Masonry tie-bar arrangement requirements and bar-count calculation (including the "600x600" vs "1200x600 staggered (quincunx)" layout determination): vertical spacing, embedment length into the wall and seismic through-tie requirements

Topic Positioning

Arrangement requirements for tie bars in masonry infill walls and block walls (and cavity-wall ties) - vertical spacing, embedment length into the wall, seismic through-ties and connection methods - together with the two methods of calculating the bar count (quantity); focusing on the determination of the "600x600" vs "1200x600 staggered (quincunx)" spacing notations and the conversion into bars per square meter.

Core Conclusions

I. Arrangement requirements (by connection scenario)

1. Connection of infill walls to frame columns (GB 50011-2010 (2016 edition) "Code for Seismic Design of Buildings", Clause 13.3.4): tie bars of 2 Phi6 shall be provided along the full height of the frame column at 500 mm to 600 mm vertical spacing; the length of the tie bars extending into the wall should preferably run through the full wall length at seismic intensities 6 and 7, and shall run through the full length at intensities 8 and 9; where the wall length exceeds 5 m, the wall top should preferably be tied to the beam; where the wall length exceeds 8 m or twice the story height, reinforced concrete constructional columns should preferably be provided; where the wall height exceeds 4 m, a reinforced concrete horizontal tie beam connected to the columns and running through the wall length should preferably be provided at mid-height of the wall; infill walls in stairwells and passageways with pedestrian traffic should further be strengthened with steel-mesh mortar facings.
2. Connection methods of infill walls to the frame (GB 50003-2011 "Code for Design of Masonry Structures", Clause 6.3.4): separated or non-separated methods may be adopted per the design requirements; where seismic fortification is required, the separated method is preferred. Non-separated method: 2 bars of 6 mm diameter are provided along the column height at 500 mm spacing (3 bars of 6 mm where the wall thickness exceeds 240 mm); the bars should extend into the infill wall by not less than 700 mm, and the tie bars shall be cut off in a staggered manner, spaced not less than 200 mm apart (to prevent cracks occurring at the same section); the top of the infill wall shall fit closely against the frame beam. Key points of the separated method: gaps of not less than 20 mm are left at both ends against the columns and at the top against the beam; constructional columns are provided at the ends (spacing preferably not greater than 20 times the wall thickness and not greater than 4000 mm); both ends should preferably clip into notch irons set at the beam/slab soffits and the column sides (vertical spacing of wall-side notch plates preferably not greater than 500 mm; horizontal spacing of wall-top notch plates preferably not greater than 1500 mm). Where the infill wall length exceeds 5 m or twice the story height, tie measures between the wall top and the beam are advisable and a constructional column should be added at mid-length of the wall; where the wall height exceeds 4 m, a horizontal tie beam connected to the columns should preferably be provided at mid-height of the wall; where the wall height exceeds 6 m, horizontal tie beams connected to the columns should preferably be provided at every 2 m of wall height, with a beam section depth of not less than 60 mm.
3. General minimum embedment length (GB 50924-2014 "Code for Construction of Masonry Structures", Clause 9.1.5): tie bars extending into the masonry, measured from the joint, shall be not less than 500 mm; for perforated brick walls and block walls they shall be not less than 700 mm.
4. Small-block enclosure walls to structural columns (JGJ/T 14-2011 "Technical Specification for Small Hollow Concrete Block Buildings", Clause 8.9.2): the tie bars shall be 2 Phi6 bars at 400 mm vertical spacing, embedded in the horizontal mortar joints of the wall for a length of not less than 700 mm.
5. Block walls (Guangdong DBJ/T 15-18-2021 "Technical Specification for Concrete Block Wall Engineering", Clause 4.3.5): tie bars of 2 Phi6 with hooks, or welded steel fabric, should be provided along the wall height at about 600 mm spacing (matching the block module); the length embedded into the masonry shall be not less than 700 mm; in seismic fortification zones of intensity 6 and 7 not less than 1000 mm and preferably running through the full wall length, and in intensity 8 zones through the full length; the anchorage depth of post-installed bars follows JGJ/T 271 as the greater of 12d and 150 mm (for 6 mm tie bars the embedment depth commonly used is 80 mm to 100 mm).
6. Cavity-wall ties (GB 50003-2011 Clause 6.4.5, "quincunx pattern" in the original wording): the ties shall be arranged in a vertical staggered (quincunx) pattern, with maximum horizontal and vertical spacings preferably not greater than 800 mm and 600 mm respectively; where vibration or seismic fortification requirements exist, not greater than 800 mm and 400 mm respectively.
7. Construction and acceptance (GB 50203-2011 "Code for Acceptance of Construction Quality of Masonry Structures", Clause 9.3.3): the positions of tie bars or fabric left in infill walls shall match the block course count and be placed in the mortar joints, with embedment lengths per the design and vertical position deviation not exceeding one course height; not fewer than 5 spots shall be checked per inspection lot. Beijing DB11/T 1832.4-2021 "Specification for Construction Technology of Building Works, Part 4: Masonry Structure Works", Clause 8.4.9: where the design is silent, tie bars of 2 Phi6 run through the full wall length in the joints (3 Phi6 preferred where the wall thickness exceeds 240 mm) at 500 mm to 600 mm vertical spacing, and 180-degree hooks are preferred for HPB300 bars; chemically post-installed bars shall be pull-out tested.

II. Bar-count calculation (two methods)

• Row-by-row method (horizontal tie bars between infill wall and columns, the most common): count = number of vertical rows x bars per row (2 Phi6 per row; 3 Phi6 where the wall thickness exceeds 240 mm); number of vertical rows = arranged height / vertical spacing (500 mm or 600 mm, rounded per the starting and ending block courses). Single-bar length = embedment into the wall + anchorage/post-installation depth (post-installed bars: the greater of 12d and 150 mm; for Phi6 commonly 80-100 mm, per the design) + hooks. Total weight (t) = sum of (count x single-bar length x unit theoretical mass), with Phi6 = 0.222 kg/m.
• Point/area method (ties, post-installed bar points and other area-type point layouts): count = coverage area / (product of the two spacings), then rounded for edge distances and boundaries.

III. Determination of "600x600" vs "1200x600 staggered"

• Step 1: first confirm whether it is a "two-way point layout" - this determination applies only where both a horizontal and a vertical spacing are given (ties, post-installed points); for row-by-row horizontal tie bars only the number of vertical rows is counted, and no "600x600" question arises.
• Step 2: read the two annotated numbers directly; the area served per bar = the product of the two numbers, and the stagger offset does not enter the calculation. 600x600: 0.6 x 0.6 = 0.36 m2 per bar, about 2.78 bars/m2; 1200x600 staggered: 1.2 x 0.6 = 0.72 m2 per bar, about 1.39 bars/m2 (adjacent rows staggered by half a spacing). Staggering only improves the uniformity of the layout and does not change the count per unit area; converting the stagger offset into a densified spacing (e.g., re-counting at a 600x600 basis) would double the count.

Applicable Boundaries

• Tie-bar spacing and embedment values depend on the seismic fortification intensity, the connection method (separated/non-separated), the wall material (solid brick/perforated brick/block) and the local standards of the project location; where the design is explicit the design prevails, and local standards differ (e.g., Beijing requires full-length through ties where the design is silent).
• The 800x600 (seismic 800x400) values for cavity-wall ties are the maximum spacings of point-type ties between the outer and inner leaves - a different scenario from the 500-600 mm values for infill-wall tie bars; do not mix the two sets of figures.
• In GB 50011 Clause 13.3.4, wall length > 5 m/8 m or wall height > 4 m triggers the provision of constructional columns and horizontal tie beams, not the tie-bar spacing itself.
• The area method applies only to two-way point layouts, not to row-by-row tie bars; count rounding, edge distances and additional construction at openings (e.g., concrete columns added at both sides of an opening) must be handled separately.
• The anchorage/post-installation depths in concrete (12d and not less than 150 mm; Phi6 commonly 80-100 mm) are constructional references; the design and the project-specific post-anchoring requirements prevail.

Further Reading

• GB 50011-2010 (2016 edition) "Code for Seismic Design of Buildings" Clause 13.3.4 (tie bars between infill walls and frame columns; wall length/height constructional rules);
• GB 50003-2011 "Code for Design of Masonry Structures" Clause 6.3.4 (separated/non-separated connection of infill walls to the frame) and Clause 6.4.5 (quincunx arrangement of cavity-wall ties);
• GB 50924-2014 "Code for Construction of Masonry Structures" Clause 9.1.5 (embedment 500/700);
• GB 50203-2011 "Code for Acceptance of Construction Quality of Masonry Structures" Clause 9.3.3 (course matching, sampling count);
• JGJ/T 14-2011 "Technical Specification for Small Hollow Concrete Block Buildings" Clause 8.9.2;
• Guangdong DBJ/T 15-18-2021 "Technical Specification for Concrete Block Wall Engineering" Clause 4.3.5;
• Beijing DB11/T 1832.4-2021 Clause 3.4.17 (straight-tooth joint at construction openings in foundation walls: one additional Phi6 per 120 mm increase in wall thickness, vertical spacing not exceeding 500 mm, embedment of not less than 1000 mm on each side, 90-degree end hooks) and Clause 8.4.9;
• JGJ/T 271 "Technical Specification for Post-anchoring of Inorganic Materials in Concrete Structure Engineering" (post-installed bar anchorage depth).