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Showing 1 to 10 of 10 (0.025 seconds)Spelling suggestions: "subject:"beamcolumn 4points"" "subject:"beamcolumn 5points""
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Nonlinear Cyclic Truss Model for Beam-Column Joints of Non-ductile RC FramesBowers, Jeremy Thomas 01 September 2014 (has links)
Reinforced concrete (RC) moment frames comprise a significant portion of the built environment in areas with seismic hazards. The beam-to-column joints of these frames are key components that have a significant impact on the structure's behavior. Modern detailing provides sufficient strength within these joints to transfer the forces between the beams and the columns during a seismic event, but existing structures built with poor detailing are still quite prevalent. Identifying the need and extent of retrofits to ensure public safety through nondestructive means is of primary importance. Existing models used to analyze the performance of RC beam-to-column joints have either been developed for modern, well-detailed joints or are simplified so that they do not capture a broad range of phenomena.
The present study is aimed to extend a modeling technique based on the nonlinear truss analogy to the analysis of RC beam-to-column joints under cyclic loads. Steel and concrete elements were arranged into a lattice truss structure with zero-length bond-slip springs connecting them. A new steel model was implemented to more accurately capture the constitutive behavior of reinforcing bars. The joint modeling approach captured well the shear response of the joint. It also provided a good indication of the distribution of forces within the joint.
The model was validated against three recently tested beam-column subassemblies. These tests represented the detailing practice of poorly-detailed RC moment frames. The analytical results were in good agreement with the experimental data in terms of initial stiffness, strength and damage pattern through the joint. / Master of Science
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Seismic Behaviour of Exterior Beam-Column Joints Reinforced with FRP Bars and StirrupsMady, Mohamed Hassan Abdelhamed 25 August 2011 (has links)
Reinforced concrete beam-column joints (BCJs) are commonly used in structures such as parking garages, multi-storey industrial buildings and road overpasses, which might be exposed to extreme weathering conditions and the application of de-icing salts. The use of the non-corrodible fiber-reinforced polymer (FRP) reinforcing bars in such structures is beneficial to overcome the steel-corrosion problems. However, FRP materials exhibit linear-elastic stress-strain characteristics up to failure, which raises concerns on their performance in BCJs where energy dissipation, through plastic behaviour, is required. The objective of this research project is to assess the seismic behaviour of concrete BCJs reinforced with FRP bars and stirrups.
An experimental program was conducted at the University of Manitoba to participate in achieving this objective. Eight full-scale exterior T-shaped BCJs prototypes were constructed and tested under simulated seismic load conditions. The longitudinal and transversal reinforcement types and ratios for the beam and the columns were the main investigated parameters. The experimental results showed that the GFRP reinforced joints can successfully sustain a 4.0% drift ratio without any significant residual deformation. This indicates the feasibility of using GFRP bars and stirrups as reinforcement in the BCJs subjected to seismic-type loading. It was also concluded that, increasing the beam reinforcement ratio, while satisfying the strong column-weak beam concept, can enhance the ability of the joint to dissipate seismic energy.
An analytical investigation was conducted through constructing a finite element model using ANSYS-software. The model was verified against the experimental results in this research. Then, a parametric study was performed on number of different parameters known to affect such joints including column axial load, concrete compressive strength, flexural strength ratio and joint transverse reinforcement. It was concluded that 70% of the column axial load capacity can be recommended as an upper limit to the applied axial loads on the column to avoid damage occurrence within the joint. It was also concluded that a minimum flexural strength ratio of 1.50 is recommended to ensure the strong-column weak-beam mechanism. In addition, a minimum joint transverse reinforcement ratio of 0.60% is recommended to insure that the failure will not occur in the joint zone.
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Retrofit strategy of non-seismically designed frame systems based on a metallic haunch systemChen, Te-Hsiu January 2006 (has links)
Due to the lack of capacity design principles as well as of appropriate structural details, most of the reinforced concrete building designed primarily for gravity loads as typical of pre- 1970s code provisions, are expected and has been demonstrate to suffer sever damage or total collapse under the earthquake excitation. Due to the use of plain round bar and inadequate reinforcing details, critical shear failure in the joint connection region could occur, leading to sever damage when not total collapse of the building. In this research project, a comprehensive experimental programme was carried to investigate the seismic performance of existing beam column joints prior and after retrofit intervention with a recently proposed low-invasive retrofit technique based on a metallic haunch system. The joint performance was evaluated in terms of the principal tensile stresses that caused the joint shear cracks in the joint panel zone. Quasi-static cyclic tests under uni-directional or bidirection loading regime were carried out to record the response of a series of under-designed beam column joints (with either a wide-beam or a deep-beam solution, deformed or plain round bars with end hooks). The experimental results were used to investigate the effect of structural detailing and loading regime on the seismic performance. To retrofit the potential deficiencies in the existing beam-column joints, the feasibility and efficiency of a low invasive retrofit solution based on a diagonal metallic haunch was investigated. The proposed haunch retrofit solution aims to provides an economic, ease of implementation alternative to protect the joint from the brittle shear failure by relocating the beam plastic hinge away form the joint panel zone. To achieve the desired capacity design (hierarchy of strength) and sequence of event, a simplified analytical formulation has been adopted to account for the joint shear strength in terms of principle tensile/compression stresses prior and after the retrofit intervention. A useful visualization tool based on a M-N (moment-axial load) performance domain can be adopted to evaluate the actual performance point and events, by comparing demand vs. capacity. Designed charts are proposed based on displacement compatibility conditions to evaluate the efficiency of the haunch solution. In addition, a complete step-by step design procedure to implement the retrofit strategy and intervention to achieve the desired hierarchy of strength, by using the proposed diagonal metallic haunch solution, is derived and presented. The effectiveness of the proposed haunch solution and reliability of the derived analytical design/assessment procedure, were validated through experimental tests of 2-D and 3-D subassemblies, shown in the first experimental part to have the most vulnerable behaviour in the joint panel zone. Conceptual issues related to the design of the retrofit intervention, when moving from a 2-D to a 3-D behaviour are discussed. The experimental results showed an excellent performance of the proposed intervention, able to protect the panel zone region (by limiting the principle tensile stress demand), while enforcing the formation of a plastic hinge in the beam, far away from the joint interface. As a result, a much more stable inelastic response could be developed, confirming the high potential of such a low-invasive, low-cost retrofit intervention on under-designed frame systems. In conclusion, a simple numerical model, based on a lumped plasticity approach, was developed and validated on the experimental results to capture the full response of the subassembly prior and after the retrofit intervention.
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GFRP-reinforced concrete exterior beam-column joints subjected to seismic loadingHasaballa, Mohamed 29 October 2014 (has links)
Glass fibre-reinforced polymer (GFRP) reinforcement is used in reinforced concrete (RC) infrastructure to avoid steel corrosion problems. The behaviour of GFRP reinforcement under seismic loading in RC frame structures has not been widely investigated. The behaviour of beam-column joints significantly influences the response of the Seismic Force Resisting Systems. Therefore, both the design and detailing of the beam-column joints are critical to secure a satisfactory seismic performance of these structures. However, the current Canadian FRP design codes (CSA 2012, CSA 2006) have no considerable seismic provisions, if any, due to lack of data and research in this area. Such lack of information does not allow for adequate designs and subsequently limits the implementation of FRP reinforcement as a non-corrodible and sustainable reinforcement in new construction. Therefore, it deemed necessary to track areas of ambiguity and lack of knowledge to provide design provisions and detailing guidelines.
This study investigated the seismic behaviour of the GFRP-RC exterior beam-column joints. The study consisted of an experimental phase, in which ten full-scale T-shaped GFRP-RC specimens were constructed and tested to failure, and an analytical phase using finite element modelling (FEM). Specimens in the experimental phase were designed to investigate the anchorage detailing of beam longitudinal reinforcement inside the joint (using either bent bars or headed bars) and to evaluate the shear capacity of the joint.
In the analytical phase, a commercial FEM software (ATENA-3D) was used to run a parametric study that investigated the influence of the presence of lateral beams, axial load on the column, applied shear stresses in the joint, and the concrete strength.
Test results showed that the performance of the specimens reinforced with GFRP headed bars was comparable to their counterparts reinforced with bent bars up to 4.0% drift ratio. The difference in the reinforcement surface conditions had insignificant influence on the overall behaviour. Moreover, it was concluded that the shear capacity of GFRP-RC beam-column joints is 0.85 √f'c. Furthermore, an evaluation of the relevant seismic provisions in the CSA/S806-12 (CSA 2012) was carried out and some recommendations were proposed for consideration in the future updates of the CSA/S806-12.
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Seismic Behaviour of Exterior Beam-Column Joints Reinforced with FRP Bars and StirrupsMady, Mohamed Hassan Abdelhamed 25 August 2011 (has links)
Reinforced concrete beam-column joints (BCJs) are commonly used in structures such as parking garages, multi-storey industrial buildings and road overpasses, which might be exposed to extreme weathering conditions and the application of de-icing salts. The use of the non-corrodible fiber-reinforced polymer (FRP) reinforcing bars in such structures is beneficial to overcome the steel-corrosion problems. However, FRP materials exhibit linear-elastic stress-strain characteristics up to failure, which raises concerns on their performance in BCJs where energy dissipation, through plastic behaviour, is required. The objective of this research project is to assess the seismic behaviour of concrete BCJs reinforced with FRP bars and stirrups.
An experimental program was conducted at the University of Manitoba to participate in achieving this objective. Eight full-scale exterior T-shaped BCJs prototypes were constructed and tested under simulated seismic load conditions. The longitudinal and transversal reinforcement types and ratios for the beam and the columns were the main investigated parameters. The experimental results showed that the GFRP reinforced joints can successfully sustain a 4.0% drift ratio without any significant residual deformation. This indicates the feasibility of using GFRP bars and stirrups as reinforcement in the BCJs subjected to seismic-type loading. It was also concluded that, increasing the beam reinforcement ratio, while satisfying the strong column-weak beam concept, can enhance the ability of the joint to dissipate seismic energy.
An analytical investigation was conducted through constructing a finite element model using ANSYS-software. The model was verified against the experimental results in this research. Then, a parametric study was performed on number of different parameters known to affect such joints including column axial load, concrete compressive strength, flexural strength ratio and joint transverse reinforcement. It was concluded that 70% of the column axial load capacity can be recommended as an upper limit to the applied axial loads on the column to avoid damage occurrence within the joint. It was also concluded that a minimum flexural strength ratio of 1.50 is recommended to ensure the strong-column weak-beam mechanism. In addition, a minimum joint transverse reinforcement ratio of 0.60% is recommended to insure that the failure will not occur in the joint zone.
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Experimental Evaluation of Reinforcement Methods for Concrete Beam-Column JointsFisher, Matthew John 03 September 2009 (has links)
No description available.
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Seismic performance of GFRP-RC exterior beam-column joints with lateral beamsKhalili Ghomi, Shervin 14 February 2014 (has links)
In the past few years, some experimental investigations have been conducted to verify seismic behaviour of fiber reinforced polymer reinforced concrete (FRP-RC) beam-column joints. Those researches were mainly focused on exterior beam-column joints without lateral beams. However, lateral beams, commonly exist in buildings, can significantly improve seismic performance of the joints. Moreover, the way the longitudinal beam bars are anchored in the joint, either using headed-end or bent bars, was not adequately addressed. This study aims to fill these gaps and investigate the shear capacity of FRP-RC exterior beam-column joints confined with lateral beams, and the effect of beam reinforcement anchorage on their seismic behaviour. Six full-scale exterior beam-column joints were constructed and tested to failure under reversal cyclic loading. Test results showed that the presence of lateral beams significantly increased the shear capacity of the joints. Moreover, replacing bent bars with headed-end bars resulted in more ductile behaviour of the joints.
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Seismic performance of GFRP-RC exterior beam-column joints with lateral beamsKhalili Ghomi, Shervin 14 February 2014 (has links)
In the past few years, some experimental investigations have been conducted to verify seismic behaviour of fiber reinforced polymer reinforced concrete (FRP-RC) beam-column joints. Those researches were mainly focused on exterior beam-column joints without lateral beams. However, lateral beams, commonly exist in buildings, can significantly improve seismic performance of the joints. Moreover, the way the longitudinal beam bars are anchored in the joint, either using headed-end or bent bars, was not adequately addressed. This study aims to fill these gaps and investigate the shear capacity of FRP-RC exterior beam-column joints confined with lateral beams, and the effect of beam reinforcement anchorage on their seismic behaviour. Six full-scale exterior beam-column joints were constructed and tested to failure under reversal cyclic loading. Test results showed that the presence of lateral beams significantly increased the shear capacity of the joints. Moreover, replacing bent bars with headed-end bars resulted in more ductile behaviour of the joints.
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Behaviour of three-dimensional concrete structures under concurrent orthogonal seismic excitationsZaghlool, Baher SalahElDeen Othman Ahmed January 2007 (has links)
This thesis is a study into the response and seismic safety of three-dimensional multi-storey concrete structures under concurrent orthogonal seismic excitations. It employs the nonlinear time-history method as its analysis tools. Time-history analyses rely heavily on their utilised earthquake records. Accordingly, this study examines the different approaches of selecting earthquake suites and develops a methodology of selecting representative earthquake scenarios. This methodology is credibly implemented in selecting a far- and a near field suites representative of the New Zealand seismic hazard. The study investigates the response of 6-, 9- and 12-storey concrete structures of different n-X-bays × m-Y-bays. Bidirectional responses of these considered structures are examined and consequently the current combination rules are scrutinised. Consequently this study strongly recommends the use of the 40-percent combination rule in lieu of the widely used 30-percent rule; and the use of time-history analysis in lieu of quasi/equivalent static and response modal analysis methods to avoid their strong dependence on combination rules. An intensive study is conducted employing the incremental dynamic analysis (IDA) technique to investigate structural demands of interstorey drifts, lateral storey drifts and storey accelerations. The study utilises the developed far-field suite and identifies the 50th and 90th percentile demands. Hence it provides easy-to-use expressions to facilitate rapid calculation of the structural demands and the effects of biaxial interactions. An implementation into the Demand and Capacity Factor Design (DCFD) format is presented that infers confidence in the performance levels of the considered structures. The study also draws attention to the importance of considering storey accelerations as their storey values reach as high as 10 × PGA. A sensitivity study is conducted by repeating the IDA investigation while using the developed near-field suite. Subsequently a comparison between the near- and the far-field results is conducted. The results were markedly similar albeit of less magnitudes until the (seismic hazard) intensity measure IM = Sa(T₁) = 0.4g when the near-field results show sudden flat large increase in demands suggesting a brittle collapse. This is attributed to the higher content of the higher mode frequencies contained in near-field ground motions. Finally, the study examines the (vectorial) radial horizontal shear demands in columns and beam-column joints of the previous far- and near-field studies. The combined radial shear demands in corner, edge and internal columns and joints are evaluated that roughly show a square-root proportional relationship with IM that exhibit somewhat brittle failure at IM ≥ 0.35g. Shears demands in the (4-way) internal columns and the (2-way) corner joints show highest magnitude in their respective class. The results suggest transverse joint shear reinforcement of 1.5, 1.0 and 0.5 of the longitudinal reinforcement of the neighbouring beam respectively for corner, edge and internal joints. An implementation of a proposed practical (and simpler) DCFD format shows satisfactory confidence in columns performance in shear up to IM = 0.35g, conversely to joints unsatisfactory performance in shear at the onset of inelastic behaviour (IM > 0.05g).
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Rehabilitation of Exterior RC Beam-Column Joints using Web-Bonded FRP SheetsMahini, Seyed Saeid Unknown Date (has links)
In a Reinforced Concrete (RC) building subjected to lateral loads such as earthquake and wind pressure, the beam to column joints constitute one of the critical regions, especially the exterior ones, and they must be designed and detailed to dissipate large amounts of energy without a significant loss of, strength, stiffness and ductility. This would be achieved when the beam-column joints are designed in such a way that the plastic hinges form at a distance away from the column face and the joint region remain elastic. In existing frames, an easy and practical way to implement this behaviour following the accepted design philosophy of the strong-column weak-beam concept is the use a Fibre Reinforced Plastic (FRP) retrofitting system. In the case of damaged buildings, this can be achieved through a FRP repairing system. In the experimental part of this study, seven scaled down exterior subassemblies were tested under monotonic or cyclic loads. All specimens were designed following the strong-column weak-beam principal. The three categories selected for this investigation included the FRP-repaired and FRP-retrofitted specimens under monotonic loads and FRP-retrofitted specimen under cyclic loads. All repairing/retrofitting was performed using a new technique called a web-bonded FRP system, which was developed for the first time in the current study. On the basis of test results, it was concluded that the FRP repairing/retrofitting system can restore/upgrade the integrity of the joint, keeping/upgrading its strength, stiffness and ductility, and shifting the plastic hinges from the column face toward the beam in such a way that the joint remains elastic. In the analytical part of this study, a closed-form solution was developed in order to predict the physical behaviour of the repaired/retrofitted specimens. Firstly, an analytical model was developed to calculate the ultimate moment capacity of the web-bonded FRP sections considering two failure modes, FRP rupture and tension failure, followed by an extended formulation for estimating the beam-tip displacement. Based on the analytical model and the extended formulation, failure mechanisms of the test specimens were implemented into a computer program to facilitate the calculations. All seven subassemblies were analysed using this program, and the results were found to be in good agreement with those obtained from experimental study. Design curves were also developed to be used by practicing engineers. In the numerical part of this study, all specimens were analysed by a nonlinear finite element method using ANSYS software. Numerical analysis was performed for three purposes: to calculate the first yield load of the specimens in order to manage the tests; to investigate the ability of the web-bonded FRP system to relocate the plastic hinge from the column face toward the beam; and to calibrate and confirm the results obtained from the experiments. It was concluded that numerical analysis using ANSYS could be considered as a practical tool in the design of the web-bonded FRP beam-column joints.
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