Slab distribution reinforcement: position, function, and construction requirements (GB 50010-2010 (2015 edition) Clause 9.1.7; TB 10064-2019 Clause 4.1.5)

Topic Positioning

This card explains the position and function of slab distribution reinforcement and its diameter, spacing, and area requirements under the building code (GB 50010-2010 (2015 edition) Clause 9.1.7) and the railway code (TB 10064-2019 Clause 4.1.5), plus its pairing with slab negative moments.

Core Conclusions

Position and function: distribution bars are perpendicular to the main bars and on their inner side, fixing the main bars in position, forming the mesh, distributing load, and resisting temperature-shrinkage stresses in cast slabs.

Building caliber (GB 50010-2010 (2015 edition) Clause 9.1.7):

• "Where a slab is designed as one-way, distribution reinforcement perpendicular to the main direction shall be provided; per unit width it should be not less than 15% of the unit-width main steel, with a reinforcement ratio not less than 0.15%; bar diameter preferably not less than 6 mm, spacing not greater than 250 mm; under heavy concentrated loads, the area shall be increased and spacing not greater than 200 mm."
• "With proven experience or reliable measures, precast one-way slab distribution steel is exempt from this clause."

Railway caliber (TB 10064-2019 Clause 4.1.5): "Distribution bars perpendicular to the main bars shall be provided in slabs, placed on the inner side of the main bars", and:

1. Trafficable deck distribution bars >= 8 mm diameter; sidewalks and trench covers >= 6 mm;
2. Per unit width, distribution area preferably >= 15% of main steel;
3. Where main bars bend, distribution bars shall be provided at the bends. Related: cantilever distribution >= 15% of transverse tension steel; lower transverse bars may be at twice the upper spacing, diameter >= 10 mm (Clause 4.1.10); integral skew slabs (B/L <= 0.75) distribution >= 1/4 of tension main steel area (Clause 4.1.12).

Pairing with slab negative steel: the top slab mesh comprises the support negative-moment bars and their perpendicular distribution bars; on site, all intersections of top longitudinal/transverse and negative bars shall be fully tied (DB11/T 1832.3-2021 Clause 16.4.7).

Applicable Boundaries

• GB 50010 Clause 9.1.7 applies to "one-way slab" design: main bars in the spanning direction, distribution bars perpendicular; two-way slabs have main steel both ways — the clause's limits do not transfer directly.
• Precast one-way slabs with proven experience or measures are exempt.
• Building and railway values differ (traffic decks start at 8 mm) — no cross-industry mixing; projects follow their industry code and design.

Further Reading

• GB 50010-2010 (2015 edition) Code for Design of Concrete Structures, Clause 9.1.7; related Clauses 9.1.4 (bottom bars into supports, negative-bar extension), 9.1.6 (face reinforcement).
• TB 10064-2019 Code for Reinforcement Design of Concrete in Railway Works, Clauses 4.1.5, 4.1.10 (cantilevers), 4.1.12 (skew slabs).
• DB11/T 1832.3-2021 Construction Technology Specification for Building Works, Part 3: Concrete Structures, Clause 16.4.7 (slab tying).