Construction Technology (CE-402) - Unit 5 Short Notes

UNIT 5: CONSTRUCTION TECHNOLOGY - SHORT NOTES

I. FOUNDATIONS (SUBSTRUCTURE)

A. Introduction & Requirements

• Definition: The foundation is the lowest part of a building that transfers all loads (dead, live, wind, seismic) from the superstructure to the underlying soil/rock safely.

• Basic Requirements:

  1. Safe Bearing Capacity: Must not exceed the soil's bearing capacity.

  2. Settlement Control: Should limit total and differential settlement within permissible limits.

  3. Rigidity: Provide adequate rigidity to distribute loads evenly.

  4. Depth: Placed below the frost line to avoid frost heave.

  5. Resistance: Resist lateral forces, uplift, and sliding.

• Forces Acting on Foundation:

  • Vertical Loads (P): Dead load, live load.

  • Lateral Loads (H): Wind, earthquake, water pressure.

  • Uplift Force (U): Buoyancy, seismic overturning.

  • Soil Reaction (q): Distributive pressure from soil.

  [!TIP] Exam Focus: Sketch showing a foundation with all these forces labeled is a common question. Remember P (down), H (horizontal), U (upward), and distributed q (upward from soil).

B. Shallow Foundations

(Depth ≤ Width)

C. Deep Foundations

(Depth >> Width)

• Purpose: Transfer load to deeper, stronger strata when shallow soil is weak. Used for high loads, soft topsoil, or scour.

• Pile Foundation Classification:

  • By Material: Timber, Concrete, Steel.

  • By Function: Bearing Piles (end bearing), Friction Piles (skin friction), Combination.

  • By Installation: Driven (precast, displacement), Bored/Drilled (cast-in-situ, minimal displacement).

• Precautions for Bearing Piles on Rock:

  • Driven Piles: Risk of splitting/cracking rock. Use pre-drilled holes or cushioning.

  • Cast-in-situ Piles: Ensure clean rock surface, remove debris, use rich concrete for good bond.

• Caisson & Well Foundations:

  • Caisson: Watertight retaining structure (open, pneumatic, box). Sunk by excavation.

  • Well Foundation: Sinking of precast wells (cylindrical) by excavation. Used for bridges, docks.

  • Parts of Well: Well curb (bottom), well steining (top enlargement), shaft, bottom plug, top plug, sand filling.

  • Forces on Well: Skin friction (vertical), bearing pressure (bottom), wind/water (lateral), scouring.

  [!TIP] Common Pitfall: Confusing Caisson (built/sunk in-situ) with Well (precast segments sunk). Wells are a type of open caisson.

D. Foundation Failures & Soil

• Causes of Failure:

  1. Excessive Settlement/Differential Settlement: Uneven loading, weak soil.

  2. Shear Failure (Sliding): Soil shear strength exceeded (e.g., slope failure).

  3. Piping/Erosion: Water flow carries soil particles (in sandy soil).

• Site Investigation & Soil Analysis: Mandatory to determine:

  • Soil profile, bearing capacity, settlement potential, groundwater level, soil type.

  • Methods: Test pits, boreholes, SPT, lab tests.

• Frost Heave: Upward swelling of soil due to ice lens formation in freezing zones. Occurs in frost-susceptible soils (silty, clayey) with water supply. Solution: Place foundation below frost depth.

II. MASONRY & WALL CONSTRUCTION

A. Masonry Units & Properties

• Bricks:

  • Efflorescence: Migration of soluble salts (from bricks/mortar) to surface, forms white powder. Classification:

    • Light: Easily brushed off.

    • Heavy: Requires washing.

    • Crystalline: Permanent, hard deposit.

  • Characteristics: Uniform size, sound, low water absorption (<20%), high compressive strength.

  • Testing: Compressive strength, water absorption, efflorescence, dimension, hardness.

• Stones:

  • Characteristics: Hard, durable, dense, low porosity, no cracks.

  • Testing: Abrasion, impact, acid, water absorption, crushing.

  • Types: Granite, Basalt, Limestone, Sandstone, Laterite, Marble.

• Other Units:

  • Hollow Concrete Blocks: Concrete blocks with cored holes (lightweight, insulating, faster construction).

  • Composite Masonry: Two different materials (e.g., brick outer leaf, concrete inner leaf).

B. Masonry Types & Bonds

• Rubble Masonry: Stones roughly dressed. Coursed (layers) or Uncoursed.

• Ashlar Masonry: Stones finely dressed (uniform size/shape). Coursed (each course same height) or Random (different sizes but carefully fitted).

• Brick Bonds:

  • Header Bond: All bricks laid as headers (end face visible). Used for thick walls (1½ brick).

  • Stretcher Bond: All bricks laid as stretchers (long face visible). Used for half-brick walls (partition).

  • English Bond: Alternate header-stretcher courses. Strongest.

  • Flemish Bond: Header and stretcher alternate in same course. Better appearance.

  [!TIP] Differentiation: Header Bond = all headers (thick wall). Stretcher Bond = all stretchers (thin wall). English Bond = alternate courses of headers/stretchers. Flemish Bond = alternating headers/stretchers in one course.

• Load Bearing vs. Non-Load Bearing:

  • Load Bearing: Carries structural load (from floors/roof). Thicker, load-bearing material.

  • Non-Load Bearing: Partition walls only, carries self-weight only. Can be thinner (e.g., hollow blocks).

C. Masonry Construction Techniques

• Principles: Layout (plan alignment), Bonding (overlap joints), Levelling (each course plumb/level).

• Corner Reinforcement (Earthquake):

  • Placement: Vertical bars at corners and openings.

  • Anchoring: Bars extended into floor/roof slabs (150-200mm).

  • Integration: With RC bands (lintel, sill, roof band).

• Construction Joints:

  • Need: When concreting interrupted (end of day, equipment breakdown).

  • Types: Vertical (in columns/walls), Horizontal (in slabs/beams). Must be keyed or roughened.

  • DiagramCANVAS: Sketch showing vertical joint in wall with key, and horizontal joint in slab with shear key

• Seismic Stone Masonry (Codal):

  • Use mortar with low cement content (1:3 to 1:6).

  • Avoid large stones at corners/edges.

  • Provide through stones every 600-900mm.

  • Limit wall height/thickness ratio.

III. BUILDING ELEMENTS: DOORS, WINDOWS & VENTILATION

A. Doors & Windows

• Technical Terms (Doors):

  • Stile: Vertical side members.

  • Rail: Horizontal top/bottom members.

  • Panel: Insert within frame.

  • Casing/Architrave: Trim around frame.

  • Lintel: Horizontal support above.

• Sizing, Location, Orientation Factors:

  • Function: Privacy, light, ventilation, access.

  • Traffic: Main vs. secondary.

  • Furniture: Clearance for movement.

  • Climate: Windows on windward side for ventilation, avoid west for heat.

  • Safety: Egress windows in bedrooms.

• Types of Windows: Casement, Sliding, Fixed, Louvered, Bay, Clerestory.

• Door Repair Techniques: Shimming (tighten hinges), planing (bindings), weatherstripping (drafts), refinishing (rot).

B. Ventilation & Lighting

• Passive Ventilation: Uses natural forces (wind, buoyancy). Cross-ventilation (opposite openings), stack effect (high outlet).

• Natural Daylighting: Maximizes sunlight penetration via windows, skylights, light shelves. Reduces energy.

• Requirements:

  • Good Ventilation: Adequate openable area (5-10% floor area), proper placement (low inlet, high outlet), unobstructed airflow.

  • Good Lighting: Sufficient window area (10-20% floor area), diffused light (avoid glare), light-colored interiors.

IV. FLOORING & ROOFING

A. Floors

• Floor Finishes: Top wearing layer (tiles, wood, marble). Common: Terrazzo, Marble, Granite, Wood, Vinyl, Ceramic.

• Types of Floors:

  • Ground Floor: Surface preparation (consolidate soil, waterproofing, blinding), sub-base (sand, PCC), flooring.

  • Upper Floor: Joists/beams, decking (concrete slab, wood), finish.

  • Special - Bengal Terrace Roof:

    1. Brick flat arches on beams.

    2. Brick jelly (1:4 lime mortar) over arches.

    3. Lime concrete (1:2:4) with brick pieces.

    4. Waterproofing (lime, bitumen).

    5. Finishing (mud phuska, tiles).

    DiagramSEARCH: Bengal terrace roof cross section

• Characteristics of Ground Floorings:

  • Mud: Cheap, poor durability, cold.

  • Brick: Durable, cool, hard.

  • Concrete: Strong, durable, can be finished.

  • Marble/Granite: Aesthetic, durable, expensive.

• Terrazzo Flooring: Chip marble/quartz in cement/resin matrix, ground/polished. Attractive, durable, seamless.

• Marble Flooring: Thin marble slabs (20-25mm) on mortar bed. Adhesive or mechanical fixing. Grouted joints.

B. Roofs

• Introduction: Weatherproof enclosure protecting from rain, sun, wind.

• Pitched Roofs:

  • Sketch: Sloping surfaces (trusses/rafters), ridge, eaves, purlins (horizontal supports), common rafters (sloping members).

  • Advantages: Good drainage, attic space, traditional look.

  • Disadvantages: Complex construction, more material, unsafe for maintenance.

  • Roof Coverings: Tiles (clay, concrete), slates, sheets (GI, asbestos - phased out), thatch.

• Technical Terms:

  • Common Rafters: Sloping members supporting roof covering.

  • Purlins: Horizontal members supporting rafters (in truss roofs).

V. EARTHQUAKE-RESISTANT CONSTRUCTION

A. Design Principles

• How Protection Achieved:

  1. Ductility: Allow controlled deformation (steel, RC).

  2. Symmetry & Regularity: Avoid irregular plans/ elevations.

  3. Strong Column-Weak Beam: Columns stronger than beams to avoid column failure.

  4. Adequate Connections: All joints (column-beam, wall-roof) must be strong and ductile.

  5. Mass & Stiffness Control: Avoid abrupt changes.

• Key Planning Factors:

  • Simple, regular shape (square/rectangle).

  • Uniform distribution of mass and stiffness.

  • Adequate number of shear walls.

  • Proper separation from adjacent buildings.

B. Construction Techniques

• Beams & Columns:

  • Close spacing of longitudinal reinforcement.

  • Tight confinement of concrete in joint region (more ties, closer spacing).

  • Adequate development length for bars.

• Corner Reinforcement in Walls: As detailed in Section II.C.

• Seismic Stone Masonry: As detailed in Section II.C.

C. Retrofitting

• Definition: Strengthening/upgrading existing structures to meet new seismic codes.

• Global Retrofitting: Improves overall structural integrity (e.g., adding shear walls, jacketing columns).

• Local Retrofitting: Targets specific weak elements (e.g., beam/column jacketing, adding steel braces).

• Importance: Life safety in old, non-compliant buildings.

VI. TEMPORARY STRUCTURES & PRECONSTRUCTION

A. Formwork (Shuttering)

• Definition: Mould for casting concrete. Must be strong, rigid, watertight.

• Materials:

  • Timber: Flexible, easy, reusable 10-20 times, warps, limited spans.

  • Steel: Durable (100+ uses), strong, smooth finish, expensive, heavy.

  • Plastic: Lightweight, corrosion-proof, smooth finish, limited reuse, for complex shapes.

• Design Considerations: Loads (concrete pressure, live load), stiffness (deflection < span/250), supporting props, safety factors.

• Techniques:

  • Stationary Form: Fixed for entire casting. Flexible for shapes.

  • Slip Form: Continuous lifting as concrete sets. For towers, silos, cores. High speed, uniform.

  [!TIP] Compare: Stationary = fixed, versatile. Slip = moving, for tall/ repetitive elements.

• Stripping/Removal:

  1. Check concrete strength (usually > 1.2 N/mm² for beams, > 5 N/mm² for slabs).

  2. Remove props gradually (start from top).

  3. Dismantle form carefully (avoid impact).

  4. Clean and repair formwork for reuse.

  5. Safety: No one under striking forms.

B. Support & Access Structures

• Scaffolding: Temporary platform for workers/materials.

  • Types: Single (brickwork), Double (painting), Suspended, Cantilever.

• Underpinning: Strengthening foundation by constructing a new, deeper foundation beneath existing.

  • Methods: Mass concrete (simple), Pile (weak soil), Pier & Beam (heavy loads).

• Shoring: Temporary support to prevent collapse of structure/ excavation (e.g., during underpinning).

C. Prefabrication

• Definition: Manufacturing components off-site, transported and assembled on-site.

• Advantages: Speed, quality control, weather independence, less waste.

• Disadvantages: High transport cost, heavy equipment needed, less flexibility, design changes difficult.

D. General Temporary Construction

• Purpose: Support construction activities (access, material storage, protection).

• Types with Sketches:

  • Barricading/Fencing: Site security.

  • Temporary Sheds: Material storage.

  • Access Roads & Platforms: For equipment.

  • Protective Canopies: Over pedestrian areas.

  • Temporary Utilities: Water, power, toilets.

  DiagramCANVAS: Sketch showing site layout with scaffolding, temporary shed, access road, barricades

VII. BUILDING FINISHES & MATERIALS

A. Surface Finishes for Walls

• White Washing: Lime + water (sometimes with glue). Cheap, temporary, for interior/exterior.

• Colour Washing: White wash + colour (yellow, red earth). More attractive.

• Distempering: Water-based paint on distemper primer. Cheap, for interior, not washable.

• Plastering: Mortar coat (cement/lime/sand) for smooth, strong surface.

• Pointing: Finishing joints of exposed masonry with cement/lime mortar.

B. Paints

• Constituents:

  1. Pigment: Colour, opacity.

  2. Vehicle/Binder: Holds pigment, forms film (oil, varnish, latex).

  3. Solvent/Thinner: Adjusts viscosity (turpentine, water).

  4. Additives: Driers, fillers, anti-fungal.

• Desirable Properties: Good coverage, durability, adhesion, colour retention, weather resistance, easy application.

• Types: Oil Paint, Emulsion (Plastic) Paint, Distemper, Cement Paint, Enamel, Bituminous, Aluminium, Fire Retardant.

C. Dampness Prevention

• Definition: Unwanted moisture in building elements.

• Effects: Efflorescence, plaster damage, timber rot, health issues, reduced insulation.

• Causes:

  1. Rain penetration (defective roof, walls).

  2. Capillary action from ground (no DPC).

  3. Condensation (poor ventilation).

  4. Leakage (pipes, tanks).

• Prevention Techniques:

  1. DPC (Damp Proof Course): Impervious layer (bitumen, HDPE, metal) at plinth level.

  2. Waterproofing: Coatings (bituminous, chemical) on roofs, tanks.

  3. Proper Drainage: Sloped roofs, gutter, site grading away from building.

  4. Ventilation: Air bricks, windows.

  5. Quality Materials: Low absorption bricks, dense concrete.

• DPC Types: Horizontal DPC (walls), Vertical DPC (external walls), Under-slab DPC.

VIII. STAIRS, LIFTS & RAMPS

• Essential Elements of a Stair:

  • Tread: Horizontal step (foot space).

  • Riser: Vertical step (height).

  • Flight: Series of steps without landing.

  • Landing: Platform between flights.

  • String/ Stringer: Inclined member supporting treads/risers.

  • Newel: Post at foot/top/landing.

  • Baluster/Handrail: Safety support.

• Types of Stairs (with Cross-Sections):

  • Straight: Single flight, no landing. Simple, direct.

    DiagramCANVAS: Cross-section of straight stair showing tread, riser, stringer, handrail

  • L-Shaped: 90° turn using winders or landing.

  • U-Shaped: 180° turn via landing.

  • Spiral/Circular: Compact, around central post. Limited width.

  • Helical: Continuous curve without central post (requires careful design).

• Definitions:

  • Ladder: Inclined rungs, no treads, for access only (not regular circulation).

  • Lift/Elevator: Powered vertical transportation in shaft.

  • Ramp: Inclined plane (slope 1:12 to 1:20) for wheelchair access.

IX. CONSTRUCTION JOINTS & REPAIRS

A. Construction Joints

• Need: When concreting cannot be done in single operation (end of day, equipment failure). Must be planned.

• Types with Sketches:

  • Vertical Joint: In walls/columns. Keyed or shear key.

    DiagramCANVAS: Vertical construction joint in column with shear key

  • Horizontal Joint: In slabs/beams. Grooved or keyed.

    DiagramCANVAS: Horizontal construction joint in beam with shear key

  • Armored Joint: For movement (isolation joints) with preformed compressible filler.

B. Repairs & Base Isolation

• Actions for Repair (Regain Architectural Shape):

  1. Assess damage (structural vs. cosmetic).

  2. Remove damaged material carefully.

  3. Prepare substrate (clean, key).

  4. Match original materials (brick, stone, mortar).

  5. Use skilled craftsmanship for replication of details.

  6. Finish to match surrounding area.

• Base Isolation (Earthquake):

  • Definition: Decoupling building from ground motion using flexible supports.

  • Components:

    • Isolators/Bearings: Elastomeric (rubber-steel), sliding (PTFE), friction pendulum. Provide flexibility.

    • Damping Devices: Dissipate energy (viscous dampers, yielding steel). Reduce displacement.

\boxed{\text{END OF UNIT 5 NOTES}}