Prefabricated Structures (Unit-4) Anna university
- 2. Joints and Connections in structural members • In prefabricated (prefab) structures, joints and connections are critical for ensuring structural integrity, ease of assembly, and durability. • They are designed to be strong, flexible where needed (especially in seismic or wind-prone areas), and easy to fabricate or transport. • Here’s an overview of the common types of joints and connections used in prefab structures:
- 3. Types of Joints in Prefab Structural Members 1. Bolted Connections • Common in: Steel prefab frames, precast concrete panels. • Advantages: Easy to assemble/disassemble; allows for future expansion. • Types: Lap joints, butt joints, splice joints. 2. Welded Connections • Common in: Steel structures (on-site or shop welding). • Advantages: Strong, rigid, seamless look. • Disadvantages: Requires skilled labor and on-site welding equipment.
- 4. 3. Grouted Joints • Common in: Precast concrete panels and columns. • How it works: Steel bars are inserted into sleeves and filled with grout. • Advantage: Ensures monolithic behavior after curing. 4. Dry Connections / Mechanical Joints • Common in: Modular and panelized prefab systems. • Includes: Clips, clamps, brackets, inserts. • Advantages: Fast assembly, no curing time needed.
- 5. 5. Post-tensioned / Pre-stressed Connections • Common in: Precast concrete members (e.g., beams, slabs). • Purpose: To introduce compressive force to counteract tensile stress.
- 6. Key Structural Member Connections Member Type Typical Connection Details Column-to-Foundation Anchor bolts, base plates Often grouted or bolted. Beam-to-Column Bolted bracket, welded plate Can be moment or pinned connection. Panel-to-Panel (Walls) Grouted keyways, dowels, mechanical locks May include insulation for thermal control. Slab-to-Beam Shear keys, grout, connectors Ensures load transfer and continuity. Roof Truss Joints Gusset plates, bolts, welds Designed for uplift and horizontal loads.
- 7. Types of joints based on action of forces • Joints in structural members can also be classified based on how they transmit and resist forces. • This classification helps in understanding how loads (axial, shear, moment) are transferred between connected elements.
- 8. Types of Joints Based on Action of Forces 1. Rigid (Moment-Resisting) Joints • Force Transfer: Transfers moment, shear, and axial forces. • Behavior: No relative rotation between connected members. • Example: Beam-column connections in moment-resisting frames. • Common in: Earthquake-resistant buildings, steel and reinforced concrete structures.
- 11. 2. Pinned (Hinged) Joints • Force Transfer: Transfers only axial and shear forces; no moment. • Behavior: Allows rotation but not translation. • Example: Truss connections. • Common in: Steel trusses, precast concrete joints with dowels.
- 13. 3. Sliding or Expansion Joints • Force Transfer: Allows for translation (movement), resists minimal force. • Behavior: Used to accommodate thermal expansion, settlement, or seismic movement. • Example: Expansion joints in bridges, buildings. • Common in: Long-span structures, bridge decks, industrial buildings.
- 15. 4. Semi-Rigid Joints • Force Transfer: Transfers some moment, along with shear and axial forces. • Behavior: Intermediate between rigid and pinned. • Example: Bolted end-plate connections with partial fixity. • Common in: Steel frames where partial moment resistance is acceptable.
- 17. 5. Ductile Joints • Force Transfer: Designed to deform plastically under high force (e.g., earthquakes). • Behavior: Absorbs energy through controlled yielding. • Example: Special detailing in beam- column joints (e.g., stirrups, confinement). • Common in: Seismic design zones.
- 18. Compression joints shear joints and tension joints 1. Compression Joints • Function: Resist compressive forces (pushing forces). • Behavior: The connected elements are pressed toward each other. • Design Considerations: – Needs full bearing surface contact. – Often does not require complex fastening if friction and end-bearing are sufficient. • Examples: – Precast concrete columns stacked on each other. – Masonry block walls. – Steel columns seated on base plates with gravity loads.
- 19. 2. Tension Joints • Function: Resist tensile forces (pulling forces). • Behavior: The members are pulled away from each other, and the joint must hold them together. • Design Considerations: – Requires fasteners like bolts, welds, cables, or adhesive to prevent separation. – Connections must be stronger than the member to avoid failure at the joint. • Examples: – Tension members in trusses (tie rods, hangers). – Bolted steel connections in roof bracing. – Pre-stressed cable anchors.
- 20. 3. Shear Joints • Function: Resist shear forces (sliding or cutting forces). • Behavior: Forces act parallel to the joint plane, trying to slide the members relative to each other. • Design Considerations: – Requires shear keys, bolts, dowels, or rough surface contact. – Must prevent relative displacement between members. • Examples: – Beam-to-column connections. – Concrete slab joints with shear connectors. – Steel plate connections with multiple bolts.
- 21. Shear keys
- 22. Shear keys
- 23. Shear keys
- 24. Types of Joints Based on Function 1. Structural Joints • Function: Transfer structural loads between members. • Examples: – Beam-to-column joints – Column-to-foundation joints • Role: Critical for load path continuity; designed to resist forces like tension, compression, shear, and moment.
- 25. 2. Expansion Joints • Function: Allow thermal expansion and contraction of building elements. • Examples: – Gaps in bridges, slabs, or long buildings filled with flexible materials. • Role: Prevent cracking or damage due to temperature or shrinkage movement.
- 26. 3. Contraction Joints (Control Joints) • Function: Control shrinkage cracks in concrete or masonry. • Examples: – Grooves in pavements or walls. • Role: Provide a weak plane for cracking to occur in a controlled way.
- 27. 4. Construction Joints • Function: Interface between different concrete pours or construction stages. • Examples: – Slab pours on different days. • Role: Ensure continuity in monolithic behavior despite staged construction.
- 28. 5. Seismic Joints • Function: Allow relative movement between structural blocks during earthquakes. • Examples: – Separation between building wings or podium and tower. • Role: Prevent pounding and damage by isolating movement.
- 29. 6. Isolation Joints • Function: Completely separate structural elements to prevent force transfer. • Examples: – Between floor slab and column, or machine foundation and building. • Role: Reduce vibration transmission, stress concentration, or differential settlement effects.
- 30. Isolation Joints
- 31. Isolation Joints
- 32. Design of expansion joints dimensions and detailing • Designing expansion joints involves specifying the width, spacing, depth, and detailing so the structure can safely accommodate thermal movements, shrinkage, creep, and seismic actions without cracking or damage. Expansion joints are critical in long-span buildings, bridges, pavements, slabs, and walls.
- 33. 1. Expansion Joint Width (Gap) – Design Criteria • The joint width depends on: 🔸 Thermal expansion/contraction 🔸 Material type (concrete, steel, masonry) 🔸 Temperature range 🔸 Length of the structure 🔸 Movement allowance (ΔL) 🔹 General Formula: ΔL=α⋅L⋅ΔT Where: ΔL = required movement (mm) α = coefficient of thermal expansion (e.g., 12×10−6/∘C for concrete) L = length of structure (m) ΔT = temperature variation (°C)
- 34. • Example: For a 30-meter-long concrete wall with a temperature variation of 40°C: • ΔL=α⋅L⋅ΔT • ΔL=11×10−6×30,000×40=13.2 mm. • Thus, the expansion joint should accommodate a movement of approximately 13.2 mm.
- 35. Expansion Joint Width (Gap) Structure Type Typical Joint Width Concrete Pavement 10–20 mm Building Slabs 20–30 mm Long Masonry Wall 20–40 mm Bridge Decks 30–100 mm or more
- 36. 2. Expansion Joint Spacing Material Typical Max Spacing Concrete Slabs 20–30 m (indoors), 12–15 m (exposed) Masonry Walls 12–15 m Steel Structures 30–60 m Bridges Varies by span and climate
- 37. 3. Expansion Joint Detailing A. In Buildings • Use compressible filler boards (e.g., bitumen-impregnated fiberboard) in the joint gap. • Cover with metal or rubber expansion joint covers for floors and facades. • Ensure continuity of waterproofing membranes and fire barriers across the joint. • Use slip joints or telescoping covers in walls.
- 38. B. In Concrete Slabs (Pavements/Floors) • Provide load transfer devices (e.g., dowel bars) if required. • Seal joints with elastomeric sealant or pre- moulded seal strips. • Fill gap with compressible foam if joint is wide.
- 39. C. In Bridges • Include modular joint systems or finger joints. • Allow for vertical and horizontal movements. • Install neoprene seal, steel plates, or sliding bearings under joint.
- 40. Recommended Spacing of Expansion Joints as per IS 3414 Structural Element Maximum Spacing Load-bearing masonry walls with cross walls at intervals 30 meters Masonry walls without cross walls (e.g., warehouse walls) 30 meters Chajjas, balconies, and parapets 6 meters RCC roof slabs with insulation (e.g., mud phuska) 45 meters Thin, unprotected RCC roof slabs 30 meters RCC framed structures (joints through slabs, beams, columns) 45 meters Copings and parapet walls 30 meters
- 41. Types of sealants • Sealants are materials used to block the passage of fluids through surfaces, joints, or openings. • They play a crucial role in expansion joints, structural glazing, waterproofing, and finishing works. • The type of sealant used depends on movement tolerance, adhesion, weather resistance, durability, and surface compatibility.
- 42. Types of Sealants (Based on Composition & Performance) Sealant Type Base Material Key Properties Typical Applications Polysulfide Synthetic rubber High flexibility, chemical resistant, UV stable, long- lasting Expansion joints, bridges, tanks Polyurethane (PU) Polyurethane resin Tough, flexible, paintable, good adhesion, weather- resistant Concrete joints, façades, precast panels Silicone Silicone polymers Highly elastic, UV & weather resistant, waterproof, not paintable Glass glazing, curtain walls, wet areas Acrylic Water-based acrylic Paintable, low movement tolerance, economical Interior gaps, non- structural joints Bituminous Asphalt/bitumen based Waterproof, non-elastic, cheap Roofing, substructures, damp- proofing Butyl Rubber Butyl polymer Sticky, flexible, low movement, good vapor resistance Roofing membranes, window perimeters Epoxy Sealants Epoxy resin Rigid, strong, chemical & abrasion resistant Industrial joints, rigid bonding applications Flexible, UV-stable,
- 43. Selection Criteria for Sealants 1. Joint movement – Use silicone or polysulfide for high-movement joints. 2. UV/weather exposure – Silicone, MS polymer preferred. 3. Paint ability – Polyurethane, acrylic. 4. Chemical resistance – Polysulfide, epoxy. 5. Cost factor – Acrylic and bituminous are economical.
- 44. Types of structural connections • Structural connections are critical in joining various structural elements like beams, columns, slabs, trusses, and walls to ensure stability, load transfer, and structural integrity. • These can be classified based on force transmission, rigidity, method of construction, and material used.
- 45. 1. Based on Force Transmission Type of Connection Function Example Tension Connection Transfers axial tension Tie rods, bracing systems Compression Connection Transfers axial compression Columns, struts Shear Connection Transfers shear force between members Beam-column simple connection Moment (Rigid) Connection Transfers bending moments Fixed beam-column connection Combined Force Connection Transfers a combination of loads Frame joints, base plates
- 46. 2. Based on Rigidity / Fixity Type Characteristics Applications Pinned (Hinged) Allows rotation but resists translation Trusses, simply supported beams Rigid (Moment) Resists rotation and translation Moment-resisting frames Semi-Rigid Offers partial rotational restraint Steel beam-column joints in practice
- 47. 3. Based on Construction Method Type Features Examples Bolted Connection Easy to assemble/disassemble; allows for inspection Steel frames, prefab steel buildings Welded Connection Monolithic behavior, strong but difficult to modify Heavy steel structures, bridges Riveted Connection Obsolete, replaced by bolting/welding Heritage structures Mortise and Tenon / Doweled Common in timber construction Traditional wooden buildings
- 48. 4. Based on Material Material Common Connection Types Steel Bolted, welded, riveted, end plates Concrete Monolithic (cast-in-situ), dowel bars, grouted sleeves Timber Bolted, nailed, mortise and tenon, glued Composite Shear connectors, headed studs, bolts/welds
- 49. Typical Structural Connections in Precast Construction • Column-to-Foundation: Pocket foundation with grouted connection • Beam-to-Column: Corbels or steel brackets with bolts/grouting • Slab-to-Slab: Keyed joints with shear connectors • Wall-to-Wall/Wall-to-Slab: Tongue-and- groove with joint sealants and dowels
- 50. Types of structural connections • Here’s a concise explanation of the typical types of structural connections used in beam-to-column, column-to-column, beam- to-beam, and column-to-footing assemblies, especially relevant to reinforced concrete (RCC) and precast systems:
- 51. 1. Beam-to-Column Connections • In Cast-in-Situ RCC: • Monolithic Joint: – Beam and column are cast together. – Reinforcement is lapped or anchored properly. – Ensures full moment transfer and continuity. • ◻In Precast: • Pocket Connection: – Column has a pocket; precast beam sits in it. – Gap filled with non-shrink grout or concrete. • Bolted/Welded Steel Inserts: – Embedded plates and bolts transfer loads. – May allow semi-rigid or rigid behavior.
- 56. 2. Column-to-Column Connections • In Cast-in-Situ RCC: • Monolithic vertical casting with lap splices or couplers. • ◻In Precast: • Socket Base Connection: – Lower column has a pocket; upper column inserted and grouted. • Dowel Bar Connection: – Dowel bars project from lower column into sleeves of upper column. • Mechanical Splices (Couplers): – Used when precise alignment is needed.
- 62. 3. Beam-to-Beam Connections • Used in continuous beams or for secondary beam framing: • ◻In Cast-in-Situ RCC: • Beams intersect and reinforcement is lapped or extended across. • ◻In Precast: • Corbel with Shear Key: – Precast beam sits on a corbel of another. • Bolted Joint: – Bolts or dowels connect adjoining beams internally. • Wet Joint: – A cast-in-situ joint between precast beams with shear connectors.
- 64. Corbel with Shear Key
- 65. Bolted Joint
- 66. Wet Joint
- 67. 4. Column-to-Footing Connections • In Cast-in-Situ RCC: • Column reinforcement is extended into footing with proper development length. • ◻In Precast: • Socket Foundation: – Column placed in a preformed pocket in the footing and grouted. • Base Plate and Anchor Bolt: – Steel plate at column base anchored to footing with bolts. • Dowel and Sleeve: – Dowels embedded in footing align with sleeves in the precast column.
- 70. Base Plate and Anchor Bolt
- 71. Dowel and Sleeve
- 72. END