PCI ARCHITECTURAL PRECAST CONCRETE DESIGN MANUAL (3RD EDITION):
Architectural precast concrete is a child of the 20th century and modern technology, but it can trace its lineage back to ancient history. As such, it is a building material almost without precedent. Concrete in its cruder forms was used by the Romans in the construction of their aqueducts. Europe refined the time-tested formula in the 19th century, developing reinforced concrete that combined the compressive properties of concrete and the tensile strength of steel. Continuing technological growth and industrialization created a genuine need for new techniques and materials that could be used in prefabricated construction. Architectural precast concrete was developed to fulfill this need.
PCI DESIGN ECONOMY PART1:
Understanding architectural precast costs is essential to designing elaborate façades that enhance the overall building design while meeting the owner’s budget. Understanding the architectural precast manufacturing process can help achieve design goals and control costs. Many variables need to be considered to determine what a typical architectural precast project will cost. All engineering, production, delivery and installation costs must be compiled for each specific project to derive an applicable budget price.
During a project’s conceptual stage, the designer has many items to consider. These include material selection, textures, surface geometry, cross section, unit repetition and erection methods. The custom, sculptured designs that are possible with precast concrete may be achieved within a limited budget by selecting economical aggregates and textures combined with repetitive units and effective production and erection details. A local precast manufacturer can assist with preliminary design and budget estimating early in the project’s design phase.
PCI DESIGN ECONOMY PART2:
Panel Size
Precast pricing is determined primarily by the size of the pieces and piece repetition. Also, precast pricing is more dependent upon large pieces than upon a large project. For example, a 100-piece project of large panels can be less expensive per square foot than a 1,000-piece project of much smaller panels.
The reason piece size is so important is because most every labor function performed by an architectural precaster and erector is required because of the existence of a piece. The more pieces the project has, the more labor hours it will take to engineer, cast, strip, finish, load, deliver and install the panels. Therefore, it is more economical to cover a larger portion of the building’s exterior with fewer precast panels.
PCI DESIGN ECONOMY PART3:
Design Options
Design options are literally endless. Employing these options intelligently adds a great deal of design interest to a project with only minimial cost increases. The following design strategies can cost from pennies per square foot to a few dollars per square foot.
Incorporate multiple colors throughout a building façade.
Panels can contain more than one concrete face mix.
Panels can be produced with multiple finishes. The combination of finish methods will determine the cost impact.
Add a special shape to one distinct building area.
Design an appendage to an existing form. Doing so will cost less than adding a full form, yet will provide a nice building detail.
Set windows back from the building’s face at one or two column bays or at certain levels.
Add a few small ornate pieces at the entrance or as site walls. The small panels will be more expensive per square foot, but a few of them amortized over the entire project will add a minimal additional charge ($15,000 increase/30,000 square feet = $.50 premium).
Apply a partial facing material to the precast at the plant. Brick, tile, terra cotta or natural stone accents can be added in limited number at minimal cost.
On steel-frame structures, gravity and lateral support brackets (for precast connections) should be in the structural steel fabricator’s scope of work and should be shop-welded to the structural-steel columns rather than field-welded. It is much less expensive to shopfabricate and shop-weld them than to hoist and field-weld heavy support brackets. In most cases, design interest can be enhanced without increasing price by using more complex precast in one area and offsetting the cost premium by economizing in another area. For example, trade some details for more repetition. Eliminate small column covers at one level and place more ornate ones at the entrance.
GETTING STARTED DESIGNING WITH APC:
Architectural Precast Concrete
Whether the project being considered is a small one-story building or a high-rise structure, involving the precaster in the early design development stage of a project is advisable. Ideally, a precaster performs value engineering in response to performance requirements or offers design alternatives in response to identified needs early in the preliminary design phase to control construction costs, improve structural efficiency, facilitate erection, enhance precast concrete performance, and meet aesthetic objectives.
ARCHITECTURAL PRECASTERS’ DESIGN ASSIST ROLE:
Design Assist is the procurement method by which, prior to completion of design, a construction contract may be awarded on a best value basis pursuant to which a contractor/ subcontractor provides design assistance to the design team and ultimately the owner.
SUCCESSFUL PLANNING WITH ARCHITECTURAL SAMPLES:
The proper selection of color, form, and texture for a building’s architectural precast concrete exterior is critical to creating a successful aesthetic appearance. Different colors and textures can be achieved by varying and combining aggregate, matrix color, finishing processes, and depth of exposure. Knowing how to use samples and what sizes or mockups are required can ensure the project’s success.
DESIGN AND CONSTRUCTION RESPONSIBILITIES FOR ARCHITECTURAL PRECAST CONCRETE:
Design and construction with architectural precast concrete are simplified when all parties are working as cooperative partners. Clearly defining the scope of work and the responsibilities of the involved parties by means of the contract documents is critical to achieving a high-quality structure. This article provides a guide for all parties involved in a precast concrete project and defines the responsibilities of each party. These responsibilities and relationships between the parties should be defined in the contract documents for a particular project.
