Negative Stiffness Seismic Device Using Rotational Linkage
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Solution Overview
Problem
Current seismic protection systems for large structures, such as buildings and bridges, face challenges in applying negative stiffness effectively due to the high preload forces required, which are economically and physically impractical, and often rely on complex active or semi-active systems that demand high power and continuous feedback.
Innovation Solution
A passive mechanical system that introduces negative stiffness by using a compressed spring and linkage mechanism, allowing for amplification of spring force during seismic activity, reducing the need for high preload forces and eliminating the need for external power, and can be configured to minimize additional loads on the structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional negative stiffness devices are applied to massive structures, then seismic protection is improved, but the preload forces required become economically and physically prohibitive
Solution Approach 1:
The patent transitions from direct axial spring force application to a rotational moment mechanism. By arranging springs at an angle and utilizing rotational movement about a pivot point, the system generates negative stiffness through moment amplification rather than direct force application. This dimensional change from linear to rotational mechanics allows massive structures to be protected without requiring prohibitively large preload forces.
Solution Approach 2:
The invention employs a dynamic linkage mechanism with pivot points that allows the system to adapt its mechanical advantage ratio during seismic events. As the structure moves, the angular position of the linkage changes, dynamically adjusting the moment arm and amplification factor. This dynamic behavior enables the system to provide appropriate negative stiffness across varying displacement amplitudes without requiring excessive static preload.
2Reliability
If active or semi-active hydraulic devices are used to produce negative stiffness, then seismic protection is achieved, but the system complexity and power requirements increase
Solution Approach 1:
The patent implements a purely passive mechanical system that generates negative stiffness through the inherent mechanics of pre-compressed springs arranged in a rotational linkage. The system requires no external power supply, control algorithms, or feedback signals. During seismic events, the pre-compressed springs automatically engage and provide the necessary negative stiffness through geometric nonlinearity and moment amplification, making the system self-sufficient and eliminating complex active control infrastructure.
Solution Approach 2:
The invention replaces complex active/semi-active hydraulic control systems with a simple passive mechanical arrangement. Instead of using hydraulic actuators with sensors and control algorithms, the patent uses pre-compressed mechanical springs with a rotational linkage that naturally produces negative stiffness through its geometry. This substitution dramatically reduces system complexity while maintaining seismic protection effectiveness.
3Force
If convex pendulum bearings are used to generate negative stiffness, then low effective stiffness is achieved, but the vertical load transfer becomes unstable
Solution Approach 1:
The patent separates the functions of vertical load support and horizontal seismic protection into distinct components. The vertical load is carried by stable support structures, while the negative stiffness mechanism operates independently in the horizontal plane through rotational linkage. This segmentation allows the negative stiffness system to function without compromising vertical load stability, unlike convex pendulum bearings where the same structure must perform both functions.
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 system significantly reduces the demand for preload spring force, effectively reduces structural stiffness and natural frequency, and can be installed in massive structures without imposing excessive loads, thereby enhancing seismic protection while maintaining structural integrity.
Implementation Method 1
A compressed spring has a first end attached to the extension portion of the movement frame and a second end attached to the linkage. The compressed spring has a spring force.
Implementation Method 2
The spring force is amplified by the linkage when the movement frame is laterally displaced to an amplification point.
Data Source
AI summary
Negative stiffness systems and methods for seismic protection of a structure is described. A system can include a negative stiffness device having a first linkage pivotably connected to an anchor frame at a first pivot point and pivotably connected the movement frame at a second pivot point. The negative stiffness device can include a spring having a first end operably coupled to the anchor frame and a second end operably coupled to a movement frame. In a rest state, the spring can be compressed to exert a preload force to the first linkage and the anchor frame and not displace the first linkage and the movement frame. In an engaged state, the spring can be configured to apply a force to the first linkage such that the movement frame is displaced in a same lateral direction of a seismic load. The spring force can be amplified by the first linkage.