Abstract
The paper describes the testing of two reinforced concrete beam-column joint units tested under incremented-static cyclic loading. The full size test units were based upon an interior beam-column joint of a four-storey framed building designed to the current NZ loading code and represent refinements on two previously tested conventional joints of similar dimensions. One unit differed from common practice by having a post-tensioned beam stressed to balance the floor dead load of the prototype structure whilst the second unit was detailed with haunched beams. Hinge formation occurred in the beams and stable hysteretic behaviour was obtained up to displacement ductilities of 10 for the prestressed unit and 6 for the haunched unit. The test results are analysed in terms of the draft NZ design code, DZ 3101, and the ACI Recommendations for beam-column joint design.
Highlights
1.1 Background to TestsThe behaviour of two previously tested full-size beam-column units(4) showed that the joint region of conventional reinforced concrete frames could be detailed with closed ties to satisfactorily withstand load reversals with little loss of strength or stiffness up to beam and displacement ductility factors of 8
(a) the use of additional flexural steel through the joint and into the beam to force plastic hinge formation away from the column face; (b) the use of bond plates attached to the flexural steel in the column and beams to assist in transmitting the bar forces to the diagonal concrete compression strut which develops across the joint diagonal; (c) the use of partial prestressing through the joint to promote diagonal strut action in the concrete and so increase the shear carrying capacity of the joint; (d) the use of haunched beams or crossing over of some top and bottom beam steel to spread the zone of plasticity
ductility factor (DF) = 2: Flexural cracking which had developed at the top and bottom of the beams intersected and some horizontal cracking along the longitudinal beam steel was observed
Summary
The behaviour of two previously tested full-size beam-column units(4) showed that the joint region of conventional reinforced concrete frames could be detailed with closed ties to satisfactorily withstand load reversals with little loss of strength or stiffness up to beam and displacement ductility factors of 8. Several innovative schemes to refine the joint design by reducing the number and size of the joint shear ties have been put forward. (a) the use of additional flexural steel through the joint and into the beam to force plastic hinge formation away from the column face;. (b) the use of bond plates attached to the flexural steel in the column and beams to assist in transmitting the bar forces to the diagonal concrete compression strut which develops across the joint diagonal;.
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