Cracking of RC beam/column joints: Implications for the analysis of frame-type structures

The work presented herein is concerned with an investigation of the behaviour of reinforced-concrete two-storey frames under both static (monotonic and cyclic) loading and seismic excitation in an attempt to assess the effect of cracking suffered by the beam–column joints on the overall structural response of the frames. The behaviour of the structural forms investigated is established via nonlinear three-dimensional finite-element analysis, after the latter is first validated through a comparison of its numerical predictions with published experimental data. In all case studies presented, the beam–column joints, although designed in accordance with the current codes of practice specifications, were found to suffer considerable cracking that initiated early in the loading process leading to predictions of structural behaviour, regarding the deformational response and the magnitude of the internal actions, that deviate significantly from those predicted when assuming elastic material properties for the joint-regions. Such behaviour indicates that current code provisions cannot ensure joint behaviour compatible with the assumptions that underlie the analysis packages used in practical applications for safeguarding compliance with safety margins and structural performance with the code specified requirements.

► Investigate the effect of cracking within the joints on the response of RC frames.
► The FE model adopted yields realistic predictions of the response of RC frames.
► Crack formation within the joint can have a significant effect on global response.
► The “rigid-joint” assumption does not safeguard the code specified requirements.
► Current design methods need to improve in order to account for cracking within the joints.