CONTROL JOINTS FOR CONCRETE MASONRY WALLS— TEK …

1 Provided An i n f o r m aby: tion series from the national authority on CONCRETE MASONRY technology Cemex, Inc. CONTROL JOINTS FOR. CONCRETE MASONRY WALLS TEK 10-2C. EMPIRICAL METHOD Movement CONTROL (2010). INTRODUCTION. CONCRETE MASONRY is a popular construction material MASONRY veneers differ from the guidance presented be- because its inherent attributes satisfy the diverse needs of low. The reader is referred to TEK 10-4, Crack CONTROL both exterior and interior walls. While these attributes for CONCRETE Brick and Other CONCRETE MASONRY Veneers are the primary basis for CONCRETE MASONRY 's popularity, (ref. 3), for more detailed information. performance should not be taken for granted. Like all con- CONTROL JOINTS are one method used to relieve hori- struction systems, design decisions significantly influence zontal tensile stresses due to shrinkage of the CONCRETE field performance of the CONCRETE MASONRY wall system. MASONRY units, mortar, and when used, grout.

2 They are Proper application of crack CONTROL measures, including essentially vertical planes of weakness built into the wall CONTROL JOINTS when required, can help ensure satisfactory to reduce restraint and permit longitudinal movement due performance of the CONCRETE MASONRY . to anticipated shrinkage, and are located where stress con- Note that crack CONTROL considerations for CONCRETE centrations may occur. A bond break is accomplished by Between main and At maximum of intersecting wall one-half CONTROL joint spacing from corners At changes in wall height At pilasters and changes in wall Adjacent to lintel and through thickness opening if not crossing vertical reinforcement Figure 1 Typical CONTROL joint Locations Related TEK: Keywords: bond beams, construction details, CONTROL 7-1C, 10-1A, 10-3, JOINTS , crack CONTROL , joint reinforcement, reinforcing bars, reinforced CONCRETE MASONRY , shrinkage, wall movement 10-4. NCMA TEK 10-2C 1. replacing all or part of a vertical mortar joint with a backer In addition, care should be taken to provide JOINTS at rod and sealant.

3 This keeps the joint weather tight while locations of stress concentrations such as (see Figure 1): accommodating small movements. joint reinforcement and 1. at changes in wall height, other horizontal reinforcement should be discontinued at 2. at changes in wall thickness, such as at pipe and duct CONTROL JOINTS unless it is required for structural purposes, chases and pilasters, as it will act to restrain horizontal movement. 3. at (above) movement JOINTS in foundations and When CONTROL JOINTS are required, CONCRETE MASONRY floors, only requires vertical CONTROL JOINTS . When materials with 4. at (above and below) movement JOINTS in roofs and different movement properties, such as CONCRETE MASONRY floors that bear on a wall, and clay MASONRY , are used in the same wythe the move- 5. near one or both sides of door and window openings, ment difference needs to be accounted for in the design. (see following subsection, CONTROL JOINTS at Openings), Normally, joint reinforcement is used in the common and joint between the two to distribute the forces and keep 6.

4 Adjacent to corners of walls or intersections within a any cracks that form tightly closed. Another option is to distance equal to half the CONTROL joint spacing. provide a horizontal slip plane between the two materials Consideration must also be given to the effect of to accommodate the differential movement. See Clay and CONTROL joint placement on load distribution within the CONCRETE MASONRY Banding Details, TEK 5-2A (ref. 1), wall. For example, locating CONTROL JOINTS at the ends of for more detailed information. lintels may compromise arching action. Therefore, it may CONTROL JOINTS are typically required in exposed above be prudent to design the lintel to carry the full weight of grade CONCRETE MASONRY walls, where shrinkage cracking the wall above it in addition to any superimposed loads. may detract from the appearance of the wall, and to limit moisture or air infiltration. Shrinkage cracks in CONCRETE CONTROL JOINTS at Openings MASONRY are not a structural concern.

5 In addition, walls Because cracking occurs in the planes of greatest with adequate horizontal reinforcement may not require weakness, openings are particularly vulnerable. For CONTROL JOINTS , as the reinforcement effectively reduces the an opening of up to 6 ft ( m) in width that are not width of shrinkage cracks. See TEK 10-3, CONTROL JOINTS wrapped with reinforcement, a CONTROL joint should be for CONCRETE MASONRY Walls Alternative Engineered placed at one side of the opening as shown in Figure 2a. Method (ref. 2), for more information. Notice that the joint goes around the lintel and allowance Foundation walls traditionally do not include con- for movement (a slip plane in the form of flashing or trol JOINTS due to concerns with waterproofing the joint other bond breaker) between the lintel and the MASONRY to withstand hydrostatic pressure. Additionally, since must be provided. Because the lintel is not laterally sup- foundation walls are subjected to relatively constant ported at the bottom due to the slip plane, CONTROL JOINTS temperature and moisture conditions, shrinkage cracking capable of providing load transfer between panels are in below grade walls tends to be less significant than in required, such as the JOINTS shown in Figures 3a, 3d, 3e, above grade walls.

6 3f, 3h and 3i. This TEK focuses on cracking resulting from inter- In Figure 2a, continuous vertical reinforcement can- nal volume change of the CONCRETE MASONRY . Potential not be provided in the cell adjacent to the opening on cracking resulting from externally applied design loads the left, as crossing the horizontal portion of the CONTROL due to wind, soil pressure, seismic forces, or differential joint ( , the slip plane) would effectively pin the two settlement of foundations is controlled by structural design sections together, restraining relative movement. To resist considerations not addressed here. Where external loads the lateral movement around the slip plane, 24-in. (610- are an issue in combination with internal volume change, mm) long horizontal joint reinforcement may be placed the design should consider the combined effects of these at the lintel bearing location and two courses below. If influences on cracking. utilizing CONCRETE MASONRY veneered steel beams over openings in lieu of CONCRETE MASONRY or precast lintels, CONTROL joint PLACEMENT it is critical that the steel beam not be welded to the bearing plate(s) where designated CONTROL JOINTS are to When required, CONTROL JOINTS should be located where be constructed, as this will pin the two sections together, volume changes in the MASONRY due to drying shrinkage, restraining movement.

7 Carbonation, or temperature changes are likely to create When a slip plane under the bond beam is used for tension in the MASONRY that will exceed its tensile capacity. openings larger than 6 ft ( m), CONTROL JOINTS are In practice, this can be difficult to determine, but several recommended on both sides of the opening as shown in methods are presented in the following sections to provide Figure 2b. Again, the CONTROL joint goes under and up the guidance in locating CONTROL JOINTS . side of the lintel, and allowance for movement between 2 NCMA TEK 10-2C. the lintel and the MASONRY must be provided. Because reinforcement is placed above, below and beside the there is no lateral support at the bottom of the lintel, opening as discussed below. provision must also be made for load transfer between In walls containing vertical reinforcement, the cell the panels. adjacent to the opening is usually grouted and reinforced An alternative to avoid having the vertical reinforce- to provide solid support and additional strength for jambs.

8 Ment cross the slip plane is to place the reinforcement Using the same type of detail as for the unreinforced in the next cell over. Another alternative is to place the wall would require the CONTROL joint to cross the vertical CONTROL joint away from the opening if adequate tensile reinforcement, thereby preventing movement and de- CONTROL joint with load transfer CONTROL joint with load transfer capability to adjacent panel capability to adjacent panel Lintel Lintel Slip plane to permit relative movement Slip plane to permit relative movement in in the plane of the wall. No vertical the plane of the wall. No vertical reinforcement permitted to cross CONTROL reinforcement permitted to cross CONTROL joint . joint . 24-in. (610-mm) long joint reinforcement at lintel 24-in. (610-mm) long joint bearing and two courses below lintel bearing reinforcement at lintel bearing and two courses below lintel bearing, each side 2a Openings less than 6 ft (1,829 mm) 2b Openings wider than 6 ft (1,829 mm).

9 CONTROL JOINTS at Openings in Walls With No Reinforcement in Adjacent Cells Maximum CONTROL joint 12 in. (305 mm) Maximum CONTROL joint spacing per Table 1 min. typ. spacing per Table 1. MASONRY lintel or precast lintel (notched Ladder joint if vertical reinforcement in reinforcement in cell first two JOINTS next to opening) above opening from CONTROL joint to Vertical reinforcement CONTROL joint (min.). in grouted cell each or a single course side of opening (typ.) reinforced bond (alternate-place in beam Lintel reinforcement second cell from Sill Sill opening) CONTROL joint (typ.). Ladder joint reinforcement in 1 st or 2 nd mortar joint below sill from CONTROL joint to CONTROL joint (min.) or reinforced bond beam below sill 2c Preferred strengthening of opening with 2d Opening strengthened with joint reinforcement reinforcement extending lintel reinforcement (first two courses over opening and under sill). and joint reinforcement under the sill CONTROL JOINTS at Openings Wrapped with Reinforcement Figure 2 CONTROL JOINTS at Openings NCMA TEK 10-2C 3.

10 Table 1 Recommended CONTROL joint each side, or a horizontal bond beam could be used, as Spacing for Above Grade Exposed shown in Figure 2d. CONCRETE MASONRY WallsA For best performance, the vertical reinforcement Distance between JOINTS not to exceed the lesser of: should be placed in the cell immediately adjacent to the Length to height ratio or ft (m) opening. However, due to congestion in the cell at this location, vertical reinforcement is sometimes placed in the 1 : 1 25 ( ). second cell from the opening. In this case, the cell next to A. Notes: the opening should be grouted, as should the cell contain- 1. Table values are based on the use of horizontal ing the reinforcement, to provide additional resistance for reinforcement having an equivalent area of not attaching the door or window frames. These details may less than ( mm2/m) of height to also be used in unreinforced walls and walls utilizing keep unplanned cracks closed (see Table 2). steel lintels, since the area surrounding the opening is 2.