Seismic Isolation Pad Geometry for Stable Friction Under Variable Loads
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Solution Overview
Problem
Existing seismic isolation devices for structures, such as warehouses, exhibit varying behavior under different load conditions due to changes in friction coefficients between plastic pads and steel surfaces, leading to risks of toppling during earthquakes, as the friction coefficient is affected by the suspended mass and contact pressure, which can be high with light loads and low with heavy loads.
Innovation Solution
The seismic isolation device features support legs with polymeric pads made of materials like UHMWPE, PTFE, or PVDF, which have a variable contact area that adjusts with load changes, maintaining a constant average contact pressure and reducing friction coefficient variability, and includes elastic return mechanisms to ensure stable structure positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a plastic pad sliding on a spherical steel seat is used for seismic isolation, then the structure can oscillate during earthquakes with friction-based isolation, but the friction coefficient varies significantly with suspended mass and contact pressure, leading to inconsistent seismic isolation behavior under different load conditions
Solution Approach 1:
The invention changes the geometric parameters of the support element by providing convex or concave contact areas instead of flat surfaces. This geometric modification allows the contact area to vary with applied load, thereby maintaining relatively constant average contact pressure and friction coefficient across different suspended mass conditions, resolving the inconsistency in seismic isolation behavior
Solution Approach 2:
The invention pre-configures the support element with specific convex or concave geometries before the earthquake occurs. This preliminary geometric design ensures that when loads vary during seismic events, the contact area automatically adjusts to maintain optimal friction characteristics, eliminating the need for real-time adjustments or multiple support configurations
2Ease of manufacture
If the support element has a flat contact area, then the structure is simple to manufacture and install, but the friction coefficient becomes highly sensitive to load variations, causing toppling risks with light loads and excessive lateral movements with heavy loads
Solution Approach 1:
The invention modifies the contact area geometry from flat to convex or concave shapes. This parameter change is straightforward to implement during manufacturing and allows the contact area to self-adjust with load variations, maintaining reliable friction-based seismic isolation across the full range of operational loads without compromising manufacturing simplicity
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
This solution minimizes differences in seismic isolation behavior across varying load conditions, reducing the risk of lateral movements and toppling by maintaining consistent friction forces, effectively stabilizing structures during transverse accelerations.
Implementation Method 1
Each support leg (2) is provided with at least a support element or pad (4, 5, 10, 15) made of a polymeric or plastic material, and adapted to rest on a sliding surface (3) with a deformation
Implementation Method 2
elastic return means (18), which act to bring the structure (1) back to its initial position
Implementation Method 3
The friction coefficient between the plastic materials and steel is affected by the suspended mass and depends considerably on the average contact pressure between the pad and the sliding surface (3)
Data Source
AI summary
A seismic isolation device for structures of the type in which the structure to be isolated is provided with at least one support leg is constrained to the same structure, includes at least a support element or pad adapted to rest on a sliding surface with a deformation, and includes a contact area in contact with said sliding surface whose extension is variable and depends on the load resting on the support. The sliding surface is rigid and the contact area in contact therewith has a variable extension and depends on the load resting on the support.