| Author: | Ding, Yan |
| Title: | Structural behaviour of shear connections of large resistances for simple on-site assembly of prefabricated composite beams |
| Advisors: | Chung, K. F. (CEE) |
| Degree: | Ph.D. |
| Year: | 2025 |
| Department: | Department of Civil and Environmental Engineering |
| Pages: | xxxi, 291 pages : color illustrations |
| Language: | English |
| Abstract: | Since composite structures are highly effective in providing high stiffnesses and resistances under large applied loads, they are extensively used in high-rise buildings and long-span bridges. In composite beams, the performance of shear connectors is critical for an effective load-transfer between concrete slabs and steel members. Although many researchers have examined the deformation characteristics of various shear connectors with different configurations and concrete grades, there are only a limited number of investigations into bolted shear connections in precast concrete slabs. Among these investigations, many shear connections are shown to have low shear resistances and stiffnesses despite of their good ductility, and multiple use of these bolted shear connections is often needed in composite beams of road bridges. Hence, it is highly desirable to investigate and quantify the behaviour of high-strength bolted shear connections with high performance concrete in prefabricated composite beams for simple on-site assembly of road bridges. This thesis presents a comprehensive investigation into the structural behaviour of a newly proposed shear connection incorporating a steel block and a pair of high-strength large-diameter steel bolts in conjunction with steel fibre reinforced concrete blocks. Both experimental and numerical investigations have been conducted to the proposed shear connection, and it is demonstrated that the proposed shear connection acts effectively as a twin shear connection due to the provision of a steel connector fully embedded into an infilled concrete block, and three typical modes of failure are identified: a) concrete failure of the concrete block; b) shear failure of the bolts; and c) concrete failure of the precast concrete slabs. The present study takes the following forms of investigations: i) An investigation into connections with six types of shear connectors using single-sided push-out tests was conducted to examine their structural performance in terms of resistance, stiffness, and ductility, and a suitable configuration of the proposed connection was identified, in which a steel block was pre-welded onto the beam flange to increase the initial stiffness, while steel fibres were added into the infilled concrete to improve their tensile strengths. ii) An investigation into the proposed shear connection using large-scale standard push-out tests and non-linear numerical simulations was also conducted to examine typical failure modes, deformation characteristics as well as the internal force distributions within the shear connections. After extensive calibrations against test data of the present study and also reported in the literature, various damage parameters were incorporated to simulate concrete crushing and cracking. iii) A systematic parametric study was then performed to identify load transfer mechanisms, and to formulate effective design rules for shear resistances and load-slippage curves of the connections for applications in prefabricated composite beams. Key findings are summarised as follows: a) Effective bolted shear connection Based on data analyses and interpretation on the deformation characteristics of the shear connections described in this investigation, the use of a 30 mm thick steel block together with a pair of specially designed high strength bolts, each with a diameter of 30 mm, in the proposed shear connection is shown to have a large stiffness (≥ 1,500 kN/mm), a large resistance (≥ 1,000 kN), and a large ductility (≥ 6 mm). Hence, the proposed shear connection is demonstrated to meet all the requirements for prefabricated composite beams in road bridges. With a proper design, only two different failure modes are identified in these tests, namely concrete failure (Mode CF), and shear fracture of bolts (Mode SFB). b) Effects of various components The results showed that the shear resistance of the proposed shear connection depends primarily on the bearing area of the steel block, and also the pull-out resistances offered by the pair of steel bolts. Increasing the thickness of the steel block from 30 to 50 mm offers only minimal benefits to the overall connection behaviour, and a reduction in its resistance at large deformations is also evident. As the concrete block acts as a "concrete shear connector", it should be made of high performance concrete reinforced with steel fibre, and the dimensions of the concrete block together with a properly designed arrangement of steel rebars are shown to have considerable effects on the structural behaviour of the proposed shear connections in both ultimate and serviceability limit states. c) Load transfer mechanisms The non-linear finite element models are able to predict the structural responses of the proposed shear connections, and the distributions of internal forces among the steel block, the pair of the steel bolts, the infilled concrete block, and also the precast concrete slabs are carefully established. Ductile damages in the steel bolts and local damage in the concrete are readily quantified through data interpretation of the finite element results. d) Design recommendations Design rules for the shear resistances of the proposed bolted shear connections are proposed after calibration against both test and numerical data, and the shear resistances of individual components of the connections are readily predicted to a high level of accuracy. Simplified load-slippage curves of the connections are also proposed which are readily adopted for numerical modelling to simulate the structural behaviour of the composite beams. |
| Rights: | All rights reserved |
| Access: | open access |
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