No description available.

A parametric analysis on 58 beam-column joint specimens has been conducted. The analysis considered 14 fundamental parameters in the design of each specimen and two performance indicators: the horizontal shear strength ratio between the maximum measured strength and the theoretical strength at beam yield, and the nominal curvature ductility of the adjacent beams. Each parameter was varied by a power function, while the linear correlation coefficient between each parameter and performance indicator was recorded. A combined multiple parameter analysis was then conducted to show the interaction of the design parameters and show the representative influences of each parameter based on the magnitude of the applied power functions. Two design equations were constructed from the most influential design parameters, one for each performance indicator. The shear strength ratio was found to be governed by the horizontal joint shear stress, the column axial stress and the yield strength of the longitudinal beam reinforcement. The available curvature ductility of the adjacent beams was also found to be governed by the horizontal joint shear stress, the column axial stress and the yield strength of the longitudinal beam reinforcement, but also the quantity of the horizontal joint shear reinforcement. The influence of the column axial stress on both performance indicators was found to be best represented by a quadratic function. This was because the column axial stress was found to be beneficial up to stress levels of , but axial stress levels exceeding were found to be detrimental to the performance of the beam-column joint, compared to a joint with no axial stress on the columns. The non-linear relationship of the column axial stress agreed with the design assumptions in NZS 3101 for low axial stress values, but at higher axial stress values NZS 3101 assumes a continued performance increase as a result of increasing axial stress, which has been found to be un-conservative. Additionally, an interaction between the column axial stress and the horizontal joint shear stress has been identified. As a result, beam-column joints with high column axial stress levels above 0.40 and horizontal joint shear stress levels in the order of have been shown to fail in a brittle crushing of the concrete in the joint core. Considering this behaviour, it is recommended that the column axial stress levels in earthquake designed beam-column joints should not exceed 0.35 . The results of the parametric analysis were then compared against the current NZS 3101 design equations for conservatism. It was found that a reduction in the horizontal joint shear reinforcement may be possible for beam-column joints incorporating Grade 300 steel in the longitudinal reinforcement of the beams and axial stress levels below 0.25 , but when Grade 500 steel is used or the column axial stress is greater than 0.25 , an increase in the joint shear reinforcement is required compared to NZS 3101. The current NZS 3101 design requirement of at least 40% of the joint shear force, to be resisted by means of joint shear reinforcement, has been found to be appropriate.

No description available.

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

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.

Recent research on jointed unbonded post-tensioned precast concrete frames has demonstrated their superior seismic resistance. Inelastic rotation generated during large earthquake motions is accommodated through gap opening and closing at the beam-to-column connections in the frame. By applying the principles of Damage Avoidance Design (DAD), a steel-steel armoured connection has been demonstrated to be effective in protecting the precast elements from damage. The re-centring ability of the unbonded prestressed post-tensioned system allows the building to return to its original undeformed position after the earthquake with negligible residual deformations. This research experimentally assesses the biaxial performance of the unbonded precast beam-to-column joint and simplifies the steel-steel armoured connection details in the joint. The experimental results of both quasi-static unidirectional lateral loading tests and biaxial lateral loading tests conducted on a 80% scaled unbonded jointed beam-to-column joint are presented. The performance of the proposed simplified steel-steel connection is assessed. A theoretical model is developed based primarily on rigid body kinematics and is validated using the test results. A formulation is also developed based on St Vennants' principle, to estimate the effective stiffness of the precast concrete beams under bidirectional rocking. Based on the experimental findings, improvements to the steel-steel armoured connection and joint details are proposed.

Reinforced concrete structures designed in pre-1970s are vulnerable under earthquakes due to lack of seismic detailing to provide adequate ductility. Typical deficiencies of pre-1970s reinforced concrete structures are (a) use of plain bars as longitudinal reinforcement, (b) inadequate anchorage of beam longitudinal reinforcement in the column (particularly exterior column), (c) lack of joint transverse reinforcement if any, (d) lapped splices located just above joint, and (e) low concrete strength. Furthermore, the use of infill walls is a controversial issue because it can help to provide additional stiffness to the structure on the positive side and on the negative side it can increase the possibility of soft-storey mechanisms if it is distributed irregularly. Experimental research to investigate the possible seismic behaviour of pre-1970s reinforced concrete structures have been carried out in the past. However, there is still an absence of experimental tests on the 3-D response of existing beam-column joints under bi-directional cyclic loading, such as corner joints. As part of the research work herein presented, a series of experimental tests on beam-column subassemblies with typical detailing of pre-1970s buildings has been carried out to investigate the behaviour of existing reinforced concrete structures. Six two-third scale plane frame exterior beam-column joint subassemblies were constructed and tested under quasi-static cyclic loading in the Structural Laboratory of the University of Canterbury. The reinforcement detailing and beam dimension were varied to investigate their effect on the seismic behaviour. Four specimens were conventional deep beam-column joint, with two of them using deformed longitudinal bars and beam bars bent in to the joint and the two others using plain round longitudinal bars and beam bars with end hooks. The other two specimens were shallow beam-column joint, one with deformed longitudinal bars and beam bars bent in to the joint, the other with plain round longitudinal bars and beam bars with end hooks. All units had one transverse reinforcement in the joint. The results of the experimental tests indicated that conventional exterior beam-column joint with typical detailing of pre-1970s building would experience serious diagonal tension cracking in the joint panel under earthquake. The use of plain round bars with end hooks for beam longitudinal reinforcement results in more severe damage in the joint core when compared to the use of deformed bars for beam longitudinal reinforcement bent in to the joint, due to the combination of bar slips and concrete crushing. One interesting outcome is that the use of shallow beam in the exterior beam-column joint could avoid the joint cracking due to the beam size although the strength provided lower when compared with the use of deep beam with equal moment capacity. Therefore, taking into account the low strength and stiffness, shallow beam can be reintroduced as an alternative solution in design process. In addition, the presence of single transverse reinforcement in the joint core can provide additional confinement after the first crack occurred, thus delaying the strength degradation of the structure. Three two-third scale space frame corner beam-column joint subassemblies were also constructed to investigate the biaxial loading effect. Two specimens were deep-deep beam-corner column joint specimens and the other one was deep-shallow beam-corner column joint specimen. One deep-deep beam-corner column joint specimen was not using any transverse reinforcement in the joint core while the two other specimens were using one transverse reinforcement in the joint core. Plain round longitudinal bars were used for all units with hook anchorage for the beam bars. Results from the tests confirmed the evidences from earthquake damage observations with the exterior 3-D (corner) beam-column joint subjected to biaxial loading would have less strength and suffer higher damage in the joint area under earthquake. Furthermore, the joint shear relation in the two directions is calibrated from the results to provide better analysis. An analytical model was used to simulate the seismic behaviour of the joints with the help of Ruaumoko software. Alternative strength degradation curves corresponding to different reinforcement detailing of beam-column joint unit were proposed based on the test results.

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.

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.

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.