۱- Introduction

۲- Test program

۳- Results and discussion

۴- Lateral resistance model of DSTCRC piers

۵- Conclusions

References

Abstract

To improve the strength and ductility of short reinforced concrete (RC) piers, dumb-bell steel tube confined reinforced concrete (DSTCRC) piers were proposed and studied, in which the dumb-bell steel tube is disconnected at the foundation and cap beam to avoid the difficulty of inserting steel tubes into RC members. In this paper, five DSTCRC piers and one reference dumb-bell RC pier were tested under pseudo-static loading. The test parameters included shear span-depth ratio (1.25 and 1.75), axial load ratio (0.12 and 0.24), and width of the web (75 mm and 100 mm). Because of the confinement and enhancement effect from the dumb-bell steel tube, failure modes of RC piers changed from shear failure to bending failure, and the strength, ductility, and energy dissipation capacity significantly improved. The seismic performance of DSTCRC piers improved slightly with the increasing axial load ratio and width of the web within the scope of this study. Shear failure of the concrete in the web cavity exhibited in DSTCRC specimens with a shear span-depth ratio of 1.25, but the lateral resistance increased by approximately 90% as the shear span-depth ratio decreased from 1.75 to 1.25 despite slight drops of the ductility ratio and ultimate displacement ratio. A simplified model considering the bending of RC cores and shear of steel webs and concrete web was proposed to predict the lateral resistance of DSTCRC piers, and the predicted results showed a good agreement with the test results.

Introduction

Large cross sections are commonly used for reinforced concrete (RC) piers to resist the lateral seismic load, resulting in heavy structural weight and wasting materials. In addition, RC piers have been demonstrated to be vulnerable to large earthquakes [1,2] as short RC piers, especially, without sufficient stirrups often suffer brittle failure. Concrete filled steel tube (CFST) piers, by contrast, have higher strength and better ductility benefitting from the composite effect between the steel tube and concrete [3–۵]. The reduced cross-section and selfweight of piers, contribute to a saving in construction materials and labor. However, the application of CFST piers is often limited by the inherent difficulty of connections with the foundation or RC cap beam. The embedded depth of the steel tube at connections generally needs to be twice larger than of the cross-sectional diameter to meet the anchoring requirements, which is difficult for large-diameter CFST piers. In addition, the deeply-embedded steel tube will cause a complicated layout of reinforcement in the foundation [6–۸]. To solve the aforementioned problems, an innovative composite bridge pier termed as Dumb-bell Steel Tube Confined Reinforced Concrete (DSTCRC) pier is proposed in this study. As shown in Fig. 1, a DSTCRC pier consists of a dumb-bell steel tube and infilled reinforced concrete, where the dumb-bell steel tube is made up of two circular steel tubes and two steel web plates. It should be noted that gaps are left between the dumb-bell steel tube and the adjacent foundation/cap beam to simplify the construction process of connections and alleviate the flexural demand on the joint [9]. In a DSTCRC pier, the flexural strength is provided by the inner concrete and reinforcing bars. Of using dumb-bell steel tube include: (1) the compressive strength and ultimate compressive strain of concrete core are improved due to lateral confinement of the steel tubes, thus enhanced the deformability of flexural plastic hinge; (2) the shear strength of squat piers is enhanced owing to the steel web plates shearing; (3) dumb-bell steel tube can be used as a formwork for casting concrete in construction. The dumb-bell steel tube terminates at the connections and carries no direct axial load, therefore, the probability of local buckling is significantly reduced. As a result, high-strength and thin-walled steel tubes could be used in DSTCRC piers to optimize the economic benefits.