7/25/2019 Architectural Concept13

1/2

return piece is removed from its form and is connected to amaster mold. The return is cast monolithically to the masterpiece. Two-stage concrete placements create a moreuniform texture on all sides of the panel. A quirk shouldbe provided in the corner so the return is not formed to asharp edge that is easily chipped.The details for casting individual panels should always

be left to the precaster. Elevations, wall sections, anddetails of each different type of wall panel should bedrawn by the architect. When using large elements,if the appearance of smaller panels is desired for aestheticreasons, false joints (rustications) can be used toachieve this effect.At times a compromise may be required betweenthe finish and the shape of a precast concrete panel.Wherever possible, the designer should avoid fragileedge details. Chamfered or eased edges reduce edgedamage and mask minor irregularities in alignment.2.2.4 Panel Size and Panelization

Precast concrete pricing is determined primarily bythe size of the pieces and repetition. Pricing is moredependent on large pieces than on a large project. Forexample, a 100-piece project of large panels can beless expensive per square foot (m2) than a 1000-pieceproject using much smaller panels.The reason piece size is so important is because mostlabor functions performed by an architectural precasterand erector are required because of the existence of apiece. The more pieces the project has, the more laborhours it will take to engineer, cast, strip, finish, load,deliver, and install the panels. Therefore, it is more economicalto enclose a larger portion of the buildings

exterior with fewer precast concrete panels (see alsoSection 3.3.10).For maximum economy, minimize the number ofpieces by making them as large as possible within normalmanufacturing and shipping limitations. Handlingand erecting precast concrete components constitutesa significant portion of the total precast concrete expense.The cost difference in handling and erecting alarge rather than a small unit is insignificant comparedto the increased square footage of a large unit, Table2.2.2. To be economical, a projects average piece sizeshould be at least 100 to 150 ft2 (9 to 14 m2) and, ideally,

larger than that.There is no exact optimum panel size. Usually theoptimum panel size is dictated by size and weightlimitations imposed by transport (for example, weightrestrictions and bridge or power line clearances), siteaccess, or crane capacity. The panel size is also a functionof the design loads and support locations for connections.Close collaboration between the designerand a precaster is required during the early stages of abuildings design to determine the optimum panel sizeor panelization scheme. Piece sizes that require highwaypermits for over height, width, length, or weightgenerally should be avoided.

There is a balance between maximizing potentialeconomy of the faade elements and maintaining theeconomy of the supporting structural system. The key

7/25/2019 Architectural Concept13

2/2

is to recognize where localized loads will occur. Oftenthe added cost of local reinforcing of the supportingstructure that may be required to accommodate largerprecast concrete panels will be more than offset bysavings that result from erecting fewer panels.The designer can ensure a good average piece size byspanning a full bay with spandrels, and designing multistory

column covers and large wall panels. Designinglarger panels, even though they may carry a haulingpremium, may be the most cost efficient. For example,an office building with 30 x 30 ft (9.1 x 9.1 m) columnspacing requires fewer columns and concrete panelsand yields a more wide-open interior than the samebuilding with a 20 or 25 ft (6.1 or 7.6 m) column spacing.The cost premium (if any) to haul two 30-ft-long(9.1 m) panels versus three 20-ft-long (6.1 m) panelsusually can be more than overcome by cost savings inother manufacturing areas like engineering, production,and installation. The typical parking structure

may have perimeter panels that are 60 ft (18.3 m) long