Precast Reinforced and Prestressed Concrete Systems

Structural Systems in Precast Concrete

Precast reinforced and prestressed concrete systems form the backbone of modern industrial and multi-storey construction, utilizing standard linear elements such as beams and columns.

Frame and Skeleton Structural Systems

The skeleton frame system is composed of columns, beams, and horizontal slabs:

• Building Height: Typically utilized from two storeys upwards, where continuous columns can span heights between one and four storeys.
• Beam-to-Column Support: Beams rest directly on column brackets or corbels using half-lap joints (a media madera) or hinged, articulated seating.
• Floor Diaphragms: Hollow-core precast slabs (placas alveolares) are predominantly used to construct intermediate floor decks.

Portal Frame Structural Systems

Portal frame assemblies are composed of monolithic structural components, connecting beams and columns continuously:

• Fabrication and Logistics: These large continuous units present significant challenges in manufacturing, handling, and site transportation.

Vertical Bracing and Stabilization Systems

Structural stability against lateral loads is achieved through diverse bracing mechanisms:

Cantilever Effect in Slender Columns and Walls

Slender columns and walls embedded directly into the foundation behave like vertical cantilevers. The fixed foundation embedment absorbs all horizontal forces, requiring rigid, moment-resisting base joints.

Core Cantilever and Portal Frame Effects

• Vertical Core Cantilever: Commonly implemented in multi-storey buildings, horizontal stability is secured through rigid vertical central service cores.
• Portal Frame Effect: Rigid frame connections (moment-resisting embedment) between beams and columns continuously resist lateral forces across the entire structural bay.

Diaphragm Action and Shear Walls

• Diaphragm Action: A diaphragm is defined as a planar horizontal structure whose primary function is to distribute and transmit lateral forces to vertical stabilizing members. Floor slabs and roof decks must be perfectly bonded, utilizing a cast-in-place concrete topping (compression layer) to guarantee monolithic structural action.
• Shear-Resistant Walls: These elements function as deep beams spanning floor to ceiling. They resist lateral loads through combined cantilever action and substantial wall thickness.

Precast Block Stabilization

Lateral structural stability is achieved through solid precast modular blocks completing and tying the prefabricated structural frame.

Forces Transmission Through Structural Joints

Transmission of Horizontal Forces

Joints and connections must fulfill fundamental transmission roles:

• They must transmit all applied lateral loads across the building without structural failure.
• They must maintain a continuous and perfect connection between different prefabricated members.
• They must transfer horizontal loads directly into the main stabilizing systems.
• They must ensure the full intended operational capacity of the bracing systems.

Shear and Tensile Force Transmission

Shear Force Transmission (requiring metallic fittings):

• Bond and Adhesion: Restricted to smaller structural elements.
• Shear Keys: Formed with indented, grooved friction surfaces under compressive stress, reinforced across the interface by transverse steel rebar.
• Mechanical Dowels: Steel pins providing mechanical shear resistance.

Tensile Force Transmission (requiring metallic fittings):

• Overlapping starter reinforcement and lap splices.
• Bonded rebar anchorages.
• Bolted connection plates.
• Welded joints connecting protruding starter steel bars from adjacent precast elements.

Compressive Load Transfer

• Direct Bearing: Bearing surfaces must be smooth, even, and regular.
• Mortar Bedding: Application of a leveling mortar layer (approximately 5 mm thick).
• Elastomeric Bearings: Neoprene sheets with reduced thickness for standard bearings, reinforced with metal distribution plates for heavy load transfers.

Joint Classifications and Mechanical Types

• Bending Moment-Resistant Joints: Continuity of longitudinal reinforcement achieved by lap splicing, high-strength bolting, or structural welding.
• Hinged or Knuckle Joints: Joints permitting rotational movement, utilizing steel dowel bars encased in mortar-grouted sleeves or recesses.
• Torsion-Resistant Joints: High-performance, rigid connections preventing torsional deformation.
• Wet Connections: Require cast-in-place concrete pouring to guarantee structural continuity and transmission of lateral loads through overlapping or welded reinforcement cages.
• Dry Connections: Do not require site concrete pouring to transfer lateral loads, relying exclusively on bolting or structural welding; concrete is only optionally applied as protective cover.

Prefabricated Connection Typologies

Column-to-Foundation Connections

• Pocket or Socket Foundation (Cáliz): The column is inserted into a preformed foundation cavity and subsequently grouted with concrete. Column penetration depth into the footing socket must represent 10% to 15% of the total column length. A clearance gap of 5 to 10 cm must be maintained between the column faces and socket walls. This system is ideal for small to medium columns with heavily reinforced bases; it is not suited for excessively long columns. It ensures simple plumb alignment and offers high positional tolerances.
• Base-Plate Rigid Embedment: Formed through structural welding or high-strength bolting of metallic plates, protected against environmental degradation with anti-corrosive paint coatings.
• Grouted Sleeve Embedment: The column features vertical hollow ducts that receive foundation starter bars. Precise placement is essential to prevent rebar displacement during grouting.

Column-to-Column Splicing Details

• Welded Rigid Splice: Steel base plates welded to the column ends are welded together, occasionally incorporating an intermediate leveling plate.
• Grouted Rigid Embedment: Protruding reinforcement bars are aligned, spliced or welded, and fully encased in site-cast concrete.
• Articulated Column Joint: Restricted to axial loads under 40 metric tons, utilizing an intermediate elastomeric neoprene pad and subsequent grouting.

Beam-to-Column Structural Connections

• Welded Rigid Embedment: Starter reinforcement projecting from both the beam and column is welded together and grouted with concrete.
• Grouted Sleeve Connection: Column starter reinforcement inserts into corrugated vertical ducts housed within the precast beam.
• Articulated Connection: The beam rests upon an elastomeric neoprene pad and is mechanically anchored to the column via a high-strength vertical steel dowel.
• Sliding Bearing: Designed for expansion accommodation without transferring horizontal moment, resting directly on a low-friction neoprene bearing pad.

Beam-to-Beam Connection Considerations

Secondary framing with dapped ends or notched corbels (brochales) should generally be minimized; where unavoidable, detailing must strictly eliminate significant torsional stresses arising from lateral forces.

Joint Sealing and Weatherproofing Methods

• Mastic Sealants: Application of elastomeric caulking mastics, which perform significantly better than rigid plastic sealants for exterior weatherproofing.
• Mortar Grouting: Applied to internal structural joints that remain non-exposed.
• Open Joints: Deployed in back-ventilated rainscreen facades, utilizing rigid plastic profiles to deflect water ingress.
• Pneumatic and Vacuum Seals: Inflatable hollow rubber tubes deflated for installation, then pressurized in place to hermetically seal joint cavities.
• Plastic Extrusion Profiles: Pre-shaped profiles inserted to mechanically impede moisture infiltration.

Functional and Structural Design Criteria

Functional Performance Requirements

• Thermal Insulation: Joint interfaces must eliminate thermal bridging.
• Acoustic and Weather Tightness: Must offer continuous soundproofing, air barrier performance, and wind-driven rain resistance.
• Durability: Mitigation of steel corrosion and concrete spalling through specialized epoxy resins, mortars, and protective coatings.
• Dynamic Damping: Adequate structural response to machine and traffic vibrations.
• Demountability: Provision for future dismantling or structural reconfiguration.
• Aesthetic and Deformation Compatibility: Flexible detailing capable of accommodating thermal and creep deformations without visual degradation.

Structural Design Requirements

• Must withstand all combined vertical and lateral load combinations acting on the building frame.
• Must remain structurally stable against volumetric changes (concrete shrinkage, creep, and thermal contraction/expansion).
• Must resist eccentric vertical loads and accidental lateral impacts.
• Must safely absorb transient load distributions induced during demoulding, transport, crane lifting, and erection.