Masonry Magazine April 1999 Page. 18
The New Building Codes
Continued from page 14
Prestressed Masonry
There is a new design section on prestressed masonry, which includes prestressed masonry with bonded and unbonded tendons. This specialty application uses the principles of reinforced masonry without the requirement of grout when tendons are unbonded.
Within Products Section 4 of the Specification (ACI 530.1-99) are new material requirements, such as ASTM requirements for prestressing tendons, corrosion protection for tendons, tendon sheathing protection and prestressing anchorages, couplers and end blocks. Execution Section 3.6 is dedicated to prestressing tendon installation and the stressing procedure, and includes a subsection for grouting bonded tendons. The provisions contained in these sections, as applicable to prestressed masonry, do not apply to other types of masonry.
Adhered Masonry Veneer
Adhered masonry veneer has been added to ACI 530-99 and contains some nominal prescriptive requirements. Naturally, the veneer may be designed, with consideration that out-of-plane curvature must be limited to prevent separation of adhered veneer from backing. This design approach is no less than interesting, since I have only encountered adhered veneer applied prescriptively for the past 25 years. It is evident from the photo that prescriptively applied adhered veneer will not separate from the substrate when veneer is properly applied. Another Code provision is that adhered veneer is to develop a shear bond of at least 50 psi.
The prescriptive requirements of adhered veneer include a maximum unit thickness of 2-5/8 inches. Most thin brick veneer, the type utilized for adhered application, is approximately 1 inch in thickness. The Code also limits any face dimension of adhered units to 36 inches and the face are to 5 square feet. Adhered veneer weight is limited to 15 pounds per square foot.
Conclusion
The 1998 edition of ACI 530 and ACI 530.1 moves the Code and Specification forward with more comprehension and clarity to previously assumed guidelines, and is one step closer toward national recognition by reference in the International Building Code. Understanding and implementing the Code changes will help improve the industry quality standards, which is a win-win proposition for the entire masonry industry.
John Chrysler is Executive Director of the Masonry Institute of America.
References
Working Draft of Buliding Code Requirements for Masonry Structures (ACI 530-99/ASCE 5-99/TMS 402-99)
Working Draft of Specification for Masonry Structures (ACI 530.1-99/ASCE 6-99/TMS 602-99)
Hot & Cold Weather Masonry Construction, Masonry Industry Council (1999)