cloud technologies in Sri Lankan Civil Engineering Industry
(2021-03) Subakaran, R; Herath, HMST
With the rapid advancement of technologies such as Laser Scanning and Point Cloud Data processing, the influence of these technologies in Civil Engineering Projects are inevitable. These technologies are used in various industries, including Civil Engineering, in tasks namely, 3D model preparation, Construction progress monitoring, Quality control, Virtual walk-throughs, etc. Many countries have already made the most out of these technologies whereas Sri Lanka as a developing country, seems to have lagged in implementing such tools, especially in the construction sector. Further applications of these digital technologies extend to preserve ancient monuments from disasters, create digital copies of structures, update timely variations of structures and predict the life-cycle of buildings. For instance, during renovations, the availability of any BIM models or any related drawings may be limited and renovations with destructions must be avoided; these limitations pave the way to the adaptation of non-destructive laser scanning and other related technologies. Moreover, there are significant advancements in efficient 3D point cloud data acquisition and accurate processing techniques around the globe, making it a reliable and effective solution for various civil engineering challenges. This study reviews the available technologies and their applications in the civil engineering domain and the feasibility of implementing these technologies in the Sri Lankan civil engineering industry.
item: Conference-Abstract
Homogenisation of ultra-thin woven fibre composite structures under high curvatures
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Weerasinghe, WUD; Herath, HMST; Mallikarachchi, HMYC; Mallikarachchi, C
Utilising fibre-based textile structure as the composite reinforcement results in making composite more tailorable and effective for applications where various types of loads are anticipated to be supported by the structure. Owing to that, growing demand for ultra-thin woven composites can be identified in weight-sensitive applications, especially in space engineering applications such as self-deployable structures. Both complex geometry and nonlinear behaviour of constituents of these composites make it more difficult to forecast the overall mechanical behaviour. Multiscale modeling approach can be identified as a popular strategy to overcome this issue where several models at various scales are utilised simultaneously to describe the system. For woven fibre composites, considered scales are micromechanical, meso-mechanical and macro-mechanical scales. Physical experiments revealed in the literature that these ultra-thin structures have experienced a significant drop in bending stiffness when subjected to extreme curvatures. This is a numerical study in meso-mechanical scale on the homogenised response of two-ply plain woven carbon fibre composites considering the inter-connection behaviour between contact surfaces within the ply and in between two plies. With dry fiber geometry and resin pocket introduced geometry, two distinct models were used in the analysis. To estimate the behaviour under higher curvatures, the study has been advanced further into the non-linear regime. Due to the severe curvatures that these ultra-thin woven composites are subjected to, slippage behaviour between yarns and between plies may take place, which would result in a drop in bending stiffness at those higher curvatures. Surface based cohesive constraints were defined to simulate the slipping behaviour using linear elastic traction-separation stiffness values. The dry fibre model captured the bending stiffness and Poisson’s ratio with good accuracy while the resin model captured the shear response better than the dry fibre model. Axial stiffness predictions remained almost the same for both cases. It is demonstrated that the proposed models can accurately predict the nonlinear flexural behaviour based on the experimental findings. Both models have shown their ability to accurately capture the bending stiffness reduction up to a curvature value of 0.14mm-1 and the stiffness reduction was overpredicted beyond that point. Reason behind the overprediction can be the allowance of relative moment between plies which can lead to the loss of compatibility between two plies and hence, each lamina contributes separately to the second moment of area instead of full thickness. Further development of resin model to capture both in-plane and out of plane properties in a single model can be recommended for future studies and also the effect of relative movement of plies to the second moment of area of laminate is recommended for further studies.
item: Conference-Abstract
Modelling structural steel elements under various corrosive environments
(Department of Civil Engineering, 2023-09-27) Rathnayaka, RMRPM; Herath, HMST; Mallikarachchi, C; Hettiarachchi, P; Herath, S; Fernando, L
Atmospheric corrosion can affect age-related structural degradation, leading to changes in the structural integrity of metals. European codes provide only general provisions to prevent the effects of corrosion during the lifetime of steel structures. Currently, there is only a few studies have been done considering realistic varying corrosion thickness loss models and almost all of them focus only on extreme corrosion conditions like in industrial, coastal, and urban areas. In this paper, the behaviour of axially loaded corroded steel sections under exposure to different atmospheric corrosivity conditions are investigated. First, five different critical corrosion loss models are proposed to represent actual corrosion decay scenarios including the control specimen (CM0), one uniform thickness loss model (CM1) in which corrosion occurs in the entire cross-section, and three varying thickness loss models (CM2, CM3 and CM4) in which corrosion occurs only in some parts of the cross-section. The corrosion rate model is selected based on the ISO 9224:2012 to estimate the amount of corrosion thickness loss of steel with the time of exposure. ISO 9223:2012 is used to classify atmospheric corrosivity into six different categories namely, Very Low Corrosivity (C1), Low Corrosivity (C2), Medium Corrosivity (C3), High Corrosivity (C4), Very High Corrosivity (C5), and Extreme Corrosivity (CX) considering both high and low corrosivity conditions. Next, with the help of Eurocode 3 guidelines, an analytical framework is established to calculate both the tensile and compression capacities of corroded steel I-sections subjected to axial loads. Prediction of residual crosssection capacities with the changing cross-section is achieved through a programme designed to perform repetitive calculations using MATLAB environment. Results are validated using numerical modelling results after performing both linear and non-linear analyses for different cross-sections by ABAQUS Explicit Solver. The obtained results not only help in designing steel members exposed to corrosion but also in explaining possible reasons for the variations of cross-section capacity in different scenarios. Both tensile and compression capacities get reduced with the corroded age and the residual capacity gets reduced when the severeness of the corrosivity increases from C1 to CX. It is observed that sudden changes may take place in compression capacity curves because of the changes in the cross-section class from class 3 to class 4. This change can cause a member to fail by local buckling before overall buckling or material crushing. The probability of being subjected to local buckling failures is higher in higher corrosive environments like C5 and CX. Results show that the reduction factor in compression capacity is less than 5% which is a very minimal value even after the exposure of 50 years for corrosivity categories from C1 to C4. It suggests that failures are unlikely to happen when exposed to those four corrosive environments. For corrosivity categories C5 and CX, the reduction factor is approximately 10% and 35%, respectively. Therefore, unexpected structural failures can occur during the lifetime of structures, in those two environments. Since the CM1 corrosion loss model has the highest area reduction due to corrosion, it has the highest capacity reduction factor of 0.35 while the other three models (CM2, CM3, and CM4) have a factor around 0.1-0.2. This work can be extended to investigate the behaviour of flexural members subjected to corrosion losses in various corrosive environments.
item: Conference-Abstract
Modified ply thickness for classical lamination theory for thin woven fibre composites
Herath, HMST; Mallikarachchi, HMYC
This paper considers the applicability of classical lamination theory for woven composites for the analysis of bending behaviour of such composites. Although the Classical lamination theory is directly used for the analysis of uni-directional laminates with a good accuracy, it cannot be directly used for the analysis of bending behaviour of woven composites, because it is found that it gives a significant error margin. Therefore this paper has looked into the possible causes for that error margin and significance of the contribution from each cause to the overall error margin. This papers has identified that the sensitivity of the thickness of a tow has a significant contribution to the error margin and therefore a suitable modification factor has been introduced to reduce the error margin caused by the thickness variation. A representative unit cell model was developed to predict the stiffness, failure of fibre composites and verification of the thickness modification to Classical lamination theory.
item: Conference-Abstract
Multiscale modeling of lattice structures under large deformations
(Department of Civil Engineering, 2023-09-27) Ahangamage, PN; Herath, HMST; Mallikarachchi, C; Hettiarachchi, P; Herath, S; Fernando, L
The rapid advancement of additive manufacturing (AM) enables the fabrication of strong, lightweight structures with a topology that is unreachable using conventional manufacturing processes, such as complex lattice structures. Among these lattice structures, soft lattice structures can undergo large elastic deformations, absorb energy and dampen vibrations in a reversible manner, exploit mechanical instabilities and buckling, exhibit auxetic behaviour, possess negative thermal expansion, and have shape-memory and shape-morphing capabilities. These unique characteristics of soft lattices open up new pathways to a wide range of multifunctional applications, including soft robotics, biomedical devices, energy harvesting, and storage. Hence, the modelling of soft lattice structures has become very important thing. This research study introduces a computational modelling framework for characterising the effective nonlinear micromechanical behaviour of soft lattice structures under uniaxial loading conditions with large deformations. It also explores the impact and necessity of joint stiffening in modelling soft lattices. Furthermore, it investigates the effects of parameter variations on the overall micromechanical behaviour of unit cells. Under uniaxial loading, certain soft lattice structures present buckling-dominated behaviour, while others present bending-dominated characteristics. In developing and validating the computational modelling framework, Body Centred Cubic (BCC) structures were used to represent buckling behaviour, and Body Centred (BC) structures were used to represent bending behaviour. Numerical simulations were performed using Abaqus FEA software. For micromechanical analysis, Periodic boundary conditions were applied to simulate unit cell behaviour, facilitating the extraction of effective homogenised responses. To achieve the required joint stiffness in soft lattices, it is necessary to increase the joint thickness by 100% of the strut diameter for a length equal to the diameter. During uniaxial testing, lattice structures dominated by bending and stretching can be modelled using the ABAQUS/Standard Static General solver, avoiding the introduction of buckling mode shapes. Conversely, lattice structures exhibiting buckling behaviour can be modelled employing the ABAQUS/Standard Dynamic Implicit solver, incorporating proper scaling factors to simulate buckling mode shapes within ideal lattice structures. The developed effective stress-strain responses of unit cells under uniaxial loading can be used to develop a material model for soft lattice structures. Curve fitting techniques and artificial neural networks are recommended methods for material model development in further studies.
item: Conference-Full-text
Nothing is better than something – Perspective of Structural Optimization in Civil Engineering Applications
(2022-08-23) Lowhikan, S; Herath, HMST; Mallikarachchi, HMYC
Structural optimization of solids aims to find the optimal designs of structures by minimizing a constrained objective function such as the material compliance within a given problem domain. This constrained optimization problem is subjected to a set of displacement and load boundary conditions which in turn will be minimized with respect to a structural parameter. Although various structural optimization techniques have a sound mathematical basis, the practical constructability of optimal designs poses a great challenge in the manufacturing stage. The recent development in additive manufacturing partially side-steps this problem predominantly in the domain of Mechanical Engineering. However, in Civil Engineering structures, there is a great possibility of utilizing these optimization tools, especially in precast constructions. Currently, there is only a limited number of unified frameworks which output ready to manufacture parametric Computer-Aided Design (CAD) of the optimal designs. From a generative design perspective, it is essential to have a single platform that outputs a structurally optimized CAD model because CAD models are an integral part of most industrial product development and manufacturing stages. This study focuses on developing a novel unified workflow handling both topology and size optimization in a single parametric platform (Rhino-Grasshopper) which outputs a readyto-manufacture CAD model with the assessment of their structural integrity. In the proposed method, the first topology optimized pixel model is generated for any two-dimensional problem and converted into a one-pixelwide chain model using skeletonization. From the obtained skeleton, a spatial frame structure is extracted, and its members are sized optimally. Finally, the CAD model is generated using Constructive Solid Geometry (CSG) trees and its structural performance is assessed. In addition, industry-standard structural sections can be assigned to the CAD model to be analyzed and designed in accordance with standard codes of practice.
item: Conference-Abstract
A novel optimization strategy for form-finding and structural stability enhancement of dome-type grid-shell structures
(Department of Civil Engineering, University of Moratuwa, 2024) Abeyrathna, HMAM; Herath, HMST; Pasindu, HR; Damruwan, H; Weerasinghe, P; Fernando, L; Rajapakse, C
Domes are highly efficient structures designed to span long distances while effectively resisting gravity loads. Traditional domes can be categorized into two types: continuous shells, which are typically constructed from monolithic concrete or masonry, and grid-shells, which utilize lattice members to create depth throughout the shell thickness. Although grid-shells have gained popularity in recent years, the integration of topology optimization and size optimization for the form-finding of these structures remains relatively unexplored. This paper presents a novel framework for optimizing deep grid-shell structures through topology and size optimization techniques. The framework is structured as a multi-phase process. Initially, a deep grid-shell structure and the associated load type are defined. Subsequently, an equivalent continuous shell structure is established and subjected to an optimization process aimed at minimizing strain energy to determine the optimal grid arrangement. This arrangement is then utilized for size optimization to identify the optimal member sizes. Finally, a linear elastic analysis is conducted to compare the structural performance of the initial grid-shell, the topology-optimized continuous shell, and the grid-shell inspired by structural optimization. Two case studies demonstrate the framework's capability to generate innovative and practical grid-shell structures. In test case 01, a ring load of 1 N was applied at the apex of a deep dome with a radius of 12 m, resulting in a corresponding structural optimization-inspired grid-shell. The buckling capacity increased from 3.5 MN to 31.5 MN, while maximum stress decreased from 4.2 Pa to 3.0 Pa, and maximum displacement was reduced from 31.5 nm to 25.3 nm when compared to the initial defined grid-shell. In test case 02, a total point load of 1 N was applied to the same deep dome, yielding another structural optimization-inspired grid-shell. The buckling capacity improved from 8.5 MN to 10.1 MN, maximum stress decreased from 0.9 Pa to 0.2 Pa, and maximum displacement was reduced from 10.1 nm to 2.5 nm compared to the initial defined grid-shell. The results indicate significant enhancements in material efficiency and structural performance, with optimized designs achieving over a hundred percent increase in buckling capacities and reductions in stresses and displacements exceeding seventy percent. Future work will investigate the complexities of topology optimization for shallow versus deep shells, assess the impact of more realistic load applications on structural stability, and explore the flexural capacities of grid-shells with topology-optimized continuous arrangements. Additionally, potential challenges related to node connections due to wider members resulting from optimization will require further investigation to refine the framework for broader applications.
item: Conference-Abstract
Parametric modelling and analysis of tensegrity structures
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Samarawickrama, SKSR; Herath, HMST; Mallikarachchi, C
Tensegrity structures are based on a set of discontinuous compressible elements within a network of continuous tension elements, with isolated compressed elements (struts or bars) and prestressed tension elements (tendons or cables) that form a stable network. They are dominated by tensile elements, while more material-intensive compression elements are minimised. Tensegrity structures fail mainly due to low material efficiency, member instability, and excessive deflections when compared to rigid structures made with slender elements. The spatial geometry, axial stiffness, member layout, and connectivity of tensegrity structures directly affect the type of structural failure, including strength, instability, and stiffness. This study presents a systematic parametric study on overall axial stiffness variation of the 3-bar tensegrity prism to check the effect of the level of prestressing and other geometric parameters such as the height of the tensegrity cell, type of the tensegrity cell (number of compression members), radius of the tensegrity cell, area of the cables & struts, twisted angle of the top and bottom cable tringles, and the point load acting on nodes. The tensegrity unit studied here is the T3- prism. It is also termed 3-bar tensegrity. The 3-bar tensegrity has nine cables and three struts in which struts are isolated from each other. The cables are assumed to have solid circular cross-sections whereas struts are assumed to be circular hollow to achieve an optimum structure. All members of tensegrity structures are either loaded in axial compression or tension. This means the structure will only fail due to cable yield or buckling of struts. Since the compression members are not transmitting loads over a longer distance, they are not subject to higher buckling loads. The prestressed cables are mostly used for these structures to have better stability to resist higher deflections. In this study, a 3- bar tensegrity cell was analysed using parametric modelling by applying three-point loads in the z-direction to the cell's top nodes. In order to determine the minimum mass necessary under yielding constraints, the static analysis optimises the tensile forces in the cables and the compressive forces in the struts in the presence of certain external forces. In order to acquire the parametric results of the 3-bar tensegrity cell, the Karamba3D structural analysis tool was utilised. It is fully embedded within the Grasshopper parametric design environment, a plug-in for the Rhinoceros3D computer-aided design program. The tensegrity cell's stability improves with height, which also causes an increase in mass and displacements. When the radius, type, and point loads acting on the tensegrity cell increase, the tensegrity cell tends to become more unstable, leading to cell instability because of poor stress distribution among the members. The tensegrity cell becomes more stable while simultaneously increasing its mass by increasing its compression area, tension area, and twisted angle. As a result, while designing the optimised design, mass and stability should both be taken into consideration. Most of the tensegrity structures are constructed by combining diverse types of general tensegrity configurations. After modelling and finalising the solutions for tensegrity configurations, an optimum tensegrity geometry for any application can be defined by combining and scaling these basic tensegrity configurations.
item: Conference-Full-text
Point Cloud-Based Analysis and Validation of As-Design versus As-Built Drawings
(2022-08-23) Kohulan, S; Herath, HMST; Mallikarachchi, Chinthaka
Design to build variations are common in the construction field which can result in demolition or reworks and a waste of resources. It is important to detect these variations during their early stages to minimize the consequences. Total stations, leveling equipment and measuring tapes are the conventional tools used in detecting these variations which require huge manual work and time. Usual construction activities do not offer enough time for these sorts of checks which result in a search for methods that can be automated, and which can be operated with minimum human interventions. Point cloudbased analysis is one of such methods which can be efficiently used for such purposes. The data collection and analysis can be fully or partially automated and the time required for the entire activity will be a fraction of the time spent in conventional methods. Several commercial and open-source software offers a platform to work with point clouds, but it is hard to modify the functionalities of that software as per our needs. This research focuses on using MATLAB to process synthetic point cloud data with a user-friendly GUI to achieve the research aim.