Master of Engineering in Structural Engineering Design

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item: Thesis-Full-text
Cost comparison between conventional and flat slab structures
Hewavitharana, N; Baskaran, K
In present era,conventional Reinforced Concrete(RC) frame buildings are commonly used for the construction. The use of flat slab building provides many advantages over conventional RC frame building in terms of architectural flexibility,use of space,easier form work and shorter construction time. In the present work conventional and flat slab four story buildings are considered for cost comparison. In this research flat slab building andnormal symmetric RCframe buildings of different spans have been studied. The cost of construction for these buildings has also been compared. To find out the cost of reinforcement, formwork, concrete on structural elements slab,beam,columns are considered.For modeling and analysis of conventional and flat slabstructures,SAP 2000 software is used.The dead loads, live loads are considered as per British Standard. The investigation shows that weight of flat slab structure is less compared to conventional slab structure. The cost of flat slab structure is less by around 12%-16% as compared to conventional slab. This study concludes that flat slab structures are the best suited for high rise buildings as compared to conventional slab structures,in terms of costof material.
item: Thesis-Full-text
Early age cracks in concrete walls
Hettiarachchi, DS; Dias, P
During the development of construction industry, people looked forward on building their houses by Construction of a concrete structure requires a large volume of concrete. Due to the small surface area-to-volume ratio, concrete structures are often subjected to high potential of thermal cracking, caused by the heat generation from cement hydration. To reduce the thermal cracking and ensure structural integrity, a good understanding about the crack patterns in concrete elements is required. These kinds of cracks mostly occur during the early age state of concrete. Since Sri Lanka is very near to the equator, the probability of early age crack occurring is even higher. The purpose of this research is to explore the potential early age crack patterns in vertical concrete walls. Main reason for the early age cracking in vertical walls are shrinkage and thermal contraction. This research focuses on the understanding of early age thermal cracking in concrete and developing a simple method to model this phenomenal computationally. Series of boundary conditions were modelled to obtain stress distributions using walls 3m high and 4m & 8m long. Boundary conditions were imposed according to guidelines in BS8007 and wall thickness maintained as 300mm during the analysis. All the analysis was carried out using FEM commercial software Sap 2000 (V19.1). Two approaches were followed initially to identify the best method to represent the restraint conditions as per BS8007. End restraints reduced by using roller supports up to a 2.4m distance from the free edge of the wall with gradually increasing applied horizontal forces proved to be the better technique than that of using reduced E-values. The case studies yielded the following general findings that agree with the literature and field observations; (i) 4m walls can have possible vertical and horizontal cracks. (ii) 8m walls can have possible cracks approximately 2.4m away from the free edges with an inclination of approximately 45º-60º. (iii) 8m walls get the highest stress close to 2.4m from the free edges whereas the 4m walls get the highest stress at the centre. (iv) In 8m walls higher stresses are distributed over a central length whereas in 4m walls the higher stress is concentrated at the centre. (v) 4m wall with top movement can cause possible inclined cracks. (vi) 8m wall with top movement can lead to two possible dominant cracks and two minor cracks. This validation was done qualitatively using the literature and on-site observations.
item: Thesis-Full-text
Investigation of structural defects in government hospital buildings in Sri Lanka
Dilrukshi, ALA; Baskaran, K
Sri Lanka has a free of charge health care system heavily subsidized by the government. The national health system of Sri Lanka is guided by the concept ofthe welfare state. The major armed conflict, which started in 1983 came to an end in May 2009 affecting almost all the sectors in the whole country. At present, Sri Lanka aspires to become a higher middle income country. It faces the challenge of becoming a high performer in all sectors affected. Social health protection is hailed to be placed high on the national agenda. Within this context safety of built environment ofthe government hospital sector too is one ofthe most important matter and the upgrading ofaesthetic aspect ofthe built environment is also a long await need. A government hospital complex is a main component ofmajor cities all over the country. But the common perception of government hospitals is attributed to the unpleasant experience due to the poor condition of built environment rather than the valuable and highly committed service being provided free of charge to the society. This particular study was conducted to investigate structural defects in Government Hospital Buildings (GHBs). Government Hospitals in Western province were selected for visual observation and photographic survey based on convenience and by judgement ofthe fact that over utilization of hospitals in Western province. Also, it was highly important being aware ofthe local and international picture referring to past studies regarding the same area ofstudy. As the chiefstructural material ofmost ofthe GHBs is Reinforced Concrete (RC), attention was drawn to refer to cracking inherent to RC as well. Observations and information gathered were carefully reviewed. Direct and indirect causes of defects could be identified based on the historical data and the observations made. Further the attention was drawn on the current practice of Designing ofHospital Buildings in Sri Lanka and an attempt was made to find whether structural and performance issues identified and the maintainability aspect are addressed at the initial design stage. It was revealed that there is neither detailed registry ofGHBs nor detailed building audit ofdefects being earned out. The main reason for immerging poor quality building either by new construction or renovation work is the lack ofsupervision ofthe work by competent personnel. The Attention on setting up a well-structured Building Management Division which is entrusted clearly with the entire responsibility regarding the GHBs is identified as a necessity in upgrading the condition ofGHBs. A special attention on performance and maintainability aspect ofGHBs at the initial design stage has hardly been paid rather than adopting the common practice of designing of all' types of buildings. Despite the constraints in vertically expanding, the government hospital buildings observed are at an acceptable structural condition thus not requiring complete demolition.
item: Thesis-Full-text
Study on behavior of concrete fins against blast pressure
Prasad, RMB; Baskaran, K
Designing structures against blast loading is becoming more and more important as the number of terrorists attacks are increasing day by day. It is necessary to protect the structures against a credible blast load to ensure the safety of the occupants. In this context, blast resisting facades are incorporated in buildings to avoid the blast pressure waves entering into the building as the highest damage is done by the pressure waves when compared with the fragments moved by an explosion. Pressure waves could damage the axially loaded elements and it may lead to progressive collapse of the structure. This study investigated the behaviour of concrete fins and they were categorized depending on the failure mode which is based on the occupancy levels such as immediate occupancy, life safety and collapse prevention. Concrete fins were analysed using Sap2000 software by taking into account the material nonlinearity and loading nonlinearity. Weight of blasting materials, standoff distance, fin spacing, fin size and reinforcement ratios were varied to create different analysis cases. When the standoff distance was 50m, all the analysis cases were in immediate occupancy level, and it was found that standoff distance of 25m is as the manageable distance in blast. However, standoff distance of 10m resulted many analysis cases exceeded the collapse prevention limit. It was identified that standoff distance of 25m as the manageable limit with respect to the safety and the cost.
item: Thesis-Abstract
Geosynthetic reinforced pile supported embankments
Kumara, JMP; Jayasinghe, MTR; De Silva, LIN; Karunawardena, A
The design of embankments on weak foundation soils is a challenge to the geotechnical Engineer. There are several issues related to bearing capacity failures, intolerable settlements and slope instability that need to be addressed. The piled embankments with the inclusion of a geosynthetic layer have proved to be one of the economic and effective techniques to handle such problems. The inclusion of the geosynthetic reinforcement eliminates the need for inclined piles used in conventional piled embankments for resisting large lateral pressures. The geosynthetic layer enhances the load transfer mechanism and considerably minimizes the differential and maximum settlements. This study attempts to analyze the various methods available today for the design of these structures. A numerical study is carried out. The effects of certain factors like pile modulus, stiffness of the geosynthetic reinforcement, height of the embankment, effect of the soil layer directly below the geogrid which are not considered by other available methods aire studied using a finite element program - Plaxis 2D. The results from two design methods are evaluated and compared with the results from Plaxis. It is found that numerical analysis was able to address many factors that were neglected by all the other available methods. It was also found to be more reliable than currently used methods. The German Draft Standard (EBGEO) approaches the numerical Plaxis calculations better than British Standard 8006 ii
item: Thesis-Full-text
Bolted end plate beam to column connections – are they semi rigid?
Kalyani, P; Hettiarachchi, MTP
The most commonly used moment resisting connections are bolted end plate beam to column connections. Connections are usually designed as simple or continuous although the actual behavior is known to fall between these two extreme cases. The use of semi- continuous connection results substantial savings in steel weight of the overall construction. Extended endplate, Flush end plate and partial depth connections are the widely used type of connections in steel frame construction. To understand the real behavior of semi- continuous connection, full scale laboratory test is the most accurate approach, but it is time consuming and costly to undertake. Therefore other methods were developed to predict the capacity of connections. Thus, in this study 48 extended end plate and 48 flush end plate connections are analyzed to find the connection’s behavior with variations in bolt diameter, end plate thickness, and grade (4.6/8.8) and bolt gauge length. A method proposed by Steel Construction Institute (SCI) is taken into account for analyzing. The analyzed connections are classified based on strength and stiffness.
item: Thesis-Full-text
Study on structural design of highway box structures
Chinthaka, SSLD; Baskaran, K
I would like to express my sincere gratitude to my research supervisor Dr.K.Baskaran, Senior Lecturer, Department of Civil Engineering, University of Moratuwa, Sri Lanka for his guidance, suggestions and continuous support throughout my M.Eng. research work. I am also much grateful to the Head of the Department of Civil Engineering, the Course Coordinator of Master of Structural Engineering, and the staff of the Department of Civil Engineering for their valuable guidance and cooperation given in many ways. I also extend my sincere gratitude towards my employer, Road Development Authority (RDA) for granting leave to follow this course and other assistances provided for my research works. I would like to take this opportunity to convey my sincere gratitude to Mr.L.V.S.Weerakoon (Project Director, Central Expressway Project, RDA), Dr.Ruwan (Head , Structural design office, Central Expressway Project, RDA),for the assistance extended to me in numerous ways throughout, and Dr.Naveed Anwar (AIT,Thailand/International Consultant for Central Expressway Structural design works ) for the guidance given in finite element modelling. Finally, I thank for all my colleagues and family members for the valued cooperation and encouragement received to complete my M. Eng. Program successfully.
item: Thesis-Full-text
Investigation on performance of heavily cracked concrete beam strengthened with carbon fiber reinforced polymer (cfrp) sheets
Dharmaratne, PD; Gamage, GCPH; Nanayakkara, D
Repair and retrofit of existing structures especially buildings, bridges, water tanks etc., have been amongst the most significant challenges in Civil Engineering. In the past construction was evolved from thousands of years back with various construction materials such as rocks, clay bricks and timber etc. There after concrete was introduced as a sustainable construction material which is most suitable than that of previously used materials. Although concrete has high compressive strength, it is very weak in tension and become brittle under tensile loads. Because of these reasons, Engineers moved to reinforced concrete structures. Since concrete structures are long lasting structures, carrying out the rehabilitation work of existing structures becomes more vital. Nowadays, there are different kind of problems were encountered in construction field due to original design, construction errors or poor construction supervision, damages of earthquakes etc.. That needs to be retrofitted to meet the demand usage in a more economic and effective ways. The techniques based on the externally bonded Fiber Reinforced Polymer (FRP) materials is one of the most widely application for retrofitting existing damaged structures. The use of Carbon Fiber Reinforced Polymer (CFRP) in strengthening reinforced concrete structures has become popular retrofit technique. The technique of strengthening reinforced concrete structures by externally bonded CFRP fabric was started in 1980s and has attracted researchers around the world wide. The aim of this research is to investigate the flexural behavior of pre cracked and non-cracked reinforced concrete beams going to be strengthened with different configurations of Carbon Fiber Reinforcement Polymer layers. 12 Nos. of Reinforced concrete beams of the width 125mm, depth 200mm and length of 1900mm were prepared and tested for this investigation. Beams were tested in accordance with ASTM C78 guidelines. Beams consist of different CFRP arrangements such as non-anchored CFRP sheet, CFRP sheet with end anchors and CFRP sheet with end and intermediate anchors at cracked locations. FRP can be bonded to reinforced concrete elements using different methods such as external bonding, wrapping and near surface mounting. FRP sheets can be sticked to the tension face of a structural element to provide flexural strength or sticked along the web of a beam to provide shear strength. Observation shows that increment of flexural capacity is in between 81% to 110% in beams those strengthened with CFRP sheets with respect to non-strengthened beams. Highest strength gained was observed in cracked beams strengthened with CFRP with end anchors and intermediate anchors. Similar behavior was observed in non-anchored CFRP strengthened cracked and non-cracked beams. However the flexural capacity was high in CFRP strengthened cracked beams. All the cracked beams failed in debonding. But some non-cracked beams failed by rupture of CFRP. At the end of this dissertation, presents the experimental procedure, results, analysis and conclusion.
item: Thesis-Full-text
Design bending moment in concrete box structures : a comparative analysis between shell and soild element models
Rasikamal, AADI; Baskaran, K
Concrete box structures are mainly used in railway and highway projects as culverts or frame bridges. Structural engineers prefer to do finite element method (FEM) analysis using shell or frame element models to obtain bending moment diagram (BMD) for design. Structures are modelled center to center supports in shell element models. BMD of general shell element models are continuous throughout the center to center spans and maximum support moment occurs at center of supports. ACI design practice recommends selecting bending moment at face of the support as design value, but BS design practice is different and obtains bending moment value at center of the support for designs. Some literature suggests tedious bending moment correction according to the stiffness of the members of the joint. In general shell element modeling, inside rigidity of supports is not considered. However general shell element models can be modified at support region to represent the rigidity of the support area. Previously tested concrete box structure was modelled using general shell, modified shell and solid elements. Results of solid element model are much closer to experimental results at supports and spans than other models. This result validated that solid element of box culvert can be used as a base for comparison of general and modified shell models. In this study, BMD of general shell, modified shell and solid element models relevant to concrete box structures were compared to load combinations relevant to Sri Lankan Railways. The results show that BMD of solid and modified shell elements are much more similar than the general shell models. Support design bending moment can be obtained from modified shell models with reliability without confusion of center or face value to select for the design as for the general shell element models.
item: Thesis-Full-text
Seismic hazard assessment for Colombo city with local site effects
Priyantha, SM; Lewangamage, CS
floods, droughts, landslides etc. Due to the experiencing of ground shaking in last few decades and the disaster on 26th December, 2004 due to tsunami, Sri Lanka cannot further treated as an earthquake damage free country. Few research has been carried out to investigate seismic hazards at Colombo city area and the response spectrum at rock level for Colombo city area has been proposed with the PGA (Peak Ground Acceleration) of 0.1g. However, no studies have been carried out to develop earthquake response spectrum for Colombo city with local soil variations. This study discusses generalized soil profiles for Colombo city and earthquake response spectrum with local site effects for Colombo city area. 77 borehole logs done at the study area are collected and locations were plotted on a map of study area. Eight vertical sections were obtained through the study area and using them eight soil profiles which have horizontal soil layers were developed. All eight profiles highlight that the average soil cover in Colombo city area is about 20m. Just above the basement rock dense to very dense silty sand/ sand layer is present. Topmost layer also having loose to dense sandy soil. In between both of sand layers, very loose to loose clay/ silt or organic material layer is encountered in all boreholes. The developed soil profiles were used to analyze with earthquake motions using the computer software called EduShake. The six earthquake motions are applied at rock level as input motions. The response spectra at rock level and the response spectra with the local soil effects were obtained as the output file. The program was run for the eight soil profiles and obtains the average value of both output files as final result. Finally, earthquake response spectrum has been proposed for Colombo city area and it was compared with existing response spectrum at rock level for Colombo city. According to this study, the PGA with local site effects is 0.13g for Colombo city area.
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Feasibility study on polyurathene sandwich panel for domestic construction
Fernando, WB; Baskaran, K
The place to live is the third need of mankind. Everybody try to build up a suitable mean to meet their own requirements. The Sri Lankan need always changes drastically after two decades from initial construction as the social and economical changes in the society. The use of none renewable material for short period may degrade the scarce resources. And also generate ample amount of green house gasses, which lead the global warming. Therefore in time to come, we have to switch to renewable material or reusing material. There are some materials, those are produced from garbage. This creates regenerative products on earth resource extraction circle. The polyurethane sandwich panel is a reusing material which is produced from garbage. This thesis is on feasibility study on polyurethane sandwich panel for domestic constructions. The product establishment is a derivation as a regenerative product to meet the human need of this scenario. Additionally there is a shortage of skilled labour in the country. And the cost of labour for domestic construction is a considerable portion. The time consumed for domestic construction is more than months. Therefore by introduction of polyurethane sandwich panels for domestic constructions may resolve the major problems in the domestic construction field in the country. The aim of this thesis is to introduce an engineered solution from polyurethane sandwich panel to aforesaid problems. The only drawback is the less fire rating. But currently produced materials meet the legislative and regulatory stipulations. The science and technology on this field is to be improved in time to come. The sandwich panels are having very high stiffness compared to weight and a cost effective product. Polyurethane sandwich panel material may last more than two decades without much maintenance. The polyurethane sandwich panels are used for the construction of walls and ceiling on the cold room constructions as a good thermal barrier. This thesis is to see the validity on cold room construction material for the domestic constructions. The material properties changes from supplier to supplier. Therefore it is very difficult to adopt the standard practice in design. Even though “European Recommendations for Sandwich Panels Part 1; Design”;[14] has released on year 2000. The publication has been criticized by various researches such as Narayan Pokharel and Mahen Mahendran on their publication to “Thin Walled Structures” [13]. In addition the both published documents’ equation ranges on “European Recommendations for Sandwich Panels Part 1; Design” [14] and “Thin Walled Structures” [13] do not comply with the encountered polyurethane insulative sandwich panel. Therefore the serviceability limit published by “European Recommendations for Sandwich Panels Part 1; Design” [14] has been incorporated for design serviceability limit checking. This thesis is on feasibility study of sandwich material for house constructions by means of walls, slabs and roofs. The typical two-story house and the two story cluster houses are modelled to see the engineering viability under standard loadings. The outcome revealed that the construction up to two stories is safe. Therefore further studies in this stream shall be followed in future. As per the project outcome on the clause 6.6; it reveals that the domestic constructions up to two stories may be possible under some form of local capacity enhancement methods adapted to high stresses applied locations. The economical analysis is also made in Chapter five. Accordingly the cost on individual houses and cluster houses do not change and it revealed that there is more than 41% saving compared to the conventional constructions.
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Study improvements to the structural performances and cost optimization of existing telecommunication poles
Kumara, WAKB; Baskaran, K
Presently SLT invests huge capital on production of RCC poles to draw various types of telecommunication cables and hence explores the possibilities of minimizing the investment on production of RCC poles by introducing economized pole design or modifying the existing RCC poles with less production cost. There are numerous problems associated with conventional telecommunication posts currently being used in practice such as prone to corrosion in coastal belt areas. Much difficult to maintain uniform quality throughout the pole length due to manual practices of concrete mixing, bar bending, formwork etc., this will further aggravate due to lack of skilled personals for operation. In such a situation life span of the final products are doubtful. Manufacturing processes are often been carried out by subcontracting labour groups so that they can produce maximum number of poles in very limited period to cater for the demand. At the same time they are trying their best to make maximum profit, result is sub standard products. Sri Lanka Telecom currently invest huge sum of money for the production of telecommunication posts in an yearly basis as demands are high, therefore Sri Lanka Telecom is compelled to invest additional amount to investigate and overcome the above problems in sought of producing good quality products with optimum cost. External forces encountered by the telecom poles are bending, axial forces, torsion forces or a combination of those three forces. These primary influences may be accompanied by shearing forces and sometimes by torsion. Effects due to changes in temperature, shrinkage, creep of the concrete, and the possibility of damage resulting from overloading, local damage, abrasion, vibration, chemical attack and similar causes may have also to be considered. An efficiently designed poles are one in which the weight, loads and forces are transmitted to the foundations by the economical means consistent with the intended use of the pole and the nature of the ground situation. The objective of this research work is to study on current designs and their pros and cons, applicable standards, manufacturing process and simulation of structural performance of poles under recommended loading criteria by modern analytical tools. At the initial stage of study variety of sections are analysed under applicable loading criteria to select most suitable one. Sections considered for analysis are square solid section with pre-stressed reinforcement, square hollow section with normal and prestressed reinforcement, circular section with normal and pre-stressed reinforcement, circular hollow section with normal and pre-stressed reinforcement. SAP2000 finite element programme was used to analyse the poles under different loading conditions as specified. Circular hollow section with pre-stressed reinforcements gave the best option and optimum results for the requirements with respect to structural performances, weight and cost. As a result of this research study, most economical solution has been recommended to overcome the above difficulties. Usual casting practices are revised to spun casting technique with pre-stressed reinforcements and high grade concrete. This will result in finding the superior structural performances, high quality, comparatively low cost and less weight product. Few samples of the new designs are cast and been tested to witness their structural behaviours under the laboratory conditions. Finally the current and proposed designs are compared to demonstrate the weight reduction. Structural details and specifications for new designs are prepared under different height category of poles to suit manufacturing facilities.
item: Thesis-Full-text
Investigation of cement based adhesives to replace epoxy bond in cfrp/concrete composite
Kumari, DGN; Gamage, JCPH
107252-1.pdf The completion of this thesis was made possible by the help of many individuals. I take this opportunity to express my gratitude and indebtedness to my supervisor Dr. Mrs. J C P H Gamage, for her scholarly guidance, enthusiasm, proactive attitude and advice at every stage of the research study to complete it successfully. Without her direction, this thesis could not possibly have been completed in such an organized and timely manner. Much appreciation is conveyed to Ms. Dedunu Wimalasiri who is a graduate diploma student at IESL for the support, dedication and untiring efforts to ensure that this study progressed smoothly without any hindrance. Also, I would like to thank Ms Erandi, postgraduate student of department of civil engineering, university of Moratuwa for the support extended to conduct the testing. I would like to thank for all technical staff of building materials and structural testing laboratories, university of Moratuwa for their assistance. Mr Namal Liyanage of Liyanage Construction is greatly acknowledged for supporting to sand blast the test specimens. I would like to thank my husband and daughter for bearing with me and supporting me to do this research study during weekends and nights and sacrificing limited time available for family get-together. Finally, I offer my appreciation to all officers in National Water Supply & Drainage Board who helped me to complete this research successfully.
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Comparative study on seismic analysis of buildings for different code of practices commonly used in Sri Lanka
Prasanna, KPN; Lewangamage, CS
Earthquake threat has been identified by many countries and analysis and design against seismic effects have therefore become almost a basic part of their structural design process. Sri Lanka has also identified the importance of designing buildings against seismic actions, specially due to recent incidents, which took place in and around the Island. However, Sri Lanka does not have its own code of practice for designing against seismic actions. Also there are not many established guidelines available in the country for this purpose. As a result, when it is required to analyze and design buildings against seismic actions, the engineers and scientists in the country face difficulties, basically with which codes and guidelines to follow. It is obvious that all of those codes are not equally suitable for conditions in Sri Lanka and also will not give out similar results. The aim of this research is to check the performance level that a building can achieve when analyzed according to different codes of practice, which are commonly used in Sri Lanka in seismic analysis. In this context, three codes of practice were considered, taking into account their applicability over the others in Sri Lankan context, namely the Australian code (AS1170.4-2007), the Indian code (IS 1893 (Part 1):2002) and the Euro code (BS EN-1998-1:2004). The recommendations provided in the research, conducted by the University of Moratuwa, Sri Lanka, aimed at providing guidance on suitable analysis procedures for buildings in Sri Lanka, based on the euro code were also inco-operated in the analysis. First, the seismic analysis procedures outlined in those codes with respect to both static and dynamic analysis were discussed in detail. Then, the analysis procedures introduced in the respective codes of practice were compared and contrasted, considering how they handle the major effects, characteristics of the structures and geotechnical considerations etc. In order to demonstrate the analysis procedures and to make a comparison on results, three high-rise buildings, having floors between 10 to 20 were selected and analyzed according to the guidelines provided in the three selected codes of practice respectively. In this case, all the structures were analyzed for three different soil conditions, which could be found in Sri Lanka. The computer software "ETABS" has been used for finite element modeling of all the structures. Response Spectrum Analysis (RSA) was used in all the dynamic analysis purposes. Equivalent static analysis was also carried out as per requirements, established in particular codes of practice. According to the results obtained in the analysis, it has been found that, irrespective of the code of practice, which has been used in the analysis, the structures have achieved Immediate Occupancy Level (IOL)in all twenty seven cases, according to FEMA356 standards. It was also found that the Indian code has given the highest drift values in many occasions while the Euro code also has given very close or sometimes similar drift values. In contrast, the Australian code has generally resulted lowest drift values. Further, it has also been identified that the Euro code has given the highest design base shear forces in all eighteen occasions. On the other hand, the Indian code has given lowest design base shear force in many occasions. The Australian code has also shown the lowest design base shear forces in few occasions.
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Design of Dowels for shear transfer at the interface between concrete cast at different times : a case study
Karunarathna, SMP; Nanayakkara, SMA
Enlargement of original cross-sections or replacement of defective concrete layers with new concrete are usual situations in strengthening operations of reinforced concrete structures. In these situations, the shear strength between concrete cast at different times is crucial for the monolithic behavior of the strengthened members. Most design standards for concrete structures present design procedure for estimating the shear resistance between concrete layers based on the shear friction theory. The study includes three-dimensional and two-dimensional finite element model (FEM) analysis for calculation of shear stresses and comparison of three different code approaches, i.e. BS8110, ACI 318 and EN 1992, for determination of design shear resistance at an interface between concrete cast at different ages of a pile cap supported on precast concrete piles. Based on the results of the analysis carried out, it can be stated that complicated three dimensional finite element model analysis is not always essential for analysis of structures, which are having complex geometrical shapes. It is possible to transform three-dimensional problems to a simplified two-dimensional problem based on the level of accuracy required. For the selected surface characteristics and r/f percentage, the estimated design shear resistance based on recommendations of EN-1992-1-1-2004 was found be lower than the corresponding estimated value based on ACI 318M-11 recommendations. It was further observed that BS 8110-1-1997 recommendations gives the highest value for the design shear resistance independent of r/f percentage provided. EN-1992-1-1-2004 can be used to compare contribution of concrete interface roughness and interface reinforcement on design shear resistance without any limitation of design shear stress as specified in ACI 318M-11. Furthermore, the EN-1992-1-1-2004 recommends a conservative value for design shear resistance compared to other two standards.
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Evaluation of seismic capacity of existing highway bridges in Sri Lanka
Aluthapala, UL; Lewangamage, CS; Baskaran, K
Sri Lanka is an island located in the Indian Ocean and it lies in the large Indo-Australian plate seemingly far away from any of the plate boundaries. Therefore, many people believe that this fortuitous scenario makes Sri Lanka safe from earthquakes. But an intra-plate earthquake can occur anywhere at any time. Some geologists pointed out that the Indo Australian plate is being separated into two and its boundary lies 500km away from the southern coast of the country. Therefore, Sri Lanka has a moderate risk to face an earthquake. There are over 4000 bridges on National Road Network with length varying from 3.0m to 500.0m. These bridges have varying widths about 3.0m to 25.0m and some of these have been constructed more than 50 to 100 years back. They were constructed using steel concrete composite or steel. These bridges have not been designed for seismic loads and they have not been detailed for seismic effects. Therefore, it is a must to evaluate the seismic capacity of those bridges and retrofit those if necessary. This study was focused to develop a priority list (Bridge Rank) for the purpose of further investigation on seismic capacity. It was also focused to carry out a case study for a selected bridge from the developed priority list to find out its seismic capacity. Bridges on the “A” class roads with the overall length of the bridge is greater than 25m were considered in this study. To develop the priority list for thesebridges, the method given in the “Seismic Retrofitting Manual for Highway Bridges” published by the Federal Highway Administration (Report No. FHWARD- 94-052) was used. The parameters required to input to the above methodology were obtained from the previous research findings and the bridge inventory that is maintained by the Planning Division of RDA, Sri Lanka. The bridges considered under this study have low risk to fail due to possible earthquake loadings with local conditions since the bridge rank is between 0 to 24 on the scale of 100. Bridge No 1/1 on PeliyagodaPuttalam road (Japanese Friendship Bridge) was selected for further investigation from the developed priority list since it gives the bridge ranking 12. A response spectrum analysis was carried out to find the actions of the bridge during an earthquake. For the analysis of the bridge, a Finite Element Model was developed using SAP 2000. Codes of practices for Australian standards were used to find out the seismic capacities of the substructure and the actions of superstructure was compared with the originally designed actions. The bridges considered under this study have low risk to fail due to possible earthquake loadings since the bridge rank is between 0 to 24 on the scale of 100. It is proposed to replace the bridge bearings of the bridge no 1/1 on PeliyagodaPuttalam road based on the results of the case study.
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Evaluation of present safety limits of steel lattice type telecommunication antenna towers in Sri Lanka
(2016-05-28) Perera, GRV; Hettiarachchi, MTP
Sri Lanka has made a significant development in the telecommunications sector since the inception of sector reforms in 1991, resulting in a competitive market environment. The results of liberalization have been impressive, with the telecommunications sector growing at one of the fastest paces in Asia. Along with above rapid growth of telecommunication industry, the numbers of antenna towers also have been increased from about 400 (in 1990) up to nearly 5100 towers during the last two decades. During the above boom period of development, some aspects of safety and reliability seem to have been overlooked. This report provides detailed discussion on the technical aspects of steel lattice antenna tower designs, codes of practice and different factors of safety. Postcollapse assessments of four incidences of recently collapsed tall antenna towers in Sri Lanka are also included in this report. Several shortcomings existing in currently available technical specifications, tender bidding processes and construction were also highlighted. The possible solutions and methods for eliminating above mentioned shortcomings are also discussed in detail. The void that exists in telecommunication industry due to the absence of properly qualified structural engineering experts are also highlighted. Further to that, the resulting negative effects such as neglecting public safety, lower reliability of telecommunication network, high possibility of accidents occurring, etc. are discussed in detail. The cost of construction vs safety of antenna towers is discussed with a desk study. Effectiveness of some common practices and beliefs which are influencing current antenna tower constructions are also discussed. Concluding remarks along with several basic recommendations are supplied for correcting the present mistakes while making more reliable telecommunication networks as well as ensuring public safety.
item: Thesis-Abstract
Strength assessment of axially loaded RC column strengthened by steel cages
(2015-09-17) Thenuwara, TATE; Baskaran, K
In reinforced concrete buildings the columns are the main vertical elements, which sustain and carry the entire weight. Hence they should be capable to withstand the loads transferring from the beams and slabs without any failure. Any deficiency of the column may cause total collapse of the structure and it may lead to destruction of human life and also physical damages to other structures. But due to reasons such as change in use, design, number of floors, addition of other installations or deterioration, it is often necessary to strengthen RC columns in buildings during construction or post construction. Three main methods; concrete jacketing, steel jacketing and composite jacketing are used to strengthen RC columns. Concrete jacketing is popular in Sri Lanka but it is worth to implement steel jacketing in the construction industry due to the easiness of the usage. The composite jacketing cannot be implemented due to high cost. Hence the aim of the present study is to encourage the use of steel jacketing in Sri Lanka. To have economical use of steel, angles and strips can be used to strengthened RC columns. The objective of the present study is to check whether EUROCODE 4 (2004) or BS 5400-5 (1979) can be used to evaluate the load carrying capacity in compression for RC columns strengthened with steel angles and strips. The experimental results from foreign and local researches were gathered and compared with the calculated theoretical values. The ratio between gross capacity without safety factor and experimental value is ranging 0.95 to 1.05 based on EC4 and 0.96 to 1.06 based on BS 5400 5 in the experiment II of Ester G with five strips and it is 0.84 based on EC4 and 0.85 based on BS 5400 5 in the experiment I of Ester G. with seven strips. But, for the experiment of Kumaranjan A. the ratio between gross capacity without safety factor and experimental value is ranging 0.97 to 1.03 for seven and five strips. The ratios between theoretical ultimate values of BS 5400 5 and EC4 are varying from 0.87 to 0.88 in experiment done by Ester G. and 0.84 in the experiment done by Kumaranjan A. The experimental values are higher than the theoretical ultimate values and the safety factor of 1.1 to 1.6 is for EC 4 and 1.36 to 1.85 is for BS 5400 5. It is confirmed that the safety factor of the both codes have sufficient provisions for the capacity of strengthen RC columns using steel cages. Also, when using seven strips the capacity has increased but it is not quantified using the codes calculations. It is recommended to test the real size columns with several L angles sizes with load on it while strengthening to simulate a constructed column in a building. Also, an experimental study by varying the number of strips connected to the cage would lead to identify the limits of the enhancement of strength capacity.
item: Thesis-Abstract
Height limits for reinforced concrete wall-slab residential buildings
(2015-09-17) De Silva, AKTV; Dias, P
It is common in urban areas for medium rise residential buildings to be constructed with a scarcity of land. With rapid urban growth in developing countries like Sri Lanka, it is crucial that low income families are provided with better living conditions. Construction of residential buildings with higher number of stories for low income families in Colombo has already started and further plans for constructing more buildings are likely. In order to eliminate the space taken by columns and beams in vertical and horizontal spaces in each floor and to reduce the time spent for partition wall construction, reinforced concrete wall-slab structures are arguably the best structural form for residential buildings. In this research, the wall thickness requirements in several codes of practices were analyzed to select the minimum possible wall thickness with respect to durability and fire requirements as well as practical feasibility. Three building layouts were generated with approximately similar floor areas, wall densities and number of stories but with different aspect ratios and modeled using computer software. By using the maximum stress figures obtained from the analysis, calculations were made to predict the maximum number of stories achievable with selected wall thicknesses in each building. Further a seismic analysis was done for all three buildings to compare their behavior under an earthquake. Comparing several codes of practices and considering practical feasibility, the minimum wall thickness for double layered reinforced concrete walls was obtained as 180mm and for single layered reinforced concrete walls as 130mm. The maximum stories achievable in buildings with aspect ratios of 2, 1.15 and 6.7 ranged from 16 to 8, 16 to 8 and 14 to 8 respectively, depending on its grid spacing (i.e. whether 3m or 6m) and wall thickness (i.e. whether 180mm or 130mm). Buildings having aspect ratios of 2 and 1.15 with 12 stories showed sufficient capacity under seismic action too.
item: Thesis-Abstract
Sizing of reinforced concrete structural members based on Sri Lankan design data
(2015-09-17) Konara, MRN; Dias, WPS
The majority of building structures in Sri Lanka, are of reinforced concrete. Often it is required to estimate structural member sizes at the initial stage of a building construction project for load evaluation, cost estimation and reinforcement design. For member dimension estimation, theoretical knowledge alone is inadequate as there are some practical issues also to be addressed. This study proposes reinforced concrete member sizes for future projects based on design data of past low to medium rise buildings in Sri Lanka. Standards available for member size estimation, difficulties encountered by the designers while following available standards, gaps in existing sources, and applicability to local conditions are discussed. Structural and architectural drawings of twenty one buildings from two to thirteen storeys were used to extract design details related to slabs, staircases, beams, columns and footings elements. Data gathered for each element type are used to interpret relationships between member dimensions and design parameters. Artificial Neural Networks (ANN) is an artificial intelligence technique for recognizing patterns among data that are difficult to represent algorithmically. This study also explores the potential of using Sri Lankan design data from past buildings in Artificial Neural Network models for predicting reinforced concrete member sizes. Recommended structural member sizes are presented in graphs and tables, and compared with the ANN model results. Finally the member sizes recommended by the study are compared with the sizes derived according to the available literature.