Quantity measurement of chair bars (iron horses, support rebar): the position that auxiliary rebar not required by the design is not measured separately, the setting method when no construction method statement exists (diameter / spacing / height), and per-piece weight conversion (theoretical mass 0.00617d2)

Topic Positioning

Quantity measurement of chair bars (also called iron horses or support rebar, a class of auxiliary rebar) where no construction method statement exists: first decide "can they be measured separately" (the bill-of-quantities and consumption-standard positions), then "how to compute" (setting the diameter / spacing / height and converting weight per piece).

Core Conclusions

1. Measurement position: not required by the design - not measured separately; required by the design (including by code) - merged in

• GB/T 50854-2024 (quantity take-off standard for building and decoration works), Annex E rebar, bolts and steel pieces, notes: "the rebar items shall not measure the quantities of chair bars, diagonal bracing bars, anti-floating bars, packing steel and other auxiliary rebar not required by the design"; the work content of each rebar item shall include the corresponding auxiliary rebar; "anchorage bars projecting from each cast-in-place member shall have their length determined as required by the design and be merged into the rebar quantities of that member"; "post-installed rebar not required by the design shall not be listed or measured separately" (where the design requires it, list under the corresponding member rebar item code).
• GB/T 50857-2024 (quantity take-off standard for municipal works), Annex J.2.1: "anchorage bars projecting from cast-in-place members, lifting hooks of precast members, and support rebar fixing positions shall be merged into the rebar quantities. Except splices expressly stated in the design, other splices are not measured in the quantities. The rebar items shall not measure the quantities of chair bars, diagonal bracing bars, anti-floating bars, packing steel and other auxiliary rebar not required by the design."
• GB/T 50860-2024 (quantity take-off standard for structures works), Annex A.15.8: "chair bars, diagonal bracing bars, anti-floating bars, packing steel and other auxiliary rebar not required by the design shall not be measured in the bill of quantities."
• DB11/T 638-2016 (quantity measurement code for building repair works): "support rebar fixing positions in cast-in-place concrete members, 'iron horses' for double-layer rebar, anchorage bars projecting from members, and lifting hooks of precast members shall be merged into the rebar quantities." That is, chairs required by the design (including by code) are position-fixing support rebar and are merged in; those not required by the design are not measured.

2. The position when measuring against an approved method statement

• SJG 181.2-2024 (municipal consumption quota standard, bridges and culverts) clause 5.2.2: "the quantities of support rebar fixing positions (such as iron horses, chair bars, packing steel), anchorage bars projecting from members, and hanger bars shall be computed in tonnes as required by the design, by the code, or by the approved project execution plan, and merged into the rebar quantities." Where an approved project execution plan exists and the contract agrees measurement per the plan, chair bars are merged into the rebar quantities in tonnes per the plan.

3. Beijing consumption-standard position (DB11/T 2382-2024) - when compiling budgets and building up rates

• Clause 4.6.5: "the construction consumption of rebar fabrication, of fabrication-and-fixing of rebar mesh, and of fabrication-and-fixing of diaphragm-wall rebar shall be determined, according to building function, building design grade and other factors, to include auxiliary bars such as chairs, supports and positioning bars; where data is unavailable, it is preferably taken with rebar wastage plus auxiliary rebar together at 5% of total rebar"; municipal clause 7.1.32, same rule: "for rebar (except pile-cage rebar), the wastage covering fabrication loss plus chairs, supports, positioning and other auxiliary bars is preferably taken at 5%".
• Clause 4.6.9: rebar, rebar mesh and rebar cages of cast-in-place members are all computed by mass at the design-shown dimensions; splices follow the drawings or the code; where not noted: for rebar within d10, one splice per 12 m; beyond d10, one splice per 9 m; for cast-in-place concrete walls, one splice per storey height. Municipal clause 7.1.32: rebar fabrication and installation quantities are computed by mass at the design-shown dimensions, and "where the design drawings require mechanical connection, the parallel-thread sleeve-coupler item applies and splice rebar quantities are no longer measured".
• Rate build-up meaning: under this position the chair-bar quantity is already absorbed into the rebar item consumption (5% where data is unavailable), so budget rate build-up must not compute chair-bar quantities separately, otherwise double counting arises.

4. Setting the values without a construction method statement (estimating position)

• Diameter: slab thickness not over 140 mm with main and distribution bars not over 10 mm - d8; thickness over 140 mm and under 200 mm with main bars not over d12 - d10; thickness over 200 mm - d12 (DB22 JT 143-2015 clause 5.2.1). Cantilever slabs: chair bar diameter not less than 14 mm, spacing not more than 1000 mm (DB11/T 1832.3-2021 clause 16.4.7).
• Spacing: chairs under the top slab mesh not more than 1000 mm apart (about 1 per m2); for bars below 8 mm, chair spacing not more than 600 mm x 600 mm (DBJ 43/T 302-2025 clause 4.2.3). Foundation slabs: the placing positions and spacing of support chairs are set by the construction method statement design (DB11/T 1832.3-2021 clause 15.4.7); for double-layer foundation mats, chair spacing is preferably about 1 m (DB 51/T 5046-2007 clause 4.3.2).
• Height: the chair height shall be determined by computing along the rebar layout directions, and the chair material and fabrication quantity shall be set per the weight of the supported rebar mesh (DB11/T 1832.3-2021 clause 15.1.4); support chairs shall rest on the lower-layer bars, placed perpendicular to the lower bars of the top layer (clause 15.4.7). Simplified: h about slab thickness - top cover - bottom cover - top bar diameter - bottom bar diameter.
• Simplified single-piece length: about 2 x slab thickness + 0.2 m (two legs plus the top cross piece); at a 120 mm slab, about 0.44 m/piece.

5. Converting weight per piece

• Universal formula for the unit theoretical mass of rebar: 0.00617d2 (kg/m), i.e. d8 = 0.395 kg/m, d10 = 0.617 kg/m, d12 = 0.888 kg/m.
• Weight per m2 = pieces per m2 x single-piece length x unit theoretical mass; example: 120 mm slab, 1 piece/m2, d8: 0.44 m/piece x 0.395 kg/m = about 0.174 kg/m2; a 5000 m2 cast-in-place slab example totals 868.736 kg, about 0.869 t.

Applicability Boundaries

• Under bill measurement (GB/T 50854 / 50857 / 50860-2024): auxiliary rebar such as chair bars not required by the design is never measured; its cost is absorbed by the work content / consumption. Position-fixing support rebar, anchorage bars projecting from members and precast-member lifting hooks required by the design (including by code) are merged into the rebar quantities, not listed separately.
• Under the Beijing DB11/T 2382-2024 position, the rebar fabrication consumption is already determined including chairs, supports and positioning bars (5% where data is unavailable), so budgets must not compute chair-bar quantities separately; under other regional standards or editions, follow the local current quota and measurement rules.
• The no-statement setting values and per-piece weight conversion apply only to: measurement per an approved project execution plan where the contract so agrees, or estimating and review reference scenarios; formal measurement follows the design marking or the approved plan first.
• Regional requirements on chair diameter and spacing differ; check the project's local rules before cross-region use; where seismic, civil-defence or other special requirements exist, those prevail.
• The conversion example is a simplified estimating basis and omits fine corrections such as the hooks on the chair bars themselves.

Further Reading

• GB/T 50854-2024 Annex E "rebar, bolts and steel pieces", notes 1, 2, 3, 8, 12 and 13, and the corresponding rebar items
• GB/T 50857-2024 Annex J.2.1 rebar works; GB/T 50860-2024 Annex A.15.8
• DB11/T 2382-2024 clauses 4.6.5 and 4.6.9 (building works) and 7.1.32 and 7.1.33 (municipal)
• DB11/T 1832.3-2021 clauses 15.1.4, 15.4.7 and 16.4.7; DB22 JT 143-2015 clause 5.2.1; DBJ 43/T 302-2025 clause 4.2.3; DB 51/T 5046-2007 clause 4.3.2; SJG 181.2-2024 clause 5.2.2; DB11/T 638-2016 Annex A questions and notes
• Government web pages found by search (for further verification; the original texts prevail): http://zjt.gxzf.gov.cn/zfxxgk/fdzdgknr/wjtz/t27789614.shtml ; https://zjt.jiangxi.gov.cn/jxszfhcxjst/gsgg/pc/content/content_1765237295630970880.html ; https://zjj.jiaozuo.gov.cn/2026/06-11/605303.html ; https://jst.nx.gov.cn/xwdt/zjdt/202602/t20260205_5160723.html ; https://www.klmy.gov.cn/klmys/tpxw/202605/9c74717f73b6468dabdfc1a8de6fa282.shtml ; https://zjj.hld.gov.cn/jcxxgk/zfxxgk/fdzdgknr/jyta/zxtadf/202408/t20240808_1182694.html ; http://www.jms.gov.cn/jms/c100047/202507/c04_32251.shtml ; https://js.zibo.gov.cn/art/2016/5/14/art_1146_588703.html ; https://www.klmy.gov.cn/klmys/tpxw/202606/ee7e1d8b91a94703ae09651728bc1fc9.shtml ; https://js.zibo.gov.cn/art/2016/5/14/art_1146_588731.html