Seismic strengthening of RC beam–column connections

Cyclic load tests on six reinforced concrete (RC) exterior beam-column subassemblages simulating joints of buildings constructed before the 1970s, with nonoptimal reinforcing details to resist earthquakes, are described. The exterior beam-column joints were reinforced by plain bars and lacked transverse reinforcement, and the longitudinal beam bars were poorly anchored. Two of them had inadequate beam top reinforcement. All of the beam-column joints were also tested after the upgrade, except one, which was upgraded and then tested for the first time. The proposed upgrade techniques were aimed at providing an effectual anchoring to the beam longitudinal bars and at increasing strength and stiffness of the beam-column joints. As expected, the performance of reference specimens (without upgrade) was found to be unsatisfactory in terms of lateral load capacity and stiffness. The improvement in the performance of the upgraded specimens is demonstrated.

Proceedings of the 8th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2015), 2021

As widely investigated in literature, the local behavior of the joints strongly influences the whole performance of the steel structures; thus, both in the design and assessment of the moment resisting frame (MRF) the joint performance should be properly accounted for. The present work is focused on local assessment and retrofit the beam-to-column joints of an existing non-conforming steel building. Therefore, the monotonic and cyclic behaviors of internal beamto-column joints are investigated by means of finite element analyses (FEAs). The main peculiarities of these joints are the continuity of beams and hollow square columns interrupted at each level and connected both by bolts and fillet welds to the tapered flanges of the beams. Onsite surveys allowed fully characterizing the geometry of the joints. The joint assemblies were sub-structured from the moment resisting frames and analyzed against both the vertical loads and seismic actions. The results showed that these types of joints exhibit very poor seismic behavior, concentering most of the damage within the welds. Therefore, different local strengthening interventions were designed and numerically checked. The comparison between the response of the unreinforced and the various strengthening joints is described, and the best solutions in terms of both cyclic behavior and technological feasibility are subsequently identified.

International Journal for Modern Trends in Science and Technology, 2020

Earthquakes are one of the biggest life-threats in the world. The effect is immediate, with little to no warning about damage plans and the collapse of buildings/structures. Prevention of earthquake-related disasters has become more and more important in recent years. Preventing disasters involves reducing seismic risk by retrofitting existing buildings. Seismic retrofitting has now become a crucial issue. Retrofitting helps improve the structure's strength, resistivity and overall lifespan. Recent occurrences of earthquakes in various parts of the world have clearly shown the urgency of repairing deficient seismic structures. The paper summarised many past studies in the form of a seismic strengthening solution, based on the type of beam-column joints, retrofitting technology and fiber reinforced polymers (FRP).

Recent earthquakes showed that most existing structures are characterized by high seismic vulnerability. In particular, the observations of the damages have individuated in masonry arches and barrel vaults the most critical elements in the seismic vulnerability of existing structures. Therefore, the understanding of their seismic performance has become a crucial problem in the field of structural engineering. Their dynamic behavior is generally evaluated according to simplified methods or, as an alternative, to complex FEM analyses. However, a deep knowledge of their dynamic behavior is still lacking from an experimental point of view and, so far, only few experimental researches have been conducted. At this regard, shaking table tests have been performed to investigate the seismic behavior of a full scale masonry vault with abutments. The vault presents a segmental arch with a span of 298 cm, a rise of 114 cm and 116 cm depth. The vault is made of solid facing clay brick and pozzolanic masonry mortar. The use of composite materials has shown to be effective for these structures. In this background the experimental tests can provide an efficient contribution to the interpretation of the reinforcement effects. The present paper presents a comprehensive overview of the main results of the experimental tests. In particular, the experimental results of an innovative reinforced system coupled with other traditional strengthened systems are herein presented. The reinforcement technique is based on TRM system (Textile Reinforced Mortar). The effects have been investigated by using the shaking table tests, both before and after the TRM reinforcement application. The strengthening systems have been applied to a full-scale masonry vault typically used as roofs in religious buildings. After strengthening, the seismic behavior of the vault was significantly improved. Increasing the PGA, the instrumental response of the specimen started to change, however first visible damage occurred at an almost doubled PGA. The seismic capacity of the unreinforced specimen was more than doubled and the vulnerability moved from the curved element to the masonry abutments. Therefore, additional interventions should be eventually made on the lateral abutments. The strengthening strategy (combination of innovative and traditional systems) was effective in preventing failure of the masonry vault.

Proceedings of the 6th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2015), 2017

The beam column joint is the most affected area in a reinforced concrete moment resisting frame. It is unprotected to large forces during severe ground shaking and its behavior has a significant influence on the retort of the structure. Joints are crucial part for the transfer of force reactions and moments effectively between the connecting elements like beams and columns. As a result, joints often become the weakest links in the structural system. The main objective of this paper is to analytically check different types of strengthened beam column (B-C) joint with different and compare the final results. A cyclic load is applied to beam column joint model to check the reactions, ultimate load, total deformation and ductility. The retrofitting techniques for strengthening a weak structure are researched in many ways during the past and contemporary. Here we use some costeffective techniques to strengthen, they are TRM, SRP layer coating, Kevlar-149 lamination over the structure based on the ultimate load and lateral deflection, a comparative study is done with different strengthened models. The project also explains about the shear stress, normal stress, deflection, reactions and moment acting on the model. Analysis of the structure is done with computational aided software "ANSYS Workbench 16.2".

2000

Many opportunities are becoming available for using composite materials to strengthen/upgrade existing reinforced concrete (RC) structures. This paper focuses on a new technique for the seismic upgrade of RC beam-column connections in gravity load-designed (GLD) frames by the application (combined or not) of FRP rods and laminates. The FRP rods provide flexural strengthening, whereas the lay-up laminates provide confinement and shear strengthening. Along with the modeling of such upgraded connections to assess the increase of strength and/or ductility provided by the composite reinforcement, an experimental program was planned and it is being undertaken. A preview of it is given in this paper together with an explanation of its philosophy; furthermore, interesting preliminary results are presented and discussed. It appears that the proposed upgrade method will have a significant impact of the engineering practice in the near future.

Periodica Polytechnica Civil Engineering, 2018

Strong earthquakes always occur in countries with seismic risk and can potentially cause multiple deaths. This study investigates the seismic vulnerability of RC beam-column connections. Generally, it is impractical to simultaneously set up the molds of the concrete beam, ceiling and column and achieve a uniform concrete and this can cause numerous constructional deficiencies. Usually, these deficiencies can be instrumental in the failure of RC frames. Therefore, this study investigates the performance of a defective RC beam-column connection and provides a method to improve the behavior of the connection. The defective connection studied herein belongs to a high school in the city of Kermanshah, Iran. Many factors that affect the performance of the retrofitting designs are studied. Also, all of the parameters used in the analyses were obtained based upon the actual behavior of the material through core extraction and tensile tests. Finally, an optimal design is proposed.

International Journal of Science and Research (IJSR), 2023

Most structures, including industrial, commercial, and residential buildings, are constructed using reinforced concrete (RCC). While these structures generally perform well under normal conditions, they can sustain significant damage in the face of major earthquakes or higher load impositions. Retrofitting such structures presents a more complex challenge for structural engineers compared to constructing new buildings. This complexity arises from various factors such as non-engineered construction practices and general wear and tear that existing buildings may exhibit. Rather than demolishing the entire structure, a more feasible approach is to strengthen the deficient structural elements. Thanks to advancements in technology, non-destructive testing methods can easily identify these weak elements. Once identified, the optimal solution is to retrofit these elements. Retrofitting differs from repair or rehabilitation, as it involves strengthening and improving the performance of deficient structural elements or the entire structure as a whole. This can be achieved by enhancing the strength, stiffness, and/or ductility of specific components or the entire building, depending on the specific requirements. In some cases, a combination of these measures may be chosen. Retrofitting at the individual member or element level is known as local retrofitting.

International Journal for Research in Applied Science & Engineering Technology (IJRASET), 2022

The beam-column joint is measured as the most important zone in a reinforced concrete moment resisting frame. It is subjected to large forces during earthquake and its behaviour has a major influence on the response of the entire structure. As a result, a great attention has to be paid for good detailing of such joint. The absence of transverse reinforcement in the joint, insufficient development length for the beam reinforcement and the inadequately spliced reinforcement for the column just above the joint can be considered as the most important causes for the failure of the beam-column joint under any unexpected transverse loading on the building. The recent earthquakes revealed the importance of the design of reinforced concrete (RC) structures with ductile behaviour. Ductility can be described as the ability of reinforced concrete cross sections, elements and structures to absorb the large energy released during earthquakes without losing their strength under large amplitude and reversible deformations.

International Journal of ICT-aided Architecture and Civil Engineering, 2015

The high intensity and frequency of earthquakes occurred in the past two decades has brought a deep trauma to the Indonesian people, particularly those who live in the highly seismic regions. According to the latest building codes including the Indonesian building standards, a multistory or high-rise building should be designed to have a ductile manner during the severe earthquake strikes. The structural components such as beam-column joints as parts of a frame system must be sound and ductile so that the building will withstand a moderate or even severe earthquake. The research conducted here is to study the ductile behavior of monolithic joints of a ductile frame system with partially prestressed concrete beams and reinforced concrete columns under cyclic loading to simulate the earthquake. As the results, the ratio of the yielding load capacity to the designed/ideal load in accordance with the Indonesian seismic code (SNI 03-1726-2002) at story drift of 3.50 percent is about 1.25, which is larger than 1.20 as required by the design code. Three criteria of structural stability as per ACI-374.1-05, i.e. (1) the ratio of the test capacity to the designed capacity of the specimen at story drift of 3.50 percent, which is found as 100,0 percent under pushing lateral loading, which is higher than 75.0 percent as required, whereas under pulling lateral loading it could reach up to 100.0 percent which is higher than the requirement; (2) the dissipation energy ratio (), at drift ratio of 3.50 percent, it could reach up to 0.88 which is larger than 0.75 as required; (3) the ratio of hysteretic loop gradient, which is limited by the abscissa X from -X and +X, at drift ratio of 3.50 percent, is about 0.0735 which is larger than 0.05 under pushing lateral loading and it is about 0.068 which is also larger than 0.05 under pulling lateral loading; The structural ductility, , at drift ratio of 3.50 percent are 4,64 and 4,58, that are greater than 4.0. According to the requirements of both NEHRP and ACI, a building structure with load capacity higher than 75 percent of the maximum load capacity at story drift of 3.50 percent, has been considered to satisfy the requirements for ductile structures.

Frattura ed Integrità Strutturale

The Algerian seismic code assumes that the beam-column joints in monolithic reinforced concrete (RC) buildings are fully rigid. However, many experiments have proven the existence of relative rotations in these connections, and then the presence of relative transfer of bending moment. The present work aims to investigate the effect of beam-column joints modelling on the global seismic behaviour of reinforced concrete (RC) moment-resisting frames buildings, designed according to the Algerian seismic code recommendations. To consider the nonlinear deformation of the connections, an analytical model developed recently is used. This model includes two important deformation mechanisms; the first one covers the slippage of the continuous reinforcement within the column, whereas the second involves slippage caused by creating bending cracks at the extremities of the beams. Three multi-storey RC frames with different setback geometry, including a reference frame, are studied considering the...

Engineering Structures, 2019

This paper reports an experimental investigation of the seismic performance of exterior beam-column joints reinforced with Grade 600 longitudinal reinforcing bars in beams and columns made with high strength concrete of 70 MPa. For this purpose, six half-scale reinforced concrete (RC) exterior connections were designed in accordance with the ACI 318-14 Code requirements for a special moment frame. The variables yield strength of longitudinal bars, concrete compressive strength, flexural reinforcement ratio, ratio of the column to beam flexural capacity, and longitudinal bar size were investigated by subjecting all the specimens to quasi-static reversed cyclic loading at drift ratios of up to 5.3%. In specimens with identical flexural strengths, the amounts of longitudinal reinforcing bars were reduced in beam and column by approximately 27% due to enhancement in their yield strength. Up to a drift ratio of 4.5%, all the specimens reinforced with high-strength steel (HSS) reinforcing bars exhibited an overall seismic behavior comparable to that observed for joints containing Grade 420 MPa bars regarding load-carrying capacity, failure mode, energy dissipation capacity, pinching width ratio, and secant stiffness. It was while all the specimens reached their theoretical load-carrying capacities. In the case of specimens with identical reinforcing bar ratio of Grade 600, the experimental evidence revealed that utilizing high-strength concrete (HSC) was able to improve the cumulative energy dissipation and pinching width ratio by a maximum of 30% and 26%, respectively, at a drift ratio of 4.5%; while HSC did not considerably affect secant stiffness and average peak load. A parametric study was also performed through finite-element analysis (FEA) to investigate the influence of different design parameters such as the grade and spacing of joint hoops, the ratio of the column-to-beam flexural capacity, and column depth-to-bar diameter, on the strength, stiffness, energy dissipation capacity and equivalent damping of the specimens.

2007

ABSTRACT: The beam-column joints that are not detailed and built in accordance with seismic codes present a serious hazard that can affect the overall ductility of a structure subjected to severe earthquake shocks. Due to the hazards associated with such deficiencies, many existing buildings have to be rehabilitated. Four half-scaled exterior beam-column joint specimens were prepared with only one of them conforming to the guidelines of ACI 318-02.