Theses supervised by Doç. Dr. Esra Mete Güneyisi
42 theses · Gaziantep University
A study on seismic behaviour of mega braced RC frames
This study investigates the seismic response of reinforced concrete (RC) frame structures before and after applying mega bracing system. For this, an eight story and four bay RC frame (bare frame) was used. The case studied frame had an inter-story height of 3.5 m for all floors and a span length of 6 m. In braced frame cases, five different bracing configurations in which bracing were installed across four bays of the structure were utilized. The diagonal brace members were selected as circular hollow section (CHS). Five different sizes of CHSs with an outer diameter ranged from 80 to 180 mm and two different wall thicknesses (4 and 6 mm) were used. Thus, a total of 51 different cases were considered in this study. Nonlinear pushover analysis was conducted to assess the structural performance of different frames. The capacity curve in terms of base shear coefficient vs. roof drift, displacement distribution at mechanism, maximum base shear, initial stiffness, plastification were evaluated to compare the seismic response of the bare and braced frames. The results indicated that the brace layout and section properties used in the application of mega bracing were very effective in the response of the structure under lateral loading.
Response evaluation of reinforced concrete frames with masonry infill walls through nonlinear static analysis
The structural response of reinforced concrete (RC) buildings subjected to lateral load is noticeably influenced by the masonry infill walls because of their contribution to strength and stiffness. In the literature, there are several modelling approaches for the infill walls. But, they provides different results. In this study, the equivalent diagonal strut model was utilized. The key parameter of this strut is its equivalent width. In the first part of the study, different expressions exist in literature for computing the width of compressed diagonal strut were examined. Among them, the Paulay and Priestley relationship which gives average value was chosen for modelling of the masonry infill walls. In the second part of the study, a sensitivity analysis was performed by considering 2, 4, 6 and 8 storey RC bare frames and those with infill walls. Four different infill wall frame configurations, namely, fully infilled frame, fully infilled-soft storey frame, interior bay infilled frame, and interior bay infilled-soft storey frame, were adopted. Single-strut and three-strut models for simulating wall panels were employed in all infilled frames. Thus, a total of 36 different RC frame models (covering 4 bare and 32 infilled frames) was evaluated through nonlinear static analysis in order to appraise the infill wall effect on the overall response of the case study frame buildings. The results of the analysis showed that the arrangement of the infill panels over the elevation of the frame had considerable effect on the performance of the structures. Additionally, the serious capacity reduction was observed particularly for the case of infills discontinued at the ground storey.
Nonlinear behavior of one-story one-bay steel frames with off-center bracings having different eccentricities
Steel bracing system is one of the structural systems utilized to resist the seismic loads. In off-center bracing system (OCBS), the diagonal bracing is not straight and the diagonal member is connected to the corner of the frame by another brace member, so the bracing system is formed by three brace members. In this study, the effect of the location of connection point of these three brace elements, in other words, the eccentricity of the OCBS was investigated. To this aim, one-story one-bay frame as a single degree of freedom system, having various height to span length ratios of 3/3, 3/5, 3/7, 4/3, 4/5 and 4/7, and having OCBS with various eccentricities (e1 and e2) of 0.1 to 0.9 were studied. For each frame system, two cases were adopted. In the first case, the eccentricity e1 was kept constant and possible e2 variations were considered while in the second one, the eccentricity e2 was maintained constant and possible e1 variations were taken into account. Thus, a total of 506 different cases were examined by means of the nonlinear pushover analysis. The results in terms of the capacity curve, maximum base shear capacity, and the initial stiffness of the frames were evaluated. It was observed from the results of the analysis that this great range of eccentricity values considered in the design of the OCBS had significant effects on the overall behavior of the frame structures under the lateral load.
Performance assessment of a reinforced concrete frame retrofitted with fiber reinforced polymer sheets
In new construction or retrofitting of existing structures, fiber reinforced polymer (FRP) composites have gain substantial worldwide interest over the past few decades. In this study, the effectiveness of using FRP composites to enhance the seismic performance of a 5 story reinforced concrete frame was investigated. For this, a gravity load designed bare frame was chosen as a case study. To upgrade the performance of the structure, glass FRP sheets were applied with the aim of increasing the capacity of the beams and columns. The FRP sheets utilized in this study have a tensile strength of 3241 MPa and thickness of 0.589 mm per layer. They were applied at the end regions of all beams and columns for increasing lateral load resistance of the bare frame. The performances of the structure with and without FRP application were examined through nonlinear static and nonlinear dynamic analysis. The capacity curves in terms of acceleration displacement response spectra (ADRS) format and modified ADRS demand plots (MADRS) for a demand earthquake with base accelerations of 0.25g, 0.30g, and 0.35g were studied. Additionally, the variation of maximum inter-story drift ratio, story displacement, drift time history, and plastifications were evaluated comparatively by using earthquake motions.
Inelastic seismic response of buildings with passive energy dissipation devices
This thesis presents an analytical study aimed at evaluating the inelastic seismic performance of moment resisting frames (MRFs) retrofitted with different approaches. For this, a set of MRFs covering steel moment resisting frames (SMRFs) and reinforced concrete moment resisting frames (RC-MRFs) were studied. They were three regular four equal bay frame models having three different numbers of storeys (3, 6 and 12). The frames were considered to be representative of exterior moment resisting frames found in typical residential buildings. All frame models were designed with lateral stiffness insufficient to satisfy code drift and hinge limitations in zones with high seismic hazard. Three different retrofit strategies including traditional diagonal bracing system and passive energy dissipation devices such as buckling restrained brace and viscoelastic damper were utilized for seismic upgrading of the existing structures. In the nonlinear time history analysis, a group of ground motions indicating the design earthquake with 10% exceedance probability in fifty years was taken into account. Considering the local and global deformations, the analysis results in terms of plastic hinge formations, interstorey drift index, global damage index, roof drift time history, height-wise distribution of peak storey drift and base shear demand were compared. The results pointed out a considerable enhancement in the earthquake performance of retrofitted structures and it was shown that both buckling-restrained braces and viscoelastic dampers allowed for an efficient reduction in the seismic demands of the upgraded frames as compared to traditional braces.
Code assessment and modeling of the axial capacity of recycled aggregate concrete filled steel tube stub columns
In this thesis, a wide range of experimental data and associated analytical results were utilized comparatively to assess the applicability of four widely used design codes (i.e., American Concrete Institute (ACI), Eurocode 4 (EC4), Architectural Institute of Japan (AIJ), and Chinese Design Code for Steel-Concrete Composite Structures (DL/T)) for calculating the capacity of recycled aggregate concrete filled steel tube (RACFST) columns. To this aim, a total of 97 experimental test results on the circular RACFST columns under axial compression were employed to propose a new model for predicting the axial capacity of such composite columns. The test specimens had a length to diameter ratio ranging from 2.0 to 3.5, indicating that they were the stub column and not failing in overall buckling. The proposed model was generated based the technique of gene-expression programming. The independent variables used for the development of the model were outer diameter and thickness of steel tube, length of the column, replacement ratio of recycled coarse aggregate, concrete compressive strength, and yield strength of the steel. A statistical analysis was also conducted to appraise the contributions of each parameter influencing the axial capacity. The analysis of the results exhibited that the proposed model gave reasonable predictions of the axial capacity of RACFST stub columns compared to the current design codes.
Performance assessment of vertically irregular low-rise and mid-rise reinforced concrete structures
Nowadays, the application of vertically irregular type of buildings gains a lot of interest in seismic research field. Many structures are designed with vertical irregularity, which are widely used to achieve architectural and/ or functional purposes. This study investigated the structural response of various regular and vertically irregular low-rise and mid-rise buildings. All reinforced concrete (RC) frame models considered had three and seven stories having four bays with a uniform bay width of 4 m and uniform story height of 3 m. As a vertical irregularity, stiffness/strength irregularity with missing beams or columns, mass irregularity, and vertical geometric irregularity (set-back) were studied. Each irregularity type composed of various cases. A total of two regular and thirty irregular frame models were examined through nonlinear pushover analysis. The capacity curve and plastic hinge formation in the structural members were determined for all models. In addition, the variation in the axial force of the columns of the RC frame buildings having the discontinuous column was evaluated. The analysis of the results showed that different types of structural irregularities had different types of influences on the case study structures.
Influence of openings in shear wall on lateral load carrying capacity of rc frame systems
Shear walls are specially designed as structural walls included in the buildings to withstand horizontal forces induced by wind and earthquake. Among the factors which affect the capacity of seismic response of reinforced concrete (RC) shear walls, an important role is played by openings. In many shear walls, a regular pattern of openings has to be provided due to various functional requirements such as windows in external walls, doors, corridors in internal walls and service ducts. The scope of the present study was to investigate the influence of the various size of openings in the shear wall on the nonlinear static and dynamic responses of RC buildings. For this, as a case study, the three-dimensional (3D) model and analysis of the 5 story RC shear wall buildings with 3 bays in x-direction and 5 bays in y-direction were carried out by using ETABS 2015 software. The comparative results were obtained in terms of capacity curve, displacement, storey drift, displacement time history, and base shear time history. Results revealed that openings with an area up to 11.1% of the wall area yielded minor effects on the seismic response of RC wall-frame structural systems but higher opening ratios eventually resulted in reducing the overall performance of the case study structures.
A numerical study on seismic behavior of plan irregular buildings
The shape, size and geometry of the building affects critically its seismic performance. Buildings with simple geometry in plan had performed well during the past strong earthquakes. But buildings with plan irregularity are more vulnerable and expected to be experienced more damage during seismic excitation. In this study, an eight story reinforced concrete regular building having a typical 6 bay x 6 bay frame with plan dimensions of 36 x 36 m and twenty four irregular buildings with different irregularities of +, C, O, H, ┴, L and Z shapes were examined. The structures were modeled using a finite element method and evaluated by both nonlinear static and dynamic analyses. Three-dimensional structural models were utilized for the analysis. Capacity curves, variation of storey displacement, and roof displacement, base shear time history were computed for the regular and irregular buildings. The analysis of the results showed that the regular building had considerably greater capacity in comparison to the irregular buildings due to the fact that irregularity caused decreasing the capacity of the buildings and the structures were more doubtful when they were more irregularities. Moreover, the displacement demands of the buildings were sensitive to type and amount of irregularity, especially at roof level.
Retrofitting of rc columns to enhance the seismic response of moment resisting frames
The gravity load designed or previous code designed buildings did not behave well during recent earthquakes on account of insufficient capacity and ductility. To lessen the seismic risk, special attention needs to be paid on such existing building stock. In this study, an attempt has been made to retrofit 3, 5, and 7 storey existing reinforced concrete (RC) buildings by means of RC jacketing. For this, different thicknesses of RC jacketing and column jacketing strategies were considered. The internal, external and full old columns of the case study structures were strengthened by applying 10, 15 and 20 cm thicknesses of RC jacketing. All structures were modeled as 2D RC frames having square columns using a finite element program. The seismic performance of the unretrofitted and retrofitted frame models were examined through the nonlinear static (pushover) analysis and nonlinear time history analysis. Capacity curve, base shear ratio, initial stiffness ratio, roof displacement versus time history, storey displacement, and inter-storey drift ratio were computed and discussed comparatively for each structural system.
Properties of self-compacting recycled aggregate concrete and its impact on structural behavior of composite tube columns
This thesis mainly consists of two parts. First part covers the material characterization of recycled aggregate self-compacting concrete in terms of fresh, mechanical and fracture responses; while the second part of the thesis presents the research results on the structural behavior of the axially loaded steel tube columns filled with such concretes. Study parameters included single and combined uses of recycled fine and coarse aggregates, substitution levels, compressive strength of concrete core, cross-section slenderness (D/t ratio) and yield strength of steel tube. To this aim, the hardened concrete properties were evaluated in terms of compressive strength, splitting tensile strength, static modulus of elasticity and net flexural strength. Failure mechanism of the notched concrete beams was also monitored via three-point bending test to observe the ductility level with respect to the fracture parameters. The statistical analysis based on GLM-ANOVA was also performed to assess the significance of the test parameters. Furthermore, comparison and code assessment for the axial load carrying capacity of the recycled aggregate concrete filled steel tube composite columns were studied by using four different design code equations (American Concrete Institute (ACI), Eurocode 4 (EC 4), Architecture Institute of Japan (AIJ) and Chinese Design Code for Steel-Concrete Composite Structures (DL/T)).
Factors influencing the properties of sclc and structural steel tube columns infilled with sclc
The main utilization of structural lightweight concrete is to decrease the dead load of the structure, which then permits the structural designer to diminish the size of columns, footings, and other load bearing members. The aim of the present thesis is twofold, firstly, it attempts to identify and describe experimentally the behavior of self-compacting lightweight concrete (SCLC). Secondly, it investigates numerically the ultimate strength of concrete filled steel tube (CFST) stub columns with SCLC concentrically loaded in compression to failure. To this aim, 18 SCLC mixtures were designed by considering different water to binder ratios (w/b) of 0.25 to 0.5, nano-silica (nS) contents of 0 to 5.0%, and untreated/treated artificial lightweight aggregates. They were tested for the fresh, mechanical, and durability performance at different ages. Thereafter, to assess the compression resistance of the circular composite columns, various diameter to wall thickness ratios (D/t) of 25 to 100, steel tube yield strength (fy) of 200 to 650 MPa and compressive strength of SCLC of 30 to 85 MPa were used in the investigation. Comparison were made with predicted column strengths using the existing design codes such as ACI, Eurocode 4, and DL/T. For each code, a total of 576 strength results for the circular CFST columns with SCLC were obtained and discussed accordingly. It was observed that the designed SCLC mixtures had comparable and satisfactory engineering performance. In addition, the results in this study showed that the codes estimated a reasonable capacity for the composite columns incorporating SCLC.
Influence of infill wall openings on pushover response of reinforced concrete moment resisting frame structures
In this study, the pushover behavior of reinforced concrete (RC) moment resisting frame structures with masonry infill walls having different opening percentages was investigated. The equivalent diagonal compression strut method was used to model the infill panels. The essential point in this method is the equivalent strut width. Firstly, five different expressions suggested by the researchers exist in the literature and one formulation given in a provision of FEMA 306 for calculating the width of compression diagonal strut were examined by analyzing 2, 4, 6 and 8 storey RC frames as full-infill frames. Then, various opening contents in infill walls have been studied. The openings in the walls were located at the center. The opening was formed at the percentages of 20, 40, 60, 80, and 100. A reduction coefficient proposed in the literature was adopted to find the equivalent width of the diagonal strut for the cases of the infill wall with opening. Thus, a total of 144 different RC frame models were evaluated through nonlinear static (pushover) analysis. The results on the capacity, initial stiffness, strength, and plastic hinge formation at mechanism as well as the energy dissipated by the buildings were discussed comparatively.
Earthquake analysis of lead core rubber bearing isolated steel buildings
The safety and damage control are the key parameters in the philosophy of earthquake resistant design. To protect the structures, the utilization of base isolation is one of the economical and practical solutions and it mitigates the seismic load by providing both lateral flexibility and energy dissipation. In this study, the effect of using lead core rubber bearing isolator on the seismic performance of the mid and high rise buildings were investigated. For this, 5, 10, and 15 story steel frame buildings were used as the case study. These buildings had the same plan with 6 bays of 6 m span in x-direction and 3 bays of 6 m, 4 m and 6 m spans in y-direction. These spans of the buildings were selected to indicate the typical residential building spans. Modeling and time history analysis of the base isolated and fixed based cases were performed by means of a finite element program. Three earthquake ground motion records were used in the earthquake analysis. The characteristics in terms of relative displacement, drift ratio and time history variation of some response parameters were studied. From analytical results, it was observed a significant reduction in the seismic response of the isolated buildings as compared to the fixed base cases
Comparison of structural response of traditional and tied eccentrically braced frames
Braced frame system is one of the structural systems used to resist the lateral loads such as earthquake and wind loads. In the last decades, among the bracing systems, tied braces have been developed as a new alternative for eccentric bracing systems in steel structures. In the first part of this study, two, four, six and eight storey bare frames and tied braced frames having the same plan and five bays in each direction were investigated. In this regard, the effects of different levels of eccentricity (or link length) and various bracing cross-sections were considered. In the second part of this study, the traditional eccentric bracing system and tied bracing system effectiveness on the seismic behaviour of the eight storey frame were examined comparatively. For all frame model, the nonlinear pushover analysis were applied and the results in terms of the capacity curve, the normalized maximum base shear ratio and the normalized initial stiffness ratio were investigated. The results indicated a considerable enhancement in the earthquake performance of the braced structures, and it was observed that the tied braced frames had more lateral load carrying and energy absorption capacity than traditional eccentric braced frames.
Use of friction pendulum isolator to improve the earthquake response of steel building
Base isolation systems have become a significant element of a structural system to enhance the reliability and safety of the structures during an earthquake. In this thesis, the earthquake behavior of a five story steel building with base isolation was investigated. To this aim, firstly the fixed base case of the structure was analyzed and then compared with the base isolated case. The building under consideration was rectangular in plan, measuring 30 m by 15 m with 5 m bays in both direction. The isolated building was assumed to be supported by friction pendulum system (FPS). The parametric study focused on different friction coefficients of seismic base isolators of FPS and its effect on the response of the structure. The modeling and dynamic analysis were done using finite element program. Three earthquake ground motion records were utilized. The analysis of the results showed a significant improvement in the dynamic response of the model structure after the application of the base isolation.
Properties of glass fiber reinforced scc and structural performance of short composite columns having such concrete core
Tüpler içerisine yerleştirilerek sargılanan cam fiber takviyeli kendiğinden yerleşen betonun (CFTKYB) yapısal davranışı üzerine yapılmış çalışmalar oldukça azdır. Benzer olarak, yapısal betonlarda cam fiber takviyesi de sınırlıdır. Bu tez kapsamında, iki bilimsel program detaylı olarak tanımlanmıştır. Birincisi, CFTKYB'un davranışını incelemek amacıyla deneysel çalışmalar yapılmıştır. Toplam 15 fiber takviyeli karışım farklı nano silika içeriğinde hazırlanmıştır. Bu karışımların taze ve mekanik performansları test edilmiştir. Tezin ikinci kısmında CFTKYB dolgulu çelik tüplerin yapısal performansları incelenmiştir. Kolonların mühendislik özellikleri, 3 farklı çap-cidar kalınlığı oranında ve çelik akma dayanımında kabul edilerek nümerik olarak değerlendirilmiştir. Beton çekirdek dayanımı üzerine yapılan deneysel çalışmalar, kolonların performansının Eurocode 4, ACI, AIJ ve DL/T standartlarına göre belirlenmesinde kulanılmıştır. Toplam 1080 farklı durum değerlendirilmiştir. Sonuç olarak, CFTKYB'nun tatmin edici mühendislik performansına sahip olduğu görülmüştür. Buna ek olarak, mevcut nümerik çalışma, tasarım yönetmeliklerinin bu yapısal betonlar ile entegre edilmiş kompozit kolonların kapasitelerini makul ölçüde tahmin ettiğini göstermiştir.
Mechanical characteristic of conventional and geopolymer modified uhpc and design code assessment of axially loaded composite members with such concrete
The need for developing new structural members having high performance has gained significant attention in the construction industry all over the world. This thesis covers the material aspects of ultra-high performance conventional and geopolymer concrete (UHPC/UHPGC) and the structural aspects of the composite columns in the case of UHPC/UHPGC used as an infill. For this, the experimental and numerical works were carried out. The experimental work included two phases aim to investigate the possibility of producing and developing UHPC/UHPGC. In the first, a total of 11 conventional UHPC mixes were designed with different binder type and content at fixed micro steel fiber volume fraction. Whereas in the second, a total of 10 UHPGC mixtures were produced with the same parameters used in the first, but with a constant material/alkaline solution ratio. Three curing methods were adopted for the specimens and then they were tested for identifying the material characterization. On the other hand, the numerical work included the structural behavior of the steel tubular columns infilled with conventional and geopolymer modified UHPC. For the composite columns, circular cross-section with fixed slenderness ratio and wall thickness were taken account. However, the diameter to wall thickness ratio and yield strength of the steel tubes varied. Furthermore, a special theoretical procedure was adopted to take the benefit of compressive strength results on the axial behavior of CFST column. Three international design codes of ACI-318R, Eurocode 4 and Chinese code DL/T were used to evaluate and discuss the performance of the composite compression members.
Experimental and numerical study on steel fiber reinforced scc and those filled circular structural steel tubes
The present study aims firstly to investigate experimentally material behavior of steel fiber reinforced self-compacting concrete (SFRSCC) and secondly to introduce a numerical investigation regarding the structural performance of circular structural steel tube columns infilled with SFRSCC. To this purpose, twelve different mixtures were designed. Hooked ends steel fiber was used to produce SFRSCC. Some engineering properties in terms of workability, compressive and flexural strength, fracture energy and steel-concrete bond strength were tested. Thereafter, to simulate the behavior of SFRSCC filled steel tubular short column under concentrically compression load, the experimental results obtained in the first part of the study were utilized in the evaluation of ultimate axial capacity of concrete filled steel tube column. In this context, different diameter to tube thickness ratio and steel grade were utilized. Based on the predicted column axial capacity, a comparative analysis was made by means of international design codes such as Eurocode 4, ACI, AIJ and DL/T. At each code, a total of 216 column capacity results were assessed and discussed herein. The results revealed that the experimental parameters significantly affected the fresh and mechanical performance. Furthermore, the analytical study presented in this thesis showed that the codes assessed a rational capacity for such special composite column.
A parametric investigation on gate braced frames
This study reported the results of a parametric investigation on the nonlinear behavior of multi-storey reinforced concrete buildings before and after upgraded with gate bracing systems having different eccentricity parameters and configurations. Gate bracing system contains of six members that are symmetrical, and in each side, three members connected to the certain point in the frame bay were employed. Two of them were non-straight diagonal elements while the third one was stretched on one side and connected to the edge of the frame. The case study structures with 2, 4, 6, and 8 storey had the same floor plan (3x3 bays) having the same bay length 5.5 m and storey height 3.3 m for all cases. In the current study, four different eccentricity parameters ranged from 0.2 to 0.8 and eight different configurations of gate bracing over the frame height were introduced. Each bracing part was chosen as circular hollow section with the fixed diameter and wall thickness. A total of 132 frame models (covering 4 without bracing and 128 with gate bracing) were subjected to the nonlinear static pushover analysis. The comparative analysis showed that the lateral load carry capacity of the structure was very close to existing building in 2 storey building in configurations that had no brace in ground floor, but in other cases we noted that decreasing the eccentricity from 0.8 to 0.2 dramatically increased the seismic capacity of all case studied structures.
Fiber reinforced uhpc and its effect on load carrying capacity of composite tube members according to current design codes
The main objective of using reinforced ultra-high performance concrete (UHPC) by different type and volume of fibers with concrete filled steel tube (CFST) structure is to minimize the size of the structural steel tube and to improve the mechanical, fracture, and shrinkage properties of concrete core. This provides high strength and performance for the composite elements. Accordingly, this thesis consists of two parts: First describes the experimental behavior of UHPC reinforced with various fiber types and concentrations. While the second part presents the research results of the structural behavior of axially loaded steel tube column filled with ultra-high performance fiber reinforced concrete (UHPFRC). For this, 19 UHPC mixtures containing micro-steel, hooked-steel, and micro glass fibers up to 2% volume fractions were produced. All designed mixtures were tested for the mechanical, fracture and physical performance. On the other hand, three outer diameters to wall thickness D/t ratios (30, 60, and 90) corresponded by 300, 450, and 600 MPa of yield strength (fy) of the steel tube were used to calculate the axial load capacity (Nu) of circular CFSTs infilled with mentioned UHPFRCs via design equations given by Eurocode 4 (EC4), American Concrete Institute (ACI), American Institute of Steel Construction (AISC), Architectural Institute of Japan (AIJ), and Chinese (DL/T) codes. The results of code comparison revealed that AIJ and DL/T were so near to EC4 followed by AISC then ACI.
Mechanical behavior of uhpc having various binder compositions and influence of such infilled concrete on the structural response of cfst columns
To enhance the sustainability of a structure, three pillars of the sustainability, namely, environmental, social, and economical factors are needed to be considered in the design. On this issue, the development of new structural composite systems with high performance plays a critical role. This study contained two parts: Firstly, the experimental results on the mechanical behavior of ultra high performance concrete (UHPC) mixed with various binder types and volumes were given. Whereas, the second part provided the numerical results on the structural behavior of steel tube column infilled with such UHPC. For this, single, binary, ternary and quarternary binder systems up to 75% replacement levels were used to develop 26 different UHPC mixtures with low cement content. All designed mixtures were tested for identifying the properties of core concrete. Moreover, three diameter to wall thickness D/t ratios (35, 65, and 95) matched by 300, 450, and 600 MPa of yield strength (fy) of the steel tube were used to calculate and examine the axial load capacity of circular concrete filled steel tube (CFST) with UHPCs through design equations given by Eurocode 4 (EC4), American Concrete Institute (ACI) and Chinese (DL/T) codes. The results of experimental and numerical study were given and discussed accordingly.
Experimental behavior of scc with nano-silica andnumerical analysis of cfst composite columns usingscc as an infill
Composite sections are being increasingly popular in constructionindustry. Among them, concrete lled steel tube (CSFT) members areprimarily suited for dierent structural applications. This compositesystem uses the compressive strength of the concrete core as well asthe strength, stiness and connement eect of the surrounding steeltube. In this thesis, rstly, an experimental study on the behavior ofself- compacting concrete (SCC) containing high volume of nano- silica(up to 6%) and 'y ash (up to 75%) was conducted. Secondly, anumerical investigation on short CFST columns made with SCCproduced in the rst part of study was carried out. The structuralresponse of the composite columns were evaluated under the eect ofcompression up to failure. Two design codes such as AmericanConcrete Institute (ACI) and Eurocode 4 (EC4) were used forcalculating the ultimate axial strength of CFST columns lled with SCC.The 16 SCC mixtures were studied and their concrete compressivestrength results at two dierent testing ages were used to get the code predicted ultimate axial strength of the composite columns. Theexperimental and numerical results were given and discussedcomparatively.
Mechanical performance of self-compacting glass concrete and its application in concrete filled steel tubular members under compression
Composite construction including the utilization of steel and concrete has been widely used in structural engineering. Recently, the reuse of the waste products in engineering applications such as concrete production promotes the development of the eco-friendly structures and encourages the concept of sustainable production. In this thesis, firstly, the possible use of green-colored waste glass (WG) in the production of structural self-compacting concrete (SCC) was studied. For this, mechanical and fracture properties in term of compressive, splitting tensile, net flexural strengths and modulus of elasticity were evaluated. The failure characteristics were also measured by means of three-point bending test on the notched beams. In the second part of the thesis, the structural response of the steel tubular members filled with SCCs having WG and subjected to axial loading were investigated numerically. The main parameters of the study were fine/coarse WG aggregate content in SCCs (0 to 100 %), compressive of concrete core (46-67 MPa), diameter to thickness ratio D/t (40 to 100) and yield strength fy (250 to 750 MPa) of the steel tube used. ACI design code was utilized for computation of the axial load carrying capacity (Nu) of the composite columns. Moreover, for comparison purposes, two new empirical formulations proposed by the researchers were employed for calculating Nu values. Results indicated that the use of WG caused a reduction up to 30 % in strength, however less brittle behavior was observed. With increasing D/t ratio and fy of the steel tube, reasonable ultimate strength levels for the composite columns having WG-SCCs were successfully obtained.