Elsevier

Structures

Volume 27, October 2020, Pages 37-45
Structures

Investigation of U-bar joints between precast bridge decks loaded in combined bending and shear

https://doi.org/10.1016/j.istruc.2020.05.041Get rights and content

Highlights

  • Mechanical properties of U-bar joints subjected to bending/shearing were studied.

  • T-shape joint influences on the crack resistances of concrete interfaces were studied.

  • A formula is proposed for the estimation of the bearing capacities of U-bar joints.

  • Analyses were based on experimental measurements and finite element simulations.

Abstract

This study proposes two types of U-bar joints: rectangular joints with stainless steel ties and T-shaped joints. The mechanical properties of four joint specimens subjected to combined bending and shear forces were studied experimentally and numerically. The T-shaped joint details effectively increased the cracking load and controlled the development of interface cracks. The bearing capacity of the four joint details were similar. Furthermore, a formula to estimate the bearing capacities of the T-shaped U-bar lap joint specimen is proposed, and its accuracy is verified.

Introduction

Steel-concrete composite bridges are usually connected by U-bar joints that are used between the prefabricated decks [1]. The joint details consist of cast-in-place concrete and U-bars extending from two adjacent prefabricated members. U-bars are overlapped with each other and transverse reinforcements are placed in the core concrete. When this joint detail is used in a steel–concrete composite bridge, usually a combination of bending and shear is transmitted (Fig. 1). Several researchers worldwide have carried out studies on the mechanical properties of U-bar joints.

The first tension test of the joints was completed by Leonhardt et al. [2]. The test consisted of 13 specimens without transverse reinforcements. The specimens consisted of two pairs of gapless lap joints. Based on the test results, the authors suggested that when the lap length is less than 15 times the longitudinal reinforcement diameter, transverse reinforcement should be placed in the core concrete of the joint. Dragosavic et al. [3] conducted a flexural test of 151 U-bar joint specimens. Most of the specimens had small U-bar diameters (φL ≤ 12 mm), and ∼50% of the specimens were not provided with transverse reinforcements. Rosenthal and Shimoni [4] conducted flexural tests on three U-bar joints, and the U-bars between the two prefabricated panels were joined by a closed stirrup. Hao [5] carried out 36 tension tests and 19 flexural tests on U-bar joints. All of the test specimens were designed to use one or two interlaced joints. In other words, these are connections that have one or two U-bars. Gordon [1], [6] conducted a tension test of 18 U-bar joints. The U-bars were staggered, and the specimens were divided into 3–4 symmetric joints and 3–3 asymmetric joints. Ryu et al. [7] conducted flexural tests on nine U-bar joints, and the U-bars were interlaced in a 5–5 configuration. Ma et al. [8] conducted four tension tests and four flexural tests. The specimens did not have wet joints in the cast, the U-bars were 3–2 interlaced, and two transverse reinforcements with anchor plates at the ends were placed in the core concrete. Ma et al. [9] presented the tension testing results of some potential alternate reinforcing materials and the joint details in two phases. The headed bar and U-bar specimens with the same joint detail configuration were tested and compared in phase I, followed by testing of U-bars with varied concrete strength, bar spacing, and overlap length in phase II. Jørgensen [10] conducted a test on U-bar joints that were loaded with combined tension and bending, which resulted in a proposed plastic model for the calculation of the combined strength of the U-bar joints. Zhu et al. [11] pointed out that U-bar joints balance the tensile strengths of the lap joints with the shear of the core concrete columns rather than with the bonds between steel and concrete. Zhu et al. also established an equation to calculate the length of the U-bar lap joints. Wang [12] analyzed the influence of the lap length, concrete strength, and reinforcement ratio on the mechanical properties of the prefabricated concrete bridge deck joints using the finite element method.

The bonding strength between the cast-in-place joint concrete and the precast concrete is not high [13]. In bridge applications, water and deicing salts penetrate the bridge through the cracks at the interface to accelerate the corrosion of the steel bars. To solve this problem, numerous research studies have been conducted by scholars. Zhang et al. [14] studied UHPC-U-bar joints and showed that UHPC can significantly improve the crack resistance of the joints. Chen et al. [15] compared the crack resistance of wet joints treated with brushed epoxy resin, use of high-pressure water guns that removed fine aggregates, and use of high-pressure water guns that removed coarse aggregates. It was experimentally confirmed that the interface between the new and old concrete was the weakest position of the bridge deck. Zhang et al. [13] performed FEA on five common joint details. The results showed that the joints of the different joint construction types have a better flexural capacity than a complete concrete slab. Moreover, it was shown that the perforated and densely stitched joint types can significantly improve the flexural capacity of the joint plate, and the wedge-shaped joint pattern and diamond-shaped joint pattern have the second largest effects. In contrast, the rectangular joint pattern has the worst effect. Qi et al. [16] investigated the flexural behavior of an innovative dovetail UHPC joint in seven UHPC slabs with a negative bending moment. An innovative method using steel wire mesh is presented to enhance the interface between precast and cast-in-place UHPC at the joints. Qi et al. [17] investigated the flexural behavior of an innovative dovetail UHPC joint for connecting precast UHPC slabs in composite bridges, which is also reported in this study. The test parameters include the interface treatment method, the joint materials, the reinforcing bar overlapping form, and the prestressing level. Specifically, a new steel wire mesh interface treatment is proposed, which can generate an additional fiber-bridging mechanism along the joint surface.

Researchers have focused on the mechanical behavior of U-bar joints that are subjected to the actions of tension [1], [2], [5], [6], [8], bending [3], [4], [5], [7], [12], and combined tension and bending [10]. However, the mechanical behaviors of the U-bar joints subjected to combined bending and shear loads have been rarely studied. Herein, the mechanical properties of four U-bar joints subjected to combined bending and shear loads are studied. In addition, research on improving the crack resistance of new and old concrete types has been focused on the use of high-performance concrete [14], [16], [17] and different interface construction methods [13], [15], [16], [17]. There are few studies that are focused on new joint shapes. The purpose of the T-shaped joint is to increase the cracking load of the interface between the cast-in-place joint concrete and the precast concrete. The welding U-bar joint requires a large amount of on-site welding work and labor work. To avoid on-site welding work and expedite the construction progress, the lap U-bar joint with stainless steel ties is proposed. Furthermore, a formula is proposed for estimating the bearing capacity of the U-bar joints subjected to combined bending and shear loading according to the test and FEA results.

Section snippets

Specimen geometry and material properties

The four U-bar joint details studied herein are: a) U-bar welding rectangular joint, b) U-bar lap rectangular joint, c) U-bar rectangular joint with stainless steel ties, and d) U-bar lap T-shaped joint. All connections are designed as 4–4 rebar connections, i.e., four U-bars with and four U-bars without gap connections, as shown in Fig. 2.

The test specimens consist of two prefabricated panels and intermediate joints. The I-beam is connected to the joint by studs. In the joint concrete,

Strength and load–deflection response

The main mechanical parameters of each specimen are presented in Table 2, which includes the cracking load Py, ultimate load Pn, and failure deflection δs. As described in Table 2, the cracking load of the T-shaped joint specimen is 56 kN, and the cracking load of the three rectangular joint specimens is 23–40 kN. The T-shaped joint cracking load is higher than the other three specimens by 40–143%. This indicates that the T-shaped joint specimen has a better crack resistance.

The bearing

Numerical modeling

It can be deduced from the test that the bearing capacity, the load–deflection relationship of the four specimens, and the stress states of the steel bars in the joint are similar. However, the T-shaped joint can increase the cracking load and it effectively controls the development of the crack. The nonlinear finite element model of the LUJ specimen was established with the use of the ABAQUS standard module (ABAQUS 2014). The comparison with the experimental results showed that the model can

Conclusions

Two new U-bar joint details were proposed in this paper. The mechanical properties of the four joint specimens subjected to combined bending and shear forces were studied via the test method and FEA. According to the results, a calculation formula is suggested for the estimation of the bearing capacities of the T-shaped U-bar lap joint specimen.

Based on the experimental program and the finite element analysis, the following conclusions are inferred:

  • a)

    T-shaped joints can effectively increase the

Funding

This work was supported by the National Key R&D Program of China (2016YFC0701202), the Chongqing Basic and Frontier Research Projects of China (cstc2015jcyjys0011), and the National Natural Science Foundation of China (51408286).

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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