Development of Draft Protocol for Testing of Structural Components and Systems

(a joint initiative of MoHUPA under technology submission of Pradhan Mantri Awas Yojna & IIT, KANPUR)

Confined Masonry

Confined Masonry is a construction system where the walls are built first, and the columns and beams are poured in afterwards to enclose (confine) the wall as shown in fig. 1. Confined masonry construction is similar to unreinforced masonry except for the inclusion of RC confining elements. It is different from the regular infilled RC frame because of its construction methodology and load transfer mechanism. For further details about seismic behavior of confined masonry and its design method refer to Ph. D theses of Dr. Vaibhav Singhal,IIT Patna (Thesis link)

  1. Advantages of confining walls with tie-beams and tie-columns:
    1. Improved wall-to-wall and floor/roof-to-wall connection which guarantees better transfer of forces analogous to closed box-type action during a seismic event.
    2. Greater in-plane and out-of-plane stability of slender structural walls
    3. Enhanced strength, ductility, and energy dissipation capacity when compared to the unreinforced load bearing masonry walls

    Figure 1: Key components of the Confined Masonry

    Courtesy: Dr. Vaibhav Singhal, IIT Patna

  2. Lateral load carrying capacity of Confined Masonry walls will depend on:
    1. Strength of the masonry used
    2. Location of RC tie-columns and tie-beams
    3. Cross-sectional details of RC tie-columns

  3. Confined masonry shall conform to following standards:
    1. IS 1077-1992 or IS 2180-1988 or IS 2222-1991: For Burnt Clay Building bricks
    2. IS 2185(part 1)-2005: For Concrete blocks (Solid and Hollow)
    3. IS 3952-1988: For Burnt Clay Hollow bricks
    4. IS 2185(part 3)- 1984: autoclaved cellular (aerated) concrete blocks
    5. IS 456: Minimum grade of concrete shall be M15. Concrete mix should provide adequate workability (slump of 75-100 mm) and Size of the coarse aggregate should be less than 12.5 mm
    6. IS 1786-2008: Fe 415 grade steel shall be used for reinforcement
    7. IS 1905: Type M1, M2, H1 and H2 mortars shall be used

  4. Role to Wall-to-Tie column Interface: Good bonding between a masonry wall and adjacent RC tie-columns can be achieved by ‘toothing’ at the wall-to-tie-column interface and by providing dowels anchored into RC tie-columns as shown in fig. 2.
  5. Figure 2: Toothing and dowel anchors

    Courtesy: Dr. Vaibhav Singhal, IIT Patna

  6. Minimum Design Dimensions Requirements:
    1. Wall thickness (t) should not be less than 110 mm
    2. Maximum wall height/thickness (H/t) ratio shall not exceed 25
    3. Unsupported wall height (H) shall not exceed 2.5 m
    4. Height-to-width ratio of wall should be kept less than 2 for the better lateral load transfer
    5. When a parapet is not confined by tie-beams, height should not exceed 500 mm otherwise height limit is 1.2m

  7. Building Configuration:
    1. A regular building configuration is one of the key requirements for satisfactory earthquake performance
    2. The building plan should be of a regular shape
    3. The building’s length-to-width ratio in plan shall not exceed 4
    4. The walls should be built in a symmetrical manner
    5. The walls should be placed as far apart as possible, preferably at the façade, to avoid twisting (torsion) of the building in an earthquake
    6. There are at least two lines of walls in each orthogonal direction of the building plan, and the walls along each line extend over at least 50% of the building dimension
    7. The walls should always be continuous up the building height – vertical offsets are not permitted
    8. Openings (doors and windows) should be placed in the same position on each floor

  8. References:
    1. IITK-GSDMA Codes on confined Masonry