Square CFST Column Connection to RC Footing
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Solution Overview
Problem
There is a lack of efficient and effective connections for square concrete-filled steel tubular columns to reinforced concrete footings that can transfer combined bending and axial loads and sustain multiple inelastic deformation cycles under extreme seismic loading.
Innovation Solution
A system and method involving forming a cavity in the reinforced concrete footing with an elliptical opening at the top and a circular base, embedding a short steel pipe with flanges, welding an elliptical base plate to the tubular steel column, and rotating it to interlock with flange slots, followed by filling with concrete grout to create a durable connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional connection methods are used for square CFST columns to RC footings, then construction simplicity is maintained, but the connection cannot reliably transfer combined bending and axial loads under seismic loading
Solution Approach 1:
The connection system is divided into distinct components: an elliptical base plate attached to the column, a circular cavity in the footing, and interlocking flange elements. This segmentation allows each component to be optimized for its specific function while maintaining overall connection reliability under seismic loads.
Solution Approach 2:
The connection mechanism employs a nested structure where the elliptical base plate with flange slots receives and interlocks with the circular pipe with flanges. The flanges extend through the base plate and lock into the slots, creating a nested arrangement that provides reliable load transfer while maintaining compact geometry.
2Strength
If a reliable connection system is designed for square CFST columns, then load transfer capability is improved, but fabrication work increases
Solution Approach 1:
The elliptical base plate is pre-welded to the square CFST column before installation, and the circular cavity with embedded pipe is pre-formed in the RC footing. This preliminary preparation allows for quality control during fabrication and simplifies the on-site assembly process, reducing overall fabrication work while ensuring strong load transfer capacity.
Solution Approach 2:
The connection system employs asymmetric geometry with an elliptical base plate and circular cavity that create a specific interlocking mechanism. The flange slots are positioned at specific orientations relative to the ellipse, requiring a 90-degree rotation for proper engagement. This asymmetric design provides unique load path mechanisms that enhance strength while the standardized components keep fabrication manageable.
3Adaptability or versatility
If the column is rotated to interlock flanges with flange slots, then connection deformability is enhanced, but installation complexity increases
Solution Approach 1:
The 90-degree rotation requirement creates a unique engagement mechanism where the asymmetric elliptical base plate with flange slots must be rotated to align with the circular pipe flanges. This rotational engagement provides mechanical interlocking that enhances deformability under cyclic seismic loading, as the interlocked flanges can accommodate lateral movements while maintaining connection integrity.
Solution Approach 2:
The connection system incorporates dynamic engagement through the rotational mechanism. The flanges are designed to extend through the base plate and lock into slots that can accommodate movement. This dynamic interlocking mechanism allows the connection to adapt to cyclic loading conditions, providing the necessary deformability for seismic performance.
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 connection enhances the load-carrying capacity and deformability of square CFST columns, minimizing fabrication work and controlling story drift in high-rise buildings, while maintaining the benefits of precast construction.
Implementation Method 1
An elliptical base plate is welded to the bottom of the tubular steel column
Implementation Method 2
The cavity is filled with concrete grout
Data Source
AI summary
The system and method for connecting a square concrete-filled steel tubular column to a reinforced concrete footing includes a short steel pipe partially embedded in the footing, the pipe having a top end having flanges extending radially therefrom, the top end extending into a cavity in the footing having an elliptical top opening and circular base, the flanges extending above the base. An elliptical base plate is welded to the bottom of the tubular steel column, the base plate having a circular opening defined therein and a plurality of spaced flange slots depending therefrom. The bottom end of the column is lowered into the cavity, the elliptical base plate passing through the elliptical opening in the cavity, and the column is rotated 90° to interlock the flanges with the flange slots. The cavity is filled with concrete grout, and the square or rectangular steel column is filled with concrete.