Historical Version s - view previous versions of standard. Work Item s - proposed revisions of this standard. More C The strength of a limited length of anchor may be related to a longer length of support when the flexibility of the support is properly considered by the designer. Refer to Guide C Load is applied, separately, perpendicular to the surface of the panel and parallel to the surface of the panel.
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Natural stone products have perhaps the longest history of use of any construction material. Materials introduced in modern eras typically underwent more vigorous testing and engineering to prove their worthiness as a construction component.
For example, the number of standards and test methods for the use of steel in construction far outweighs the ones for stone. One of the reasons for this is steel, having been used in construction for only a couple of centuries, needed those quality control QC assurances to gain acceptance in the industry. Stone, with several millennia of historic use, did not require a similar validation of its usefulness in construction.
However, stone construction methods have changed; the days of loadbearing masonry walls built with massive, cubic sections of stone are no longer. This thin shell of stone then needs to be attached to the structure of the building by one of two methods: adhesion or mechanical anchorage. Both adhesive and mechanical anchorage are used and accepted. However, there are limitations on what can be adhesively attached. Stone products heavier or larger than these parameters must be mechanically anchored to the building.
Surprisingly, on smaller projects of less than perhaps several hundred square meters, the capacity of these anchors may not actually get tested. The recommendation is accompanied by a host of cautions, as it should be, since multiple anchorage locations on a stone panel do not always equate to uniform loading of those anchors, and there needs to be some discretion used in the selection and performance verification of the anchor in the stone. However, for someone applying a stone base course to a retail store front, following this rule of thumb is likely adequate.
If the stone is being installed at higher levels or in regions of greater loads, building professionals need to get serious about verifying loads, anchor capacities, and safety factors. It is also written with frequent usage of permissive language, as opposed to mandatory language. It is one of the few documents with recommended safety factors for stone attachments. Predictably, the recommendation is accompanied by a host of cautions and warnings saying the factors of safety may not be adequate in all cases, but they at least provide a starting point from which one can make modifications.
It may seem alarming to some people to know travertine, for example, is recommended to have almost three times the factor of safety as granite. However, the recommendations are influenced by the variability of the stone and the concern of strength degradation over time. Sedimentary stones, such as limestone, travertine, and sandstone, are typically the most variable types. Physical and mechanical test results in these stones will frequently have noisy data sets with large standard deviations.
Additionally, there is no published test method within ASTM to assess degradation of strength due to weathering exposure. Both the variability of the material and the concern of possible degradation of strength over time are unknowns which the authors of ASTM C have guarded against by recommending a high factor of safety. There are two methods within ASTM to test stone anchorage. This does not mean anchors were not tested prior to , but that there was no standardized, published protocol for the laboratory to follow.
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Proofing of stone anchors