Tension-Resistant Friction Pendulum Bearings(tFPB)

(Compliant with International Standards for Seismic Isolation and Energy Dissipation Devices)

I. Executive Summary

The Tensile-Resistant Friction Pendulum Bearing (TFPB) is an advanced seismic isolation device designed for modern infrastructure that requires both horizontal flexibility and vertical uplift resistance. Unlike conventional friction pendulum bearings (FPBs), which are limited to compressive load transfer, the TFPB integrates anti-uplift anchoring systems, ensuring structural integrity under combined seismic and wind actions.

This manual introduces the working principle, design parameters, testing requirements, and international compliance of the TFPB. It also provides practical guidelines for installation, inspection, and long-term maintenance in accordance with EN 15129:2018 (Europe), AASHTO Seismic Isolation Guide (USA), and ISO 22762 (International).

II. Background and Industry Needs

2.1 Seismic Isolation in Modern Structures
Since the 1970s, friction pendulum systems have been applied globally for seismic isolation in bridges, nuclear plants, and high-rise buildings. Traditional isolators (elastomeric bearings, HDRB, LRB) provide energy dissipation but cannot always address uplift forces caused by overturning moments.

2.2 The Uplift Challenge
Uplift occurs when vertical components of earthquake ground motion, wind suction, or unbalanced structural loads generate tensile forces at the support level. In bridges, uplift can result from asymmetric deck loading. In tall buildings, it may occur due to torsional overturning under seismic excitation. Without resistance, conventional FPBs may detach from the substructure, leading to catastrophic failure.

2.3 Why TFPB?
The TFPB is a next-generation seismic device that extends FPB capability by resisting both compression and tension, making it ideal for critical facilities, long-span bridges, and offshore platforms.
- Dual compression + tension capacity.
- Long design life (50–70 years).
- Adaptable to large displacements and long periods.
- High seismic safety margin.
- Compatible with international certification and CE marking

III. Functions and Performance

3.1 Energy Dissipation and Re-Centering
Sliding along a spherical surface ensures:
- Controlled period elongation (shifting structural natural period away from seismic spectrum peaks).
- Energy dissipation through surface friction (μ adjustable by material selection).
- Reliable re-centering force due to gravity effect.

3.2 Tensile Resistance
Achieved through mechanical anchorage systems:
- Prestressed tension rods embedded in the bearing.
- Anti-lift bolts directly connected to the substructure.
- Confinement housings to prevent dislodging.

3.3 Multi-Hazard Adaptability
Performs under seismic loading, wind excitation, traffic vibration, and thermal movement. Operates reliably in low-temperature environments (down to –30 °C with special materials).

IV. Standards and Normative References

The TFPB is designed and tested according to the most widely recognized international standards:
- EN 15129:2018 – Anti-seismic devices
- EN 1337 series – Structural bearings
- AASHTO Guide Specifications for Seismic Isolation Design (2014, 2022)
- ASCE/SEI 7-22 – Minimum Design Loads
- ISO 22762-3 – Seismic-protection isolators – Elastomeric bearings
- ASTM D4894 / D4895 – PTFE materials
- ASTM E595 – Friction and wear tests

Where national requirements apply, Eurocode 8, ACI 318, DIN 4149, and Japanese JIS C-Edition seismic codes are referenced.

V. Structural Components

1. Upper Bearing Plate – carbon steel plate with stainless-steel sliding surface.
2. Concave Sliding Dish – machined spherical seat, providing pendulum geometry.
3. Sliding Interface – PTFE or composite material bonded to ensure stable friction.
4. Tensile Resistance System – high-strength tie rods, prestressed anchors, or confinement bolts.
5. Housing and Dust Seals – prevent ingress of water, dust, or chemicals.
6. Protective Coating – corrosion resistance (epoxy, hot-dip galvanizing, or stainless steel).

VI. Working Principle

Based on the conventional friction pendulum bearing, vertical tension-resisting capability is added. It can achieve sliding and rotation under tensile conditions, as well as the seismic reduction function of a conventional friction pendulum bearing.

6.1 Compressive Mode
Superstructure load is transferred through spherical sliding. Displacements absorb seismic energy while maintaining stability.

6.2 Tensile Mode
During uplift, anchorage systems engage, transmitting tension safely into the substructure. Prevents gap formation or unseating.

6.3 Combined Loading
Under realistic seismic events, compressive, tensile, and shear actions occur simultaneously. The TFPB provides a continuous force–displacement response, ensuring no performance degradation.

6.4, Comparative Analysis

Feature	Conventional FPB	TFPB
Compression load	✔	✔
Uplift resistance	✘	✔
Seismic energy dissipation	✔	✔
Service life	50 years	50–70 years
Suitable for tall buildings	Limited	Excellent
Offshore performance	Not suitable	Suitable

VII. Research & Development

7.1 Design Parameters and Calculations

1), Governing Equation
The effective period of isolation system:

where R = radius of curvature, g = gravitational acceleration.

2), Material Standards
- Steel: EN 10025 S355 / ASTM A709 Gr.50
- Stainless steel: ASTM A240 Type 316L
- PTFE composites: ASTM D4894 reinforced with glass or bronze fillers
7.2, Technical Data Sheet

Parameter	Specification	Test Method
Vertical Tension-Bearing Capacity	Ranges from 50 kN to 6,000 kN (customizable based on project requirements)	AASHTO LRFD Bridge Design Specifications, Section 14.4; EN 1337-3
Vertical Compression-Bearing Capacity	1.2–2.0 times the vertical tension-bearing capacity (varies by model)	AASHTO LRFD Bridge Design Specifications, Section 14.3; EN 1337-2
Seismic Isolation Efficiency	Reduces upper structure acceleration by ≥ 50% under design seismic intensity (e.g., PGA = 0.4 g)	FEMA 461 (Evaluating Seismic Retrofit Alternatives), EN 1337-6
Maximum Sliding Displacement	<400 mm (depending on spherical surface radius and design requirements)	AASHTO LRFD Bridge Design Specifications, Section 14.5; EN 1337-4
Friction Coefficient	0.02–0.05 (at 23°C, under design vertical load)	ASTM D1894 (Standard Test Method for Static and Kinetic Coefficients of Friction of Plastic Film and Sheeting)
Service Life	≥ 50 years (under normal operating conditions, with regular maintenance)	EN 1337-1 (General Requirements for Structural Bearings)

7.3 Patent

7.5, Specifications

VIII. Quality Assurance and Manufacturing

- ISO 9001 certified production facilities.
- Non-destructive testing (NDT) for welds (UT, MT, RT).
- Machining tolerances: ±0.05 mm for sliding radius.
- Surface roughness: Ra ≤ 0.8 μm for sliding surface.
- Protective systems: tested per EN ISO 12944 for corrosion class C5.

IX. Testing and Certification

9.1 Factory Acceptance Tests (FAT)
- Material verification and dimensional checks.
- Static compressive and tensile load test.
- Sliding friction measurement at ambient temperature.

9.2 Type Testing (EN 15129 Requirements)
- Cyclic shear tests with imposed displacements.
- Vertical load tests under compression and uplift.
- Long-duration creep and relaxation tests.
- Durability evaluation (temperature cycling –30 °C to +50 °C).

9.3 Seismic Qualification
- Full-scale shake table testing for bi-directional displacement + uplift resistance.
- Compliance with AASHTO dynamic protocols.
9.4, Testing reports by the third party

9.5, Testing equipment in house

X. Installation Guidelines

1. Prepare foundation with flatness tolerance ±2 mm.
2. Install anchors and tension rods per approved drawings.
3. Align concave sliding surface to design radius.
4. Apply protective grease film (if specified).
5. Verify tension preload with calibrated torque.
6. Conduct trial sliding before structural load transfer.

XI. Maintenance Protocols

- Routine inspection every 5 years (EN 15129 §10).
- Check points:
- Sliding interface wear (thickness reduction < 0.5 mm).
- Anchor preload verification.
- Protective coating condition.
- Corrective actions:
- Re-tension bolts if preload loss >10%.
- Replace PTFE liner after exceeding wear limit.
- Apply anti-corrosion paint if degradation is observed.

XII. Applications and Case Studies

The tension-resistant friction pendulum bearing is ideally suited for structures where upward pull-out risks exist, including but not limited to:
Long-span bridges (e.g., cable-stayed bridges, suspension bridges), where dynamic loads from wind or earthquakes may generate upward tensile forces on the support bearings.
High-rise buildings and tall structures located in seismic zones (e.g., regions conforming to FEMA 356, ASCE 7, or Eurocode 8 standards), where seismic-induced structural vibrations may lead to tension at the bearing interfaces.
Industrial facilities with large dynamic loads (e.g., heavy machinery foundations, power plant structures), where both vertical load-bearing and tension-resistant capabilities are required to ensure operational safety.
Offshore and coastal structures (e.g., piers, jetties), where combined effects of wind, waves, and seismic activity may impose tensile forces on the bearing systems.

Conclusion

The Tensile-Resistant Friction Pendulum Bearing (TFPB) represents a state-of-the-art innovation in seismic protection technology. By combining frictional energy dissipation, pendulum period shifting, and uplift resistance, the TFPB ensures structural safety under the most demanding conditions.

Its proven compliance with EN 15129, AASHTO, ASCE, ASTM, and ISO standards makes it suitable for international application in bridges, tall buildings, nuclear facilities, and offshore structures. With proper installation and maintenance, the TFPB guarantees long-term durability, high performance, and enhanced resilience for critical infrastructure worldwide.