Theses supervised by Doç. Dr. Nildem Tayşi
15 theses · Gaziantep University
Optimum usage of mixed damping systems (rubber concerete or x diagonal dampers) on multystory building
This research aims to compare usage of X plate chevron dampers (Wen Plasticity Dampers) in a concrete multi-story framed building which installed in different locations of the structure, in accompany of using rubberized concrete - treated crumped rubber added to concrete aggregates - using different rubber percentages for the building's members. Comparison of Nonlinear Push Over Analysis of models' results were done, such as transmitted base shear forces, roof displacement, pseudo acceleration, pseudo displacement, effective period, ductility ratio and most importantly effective damping ratio which plays major role in reducing demand curve of the design response spectrum. Two and three-dimensional multi story building models had analyzed by SAP2000 and ETABS, compared analysis results according to multiple study cases will be shown, trying to reach optimum usage of such damping systems.
Comparison of hollow core reinforced concrete slabs types
A hollow core slab is a concrete member with continuous voids provided to reduce the weight and cost of the building. Because of the less concrete used in constructing these slabs, hollow core slab systems are lighter than solid concrete slabs while maintaining the ability to have large spans. This thesis deals with the nonlinear numerical design of two types of reinforced concrete hollow core slabs (voided and waffle slabs). Firstly, 30 slab models are designed via SAFE software. Next, these 30 samples are divided into the waffle and voided slabs with five different lengths (L) of the span and three different widths of the beam (wb) for each span. After the design stage, the models are subjected to a uniform distributed load (live and dead), then the slabs are analyzed by the nonlinear FEM via the same software. The numerical results showed that the long-term deflection, reinforced steel area, and concrete consumption for voided slab waffle slabs are affected by the slab span, thickness, and width of the beam. Furthermore, the results showed that the required amount of concrete in the hollow slabs is reduced by 30 % (or more) than the traditional slab.
Nonlinear finite element modeling of post tensioned cantilever concrete beams using different tendon profiles
Prestressing is widely used technic all over the world for constructions of buildings, bridges, towers, offshore structures etc. due to its efficiency and economy for achieving requirements the long span with small depth. It is used for flexural strengthening of reinforced concrete structures for improving cracking loads and decreasing deflections due to service loads. There are two methods for prestressing (pre-tensioning and post-tensioning). In this thesis, a three-Dimensional (3-D) nonlinear Finite Element (FE) method is used to determine the behavior of Post-Tensioned (PT) cantilever concrete beams with different tendon profiles. Numerical analyses ANSYS package program is used for analysis of beams. The results from FE analysis is verified by experimental reference test result and good agreement is achieved. To investigate the effect of different tendon profiles on the flexural behavior of Bonded Post Tensioned (BPT) cantilever reinforced concrete beams, six models are chosen. These models are without tendons, two tendons at the bottom, middle, top, parabolic tendons with one draped point and two draped points. Failure loads, deflections, and load versus deflection relationships for all models are examined and it is seen that the beam with one draped tendon profile shows the highest performance.
Nonlinear finite element analysis of composite steel-concrete cantilever beams with external prestressing
Composite steel-concrete beams prestressed with high strength external tendons have demonstrated many advantages like, increase in the ultimate moment capacity of the structure, enlarge the range of elastic behavior before yielding for the structure with the introduction of internal stresses. The stresses can oppose the moment generated by the loading. The amount of structural steel used in construction, based on yield strength alone, can be significantly reduced by the use of high-strength tendons, thereby reducing the cost of construction. In this thesis, a nonlinear finite element model for the analysis of cantilever composite steel-concrete beam with external prestressing of different tendon profiles was developed. The numerical analysis was conducted by the finite element software ANSYS. The results from finite element analysis is verified by experimental reference test result and good agreement is achieved. The thesis focuses on the effect of different tendon profiles on the flexural behavior of cantilever composite steel-concrete beam with external prestressing. Five models with different tendon profiles are straight top profile, straight bottom profile, one-point draped down profile, two-point draped down profile and two-point draped top profile. Failure loads, deflections, and load versus deflection relationships for all models are examined and it is seen that the beam with straight top profile shows the highest performance
Experimental and numerical analysis of thermal behavior of composite bridge girders
Due to their permanent external exposure, bridge structures are under the continuous exposure to the temporal thermal loads. These loads are mainly due to the temporal fluctuation of solar radiation and air temperature. In this research, experimental and FE studies were directed to investigate the thermal behavior of composite girders under the variation of solar radiation and air temperature. This research is divided into four parts. In the first, an experimental work including two composite girder segments, T-Beam and I-Beam, was conducted. The segments were instrumented with thermocouples, strain gages and weather sensors. In the second part, a thermo-mechanical FE analysis was conducted using COMSOL for the two segments, which was verified using the experimental temperature records. Using the verified FE model, a parametric study was conducted in the third part to evaluate the effect of the girder's size. The fourth part was directed to evaluate the long-term temperature variations in Turkey. In this part, the verified FE model in addition to weather history records for more than 50 years of 10 Turkish cities were utilized. The experimental results showed that the temperature variation in concrete parts was higher than in steel for the two segments. Comparisons between the experimental and FE temperatures revealed that the FE models could capture the temperatures accurately. The parametric study disclosed that the thickness of the top concrete flange was the most effective geometrical parameter. The extreme temperature analysis showed that based on the vertical temperature gradients, Turkey can be divided into two regions.
Investigation of ductility behavior of polypropylene fiber reinforced concrete beams
Fibers are widely used in structural concrete members in recent years, because of its ability in improving many parameters of concrete. Present research is attempted to employ a balance among the three factors (cost, quality, and construction time). This study aims to investigate the methods of improving ductility behavior of polypropylene (PP) fiber reinforced concrete beams. This will be done through constructing a conventional high strength concrete that have ability to gain its strength quickly after the casting, by increasing the fine aggregate and fine additive materials which complementing by decreasing the coarse particles. In order to improve the mechanical properties of both fresh concrete in term of slump and fiber dispersion efficiency, furthermore in hardened concrete in term of displacement, and robust multiple cracking behavior under tensile action tests are done. Several concrete beams reinforced with different percentages of PP fiber (0.5, 1.0, 1.5 %) are constructed with different number of conventional longitudinal steel reinforcement and compared with control beams. The clear dimensions of the beams used in this investigation are 150 X 150 X 850 mm. In general, the addition of PP fiber improved the mechanical properties of concrete. As well as the more ductile behavior is found in beams with PP fibers compared with normal concrete beam, so increase of the volume fraction is giving better ductility. Where the ductility of beam 1.5 PP-2R has improved by 53 %. Key Words: Polypropylene, fiber-reinforced beams, ductility
Experimental investigation for flexural behavior of RC beam containing glass fiber
Concrete fails in a brittle manner, failure of Reinforced Concrete (RC) beams are brittle and suddenly occurs. These shortcomings are generally overcome by using several technics. One of them was the inclusion of fibers into the concrete such as steel, glass, basalt, carbon etc. By using Glass Fiber (GF) into the concrete reduces reinforcement congestion. This thesis presents the effect of GF and Hybrid Fiber (HF) on the compressive, tensile, flexural strength and weight of concrete M-30 grade. In this investigation, ten different RC beams were cast and tested. All beams were tested over an effective span of 1300 mm up to the failure under 4-point flexural test loading. The beams were designed as a balance-section. All beams are the identical size of "1500 x 150 x 200 mm" and divided into three groups, Group A consist of three beams strengthened with different volumetric ratios (0.5, 1.0, and 1.5 %) of GF. Group B consists of three beams (0.25-0.75, 0.5-0.5, and 0.75-0.25 %) of glass and steel fiber and Group C consists of three beams (0.25-0.75, 0.5-0.5, and 0.75-0.25 %) of glass and basalt fiber. For each mix cast 3-cubes by dimensions "100 x 100 x 100 mm" and cylinders "Ø100 x 200mm" to obtain the compressive and tensile strength of samples. Addition of GF increase the compressive and tensile strength and decrease the weight of concrete.
Modeling of thermal behavior of concrete bridge girders
Bridges continuously lose and gain heat due to climatological changes in the surrounding environment. The heat transfer occurs through three principal mechanisms: radiation from the sun, convection of heat between the surface and the ambient air, and re-radiation of the surface to or from the surrounding environment. The interaction between the surface of the structure and the climatological environment results in temperature difference between the elements of the structure. These temperature differences, in turns, produce deformations, cracks and strains in bridge girders and concrete part of bridges. In this research, finite element analysis is carried out to understand the temperature distribution and temperature gradients that occur within the different parts of the concrete deck and girders of prestressed concrete bridges under time dependent Gaziantep thermal conditions. The finite element package COMSOL Multiphysics and CSI Bridge are used to conduct the thermal analysis of the bridge girders, statistical analyzes have been carried out which should be taken into consideration during bridge design.
Experimental and comparative investigation of flexural behavior of basalt and steel fiber reinforced concrete beam
Concrete is a widely used material in structural engineering construction in different ways, whereas concrete has a low tensile strength and fails in a brittle manner. These shortcomings are generally overcome by using several technics. One of them was the inclusion of fibers into the concrete. The experimental study in this thesis is achieved to show the improvement gained by the addition of basalt, steel, and glass fibers to the concrete mix on the flexural performance of reinforced concrete beams. Thirteen different beams were tested and the results are compared. All beams with an effective span of 1300 mm were tested until failure under 4-point flexural test. The beams were designed as a balance-section. All beams are the identical size of "1500 x 150 x 200 mm" and divided into four groups. Group A consists of three beams strengthened with different volumetric ratios (0.5, 1.0, and 1.5 %) of basalt fiber. Group B consists of three beams strengthened with different volumetric ratios (0.5, 1.0, and 1.5 %) of steel fiber. Group C consists of three beams (0.25-0.75, 0.5-0.5, and 0.75-0.25 %) of basalt and glass hybrid fibers. Group D consists of three beams (0.25-0.75, 0.5-0.5, and 0.75- 0.25 %) of steel and glass hybrid fibers, and the last one is a control beam. The concrete mixtures was designed for high strength concrete. For each mix three-cubes and three cylinders are cast to obtain the effect of the fibers on concrete compressive and tensile strength. Very few researchers were presented in literature on the hybrid effect of steel, glass and basalt fibers in reinforced concrete beams. This thesis presents the effect of hybrid fiber on the compressive, tensile and flexural strength of concrete. Basalt fiber concrete usually has a high tensile strength but slightly smaller than steel fiber. The flexural strength of basalt fiber reinforced concrete increased with increasing fiber content in a gradual fashion. It is observed from the test results that there is a negative effect of fiber inclusion on the compressive strength of concrete.
Nonlinear finite element modeling of post-tensioned two-way concrete slabs
Post-tensioning is a technique that was used for constructions of (buildings, bridges, towers and offshore structures… etc..), Due to its efficiency and economy for achieving the requirements of long span with small depth. Post-tensioned concrete two-way slabs are one of the widely used slabs because of their good performance and cost effective compared with another slab type. This thesis investigates the structural behavior of post-tensioned two-way spanning concrete slabs. A nonlinear finite element model for the analysis of post- tensioned bonded concrete slabs was developed. The interface between the tendon and surrounding concrete was also modelled, allowing the tendon to retain its profile shape during the deformation of the slab. The load–deflection behavior, crack pattern in concrete and the failure modes are presented. The numerical analysis was conducted by the finite element ANSYS software and was validated by post-tensioned two-way concrete slab chosen from literature. A parametric study was conducted to investigate the effect of several selected parameters on the overall behavior of post-tensioned two-way concrete slab. The parameters are the effect of tendon layout, type of support, type of loading, position of the tendons, number and area of the tendons. Comparison between one-direction and two-direction tendon layout with the same number of tendons showed that two-direction tendon slab has higher failure load capacity.
Investigation of ductility behavior of pva fiber reinforced beams
Polyvinyl Engineered Cementations Composites (PVA-ECC), had been extensively investigated by many researchers. However, adding PVA to the normal concrete has not been much investigate the mechanical and structural characteristics in concrete beams. This research aimed to investigate the mechanical properties of the fibrous concrete reinforced with conventional reinforcement. The tested parameter was the volume fraction of the fiber (Vf %), and reinforcement ratio (ρ) on the conventional concrete beam. To achieve this aim, a set of experiments were carried out. Concrete mixes containing different PVA fiber volume fractions ranging between 0.5 % and 1.5 % with different conventional reinforcement ratio ranging from 0.5 % to 1.0 % were prepared and tested. Material tests are done for compressive strength (f 'c), tensile strength (fsp) and modulus of elasticity of fiber reinforced concretes. And also beams are tested under 4-point monotonic test, to assess their structural behaviors. The results showed that the PVA fibers is significantly enhanced the compressive strength up to 44 % and improved the beam ultimate strength up to 10 %. Moreover, the inclusion of PVA increases the beam ductility factor up to 130 %. These improvements also affect the initiations of the first crack and its depth in the tension zone, where the load resistance of the compression zone is increased with increasing the fiber percentages. Key Words: PVA fiber reinforced concrete, ductility of fiber reinforced beams.
Comparative study of seismic performance of multistoried reinforced concrete buildings with different slab systems
Flat slab system is becoming widely popular for multistory buildings due to its several advantages, e.g., easy to construct, economical, larger clear height, and lesser building height, as well as for their flexibility in architectural remodeling. Though flat slab structures have several advantages, their performance under earthquake loading is doubtful. They are very flexible and undergo large deflection under lateral load induced by the earthquake and generally fail in punching shear mode, which is a brittle mode of failure and reduces the structures' ductility. This research goal is investigating alternative structural slab systems to improve seismic performance and durability of structures. Two more alternative reinforced concrete slabs are analyzed and compared. Three groups of buildings are classified according to the height and fundamental period of vibration. Low-rise buildings (6 stories), mid-rise buildings (12 stories), and high-rise buildings (18 stories) with three different slab systems (flat slab, solid slab, and waffle slab) are analyzed. Nonlinear pushover static analysis is used to predict the behavior of buildings under seismic effects to estimate the strength capacity beyond its elastic limit up to its ultimate strength in the post-elastic range. The method also predicts potential weak areas in the structure by keeping track of the sequence of damages of every member in the structure. The seismic response assessment is based on the global structure behavior, seismic performance level, maximum story drift, maximum displacement, numbers of plastic hinges occurred, and base shear.
Effect of curing regimes, fly ash/slag ratios and steelfibers on mechanical properties of geopolymer concrete
Ordinary Portland cement (OPC) production results in a havoc to the environment due to CO2 emission, so it is needed to find an alternative material. The properties of fly ash (FA)-based geopolymer concrete (GPC) was extensively studied in recent years. In this study, as a first step FA-based, GPC was prepared, and activated by a mix of sodium hydroxide (NaOH) and sodium silicate (Na2Sio3) solutions. Ground granulated blast furnace slag (GGBFS) was added as (0, 25, and 50) % of the total binder. Samples were cured under furnace 60 ⁰C, 80 ⁰C, and ambient state. In the second study, the effect of steel fiber on GPC was investigated. For this purpose, specimens of GPC without and with steel fiber (0.5, 1, and 1.5 %) were produced. Constant Na2Sio3/NaOH and alkaline activator to binder ratios of 2.5 and 0.5, respectively, were adopted. Experiments were made via slump, compressive strength, splitting tensile strength, flexural strength testes to detect the influence of steel fiber, GGBFS, and different curing regimes on FA-based GPC, tested at different curing dates 7, 28 and, 56 days. Test results showed that the addition of steel fiber and GGBFS affected the fresh properties negatively and notably developed bond strength and flexural performance. The effect of GGBFS was detected to be dominant on compressive strength and workability. The highest compressive strength was detected for steel fiber reinforced GPC (SFRGPC) cured at temperature 80 ⁰C for 24 hr.
Early age performance and mechanical characteristics of concrete which is used in service buildings
Concrete has an important place in the construction industry and widespread use of concrete requires to be searched and examined in every aspect. Concrete generally reaches its characteristic strength within 28 days. But, as a result of the hydration process, concrete gains certain quantities of strength in earlier days. The longtime performance of reinforced concrete buildings, is affected greatly by the quality and behaviour of concrete at early ages. However, the basic mechanisms affecting the early age behaviour of concrete have not yet been fully understood. The research subject of this thesis is investigating the early age compressive strength of concrete, which is one of the mechanical properties of concrete. Exclusively, it is important to investigate the early age compressive strength of concrete that is used in the large-scale service buildings and to make suggestions about formwork removal time. To achieve this aim, compressive strength tests were performed on samples of C25/30 and C30/37 concrete classes which are used in GIHC (Gaziantep Integrated Health Campus) project, in different days (3, 7 and 28). Test results were examined according to relevant standards and the relationship between early age, characteristic and realized compressive strength of concrete, is given. As a result of this analysis, it was observed that capacity of early age concrete is reached average 45% (3 days) and 70% (7 days) and possible advantages of concrete capacity are evaluated.
Analysis and optimum design of curved roof structure
Curved roof structures are frequently designed to supply the users of the structure with ordinary light with a sense of capaciousness as well as grandness in public facilities such as stations, buying malls, leisure centers and airports.This thesis? presents a method for analysis and optimum design of 2D and 3D curved roof structures subjected to static loading. Here the optimization refers to minimization of total weight of curved roof structures such that they can resist applied forces (stress constraint) and don?t exceed certain deformations (displacement constraints). The finite element formulations are implemented for the static analysis of curved roof trusses to determine the stresses and displacements.Optimization is an automated design procedure in which the computers are utilized to obtain the best results. A program was modified and used to automate analysis and optimization of the structure written in FORTRAN language based Finite Element analysis and Genetic Algorithm optimization technique. The developed method is tested on several examples and compared with previous researches or SAP2000 results. It is concluded that this method can serve as a useful tool in engineering design and optimization of curved roofs.Keywords: curved roof structures, size optimization, finite element method, genetic algorithm.