Chapter 1: Basic Knowledge of Prefabricated Concrete Structures
Content Summary
This chapter covers the concept, characteristics, and classification of prefabricated concrete structures. It introduces the classification, features, and challenges associated with prefabricated concrete structures, particularly focusing on prefabricated enclosure wall panels through engineering examples. Topics include typical vertical connection methods between prefabricated components, connections between enclosure wall panels and main structures, and the types and characteristics of connectors used for prefabricated sandwich wall panels. The development history of prefabricated concrete structures is also discussed.
1.1 Concept of Prefabricated Concrete Structures
The construction industry is a pillar of the national economy, contributing over 20% of GDP. However, it also accounts for 32% of total national energy consumption, making it the largest single energy-consuming sector. To address issues of high energy usage, pollution, and low efficiency, the industry must innovate technologically and pursue industrialized construction methods to sustain vitality amid rapid economic and social development.
In this context, construction production is shifting towards factory-based manufacturing, making prefabricated concrete buildings an inevitable trend. Compared to traditional buildings, prefabricated buildings adopt standardized designs, industrial production, mechanized construction and installation, and information management. They replace wet processes with dry operations to ensure quality, reduce labor intensity, lower costs, minimize environmental impact, and conserve natural resources.
Prefabricated concrete structures consist of concrete elements manufactured off-site and assembled on-site using reliable connection methods. These include assembled integral concrete structures and fully assembled concrete structures. In construction engineering, these are called prefabricated buildings, while in structural engineering, they are referred to as prefabricated structures.
Common connection methods include on-site concrete pouring at joints, bolted connections, and prefabricated stress connections. Steel reinforcement connections can be made using steel bar sleeve grouting, steel bar slurry anchoring with overlap, welding, mechanical connections, or reserved hole overlaps.
Typical prefabricated concrete components include:
- Fully prefabricated columns and beams
- Composite beams
- Fully prefabricated shear walls
- Single-layer and double-layer composite shear walls
- External wall panels
- Prefabricated concrete sandwich insulation exterior wall panels
- Prefabricated composite insulation exterior wall panels
- Fully prefabricated floor slabs and composite floor slabs
- Fully prefabricated and prefabricated balcony slabs
- Prefabricated bay windows
- Fully prefabricated air conditioning panels and parapets
- Decorative columns
It is important to distinguish between prefabrication rate and assembly rate in prefabricated concrete buildings:
- Prefabrication rate: The volume ratio of prefabricated components’ material consumption in the main and enclosure structures above the outdoor floor compared to the total material consumption of corresponding parts.
- Assembly rate: The ratio of the quantity or area of prefabricated components and building parts to the total quantity or area of similar parts in prefabricated R&D buildings.
1.2 Characteristics of Prefabricated Concrete Structures
Prefabricated concrete structures exhibit several key characteristics:
- Major components are prefabricated in factories or on-site, lifted mechanizedly, allowing simultaneous progress with other specialized construction tasks. This results in faster construction speed, shorter project duration, and suitability for winter construction.
- Prefabrication uses standardized flat templates, replacing the three-dimensional operations of cast-in-place structures. This approach improves production efficiency, product quality, safety, environmental protection, and cost reduction.
- Special requirements such as insulation, decoration, door and window accessories, and concrete wall panels can be fulfilled in factories using reverse molding or formwork technology. This enhances waterproofing and durability around window frames and addresses exterior wall decoration challenges.
- Highly integrated functions reduce material waste and simplify construction processes.
- Due to the high technical management demands and required engineering experience, the design and construction of prefabricated buildings require thorough early-stage planning, including scheduling, component standardization, and resource optimization.
1.3 Types of Prefabricated Concrete Structures
Prefabricated concrete buildings represent an industrial upgrade in construction technology. Unlike typical classifications based on building function, these structures are categorized by their prefabrication techniques.
Based on the structural system, prefabricated concrete buildings are divided into:
- Assembled integral frame structures
- Assembled integral shear wall structures
- Assembled integral frame-shear wall structures
According to the types of prefabricated enclosure components, they include:
- Prefabricated external wall panels
- Single-layer composite shear walls (PCF)
- Double-layer composite shear walls
- Prefabricated insulation composite exterior wall panels (PCTF)
- Prefabricated sandwich insulation wall panels
- Prefabricated shear wall exterior panels
- Prefabricated enclosure wall panels
- Fully prefabricated women’s walls
Connection methods in prefabricated concrete structures are critical and fall mainly into three categories:
- Connections between prefabricated components
- Connections between prefabricated enclosure components and the main structure
- Connections between prefabricated sandwich insulation wall panels and their inner and outer leaf walls
Vertical connections of prefabricated components typically include bolt connections, steel sleeve grouting connections, and steel slurry anchor overlap connections. Connectors for sandwich insulation wall panels often use FRP, stainless steel, or basalt reinforcement.
1.3.1 Classification of Prefabricated Concrete Structures
1. Assembled Integral Frame Structure
This structure uses prefabricated components for all or part of the frame beams and columns. It is common in buildings with high spatial demands such as shops, schools, and hospitals. The load transmission path follows: floor slab → secondary beam → main beam → column → foundation.
Main load-bearing components include fully prefabricated columns, beams, floors, and non-load-bearing elements like walls and exterior decorations. Vertical connections for fully prefabricated columns typically use grouting sleeves.
Technical features: High component standardization, limited variety with similar weights, full use of lifting machinery capabilities, and excellent technical and economic efficiency. The standardized assembly nodes improve work efficiency. Steel bar connections are unified, enabling mechanized construction, reliable quality, structural safety, and environmental protection. The complexity arises with high-density steel bar nodes requiring precise processing.
Case Project: Building 39, Plot 128-3, Pujiang Town
Overview: A three-story commercial building with 1,695 m² of construction area.
Prefabrication details: 75% prefabrication rate including columns, composite beams, and composite floor slabs.
2. Assembled Integral Shear Wall Structure
This is a common structural system for residential buildings. The load path is floor slab → shear wall → foundation. Shear wall buildings lack protruding beams and columns, providing orderly indoor space.
Main load-bearing components include shear walls and floor slabs; non-load-bearing elements include walls and exterior decorations. Prefabricated components include enclosure panels (fully prefabricated shear walls, single-layer and double-layer composite shear walls, sandwich insulation panels, composite insulation exterior panels), interior shear walls, beams, panels, balconies, sunshades, bay windows, air conditioning panels, stairs, and parapets.
Vertical connections for shear walls use bolt connections, steel sleeve grouting, or steel slurry anchor overlaps. Enclosure wall panels generally use threaded blind hole grouting connections.
Technical features: High standardization of flat wall and floor components leads to efficient production and transportation. Vertical connections employ bolts, grouting sleeves, and anchor overlaps with concrete poured after horizontal connections. T-shaped and cross-shaped shear wall connections have high steel bar density, posing operational challenges.
Case Projects:
Vanke Dijie B (Legend of the Sea)
An 18-story residential building with 36,200 m² of construction area.
Prefabrication rate: 15%, including partial prefabricated shear walls, balconies, bay windows, and fully prefabricated stairs.
Taihe Hongqiao
An 18-story residential building with 42,000 m² of construction area.
Prefabrication rate: 45%, including prefabricated shear walls, composite floor slabs, and stairs.
3. Assembled Integral Frame-Shear Wall Structure
This structural system is common in office and hotel buildings. Shear walls act as the primary seismic defense, while prefabricated frames serve as the secondary defense.
Prefabricated components include external wall panels, fully prefabricated columns, composite beams, fully prefabricated slabs, composite panels, and parapets. Vertical connections for columns typically use steel sleeve grouting.
Technical characteristics: The main lateral force-resisting elements, the shear walls, are generally cast-in-place, while the frame components are prefabricated. This results in relatively high standardization of prefabricated components. Columns, beams, and floor components are planar, facilitating efficient production and transportation.
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