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 precast installation and erection considerations.
Precast structures can be manufactured in large sizes and installed quickly, significantly reducing construction timelines. However, these benefits come with essential considerations that can influence the overall product design, including size, weight limits, and total cost of ownership. Questions such as: How large should each piece be? How much can it weigh? How many units are required? Is the cost of obtaining a transportation permit higher than the cost of erecting each piece on site? What impact will these decisions have on production costs? Additionally, is there a need for architectural precast concrete components?
These variables can significantly affect the outcome, so thoroughly understanding the parameters that determine the most efficient and cost-effective configurations is essential. The process can be complex, but our primary focus remains on key installation factors, including logistics, equipment, coordination, and connections. We can optimize the design and installation process by carefully considering these elements to ensure a successful project.
Precast Concrete Construction Logistics Considerations:
Effective logistics planning is crucial for the successful installation of precast structures. Given these components’ large size and weight, careful attention must be paid to various logistical factors to ensure smooth delivery, handling, and placement. The logistics strategy begins long before the product arrives on-site and continues to its final installation. Here’s a breakdown of the key logistical considerations:
- Site Location & Property Size: Evaluate the overall property dimensions, street width, and access points to and around the site.
- Proximity to Adjacent Structures: Consider the impact of nearby buildings or infrastructure on the delivery and installation process.
- Access for Hoisting Equipment: Ensure adequate space and positioning for cranes and other lifting equipment.
- Unloading Area for Deliveries: Designate a suitable area for safely and efficiently unloading precast components.
- On-Site Storage & Marshalling Yard: Plan temporary on-site storage and a nearby marshaling yard for staging materials
- Underground Structures & Overhead Obstructions: Identify any underground utilities or overhead obstacles that could interfere with installation.
- Proximity to Railways: Account for nearby railways, whether on-ground, overhead, or sub-surface.
- Precast Transportation Restrictions: Assess the need for legal load permits versus overweight and oversize permits, considering bridge crossings and accessible routes, as these factors will influence precast transportation costs.
Precast Concrete Construction Equipment Considerations:
The selection and use of equipment in precast installation are critical to the success and efficiency of the project. Here are the key equipment considerations to keep in mind:
- Cranes, Aerial Lifts & Shoring: Select equipment such as cranes, aerial lifts, and shoring systems based on project requirements.
- Crane Type, Size & Capacity: Determine the crane specifications based on logistics and the weight of precast panels.
- Installation Cost Per Piece: Calculate installation costs per piece rather than by square or linear foot.
- Sequence & Shoring Requirements: Plan the installation sequence carefully, as it may influence the type and cost of shoring needed, especially for load-bearing walls with steel frames.
- Product Location on the Structure: Consider the placement of precast elements within the overall structure to ensure proper installation.
- Structure Shape: Consider the structure’s shape, as it can affect the equipment selection and precast installation.
Precast Concrete Coordination Considerations:
Effective coordination is crucial in installing precast structures, ensuring all project elements come together smoothly and efficiently. Here are the key coordination considerations to keep in mind:
- Precast Concrete Erection Starting Point, Direction & Sequence: Establish the erection starting point, direction, and sequence during the shop drawing phase, as these factors can influence the production sequence, especially if there is significant time between production and installation.
- Coordination of Adjoining & Interfacing Trades: Ensure the coordination of adjoining and interfacing trades during the shop drawing phase, with the understanding that these trades must be designed and procured simultaneously for seamless integration.
Precast Connections Considerations:
The connections between precast elements and the overall structure are vital to the integrity and stability of the entire project. These connections must be carefully planned and executed to ensure the safety, durability, and efficiency of the installation. Here are the key connection considerations to take into account:
- A/E Drawings with Basic Types & Quantities: Include basic connection types and quantities in the A/E drawings, with the final engineered connection design delegated to the producer.
- Gravity, Lateral & Seismic Connections: Ensure connections are designed to handle gravity, lateral, and seismic forces for structural stability.
- Bridging Components & Dual-Purpose Connections: Determine the location and number of bridging components required, including miscellaneous steel needed to connect structural steel or cast-in-place (CIP) to precast products, considering dual-purpose connection requirements.
- Coordination of Adjoining & Interfacing Trades: Coordinate closely with adjoining and interfacing trades (e.g., steel, CIP concrete) as finalized A/E designs and purchasing decisions can significantly impact the project schedule.
- Field Labor Connections: Minimize field welding where possible, opting for mechanical connections, such as bolted connections, to reduce costs and installation time.
- Number of Panels & Connections: Consider the number of panels required, as this will drive the number of connections and overall installation costs, typically calculated per connection rather than per square foot of product.
Who is responsible for precast connections?
The A/E drawings should outline the basic or generic types and quantities of connections required; however, the precast producer typically delegates the responsibility for the final engineered design of these connections. It is essential that the A/E design team fully understands and delineates the fundamental types of connections needed to ensure compatibility with the overall structural and architectural goals. This approach allows for greater precision and customization in the final design, ensuring that the connections are effective and efficient for the specific project requirements.
What are common precast connection types?
Standard connections in precast structures include gravity, lateral, and seismic connections and bridging components like miscellaneous steel used to connect structural steel or CIP concrete to precast products. Connections are fundamental to all buildings and construction, regardless of the materials used. Their primary purpose is to transfer loads, restrain movement, and stabilize individual components or the entire structure. The design of these connections is one of the most critical aspects of the overall design and engineering process for precast structures. Properly engineered connections ensure that the structure can withstand various forces and maintain its integrity over time, making connection design a key factor in the project’s success.
- Gravity Connections: Designed to support vertical loads, gravity connections transfer weight from precast elements to the foundation, ensuring even distribution. Common examples include beam-to-column and column-to-footing connections. In precast installation, these connections often use bearing pads, dowels, or corbels to facilitate load transfer while allowing for some flexibility.
- Lateral Connections: Lateral connections resist horizontal forces, such as wind or pressure from adjacent structures, preventing swaying or shifting. Precast structures typically involve shear walls, diaphragms, or bracing elements, using embedded plates, weld plates, or bolted connections to link precast panels securely and distribute forces.
- Seismic Connections: Engineered to withstand earthquake forces, seismic connections allow movement to absorb and dissipate energy, reducing the risk of structural failure. These connections may include flexible joints, energy-dissipating devices, or specialized anchorage systems, ensuring the structure can flex without compromising integrity, especially in earthquake-prone regions.
The variety of sizes and shapes of precast concrete components, along with different support conditions, results in a wide range of possible connection details. Over the years, individual precast producers have developed specific connection details tailored to their production and erection processes. Considering these details early in the design stage is crucial to ensure alignment with the project’s needs. All connections must comply with applicable building codes, and a licensed engineer in the project’s location should complete the final structural design.
Typically, the architect and engineer of record will indicate connection loads and locations on the contract documents. At the same time, the selected precast producer’s engineering team is responsible for finalizing the connection design and details. 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 are critical in ensuring that individual precast concrete members are positioned accurately as they’re installed within the overall structure. Tolerances help control alignment, fit, and stability, ensuring the assembled structure meets the specifications. Below are some key rules of thumb regarding precast erection tolerances:
- Ensure uniform joint widths, level floor elevations, and consistent planar wall conditions.
- Determine based on individual unit design, including shape, thickness, material composition, and the unit’s scale relative to the building.
- Consider the impact on multiple building trades and ensure consistency with the specified tolerances for each trade.
- Depend on both equipment capabilities and site-specific conditions.
Precast concrete erection tolerances can vary depending on the unique conditions of each project. In such cases, the designer and contractors should carefully review these tolerances and adjust as needed to meet the project’s specific requirements. The designer must assess how adjusted tolerances might impact details at joints, connections, and other critical locations within the structure. Different design elements may have varying degrees of sensitivity to these tolerances, making it essential to evaluate the effects thoroughly.
For more detailed information on precast concrete erection tolerances, you can download PCI’s Designer’s Notebooks: Envelope Tolerances for Architectural Precast, available as a free PDF. You can also locate a PCI-Certified Erector in your state or region using the PCI-Certified Erector Directory.
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