Mandatory scope and three performance indices of Grade-E seismic rebar: longitudinal tension bars of frames and diagonal-bracing members designed for seismic grades 1-3 (strength ratio >= 1.25, overstrength ratio <= 1.30, ultimate elongation >= 9%)

Topic Positioning

This card defines which rebar in concrete structures must be Grade "E" seismic rebar (HRB335E, HRB400E, HRB500E, HRBF335E, HRBF400E, HRBF500E), the applicable member caliber, the three mandatory performance indices, exclusions, and the relation between current and superseded clauses — for design, construction, budgeting, and drawing review.

Core Conclusions

1. Mandatory scope and indices (current basis: GB 55008-2021, 3.2.3) For frames and diagonal braces of buildings designed at seismic grades 1-3, the longitudinal ordinary tension bars shall satisfy: 1 measured tensile / measured yield >= 1.25; 2 measured yield / yield standard <= 1.30; 3 measured total elongation at maximum force >= 9%.

2. Construction implementation (former GB 50666-2011, 5.2.2, superseded and absorbed) "For seismic structures, longitudinal bar performance shall meet design; where design is silent, frames and braces (incl. stair flights) designed at grades 1-3 use HRB335E...HRBF500E", with measured strength and elongation meeting the three rules. Acceptance (former GB 50204-2015, 5.2.3) identical: sampling per incoming batches and the product sampling plan; check sampling test reports.

3. Member caliber (commentary)

• Frames include frame beams and columns, transfer beams and columns, and columns of flat-slab/shear-wall systems, seismic grades per current standards;
• Braces include outrigger-truss diagonals and stair flights; where standards assign no seismic grade to braces but other members need Grade-E bars, all braces in the building comply;
• Simply supported precast stairs not acting as loaded braces need not comply.

4. Exclusions Shear walls and boundary elements (incl. coupling beams), cores/tubes, slabs, and foundations are outside; grade-4 and non-seismic members are outside "grades 1-3"; stirrups are not "longitudinal tension bars" — not Grade-E controlled (seismic stirrups have their own hook requirements).

5. Decision path and values Mandatory Grade E = member seismic grade (1/2/3) x member type (frame/brace) x bar direction (longitudinal tension), all three met. Grade-E bars are produced specifically with rolled marks; non-E compliance must be tested. Grade-E strength and modulus equal the same non-E grades (former GB 50010-2010, 11.2.2 commentary) — pricing per the same grade; the difference is procurement and the three measured values at incoming inspection.

6. Mechanism (former GB 50010-2010, 11.2.3 commentary) Strength ratio >= 1.25: after plastic hinges, bars retain strength potential under large deformation, preserving basic seismic capacity. Overstrength <= 1.30: scatter of yield strength does not defeat "strong column-weak beam" and "strong shear-weak bending". Elongation >= 9%: adequate plastic deformation capacity under seismic deformation.

7. Precast prestressed frames JGJ/T 502-2024, 4.3.1: beam-end connection bars of prestressed precast frames use HRB400E or HRB500E, performance per GB 1499.2 (i.e., the three indices).

8. Version linkage (important) GB 55008-2021 effective 2022-04-01 superseded GB 50010-2010 (2015 ed.) 11.2.3, GB 50204-2015 5.2.3, GB 50666-2011 5.2.2; GB 50011-2010 (2016 ed.) 3.9.2 was superseded by GB 55002-2021 from 2022-01-01. Substance unchanged — review/acceptance still by the three indices; cite GB 55008-2021, 3.2.3 first.

Applicable Boundaries

• Mandatory objects are "longitudinal ordinary tension bars": prestressing tendons and stirrups excluded; grade-4 and non-seismic members excluded.
• The Grade-E list is the construction fallback "where design is silent"; explicit design governs.
• Simply supported precast stairs (not loaded braces) may be exempt; shear walls, coupling beams, boundary elements, cores, slabs, foundations out of scope.
• Grade-E strength values equal the non-E same grade — no uplift in strength or modulus for being Grade E.

Further Reading

• GB 55008-2021, 3.2.3 — current direct basis (from 2022-04-01).
• GB 50204-2015, 5.2.3 (superseded; sampling/inspection reference).
• GB 50666-2011, 5.2.2 (superseded; construction fallback).
• GB 50010-2010 (2015 ed.), 11.2.2/11.2.3 (superseded; commentary on mechanisms and value rules).
• GB 50011-2010 (2016 ed.), 3.9.2 (superseded; material minimums).
• JGJ/T 502-2024, 4.3.1 (beam-end connection bars HRB400E/HRB500E).
• GB 1499.2 — Grade-E product standard.