Experimental and computational evaluation of current and innovative in-span hinge details in reinforced concrete box-girder bridges, Part 2: Post-test analysis and design recommendations

Abstract

This report focuses on post-test finite element analysis (FEA) of and design recommendations
for in-span hinges (ISHs) of reinforced concrete (RC) box-girder bridges when subjected to
vertical loads through the bearings. ISHs are disturbed regions due to a complex threedimensional
(3D) stress state caused by the concentrated bearing loads and the possible existence
of utility and maintenance openings. The common modeling practice for ISHs is the use of
simplified two-dimensional (2D) modeling as short cantilevers, following standard procedures,
e.g., those in ACI318. Such simplified analytical and design procedures lead to inefficient
detailing because they do not take into account the expected failure modes of ISHs, where
punching shear is one of these critical modes. For the post-test analysis, a 3D finite element
analysis (FEA) is developed and validated against the results of five tested ISH specimens. This
computational model considers the cracking behavior of concrete and the elastic-plastic behavior
of the reinforcement. The reinforcing steel is modeled using an embedded reinforcement
formulation assuming perfect bond between the concrete and the reinforcement. The concrete
material is modeled using the total strain rotating crack method. The reduction of compressive
strength due to perpendicular cracking is incorporated in the constitutive model. With the
validated FEA, a parametric study is conducted to predict the behavior and the strength of ISHs
with different detailing and geometrical characteristics. As a result of this study, detailed design
recommendations and guidelines are presented for ISHs in RC box-girder bridges. These
recommendations are aimed to obtain optimal designs with less congestion and improved
structural behavior. The findings from this study revealed that the strength of the ISH should be
estimated from five critical design criteria: (1) sliding shear friction, (2) bending moment, (3) 2D
SAT, (4) one-dimensional shear, and (5) punching shear. Additionally, it is concluded that the
strength of ISHs is improved most by increasing the amount of diagonal reinforcement of the seat.