Overview
ISO 1288-2:2016 - Glass in building: Coaxial double-ring test on flat specimens with large test surface areas specifies a standardized laboratory method to determine the bending strength of flat glass used in buildings, while excluding edge effects. Part 2 of ISO 1288 describes the coaxial double‑ring loading arrangement (large test area variant), the required apparatus, specimen preparation, test procedure and evaluation needed to produce reproducible, comparable bending-strength data for the central surface of glass panes.
Key topics and technical requirements
- Test principle: a square flat specimen rests on a supporting ring and is centrally loaded by a concentric loading ring while the area inside the loading ring is subjected to a controlled surface gas pressure. This produces a predominantly radial tensile stress field in the central region where breakage is expected to originate.
- Measured outcome: the bending strength (or equivalent bending strength for patterned/uneven-thickness glass) is calculated from the piston force at break and the specimen thickness, taking into account device geometry and material constants.
- Apparatus & components:
- Testing machine with stepless loading, controlled stressing rate and load measurement accuracy (±2.0%).
- Loading and supporting rings supplied to the standard dimensions (e.g., loading ring and supporting ring radii and effective surface area are specified).
- Rubber profiles on rings (typically 3 mm thick, hardness ~40 ± 10 IRHD per ISO 48) and bearing surface radius ~5 mm.
- Surface pressure regulator capable of tracking the prescribed nominal p(F) relationship.
- Measurement accuracy: width to nearest 1 mm and thickness to nearest 0.01 mm.
- Specimen handling: square specimens with prescribed dimensions and conditioning; see ISO 1288-1 for fundamental limitations and edge considerations.
- Test procedure elements: specimen positioning, loading rate control, thickness measurement, residual stress assessment and required test reporting.
Practical applications and who uses this standard
- Glass manufacturers - product qualification, process control and material comparison.
- Independent testing laboratories - standardized test reports for clients and certification bodies.
- Façade engineers and structural designers - material property data for strength-based glass design and safety assessments.
- Architects and specifiers - selecting glass types that meet performance requirements.
- Regulators and certification bodies - harmonized method for compliance verification and performance claims.
ISO 1288-2 is particularly valuable when the focus is on the central bending performance of large flat glass panes where edge damage or edge conditions are intentionally excluded from the strength assessment.
Related standards
- ISO 1288-1 - Fundamentals of testing glass (limitations and general principles).
- ISO 48 - Rubber hardness (used for ring profile specifications).
- Other parts of ISO 1288 cover different specimen sizes and loading geometries (four-point bending, channel-shaped glass, small-area double-ring test).
Keywords: ISO 1288-2:2016, bending strength of glass, coaxial double-ring test, glass testing standard, large test surface areas, glass in building.
Open preview (PDF)Glass in building — Determination of the bending strength of glass — Part 2: Coaxial double-ring test on flat specimens with large test surface areas