Effectiveness of diagonal opening reinforcement in reinforced concrete chimneys under gravity and lateral service loads

Abstract

Diagonal rebars are traditionally placed at the corners of openings in reinforced concrete chimneys in order to prevent crack formations. However, the sloping rebars pose a difficulty in the slipform construction process since they cross the vertical lines of operation of the hydraulic lifting system. This study investigates design alternatives in terms of the reinforcement configurations that may be used instead of the diagonal corner rebars. A tall reinforced concrete chimney was modeled using hexahedral finite elements for the windshield and line elements for all reinforcing steel rebars. The hexahedral elements enabled the insertion of reinforcing steel rebars into the windshield wall thickness. The vertical, hoop and additional opening reinforcements were included in the model explicitly. The lap splicing and staggered configurations of the vertical reinforcements were taken into account. Nonlinear constitutive material models were used for the windshield concrete and reinforcing steel rebars. Winfrith concrete material model was used to model the behavior of windshield concrete. Plastic kinematic material model was used to model the behavior of reinforcement. The response of the chimney under gravity and lateral service loads was investigated. The nonlinear response of the chimney was solved dynamically for the applied loads, removing the necessity of iterations that are typically used in nonlinear static analysis approaches. Crack widths and patterns around the opening, stresses at the opening region and in the corner reinforcements obtained from simulations were reported. In lights of the findings of the study, suggestions were made in terms of design alternatives for opening corner reinforcements.