Masonry Magazine April 1988 Page. 17
Technical Notes
on Brick Construction
Brick Institute of America 11490 Commerce Park Drive, Reston, Virginia 22091
44B
March 1987
WALL TIES
FOR BRICK MASONRY
ABSTRACT: The use of metal ties in brick masonry dates back to the 1850's. Heretofore, the size, spacing and type of ties have been entirely empirical. An attempt to replace masonry bonders, the use of thinner masonry walls, the use of backup systems other than masonry and a need for adjustability have resulted in ties of various sizes, configurations and adjustability being used without a rational basis for their selection and use. This Technical Notes addresses the selection, specification and installation of wall tie systems for use in brick masonry construction. Information and recommendations are included which address tie configuration, detailing, specifications, structural performance and corrosion resistance.
KEY WORDS: anchors, brick, cavity walls, corrosion, design, differential movement, fasteners, grout, masonry, structural masonry, ties, veneer, walls.
INTRODUCTION
This Technical Notes is the third in a series that addresses anchor bolts, fasteners and wall ties for brick masonry. This Technical Notes discusses wall ties commonly used in brick construction, their function, selection, specification and installation. The term "wall tic", as used in this Technical Notes, refers to wire or sheet metal devices used to connect two or more masonry wythes or used to connect masonry veneers to a structural backup system.
GENERAL
The first use of wall ties in brick masonry construction can be traced to England in the mid-nineteenth century, where wrought iron ties were used in brick masonry cavity walls. Use of wall ties in the United States grew after testing showed that metal-tied walls were more resistant to water penetration than were masonry-bonded walls. Bonders or "headers", used in masonry-bonded walls may provide direct paths for possible water penetration. Testing also indicated that the compressive strength of metal-tied cavity walls and solid walls, and the transverse strength of metal-tied solid walls were comparable to those of masonry-bonded walls.
The use of wall ties has continued to increase over the years due to a trend away from massive, multi-wythe masonry walls to relatively thin masonry cavity walls, double-wythe walls and veneers. An increase in construction using backup systems other than masonry, i.e., steel, concrete and wood, has rendered bonding with masonry headers impossible, leading to the development of a number of different metal tie systems.
During this period of evolution, little progress was made in the area of rational design of wall tie systems. Typically, the structural selection (sizing and spacing) of wall ties has been based largely on empirical information and the designer's judgment. Recently, questions concerning strength, stiffness, corrosion and the effects of these on the long-term performance of wall ties, have been posed. Selection of a tie system to function properly under these conditions is further complicated by the vast number of tie types available and the variety of materials from which they are fabricated. Most tie systems perform well for their intended application. Some tie systems, however, are poorly designed and do not provide adequate support for brick masonry. The distinction between the two is often subtle and requires an understanding of the properties and characteristics of brick masonry.
Function of Wall Ties
Typically, wall ties perform three primary functions: 1) provide a connection, 2) transfer lateral loads, 3) permit in-plane movement to accommodate differential material movements and, in some cases, restrain differential movement. In addition to these primary functions, metal ties (as joint reinforcement) may also be required to serve as horizontal structural reinforcement or provide longitudinal continuity.
For a tie system to fulfill these functions, it must: 1) be securely attached and embedded, 2) have sufficient stiffness to transfer lateral loads with minimal deformations, 3) have a minimum amount of mechanical play, 4) be corrosion-resistant and 5) be easily installed to reduce installation errors and damage to the tie system. This listing is far from complete; special project conditions, unusual details and special building code requirements must also be considered. Availability and cost are always factors in product specifications. However, cost should not have a major influence on the selection of a wall tie system since the cost of ties is typically a very small part of the total wall cost.