WINDOW PANELS OFFER MANY OPTIONS:
Window openings can be provided in architectural precast concrete panels with ease, in any shape or size desired. However, achieving design efficiency requires thoughtful panel system configuration. The most economical wall unit consists of a panel where the window openings are fully contained within one precast piece. The plasticity of concrete lends itself to the manipulation of voids and solids. The design options for window wall panels are extensive:
They may contain a single opening or a series of windows
They are either one story in height and made as wide as possible, or cast narrower to span vertically for two or three floors
They can be recessed to optimize seasonal solar heat or to reduce glare
They can be in the same plane (punched), without sills or projections
They can be boxed out from the general wall face
They can be set in a deep coffer with margins projecting slightly
They can be set in a deep recess with or without a projecting sill
WINDOW HEAD DESIGN:
Window heads should be designed so they don’t splay down and back toward the glass, unless drip details are incorporated into the frame. A drip groove also should be provided under any outward-sloping sills to prevent water from staining the panels. The drip section should be designed in elation to the slope of the concrete surface, to prevent water from bridging the drip. To avoid a weakened section, the drip should not be located closer than 11⁄2 inches to the edge of the precast unit. Where the window is not at least three to four inches back, it is difficult to get a drip groove in the panel. Alternate solutions include using a clear sealant bead, plastic drips, or extrusions with a gutter or one inch drip lip.
Precast concrete offers the architect total flexibility in design. This means the designer can produce window panels that:
Promote the use of a master mold
Offer flat or heavily sculptured profiles
Provide curved surfaces
Work as corner units
Incorporate a bullnose, a cornice or reveals
PCI BULLNOSES:
Precast concrete can replicate traditional shapes from the classical architectural vocabulary or produce the sleek contemporary look of today. To achieve these goals cost-effectively, however, requires working with the precaster and understanding the inherent advantages of the material so its use can be maximized. A key ingredient in that recipe comes in exploiting precast’s lowcost repetition and its ability to cast many pieces from the same mold.
Costs naturally increase on a design as surface features become more extensive or intricate, as well as when the panel cross-section becomes more complex. However, the ability to cast many pieces from the same basic mold has made complex shapes economically feasible with precast concrete.
PCI CORNERS & RETURNS:
Each project requires special attention to the design and detailing of its corners to create the optimum appearance, jointing and economy. For this reason, corner detailing should be decided early. Economy results when the building elevations are designed from the corners inward, using typical panels, thus avoiding specially sized end or corner pieces.
All edges of precast concrete units should be designed with a reasonable radius or chamfer, rather than leaving sharp corners. This is particularly important where the panels are close to pedestrian or vehicular traffic. When the edge is sharp, only fine aggregate collects in these locations, and this weakens the edge. Voids also occur due to the interference of larger aggregate. Sharp corners chip easily, both during handling and during service on the finished building. For typical edge details, see Fig. 1.
The size of the edge’s radius should be discussed with the precaster. Determining the optimum size depends on the selected aggregate size, mold materials and production techniques. A 3/16- or 5/16-inch minimum radius should be satisfactory for smooth concrete or a light textured surface. A 1/4- or 5/16-inch rounded edge should be satisfactory for an exposed-aggregate finish with a maximum aggregate size of 1/2 inch. Above that aggregate size, the edge must be progressively more rounded.
PCI CORNICES:
Cornices provide a number of significant aesthetic and functional advantages when designing virtually any type of building. Their ability to break up long expanses of the façade adds visual interest, and they can shade windows from sun, reducing energy costs and other internal shading needs. Designers who keep the available options in mind as they plan their projects will find a host of possibilities that will serve them well.
A cornice consists of a horizontal projecting overhang comprising multiple surfaces, planes and profiles with infinite variations. It usually is located along a parapet or at the top of a given plane. The cornice crowns or finishes the part to which it is affixed.
Cornices can be used in a variety of styles and combined with several different components to achieve different purposes. Options include cornices that are:
Made to look contemporary
Made to look traditional
Doubled to create even more design interest
Incorporated with a reveal
Incorporated with a void to reduce weight and add coping on the crown
Created so large that it requires special support. For instance, a steel structure may require bracing to prevent rotation of structural members
Incorporated with dentils
PCI RADIUSED APC:
Radiused Precast Concrete Add Interest At Low Cost –Article X
Today we are seeing buildings which are more sculptural in form along with a trend towards more organic expressions. What is most striking in the concept of new buildings, compared to 20 years ago, is the much greater freedom in the design of the façade. Volumes, surfaces, lines and differences in planes are becoming increasingly important in providing architectural interest. Designers are conceiving of form organically, generating fluid surfaces in place of rigid structures. Design focuses on space, structure, and proportion. Architectural precast concrete provides the designer with virtually total sculptural freedom and flexibility in shaping concrete into structure and architecture. It is adaptable to a variety of building configurations.
PCI REVEALS:
Reveals Add Interest To Precast Panels
Reveal strips can add visual interest to a building clad with architectural precast concrete panels while eliminating some of the aesthetic concerns that develop when planning panel configurations. Used effectively, reveals offer the simplest way to break up the expanse of an architectural precast concrete panel or to keep the visual appearance from focusing on any differences that may occur in texture or coloration between panels.
A reveal or demarcation feature is a groove or a step in a panel face generally used to create a desired architectural effect. Another name for it is rustication or false joint. Reveals can run vertically, horizontally or diagonally, and there may be several bands of them on a building. Reveals typically measure 1/2 to 3/4 of an inch deep and 3/4 to 4 inches wide, with 45- to 60-degree beveled surfaces allowing for ease of stripping.
