Overview
ISO/TS 20656-1:2017 - Plastics piping systems - General rules for structural design of glass‑reinforced thermosetting plastics (GRP) pipes - Part 1: Buried pipes - provides a semi‑probabilistic framework for establishing partial factors used in the structural design of buried GRP pipes. The technical specification links GRP product requirements (e.g., ISO 10639, ISO 10467, ISO 25780, EN 1796, EN 14364) to civil design principles defined in ISO 2394 and Eurocode EN 1990, ensuring safety, serviceability and durability for buried piping systems.
Key topics
- Partial factor method: Describes the semi‑probabilistic approach (FORM Level II) to derive partial factors for effects of actions and resistance, converting characteristic values to design values.
- Reliability index (β): Defines target reliability linked to probability of failure and consequence classes (CC1, CC2, CC3), with guidance based on a 50‑year design life.
- Sensitivity index (α): Addresses sensitivity of design values to uncertainties in independent random variables (actions and resistance).
- Effects of actions: Detailed treatment of uncertainties and partial factors for:
- Internal pressure (model uncertainty, pressure variability, long‑term vs short‑term effects, thickness and modulus uncertainty).
- Soil and traffic loads (installation parameters, deflection models, traffic load uncertainty, pipe stiffness, deflection measurement and lag factors).
- Combined pressure and bending effects.
- Resistance factors: Procedure to establish design resistance values, including conversion from short‑term to long‑term properties and recommended conversion factor η.
- Normative annexes: Annex A (recommended pressure safety factors) and Annex B (test data analysis) support practical implementation.
Applications and users
ISO/TS 20656-1:2017 is intended for use by:
- Pipeline designers and structural engineers specifying buried GRP systems for water supply, sewerage, irrigation and similar applications.
- Manufacturers and product standards committees developing GRP pipe specifications and validation tests.
- Specifiers, contractors and asset owners assessing safety margins, installation practices and long‑term performance.
- Regulatory bodies and conformity assessors aligning GRP product standards with structural design codes.
Typical applications include design verification for buried GRP pressure and non‑pressure pipelines, assessment of installation and traffic loading scenarios, and development of manufacturer design guidance using consistent reliability targets.
Related standards (select)
Keywords: ISO/TS 20656-1:2017, GRP pipes, glass‑reinforced thermosetting plastics, buried pipes, partial factors, structural design, reliability index, pipe stiffness, internal pressure, soil and traffic load.
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