Column-Reinforcing Cage Stability and Construction Safety

Erection and bracing of column reinforcing cages are often left to the contractor’s means and methods. As such, the stability of these cages is often based on empirical methods and past practice, and thus, rarely determined based on engineering analysis. Cage stiffness is a result of composite action of the complicated combination of longitudinal bars, transverse reinforcing, and wired joints, thus making an accurate calculation of the buckling strength quite difficult. To further complicate matters, typical construction practice may require ironworkers to climb these potentially unstable cages. Current literature does not provide engineers with practical methods to assess the stability of these cages. For example, how one chooses to simplify the complex bar layouts into an assemblage, which can be easily modeled can lead to very different (and potentially unconservative) results. Using collapse case studies as an impetus, this paper expounds on a previous paper by the authors to explore the accuracy of different simplified models and analysis methods to assess cage stability for cages with ironworkers present. Finally, a brief discussion concerning required cage bracing forces is provided.