External Beam-column Joints Research Articles

Seismic design of RC external beam-column joints

The paper proposes an alternative method for the earthquake-resistant design of HDC external beam-column joints which is based on the assumption that the load transferred from the beam and column elements to the joint is predominantly resisted by a diagonal strut mechanism. The validity of the proposed method is verified experimentally through a comparative study of the behaviour of seven full-size beam-column joint sub-assemblages—three of them designed in compliance with the current European Codes and four in accordance with the proposed method—under cyclic loading. The results obtained indicate that, in contrast with the specimens designed in compliance with current code provisions, those designed so as to comply with the proposed specifications fully satisfy the code performance requirements.

Flexural behaviour of external R/C steel fibre reinforced beam-column joints

ABSTRACT A softened strut-and-tie macro model able to reproduce the flexural behaviour of external beam-column joint is presented. The model is specific for concrete with hooked steel fibres (FRC) and it is designed to calculate the flexural response, as load-deflection curve, of a beam-column sub-assemblages. The model considers the presence of a constant vertical load acting on the column and of a monotonically increasing lateral force applied at the tip of the beam.

Seismic performance of mechanically coupled reinforcing bars

Seismic performance verification of a spiral thread mechanical reinforcement connection system for use in reinforced concrete structures was investigated by conducting both in-air component tests and structural subassembly tests. Current performance verification criteria listed in NZS 3101:2006 were found to be outdated and, following a review of various international protocols for testing mechanical connection systems, it was concluded that DIS 15835 protocols should instead be considered for adoption. Two external beam–column joint subassemblies having spiral thread mechanical reinforcement couplers installed at the column–joint interface were subjected to simulated seismic cyclic loading. It was found that bar curvature and the development of a non-uniform stress distribution around the perimeter of the reinforcement–coupler connection led to coupler slippage. However, the measured pinched hysteretic response owing to coupler slippage closely matched the response of companion tests where strength degradation was instead a result of excessive beam shear deformations. It was concluded that uniaxial tensile tests are unable accurately to demonstrate probable coupler performance in plastic hinge zones and that such tests should therefore not be used to predict likely ductile response in potential plastic hinge zones of reinforced concrete members.

External beam–column joints: design to Eurocode 2

In practice external beam–column joints are seldom designed for monotonic loading. The current authors believe that this is an oversight which should be addressed. This paper presents a simple strut and tie model for the analysis and design of external reinforced concrete beam–column joints. The strut and tie model is developed from first principles using the concrete design strengths given in Eurocode 2. The main difficulty in developing strut and tie models for beam–column joints is in determining the node dimensions. The novel feature of the authors' analysis is that the joint strength is related to the flexural capacity of the beam at the face of the column which is defined in terms of the maximum moment which can be transferred through the joint into the upper and lower columns. The model is shown to give better predictions of joint shear strength than existing simple design models. A case study is presented which shows that it is often sufficient to provide only minimum shear reinforcement in beam column joints.

Strengthening and rehabilitation of RC beam–column joints using carbon‐FRP jacketing and epoxy resin injection

AbstractThe scope of this study is to present results of an experimental investigation on the behaviour of critical external beam–column joints repaired or/and strengthened with a combination of epoxy resin injections and carbon‐fibre‐reinforced plastics (C‐FRP) sheets and to extract useful and practical conclusions. The experimental program comprises 12 external beam–column joint connection subassemblages tested in cyclic loading. From the observed responses of the examined specimens it can be deduced that the technique of epoxy resin injections is appropriate for the total rehabilitation of the joints seismic capacity, since no damages have been observed at the joint area of the specimens after the repair. The combination of this technique with the use of C‐FRP sheets leads to a significant improvement of the loading capacity, the energy absorption and the ductility and finally it leads to improved type of damages compared with the damage modes of the specimens during the initial loading. Shortcomings of the application of C‐FRP sheets for practical use are also pointed out. Copyright © 2008 John Wiley & Sons, Ltd.

반복하중을 받는 외부 보-기둥 접합부에서 작은 헤드를 사용한 Headed Bar적용

The applicability of headed bars in exterior beam-column joints under reversed cyclic loading was investigated. A total of ten pullout tests were first performed to examine pullout behavior of headed bars subjected to monotonic and cyclic loading with test variables such as connection type between head and bar stem (weld or no weld), loading methods (monotonic or cyclic loading), and head shape (small or large circular head and square head). Two full-scale beam-column joint tests were then performed to compare the structural behavior of exterior beam-column joints constructed using two different reinforcement details: i.e. standard hooks and headed bars. Both joints were designed following the recommendations of ACI-ASCE Committee 352 for Type 2 performance: i.e. the connection is required to dissipate energy through reversals of deformation into inelastic range. The pullout test results revealed that welded head to the stem did not necessarily result in increased pullout strength when compared to non-welded head. Relatively large circular head resulted in higher peak load than smaller circular and square head. Both beam-column joints with conventional hooks and headed bars behaved similarly in terms of crack development, hysteresis curves, and peak strengths. The joint using the headed bars showed better overall structural performance in terms of ductility, deformation capacity, and energy dissipation. These experimental results demonstrate that the headed bars using relatively small head can be properly designed far use in external beam-column joint.

Improvement of the earthquake resistance of R/C beam-column joints under the influence of P-△ effect and axial force variations using inclined bars

In this study, theoretical and experimental results are presented which were obtained during an investigation of the influence of the <TEX>$P-{\Delta}$</TEX> effect that was caused by the simultaneous changing of the axial load P of the column and the lateral displacement <TEX>${\Delta}$</TEX> in the external beam-column joints. The increase or decrease of <TEX>${\Delta}$</TEX> was simultaneous with the increase or decrease of the axial compression load P and caused an additional influence on the aseismic mechanical properties of the joint. A total of 12 reinforced concrete exterior beam-column subassemblies were examined. A new model, which predicts the beam-column joint ultimate shear strength, was used in order to predict the seismic behaviour of beam-column joints subjected to earthquake-type loading plus variable axial load and <TEX>$P-{\Delta}$</TEX> effect. Test data and analytical research demonstrated that axial load changes and <TEX>$P-{\Delta}$</TEX> effect during an earthquake cause significant deterioration in the earthquake-resistance of these structural elements. It was demonstrated that inclined bars in the joint region were effective for reducing the unfavourable impact of the <TEX>$P-{\Delta}$</TEX> effect and axial load changes in these structural elements.

Strut and tie models for analysis/design of external beam-column joints

Strut and tie models for analysis/design of external beam-column joints

Discussion: Strut and tie models for analysis/design of external beam-column joints

Discussion: Strut and tie models for analysis/design of external beam-column joints

SEISMIC REHABILITATION OF BEAM-COLUMN JOINTS USING FRP LAMINATES

An innovative and practical technique for the seismic rehabilitation of beam-column joints using fiber reinforced polymers (FRP) is presented. The procedure is to upgrade the shear capacity of the joint and thus allow the ductile ftexural hinge to form in the beam. An experimental study is conducted in order to evaluate the performance of a full-scale reinforced concrete external beam-column joint from a moment resisting frame designed to earlier code then repaired using the proposed technique. The beam-column joint is tested under cyclic loading applied at the free end of the beam and axial column load. The suggested repair procedure was applied to the tested specimen. The composite laminate system proved to be effective in upgrading the shear capacity of the nonductile beam-column joint. Comparison between the behaviour of the specimen before and after the repair is presented. A design methodology for fibre jacketing to upgrade the shear capacity of existing beam-column joints in reinforced concrete moment resisting frames is proposed.

Strut and tie models for analysis/design of external beam—column joints

Strut and tie models have been developed for external beam–column joints with and without joint stirrups. The modelling is fraught with difficulties that include determining forces at joint boundaries and strut dimensions. In view of these difficulties, it was found necessary to define strut widths empirically. Test data were used to show that stirrups can increase joint shear strength by less than their yield capacity. The model accounts for this by using a stiffness analysis to determine the proportion of joint shear force resisted by the stirrups at failure. The resulting model predicts joint shear strength more realistically than existing non–finite–element methods and some finite–element techniques. It is necessarily complex but capable of incorporation in spreadsheet–based design techniques. The authors believe that the behaviour of beam—column joints is too complex to be modelled realistically with simple strut and tie models. If a simple design method is required, the authors recommend their simplified empirical method.

Towards the design of reinforced concrete eccentric beam—column joints

The authors have previously proposed a simplified method for the design of external beam—column joints. This paper extends that work to joints in which one of the beams is eccentric to the column. Such connections occur in practice owing to architectural and geometrical constraints. Results are presented for tests on ten specimens in which one of the two beams framing into the column was eccentric to the column. The authors are unaware of any previous tests on such specimens. The tests were designed to investigate the effects of eccentricity and reinforcement detailing on connection strength, cracking and deformation. The tests showed that such connections can be used in practice providing that the torsional capacity of the joint is not exceeded. An analytical model is developed for predicting the strength of such connections and preliminary design recommendations are made. The work is also relevant to the case of joints where the beam is wider than the column.