Masonry Anchor Strength Design Guide 2024
Nominal width of unit in . ( mm )
Minimum face-shell thickness in . ( mm )
Minimum web thickness in . ( mm )
3 ( 76 ) and 4 ( 102 ) 3 / 4 ( 19 ) 3 / 4 ( 19 ) 6 ( 152 ) 1 ( 25 ) 3 / 4 ( 19 ) 8 ( 203 ) and greater 1-1 / 4 ( 32 ) 3 / 4 ( 19 )
Adapted from ASTM C90 - 22 Table 1 . 1 Average of measurements on three units when measured as described in Test
Methods C140 .
CLAY BRICK
Clay brick is the most extensively used type of masonry unit throughout the world . Bricks are prismatic masonry units made from a suitable mixture of soil , clay , and a stabilizing agent ( emulsified asphalt ). They are shaped by molding , pressing , or extruding and are fired at elevated temperature to meet the strength and durability requirements of ASTM C62 ( solid brick ) and ASTM C652 and ASTM C216 ( hollow brick ).
8 ” ( 203 mm )
16 ” ( 406 mm )
Nominal size ( usually fictitious )
8 ” ( 203 mm )
Head Joint
Cell
7-5 / 8 ” ( 194 mm )
Web Face
Bed Joint
CMU Terminology
15-5 / 8 ” ( 397 mm )
Modular size ( actual )
7-5 / 8 ” ( 194 mm )
CMU construction can be reinforced whereby reinforcing bars are placed vertically in cells filled with grout to create a composite section analogous to reinforced concrete . If all cells , both unreinforced and reinforced are filled with grout , the CMU construction is referred to as fully grouted CMU . If only the reinforced cells are grouted , the CMU construction is referred to as partially grouted . If none of the cells are grouted , the CMU construction is referred to as ungrouted or hollow . Horizontal reinforcement may be placed in a wall via a bond beam or lintel , which is always grouted . Ladder reinforcement may also be placed in the mortar bed between courses .
Grout typically conforms to ASTM C476 and has a minimum compressive strength of 2,000 psi . Concrete masonry units have a compressive strength which may range from 1,250 psi to over 4,800 psi , although the maximum specified compressive strength of the assembled masonry will generally not exceed 3,000 psi . Both post-installed adhesive and mechanical anchors may be used in grouted CMU . If voids are present or suspected , mechanical anchors should not be used , and adhesive anchors should only be installed in conjunction with a screen tube to prevent uncontrolled flow of the bonding material . In hollow masonry , anchor strength is generally assumed to be based on the face shell thickness , which can be variable .
Depending upon the grade , clay masonry bricks can have a compressive strength ranging from 1,250 psi to over 25,000 psi . Grouted multi-wythe masonry construction typically consists of two wythes , each one-unit masonry in thickness , separated by a space ( collar joint ) 1 / 2 ” to 4-1 / 2 ” wide , generally filled with grout . The wythes are connected with wall ties . This space may also be reinforced with vertical reinforcing bars . Solid clay brick masonry consists of abutting wythes interlaced with header courses . In general , adhesive anchors are recommended for use in clay brick . In older unreinforced masonry construction ( URM ) or where the condition of the masonry is unknown , it is advisable to use a screen tube to prevent unrestricted flow of the bonding material into voids . URM construction is not currently covered under the recent changes to AC01 and AC58 .
MORTAR
Mortar is used to provide uniform bearing between masonry units and to bond individual units into a composite assemblage that will withstand the imposed loading conditions . Mortar consists of a mixture of cementitious material , aggregate , and water proportionally combined in accordance with ASTM C270 . Cement / lime mortar or masonry mortar ( each in four types ) are typically used under this standard .
Since mortar plays a significant role in the structural integrity of a masonry wall , it is important to understand how postinstalled anchors interact with the structure . Within a masonry structure , there are designated joint locations , and the proximity of a post-installed anchor to one of these locations must be considered in the design of the anchorage . Product specific guidelines are provided within this technical guide .
In the past , Hilti has provided technical data for 8 ” wide nominal CMU blocks . With the new criteria , Hilti has additional embedment depths which permit installation in wider walls , such as 10 ” or 12 ” nominal grouted CMU .
Masonry Fastening Technical Guide Edition 24 Hilti , Inc . 1-800-879-8000 | en español 1-800-879-5000 | www . hilti . com | Hilti ( Canada ) Corporation | www . hilti . ca | 1-800-363-4458
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