Want quick responses to our most asked precast questions? Our blog series, “FAQ Fridays,” is designed to answer your most popular questions, organized by topic and product category. In Part 3 of this series, we discuss key installation and erection considerations.
Precast products can be made large and installed in accelerated fashion. These considerations can sometimes constrain and drive product design size, weight limits, and costs. How big, how heavy, how many? Is a transportation permit more than the cost to erect per piece? How does it affect production costs? Are there unique or repeating sizes and shape?
There are many variables that can tip the scales one way or another. Understanding the parameters to determine the right and most economic configurations can be complicated, but our most important installation considerations are logistics, equipment, coordination, and connections.
Logistics Considerations:
- Site location, property size, street size, access to site, around site
- Adjacent structures
- Access and placement for hoisting equipment (e.g., cranes)
- Access and unloading area for product deliveries
- On-site storage, nearby marshalling yard
- Nearby underground structures or overhead obstructions
- Nearby railways (on-ground, overhead, or sub-surface)
- Transportation restrictions: legal loads vs. overweight and oversize permits, bridge crossings, accessible routes (number and type of loads will drive cost)
Equipment Considerations:
- Cranes, aerial lifts, shoring, etc.
- Logistics and panel weights drive crane type, size, and capacity
- Installation cost per piece, not per square or linear foot
- Sequence, which can sometimes drive types and cost of shores (e.g., load bearing walls with steel frame)
- Location of product on the structure
- Shape of structure
Coordination Considerations:
- Erection starting point, direction, and sequence during shop drawing phase (depending on how much time from production to installation, erection sequence can drive production sequence)
- Adjoining and interfacing of trade coordination during shop drawing phase (these trades need to be designed and purchased at same time)
Connections Considerations:
- A/E drawings with basic types and quantities (final engineered connection design is delegated to the producer)
- Gravity, lateral, and seismic connections
- Location and number of bridging components needed and dual-purpose connection requirements (miscellaneous steel needed from structural steel or CIP to precast products)
- Coordination of adjoining and interfacing trades (e.g., steel, CIP concrete; finalized A/E designs and purchasing affect schedule)
- Field labor connections (keep field welding to a minimum since it’s more expensive than mechanical connections, such as bolted)
- Number of panels, which drive number of connections and cost to install (not per square foot of product)
Who is responsible for precast connections?
The A/E drawings should include basic or generic types and quantities; the final engineered design of connections is delegated to the producer. A/E design should understand and delineate the basic types of connections needed.
What are common precast connection types?
Common connections include gravity, lateral, and seismic connections, including bridging components like miscellaneous steel from structural steel or CIP to precast products. Connections are fundamental to all buildings and construction no matter what material is used. The purpose of a connection is to transfer loads, restrain movement, and provide stability to a component or an entire structure. Connection design is one of the most important aspects in the design and engineering of precast/prestressed concrete structures.
Many different connection details will result from the combination of sizes and shapes of precast concrete components and the variety of possible support conditions. Individual precast producers have developed connection details over the years that suit particular production and erection preferences, and they should be considered for a specific project early in the design stage. All connections should comply with applicable building codes, and the final structural design should be done by an engineer licensed in the location of the project. It’s common for the architect and engineer of record to show connection loads and locations on the contract documents and allow the successful precast producer's engineering department to provide the final design and details of the connections. Learn more about connection design considerations, connection materials, and sample connection types from PCI Mid-Atlantic, and browse additional publications on the topic:
- PCI Connections Manual for Precast & Prestressed Concrete Construction (Discounted for PCI Members)
- Designer’s Notebooks: Connections (Free PDF Download)
What are precast erection tolerances?
Erection tolerances control the position of the individual precast concrete members as they’re located and placed in the assembled structure. Here are some rules of thumb regarding erection tolerances:
- They help achieve uniform joint widths, level floor elevations, and planar wall conditions
- They should be determined based on individual unit design, shape, thickness, composition of materials, and overall scale of the unit in relation to the building
- They may affect the work of several different building trades and must be consistent with the tolerances specified for those trades
- They are both equipment- and site-dependent
Erection tolerances can vary by account for unique project conditions. In these instances, they should be carefully reviewed by the designer and contractors and adjusted, if necessary, to meet the project requirements. The effects of adjusted tolerances on specific details at joints, on connections, and in other locations in the structure should be evaluated by the designer. Different details may have varying amounts of sensitivity to tolerances. For information on specific erection tolerances, download PCI’s Designer’s Notebooks: Envelope Tolerances for Architectural Precast which is free of charge and available in PDF format, and locate a PCI-Certified Erector in your state or region by entering your search criteria into the PCI-Certified Erector Directory.
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