ARCH 2602/5602 Lecture notes
Jonathan Ochshorn
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Week 11a, Monday lecture:
Cladding -- precast and metal panels
Both precast and metal panels can be used as cladding; metal panels usually are fastened to some kind of back-up system (either metal studs or CMU); whereas precast panels are often attached directly to the structure itself.
Metal panels
Metal panels used as cladding fall into two main categories: sheet metal, flat or corrugated, attached to a back-up system; and "sandwich" panels consisting of two thinner metal sheets over a rigid core. In the latter case, the core can be insulating or not (e.g., foamed plastic versus honeycombed paper). An example of the use of metal panels is shown in the image below (left): Richard Meier's Getty Center (photo by J. Ochshorn); the image at right shows manufacturer's product literature for a proprietary metal panel system. Notice the concealed connection to a back up system (in this case a horizontal angle).
An alternate approach uses sheet metal in a less "formal" manner. Many examples can be found in the work of Frank Gehry, including his project at 340 Main St. in Venice, CA shown below (left). In this case, each panel is just a sheet of metal bent at the edges over the adjacent panels so that the fasteners are hidden, and water is kept out, much like a shingle. The two strategies are contrasted (at right).
The images below show the overlapping metal panels used at Gehry's Disney Concert Hall in Los Angeles (left), and a detail of their attachment to a metal sub-structure (right). Both photos by J. Ochshorn.
A more "industrial" type of panel is the corrupgated variety, shown below. Note that these types of panels have also been appropriated for Architecture (with a capital "A"). See, for example, Gehry's project at 39 Horizon Ave. in Venice, CA (right).
Precast panels
Precast concrete panels can be load bearing or used just as non-load-bearing cladding. Only the latter use is discussed here. Typical cladding panels are attached directly to the structure, rather than to a back-up wall or sub-structure as is usual for metal panels. Characteristics of precast panels are as follows:
- Forms are created in a precast plant. Economy demands the use of repetitive shapes, or shapes that can be made by blocking off areas within a larger, standardized, form.
- Panels are typically cast once per day, with special curing processes that accelerate the curing time compared with conventional site-cast concrete. That is, the design strength is almost reached in 24 hours (rather than 28 days).
- Panels should be as large as possible, subject to transportation and erection constraints, in order to minimize the expense of attachments and sealants.
- Avoid sharp corners and edges, as these are more easily chipped and cracked.
- Avoid sharp angles also because they tend to attract stress concentrations, especially under the dynamic loading associated with transportation over bumpy roads.
- Panels are typically cast horizontally, so the bottom surface is the "good" one, i.e., the one directly in contact with the bottom of the form.
- Metal attachments are inserted into the precast concrete, both for erection purposes, and also for attachment to the actual structure.
- As an alternative to metal inserts for attachment, it is also possible to leave rebars protruding from the panel which are then inserted into holes or grooves left in the adjacent panels. At the site, such grooves or holes are then filled with grout (concrete), emulating a site-cast condition.
- A draft or angled side, is generally required, so that the panels can be easily lifted out of their reusable forms. The minimum positive draft is typically taken as 1:12.
Typical connection details for precast panels are shown below. Notice that the actual connection is metal to metal, with a steel insert embedded in the panel, and another in the structural slab.
An example of a building with precast panels is shown below: Malott Hall at Cornell, designed by Levatich, Miller, Hoffman (photo by J. Ochshorn)
Disclaimer: Students are responsible for material presented in class, and required material described on course outline. These notes are provided as a tentative outline of material intended to be presented in lectures only; they may not cover all material, and they may contain information not actually presented. Notes may be updated each year, and may or may not not apply to non-current versions of course.
first posted Aug. 24, 2007 | last updated: Sept. 5, 2008
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2007-2008 J. Ochshorn. All rights reserved. Republishing material on this web site, whether in print or on another web site, in whole or in part, is not permitted without advance permission of the author.
