Main Girder Rigid Joint Construction to Reduce Negative Bending
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Solution Overview
Problem
Existing multiple span girder bridges experience cracking at the connection points due to negative bending moments caused by dead and live loads, which are not effectively addressed by current construction methods.
Innovation Solution
A rigid coupling method involving pillow blocks, connecting plates, and connecting bar members to support and connect girder ends, allowing for the distribution of tensile forces and reducing negative moments, thereby preventing cracking and ensuring a rigid frame structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If girder ends are supported on bridge piers via bearings in a typical multiple span girder bridge, then the bridge structure can be assembled with simple support conditions, but large negative bending moments occur at the girder continuation points causing cracking of the connecting concrete
Solution Approach 1:
The bridge structure is divided into multiple spans with girder ends supported on bridge piers, allowing independent construction of each span while maintaining overall structural integrity. The connecting concrete is segmented into regions with different reinforcement densities based on moment distribution.
Solution Approach 2:
The connecting concrete is designed with non-uniform reinforcement density - higher reinforcement density is provided in regions with larger negative bending moments (near girder ends), while lower reinforcement density is used in regions with smaller moments (mid-span areas), optimizing both strength and material efficiency.
2Reliability
If the connecting concrete is reinforced to prevent cracking from negative moments, then the strength and durability of the girder continuation improve, but the complexity and cost of construction increase
Solution Approach 1:
Reinforcement is concentrated in specific high-stress regions rather than uniformly distributed, reducing overall material usage and construction complexity while maintaining reliability where it is most needed.
Solution Approach 2:
The reinforcement configuration is designed and predetermined based on calculated moment distributions, allowing contractors to follow clear specifications rather than making complex real-time decisions during construction.
3Strength
If friction welding is used to connect the connecting plate to the girder end, then a rigid connection is achieved that effectively transfers forces, but the manufacturing precision requirements increase
Solution Approach 1:
A connecting plate is introduced as an intermediary element between the girder end and the bearing assembly, providing a standardized interface that simplifies the friction welding process and reduces precision requirements for direct girder-to-bearing connections.
Solution Approach 2:
The connection design allows for parameter adjustments in the friction welding process, such as controlling the clamping force and welding duration, to achieve reliable connections within practical manufacturing tolerances.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method effectively prevents cracking in the connecting concrete by distributing tensile forces and reducing negative bending moments, resulting in a rigidly connected and integrated structure of girders and bridge piers.
Implementation Method 1
connecting the girder end of each main girder and the connecting plate by friction joint
Data Source
Figure 1(A)~1(B)
Figure 2
Figure 3
AI summary
To provide a construction method that allows both friction welding of the connecting plate and the girder end of each girder and reduction of the negative moment based on the dead load of each girder, as well as rigidly coupling each girder to the bridge pier, and came up with the present invention. The rigid coupling method for continuing main girders according to the present invention can rigidly continue both main girders while preventing the occurrence of negative bending moment, and further, can rigidly couple the continued main girders to the bridge pier since, before placing the bridge body concrete, the connecting plate is temporarily fixed to support the left span main girder and the right span main girder simply, and since the left span main girder and the right span main girder can be connected by fully fixing the connecting plate after the slight upward displacement of the girder end of each main girder caused by placing of the bridge body concrete is adequately absorbed, and each main girder and the bridge pier are connected by the connecting bar member.