Construction Technology (CE-402) - Unit 4 Short Notes

UNIT 4: CONSTRUCTION TECHNOLOGY

1. FOUNDATIONS

1.1 Introduction & Basic Requirements

• Definition of Foundation: The lowest part of a structure that transmits loads from the superstructure to the underlying soil/rock.

• Basic Requirements of a Good Foundation:

  • Must be stable and strong enough to carry imposed loads without failure.

  • Should have limited and uniform settlement to avoid damage to the structure.

  • Must be rigid enough to resist differential settlement.

  • Should be placed at a suitable depth to avoid scour, frost action, and organic matter.

  • Must be economical and constructible with available technology.

1.2 Shallow Foundations

• Spread Footings: Isolated footings supporting columns. Load spreads to a wider area of soil.

• Strip Footings: Continuous footings under load-bearing walls.

• Combined Footings:

  • Design Features: Used when two or more columns are close. Rectangular or trapezoidal shape. Designed for uniform pressure distribution.

  • Advantages: Useful for property line constraints; prevents eccentric loading.

• Grillage Foundation:

  • Types: Single-layer (rare) and multi-layer (common). Steel beams (I-sections) arranged in tiers, concrete filled between.

  • Uses: For heavy structural loads on weak soil where pile foundations are not feasible. Transfers load through beam action to a larger area.

1.3 Deep Foundations

• Purpose & Classification of Pile Foundations:

  • Purpose: To transfer loads to deeper, stronger strata; to resist uplift; to compact surrounding soil.

  • Classification:

    | Basis | Types | |-------|-------| | Material | Timber, Steel, Concrete (Reinforced/Precast) | | Load Transfer | End-Bearing Piles (rest on hard stratum), Friction Piles (skin friction) | | Installation | Driven Piles (hammered), Cast-in-situ Piles (bored & poured) |

• Bearing Piles on Rock Surfaces:

  • Driven Piles: Pre-drill a hole into rock, clean, place pile, and pack with mortar. Ensure intimate contact.

  • Cast-in-situ Piles: Drill through soil into rock, clean, place reinforcement, and concrete in one continuous operation. Use tremie method.

• Under-reamed Piles:

  • Construction: Bored cast-in-situ piles with bulbs (under-reams) at intervals.

    DiagramCANVAS: Show a pile with multiple bulbous enlargements along its shaft, typically at 2-3m intervals, with a larger bulb at the base

  • Use: In expansive, black cotton soils to resist uplift and swelling pressure.

• Advantages & Disadvantages of Pile Foundations:

  | Advantages | Disadvantages | |------------|---------------| | Can carry heavy loads | High cost | | Suitable for weak soils | Requires skilled supervision | | Resists lateral forces | Noise & vibration (driven) | | Can be installed in tight spaces | Difficult to assess capacity accurately |

1.4 Special Foundations

• Caisson Foundations (Types):

  • Open Caisson: Sunk by excavating inside; open at top & bottom. For hard strata.

  • Pneumatic Caisson: Compressed air keeps water out; for deep underwater foundations.

  • Box Caisson: Prefabricated, closed at bottom; floated to site and sunk.

• Well Foundations:

  • Elements/Parts: Well curb (cutting edge), well steining (tapered masonry), well cap (top concrete), shaft.

  • Forces Acting: Self-weight, Water pressure (inside/outside), Soil pressure, Wind/Seismic forces.

    DiagramCANVAS: Show a well foundation with forces labeled: downward self-weight, lateral water pressure differential, soil reaction at base

1.5 Foundation Design & Analysis

• Importance of Site Investigation & Soil Analysis: Determines bearing capacity, settlement potential, soil profile, groundwater level. Prevents unexpected failures.

• Forces Acting on Foundations (with Sketch):

  DiagramCANVAS: Show a foundation with arrows: vertical load (P), soil reaction (q), lateral force (H), overturning moment (M)

  • Vertical loads (dead, live, wind)

  • Lateral loads (earthquake, wind)

  • Overturning moments

• Causes of Foundation Failure (Minimum Three):

  1. Unequal Settlement: Due to variable soil bearing capacity or loading.

  2. Overloading: Exceeding soil's ultimate bearing capacity.

  3. Lateral Movement: From slope failure, excavation, or seismic forces.

• Frost Heave:

  • Causes: Water in soil pores freezes, expands (9% volume increase), and lifts the foundation. Occurs in frost-susceptible soils (silty, clayey) with freezing temperature penetration and water supply.

2. DAMPNESS AND MOISTURE CONTROL

2.1 Dampness in Buildings

• Definition: Unwanted presence of moisture in building components (walls, floors).

• Effects: Discoloration, efflorescence, plaster peeling, timber decay, unhealthy living.

• Causes: Rising damp (capillary action), rain penetration, condensation, faulty construction.

• Methods of Damp Prevention/Control:

  • Site selection: High ground, good drainage.

  • DPC (Damp Proof Course): Impermeable layer.

  • Waterproofing: For basements, roofs.

  • Proper detailing: Window sills, roof overhangs.

  • Ventilation: Reduces condensation.

2.2 Damp Proof Course (DPC)

• Purpose: Horizontal/vertical barrier to prevent moisture rise by capillarity.

• Materials: Bituminous felt, plastic sheets, mastic asphalt, cement concrete with waterproofing admixture.

• Types:

  • Horizontal DPC: In walls, above plinth.

  • Vertical DPC: In parapets, junctions.

  • Under-slab DPC: Below ground floor.

2.3 Efflorescence in Bricks

• Definition: White, powdery salt deposits on brick surface due to water-soluble salts.

• Classification:

  • Primary Efflorescence: Soon after construction; salts from bricks/mortar.

  • Secondary Efflorescence: Later, from external sources (soil, groundwater).

3. MASONRY CONSTRUCTION

3.1 Masonry Materials

• Stones:

  • Characteristics: Strong, durable, hard, dense, low water absorption.

  • Methods of Testing: Abrasion test, acid test (for weathering), impact test, water absorption.

  • Types Used: Granite, limestone, sandstone, laterite.

• Bricks: Efflorescence (link to 2.3).

• Hollow Concrete Blocks: Definition: Concrete blocks with hollow cores, reducing weight and improving insulation.

• Composite Masonry: Two or more materials in same wall (e.g., brick outer leaf, concrete inner leaf).

3.2 Masonry Types

3.3 Masonry Bonds

• Header Bond & Stretcher Bond Differences:

  | Feature | Header Bond | Stretcher Bond | |---------|-------------|---------------| | Brick Orientation | Header (9cm x 9cm face) | Stretcher (19cm x 9cm face) | | Use | Thick walls (1½ brick) | Thin walls (½ brick) | | Joint Pattern | Header courses every 5-6 stretcher courses | Continuous stretchers |

• Other Bonds: English Bond (alternating header/stretcher courses), Flemish Bond (alternating header/stretcher in each course).

3.4 Wall Classification

• Load-Bearing Walls: Carry vertical loads (dead, live) from floors/roof.

• Non-Load-Bearing Walls: Only partition or enclosure; do not carry structural loads.

3.5 Masonry Construction Principles

• Layout: Marking plan on ground, aligning corners.

• Bonding: Proper overlap (min ¼ brick length), vertical joints staggered.

• Levelling: Use spirit level; ensure each course is level.

• Corner Reinforcement in Masonry Walls:

  • Placement: At corners, junctions, openings.

  • Anchoring: Steel bars (6-8mm) in horizontal joints, tied to vertical bars.

  • Integration: Bars extended into adjacent walls/columns.

3.6 Seismic Masonry

• Stone Masonry Construction as per Codal Provisions (IS 1597):

  • Use rubble stone masonry with lime mortar (not cement) for flexibility.

  • Maximum wall height: Limited (e.g., 3m for single story).

  • Through stones: Long stones across wall thickness at intervals.

  • Bond stones: Every 3rd-4th course.

  • Avoid long, unsupported walls.

4. FORMWORK AND CONCRETE CONSTRUCTION

4.1 Formwork Basics

• Definition: Temporary moulds to shape and support concrete until it hardens.

• Purpose: Give shape, support weight, provide working platform.

4.2 Formwork Materials

4.3 Formwork Design Considerations

• Strength & Stability: Must withstand dead load (concrete), live load (workers, equipment), wind/seismic.

• Stiffness: Prevent excessive deflection.

• Watertightness: Prevent leakage.

• Ease of Stripping: Use release agents, tapered surfaces.

• Economy: Optimize reuse.

4.4 Formwork Types

• Stationary Formwork: Fixed in position; used for walls, columns, beams.

• Slip Form Construction:

  • Features: Continuous moving form; concrete poured and set as form rises. Used for silos, chimneys, cores. Requires continuous concreting.

4.5 Formwork Stripping & Removal

• Steps:

  1. Ensure concrete has attained required strength (usually 1.2 N/mm² for vertical members).

  2. Remove props/ties carefully.

  3. Strip forms in reverse order of installation.

  4. Clean and store for reuse.

• Safety & Efficiency: Do not shock load; use proper tools; inspect concrete; avoid damage to edges.

4.6 Construction Joints

• Need: When concreting is interrupted (end of day, equipment breakdown). To maintain integrity.

• Types (with Diagrams):

  DiagramCANVAS: Show two types: 1) Vertical joint in a wall with keyed surface; 2) Horizontal joint in a beam with shear key and starter bar

  • Vertical Joints: In walls/columns; often keyed or with shear keys.

  • Horizontal Joints: In slabs/beams; roughened surface, cleaned, with starter bars.

5. TEMPORARY STRUCTURES

5.1 Scaffolding

• Definition: Temporary platform for workers/materials at height.

• Types:

  • Single Scaffold: For brickwork (ledgers, standards, putlogs).

  • Double Scaffold: For stonework (two rows of standards).

  • Suspended Scaffold: Hung from overhead structures.

  • Steel Scaffold: Tubular steel frames.

• Ties in Construction:

  • Purpose: Secure scaffold to building, prevent sway.

  • Types: Through ties (through openings), box ties (around columns), raker ties (diagonal to ground).

5.2 Shoring and Underpinning

• Definitions:

  • Shoring: Temporary supports to prevent collapse (e.g., during excavation).

  • Underpinning: Strengthening existing foundation by extending it to deeper strata.

• Methods of Underpinning Work:

  1. Mass Concrete Underpinning: Sequential pits filled with concrete.

  2. Pile Underpinning: Install piles, connect with pile caps.

  3. Needle/Grouting: Inject grout to stabilize soil.

5.3 Prefabrication

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

• Advantages: Speed, quality control, less weather dependence, material saving.

• Disadvantages: Transportation issues, heavy lifting required, design changes difficult.

5.4 General Features of Temporary Structures

• Importance: Enable safe access, support during construction, improve efficiency.

• Types & Applications: Scaffolding (working platforms), formwork (concrete moulds), shoring (support), falsework (bridge decks), hoardings (site enclosure).

6. BUILDING SUPERSTRUCTURE COMPONENTS

6.1 Walls and Cladding

• Wall Cladding: Definition: External protective/s decorative layer. Materials: Brick, stone, metal panels, ACP, glass.

• Common Floor & Wall Finishing Materials: Marble, granite, tiles, terrazzo, plaster, paint.

6.2 Doors and Windows

• Technical Terms Used in Doors:

  • Stile: Vertical side members.

  • Rail: Horizontal members (top, bottom, lock, intermediate).

  • Leaf: Individual swinging panel.

  • Frame: Fixed structure holding leaf.

  • Threshold: Bottom member.

• Design Factors:

  • Size: Based on room function, furniture movement.

  • Location: For light, ventilation, circulation, privacy.

  • Orientation: Avoid direct wind/rain; consider sun path.

• Principles of Passive Ventilation & Natural Daylighting:

  • Cross-ventilation (opposite openings).

  • Stack effect (high-level openings).

  • Light shelves, reflective surfaces for daylight.

• Types of Windows: Casement, sliding, fixed, louvered, skylight, bay.

• Repair Techniques for Doors: Adjust hinges, replace weather stripping, repair frame, refinish surface.

6.3 Floors

• Types of Floors:

  • Ground Floor: On compacted soil, with DPC, floor finish.

  • Upper Floors: Supported by beams/joists; can be solid (concrete) or timber.

  • Special: Bengal Terrace Roof:

    DiagramCANVAS: Show layered section: brickbat concrete, lime concrete, waterproofing, tiles on slope

• Floor Finishing Materials:

  • Marble: Polished stone; durable, aesthetic.

  • Terrazzo: Marble chips in cement matrix; ground & polished.

  • Others: Tiles, wood, vinyl.

• Construction Method of Marble Flooring:

  1. Prepare sub-base (lean concrete).

  2. Apply mortar bed (1:4 cement:sand).

  3. Set marble slabs with adhesive.

  4. Grout joints.

  5. Grind & polish entire surface.

6.4 Roofs

• Introduction & Importance: Protects from weather, thermal comfort, structural element.

• Pitched Roofs:

  • Components: Rafters (sloping members), Purlins (horizontal supports to rafters), ridge, eaves, trusses.

  • Advantages: Good drainage, attic space, aesthetic.

  • Disadvantages: More material, complex construction.

  • Sketch:

    DiagramCANVAS: Simple gable roof showing rafters, purlins, ridge, eaves

• Flat/Other Roofs: Bengal Terrace Roof Construction:

  • Procedure:

    DiagramCANVAS: Layered diagram as above

    1. Flat RCC slab with slight slope.

    2. Brickbat lime concrete (1:2:4) for insulation.

    3. Lime concrete (1:2:9) for waterproofing.

    4. Tiles on mortar for finish.

6.5 Stairs and Vertical Circulation

• Essential Elements of a Stair:

  • Tread (horizontal step), Riser (vertical face), String (sloping support), Newel (end post), Baluster (vertical post), Handrail.

• Types of Stairs (with Cross-sections of Two Types):

  • Straight, L-shaped, U-shaped, Spiral, Helical.

  • Cross-sections:

    DiagramCANVAS: 1) Straight stair with tapered treads; 2) Dogleg stair with landing

• Definitions:

  • Ladders: Vertical/rungs, no treads.

  • Lifts/Elevators: Powered vertical cabins.

  • Ramps: Sloped surfaces for wheelchair access.

7. EARTHQUAKE-RESISTANT CONSTRUCTION

7.1 Importance & Planning

• Need: In seismic zones (II-V), to prevent collapse, save lives.

• Key Planning Factors:

  • Regular plan & elevation (avoid irregularities).

  • Symmetry, compactness.

  • Adequate stiffness & ductility.

  • Proper foundation-soil interaction.

7.2 Seismic Design Principles

• Base Isolation:

  • Definition: Decouple superstructure from ground motion using flexible supports.

  • Components: Isolators (elastomeric bearings), Bearings (lead-core, friction pendulum), Damping Devices (viscous dampers).

• Construction of Beams and Columns:

  • Beams: Strong column-weak beam concept; adequate confinement reinforcement (stirrups at close spacing).

  • Columns: Spiral ties or closely spaced rectangular ties; avoid slenderness; sufficient longitudinal bars.

7.3 Retrofitting

• Definition: Upgrading existing structures to meet seismic codes.

• Global vs Local Retrofitting:

  • Global: Improve overall structural system (add shear walls, braced frames).

  • Local: Strengthen specific members (jacketing columns, adding beams).

• Techniques: Jacketing (concrete/steel), FRP wrapping, adding dampers, base isolation.

7.4 Seismic Provisions for Masonry

• Stone Masonry as per Codes (IS 1597):

  • Use lime mortar (not cement) for flexibility.

  • Through stones at 600-900mm c/c.

  • Bond stones every 3rd-4th course.

  • Maximum wall height: Limited; provide buttresses for tall walls.

  • Avoid long, unsupported walls; provide ring beams at lintel level.

8. FINISHES AND SURFACE TREATMENTS

8.1 Paints

• Constituents: Pigment (color, opacity), Vehicle/Binder (holds pigment), Solvent (thinning), Additives (mildewcides, fillers).

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

• Types: Oil-based (enamel), Water-based (emulsion), Distemper, Cement paint, Alkyd, Epoxy.

8.2 Wall Finishes

• White Washing: Lime + water + glue; thin, temporary, for interior.

• Color Washing: White wash + color (organic/chemical); similar to white wash.

• Distempering: Distemper powder (chalk + glue) + water; better finish, for interior.

• Comparison:

  | Feature | White Washing | Color Washing | Distempering | |---------|---------------|---------------|--------------| | Material | White lime | Lime + color | Chalk + glue | | Finish | Rough, porous | Rough, colored | Smooth, matte | | Durability | Low | Low | Medium | | Use | Interior, temporary | Interior, colored | Interior, permanent |

8.3 Plastering and Pointing

• Plastering: Applying mortar (1:4 to 1:6 cement:sand) on walls/ceilings for smoothness.

• Pointing: Finishing exposed joints of masonry with mortar (1:3) for appearance & weather resistance.

8.4 Floor Finishes

• Common Materials (Link to 6.3): Marble, terrazzo, tiles, wood, vinyl, epoxy.

9. ADDITIONAL CONSTRUCTION TOPICS

9.1 Repair and Maintenance

• Actions for Repair Work to Regain Architectural Shape:

  • Assess damage (cracks, spalling).

  • Remove defective material.

  • Clean and prepare substrate.

  • Apply repair mortar/concrete (matching strength/color).

  • Cure properly.

  • Re-finish surface (paint, plaster).

9.2 Material Properties (Specific) – Stones

• Characteristics: Strength, durability, hardness, density, porosity, weathering resistance.

• Methods of Testing:

  • Abrasion Test: Los Angeles machine.

  • Acid Test: 1% HCl; weight loss indicates weathering.

  • Impact Test: Drop weight; measures toughness.

  • Water Absorption: Oven-dry vs saturated weight.

9.3 Other Technical Terms

• Definition of Hollow Concrete Block: Concrete masonry unit with hollow cores, typically 8-16 inches long, 4-8 inches wide, 4-16 inches high. Used for walls, partitions.

• Definition of Distempering: Application of distemper (water-based paint with chalk/glue) on walls/ceilings for a smooth, matte finish. Less durable than emulsion.

[!TIP] Exam Focus:

• Diagrams are crucial: Under-reamed pile, grillage foundation, forces on foundation, construction joints, pitched roof, Bengal terrace roof, stair cross-sections.

• Differentiate concepts: Header vs Stretcher bond, load-bearing vs non-load-bearing walls, white washing vs distempering, driven vs cast-in-situ piles.

• Link topics: Efflorescence (bricks & masonry), DPC (dampness), seismic provisions (masonry & concrete).

• Causes & Prevention: Dampness, foundation failure, frost heave.

• Classification: Piles (by material/load/installation), scaffolding, temporary structures, masonry types.