| A comprehensive laboratory investigation was conducted in which a total of eight large scale structural concrete bridge knee joint units were tested. These units incorporated differing joint detailing, including haunching, prestressing, and variations in the quantity of dedicated joint reinforcement. Extensive experimental data in the form of force-displacement, moment-curvature, shear stress-shear strain, and reinforcement strain histories led to an improved understanding of the force transfer mechanisms developed within joints of this type. In particular, this data assisted in identifying the influence of various details upon the development of the diagonal joint strut for both closing and opening actions applied to the joint, and upon anchorage of the embedded longitudinal member reinforcement.; In conjunction with finite element analyses, simplified strut and tie models are presented describing the various joint force transfer mechanisms which develop in typical structural concrete bridge knee joints. These mechanisms are shown to satisfy equilibrium criteria, and be consistent with the adopted capacity design approach, where column plastic hinging is generally anticipated while the cap beam remains elastic.; Having established the joint force transfer mechanisms discussed above, design and assessment examples are presented for the eight units tested in the experimental component of the current investigation for actions both closing and opening the joint. In most cases, it is necessary to combine a number of individual mechanisms to describe the total demand upon the joint. In addition, nonlinear truss analyses are presented, describing the force-displacement response of the unit and the force demand upon the model elements.; It is concluded that the presented force transfer mechanisms accurately described the behavior developed in the tested units, and that the predicted demand upon the elements of the nonlinear truss models corresponded to that measured in the laboratory, suggesting that this analysis method is suitable for design purposes when a comprehensive investigation of joint response is required. |
