Towards the design of reinforced concrete eccentric beam—column joints

Abstract

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. internal; e, external; T, torsion; V, shear due to P e P c load on concentric beam P c0 maximum possible value of P c when P e 0 P e load on eccentric beam P e0 maximum possible value of P e when P c 0 T torsion T 0 maximum possible torsional strength of concentric beam T beam tensile force in beam reinforcement T clo tensile force in closing stirrup T col resultant force in leg 1 (see Fig. 2(b)) of column stirrups at top and bottom of joint t i thickness of wall i t max maximum permissible thickness of wall i U external perimeter of cross-section V c joint shear strength without stirrups V col shear force in column V i T shear force induced in wall i by torsion V j joint shear force V j0 uniaxial joint shear strength V jc joint shear force due to P c at joint shear failure V je joint shear force due to P e at joint shear failure Notation

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

“…A previous analysis 5,8 of all known test data 6,7,9±17 showed that joint shear strength (a) is sensibly independent of column axial load unless a hinge forms in the upper column (b) is proportional to p f 9 c for joints without stirrups (c) reduces with increasing joint aspect ratio h b ah c . Test data are limited (see Fig.…”

“…The first author has carried out an extensive survey 5,8 of test data 6,7,9±13 to determine the influence of stirrups on joint shear strength. Joint stirrups were found to be effective if placed between the underside of the main reinforcement and the top of the compressive stress block in the beam (assumed to be of depth 0 X 375h b ).…”

“…6,9,10 The evidence is even more convincing for beam±column joints with U bars in the beam. 8 Fig . 4 indicates that the joint shear strength is given by the greater of V c and…”

“…4). The first author 5,8,19 has previously demonstrated the shortcomings of existing methods for determining the design joint stirrup force and proposed 8,19 a novel strut and tie model for external beam±column joints with stirrups which incorporates a stiffness analysis. This paper extends the brief outline of the method given previously.…”

“…Analysis 5,8 of test data 6,7,9±13 indicates that equation (16) progressively overestimates the joint shear strength as f 9 c increases, and that a better estimate of the maximum possible joint shear strength is given by…”