How should intersecting masonry walls be connected?

ANSWER: 

Wall intersections may be required to meet one of three conditions:  1) transfer of all forces, 2) transfer of out-of-plane forces only, or 3) transfer of no forces.

  1. All forces must be able to be transferred when the intersecting walls are both part of the lateral-force-resisting system (shear walls).
  2. When a wall (first wall) is relying upon another wall (second wall) for lateral support, but the first wall is not part of the lateral-force-resisting system, then the intersection must only transfer forces that are acting out-of-plane on the first wall.
  3. Due to differential support or loading conditions, it may be desirable for no forces to be transferred at a wall intersection.

Transfer of all forces at an intersection, including shear, can be achieved by one of three methods:

  • At least 50% of the masonry units at the interface must interlock (overlap); or
  • Steel anchors of minimum size ¼ in. x 1.5 in. x 28 in. including 2-in. long bends at each end, must be grouted into the intersection at maximum 48 in. on center; or
  • Intersecting reinforced bond beams must cross the intersection at maximum 48 in. on center.

A steel anchor detail, which is used to transfer all forces at an intersection in the absence of unit overlap or reinforced intersecting bond beams, is shown in MIM Detail 2/S-2 below.  Refer to FAQ “When are rigid steel connectors (strap anchors) required for anchoring intersecting masonry walls?” for further discussion on this type of anchorage.

structural detail 2

When a wall relies on an intersecting wall for lateral support (transfer of out-of-plane forces) only, with no shear (in-plane force) transfer, joint reinforcement or mesh hardware cloth are commonly used.  Other metal ties/anchors that provide equivalent connection to joint reinforcement or mesh hardware cloth may be employed.  However, TMS 402 currently explicitly permits this type of connection in intersecting walls designed by the Empirical provisions and in intersecting partition walls only.

The 2016 edition of TMS 402 is expected to describe how to anchor partition walls to structural walls so as to provide lateral support only.

  • Intersecting walls shall be anchored so as to transfer out-of-plane lateral load from the partition wall to the structural wall.
  • Masonry partition walls shall be isolated within their own plane at the intersection, except as required for gravity support of the walls.
  • Isolation joints and connectors at the intersections of masonry partition walls and structural walls shall be designed to accommodate the vertical and horizontal deformations of the structural wall.

A mesh hardware cloth detail, which is used to transfer out-of-plane forces only, is shown in MIM Detail 1/S-2 below.

structural detail 1

When it is desirable to prevent transfer of all forces at a wall intersection, a movement joint (expansion or contraction) is formed at the intersection.  Clay masonry expansion joints are detailed in BIA Technical Note 18A and concrete masonry control joint details are shown in NCMA TEK 10-2C.

Resources:

  1. Building Code Requirements for Masonry Structures, TMS 402-13/ACI 530-13/ASCE 5-13, Masonry Standards Joint Committee (MSJC)
  2. Joint Reinforcement: Less Is More, Masonry Magazine, July 2015, pages 44 – 50
  3. Selecting Joint Reinforcement, The Construction Specifier Magazine, June 2014, pages 50 – 58
  4. Accommodating Expansion of Brickwork, Technical Notes on Brick Construction, 18A, November 2006, Brick Industry Association, gobrick.com
  5. Control Joints for Concrete Masonry Walls – Empirical Method, TEK 10-2C, 2010, National Concrete Masonry Association, ncma.org
  6. Masonry Institute of Michigan's Structural Masonry Details

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