Theses supervised by Giray Özay
10 theses · Eastern Mediterranean University
Comparison of 1975, 1998 and 2007 Turkish Earthquake Codes on Selected RC Buildings
Throughout the years Turkey has encountered several disastrous earthquakes that had done major losses in lives and in the economy. The loss was huge and that brought the attention of Ministry of Public Works in Turkey to revise and update their design codes. Turkish Earthquake Codes have been updated and improved to meet the safety levels that are needed for this seismic area. In this thesis, the 1975, 1998, and 2007 Turkish Earthquake Codes are compared. Six different case studies were chosen and designed with different elevations; four case studies containing different type of irregularities while the other two are regular designs. The non-linear static pushover analysis method presented in TEC-2007 was chosen for evaluating and understanding how these buildings behave under a seismic activity. Moreover, the performance, the cost and the damage percentages of the buildings in respect to each of the 1975, 1998, and 2007 Turkish Earthquake Codes were conducted. Subsequently each case was investigated to find out the performance of each code in the event of an earthquake. The study has identified that the 1975 Turkish Earthquake Code is dangerous to follow in seismic activity areas due to most cases not meeting the safety criteria. While on the other hand, the 1998 and 2007 Turkish Earthquake Codes has been identified as safe to follow with minor differences. Keywords: Earthquake, Turkish Earthquake Code, non-linear static pushover, performance, cost, damage percentages.
Collapse Vulnerability of Reinforced Concrete Buildings Using Neural Networks
In this study, an Artificial Neural Network (ANN) analytical method has been developed for evaluation the collapse vulnerability (earthquake performance) of reinforced concrete (RC) buildings . In this study, collected total of 260 reinforced concrete buildings with 4 storey, that were chosen to represent the existing RC buildings. The commercial program Sta4CAD is used for modeling and analysing these buildings. The performance analysis of these 260 RC buildings have been used for training neural networks. The parameters that affect on earthquake performance represent the input and the performance represent the output. In this study 16 parameters have been thought to be effective on the performance of RC buildings were considered: Torsional Irregularity (A1), Slab Discontinuities (A2), Projections in Plan (A3), Weak Storey (B1), Soft Story (B2), Discontinuity of Vertical Structural Elements (B3), Weak Column – Strong Beam (C2), Stirrup Spacing (cm), Average Shear Wall Ratio, Average Column Ratio (CA) , Concrete Compression Strength (C), Type of Steel (Fy), Soil Type (Z), Turkish Earthquake Code (1975– 1997- 2007), Earthquake Zone (EZ) and Importance Factor (I). The output parameters are the Structural Performance (S1-S4) was obtained based on the 4 performance levels in Turkish Earthquake Code-2007 (TEC-2007). The performance analysis of RC buildings was performed according to both the linear performance analysis and nonlinear (static pushover analysis) procedures as specified in TEC-2007. iv The effect of each parameter tested in this study had various affecting ratios on the earthquake performance of the structure. It was found that shear wall ratio is the most significant structural components that affect. The projections in plan and slab discontinuities were determined to be the least significant parameters. According to the study, the prediction accuracy of ANN has been found 90% accuracy for nonlinear (pushover analysis method) and about 89% accuracy for linear performance analysis method. Keywords: Artificial neural network, collapse vulnerability, earthquake performance based design.
Common Defects and Structural Problems in the Buildings of Northern Cyprus, their Reasons and Prevailing Applicable Solutions
In the recent years, building sector grows rapidly parallel to the human needs. Sometimes these quick productions cause several types of problems on the buildings. These problems occur in varying intensities depending on the type, location, environment, materials and the construction conditions of the building. Problems and failures in buildings can be broadly attributed to either defects, deteriorations or structural problems. Mostly, these defects or structural problems arise due to error or omission that is breach of contract or negligence by designer, contractor, or user. In general, lack of care and knowledge in specification or workmanship are the main reasons of various defects and structural problems. On the other hand, deterioration is natural process, which may be unavoidable, although minimized by care in design and the selection of materials. Cracks, efflorescence, peeling on painting, mouldiness, rising dampness, soft storey, short column, shear cracks, compression cracks, irregularities in plan, irregularities in elevation and etc. are some of the most significant problems that occur in building of Northern Cyprus. These defects, deteriorations and structural problems have negative effects both on human and building lives. They mostly harm to the health and economy. Besides, they reduce the aesthetic quality. On this basis, the aim of the study is to discuss these prevailing defects and structural problems with their reasons which occur in North Cyprus. It is also expected to present the most common precautions and available applied methods for preventing or reducing these problems. Work to be carried out: 1. General search about the building defects and structural problems and categorization. 2. According to the first step (researches), the most common precautions and available applied methods for preventing or reducing these defects and structural problems were investigated and presented. 3. Case studies in different districts of North Cyprus were visited and the collected data were analysed and compared. There are a total of 125 case studies in this thesis divided into two samples. The first sample represents completed buildings contains 100 case studies consisting of 25 case studies for each of the four following districts: Mağusa, İskele, Lefkoşa and Girne. This sample is aimed for the study of reinforced concrete defects and non-structural defects. The second sample represents buildings under construction contains 25 case studies. This sample is aimed for the study of seismic design faults.
Evaluation and comparison of strengthening methods to deliver a safe, efficient and economical solution
The challenges posed in the choice selection of strengthening methods to strengthen old existing buildings which might be exposed to external loads, poor concrete grade, poor construction and review in codes has been of concern recently. Through the various guidelines for building evaluation, strengthening and with innovative structural codes for design, building assessment and strengthening are carried out using newly developed technologies worldwide. Basically, there are two major categories of strengthening; local and global methods. Local method is focused at the element level on structural members which are deficient and need improvement to perform better. This method includes adding composites, concrete or steel on the surface of a structural member. They are all effective but also have their disadvantages, while the global method acts on the structural level. Its application will lead to obtaining the behavior of the entire structure. This method consists of addition of steel bracings, shear walls and infill walls. These methods equally have their effectiveness and disadvantages. In this study, strengthening methods were discussed considering its advantages and disadvantages where some application procedures were as well highlighted. The procedures for building assessment were also discussed. A coded decision selection program for strengthening methods were constructed which will help for selecting the best option from strengthening methods. Coded strengthening programs for fiber reinforced polymer (FRP) were also prepared and it gave the same result with the referenced FRP strengthening. Two case studies were carried out in other to compare the result with the coded decision selection tool. The cases studies were modeled and designed with structural software such as STA4CAD, CSi COL and Engissol structural software. The selection tool and the case studies gave the same result for the strengthening option. Both have shown that shear wall strengthening is the best option for strengthening the two investigated buildings. The economic evaluation of the materials used in different strengthening method studied, has shown that, shear wall is the least in the cost of strengthening. Therefore, shear wall strengthening method is cheaper, efficient and has significantly contributed to the overall strengthening and improvement of the performance of the considered building. Keywords: Strengthening, Performance, Global Strategy, Local Strategy, Ductility.
Evaluation and Comparison of Different Structural Systems According to Earthquake Loads
To a certain extent, the performance of seismic analysis and design requirements for a building is considered as a substantial subject amongst Civil Engineers. In general, the lateral force resisting system is the structural system that resists against lateral forces in a reinforced concrete structure while the structures are under seismic excitation. Therefore, the structural system consisting of different lateral force resisting systems, such as the shear walls, coupled shear walls and stiffened coupled shear walls are used in majority of the tall buildings. On the other hand, the tunnel formwork is one of the common structural types in regions prone to high seismic risk due to the inherent earthquake resistance of buildings. This study attempts to introduce the safest and the most economical system using different lateral force resisting structural systems of a reinforced concrete structure. These different structural systems are tested with different story levels for the purposes of predicting the safest and the most economical system. With this objective in mind, a parametric study was carried out based on the modeling of different structural systems of a reinforced concrete structure such as the flat slabbeam, the shear wall, the coupled shear wall, the stiffened coupled shear wall and the tunnel formwork system, with seven different story levels (i.e. 2, 5, 10, 15, 20, 25 and 28). These structural systems were considered as case studies that were subjected to seismic excitation loading by using the STA4-CAD software. Turkish Earthquake Code-2007 and the Turkish Standards-500 were used with a linear performance analysis method to obtain the structural design of each case study. Out of the five currently available structural systems, the flat slab-beam and the shear wall systems were proved to be appropriate for different story levels. The safest and the most economical systems were those with up to 5 stories. The tunnel formwork system was proved to be appropriate for different story levels with 10, 15, 20, 25 and 28 story levels. The analytical results of that system are in parallelism with the results of other structural systems in terms of finding the safest system. Also, the results of the tunnel formwork system indicate that as the most economical solution when compared with the total construction cost of others structural systems. Keywords: coupled shear wall, stiffened coupled shear wall, shear wall, tunnel formwork and Turkish Earthquake Code-2007
Pushover Analysis and Incremental Dynamic Analysis of Steel Braced Reinforced Concrete Frames
The recent earthquakes in some part of the world showed the disastrous effect on civilian areas. Most of the existing RC buildings designed only considering gravity loads without seismic design criteria. Therefore, an accurate knowledge is extremely necessary for those buildings that need seismic retrofitting. Steel bracing system can be considered as the most reasonable solution for seismic performance enhancing of RC buildings. The use of steel braces for retrofitting or strengthening seismically deficient RC frame is a reasonable solution for upgrading seismic resistance. Steel bracing is easy to erect, has the flexibility to design for meeting the required stiffness and strength, occupies less space, and economical. This study discusses the seismic behavior of RC buildings strengthened with various types of concentric steel braces, Diagonal-braced, Inverted V-braced, Zipper-braced, and X-braced. The models that have been studied are 3-storey, 6-storey, 9-storey and 12-storey buildings of which are designed by using Etabs. The static pushover analysis and incremental dynamic analysis have been conducted utilizing Seismostruct software to estimate the lateral capacity and compare the results of all the frames and bracing types. It is observed that adding braces upgrade the global capacity of the buildings in terms of lateral load capacity, displacement and stiffness compared to the cases with no bracing, and the X-braced systems performed much better than the other types of bracing. Keywords: Earthquake, Seismic design, Retrofitting, Steel bracing, Pushover analysis, Incremental dynamic analysis.
A Comparison between the 2007 Turkish Earthquake Code and the Eurocode 8 for Sample Buildings
Earthquake are a natural phenomenon caused by the shifting of tectonic plate in the crest layer of the earth. Based on its magnitude it can cause a catastrophic effect on structures which expose people to losses in lives and money. The 2007 Turkish Earthquake Code and the Eurocode 8 are among many design codes that are concerned in the safety of buildings from future earthquakes. In this thesis, the 2007 Turkish Earthquake Code and Eurocode 8 are compared. Five different cases were chosen and designed, with each case study containing different type of irregularies. For the sake of evaluating the designed structure with regards to earthquake, the non-linear static pushover analysis method presented in TEC-2007 was chosen for 3 floor and 5 floor buildings. Finally the performance, the cost and damage percentage of each Eurocode 8 case with its 2007 Turkish Earthquake Code counterpart have been compared using three different analysis cases which represent different combination of spectrum, A0 and behavior factor. At the end each case was compared to find out the performance of each code in the event of an earthquake.
Earthquake Performance of Reinforced Concrete Frames with Different Infill Walls
Infill walls are used frequently as interior or exterior partitions in reinforced concrete frames in the world. The behavior of infill wall frames have been studied experimentally and analytically by a number of researchers and it has been recognized that infill walls have important effects on dynamic characteristics of structural system. However, these effects of infill walls neglected in analysis of buildings. For this reason, the horizontal rigidity effect of infill walls has not been proven to be a valid model. Therefore, infill walls generally defined as dead load in the analysis to stay on the safe side but ignoring the infill panel interaction is not always on the safe side under lateral loads. It may adversely affect the structural system during an earthquake. The main purpose of this study is the effects of infill walls on the structural behavior which are not accounted in the structural design of reinforced concrete buildings. For this purpose, nonlinear analyzes were performed using dissimilar modeling methods proposed by different researchers. These methods were analyzed using different analyze softwares. Three separate building systems were used for each different method. Hence, diverse building models have been created and the behaviors of these structures under lateral loads have been investigated in order to identify the effects of infill walls. Each building model created was analyzed in three different situations including bare frame, the frame with brick infill wall and the frame with Autoclaved Aerated Concrete (AAC) infill wall. Hereby, the outcomes obtained from analysis on bare frame and the frame with infill walls has been compared. At the end of the analysis, it is observed that infill walls have significant effect on structural period, lateral displacement, base shear force and structural behavior. Keywords: Infill wall, structural period, lateral displacement, base shear force, earthquake
Seismic Behavior of Reinforced Concrete Frame Structures with and without Masonry Infill Walls
Brick walls are often used as an infill element serving as partitions or as cladding in structure frames. In structural frame design method, infill walls are usually considered to be inert “nonstructural” elements and known for affecting on strength, stiffness and post peak behavior of the structure. The structure is assumed to carry the transverse loads by the frame elements resisting primarily in flexure. Often action of infill wall in frame analysis is ignored in the seismic area which is not on safe side and creates a major hazard during earthquake. RC frames having brick walls are a universal practice in countries like Turkey, where the region is prone to seismic activity. The structures in high seismic areas are greatly vulnerable to severe damages. Apart from the gravity load structure has to withstand to lateral load which may develop high stresses. Nowadays reinforced concrete frames are most common in building construction use around the world. In this study, all the case studies are design under Turkish Building Codes TS 500 and Turkish Earthquake Codes TEC2007. An extensive analysis of typical RC building configurations, including brick masonry infill walls arranged either regularly or irregularly (creating soft-storeys) has been carried out. Pushover analysis method was carried out in SeismoStruct. Each case was compared to find out the performance of brick wall on RC frame.
The Seismic Response of Reinforced Concrete Structure with Viscous and Friction Damper
Dampers are the energy dissipating devices which resist lateral loads and displacement in reinforced concrete structures. Viscous and Friction dampers dissipate partially the earthquake energy into heat which is transferred in return into the atmosphere. In order to check the effectiveness of viscous and friction damper in reducing earthquakes effects, time history and pushover analysis are conducted into reinforced concrete buildings of different stories levels (five, ten and twenty stories) with and without both type of dampers. In addition, the performance of viscous damper is compared to that of friction damper to find the variation between both types of dampers in dissipating earthquake energy. This comparison is performed by implementing friction dampers in the same places which viscous damper are implemented on and by achieving same analysis methods done for structural buildings with and without viscous dampers. Furthermore, for finding the optimum location of dampers in external structural frame, viscous and friction dampers are placed in three different locations in outer frames for each story level during time history and pushover analysis. In other words, this study deals with studying the effectiveness of viscous and friction damper, comparing the performance of both types of dampers and finding the optimum locations of VD and FD in external frames. Viscous damper had the priority over Friction damper in improving the seismic response of structural building and the optimum location of dampers was the middle position of the outer frame.