Experimental Study of Precast Segmental Bridge Box Girders with External Unbonded and Internal Bonded Posttensioning under Monotonic Vertical Loading

Abstract

Segmental prestressed-concrete box girders (SPCBGs) with external unbonded and internal bonded posttensioning tendons have been widely used in the construction of bridge structures. These SPCBG bridges have many attractive advantages for ductility and fast construction. However, the behavior of SPCBG bridges is affected by the tendon ratio and the combined load (bending and shear) at the joint surface between the segments. This paper presents an experimental investigation of the structural behavior of SPCBGs with different tendon ratios and combined loads. An experimental study of four different tendon ratios and two types of loads was conducted. The conclusion is that the three-point bending load mode reduced the vertical load and vertical deflection at the onset point of nonlinearity. The openings between the segments and crushing of the concrete compression region are the main reasons for the nonlinear behavior of SPCBGs. Different tendon ratios and different load types not only altered the deformation, increased external tendon stress, and increased the width of joint openings but also altered the failure mechanism. Failure modes of epoxied joints subjected to pure bending or combined shear and bending are presented in detail. For the segmental box girder with external unbonded and internal bonded posttensioning tendons, the stress increment of the external tendons could be up to 30–50% of the effective prestressing stress at the ultimate failure load. Additionally, based on scarce available segmental box-girder test data, several equations on stress increase and shear strength are discussed, and two methods are recommended.