Masonry Magazine June 1998 Page. 27
Ties, Anchors, and Joint Reinforcement
No Place to Cut Corners...
Mario J. Catani, PE, Dur O Wall
Early in the development of the Masonry Standards Joint Committee's (MSJC) "Building Code Requirements for Masonry Structures", it was determined that the improper selection or installation of ties, anchors or joint reinforcement was one of the major causes of distress in masonry structures. The other major "culprit" in causing distress in masonry was the improper spacing and detailing of movement joints. Together these two factors were responsible for about 80% of the problems facing the masonry industry. The Committee determined that a better method of communication between the designer and mason was needed to insure that building performance would improve.
Traditionally, designers have specified anchors ties and joint reinforcement in the Project Specifications and did not detail them on the drawings. In many cases, this meant that they simply copied prior specifications from one project to the next. This led to the specification of accessories that were not necessarily appropriate or adequate for the project and ultimately to poor performance of masonry.
To improve communications between the designer and mason and to bring the selection of accessory products in line with the more sophisticated design assumptions being used, new provisions were added to the Standard to require the designer to pay more attention to the selection and placement of ties, anchors and joint reinforcement. Section 1.2.2 (d) of the Standard requires that the "specified size, grade, type and location of reinforcement, anchors and wall ties" be shown on the Project Drawings. Notice that the Standard does not say the Contract Documents. This latter wording would have allowed the old practice of simply specifying accessories to continue since the Project Specifications are part of the Contract Documents. Since anchors, ties and reinforcement typically cost less than 1% of the project cost, this was considered to be a very cost-effective action.
Ties and Anchors
Selecting the right type of wall tie or anchor is not difficult. Over the years there have been an increasingly large variety of connectors introduced to the industry. If a designer or contractor considers the important parameters that a connector must possess he or she can reduce the number considerably. There are three main properties that a connector must possess. namely:
High out-of-plane stiffness
This helps to transfer wind loads from the veneer to backup wythe. Many industry sources recommend a stiffness of 2000 pounds per inch. This means that the connector will deflect about 0.05 in. when subjected to a 100-pound load.
Low in-plane stiffness
This allows the outside wythe of masonry to expand and contract in the vertical and horizontal direction with a minimum amount of resistance from the connector.
High corrosion resistance
This is essential for long term performance. Hot dipped galvanizing with 1.50 oz. of zinc per square foot of surface area has been the most widely accepted solution to this criteria and is required by the MSJC Standard Specification. Stainless steel is also a good choice but in many cases the additional cost is not justified. Recently epoxy coating has been accepted by the MSJC as a corrosion protection approach. This coating will enhance the performance of joint reinforcement in seismic applications.
Continued on next page
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