Theses supervised by Doç. Dr. Esra Mete Güneyisi
42 theses · Gaziantep University
Nonlinear pushover analysis of medium and high rise buildings with X-braces
This study aims to investigate the structural behavior of medium and high rise frame buildings with and without X-brace. The performance of the concentrically X-braced frame structures were examined using pushover analysis. For this purpose, steel moment resisting frame buildings having four to sixteen stories were considered. All buildings have the same plan and contain three bays on each direction. The existing steel frames had two different design properties and designated as flexible moment-resisting frames and rigid moment-resisting frames. Then, X-braces were introduced into the middle bay of each frame. The nonlinear analyses were performed using the finite element analysis program of SAP 2000. The parameters such as capacity curve, inter-storey drift index, global damage index, and base shear were evaluated for the frame systems. It was observed that the incorporation of concentric X-braces into the frame resulted in a significant enhancement in the structural behavior of the existing frames.
Effect of strength and stiffness of buckling-restrained braces on seismic retrofitting of reinforced concrete buildings
This thesis presents an analytical study aimed at evaluating the effect of using buckling-restrained braces (BRBs) on the seismic retrofitting of 3 and 6 storey reinforced concrete (RC) buildings. In the design of the BRBs with non-prismatic cross-sections, twelve combinations of ? and ß design parameters that influence the strength and stiffness of the BRBs, respectively, were considered. The response of the RC structures with and without BRBs under earthquake ground accelerations were evaluated through nonlinear dynamic analysis. Two sets of ground motions representative of the design earthquake with 10% and 50% exceedance probability in fifty years were taken into account. By comparing the structural performance of the original and buckling restrained braced structures, it was observed that the use of the BRBs were very effective in mitigating the seismic response as a retrofit scheme. However, the selection of the strength and stiffness parameters of the BRBs had considerable effect on the response characteristics of RC structures such as by increasing the value of ? and by decreasing the value of ß of the buckling-restrained braces, the maximum deformation demand of the structures increased.
Earthquake response of reinforced concrete buildings retrofitted with inverted-v and zipper braces
Steel bracing system is one of the structural systems used to resist the earthquake. Many existing non-ductile reinforced concrete (RC) structures need to be retrofitted to improve the lateral load carrying capacity. The use of steel bracing for retrofitting is one of the convenient solutions for increasing the earthquake resistance of the structure. In this thesis, 4 and 8 storey existing RC buildings having the same plan and three bays on each direction were considered as a case study. For the rehabilitation of the structures, inverted-V and zipper braces were used. The seismic performance of the retrofitted structures was investigated and compared with the existing ones. In this regard, the effectiveness of using inverted-V and zipper bracing in strengthening the building was examined under different earthquake accelerations. The structures were modeled using a finite element method and evaluated by both nonlinear static and time history analyses. Capacity curves, interstorey index, variation of storey displacement, and roof drift time history were computed for each structural system. The results indicated a considerable enhancement in the earthquake performance of the retrofitted structures and it was observed that the zipper braced systems had more lateral load carrying and energy absorption capacity than the inverted-V braced systems. Keywords: Inverted-V brace; Nonlinear analysis; Reinforced concrete building; Seismic performance; Zipper brace.
Structural performance assessment of an existing reinforced concrete building retrofitted with inverted Y-shaped braces
In this study, the efficiency of inverted Y-shaped eccentric steel bracing systems with different link lengths for seismic retrofitting of seismically insufficient reinforced concrete building were investigated. For this, since most of the buildings in the existing building stock of our country were constructed before 1998 and were designed according to 1975 seismic design code, firstly, a reinforced concrete building having a symmetric geometry in plan in compliance with 1975 seismic regulation was selected as a case study. As a retrofit scheme, inverted Y-shaped braces were inserted into the external bays of the existing building. In the seismic strengthening of the original building, inverted Y-bracing was designed considering three different steel link lengths. The analytical frame model having nonlinear properties of structural members of the existing and retrofitted buildings was performed. The performance of the existing and retrofitted structures under earthquake loading was comparatively examined through nonlinear static and nonlinear time history analyses. From the results of the analysis, it was found that the seismic performance of the existing reinforced concrete building with inadequate detailing exhibited considerable improvement after retrofitting with eccentric braces. The results also indicated the importance of the selection of the link length in the design of inverted Y-shaped eccentric steel braces for seismic retrofitting.
Structural evaluation of steel moment resisting frames upgraded with buckling restrained knee braces
In this study, the structural performance of three and six storey steel buildings accompanied with buckling restrained braces was evaluated. The buildings studied were regular in plan and had a typical 3 bay x 3 bay frame with plan dimensions of 14 m x 14 m. For this, two dimensional models for the buildings were created and then buckling restrained braces in knee configuration were installed above and/or below the beams of the frame system. The seismic response of the structures with and without buckling restrained knee braces was assessed through nonlinear static and dynamic analyses. Moreover, two different spectrum compatible earthquakes, namely, 1999 Hector Mine and 1999 Düzce, were used in the dynamic analyses. Analytical results indicated that the steel moment resisting frames with buckling restrained knee braces had greater lateral load carrying capacity and lower inter-storey displacement than the bare frames.
Nonlinear structural analysis and design of reinforced concrete building with base isolation system
In the recent years, the base-isolation systems are gaining great attention as a solution to protect the structures against the seismic risk. The main role of such system is to separate the structure from its foundation and then eliminate the adverse effect of the earthquake motions. In this study, an existing 9-storey reinforced concrete (RC) building having three bays on the x-direction and five bays on the y-direction direction were considered as a case study model. As a base isolation, friction pendulum type system was used. The seismic performance of the base isolated structure was investigated and compared with the existing one. In this regard, the effectiveness of using base isolation in protecting the building against the seismic actions was examined under different earthquake accelerations. The structures were modeled by means of a finite element method and evaluated by nonlinear time history analysis. The performance characteristics of the fix-based and base isolated RC structures were determined in terms of the storey displacement, interstorey drift ratio, base shear, and columns bending moment. Based on the results of the nonlinear analysis, a substantial improvement in the seismic response of the based isolated structure in comparison to the existing one was observed.
Earthquake resistance of high rise reinforced concrete structures with buckling restrained braces
Buckling restrained brace is relatively new type of structural bracing system and includes a steel core confined within a steel hollow section by a grout infill material. This bracing system utilizes the ductility of the steel more effectively than conventional one. In this study, the earthquake response of the high-rise reinforced concrete (RC) frame structures with buckling-restrained braces were investigated. For this, two RC structures having 9 and 18 stories were taken into account as a case study. The effect of using buckling-restrained braces to protect the structures against earthquakes was studied. As a bracing pattern, diagonal shape buckling-restrained braces were utilized over the height of the RC frames. The nonlinear dynamic time-history analysis was performed on the RC frame structures before and after inclusion of buckling-restrained braces. Different ground motion records, namely, 1999 Chi Chi, 1999, Hector Mine, and 1999 Düzce, were used in the analysis. It was concluded that the use of buckling-restrained braces over the frame height was found to have a significant effect on the seismic behavior of the structures. Buckling-restrained bracing cases exhibited lower displacement and more uniform inter-story drift demands compared to the cases without buckling restrained braces. Keywords: Buckling restrained brace, Earthquake, Nonlinear analysis, Reinforced concrete structure, Seismic upgrading.
Dynamic behavior of reinforced concrete structures irregular in elevation with and without brbs
This study investigates the dynamic response of high rise regular and irregular reinforced concrete frame buildings having buckling restrained braces (BRBs). As a case study, a twelve story reinforced concrete structure regular in elevation was designed. Then, the other three structures irregular in elevation were designed with the same geometric configuration in the lower six stories and different irregularities in the upper six stories. To improve the structural performance of both regular and irregular ones, the buckling restrained braces were introduced into the internal bays of each structure. Thus, a total of eight different cases were taken into account in the present study. All frame models considered had four bays (in the direction of earthquake) with a uniform bay width of 6 m. All frames were subjected to nonlinear dynamic time-history analysis for selected input earthquake waves of 1984 Morgan Hill and 1999 Hector Mine. Variation in displacement and inter-story drift ratio with story level, displacement time history and base shear time history responses of the regular and irregular structures with and without the BRBs were evaluated comparatively The analysis of the results showed that the BRBs caused a significant improvement in the dynamic behavior of both regular and especially irregular structures, depending on the characteristics of the ground motions used and amount of irregularity.
Inelastic behavior of reinforced concrete structure with tuned mass damper
The application of energy dissipation devices to control the influence of earthquake loads on the structures suggests an attractive alternative to traditional earthquake resistance design methods. In this study, the efficiency of using tune mass dampers (TMDs) to enhance the earthquake performance of an existing reinforced concrete (RC) building was investigated comparatively. To this aim, an eight story RC building having the same height of 3 m at each story level and three equal bay spacing of 5 m in both directions was designed as a moment resisting frame building. The dimension of the columns varied for each story while that of the beams were considered as 60x25 cm at all stories. The TMD system was modeled by means of two plates indicating shell elements and 13 link elements, nine linear springs and 4 viscous dampers. They were placed at roof level of the building. The nonlinear dynamic analysis was performed for the case study RC building before and after applying TMDs. The time history of displacement, drift, bending moment, and acceleration as well as the distribution of drift over the story height and base shear versus roof displacement variation were evaluated and discussed. The analysis of the results indicated that the response of the RC structure positively improved by the inclusion of TMDs in the case of earthquakes. Keywords: Dynamic analysis, Earthquake, Nonlinear behavior, Reinforced concrete building, Tuned mass dampers.
Evaluating nonlinear behavior of a reinforced concrete building with shear walls and concentric steel bracings
The susceptibility of existing buildings has become an important issue since they did not satisfy modern seismic design requirements or they have been designed and constructed in accordance with the earlier codes. A great number of reinforced concrete (RC) buildings are located in the unsafe seismic zones and they have high vulnerability to damage. Therefore, either local or global strengthening strategies are required for such structures. This study aimed to assess the seismic performance of a typical residential building and its retrofitting by means of different approaches. For this purpose, an existing 9 story reinforced concrete (RC) building having the same floor plan (5x5 bays) was used as a case study. The building had a typical beam-column RC frame with no shear walls. For seismic performance upgrading of the building, RC shear wall and concentric steel bracing systems were employed. As a concentric bracing system, X-bracing, inverted-V bracing, and diagonal bracing were utilized. Analytical modelings of the existing and retrofitted RC buildings were realized by means of ETABS 2013. The performances of all structures were evaluated using the nonlinear static and dynamic analyses. From these analyses, the pushover curves, inter-story drift ratio, story displacements, and time history plots were obtained for the existing and retrofitted buildings. It was observed that the existing building had a performance level of collapse prevention and its performance improved to life safety after retrofitting. Keywords: Reinforced concrete building; Nonlinear analysis; Retrofitting system; Shear wall; Steel bracing.
Finite element modeling and analysis of reinforced concrete beams with steel fiber and steel plate
In this study, a numerical analysis was carried out by using ANSYS finite element software to model and evaluate the structural behavior of full-size reinforced concrete (RC) beams having different properties. For this, a reference beam having a span length of 6.5 m was designed. Then, two cases were considered to enhance the structural performance of the RC beam. In the first case, the use of steel fiber in RC beam was taken account. Three steel fiber volume fractions (0.5, 1.0, and 2.0%) were investigated. In the second case, the bonding of steel plate to the tension face of the beam by adhesive resin was considered. Various thicknesses of steel plate (1, 2, and 3 mm) was utilized in this case. All beams were subjected to a three-point bending test. The nonlinear property was modeled for the concrete using three-dimensional (3D) solid element. The steel reinforcing bars were modeled as linkage elements with elasto-plastic behavior and perfect bond between concrete element and steel bar was assumed. The steel plate used for strengthening RC beam was modeled as a plane shell element connected to the lower concrete surface by using special contact surface between them. The steel fibers were considered as small units of reinforcement embedded in concrete based on the geometry of the concrete element. The efficiency of the current models was measured by comparing the results with previous experimental results. A good agreement was found between the model predictions for the load-deflection relation and experimental results. Besides, the use of steel plate for strengthening conventional RC beam significantly increased the ultimate load carrying capacity as well as the stiffness of the beam more than that of the steel fiber cases, especially when a steel plate thickness was chosen as 3 mm. Keywords: Finite element method, Reinforced concrete beam, Steel fiber, Steel plate, Strengthening.
Effect of using off-center bracing system on the capacity curve of a reinforced concrete building.
This study investigates the variation in the capacity curve of an eight story reinforced concrete (RC) building before or after applying off-center bracing system. The case study structure had the same floor plan (3x4 bays) with varying bay length. The external and the internal bays are 3 m and 4 m spans, respectively. The off-center bracing system comprised of three main members. Two of them were non-straight diagonal elements and connected at a certain point in the frame bay while the third one was connected from this point to the corner of the frame. This arrangement introduced different eccentricity parameters. In the current study, four different eccentricity parameters varying from 0.2 to 0.8 and nine different sizes of brace member with an outer diameter ranged from 80 to 240 mm were used. The brace members were selected as circular hollow section (CHS). Thus, a total of 37 different cases were considered in this study. All structural models were subjected to the nonlinear static pushover analysis. The effect of the eccentricity in the off-center bracing together with brace member size on the seismic performance of the strengthened building were evaluated. The comparative analysis indicated that the lateral load carrying capacity of the structure was very sensitive to the amount of eccentricity. Increasing the eccentricity from 0.2 to 0.8 dramatically reduced the capacity of all case studied structures. Keywords: Eccentricity, Off-center bracing, Pushover analysis, Reinforced concrete building, Seismic response.
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.