Master of Engineering in Structural Engineering Design

Permanent URI for this collectionhttp://192.248.9.226/handle/123/35

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item: Thesis-Abstract
A Study of behaviour of high rise buildings with transfer level under dynamic loading
Jayasundara, TJ; Jayasinghe, MTR
Earthquake resistant structures are not mandatory in countries located away from earthquake prone zones such as Sri Lanka. However after the occurrence of 2004 Tsunami, and considering possible environmental changers and recently observed small scale ground motions, it is advisable to consider Sri Lanka as low seismic zone. With the current trend of "Mixed Development Concept" high- rise buildings with transfer plates are common form in the vicinity as far as apartment buildings are concerned. The consequences in an event of an earthquake can be serious or even fatal for this type of highly irregular buildings and adoption of earthquake detailing alone would not adequate. Therefore, approach is needed in order to enhance the earthquake resistance at the conceptual design stage. This study has been carried out in order to identify the effects on the seismic performance of the building when the level of the transfer plate changes. Accordingly, five number of thirty five storied apartment buildings with transfer plate located at different levels were considered in the analysis. It is observed that building codes provide criteria to classify the vertically irregular structures and suggest dynamic analysis to arrive at design lateral forces. In this context, the buildings under this study were subjected to response spectrum analysis according to the design spectrum given in the UBC 97. Computer simulation has become an efficient tool in the analysis of structures under extreme loading. Therefore, three dimensional computer models generated with the help of SAP 2000 were used in this study. The transfer floor was located at the tenth floor level of the thirty five storied building as the first case. The analysis was repeated by changing the level of the transfer plate to below and above the tenth level. Results obtained for buildings with transfer plate located at different levels were compared. From the comparison of Response Spectrum Analysis results of this study it , was found that, when the level of the transfer floor moves towards the ground it enhances the earthquake resistance of such buildings. Further, it was found that the variation of the base shear, maximum absolute accelerations, maximum absolute displacement and the inter story drift is marginal with respect to the change in level of the transfer plate for this particular building.
item: Thesis-Abstract
A study of built - up timber structural elements
Mohanathevan, S; Hettiarachchi, MTP
Code on timber design CBS 5268 Part 2, 1991) gives no provisions for the design of layered braced and box timber columns except spaced timber columns. Very little information is available about these in the literature on timber structures. This paper provides procedure for determining the axial load capacity of mechanically connected built-up columns, such as layered columns, spaced columns, braced columns and box columns. In addition to that, it gives information about nail connection details and arrangement. Mainly concentrated on built-up timber columns made up with mechanical connection as it could be done locally. The theoretical development takes into account the effect of columns stability and effectiveness of the shear transfer. The experimental results obtained by under graduate students are compared with theoretical predictions. Conclusions are drawn with regards to the suitability of the design methods for built up timber columns made by nailed connections.
item: Thesis-Abstract
Analysis of elevated water retaining structures using finite element method
Rupasinghe, SKLS; Jayasinghe, MTR
In water supply schemes, concrete structures are used to store the required quantity of water for distribution for an area. In the case of design of these structures, a precise and accurate analysis is considered as a significant issue. Especially in elevated towers such as Intze Tanks, Conical Tanks and Cylindrical Tanks, the membrane shell theory is used extensively in analyzing those structures. The Intze tanks prove to be economical for storing medium and large capacities. It is useful to analyze these structures to obtain a cost effective solution. In most of the structures mentioned above have hoop tension as critical in many parts of the structures due to the water pressure on the sections. Therefore, reduction of hoop tension of the structure is important to reduce the requirement of reinforcement in the particular section. In the research, the elevated structures were analyzed by using the membrane theory. Also the structures were modeled using the Sap 2000 software to compare the results of shell theory with computer modeling. The aim is to investigate the potential for optimization. In this research, the Intze type structures were modeled and analyzed by using the finite element analyzing (FEA) software to check the difference of results between Shell theory and FEA at different locations. The model has shown that the membrane moment and forces obtained from the Finite Element Analysis was considerably lower than the results that have been obtained from manual calculations at certain locations. According to the FEA results, the membrane forces are low in the sections of cylindrical wall, conical bottom and supporting shaft. In order to assess the benefits of more accurate analysis, the structure were redesigned by using the results obtain from FEA to calculate the benefit of cost in finite element analysis& design. A cost analysis was performed to quantify the cost advantages.
item: Thesis-Abstract
Applicability of suspension bridges for transportation in rural areas in Sri Lanka
Thrimavithana, RSK; Jayasinghe, MTR
For the rapid economic development of rural villages in Sri Lanka the transportation facilities should be upgraded. In this context, one of the bottlenecks is the need of large number of bridges which is a costly item. Therefore the solution given at the moment is the provision of pedestrian suspension bridges, which can be used only for passengers. Almost all the suspension foot bridges available might not withstand dynamic forces such as wind induced dynamic forces and human induced dynamic forces. The biggest issue on these bridges is the safety. For these locations the development of a suspension bridge that can handle both human and cycles loads safely, will be a great advantage. These structures however are always lively with low stiffness, low mass, low damping and low natural frequencies./ A conceptual study has been carried out to investigate the dynamic characteristics of slender suspension foot bridges under human induced dynamic loads. As the first step, some places where suspension foot bridges are located were visited. While crossing the bridge, during the site visit it was felt that those existing bridges are not comfortable and identified as low safety. Different types of suspension bridges and different structural models were observed. Then existing suspension foot bridges were modeled using both software PROKON (V-2.1) and SAP 2000 (V9.3). Under the first step it was tried to introduce different modifications to existing bridges to satisfy comfort and more structural stability with safety. Since these bridges are having low structural factor of safeties, no modifications are allowed.
item: Thesis-Abstract
Blast resisting concrete walls
Indiketihewage, KN; Nanayakkara, SMA
Today people around the world wake up, eat, live and sleep with terrorism. It has become a global menace. As a citizen lives in a country hit by a civil war for over three decades gave me motive and courage to set off this project. The project was basically planned to carry out in two parts, i.e. the literature survey and the experimental investigation. Initially a comprehensive literature survey was carried out to cover the several areas./ As terrorism is the main reason to for this project to exist, the literature survey was started off with an insight view of terrorism, its motives, methods and objectives of terrorist organisations. Later the survey was expanded to explosives and weapons frequently used by the terrorists. At the next stage of the literature survey, a review was done on the existing knowledge of blast resisting designs followed by a study on the various structural responses to blast loadings. The literature survey was further extendedto design of blast resisting structures and finally to design of elements to resist blastloadings was also completed. As a measure to increase the resistance to blast loadings, important characteristics of steel fibre and welded meshes were also studied./ The experimental investigation of the project was directed to find solutions to two situations, in battle field or terrorist attack. First series of tests of the project were concentrated on close range high explosive detonations./ Unfortunately, this part of the project had to be abandoned due to unavailability of TNT explosives in slab form. This brought to the abrupt end to the test series one of the project./ The second series of tests were focused more on a military situation, where terrorist fire with RPG 7 at bunkers. After the testing, it was revealed that the designed concrete panel might barely withstand the RPG 7 fire. The reason for this may be the fact that the effects of small steel balls were not considered in the design. Only the amount of explosives and the distance from the centre of the RPG 7 mortar to panel were considered
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-Abstract
Comparative analysis o n simply supported pre- stressed box beams in Sri Lankan highway bridges
(2014-08-22) Jabbar, MARMA; Jayasinghe, MTR
The National Road network of Sri Lanka consists of 4326 bridges. There are 365 bridges which Have the length more than 30m .Only 800 bridges are made of prestressed concrete superstructures and all others are with reinforced concrete, steel and arches. The most popular types of prestressed beams used in Sri Lanka are inverted T, M, I, and the box beams. The inverted T and M beams are widely used. Further, for 30m span simply supported bridges, space rectangular box beams and spaced trapezoidal box beams were used. For the continuous bridges big spine beams also have been used with post tension pre-stressing system in recent bridge constructions. For longer span bridges, box beams are highly suitable. Generally box beam has higher torsional capacity because of its closed geometry. The enhanced torsional stiffness of the box beam sections improves the load distribution properties for the superstructure. It has higher bending carrying capacity and requires reduced beam height compared to other beam section for a particular span. Hollow spaces in box beams can be used for services and it is also aesthetic. In Sri Lanka 19% of the existing bridges are with prestressed concrete and presently many highway projects are under construction. Therefore, the usage of box beams will improve the effect on the time of construction, cost, construction easiness, aesthetic considerations and utility services. There are different types of box beams available that can be used for this simply supported span range. They are standard box beam, standard U beam and spaced box beams. The rectangular spaced box beam has been used for a two lane bridge in a 30m simply supported span and the trapezoidal spaced box beam has been used for a four lane elevated flyover in Sri Lanka. Comparative analysis and design on all these box beams are useful for future bridge constructions. This research is concentrated on the design of 30m simply supported four lane bridge super structures using the above different types of prestressed box beams separately. The results of analysis and design and the properties of the beams are compared. The total width of the designed bridges is 17.4m. It has a central reserve of 1.2m. There are four lanes; each lane is 3.5m width. There are two pedestrian walk ways of 1.1m width. All the bridge decks were modeled in SAP 2000 for the grillage analysis. Loading was done according to BS 5400: Part 2, 1978, and bending moments, shear forces and torsional moments were found for critical load combination. Prestressing designs were carried out for all beams and the final results are compared. Cost for each deck also compared. The different launching methods adapted for these Bridges are also compared. Conclusions and recommendations are laid down based on these compared results.
item: Thesis-Abstract
Comparative study on code based analysis of steel moment resisting connections
(2015-02-22) Kodikara, KANT; Baskaran, K
Moment resisting 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 and Flush end plate 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 three EEP and three FEP connections were analyzed using two standards (BS 5950 Part 1: 2000 and EC 3– with UK national application document). A method proposed by Steel Construction Institute (SCI) was taken into account for analyzing. The results obtained from the numerical analysis were then compared with the existing experimental test results on the resistance of moment and mode of failure to determine the accuracy of numerical analysis. Comparison between the results from numerical analysis and experiment results satisfactorily agreed.
item: Thesis-Full-text
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.
item: Thesis-Abstract
Comparative study on simply supported pre-stressed box girders and double T beams for Two lane highway bridges
Wijendra, WSN; Jayasinghe, MTR
There are about 3800 bridges on National Road Network with length varying from 3.0 m to 300.0m.These bridges have varying widths about 3.0m to 20.0m and some of these have been constructed more than 50 to 100 years back. Most of the bridges span 30m and above. They were constructed using steel concrete composite or steel. Steel is a very costly material, even though it has some very good structural advantages./ Few bridges have been constructed in the recent past using T,M,Y,I beams in the span around 30m by launching side by side. And this was a very tedious procedure. Aesthetic view of a bridge has been neglected during the past 50 years or more due to the design complexity. Time for completion of a bridge has become an uphill task these days due to the price fluctuation and other constrains such as traffic and utility services./ This study is concentrated on the design of a simply supported 30m pre-stressed post tensioned box girder and comparing the properties and other advantages mainly with the Double T beams. Mainly the geometry of the box girder was selected with the help of past research papers and the geometry of the double T beam was selected where the cross sectional area is approximately equal to the cross sectional area of the box girder. Design of the box girder is done using three dimensional finite element method and the spine beam method. Although the Finite Element method is very versatile and powerful manual, calculations is also done as box girders designs are very rare. As the history of the double T beams arc also very rare, it is also designed using SAP 2000, spine beam, and three dimensional Finite Element methods./ Both beams are analyzed for HA,HB moving loads. Load combinations are considered, dead plus HA live load as load combination 2 and dead plus HB as load combination 3 Shear force, bending moment, tortional moment, support reactions, stresses, amount of tendons were compared. In spite of that, the launching method, capability for utility services were also compared. Conclusions and the recommendations of the study will be laid down based on the results in the study
item: Thesis-Abstract
Comparison of portal frames of UB sections with the lattice girder portal frames
Jayasinghe, S; Hettiaracchchi, MTP
Portal frame structures are very popular in industrial buildings due to their pleasing appearance and shorter construction period. In Sri Lanka too, steel construction is increasingly being used for single storey buildings. Basically there are two types of steel portal frames adopted in Sri Lanka; these are called Prefabricated and pre- engineered portal frames./ Although the portal frame is inherently pleasing to the eye, given a well proportioned and detailed design, and less in cost for providing controlled environments, industrial connotation, together with increased service requirements has encouraged the use of lattice trusses for the roof structures. /The structural forms both in the simple form fixed column bases and as portal frames with moment resisting connections between the tops of columns are used for long span structures./ Although it is widely used, portal frame may not be the best solution for large span single story buildings. Lattice girders are successfully used for medium size spans. However it is not widely used for large span buildings in Sri Lanka./ The construction industry here has many years of experience and necessary skills on fabricating truss or lattice type structures. Even though skilled and unskilled labor involvement is high, it will not reflect crucially on ultimate cost of the structure as the labor cost is less here in Sri Lanka, compared to European countries. Therefore in Sri Lanka lattice girder construction for large span buildings may be more cost effective. The main objective of this research is to compare the portal frames formed with lattice girders with the conventional portal frames with Universal Beam sections for different span ranges and compare them in same spans, in the context of optimum cost and space requirements.
item: Thesis-Abstract
Comparison of prestressed and reinforced concrete ground reservoirs
Fernando, KMNS; Nanayakkara, SMA
There is a great demand for new pipe borne water supply schemes as well as expansion of existing pipe borne water supply schemes due to rapid urbanization, industrialization and host of other reasons demanding construction of more and more ground reservoirs to feed water to meet these water supply needs. Traditionally, ground water storage reservoirs have been built out of reinforced concrete and most of them are rectangular in shape with a few being circular. In Sri Lanka only two pre stressed ground reservoirs have been constructed, one in Galle Water Supply Scheme in Beak and the other one is for Greater Colombo Water Supply Scheme in Maligakanda having capacities of 2.0 and 3.0 million gallons respectively (9000 m3& 13,500 m3)./ The land and space available for construction of ground reservoirs in urban areas becoming less and less and construction materials such as cement, aggregates, reinforcing steel and skilled labor etc becoming scarce and construction of prestressed ground reservoir could offer a solution to these problems./ Based on data collected on some of the ground reservoirs already constructed in Sri Lanka it could be seen that the prestressed concrete reservoirs could offer economical solutions when compared with reinforced concrete construction with respect to the usage of land and construction materials due to structural configuration and the ability of prestressing to reduce concrete sections./ A major draw back in the prestressed reservoir design is its inability to adapt to the land shape due to shape restriction to circular only and also lack of experienced contractors in prestressed construction presently in Sri I.anka. The selected structural arrangement for the dome roof consists of spherical dome roof with shell structure with prestressed ring beam resting on a rubber pad which is resting on the top of the wall.
item: Thesis-Abstract
Comparison of shell element forces obtained through classical analysis and computer software
(2015-09-17) Vithanage, SC; Nanayakkara, SMA
The “intze” type water tanks are economical for storing large capacities of water. Therefore accurate analysis of these structures is essential. Modern trend is to use computer software for analysis and design of structures. It is easy and time saving. There are many commercial software available for the structural analysis. However, the accuracy of the output of the software depends on how well the actual structure is modeled. All those software are finite element based. There are many types of finite elements developed for the purpose of structural modeling. These elements have their own advantages and limitations in different situations. Selection of correct type of element and proper fineness of mesh is very important in achieving accurate results. The aim of this research is to study the proper type of finite element and the optimal fineness of mesh suitable for different types of shells. In this context, the results obtained using different type of finite elements and different fineness of mesh used for analysis of “intze” type water tower were compared with the results obtained through classical analysis. A 1500m3 intze type water tank was selected as a structure to analyse and compare the results. First, the structure was analyzed using elastic theory of thin shells with certain approximations. Stress analysis of “intze” tanks is extremely complicated due to many degrees of redundancies. The computer software “STAAD Pro” was used for the finite element modeling of the tank. Initially 2-noded beam elements and 4-noded plate bending elements were used to model the structure. Many different models were created modifying the initial model until a result which is well comparable with classical results is obtained. Following models were created in “STAAD Pro”, Model 1. Beams were modeled as 2-noded beam elements and shells were modeled as 4-noded plate bending elements. Model 2. Vertical axis and horizontal axis bending moments were released from the 1st model. Model 3. Actual member eccentricities were given for the beams in 2nd model. Model 4. Both beams and shells were modeled as 4-noded plate bending elements. By comparing the results of above 4 models with results obtained through classical analysis, most suitable model was identified. After identifying most suitable model representing the structure, following further studies were carried out. Model a) Use of 3-noded shell elements instead of 4-noded shell elements. Model b) Changing the fineness of the mesh to study the effect of element size in final results. The results obtained were studied and made a conclusion on the suitability of different types of finite elements for different types of elements. It has been found that the STAAD Pro model 3 is the better structural representation of actual structure. STAAD Pro model 3 is the model which has vertical and horizontal axis bending moments released and actual eccentricities were given at the member start node and end node of the ring beam elements. Shells are quadrilateral plate bending element as 4 nodes of the plate in every shell lie on same plane.
item: Thesis-Abstract
Computerized optimization of the base width of transmission towers in Sri Lanka
(2015-02-22) Ganeshwaran, R; Hettiarachchi, MTP; Baskaran, K
Transmission line towers were mainly used in electrification works in all over the world. Optimization of base width of the transmission towers becomes necessary in order to reduce the cost and to avoid public objection. The use of narrow width tower becomes essential, as the land value appreciates drastically in Sri Lanka. This research is to design the transmission towers with reduced base width to minimize the coverage land with optimum weight and adequate strength. There were number of models selected with 14.2m base width and analyzed by reducing the width in steps from 1m to 3.2m. For this purpose computerized model analysis software named PLS Tower was used. Accordingly cost analysis was carried out for different steel prices and the cost of land. As per this study Optimum base width of 6.2m was found considering both the land & steel price. When compared with the towers used in Sri Lanka, it was found that the narrow width towers designed from this study showed a considerable amount of saving in cost and favourable impact on environmental issues.
item: Thesis-Abstract
Computerized optimization of the based width of transmission towers in Sri Lanka
(2015-06-24) Ganeshwaran, R; Hettiarachchi, MTP
Transmission line towers were mainly used in electrification works in all over the world. Optimization of base width of the transmission towers becomes necessary in order to reduce the cost and to avoid public objection. The use of narrow width tower becomes essential, as the land value appreciates drastically in Sri Lanka. This research is to design the transmission towers with reduced base width to minimize the coverage land with optimum weight and adequate strength. There were number of models selected with 14.2m base width and analyzed by reducing the width in steps from 1m to 3.2m. For this purpose computerized model analysis software named PLS Tower was used. Accordingly cost analysis was carried out for different steel prices and the cost of land. As per this study Optimum base width of 6.2m was found considering both the land & steel price. When compared with the towers used in Sri Lanka, it was found that the narrow width towers designed from this study showed a considerable amount of saving in cost and favorable impact on environmental issues.
item: Thesis-Abstract
Corrosion prevention of stell structures for Sri Lanka Author Premachandrasiri, W.N.
(2015-07-07) Premachandrasiri, WN; Hettiarachchi, MTP
Sri Lanka has made a significant development in the design and construction sector during the last 10 years. The use of steel is one of the governing construction materials in the industries. One of the major concerns of existing steel structures is the durability. Corrosion and deterioration have become major challenges in the lifetime of the structure, as it is one of the major public focuses on the structures. Standards are intended to assist engineers and corrosion experts in adopting best practice in corrosion protection of structural steel at new constructions with proper identification of an actual exposure. There are six environmental corrosivity categories according to BS ISO 12944 as C1, C2 C3, C4, C5 and C5 –M. Those are according to BS standard and they should be adapted for Sri Lanka. In this research environmental corrosivity category of SC1, SC2, SC3 and SC4 are classified for Sri Lanka considering corrosion affecting factors temperature, rainfall, coastal region and industrial zones. A field survey was carried out in different locations of the structure in the country to identify the pattern of corrosion according to variation of corrosion affecting factors. Among the methods used to clean the surface of the steel before applying corrosion protection, sand blasting cleans best. However, it cannot be carried out in every location due to environmental issues and equipment required. Steel surface is difficult to clean using light tools because temporary stabilized corroded layer on the steel surface. If we change this surface (Convert surface grade A to Surface grade B), the light tools can be used for the surface preparation. Therefore a new method is proposed to change this surface grade. Firstly, sea water is sprayed on to the surface to increase the rate of corrosion and left for a day for rust to appear. Then it is cleaned by fresh water and surface salinity level should be checked using salinity meter. Then the surface can be prepared using “Cup-Brush application” method without using sand blasting. By this method well cleaned surface can be obtained and then the surface protection primer is applied on it immediately. This surface protection primer type and primer and paint thickness should be defined according to environmental corrosivity category.
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-Abstract
Delayed ettringite formation in large concrete sections and its prevention
(2015-07-07) Wanigaratne, NSA; Jayasinghe, MTR
Delayed Ettringite Formation in Large Concrete Sections and its Prevention With many large scale civil engineering construction projects undertaken, there is a possibility for having large concrete pores in thick members. Due to the hydration process, temperatures in concrete will increase during early stages and when the temperature of concrete is more than 70oC, there is a possibility for Delayed Ettringite Formation (DEF). DEF can have adverse long term effects that could lead to severe cracking of concrete with age when moisture is present. Thus, controlling maximum temperature that concrete would reach during early stages will be the key to prevent DEF. In this, mineral additives like fly ash can play a major role. This paper presents various strategies available to deal with DEF and also the likely concrete thicknesses that could be cast with different mixes and grades of concrete in the different climatic regions in Sri Lanka to minimize the potential for DEF. With the use of a validated software peak temperatures for a range of concrete grades placed at different climatic zones of Sri Lanka were predicted. A series of charts were developed from the results. These charts can be directly used by the design engineer prior to concreting and the necessary remedial action could be taken to minimize the risk of DEF occurring. Contrary to the usual practice for thin sections, the strength should be kept at a minimum, sufficient to address durability when thick sections are involved as it is necessary to address DEF related issues as well. A comparison with an alternative method of using a pipe network through the concrete to remove excess heat was also done, which showed that the use of charts is as much as effective but less expensive.
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-Abstract
Design methods for apartment buildings with thin concrete shear walls
Ratnayake, KC; Jayasinghe, MTR
Economizing the construction cost is a strict demand of the current economic environment. Many structural engineers, practicing and academics; are actively involved in finding a favourable solution for this problem through experiments and researches. Many countries like Chile, Malaysia etc. have obtained good results. Thin concrete shear wall structures shade some light on this as most apartments for low and medium income groups should have symmetrical arrangement of lateral walls. This system is somewhat new to Sri Lanka but, could be very useful. Properly designed and detailed buildings with shear walls have shown overwhelming performance in past earthquakes occurred in different parts of the world. Shear walls in high seismic regions require special detailing. However, in past earthquakes, even buildings with sufficient amount of walls that have not been specially detailed for seismic performance (but had enough well distributed reinforcements), had saved from collapse. Shear walls are easy to construct; reinforcement detailing is relatively straight forward; repetitive construction; therefore shear walls are efficient both in terms of construction cost and effectiveness in minimizing earthquake damage in structural and non-structural elements. The objectives of the thesis are to assess the suitability of thin concrete shear wall structures for medium and 'low income group apartments, to check the feasibility with respect to economy, to optimize the thickness of shear walls, to assess ongoing building projects, and to check the suitability of thin shear wall structures in case of seismic (earthquake) loads. Methodology to achieve these objectives is the use of detailed literature survey, assessing code provisions, cost implications, establishing a finite element model, structural designs to British Standards, and comparison with other forms. It is concluded that apartment buildings with thin concrete shear walls are comparatively economical with other forms.