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Evaluation and improvement of seismic performance of existing irregular reinforced concrete buildings

Number of pages: 186 File Format: Not Specified File Code: 29394
Year: Not Specified University Degree: Not Specified Category: Civil Engineering
Tags/Keywords: building - earthquake - structure - the wall
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  • Summary of Evaluation and improvement of seismic performance of existing irregular reinforced concrete buildings

    Bachelor thesis‌ Master of civil engineering, structure orientation

    September 2013

    Abstract

      Today, with the progress of science in the construction industry, many methods have been presented to improve reinforced concrete structures, among these methods is increasing the hardness with the help of reinforced concrete shear wall system. In the improvement of the structure, it is tried that the structure, in addition to having the necessary hardness against the ground vibrations caused by the earthquake, is also able to depreciate the energy caused by these vibrations.

      In the reinforced concrete shear wall system, in addition to providing the hardness required by the shear wall, the improved structure will have a high ability to absorb and dissipate energy. In this research, first, models were designed using the first edition of the 2800 regulations and after checking the vulnerability (by the guidelines for seismic improvement of existing buildings in Iran), they were improved using this shear wall system and while checking the outputs, the proper performance of this system on the structure as an efficient and acceptable system was discussed.

      In this research, in order to investigate the effect of shear wall system in concrete structures, first, three three-dimensional models were designed by the first edition of the 2800 code in Etabs v9.5 software, and then improved by PERFORM 3D V4 software after checking the vulnerability of the reinforced concrete shear wall system.

      The results of this research show that the use of the shear wall system has improved the seismic performance of all three models, so that by adding the shear wall system to the studied models, the ductility of the structure has increased by 19 to 76 percent, the amount of energy loss has increased by 23 to 37 percent, and the base shear of the floors has decreased by 33 to 50 percent. In addition, the relative displacement of the floors is mostly reduced and becomes uniform. In fact, the use of shear wall system, in addition to increasing ductility, reduces the seismic demand of structures and improves the performance of structures.

    Key words

    Seismic improvement, reinforced concrete structures, reinforced concrete shear wall, design based on performance level.

                                                         Chapter One

      General research

    -1-Introduction

      The inevitable occurrence of earthquakes and the infliction of many human and financial losses, especially the devastating earthquakes that have occurred in recent years in different parts of the world, emphasize the need to find a suitable and reliable solution to deal with this natural phenomenon. Among the destructive earthquakes  We can refer to the Tabas and Manjil earthquakes in Iran in 1978 and 1977, respectively, and the Centro earthquake in 1994. The statistics and figures of casualties and damages caused by earthquakes indicate that it is important to reconsider many methods of dealing with seismic forces or to think of safer alternative methods. Today, one of the main ways to achieve this goal is to apply and present new methods in the concepts of seismic design of structures and quality improvement of consumable materials.

      A structure that is designed for an area with a strong earthquake risk. It must have two important characteristics. First, it should have sufficient hardness to control the lateral displacement of the building in order to prevent damage to structural and non-structural components in moderate but frequent earthquakes. Second, it should have enough resistance and ductility to prevent the building from collapsing under severe earthquakes.But in this case limited structural and non-structural damages are allowed. Because the design of structures in such a way that they remain resilient in strong earthquakes with a low probability of occurrence is not economically viable.

      In conventional methods, the building resists earthquakes by using a combination of hardness and malleability as well as energy consumption. The amount of damping in such buildings is very low, therefore the energy expended in the range of elastic behavior of the structure is insignificant. During strong earthquakes, these buildings change places after the range of elastic behavior and remain stable only because of the ability to change their inelastic location. This change of inelastic places causes plastic joints to appear locally in the points of the structure, which itself increases the plasticity and also increases the consumption of energy. As a result, a large amount of earthquake energy is consumed due to local damage in the lateral resistance system of the structure.

      Due to attention to the way energy is distributed in a structure, another method has been considered in the world to reduce the effects of earthquakes. in  During an earthquake, a large amount of energy is imposed on the structure. This incoming energy appears in the structure in two forms, kinetic and potential, which must be absorbed or depleted in some way. If there is no damping in the structure, the structure will continue to vibrate indefinitely, but actually, due to the characteristics of the structure, some damping is created in it. which causes the reaction against the vibration of the structure and damping it. The efficiency of the building can be increased by adding energy attractors (formable elements) to the building.

      In such a way that these devices absorb and depreciate a part of the input energy of the earthquake alone, the amount of energy entering the structure during an earthquake is directly related to the periodicity of the structure and its ratio to the dominant period of the ground motion. Also, the damage caused to the structure is related to the amount of hysteresis energy absorbed under the inelastic forms of structural members.

    As mentioned before, the design of normal structures in such a way that they remain undamaged during a strong earthquake is uneconomical. Therefore, most of the building design codes have presented the seismic design philosophy based on the concept of deformability. Based on this, a structure must be designed in such a way that the required deformation of each member is in balance with its capacity deformation, so that during an earthquake, the energy in the member is reliably dissipated. On this basis, the following general criteria have been provided by various regulations.

    - Small earthquakes should not cause any damage to structural or non-structural members.

    - Moderate earthquakes should be the basis of the design and the building should be designed accordingly so that it can easily withstand the earthquake that caused it, without seeing significant destruction.

    - Strong earthquakes may cause serious damage to the building, but do not cause destruction and loss of life of its residents.

      The above process seems suitable for most normal buildings, but a safer process can be considered for the design of more important buildings or buildings that must provide services after an earthquake. In the improvement of the structures, it is also tried that the structure, in addition to having the necessary hardness against the ground vibrations caused by the earthquake, is also able to depreciate the energy resulting from these vibrations. In the shear wall system, in addition to providing the required stiffness, the improved structure will have a high ability to absorb and consume energy.

    The efforts of researchers in recent years in order to ensure the performance of earthquake-resistant buildings has led to the introduction and use of a new and reliable method called Performance Based Design, which by replacing this design method with force-based design, the behavior of structures in the face of earthquakes has improved, and it can be significantly more assured than the performance of the regulations. had new But on the other hand, there is an issue under the title of evaluating the performance of buildings designed based on the old method or design based on force, which is important considering that almost all existing buildings in our country are somehow included in this category, and the need for research with a guided process is obvious.

  • Contents & References of Evaluation and improvement of seismic performance of existing irregular reinforced concrete buildings

    Abstract

    Chapter 1 (research overview) 1

    1-1-Introduction..1

    1-2-Investigation of damage to reinforced concrete buildings in an earthquake. Design and spectrum of earthquake response. 6

    1-2-2-2- Brittle columns. 7

    1-2-2-3- Asymmetric arrangement of rigid elements in the plan. 7

    1-2-2-4- Soft ground floor. 8

    1-2-2-5- Short columns. 9

    1-2-2-6- Floor plan shape. 10

    1-2-2-7- The shape of the building in height. 10

    1-2-2-8 - Slabs without beams (flat slab). 11

    1-2-2-9- Damage caused by previous earthquakes. 11

    1-2-2-10- Single bending frame systems. 12

    1-2-2-11- Number floors. 12

    1-2-2-12- The effect of foundations. 13

    1-2-2-13- The location of adjacent structures in the building block. 14

    1-2-2-14-The effect of concrete characteristic strength. 14

    1-2-2-15-The effect of oscillation time. 15

    1-2-2-16- Damages caused by weak structural elements.17

    -2-2-16-1- Weakness of columns.

    Chapter Two (Measures to improve and control the seismic vibration of the structure). 21

    2-1-Introduction ..21

    2-2- Earthquake resistant structures. Hardness. 25

    2-3-3- Increasing plasticity. 27

    2-3-4- Reduction of local stiffness. 28

    2-3-5- Changing the use of the structure. 28

    2-3-6-Evaluation method based on performance. 282-4-Members controlled by force and deformation. 33

    2-4-1-Advantages of the control method based on performance. 36

    2-5- Criteria review 2-5-1- Basics of improvement

    2-5-4-1-1-Performance level 1-Continuous usability.38

    2-5-4-1-2-Performance level 2-Limited damage.38

    2-5-4-1-3-Performance level 3-Life safety.38

    2-5-4-1-4-Performance level 4-Limited life safety.39

    2-5-4-1-5- performance level 5- collapse threshold. 39

    2-5-4-1-6- performance level 6- not considered. 39

    2-5-4-2- performance levels of non-structural components. 39

    2-5-4-2-1- performance level A- continuous service. 40

    2-5-4-2-2-Performance level D-Limited life safety.40

    2-5-4-2-3-Performance level E- Not included.40

    2-5-4-3-Performance levels of the entire building.40

    2-5-5- Information on the existing condition of the building.41

    2-5-5-1- Information collection at the minimum level.41

    2-5-5-2-Collection of information on a conventional level.42

    2-5-5-3-Collection of information on a comprehensive level.42

    2-5-5-4- Knowledge factor.43

    2-5-6-Improvement solutions.43

    2-5-7- Strength of materials.44

    2-5-7-1- Expected strength of materials 44

    2-5-7-2- Lower limit of material strength. 44

    2-5-7-3- Characteristic strength of materials. 44

    2-5-8- Capacity of structural components. 44

    2-5-8-1- Linear methods. 44

    2-5-8-2- Non-linear methods. 45

    2-5-9-non-linear analysis methods.46

    2-5-9-1-non-linear static analysis (pushovers).46

    2-5-9-1-1-change of target location.48

    2-5-9-1-2-coefficient method.48

    2-5-9-1-3-capacitance spectrum method 51. 2-5-9-2-2- Figure of lateral load distribution in the height of the building. 52

    2-5-9-2-1- Limitations of non-linear static analysis (pushover). 54

    2-5-9-2-2- Advantages of non-linear static analysis (pushover). 55

    2-5-9-2-3- Non-linear dynamic analysis linear. 57

    2-5-9-2-4-non-linear methods acceptance criteria. 57

    2-5-10-adding a shear wall in an existing reinforced concrete building. 61

    2-5-11-the effect of adding a shear wall to reduce structural irregularity in the building. 61

    2-5-12-the history of using a shear wall In a concrete building. 64

    2-5-13-Regulations for the use of shear walls in existing concrete buildings. 66

    2-5-13-1- Adding shear walls and intermediate frames. 66

    2-5-13-2- Concrete shear walls. 67

    Chapter three (the building studied and its vulnerability assessment). 71

    3-1- Introduction..71

    3-2- Buildings under study..72

    3-3- Specifications of the existing building..73

    3-3-1- Geometric specifications of the building. Gravity loading..74

    3-5-Gravity load transfer system..75

    3-5-1-System resistant to side loads.75

    3-5-2-Specifications of materials used in the structure.75

    3-5-3 Gravity and side loading.76

    3-6- Side loading..80

    3-6-1- 10-story irregular buildings under study. 80

    3-6-2- 15-story irregular buildings under study. 80

    3-6-3- 20-story irregular buildings under study. 82

    3-6-2-Perform analysis..83

    3-6-4-1- Beam sections of the building Study. 87

    3-7- Qualitative evaluation of the vulnerability of the studied buildings. 88

    3-7-1- Improvement goal. 88

    3-7-1-1- Risk level.

    3-7-2-Performance level of the building.89

    3-7-2-1-Performance level of structural components.89

    3-7-2-2-Performance level of non-structural components.89

    3-7-2-3-Performance level of the whole building.90

    3-7-3-Determining the level of information and awareness factor.90

    3-7-4-Specifications of materials.91

    3-7-4-1-Concrete materials.91

    3-7-5-Acceleration maps.91

    3-7-5-1-Specifications of acceleration maps.91

    3-7-5-1-Specifications of acceleration maps.91

    3-7-5-1-1- Scaling the acceleration maps. 91

    3-7-5-1-2- Co-founding the acceleration maps. 93

    3-7-5-1-3- Earthquake records used in the analysis. 93

    3-8- Quantitative assessment of the vulnerability of buildings. 94

    3-8-1- Static analysis Nonlinear (Pushover) The target location for the 10-story building under study. 99

    3-8-1-2-Analysis. 101

    3-8-1-2-1-Definition of plastic joints. 101

    3-8-1-2-1-1-Definition of plastic joints in concrete beams. 101

    3-8-1-2-1-2-Definition of plastic joints in columns. 103

    3-8-1-3- Modeling parameters and acceptance criteria for non-linear methods – members controlled by bending..104

    3-8-1-3-Definition of different analysis modes (case)

    3-8-1-4-1- pushover analysis results of the 20-story building studied. 107

    3-8-1-4-2- pushover analysis results of the 15-story building studied. 109

    3-8-1-4-3- pushover analysis results of the 10-story building studied. 110

    3-8-1-5- Simultaneous effect of earthquake components 111

    3-8-1-6- Dynamic analysis of non-linear time history. 111

    3-8-1-6-1-Performing the analysis. 111

    3-8-1-6-2-Results of dynamic analysis of non-linear time history. 112

    3-8-1-6-2-1- Application ratio curves under different earthquakes for 20-story building case study 112 3-8-1-6-2-2-applicable ratio curves under different earthquakes for 15-story building case study 114 3-8-1-6-2-3-applicable ratio curves under different earthquakes for 10-story building cases

    Study..115

    3-9-Conclusion..117

    Chapter four (seismic improvement of the studied buildings). ..120

    4-3-1- Determining the change of target location. 120

    4-3-1-1-Change of target location for the studied buildings. 120

    4-3-2-Results of non-linear static analysis (pushover). 121

    4-3-2-2-Results of pushover analysis of the 15-story building studied after renovation. 123

    4-3-2-3-Results of pushover analysis of the 10-story building studied after renovation. 125

    4-3-3- Dynamic analysis of nonlinear time history. 126

    4-3-3-1- Perform Analysis. 126

    4-3-3-2-Results of nonlinear time history dynamic analysis. 127

    4-3-3-2-1-Applicable ratio curves under different earthquakes for the 20-story building under study

    After renovation.. 127

    4-3-3-2-2-Applicable ratio curves under different earthquakes for the building 15 studied floors

    after renovation. 129

    4-3-3-2-3- functional ratio curves under different earthquakes for the 10-story building under study

    after renovation.. 130

    4-3-3-3- Conclusion. Evaluation indicators. 133

    4-5-1 – Investigating the relative deformation of the floors. 133

    4-5-1-1- Comparison diagram of the deformation of the buildings 20, 15, and 10 under study before and after improvement. 134

    4-5-1-1- Comparison of the deformation results of the buildings 20, 15 and 10 floors under study. 134

    4-5-2- Hysteresis curve. 136

    4-5-2-1-The hysteresis curve of the 20-story structure studied before the improvement under the Tabas record. 136

    4-5-2-2-The hysteresis curve of the 20-story structure studied after the improvement under the Tabas record. 137

    4-5-2-3- Comparison of the results of the hysteresis curves drawn for the 20-story building under study. 137

    4-5-2-4-The hysteresis curve of the 15-story structure studied before the improvement under Tabas and Manjil record. 137

    4-5-2-5-The hysteresis curve of the 15-story structure studied after the improvement under the Tabas and Manjil record. 138

    4-5-2-6-Comparison of the results of hysteresis curves drawn for the 15-story building Study. 139

    4-5-2-7-Hysteresis curve of the 10-story structure studied before renovation under the records of Tabas and Manjil. 140

    4-5-2-8-Hysteresis curve of the 10-story structure studied after renovation under the records of Tabas and Manjil. 141

    4-5-2-9-Comparison of the results of hysteresis curves drawn for The 10-story building under study. 142

    4-5-3-Time history chart. 142

    4-5-4- Investigating the mechanism of energy loss in the structure. 146

    4-5-4-1-20-story building before renovation. 146

    4-5-4-2-20-story building after renovation. 147

    4-5-4-3-15-story building before renovation. 147

    4-5-4-4-15-story building after renovation. 148

    4-5-4-5-10-story building before renovation. 148

    4-5-4-6-10-story building after renovation.149

    4-5-4-7-Comparison of energy loss diagram results for 20 and 15-story building and 10 studied cases. 150

    4-5-5-Relative location change of floors. 150

    4-5-5-1- 20-story irregular building. 151

    4-5-5-2- 15-story irregular building. 153

    4-5-5-3- Irregular 10-storey building. 159. Sources. 160. English abstract. 163.

Evaluation and improvement of seismic performance of existing irregular reinforced concrete buildings
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