Total precast concrete building systems are becoming a popular choice for many construction projects. Architectural and structural precast, prestressed concrete components can be combined to create the entire building.
This design approach can take several forms, including precast columns and beams with panelized cladding or load-bearing precast walls and double tee or hollow core flooring. These advantages benefit every member of the construction team - specially the owner, whose goals are always paramount.
ARCHITECT: In addition to helping to meet all of the building owner's goals, total precast concrete systems provide specific advantages to architects that can make the design process smoother.
CONTRACTOR: General contractors find the use of precast concrete components make their job easier at the site, ensuring a smooth process for the owner and designer in both the short and long terms. There are fewer trades to coordinate with precast construction.
ENGINEER: Structural engineers report no difficulty in learning to design with total precast concrete systems. They also benefit from the material's ease of use and efficiency.
Developers who use total precast systems say precast can shorten the project timetable six to eight weeks when compared with steel and even more when compared with cast-in-place concrete construction. That savings can be critical in bringing a new building into a competitive marketplace or in meeting a tenant's need for occupancy on a specific date. A total precast system's speed helps keep projects on track.
1. One-stop shopping sources much of a building's shell in one efficient, precast contract.
2. Fabrication of precast elements during permitting and/or site preparation saves time resulting in fast efficient construction regardless of weather conditions.
3. Designing precast systems is easier, thanks to assistance from CPCI member’s engineering department.
4. Precast components can be erected in winter conditions, maintaining tight schedules.
5. With total precast systems, speedy erection allows the contractor to enclose the building quickly, giving interior trades faster access.
6. Precast components are naturally fire protected, because they will not burn. Precast's inherent fire resistance eliminates the messy and time-consuming fireproofing required for a steel structure and subsequent repairs caused by other trades.
Precast concrete panels offer a wide range of styles. Panels can be produced in a variety of colors, textures and finishes providing an almost endless range of aesthetic options. Precast panels can replicate granite, brick or stone, achieving a strong, institutional image at a fraction of the cost.
CPCI members supply precast concrete components certified in accordance with CSA A23.4 Precast concrete – Materials and construction. Tight control ensures that components are produced with uniform consistency.
Precast structures require less maintenance than buildings built using other materials. Incorporating the architecture into the structure using large panel sizes, minimizes the number of joints.
Because of precast concrete's tightly controlled and shorter production process, costs can be more accurately estimated earlier in the process. Changes during design development can be quickly reassessed by CPCI member engineering departments to verify that estimates remain stable. The contractor, owner and design team are assured that project budgets remain sound.
Precast construction keeps the site cleaner and eliminates trades from the construction zone, improving logistics and enhancing worker safety. Site storage is usually not required – precast components are lifted by crane directly from the truck into position in a building. A clean site is particularly vital on building additions and existing campuses and in dense urban areas, where adjacent businesses can maintain near-normal activities.
Precast manufacturers support design and coordination at the schematic stage. CPCI members can ensure the building takes full advantage of state-of-the-art fabrication and connection techniques. This input allows the project to remain cost-effective and efficiently designed.
Interior Design Flexibility
Long-span precast concrete systems help building owners adapt to changing client needs in future years. Hollow core slabs and double tees can span 14 to 16 m (45 to 50 ft) to match typical composite-steel framing and minimize the need for interior columns required with cast-in-place systems. Precast can span as far as 21 m (70 ft) to provide flexibility for challenging interior requirements. Precast also provides high loading capacity at little added cost.
CPCI members can provide early and precise design assistance to help select the most efficient sizes and shapes for components, for structural efficiency and optimization for casting, transporting and erecting precast components. Member repetition reduces form costs and aids design speed while retaining design flexibility. These cost efficiencies can free up more of the budget for other critical design areas.
Strong Finish-Approval Process
Precasters can provide finish samples, range samples and large-scale mockups, ensuring that design concepts translate into reality. Designers can inspect window interfaces, joint connections and other critical elements to ensure they are visually acceptable and will properly interface between trades. Plant visits to discuss technical and aesthetic concerns provide control without requiring constant site supervision.
Precast concrete offers a number of benefits that make it environmentally friendly a growing need as the Leadership in Energy & Environmental Design (LEED Canada) criteria become more popular. Precast’s energy efficiency, recyclability, reusability along with minimal waste in the precast plant and on the jobsite are keys to meeting environmental standards that are gaining client interest.
Precast offers high thermal mass that has become a feasible element of building design. With precast's ability to aid in meeting LEED standards, the benefits of thermal mass will become more apparent to designers in the future. The use of fly ash, slag and other waste materials aid its environmental friendliness. Precast’s high durability produces buildings with a total service life that far outpaces other designs.
Time is money for the entire construction team. Precast concrete's speed through design, fabrication and erection help meet tight deadlines. This particularly aids contractors when permitting processes slow down or unforeseen delays arise at the site due to soil conditions or other factors. Precast structural systems are ready to be erected when the foundations are prepared.
Contractors can minimize the added "cushion" created in schedules to accommodate bad weather conditions, since precast components can be produced and erected all year round.
Because precast concrete pieces are fabricated in precast plants under controlled conditions using high-quality materials, designs more exactly meet specifications. Field adjustments are reduced, creating a smooth erection process with minimal surprises.
Total precast concrete systems allow the architectural panels to serve structural functions, limiting the need to incorporate multiple materials and trades. Combining architecture and structure provides efficiencies in a building’s lateral support systems. Spandrel panels can support floor systems and windows while providing architectural exterior finishes. Precast elevators and stair cores can support floor systems while providing secure and fire rated enclosures.
A total precast concrete system ensures one-stop shopping for the entire core/shell design. CPCI members can design and supply the entire system, generating a better coordinated set of drawings to allow construction to proceed more efficiently. This eliminates the added effort needed to coordinate various trades when using mixed systems controlled by different suppliers.
Site construction moves smoothly because no special equipment or techniques are required to transport or lift a combination of structural and architectural components. These types of activities can often require additional structural review and exposure to risk.
Shape and Design
Precast/prestressed components are custom manufactured to match design requirements. Unusual shapes, sizes and specific technical requirements are expertly fabricated in CPCI member precast plants. Repetition of shapes and sizes will greatly enhance the economical use of precast components.
The continuous, uninterrupted erection of precast structural components lends itself perfectly to fast track construction schedules. Savings on financing costs, (faster return on investments resulting from bringing the structure into productive life sooner) is just one of the benefits provided by a complete precast building system.
Precast Structural Components
Precast concrete beams, columns and stairs are the ideal solution for owners and builders who want to achieve wide-open spans, fire resistance, energy savings and attractive design with one structural system.
These components are suitable for both low and high-rise structures. Highly durable, these concrete units can be installed in all weather conditions.
Precast beams may be either continuous with single story columns or single span beams with multi-story columns. The use of standardized forms accelerates the manufacturing process.
The quality of smooth formed finishes produced in a precast plant saves money by allowing designers to expose the structure in a finished building.
As a single unit, even with stone or brick inset, precast panels require only one source to create the entire exterior wall system. When a precast structural system of columns, beams and double tees also is specified, it concentrates the complete shell construction with one certified and reliable producer. This approach ensures all of the responsibility and accuracy for meeting design specifications rests with one supplier. Consistency, tolerances, deadlines, budget and other requirements are assured.
Precast's advantages are maximized when the precaster is brought onto the design team early in the planning stage. This allows the company's full expertise in designing efficient shapes, textures and finishes to be exploited, as well as their state-of-the-art knowledge on connection and erection methods.
PRECAST COMPONENTS MEET ALL NEEDS
A wide range of precast concrete architectural and structural components can be used in commercial buildings. The key pieces used most often in these designs include:
· ARCHITECTURAL PANELS:
Architectural precast wall panels are the solution of choice for the cladding on many office buildings, institutional facilities and mixed-use retail projects of all types. A key reason is that these panels offer beauty and affordable economy without sacrificing design freedom. That economy results from the low initial cost, the ability to enclose the structure quickly, the ability to continue construction through winter weather and the panel's long-term durability. In some cases, further economies can be achieved by designing load-bearing precast walls or using insulated wall panels to improve energy efficiency. These budget, scheduling and design benefits combine with precast's moldability to create dramatic and cost-effective looks for all types of commercial buildings.
· GFRC PANELS AND DECORATIVE ELEMENTS:
Glass-fiber reinforced concrete (GFRC) can expand the options for attractive exteriors by using it for architectural panels and decorative accent elements, such as balusters, medallions and cornices. It consists of a Portland cement-based composite with alkali-resistant glass fibers randomly dispersed throughout. These fibers add flexural, tensile and impact strengths, producing a The use of GFRC can save costs in a variety of ways, including the use of lighter structural framing, faster erection using lighter cranes and creative rehabilitation of older, detailed buildings. GFRC also provides energy savings and will last the lifetime of the building, ensuring an attractive and consistent look through the years.
· BEAMS AND COLUMNS:
A complete precast concrete structural system offers tremendous advantages and value for commercial buildings. The use of precast columns and beams makes an ideal framework for hanging precast panels, creating a design that offers fast construction, structural stability and enhanced fire resistance. A wide range of options is available for creating the perfect system to achieve the size and shape of commercial building required.
· DOUBLE TEES:
These components provide excellent roof and flooring units, spanning considerable distances and providing quick erection to close in a structure faster. In some cases, they also can be used as wall panels on low-rise commercial buildings, creating distinctive designs that require little maintenance and offer fire resistance and durability as with architectural wall panels.
· HOLLOW CORE PLANKS:
Precast hollow core flooring units provide long spans with cross-sections that reduce the height of the building, saving material cost, and their inorganic composition enhances fire protection. Local precasters can help determine which sizes, shapes and styles of components will best suit any individual commercial building project. Bringing the precaster into the planning early in the design process will ensure the precast components maximize their effectiveness in aesthetic appeal, functionality and cost effectiveness.