Analytical Model on the Bond Stress-Slip Relationship between Steel Reinforcement and Concrete for RC Beam-Column Joints

There are no conventionally accepted failure criteria for progressive collapse, and often times, deflection of affected beams over the “missing column” are often used as performance criteria. However, when simulating the deformation behaviour and the strength of reinforced concrete (RC) framed structures for progressive collapse analysis, besides the flexural deformations, the so-called “fixed end” rotation induced by the longitudinal bar slip at the beam-column ends connected to the joints can be significant and result in additional lateral deformations not accounted for in the initial analysis. Hence, it is important to quantify the deformations arising from fixed end rotations. Several bond stress-slip relationships between steel reinforcement and concrete were previously proposed in the literature. In the present work, their merits and demerits are discussed in terms of application limitation. To address the limitations of previous bond-slip models, a new analytical model based on the bond stress integration along the bar stress propagation length is proposed to predict the bar-slip behaviour in the RC beam-column joints. The proposed analytical model on the bond stress-slip relationship is validated against experimental studies from the literature and is shown to be simple and reliable.

Design and testing of reinforced concrete frames incorporating the slotted beam detail

Shortcomings of modern seismic design in reinforced concrete have necessitated the development of new systems capable of addressing these issues. Able to be constructed using existing industry techniques, the slotted beam is one such practicable, economic solution. While earlier research by Au (2010) showed promising results for this system, it also highlighted issues with bond of beam reinforcement within interior joints and understanding of the joint shear mechanism. This paper explains and addresses these issues through a summary of the desktop and experimental research undertaken. The results were encouraging with 2 specimens successfully tested without bar slip and minimal beam elongation.

Effective Stiffness of Rectangular Confined Concrete Columns with Continuous Compound Spiral Hoop

Existing models appropriate for design applications tend to overestimate the measured effective stiffness and are unacceptably inaccurate, because they generally neglect the influence of anchorage slip on the effective stiffness of the column. A three-component model that explicitly accounts for deformations due to flexure, anchorage-slip, and shear is shown to provide a more accurate estimate of the measured effective stiffness for the database columns. This model is simplified by neglecting small terms and approximating the results of moment-curvature analysis to obtain an accurate and rational effective stiffness model appropriate for design applications. Comparison the measured effective stiffness of reinforced concrete columns from the PEER Structural Performance Database with stiffness calculated following the FEMA 356. The FEMA 356 procedure substantially overestimates the stiffness of columns with low axial loads, in which there can be significant bar slip in the beam-column joints or footings. This model provides practical recommendations for improving estimates of effective stiffness.