Reading method, content composition and code basis of the collective annotation (plane annotation) of concrete beams in Pingfa construction drawings (GB/T 50105-2010 Clause 3.3.5, the Pingfa atlases, GB 50010-2010 Clause 11.3.7, GB 55008-2021 Clause 4.4.8)

Topic Positioning

The reading method, content composition and code basis of the "collective annotation" (plane annotation) of concrete beams in Pingfa (plane integrated representation) construction drawings: what the collective annotation contains, how to read it, and which baselines the national standard and the Pingfa atlas provide. Applicable to structural construction-drawing reading and to entry-level rebar detailing and quantity take-off.

Core Conclusions

1. Content framework of the collective annotation (GB/T 50105-2010 Clause 3.3.5, national-standard baseline) Concrete beams may be annotated on the beam layout plans by the plane-annotation and section-annotation methods:

• Plane annotation: "on the beam layout plan, one beam of each different designation may be selected and directly annotated with its designation, cross-sectional dimensions, number of spans, specific reinforcement values and relative level difference (omittable where there is no difference), etc.";
• Section annotation: "on the layout plan, one beam of each different designation may be selected, a section figure drawn out with a section mark, and the cross-sectional dimensions and specific reinforcement values annotated on it."

In the Pingfa system, the collective annotation is the set of notations led out from the beam giving the values common to the whole beam (designation including number of spans, cross-section, stirrups, full-length/holding bars, side longitudinal bars and other reinforcement information, plus the optional level difference of the beam top); special values of a particular span or position (support-top longitudinal bars, beam-bottom longitudinal bars, additional stirrups/hanger bars, etc.) are expressed by the in-situ annotations on the drawing. Reading principle: first read the whole beam through by the collective annotation (drafting), then make local corrections span by span per the in-situ annotations; where the two conflict, the in-situ value prevails (general rule of the Pingfa atlas).

2. National-standard status of the Pingfa atlas (Jian She [2000] No. 157) Upon review and approval, the eleven atlases including "Rules for Planar Integrated Representation and Detailing of Concrete Structure Construction Drawings" became national building standard design atlases, and "the atlases take effect from the date of approval" (Ministry of Construction, 17 July 2000). The symbol details of collective annotation (designation codes, stirrup notation, bracket usage, etc.) are governed by the Pingfa atlas; the current general edition is 22G101-1, replacing 16G101-1; for old drawings citing earlier editions, the edition cited by the drawings governs.

3. Construction baselines behind the annotated values (needed for reading and take-off)

• Full-length bars (GB 50010-2010 (2015 edition) Clause 11.3.7): "the reinforcement ratio of the longitudinal tension bars at beam ends should not exceed 2.5%. At least two full-length longitudinal bars shall be provided on each of the top and bottom faces along the full length of the beam; for seismic grades 1 and 2 the bar diameter shall not be less than 14 mm and shall respectively not be less than 1/4 of the larger of the cross-sectional areas of the top and bottom longitudinal bars at the two beam ends; for grades 3 and 4 the diameter shall not be less than 12 mm." "Full length" here means ensuring these bars exist at every position of the beam; it does not forbid splices at appropriate positions.
• Frame-beam ductility detailing (GB 55008-2021 Clause 4.4.8): (1) the ratio of the concrete compression-zone depth (counting compression bars) to the effective depth at the beam end shall not exceed 0.25 for grade 1 and 0.35 for grades 2 and 3; (2) the minimum reinforcement ratio of the longitudinal tension bars shall not be less than the values of Table 4.4.8-1; (3) the ratio of the bottom-face to top-face longitudinal bar cross-sectional areas at the beam end, besides being determined by calculation, shall not be less than 0.5 for grade 1 and 0.3 for grades 2 and 3; (4) the densified-zone length, maximum stirrup spacing and minimum stirrup diameter at beam ends shall meet Table 4.4.8-2; for grade 1 and 2 frame beams, where the stirrup diameter exceeds 12 mm with not fewer than 4 legs and a leg spacing not exceeding 150 mm, the maximum spacing in the stirrup densified zone may be relaxed to not more than 150 mm. (Note: in the tables d is the longitudinal bar diameter and hb the beam depth.) The purpose is to control the rotation capacity and ductility of the plastic-hinge zone at the beam ends and to confine the compression bars against premature buckling after spalling of the cover.

Applicable Boundaries

• The final basis for reading collective annotations is the Pingfa atlas (current general edition 22G101-1, replacing 16G101-1); old drawings are executed per the cited edition. This card gives the national-standard clauses and the general reading framework and does not replace the atlas or the code text.
• The specific values of Table 4.4.8-1 (minimum reinforcement ratio of beam longitudinal tension bars) and Table 4.4.8-2 (densified-zone length, maximum stirrup spacing and minimum stirrup diameter at beam ends) must be taken from the text of GB 55008-2021 and must not be applied from memory.
• Applicable to construction-drawing reading of cast-in-place concrete building beams; precast beams, bridge members and other special structures (e.g. transfer beams) have separate provisions.
• The 2.5% reinforcement ratio is a "should not exceed" upper bound (not an absolute prohibition); the full-length bar requirements apply to the longitudinal reinforcement detailing of seismic frame beams.

Further Reading

• GB/T 50105-2010 "Standard for Structural Drawings of Buildings", Clause 3.3.5: plane annotation and section annotation of concrete beams (national-standard baseline); Section 3.3 is the drafting basis of Pingfa annotation.
• 22G101-1 "Rules for Planar Integrated Representation and Detailing of Concrete Structure Construction Drawings (cast-in-place concrete frames, shear walls, beams and slabs)": symbol details and reading examples for each collective-annotation item (designation, cross-section, stirrups, full-length/holding bars, side bars, level difference); current general edition, replacing 16G101-1.
• GB 50010-2010 (2015 edition) "Code for Design of Concrete Structures", Clause 11.3.7: requirements for full-length longitudinal bars of beams.
• GB 55008-2021 "General Code for Concrete Structures", Clause 4.4.8 and Tables 4.4.8-1 and 4.4.8-2: basic (seismic) design requirements for frame beams; a mandatory engineering-construction code.
• Jian She [2000] No. 157 "Notice of the Ministry of Construction on Approving Eleven Atlases including the 'Rules for Planar Integrated Representation and Detailing of Concrete Structure Construction Drawings' as National Building Standard Design Atlases": the basis of the national-standard status of the Pingfa atlases.