Shear Wall Layout Requirements

Shear Wall Layout (Pure Shear Wall Structure)

Items and Requirements to Note

According to Section 7.1.1 of the high-rise building code:

• Shear wall structures should have appropriate lateral stiffness.
• The plan should be simple and regular. Shear walls should be arranged in two directions along the principal axes or other directions, and the lateral stiffness of the two directions should not differ excessively. Major calculation indices such as period and inter-story drift should generally not be less than 80% of each other. A structure with walls in only one direction should not be adopted.
• Shear walls should be arranged continuously from bottom to top to avoid abrupt changes in stiffness.
• Door and window openings should be aligned vertically and arranged in columns to form clear wall piers and coupling beams. In seismic design, Grade 1, 2, and 3 shear walls should generally not use coupling beams with vertically misaligned openings, and overlapping local openings should generally not be used over the full height.

Section 7.1.2:

• Shear walls should not be excessively long. Longer shear walls should be divided into wall segments of relatively uniform length by coupling beams with a larger span-to-depth ratio. The ratio of wall segment height to length should generally not be less than 3, and the wall segment length should generally not exceed 8 m.
• If the coupling beam stiffness is too small, the stiffness and energy dissipation capacity of the coupling beam will be weakened, turning the shear wall structure into a wall-frame system composed entirely of isolated wall piers and weak coupling beams. Such a structural behavior is close to that of a frame structure and is unfavorable for seismic resistance.
• The coupling beam height can be taken between 2.5 and 5. Neither excessive nor insufficient coupling beam stiffness is desirable.

Section 7.1.8:

In seismic design, short-leg shear walls must not be used exclusively. For Class B high-rise buildings and Class A high-rise buildings with seismic fortification intensity of 9 degrees, short-leg shear walls should generally not be arranged, and shear wall structures with many short-leg shear walls must not be used.

• Short-leg shear wall: a shear wall whose section thickness is not greater than 300 mm and whose maximum ratio of limb section height to thickness is greater than 4 but not greater than 8.
• Structure with many short-leg shear walls: under the specified horizontal seismic action, the overturning moment carried by short-leg shear walls at the base is not less than 30% of the total seismic overturning moment at the base.

When a structure with many short-leg shear walls is adopted, it should satisfy:

1. Under the specified horizontal seismic action, the overturning moment carried by short-leg shear walls at the base should generally not exceed 50% of the total seismic overturning moment at the base.
2. The applicable building height should be appropriately reduced. For 7 degrees, 8 degrees (0.2 g), and 8 degrees (0.3 g), it should not exceed 100 m, 80 m, and 60 m respectively.

Other principles for shear wall layout:

1. Shear walls should be as continuous and straight as possible to improve seismic capacity.
2. Avoid forming small wall piers between openings and wall edges or between openings. The width of small wall piers should generally not be less than three times the wall thickness, and concealed columns should be used for strengthening.
3. The length of wing walls should be at least three times the thickness of the supported wall.

Summary of Shear Wall Layout

1. Peripheral, uniform, symmetric, and regular.
2. Walls must be arranged at corners.
3. Walls must be arranged around staircases and elevators.
4. More walls should be placed around the perimeter; the middle should not be left without walls.
5. Prefer L-shaped, T-shaped, channel-shaped, and I-shaped wall arrangements.
6. Prefer ordinary shear walls and avoid short-leg shear walls.
7. Arrange shear walls where walls can be continuous and straight.
8. When a shear wall is longer than 8 m, structural openings are needed.
9. Common residential bay widths are 3 to 4 m, and shear wall spacing can be arranged according to bay conditions.
10. Number of shear walls: in high-rise shear wall structures, the wall ratio, meaning the ratio of shear wall area on a floor to the total floor area, is about 5%.

Frame-Shear Wall Structure

Code Content

High-rise building code:

Section 8.1.2: Forms of frame-shear wall structures:

1. Frames and shear walls, including single walls, coupled walls, or smaller cores, are arranged separately.
2. Shear walls are embedded within several spans of the frame structure, forming frame-supported shear walls.
3. Frames and shear walls are continuously arranged within a single lateral-force-resisting system.
4. A combination of two or three of the above forms.

Section 8.1.5: A frame-shear wall structure should be arranged as a two-way lateral-force-resisting system. In seismic design, shear walls should be arranged along both principal axes of the structure; otherwise, the stiffness difference may become excessive.

Section 8.1.7: Requirements for shear wall layout are similar to those for pure shear wall structures.

• When the plan shape has large projections or recesses, shear walls should preferably be arranged near the ends of the projecting parts.
• The horizontal shear carried by a single shear wall at the base should not exceed 30% of the total horizontal shear at the base of the structure.
• Shear walls should run through the full height of the building to avoid abrupt stiffness changes. When openings are made in shear walls, the openings should preferably be vertically aligned.

Shear walls should be arranged uniformly, both in distribution and section size.

Measures should be taken, such as adjusting shear wall layout, changing wall thickness, or providing structural openings, so that shear wall stiffness varies uniformly along the height and becomes larger at lower levels and smaller at upper levels.

Section 8.1.8: In long rectangular plans or buildings with a relatively long part of the plan, shear wall layout should also satisfy:

1. The spacing of transverse shear walls along the long direction should meet the requirements in the following table. When there are large openings in the floor slab between shear walls, the spacing should be reduced appropriately.
2. Longitudinal shear walls should not be concentrated at the two ends of the building, because temperature stress may cause reverse arch cracking.

Floor System	Non-Seismic Design	6 and 7 Degrees	8 Degrees	9 Degrees
Cast-in-place	5.0 B, 60	4.0 B, 50	3.0 B, 40	2.0 B, 30
Assembled monolithic	3.5 B, 40	3.0 B, 40	2.5 B, 30	-

The values in the table take the smaller value. B is the width of the long rectangular plan.

When the transverse shear wall spacing is large, the rigid-floor assumption cannot be guaranteed under earthquake action, and the cooperative behavior between frames and shear walls will decrease.

Section Changes

• The thickness of shear walls can vary by stage along the height, and each thickness reduction should preferably be 50 to 100 mm.
• In general, thickness should be set back on both sides simultaneously.
• To keep exterior wall surfaces flat, exterior walls may be set back only on the interior side.
• Due to installation requirements, elevator shafts may be set back only on the exterior side.
• Changes in shear wall thickness and concrete strength grade should preferably be staggered between floors; wall thickness and concrete grade should not be reduced at the same floor.

Reference