Phd Degree / Doktora

Permanent URI for this collectionhttps://hdl.handle.net/11147/2869

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Subject: search.filters.subject.Reinforced concrete

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Now showing 1 - 4 of 4
  • Doctoral Thesis
    Probabilistic Performance-Based Optimum Seismic Design of Reinforced Concrete Structures
    (01. Izmir Institute of Technology, 2023) Karımzada, Nisar Ahmad; Aktaş, Engin; Girgin, Sadık Can
    Traditional seismic design codes have been developed and used for decades to stipulate the rules for earthquake-resistant design of structures. They are mainly based on the Force-Based Design (FBD) approach and on some linear elastic techniques. The inelastic seismic response of the structure is not directly addressed in the traditional seismic design codes. The initial aim of the current seismic design codes is public safety. In seismic codes, some information is provided regarding the damaged states of structural components, while limited information is provided regarding the damaged states of nonstructural members. In addition, no clear information is provided regarding economic losses and business interruption. The Performance-Based Seismic Design (PBSD) approach, a reliable approach for the seismic design of structures, is capable of providing more detailed information on the performance levels of both structural and nonstructural members and content systems. Some current seismic design codes adapted concepts of the PBSD approach in a deterministic manner, considering uncertainties implicitly. In this study, efforts have been made to develop a Probabilistic Performance-Based Optimum Seismic Design (PPBOSD) methodology for Reinforced Concrete (RC) structures, considering uncertainties explicitly to provide a more practice-oriented approach. It is a powerful seismic design tool that provides structures with economical, robust, and rational design. In addition, structures designed using this approach could satisfy the target performance levels at multi-limit states. For the optimization problem, the objective function is given in terms of minimizing the expected total cost of the structure at a specific intensity level. Pacific Earthquake Engineering Research Center's Performance-Based Earthquake Engineering (PEER PBEE) methodology is used for the performance assessment of the structure. The Endurance Time method is used in the PEER PBEE methodology framework while performing optimization. After the optimum solution is obtained, the Incremental Dynamic Analysis (IDA) method is used to verify the performance levels. The proposed methodology is applied to RC frame buildings with different numbers of stories. OpenSees software is used together with codes written in python for the design and analysis purpose.
  • Doctoral Thesis
    Properties of Hybrid Fiber Reinforced Concrete for Impact Loading
    (Izmir Institute of Technology, 2021) Alami, Mohammad Musa; Saatçi, Selçuk; Erdem, Tahir Kemal
    Concrete is a brittle material and does not have significant energy absorption capacity before its fracture. Adding fibers to a concrete mix increases its ductility. Recently, there is significant development in the concrete technology to produce a concrete that can exhibit deflection hardening and show high energy absorption capacity. In this thesis, two kinds of cement based composites with high energy absorption capacity were studied: 1. Engineered Cementitious Composites (ECC). This material can exhibit deflection hardening under bending and it is produced only with synthetic fibers and fine aggregate, 2. Hybrid Fiber Reinforced Concrete (HyFRC). This material can exhibit deflection hardening under bending. It was produced with fine and coarse aggregates and hybrid fibers (both steel and synthetic fibers). The experimental program of this study consists of two main stages. The first stage is to design these composites and test their basic properties in fresh and hardened states, such as compressive strength, flexural behavior, freezing-thawing resistance, chloride ion permeability and sorptivity. In the second stage, dynamic tests (drop tests on small size specimens and pendulum impact tests on real size new generation road concrete barriers with a selected HyFRC mixture) were carried out to determine their energy absorption capacities. Based on the ECC results, fly ash/cement ratio of 1.2 and 20% perlite replacement of sand were selected for HyFRC mixtures. According to the mechanical behavior and durability test results of HyFRC, ST3,0.75_P0.25_D16 mixture (steel fiber type= ST3, steel fiber volume=0.75%, PVA volume=0.25%, Dmax=16mm) was found to have the best performance, and accordingly, this composite was selected for the real-size barrier pendulum test. The same mixture without fibers was also tested under pendulum test as control normal concrete since the present road barriers in the market do not employ fibers. As a result of this study, the HyFRC barrier was found to perform higher impact resistance.
  • Doctoral Thesis
    Impact Behavior of Textile Reinforced Concrete Slabs
    (01. Izmir Institute of Technology, 2021) Batarlar, Baturay; Saatçi, Selçuk
    Reinforced concrete (RC) technology is still the most preferable and common method to build civil engineering structures. In accordance with design purposes and needs, these structures are built to resist various loading scenarios. Throughout the lifespan of RC structures, they may be subjected to high rate loading scenarios due to either expected or unexpected reasons such as impacts caused by vehicular collisions, debris generated by typhoons, tsunami or floods, rock or object falls to protective shelters. Therefore, understanding of impact behavior of RC members plays a vital role not only for design stages but also retrofitting and strengthening purposes thereafter. For this purpose, an experimental program was carried out to reveal the impact behavior of RC slabs strengthened with carbon textile reinforcements. In this program, four slabs specimens, two unstrengthened and two strengthened with two different carbon textile reinforcements, having dimensions of 1.5 m × 1.5 m × 0.2 m were tested by using an advanced impact testing facility at Otto-Mohr Laboratiorum of Technische Universität Dresden. In these tests, all slabs were tested under repeated impact loads by using the same steel striker with a 200 mm - diameter flat contact surface in the velocity range of 25.2 to 30.2 m/s. The results obtained from these tests are presented in terms of midpoint-displacement histories, reaction force histories, slab accelerations, and strain histories of steel reinforcements for each impact. As a result of the test program, it is shown that carbon textile reinforcements have significant effects on enhancing impact capacity as well as limiting maximum and residual midpoint displacements. By using the data obtained from tests, a finite element (FE) modeling study was performed by using the LS-DYNA software tool. In this study, two FE models with different mesh sizes were created and compared with each other to obtain efficient modeling conditions. In the light of the tests and validated models, a parametric study was performed to figure out efficient impact conditions and parameters for carbon textile reinforcements. It is shown that carbon textile reinforcements are more effective for limiting damage levels under low-velocity impacts.
  • Doctoral Thesis
    Modeling of Concrete Under High Strain Rate Conditions Using Nonlinear Finite Element Method
    (Izmir Institute of Technology, 2017) Çankaya, Mehmet Alper; Saatcı, Selçuk; Taşdemirci, Alper
    In this study, a comprehensive experimental and numerical study was undertaken to model concrete under high strain rate conditions. Concrete cylinder specimens, all obtained from the same batch, were tested both under ststic and high strainrate conditions. 15 eylinder specimens were tested under 3.55x10-5, 3.23x10-4, 2.97x10-3 1/s strain rates, whereas three identical specimens were tested using a Split Hopkinson Pressure Bar SHPB) tes setup under 235, 245, 260 1/s strain rates. Used SHPB setup was modified to include quartz crystal stress developed in the specimens werw directly obtained, eliminating common isssues regarding stress readings in a conventional setup. Stress-strain behavior and other material parameters that would be necessary for numerical modeling were obtained under various strain rates. Test samples were modeled using an explicit finite element program LS-DYNA, using Holmquist-Johnson-Cook model with experimentally obtained model parameters. To verify the obtained parameters further, drop tower test on concrete plates were also performed and modeled. Numerical modeling of both SHPB samples and concrete plates were successful in capturing the observed behavior. The study also provided the literature with a reliable test data with complete parameters that can be used for further studies in the area.