227 research outputs found
Use of loadbearing brickwork for three storey houses in Sri Lanka
No full textFor residential buildings, brickwork out of hand moulded burnt bricks is widely used in Sri Lanka. The majority of these buildings are single storey construction. However, in recent times, two storey residential buildings have gained popularity due to advantages such as saving in land area required and the thermal comfort that can be offered on the ground floor during the day time.
When large houses are required on small blocks of land such as 6 perch in extent, three storey residential construction can be considered as an option. This also offers further advantages since both ground and first floor are now shaded. Thus, achieving a reasonable thermal comfort in a properly planned house would be easier despite the hot humid climatic conditions prevailing in Sri Lanka.
It was shown by Jayasinghe & Attalage (1999 b) that the reduction of external surface area and the roof area of a residential building is useful for reducing the external thermal gains. Reduced external thermal gains coupled with enhanced natural ventilation can be one of the possibilities for achieving a reasonable thermal comfort. It was shown by Jayasinghe & Attalage (1999 a) that Sri Lankans can be thermally comfortable even at elevated temperatures when sufficient ventilation is available.
When three storey houses are required, the structural form generally considered is reinforced concrete frames. However, load bearing brickwork can be a cost effective alternative when the residential buildings are planned with a considerable number of partition walls and with upper floors built on top of lower floor walls.
It is shown in this report with few examples that planning of such three storey houses is practically possible. Such houses can offer a number of advantages like reduced circulation space thus leading to better usage of space, bed rooms arranged around the courtyards, study rooms located at well shaded first floors etc.
When locally available hand moulded bricks are used for construction, it is possible to
obtain a characteristic compressive strength of 1.5 N/mm2 when 1:6 cement sand mortar
is used (Jayasinghe, 1988). It is also necessary to exercise certain quality controlling
measures while selecting the bricks for construction and carrying out the actual
construction.
Since the characteristic compressive strength is limited to 1.5 N/mm2, it is necessary to
use walls of sufficient thickness for load bearing walls at lower levels. It is shown that a
wall thickness of one and a half bricks is appropriate for the ground floor and one brick
for the first floor walls. The second floor wall thicknesses should be selected with the aim of minimising the self weight, hence half a brick thick walls would be appropriate for partition walls. The external walls can be one brick thick for enhanced resistance to wind induced forces and rain water penetration.
Since openings will act as a source of weakness in load bearing walls, guidelines that can
be used for the initial layout planning stage are developed. These guidelines are also
compared with those recommended for enhanced earthquake resistance, since when new concepts are introduced, the resistance to dynamic forces could be considered as
important. The measures that can be taken to prevent cracking in such three storey
buildings are also presented along with cost effective foundation improving methods.
The cost implications of using load bearing brickwork for three storey residential
buildings were determined by carrying out a cost study. It is shown that the saving in a
house of about 200 m2 of total area could be in the range of Rs 100,000/= when compared
with the corresponding reinforced concrete framed building. Such cost savings are
extremely important for middle income earners since the bank loans are often used for
financing the house construction. Thus, it is shown that three storey residential building construction with load bearing brickwork can have many advantages such as cost effectiveness, thermal comfort, saving in land area and possibility of creating a comfortable micro climate around the house.Senate Research Gran
Thermal and environmental performance of precast building system
No full textBuildings are the living spaces of human beings that usually get-to-gather for number of times and occasions during a day. Quality standard spaces create more secure, comfort and convenient spaces for its users and can provide many advantages in all processes of the building construction, users as well as other supplementary equipment designers. The precast building systems provide some advantage to design quality standard spaces with more secure, comfort and convenience.
This research had been conducted to study the thermal and environmental performance of buildings which were constructed using Expanded Polystyrene (EPS) based lightweight wall panels and these building performances had been evaluated through testing of thermal material properties and computer simulation of the buildings. ASHRAE standard for comfort condition is used to develop computer modelling.
Testing of small scale model and real scale model were developed under this research study and carried out in locations in Colombo and Tangalle, respectively. Testing is carried out over a two weeks period and observations are discussed in this research study. Another model house, which is located in Jaffna, was evaluated and identified significant variation due to EPS based light weight panel used as walling and celling material.
Building design strategies were considered for design of thermally comfortable houses and ECOTECT and Climate Consultant 6 software were used to simulate and generate the design strategies. Based on these strategies, a new house plan was created as a model house for dry zone of Sri Lanka to be located at Polonnaruwa. The ECOTECT simulation showed that building could achieve a reasonable thermal performance by applying the strategies identified based on Climate Consultant 6
Feasibility of using presently used pre-cast sections for M-beam type bridges
No full textFor the rapid economic development of Sri Lanka, the upgrading of transportation
facilities is one of the main criteria to be fulfilled. In this context, there may be an
increase in the construction of bridges which will need more money. This can not be
afforded by a developing country like Sri Lanka, which can not allocate too much money in construction work. So it is advantageous to carryout research, aimed at reducing the cost of them.
Most commonly used deck type for the bridges constructed in Sri Lanka is pseudo slab type bridge decks. For this type of decks, inverted T-beams are used with in-filled decks. So the cost of these types of bridge decks can be considerable. This can be reduced to some extent by adopting the M-beam type of construction with in-situ top slab. For this type of construction, it was decided to check with inverted T-beam sections, since they are readily available in Sri Lanka.
Feasible spans of the standard sections of inverted T-beams for top slab constructions
were found by trial and error. Magnel diagrams were drawn to get the feasible regions of cables positions. To facilitate the checking of these sections a spreadsheet was prepared to do the design calculations. A cost comparison was done to find the most economical deck type out of two types of bridge decks. From the results got by the case study, it can be seen that the available T-beam sections can be used for the shorter spans with the top slab construction than when they are used in the in-filled construction. Even though the reduction of span is about 2.0 m to 2.5 m, the reduction of dead weight of the super structure is considerable which may cause the reduction of foundation sizes, especially in the case of shallow foundations. As per -the results got from the cost study, it was found that the reduction of cost of construction of the superstructure is also reduced to some extent due to the adoption of the top slab construction
Development of disaster resistant school buildings
No full textThis study quantifies the seismic vulnerability of typical three storied classroom building located in Sri Lanka. A significant feature of this reinforced concrete frame building is that this has been not designed even for wind forces. Besides, there are some infill masonry brick walls, which are not arranged effectively to resist horizontal loads.
At the inception of this study, a literature review was carried out to get general knowledge on seismicity around Sri Lanka, behavior of reinforced concrete frame structures at seismic loadings, contribution of masonry infill walls to resist seismic effects.
Subsequently Shortcomings of this existing school building were investigated. In order to eliminate some of the shortcomings a existing building was modified to and also designed a new building to have more disaster resistance features.
The performance of all the three models was investigated at probable earthquake according to Australian Standard AS 1170.4. The static analysis and response spectrum analysis was used for investigation of performance. It was observed that substantial damage can be occurred to the existing three storied classroom building due to probable earthquake.
Besides, a cost analysis was carried out to evaluate probable cost increases associated with new building
Comparative analysis o n simply supported pre- stressed box beams in Sri Lankan highway bridges
No full textThe 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
Embodied analysis of a precast building system
No full textBuildings are evolving throughout the history of mankind. When a new building system is introduced, the usual evaluation method is the monetary value. The adaptability to the climate conditions, structural capabilities and constructability are some other criteria for the evaluation. The building industry is consuming a vast amount of natural resources and also been responsible for a significant energy usage. With the recent developments in the environmental concerns all over the world, there is an increased the attention for the building sector. Due to the above reason new buildings have to be more environmental friendly than more conventional building systems.
A novel walling system has been considered in this study, which consist of lightweight foam concrete panels manufactured with recycled expanded polystyrene (EPS) up to 50% of the total volume. Even though those panels have lot of advantages over the conventional construction methods, they need to be compared with the other conventional methods for the environmental aspects. Embodied energy analysis is such an established method to quantitatively analyse the environmental impact caused by a product. Therefore, detailed study was carried out to determine the embodied energy of those foam concrete panels. A comparative study carried out using a typical single storey and for a two-storey house and different building materials.
Final results done for the case studies, indicated that houses constructed with cement sand blocks has the least amount of embodied energy and embodied carbon. However, houses constructed with EPS based lightweight foam concrete precast panels, can be a good competitor in terms of embodied energy and embodied carbon analysis, since it yields results much closer to the cement sand blocks. Reduced sand usage of EPS panelled walls is also an added advantage. Hence, it has the potential to be promoted as a mainstream walling material
Structural design of prestressed concrete continuous double tee beam bridges
No full textOne of the applications of prestressed concrete is in continuous bridges. These can be
either double tee or box girders. The longitudinal shape can be prismatic, semi-prismatic or non- prismatic. The design of these bridges otTer a considerable challenge to the design engineer due to the presence of secondary moments which are induced due to the prestressing forces. These introduce a considerable complexity to the design process. In this research, an attempt is made to develop a design method that would minimize the complexity associated with the design of prismatic prestressed concrete double tee bridges.
In concrete bridges, generally the minimization of self weight is important. This is used as the criterion to start the design process. The governing criteria for the various
components of the cross section is used to determine the smallest section that is practically possible. The methods to take account of short term and long term effects such as creep and shrinkage are also included for the cross section selected. Once the cross section is available, it is necessary to find appropriate cable forces. Design methods for both constant and variable cable forces are presented based on the line of thrust. It is shown that the use of variable cable forces could reduce the total cable forces thus leading to a saving in tendons.
For the selected cable forces, it is necessary to ensure that cable profile will be available within the selected section. The line of thrust can be transformed to fit within the section by selecting a suitable set of secondary moments. Thus, the secondary moment can be selected in a straightforward manner for both constant and variable cable forces.
Thus the cable profile selected should ensure that it fits within the limits of cable profile zone and also generate the selected secondary moments. This is not a trivial task. In order to simplify this task, a design method was introduced for both constant and variable cable forces. In the case of variable cable forces, there is a possibility to
have point moments and forces acting at the cable force change points. A method to deal with such forces is also introduced.
Therefore, it is possible to consider that this thesis presents a complete design method for the preliminary design of prismatic double tee prestressed concrete beam bridges either with constant or variable cable forces. It has also shown that it is possible to minimize the complexity of difficult design tasks by approaching the problem in modular fashion.
Keywords - Prestressed Concrete, Double Tee bridge
Development of cable stayed bridge in Sri Lanka
No full textThe up gradation of infrastructure facility is very important for the economic advancement of a country. The transportation sector plays an important role in rapid development of rural economy which contributes a lot to the country. The rural roads and bridges arc to be upgraded to achieve this target. A large number of bridges which are the costly items arc required at least for light traffic to improve the rural road network and link roads. So, it is useful jo introduce some cable stayed bridges for vehicular traffic that could be designed and constructed with the available local experts.
It is necessary to make sure that an accurate analysis and design techniques arc applied when a cable stayed bridge is designed for vehicular traffic. Three dimensional computer model is used in this study to apply the relevant loadings and load combinations to structurally and dynamically analyse the structure. The output of this analysis gives the necessary information for the structural design. The final structure could be designed with some reasonable engineering judgement without any approximate analysis.
The bailey bridge components such' as deck plates, transoms, panels, bracings and other accessories are used in this modeling. The assembling detail of deck is available in the bailey manual. The technique for constructing the bridge with local expertise is also considered
Delayed ettringite formation in large concrete sections and its prevention
No full textDelayed 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
Passive techniques for energy efficiency of buildings in Sri Lanka
No full textRising demand for electricity is a major contributory factor to the energy crisis that Sri Lanka is now facing. One potential candidate for energy conservation is the domestic sector. By way of adopting an environment-friendly solution (i.e. a passive solution), there remains a potential to achieve indoor thermal comfort in houses, thus reducing, or sometimes even totally eliminating, the need for active means such as fans.
The main objective of this study is to conserve electricity in the domestic sector of Sri Lanka, by developing a set of guidelines for the achievement of indoor thermal comfort at houses in the low altitudes of Sri Lanka through passive means, which are
energy-efficient and environment- friendly.
In order to achieve the above objective, the following methodology was adopted in the study. A comprehensive literature survey was conducted to determine the passive concepts and techniques desirable to warm humid climatic conditions prevailing in the low altitudes of Sri Lanka. Then, in order to identify the undesirable features of the building envelope with respect to thermal comfort and the indoor temperatures that occur in reality, a series of thermal and comfort surveys was conducted at several existing buildings, mostly houses. In order to identify the current situation with respect to thermal comfort and their preferences which would be crucial in developing a solution, a pilot questionnaire survey was conducted among a group of adults. A series of computer simulations was carried out using the software DEROB-LTH on a simple model to determine the effect of various features of the buildings envelope on indoor thermal comfort since such simulation software is quite good in predicting the trends.
Using the findings of the literature survey and the results of thermal surveys, comfort surveys and computer simulations, a comprehensive set 'of desirable and undesirable features with respect to indoor thermal comfort was prepared. Incorporating desirable features and eliminating the undesirable ones whenever possible, a set of conceptual
house plans of various floor areas and catering to the requirements identified from the questionnaire survey, was developed. A set of land subdivision guidelines suitable to develop a passive housing scheme was developed, highlighting the need for an integrated approach for energy conservation. In addition, two sets of guidelines for the enhancement of indoor thermal comfort were developed for a house being planned and for an existing house
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