Seismic behaviour of deficient exterior RC beam-column joints.

Post-earthquake reconnaissance and results of previously conducted experiments show that stiffness and strength deterioration of beam-column joints can have a detrimental effect on the integrity and vulnerability of reinforced concrete frame structures, especially in older buildings in developing countries. As a result, there is a need to develop efficient structural evaluation techniques that are capable of accurately estimating the strength and deformability of existing buildings to facilitate the development of safer, simpler, and lower cost retrofit solutions and thus contributing to risk mitigation. The current research is part of a general effort that is being carried out at the University of Sheffield to quantify and develop strategies for the mitigation of seismic risk in developing countries. The primary aim of this work is to improve the current understanding of the seismic behaviour of deficient exterior reinforce concrete beam-column joints. Seven full-scale isolated exterior beam-column joints were tested under quasi-static cyclic loading to investigate and quantify the effects of using different types of beam reinforcement anchorages and low column axial loads on the seismic shear performance of exterior beam-column joints with no shear reinforcement. Contrary to what is reported in the literature, the test results show that increasing the column axial load even at very low levels «O.2f'oAg,) can enhance the joint shear strength of deficient exterior joints (exhibiting pure shear failure) by up to 15%. The test results also show that, for the same joint panel geometry and column axial load, the type of beam anchorage detail, whether it is a straight bar, long or short hook, can influence the joint shear strength by up to 34%. A new analytical model that predicts the shear strength of deficient exterior beam-column joints in both loading directions and takes into account the column axial load and bond conditions within the joint is developed. The model predicts with good accuracy the strength of the tested specimens in addition to other specimens reported by other researchers. Furthermore, a springbased exterior beam-column joint model for finite element analysis of deficient RC frames is proposed. The model development includes a joint shear stress-strain constitutive model based on the developed strength model. The simulated response using the proposed model shows good agreement with the experimentally observed response

Experimental behavior and design of reinforced concrete exterior beam-column joints strengthened with embedded bars

Shear-deficient reinforced concrete (RC) beam-column joints (BCJs) represent one of the main factors behind the seismic damage suffered by existing concrete infrastructure, as well as the associated loss of life. This study presents a novel technique for strengthening shear-deficient RC BCJs. The technique involves embedding carbon fiber reinforced polymer (CFRP) or steel bars into epoxy-filled holes drilled within the joint core. Six exterior RC BCJs were constructed and tested under displacement-controlled cyclic loading. Five specimens, of which four were strengthened with embedded bars, were designed with shear-deficient joints according to the pre-1980s building codes. The remaining specimen was adequately designed according to ACI 352R-02. The test parameters are the type (steel or CFRP) and number (4 or 8 bars) of embedded bars. The unstrengthened control specimen experienced joint shear failure in the form of cross-diagonal cracks. The strengthened specimens, namely those strengthened with embedded steel bars, exhibited less brittle failure where damage occurred in the beam region at the early stages of loading, suggesting the outset of a beam hinge mechanism. Additionally, the strengthened specimens exhibited enhancements in joint shear strength, ductility, dissipated energy and stiffness of 6-21%, 6-93%, 10-54% and 2-35%, respectively, compared to the control specimen. This paper also presents a mechanics-based design model for RC BCJs strengthened with embedded bars. The proposed model covers all possible failure modes including yielding of the existing steel reinforcement, concrete crushing and debonding of the embedded bars. The accuracy of the proposed model was checked against the test results. The model gave good predictions with an average predicted-to-experimental ratio of 1.05 and a standard deviation of 0.04. Keywords: Analysis; Beam-column joints; Design; Embedded bars; Fiber reinforced polymer; Reinforced Concrete; Shear strengtheningDirectorate General of Higher Education, Ministry of Research and Higher Education of Indonesi

Strengthening of seismically deficient exterior beam-column connections using embedded steel bars

Several techniques for improving performance of reinforced concrete (RC) beam-column (BC) connections have been developed in last two decades, but these techniques have been criticized for being labourintensive and susceptible to premature de-bonding. To overcome these shortcomings, a novel technique utilising embedded steel bars has been developed in this study for strengthening seismically deficient RC BC connections. This technique involves drilling holes within the joint core. After the drilled holes are cleaned, they are partially filled with epoxy. Finally, steel bars are inserted in the epoxy-filled holes. Two exterior BC connections were constructed and loaded under displacement-controlled cyclic loading. The first specimen was a control specimen designed in accordance with the pre-1970s building codes to represent BC connections requiring strengthening. The second specimen was strengthened with eight 8 mm steel bars embedded within the concrete core in the joint area and epoxied to maintain the bond between the concrete and the steel bars. The strengthened specimen had superior performance compared to that of the control specimen in terms of joint shear stress, normalised principal tensile stress demand and stiffness degradation. The results show that shear stress of the joint was enhanced by about 8% whereas the enhancement in the principal tensile stress demand was 24% compared to that of the control specimen. The results showed that the proposed technique is capable in upgrading the seismic performance of seismically deficient RC BC connections

Full-Scale Shaking Table Tests on a Substandard RC Building Repaired and Strengthened with Post-Tensioned Metal Straps

The effectiveness of a novel Post-Tensioned Metal Strapping (PTMS) technique at enhancing the seismic behaviour of a substandard RC building was investigated through full-scale shake-table tests during the EU-funded project BANDIT. The building had inadequate reinforcement detailing in columns and joints to replicate old construction practices. After the bare building was initially damaged significantly, it was repaired and strengthened with PTMS to perform additional seismic tests. The PTMS technique improved considerably the seismic performance of the tested building. Whilst the bare building experienced critical damage at an earthquake of PGA=0.15g, the PTMS-strengthened building sustained a PGA=0.35g earthquake without compromising stability

Experimental behavior and design of reinforced concrete exterior beam-column joints strengthened with embedded bars

Shear-deficient reinforced concrete (RC) beam-column joints (BCJs) represent one of the main factors behind the seismic damage suffered by existing concrete infrastructure, as well as the associated loss of life. This study presents a novel technique for strengthening shear-deficient RC BCJs. The technique involves embedding carbon fiber reinforced polymer (CFRP) or steel bars into epoxy-filled holes drilled within the joint core. Six exterior RC BCJs were constructed and tested under displacement-controlled cyclic loading. Five specimens, of which four were strengthened with embedded bars, were designed with shear-deficient joints according to the pre-1980s building codes. The remaining specimen was adequately designed according to ACI 352R-02. The test parameters are the type (steel or CFRP) and number (4 or 8 bars) of embedded bars. The unstrengthened control specimen experienced joint shear failure in the form of cross-diagonal cracks. The strengthened specimens, namely those strengthened with embedded steel bars, exhibited less brittle failure where damage occurred in the beam region at the early stages of loading, suggesting the outset of a beam hinge mechanism. Additionally, the strengthened specimens exhibited enhancements in joint shear strength, ductility, dissipated energy and stiffness of 6-21%, 6-93%, 10-54% and 2-35%, respectively, compared to the control specimen. This paper also presents a mechanics-based design model for RC BCJs strengthened with embedded bars. The proposed model covers all possible failure modes including yielding of the existing steel reinforcement, concrete crushing and debonding of the embedded bars. The accuracy of the proposed model was checked against the test results. The model gave good predictions with an average predicted-to-experimental ratio of 1.05 and a standard deviation of 0.04. Keywords: Analysis; Beam-column joints; Design; Embedded bars; Fiber reinforced polymer; Reinforced Concrete; Shear strengtheningDirectorate General of Higher Education, Ministry of Research and Higher Education of Indonesi

Various Methods of Strengthening Reinforced Concrete Beam-Column Joint Subjected Earthquake-Type Loading Using Fibre-Reinforced Polymers: A Critical Review

Fibre-reinforced polymer (FRP) composites are extensively employed in concrete technology due to their exceptional mechanical strength and durability.  They serve a dual purpose, not only reinforcing damaged elements but also supporting heavier service loads and addressing long-term concerns in new infrastructure projects. Consequently, the objective of this review is to establish a comprehensive research database that focuses on evaluating the strengthening behaviour of reinforced concrete (RC) beam-column joints (BCJ) under earthquake loads through diverse types and application methods of FRP composites. The efficacy of these strengthening techniques is assessed by considering factors such as the loading capacity and dissipated energy of RC BCJ versus the joint confinement index provided by the fibre in the joint area. Through this state-of-the-art review, it becomes evident that FRP composites effectively enhanced the normalized load of specimens up to 27 kN/?MPa and enhanced the dissipated energy until 558.6 kN-mm for the case of specimens with a lower confinement index, less than 0.3. Additionally, the specimen strengthened with the deep embedment (DE) method resulted in a moderate normalized load and dissipated energy compared to those strengthened with the external bonded (EB) method. The test results indicated that the average normalized load and dissipated energy of the DE-strengthening method was 93% and 28.5% compared to that of the EB-strengthening method. These findings reveal that FRP composites offer distinct advantages in terms of load capacity and dissipated energy when used for strengthening earthquake-affected RC BCJ. Finally, based on the compilation of the previous works, this research proposes several techniques for utilizing FRP composites to enhance RC BCJ subjected to earthquake load

Finite element parametric study of reinforced concrete beams shear-strengthened with embedded FRP bars (dataset)

The deep embedment (DE) of fibre-reinforced polymer (FRP) bars is a promising shear-strengthening scheme for existing concrete structures. In the current study, a three-dimensional nonlinear finite element (FE) model for DE-strengthened reinforced concrete beams was developed and validated. The FE and Concrete Society TR55 predictions were compared with published experimental results. The FE-predicted/experimental shear strength enhancement ratio is 1.08 with a standard deviation of 0.25, whereas the TR55-predicted/experimental shear strength enhancement ratio is 1.57 with a standard deviation of 0.54. A numerical parametric study was carried out. The results showed that the predicted shear strength enhancement was positively influenced by the use of inclined DE FRP bars and the increase in concrete compressive strength but decreased with the increase in shear span-to-effective depth ratio and internal steel stirrup-to-DE FRP bar ratio. The predicted percentage of shear strength enhancement was not significantly influenced by size effect