1.0 What is changing?
For many years, post-installed adhesive and mechanical anchors have been utilized for fastenings into masonry base materials. While the relevant model design codes( i. e., ACI and CSA) for post-installed anchors into concrete base materials have evolved, the relevant model design codes for post-installed anchors into masonry base materials have remained unchanged for decades. In recent years, testing and evaluation criteria for post-installed adhesive and mechanical anchors in masonry base materials have been based on three International Code Council Evaluation Services( ICC-ES) Acceptance Criteria: AC01 for Expansion Anchors in Masonry Elements, AC106 for Predrilled Fasteners( Screw Anchors) in Masonry Elements, and AC58 for Adhesive Anchors in Masonry Elements. In 2020, these three criteria were considerably revised with a compliance date of April 15th, 2023, assigned to adhesive anchors and February 16th, 2024, assigned to mechanical anchors. Some of the changes include but are not limited to:
• The consolidation of AC106 into AC01 to create one Acceptance Criteria for all mechanical anchors installed into masonry base materials.
• The clarification of the types of masonry systems included in AC01 and AC58 such as: fully grouted concrete masonry units( CMU), partially grouted CMU, ungrouted CMU, and clay brick.
• The adoption and adaptation of ACI 318’ s Concrete Capacity Design( CCD) method for the design of post-installed anchors into masonry base materials.
• The inclusion of cracked masonry testing and evaluation.
The Masonry Anchor Strength Design Guide is intended to present these industry changes to post-installation of adhesive and mechanical anchors into masonry base materials in a simplified and easy-to-understand format. The guide will start with discussion on common masonry definitions as well as the updated clarification of the types of masonry systems. The design of post-installed anchors into masonry base materials will closely mirror the design of post-installed anchors into concrete base materials per ACI 318 Chapter 17. The guide will discuss the similarities and the differences between concrete and masonry design. Additionally, common design considerations and design examples will be shown to demonstrate the overall design process.
Following the discussion on the changes to the testing and evaluation criteria, the Masonry Anchor Strength Design Guide will provide technical data for the various Hilti post-installed adhesive and mechanical anchors approved for anchoring into masonry base materials. Additionally, Hilti’ s PROFIS Engineering software can be utilized for post-installed masonry anchor design.
2.0 What is masonry?
Masonry is a heterogeneous building material usually consisting of concrete masonry units( CMU or clay brick bonded together using joint mortar. The primary application for masonry is the construction of walls, which are built by placing masonry components in horizontal rows( courses and / or vertical rows( wythes. The horizontal mortar joint between two courses of masonry units is referred to as the bed joint. The vertical mortar joint between two masonry units in the same course and wythe is referred to as the head joint. The head joint in CMU construction employing closed-ended units( e. g., hollow concrete block is referred to as a hollow head joint. The head joint in CMU construction employing open-ended units( including lintel or bond beam will allow grout to be placed in the head joint area and is referred to as a solid head joint.
Masonry components can be manufactured in a wide variety of shapes, sizes, materials, and both hollow and solid configurations. These variations require that the selection of an anchoring system be carefully matched to the application and type of masonry material being used. As a base material, masonry typically has a much lower strength than concrete. The behavior of the masonry components, as well as the geometry of their cavities and webs, has a considerable influence on the load capacity of the fastening.
When drilling holes for anchors in masonry with hollow cavities, care must be taken to avoid spalling on the inside of the face shell. This could greatly affect the performance of“ toggle” type mechanical anchors whose length must be matched to the face shell thickness. To reduce the potential for spalling, unless otherwise specified, holes should be drilled with hammer drills set in rotation only mode( i. e., hammering action of the drill turned off.
Concrete block
Concrete block is the term commonly used to refer to concrete masonry units( CMU made from Portland cement, water, and mineral aggregates. CMU blocks are manufactured in a variety of shapes and sizes using light, medium, and normal weight aggregates. Both hollow and solid load bearing CMUs are manufactured in accordance with ASTM C90.
CMU sizes generally refer to the nominal width of the unit( e. g., 6”, 8”, 10”, etc.. Actual dimensions are nominal dimensions reduced by the thickness of the mortar joint.
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