Theses supervised by Prof. Dr. Mustafa Özakça
30 theses · Gaziantep University
Investigation of the flexural behavior of steel fiber reinforced concrete hollow beams exposed to elevated temperature
Hollow concrete beams, when adopted in structures, must meet the required structural safety at both conditions of ambient and high temperature. The behavior of this type of beam, with the influence of high temperature, has not been investigated by any previous study yet. This study aims to experimentally explore the behavior of concrete beams of circular hollow sections (80mm diameter) using conventional steel reinforcement and with or without steel fibers (SFs) under flexural loads prior to and after exposure to high temperatures. Besides, the investigation also included the mechanical characteristics (compressive strength and splitting tensile strength) of four mixtures were used to produce the beams specimens and studied their response to different inclusions of SFs (0, 0.5, 1, and 1.5% for each) under similar conditions of the beams test. A total of ten beams of square cross-section with similar external dimensions and lengths (150 × 150 × 950 mm) were prepared, eight of which were hollow, and two were solid. All these beams specimens were loaded until failure under four-point to assess and compare their behavior in terms of temperature evolution, load versus deflection at different stages of loading, ductility, failure mode, and cracks before and after being subjected to 550°C temperature. Based on the test findings, SFRC hollow beams exhibited a more ability to preserve load carrying capacity after heating than plain concrete beams. SFRC hollow beams can be a desirable structural solution and provides a reduction in weight and an increase in ductility without a significant reduction in flexural performance even after direct exposure to a source of intense heat.
Investigation of vibration and stability behaviors of non-homogeneous orthotropic composite cylindrical shells subjected on elastic foundation
The present research studied the free vibration characteristics of non-homogeneous orthotropic thin cylindrical shells resting on elastic foundation. The cylindrical shell can vibrate in different modes and theoretically infinite modes are possible. The axial mode and circumferential mode in any of their combinations define the modes and the corresponding modal frequencies. The study divided into four groups after validation, the first group analysis of cylindrical shells, the second group Analysis for orthotropic cylindrical shells and the third group analysis for cylindrical shells on elastic foundation and finally the fourth group analysis for different cylindrical shells geometry. All the groups tested by using ANSYS software as a tool for finite element investigation. The results observed that when the value of foundation modulus increases, the frequency values increase. Also, when the shell thickness increases, the values of natural frequency increase in addition to the layer's increase which changes the frequency based on the layer's design conditions. Finally, when the length of cylindrical shells increases, the frequency decrease.
Rehabilitation of concrete structural members externally strengthened with basalt fiber polymer sheets
In this work, basalt fibers that are becoming alternative options for reinforced concrete beam strengthening are examined. Two investigations have been presented in this thesis. The first study's investigation is based on reinforced concrete beams that have been strengthened with basalt fiber reinforced polymer sheet. A variety of wrapping techniques were utilized in order to reinforce the beams using single layer basalt fiber reinforced polymer sheet. Beams were tested under the four-point bending test. The flexural behaviors of the beams strengthened with a soffit layer of basalt fiber reinforced polymer were significantly improved compared to the beam without strengthening. The second study`s thesis is to investigate the effect of higher heating regimes on the strength of concretes which are unconfined and confined with basalt fiber reinforced polymer sheets. Experimental studies show that when the heating temperature is over 100oC or exposure time increases, the compressive strength of the concrete cylinders enclosed with basalt fiber reinforced polymer decreases.
Design and improve fire truck turntable ladder
ABSTRACT DESIGN AND IMPROVE FIRE TRUCK TURNTABLE LADDER ABUHEMEIDA, Nour M.Sc. in Civil Engineering Supervisor: Prof. Dr. Mustafa ÖZAKÇA September 2016 53 pages In getting a better model for aerial ladder, the need to check for possible failure in the model of the equipment is paramount, as failure in the components might result due to fatigue in the material of the ladder, or as a result of poor failure of the truss due to over loading and poor design. The need to check for possible failure in the equipment calls for an approach that will analyse the model and optimize the existing parameters of the proposed model, or creating a new approach in the design of the model based on the Turkish and European standards TS EN 14044+A1 "for High rise aerial appliances for fire service use – Turntable ladders with sequential movements". This approach will bring about checking the figures and the design of the model in terms of the failure and the model design for the system. The data from the initial model was analysed and checked through the finite element method adopted in SAP 2000 software. This approach is used because it brings about a total check of possible failures in the model, and it comes up with a possible attainable terms and conditions for the optimum utilization of the model. Upon finalizing the initial model, a couple of changes and improvements was applied as an effort to get more efficient design and gain wider working range for the aerial ladder. Keywords: turntable ladder; platform; working range; SAP2000; curve fitting.
Comparison of different bracing patterns for self-support communication towers
The significant system providing lateral load resistance in steel lattice communication towers is the bracing system. There are various kinds of bracing systems for steel lattice towers. This study has focused on identifying the economic bracing system for a given range of tower heights. Towers of height 40 m, 50 m, and 60 m have been designed and analyzed with seven rectangular base and four triangular base towers with different types of bracing systems under design loads. TOWER program is utilized for the design and analysis of towers using the Telecommunication Industry Association (ANSI/TIA-222-G) standard code specification. The TOWER program is capable of performing both linear and nonlinear analyses with more efficiently and reliably. Comparison of the various bracing system is assigned based on the weight of tower, structure fundamental frequency, maximum element usage, maximum overturning moment, sway and twist values. The smallest weight is obtained at KD and YD type bracing systems for rectangular base towers. In the case of triangular base towers, X and XB type bracing systems give the smallest weight design. The best performance according to sway and out of plumb values are obtained at X and K type bracing system for rectangular and triangular base towers. It is worth to mention that Y type bracing system is failed in nonlinear analysis at 60 m height tower.
Comparison of bracing system for overhead transmission line tower
In this study, the design and analysis of self-supporting lattice tower 132 kV double circuit are accomplished. Additionally, five different models of bracing systems are used for tower modeling, which has the same width 7 m and height 33.5 m of all tower models, it has been modeled and the three-dimensional linear and nonlinear analysis is carried out for various load cases. Transmission towers are subjected to different loads such as wire loads, dead loads, self-weight, wind loads, ice loads, etc. In the current study, a TOWER software is used for the design and analysis according to the American Society of Civil Engineers (ASCE 10) ASCE 10 standard code specification. The TOWER program is capable of performing both linear and nonlinear analyses with more efficiently and reliably. Comparison of the various bracing system is done based on the weight of tower, maximum element usage, and overturning moment. According to present result, the Diagonal (D) bracing have been found the lightweight and more economical type compared with other types of bracing system.
Nonlinear three dimensional finite element analysis of reinforced concrete hollow beams
This research work which summed up to this dissertation describes three dimension nonlinear finite element model expediency of the analysis the reinforced concrete beams with hollow cross section and also solid resist monotonic loading. A well-known software ANSYS its finite element pioneered has been used. The advantages of the three dimension finite element model create a full concept about the model in terms of deformation, and critical areas. Among the two methods that representing the cracks, a discrete model has been used. The eight nodes isoperimetric brick element called (SOLID 65) used to model concrete body. While using (LINK 180) three dimension finite strain spar element for modelling the flexural and shear reinforcements. The base plates for each loading point and supporting has been ideally obtained by using (SOLID 185) three dimension structural solid element. For symmetry reasons, a half specimen of the beams is considered in the analysis to reduce computational time and computer. Many types of reinforced concrete hollow beams have been analyzed and the solution of finite element was compared with the data from lab work. Several parametric works were implemented. The effect of some important finite element and material parameters like distribution of mesh, density and effects of mesh size on accuracy of three dimension finite element model results accomplished to look their effects. The analysis results showed that the behavior of the modeled specimen can be clarified by the load-deflection curves at center of beam in addition to the yielding reinforcement occurrence an appropriate agreement with the compared lab test data. At the last presenting the maximum tolerance between the modeled sections and its corresponding experimented one were 6.8%.
Assessment of the seismic behavior of different braced systems for mid rise steel buildings
This study aimed to compare the seismic behavior of different bracing systems with different angles of bracing geometry for mid-rise 2D steel buildings of 2, 4, 6, and 8 stories. Nonlinear static pushover analyses carried out to assess the structural seismic performance. Eight structural configurations investigated moment resisting frames, Chevron braced frames, multi Chevron braced frames, V-braced frames, multi V-braced frames, X-braced frames, multi X-braced frames, and diagonal braced frames. Seven angles used: 30, 45, 60, 75, 90, 105 and 120 for each type of bracing system. The effects of some parameters influencing the seismic performance, including type of the bracing system, different angles of bracing geometry and the height of the building investigated. The results show that the different braced frames with different angles of bracing geometry performed well in terms of story displacement, base shear and performance point when compared with the moment resisting frame in mid-high rise steel buildings. It can be concluded, on a comparative account of the obtained results enhances structural performances. In term of base shear and roof displacement, the seismic response, diagonal braced frames and X-braced frames have better seismic response. The bracing angles between 45 and 90 degrees generally give good performance. Keywords: Nonlinear pushover analysis, Base shear and displacement, Seismic performance, steel structure building, Bracing systems.
Improvement of the structural behavior of hollow beam reinforced by both steel bars and fiber
The aim of the present experimental study is to examine the effect of steel fiber on the improvement of the structural behavior of hollow beams reinforced by both steel bars and fibers. This work is attempt to matching the both lightweight structural member with the structural ductility requirements. This is reached by combining the optimum beam's section topology with using steel fiber reinforcement. Therefore, different parameters are used to alter, named, shear span to depth ratio (a/d) and hollow shape. Three values for (a/d) used for investigating 8, 6, and 4. Two hollow type of circular and square shape are used. However, beam size, fiber type and longitudinal reinforcement ratio were left unchanged. All these parameters are compared with the control specimens of solid sections and hollow of normal concrete.
Investigation of residual shear strength of two-way slab panels exposed to high temperatures
Steel fiber reinforced concrete is an old concept, where first appearance of it was around a 100 years ago, although it's a successful material in improving the behavior of concrete especially when it combines with the conventional steel reinforcement, there's an absence of codes and standard that predict and estimate the real punching capacity of the panels containing steel fiber especially particularly when it is exposed to fire. The current work in this thesis is a twenty slab panels that is casted and tested to obtain the residual punching shear strength after exposing to different temperatures and comparing the results with slab panels in ambient condition, also it is compared with ACI (American concrete institute) predicted results. The recent research results indicate that the steel fiber has a significant improvement on the behavior of concrete in groups under the same conditions, also in general the residual punching shear strength improved after exposing to 150 °C and 300 °C when it compared to the panels containing the same mixture in ambient condition.
An experimental study on composite slabs with steel deck sheets and fiber concrete
Recently, the use of Steel Fiber Reinforced Concrete (SFRC) as an alternative to conventional steel reinforcement has proved to be an effective solution in the composite slabs to prevent temperature and shrinkage cracks, increase the ductility of the composite slabs. However, Steel Fibers (SF) have a relatively little effect on compressive strength of concrete and high SF volume fraction might lead to a lack of workability.In this thesis, the influences of different parameters on the structural behavior of composite slabs are investigated. Thirteen slab specimens were constructed and tested to failure. The tested composite slabs consisted of three composite slab specimens with plain concrete, three specimens with studs, three specimens with studs and reinforced with SF only without conventional reinforcement, three specimens with studs, SF, and conventional reinforcement, and the last one which is called control specimen, solid concrete slab without steel sheeting. The investigated parameters are ultimate load, deflection, end slip and ductility of composite slabs.The test results showed that the use of shear connectors transform the behavior of specimens from brittle to ductile. Also, the use of SF instead of conventional reinforcement in composite slabs gave better results.
Size effect on punching shear behavior of slab-column assembly made from engineering cementitious composite materials (ECC)
Bu çalışmada iki farklı tip (polivinil alkol 6-12 mm ve polipropilen 12 mm) sentetik elyaf eklenerek üretilen çimento bazlı kompozit malzemeden (ECC) oluşan düz plaka kolon bağlantısının zımbalama kesme davranışı araştırılmıştır. Toplam on iki adet döşeme üretilerek test edilmiştir. Deneyler dört gruptan oluşmaktadır. Bunlar PVA 6, PVA 12 ve PP 12 sentetik elyaf kullanılarak üretilen üç grup ile karşılaştırma amacıyla üretilen normal betondan olan dördüncü gruptur. Her bir gruptaki levhaların kalınlığı 50, 60 ve 80 mm olarak değişirken diğer boyutlar sabit (500 × 500 mm) tutulmuştur. Tüm plakalarda aynı donatı oranı 0.12 kullanılmıştır. Test sonuçları, ECC'den yapılan döşemelerin normal betona göre daha az deformasyon verdiğini göstermiştir. Bu, ECC'nin çatlak büyümesini önleme ve genişlemesini engelleme özelliğinden kaynaklanmaktadır. Elyafın eklenmesi tüm yükleme aşamalarında ve özellikle ilk çatlaktan sonra deformasyonlarda bir azalmaya yol açmaktadır. Ayrıca düz döşeme ile taşınan nihai yükün artması, elyafların, yalnızca diyagonal çatlakların ve deformasyon oluşumunu ertelemekle kalmayarak, aynı zamanda zımbalama etkisinin kırılgan davranıştan sünek davranışa doğru değişmesinden olmaktadır. Ayrıca, döşeme kalınlığı arttıkça kesme gerilmesinde azalma görülmüştür. Ancak döşeme kalınlığı arttıkça nominal kesme kuvveti artmaktadır. PVA 6 sentetik elyaf, normal beton göre % 25-43 daha fazla nominal kayma mukavemeti artışı ile diğer elyaf çeşitlerine göre en büyük artışı göstermektedir. Anaktar Kelimeler: Kolon kiriş birleşimi, PVA ve PP elyaf takviyeli beton, , zımbalama kesme.
Investigation of flexural behavior of fibers reinforced geopolymer concrete hallow beams
This study is focused influence of steel and glass fibers on mechanical and structural properties for geopolymer concrete. Furthermore, the effect of hybrid fiber of steel and glass fibers on same these properties was studied also. Where test specimens were manufactured from the geopolymer concrete composites contain of alkaline liquids, 50% fly ash and 50% ground granulated blast furnace slag. The mixtures were designed for 14M molarity and the proportion of sodium silicate equivalent 2.5 than sodium hydroxide and used for producing geopolymer concrete. With this mixture, fibers were added (1%) steel, (0.5%) glass to the full volume of concrete and obtained hybrid fiber by mixing half of amount from both types. The material tests were done for workability, compressive strength (fc') and tensile strength (fsp) for 7, 28 and 56 days. For structural parameters were casted 12 beams (4 solid, 4 circular-hollow and 4 square-hollow) and tested under 3-points monotonic test, for investigation and comparison in terms of Flexural strength, ductility and failure patterns. The experimental test results indicated that there were improved compressive and tensile strength of geopolymer concrete due to use the steel, glass and hybrid fibers. Also these fibers led to improvements in resistance the first crack and ultimate load, ductility increasing, best control on crack patterns and an appropriate converge in the behavior of solid and hollow beams. Key words: Fly ash, Glass fiber, Geopolymer concrete, Hybrid fibers, Steel fiber.
Structural behavior of geopolymer concrete beams
In this study, the effects of steel fiber and polypropylene fiber on the flexural performance of fiber-reinforced geopolymer were investigated. Fiber reinforcement has emerged as a way to improve the brittleness of geopolymer. This study aims to examine the performance of fly ash/slag-based geopolymer concrete (FA/GGBFS) with different concentration of sodium hydroxide (NaOH) and different types of fibers (steel and polypropylene fibers). Alkaline liquid consists of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) solutions. The ratio of sodium silicate solution to sodium hydroxide was fixed to 2.50. The main factors studied were the evaluation of workability, compressive strength, split tensile strength, critical stress intensity factor, and fracture toughness. The study results showed that the incorporation of steel and polypropylene fibers into fly ash/slag based geopolymer concrete resulted in superior enhancement in the splitting tensile strength, flexural strength, area under the load-deflection curve and in the degree of fracture energy however the using of the different molar concentration of sodium hydroxide observed to be less important in the behavior of fiber reinforced geopolymer concrete. Keywords: Geopolymer concrete , fly ash, slag, steel fiber, polypropylene fiber and fracture toughness.
Analysis of steel frames with soil structure interaction under seismic loads
In this research work, response spectrum and linear/nonlinear time history analysis of 2D multi-story steel frames on gravel soil with and with-out soil structure interactions have been done. Frames have different height start from 3 stories and up to 20 stories. A sub-structure method is used to model soil and shallow (footing) foundation system by linear springs and dashpots. Three earthquake records are selected, Kocaeli, Erzincan and Düzce earthquake accelerograms records are selected and scaled to specific response spectrum with PGA 0.35 and soil type B according to Eurocode 8 is considered. Fundamental period and base shears have been investigated with and without soil-structure interactions; the results have been presented and compared
Conceptual design methodology for foldable shelters
With the rapid changing in global climate and the resulting disasters, prefabricated and quick-to-install shelters can provide victims of disasters with the opportunity to survive harsh natural and man-made disasters. Seeking to cater for this need and to reflect the topic of the mobile sheltering system, this thesis focuses on the case study development of a prefabricated, modular mobile shelter, from emergency scenarios to the permanent phase. The purpose of this paper is to propose a lightweight foldable and modular shelter that can be considered for the post-disaster shelter response and can be replaced, upgraded in size and geometrical configuration, and stored in a very short period of time. Using the folding technique, the specific mobile shelter structure investigated in this study has the ability to transform from a compact closed-form to a large living space open form. The suggested structure of these shelters is incrementally expandable by adding more modular units to its ends and sides. Furthermore, this thesis examines the practicability of the proposed concept and structure systems through a literature review, design-based research and digital model development.
Numerical investigation of structural behavior of steel frames under fire load
This thesis deal with numerical investication of structural behavior of steel frames under fire load. In order to examine the fire resistance of the most widely used trusses (portal frame, truss frame) in industrial structures, two industrial structures belonging to different types of trusses were designed under static and dynamic loads in SAP2000 program first. As a result of the analysis, sections were determined and subjected to fire effect according to ISO 834 standard in this WIZARD program.Trusses systems were modeled using GID interface program and fire analyses were performed in The SAFIR program. In this way, the resistance stipulated against fire of different types of trusses used in industrial structures was obtained and necessary comparisons were made. Key Words: Steel frames, Yield stress, Resistance time, Fire load, Collapse period.
Numerical investigation of structural behavior of hollow slabs
This thesis deals with nonlinear numerical analysis on the behavior of reinforced concrete solid slabs and hollow core slabs and parametric investigation of the effect of compressive strength of concrete, shear span to effective depth ratio (a/d), reinforcement ratio (A_s/A_c), and shape and size of hollow core slabs. For this, reinforced concrete slabs specimens with rectangular in cross-section and nominally 3500 mm long, 600 mm width, and 150 mm thickness with a clear span (distance between supports) of 3300 mm are analyzed. Nonlinear finite element analysis under four points loading carry out by using the software computer ANSYS19.1 program. The hollow-core slabs having circular core shapes and square core shapes analyze with equivalent areas of two sizes for each core shape under the same loading and support conditions. The slabs verification done corresponding to previous experimental work and obtained results indicated that a perfect agreement reached. The results exhibited that the longitudinal core opening in the hollow core slab leads to decrease ultimate load and deflection as compared with the solid slab. The numerical results showed that the ultimate capacity of the slabs increases with increasing the compressive strength and reinforced ratio (A_s/A_c) of concrete. The increase of shear span to effective depth ratio (a/d), from 6 to 8 and 10 respectively leads to decreases in the ultimate strength and mid-span deflection of slabs. The hollow-core slabs sections with five circle can do the excellent distribution of loads more than the hollow-core slabs with square core.
Flexural strengthening and rehabilitation of reinforced concrete beam using BFRP composited
This research involves the study of the basalt fibers emerging as alternative forms of strengthening and rehabilitation RC beams. Basalt fibers have high strength, stiffness, and corrosion resistance. In this thesis two studies are submitted., In the first study investigation is based on BFRP strengthened RC beams, with particular attention to the ductility of strengthened elements and their failure modes. Eight beams used in this study. The ductility is increased when RC beams strengthened by BFRP and the crack patterns of strengthened elements vary more than from un-strengthen beam. Additionally, cracks in strengthened elements tend to increase in number up to failure, unlike their un-strengthened counterparts. The second study is the finite element simulation, the research submits an extensive study on the strengthening and rehabilitation of damaged full-scale RC beams due to corrosions in the main reinforcement caused by BFRP sheets. Different parameters were taken into consideration such as corrosion grade, BFRP wrapping schemes, and the number of layers. The flexural performance of the models that build up as the control model and the damaged and the repaired methodologies by BFRP that are adopted and tested by others under the effects of four-point static loadings were also underwent examination. The full interaction at BFRP-concrete interface and the full bonding between sheets presupposed were investigated for all models. The numerical analysis findings were compared with the experimental measurements and found to be in good agreement.
Structural buckling optimization of stiffened plates
In this thesis, structural buckling optimization of stiffened plates was studied. Two types of stiffeners were used. First, straight stiffeners and second T shaped stiffeners. Examined plate types have common length, width and volume constraints. In each stiffener type, some combinations of pad elements, substiffener elements and variable plate skin were used. Buckling analyses of plates were carried out using a Fortran computer code which is based on Finite Strip (FS) method and developed by Özakça[1]. Optimization of plates was carried out with same program, which uses Sequential Quadratic Programming (SQP) as optimization tool. By these applications the effectiveness of 16 plate types using straight and T shaped stiffener types were investigated. Totally 315 runs were carried out for this purpose. The buckling optimization results are fluctuating in a wide range due to used elements combinations listed above and number of stiffeners. Improvements due to used element type and number of stiffeners are listed and compared according to stiffener types.Key Words: Stiffened plates, Buckling analysis, Structural optimization, Finite strip
Geometrically nonlinear analysis of plates and shells
This thesis deals with the geometrically nonlinear analysis of prismatic plates and shells using the finite strip method. The analysis is based on the use of Mindlin plate theory and therefore includes the effects of transverse shear deformation. The nonlinearity is introduced via the strain-displacement equations and correspondingly the analysis pertains to problems involving moderate displacements but small rotations. The principle of minimum potential energy is used in the development of the element and the complete structure stiffness equations and latter equations are solved using Newton-Raphson method. The postbuckling performance of optimized panels with sub-stiffening is investigated. The panels have been optimized for minimum weight or maximum performance. The linear elastic eigenvalue finite strip code which has a built-in optimizer provided a practical way of doing so, at least for the initial (skin) buckling. Optimization is also used to obtain insight into the importance of different design variables, and derive a method for sizing. Linear finite strip analysis allowed the optimization of one of the sub-stiffened panels, revealing a potential for further improvement of the initial buckling load.
Architectural form design and structural analysis of tensile structures
This thesis deals with architectural form design and structural analysis of tensile structures. The literature survey of tensile structures about historical references, form findings and analysis methods are given. The design of tensile membrane structures is carried out in four steps. These are conceptual design, form finding, structural analysis and cutting pattern. The design procedure and numerical methods are given. Two tensile membrane structures such as, university main entrance and open sunshade lodge hall are designed. At the end, brief conclusions are presented together with some suggestions for future studies on the design of tensile structures.
Free vibration analysis and structural optimization of stiffened panels
In this thesis, free vibration analysis and structural optimization of stiffened plates was studied. Different types of straight stiffeners were used. Examined plate types have common length, width and volume constraints. In each stiffener type, some combinations of pad elements, sub stiffener elements were used. Vibration analyses of plates were carried out using a Fortran computer code which is based on Finite Strip method and developed by Özakça[1]. Optimization of plates was carried out with same program, which uses SQP as optimization tool. By these applications the effectiveness of four plate types using straight stiffener types were investigated. Totally 168 runs were carried out for this purpose. The vibration optimization results are fluctuating in a wide range due to used elements combinations listed above and number of stiffeners. Improvements due to used element type and number of stiffeners are listed and compared according to stiffener types.
Analysis and optimum design of axisymmetric plates and shells
This thesis deals with the development of reliable and efficient computational tools to analyze and find optimum shapes of axisymmetric plates and shells in static, free vibration and buckling situations. The finite element method is used to determine the stresses, displacements, natural frequencies and critical buckling loads based on Mindlin-Reissner shell theory. An automated analysis and optimization procedure is adopted which integrates finite element analysis, parametric cubic spline geometry definition, automatic mesh generation, sensitivity analysis and mathematical programming methods.Key words: Axisymmetric plates and shells, static analysis, free vibration analysis, buckling analysis, shape optimization.