Component-based reinforced concrete beam-column joint model

Abstract

A reinforced concrete (RC) beam-column (RCBC) joint model for the quasi-static monotonic analysis of cast in situ RC frames is developed and implemented in a finite element analysis program for framed structures. The joint model was developed in the framework of the component method, a method originally developed for steel joints, which consists of three steps: (a) identification of the joint relevant basic components, their interaction, and contribution to overall joint behavior; (b) characterization of the mechanical behavior of each component; and (c) assembling of the components. With regard to the model implementation, the material nonlinear analysis is performed by the fictitious forces method-all the required steps are presented and explained-while the P-Δ method for the geometrical nonlinear analysis of frames is extended to include the beam-column joint model. The paper closes with illustrative and validation examples; while some of these are fully analytical, the others simulate lab-tested subframes subjected to quasi-static monotonic loads.

Simplified assessment of the need for the explicit model of RC beam‐column joints instead of the rigid model

“…Differently from the last expression, the numerators of the elements on the left hand side of SCC1‐R (expression (39)) are not the same—this is because the components of the explicit joint model in Figure are not arranged in series and, therefore, do not have the same internal force (see ). In the simplified joint model of EN 1993‐1‐8, the column anchorage components are not included while the shear deformation mode is built‐in in the adjacent beam rotational springs arranged in series with the other components, originating a criterion of the type of (54).…”

“…Implicit joint models account for joint behaviour by modifying the mechanic and/or the geometric properties of the adjacent linear elements (e.g., bending stiffness or clear span of beams). Explicit joint models consist of a spatial layout of nonrigid elements whose mechanic properties are specifically determined to replicate the joint behaviour (e.g., [23][24][25][26][27][28][29] ).…”

“…Nonetheless, the latter model is fully avoided because the only kinematic boundary conditions usually considered are those of the former model. Consider the archetypal structure (AS1) represented in Figure 3a, which contains the explicit component based RCBC joint model developed by Costa et al 25 (Figure 3b). In this subframe, the columns, beams and anchorage components may have different stiffness-a common situation in RC frames due to the different demands on these structural elements when placed on opposite sides of a joint of a frame acted by lateral loads.…”

“…The overall critical value is α cr = min α cr,i . According to (25), for a given structure, the ratio of the critical parameter for the rigid joint model (R) to that for the explicit model (D), is given by (storey subscript omitted)…”

“…where α R cr can be approximated by expression (25), and is therefore easily determined by a linear structural analysis. Defining the interstory drift θ = d/L c.eff and the ratio ζ of horizontal to vertical forces above the considered floor, expression (25) takes the form…”