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Connectors, Anchors and Fasteners
Anchoring Stone Veneers
Excavations throughout Europe have found stone used for shelter as far back as 12,000 B.C. Cast stone was used in France as far back as 1158 A.D. Today, stone remains one of the strongest and most durable building products on the planet. When using stone as a veneer, engineering and design are critical factors in a successful building project.
Anchored veneer and adhered veneer
TMS402/ACI530/ASCE6 Building Code Requirements and Specification for Masonry Structures list several references and guidelines for adhered veneer. Anchored dimensional stone is not covered currently under the code and is considered a “special system.”
The code defines adhered veneer as a “masonry veneer secured to and supported by the backing through adhesion.” No rational design provisions exist for adhered veneer in any code or standard. The following alternative design of adhered masonry veneer permitted under Section 1.3 of the TMS402 code requires the following conditions:
The following are the prescriptive requirements for adhered masonry veneer:
The International Building Code requires that adhered veneer must meet TMS402/ACI530 requirements and, in addition, adds an interior adhered maximum weight of 20 pounds psf. If the interior backup is wood construction, the supporting members must be designed to limit deflection to l/600 of the span of the supporting members.
Wood or steel frame backup walls with adhered veneer must be backed with a solid, water-repellent sheathing. Note that care must be taken when adhered masonry veneer is used on steel frame or wood frame backing to limit deflection of the backing, which can cause veneer cracking or loss of adhesion. The surface of the backing material must be capable of securing and supporting the imposed loads of the veneer. Materials that may affect bond such as dirt, grease, oil or paint (except Portland cement paint) should be cleaned off the backing surface prior to adhering the veneer.
Anchored stone veneer
Stone veneer units are limited to a maximum thickness of 10 inches. Anchored stone veneers must be designed by a licensed engineer through a three-step process:
The vast majority of stone anchors are manufactured from Type 304 stainless steel or Type 316 for marine environments. Mechanical anchorage is achieved by cutting a kerf in the stone for placement of anchor bends or by drilling holes for placement of pins.
A contractor, when bidding on an anchored stone veneer project, should assure the engineering is factored into the bid. The engineering responsibility varies from job to job. Sometimes it is the responsibility of the mason contractor, general contractor or the stone provider. A few times a year, we get a call whereby stone already is on the jobsite, and the contractor is looking for “off the shelf” stone anchors (which don’t exist). A mad scramble ensues, during which the mason contractor, general contractor, engineer and stone provider bicker about who will pay for the engineering, since nobody put it into the bid. During this time, the job usually gets put on hold.
The four most common types of stone anchors are shown below. The pin type usually is installed with the pin loose, so the anchor can be attached to the backup and the hole used as a template to drill down into the stone. The top stone is brought into place, and a hole is drilled up. The three anchors with bends are used at the top (Z-Type), bottom (U-Type) and between two stones (Split-bend Type). The engineering process will determine the width and thickness of these anchors.
For both adhered and anchored veneers under the code:
|Last Updated on Wednesday, 08 May 2013 21:02|