thesis on structural studies

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First page of “Thesis on Concrete Structural Design for Sustainability (Optimising Structural Form) 2013”

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Thesis on Concrete Structural Design for Sustainability (Optimising Structural Form) 2013

Concrete structures have been designed throughout history by paying attention to their form. Before the invention of reinforced concrete, it was imperative to design a concrete structure that took mainly if not entirely compressive loads. This was done to avoid the relative weakness of earlier building materials, including unreinforced concrete under tensile loads. These form-active concrete structures are potentially the most efficient concrete structural components with regard to their load carrying capacity in relation to their weight. Form-active design is more complex since it requires an understanding of the shape the concrete structure would take under a particular load if it had no bending stiffness, i.e. if it were to behave like a cable. Due to the high structural efficiency, form-active structures play an important role with regard to sustainability. They use less material to achieve higher load carrying capacities, and therefore they reduce the use of natural resources. This thesis focuses on concrete floor slabs in residential buildings and small commercial buildings. The aim is to study the behaviour of these slabs under loading and analyse how structural form considerations can lead to better design solutions. These structural components were chosen due to their significant contribution to the construction of both residential and small commercial buildings. However, this choice imposes certain restrictions in the freedom of designing form-active structures; i.e. dimensional restriction such as depth of the slab, flatness of the slab on the top surface, etc. These restrictions are important since they determine whether the slab will be able to correctly perform its function. The analytical methodology involved designing a set of traditional solid slabs and improving their designs according to material and cost optimisations. These slabs were then compared with form active slabs which were designed to take the parabolic shape of their bending moment diagrams. From an analysis of the designs, it was found that form active slabs are approximately two times more efficient than the traditional solid slab. This efficiency is with regard to load carrying capacity and the amount of material used, both concrete and steel. The reduction in the concrete used for a form-active slab with the same span as a traditional solid slab, can be approximately 60% and that of steel can be approximately 70%. These values are a clear indication that the consideration of structural form can lead to better and sustainable solutions. One way spanning slabs can be applied to both residential and small commercial buildings since these buildings are commonly constructed as post-and-beam structures, with discontinuous joints. Furthermore these buildings have significantly lower and more predictable loads than other types of buildings. This helps with regard to avoiding failure by unexpected excessive point loads. Larger commercial and institutional buildings such as malls, hospitals, etc. can also adopt the application of one way spanning form-active slabs. This is because of the common attribute most of these buildings have, which is large hallways and corridors, which are suitable application areas for these types of slabs. This thesis has in this regard successfully shown the economical and sustainable advantages of concrete structural design through the consideration of structural form by investigating the special case of one way form-active slabs.

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In the current office building construction practice, flat plate is the most common floor structural system due to its economic and practical advantages. Traditionally, high material costs have had a great impact on total construction cost, so voided options as ribbed or waffle slab have been used extensively. However, recently there is a tendency to design solid slabs options, especially due to rising labor costs, simpler and quicker construction, which reduces execution timeframe and increases construction safety. The use of post-tensioned (PT) floors in building structures has been growing in recent years. This type of construction allows thinner slabs and thus, it creates lighter structures, produces a large reduction in rebar tonnage, with the subsequent advantages in transportation, storage or labor. Also, these slabs have other advantages as reduced cracking and deflections, reduced floor to floor height or quick construction. In most countries these design mechanical and economical features have enabled the system to compete economically with traditional in-situ concrete floor slabs; however, this is not the case in some other countries like Spain. Introduction of sustainability criteria and specialization in construction can allow for this system to be introduced in the market, which can also mean lower costs, improved performance and focusing on sustainability in construction. Different solutions have been studied for an actual project, in terms of material quantities, minimum structural thickness and it has also been checked the impact of costs and environmental criteria based on CO2 emission. With these data, we could assess that the current status of low production of flat slabs in Spain it is not related to real economic reasons; it is actually related to a combination of reasons as lack of technical knowledge of designers or builders, inconsistencies or deficiencies in current national codes in each country. The construction industry is following an inertial period that resists changing known systems, apparently satisfactory, and that especially shows an unsustainable view of the construction. Post-tensioned concrete slabs will not always be the most suitable and sustainable option, but it should be evaluated while considering other more familiar techniques of construction with updated considerations.

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Flat slabs and other similar slabs are preferred in those structures having larger spans. Due to advancements in civilization emphasis has been put on the construction of newer and more advanced structures like buildings, shopping malls, airports, railway stations, etc. This led to the use of flat slabs for safety, stability, and better design. This works deals with the analysis of critically flat slabs regarding their design, stability, and uses. Cost-benefit analysis gives the economic viability of the use of flat slabs in comparison to other types of slabs. Different design methodologies have been adopted and critically reviewed and inferences are made for the selection of the particular method of designing the flat slab. Using various codes during design are also used for the purpose. The stability of flat slabs under different situations has been critically studied. In civil engineering uses different types of slabs are used in buildings, parking, etc. Using flat slab buildings has numerous benefits over standard RC frame buildings in terms of simpler formwork, space use, architectural flexibility as well as quicker construction times. The analysis demonstrates that flat slab structures are lighter than traditional slab structures. When compared to a standard slab, a flat slab structure is 15 percent less expensive. As per the study's results, flat slab structures outperform traditional slab structures in terms of cost-effectiveness for high-rise structures. Flat slab structures result in financial savings, aesthetic views, and greater artistic flexibility for the architect in contrast to typical slab structures. Structures of the flat slab are the highest selection for high-rise structures in comparison to traditional slab structures.

The paper presents a set of design criteria applied in the structural design of a 25000 sqm, multistory concrete building. Initial criterion of having reduced execution time have been associated to a mixed steelconcrete structure, but the consequent, unavoidable cost criterion drove to reinforced concrete structural solutions. Beside the presented criteria several other limitations have been imposed in the design phase, rising from the specific destination of the building, the limited total building height and limited plot of land, without disclaiming the need for a short construction time. Nevertheless energy efficient, sustainable structural solutions have been requested, which have to be in accordance also with the spirit of the imposed architectural solutions. In the article a multi-criteria comparison of the structural solutions is presented, focusing on the two main criteria: the realization costs and the embedded energy of each structural solution. Evaluation of the obtained ...

Most of the reinforced concrete structures comprise of conventional beam-column frames. In the present era, the multi-story structures are given higher priority with lack of availability of land. However, there are limits for the height and weight of the structures. Thus, the construction industry is more concentrated on measures to reduce the weight and height of the storey, without compromising with usable space. The flat slab structures serve the purpose as they are the structures involving slabs directly resting on columns; hence, negating the need for beams, which would consume lot of space and also lead to heavy weight of the structure. Even though, flat slabs are found to be advantageous in functional as well as economic aspects; the key issue with flat slabs is their inability to withstand lateral loads efficiently. In the present study, the seismic behaviour of flat slab structures is studied. The 7 storey building models involving flat slab without drops, with drops and with edge beams are modelled considering both bare frame and brick infill frame structures with square columns. The buildings are located in medium soil cover with seismic zone III. The analysis is performed using ETABS 2013 V13.2. The non-linear behaviour of the building models is studied by pushover analysis, considering FEMA 440 parameters. The prime emphasis is made to consider user defined hinge properties to establish the actual hinging pattern of the members. The performance of the building models is studied by evaluating the parameters like hinge locations, ductility ratio, safety ratio and global stiffness.

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Milan Kekanović DeagoslavŠumarac Stanko Ćorić Karolj Kasaš Arpad Čeh UDK: 692.5:697.1 DOI:10.14415/konferencijaGFS2017.077 Summary: This article provides information about the possibilities of design and construction floor slabs concerning three very important aspects: the capacity, safety and energy efficiency.Nowadays, in the Republic of Serbia exclusively solid concrete slabs are designed and built,which are at least 20cm thick.The justification for this solution is to obtain, in its plane, a rigid plate-diaphragm that is able to endure seismic forces on the walls, proportionally to the stiffness of those walls.At the same time this solution has many disadvantages and it is a great load that limits the length of the span. That heavy load is directly proportional to the size of the seismic forces. The20 cm thick, solid concrete slab has a large heat capacity, and specific heat c (J / kgK), which are not energy efficient,as the warm air is accumulated, conductedtowards to the walls...

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