Construction Technology (CE-402) - Unit 1 Short Notes

1.0 FOUNDATIONS

1.1 Introduction & Design Considerations

• Definition & Purpose: A foundation is the lowest part of a structure that transfers loads from the superstructure to the underlying soil/rock. Its primary purpose is to distribute loads safely and prevent excessive settlement or shear failure of the supporting ground.

• Basic Requirements:

  1. Must be stable against all probable failure modes.

  2. Should limit settlement (total and differential) to safe limits.

  3. Must be rigid enough to distribute loads evenly.

• Site Investigation & Soil Analysis: Crucial for determining safe bearing capacity (SBC) of soil, soil profile, groundwater table, and selecting appropriate foundation type. SBC = Ultimate bearing capacity / Factor of Safety.

• Forces Acting on Foundations:

  • Dead Loads (DL): Self-weight of structure.

  • Live Loads (LL): Occupancy, furniture, etc.

  • Wind Loads (WL): Lateral forces.

  • Seismic Loads (EL): Earthquake forces.

  • Soil Pressure (Upward): From groundwater or heave.

  [!TIP] Exam often asks to sketch and label forces on a footing (DL, LL, WL, soil reaction).

• Causes of Foundation Failure:

  1. Shear Failure: Soil shears along a failure plane.

  2. Settlement Failure: Excessive consolidation or compression.

  3. Sliding Failure: Due to lateral forces (e.g., on slopes).

  4. Piping/Boiling: Erosion of soil by seepage water.

1.2 Shallow Foundations

• Definition: Foundations where depth (D) < width (B) or D ≤ 2-3m. Used when good bearing soil is near surface.

• Types with Sketches:

  1. Isolated Footing: Under a single column. Can be square, rectangular, or circular.

  2. Combined Footing: Under two or more columns. Used when columns are close or property line restricts isolated footing. Rectangular or trapezoidal in plan.

     • Design Feature: Must have center of gravity of loads coincide with center of gravity of footing to ensure uniform pressure.

  3. Strip Footing: Under a line of columns (e.g., load-bearing walls).

  4. Raft/Mat Foundation: A large, continuous slab covering the entire building footprint. Used when SBC is very low or loads are heavy.

     • Advantage: Reduces differential settlement, resists uplift.

• [!DIAGRAM] Search: "isolated footing plan and section", "combined footing trapezoidal", "raft foundation layout".

1.3 Deep Foundations

• Purpose: Transfer loads through weak/compressible soil to a stronger stratum at depth. Used when SBC is low, for heavy structures, or for uplift resistance.

• Classification:

  • By Material: Timber, Steel, Concrete (RCC, Precast).

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

  • By Installation Method:

    1. Driven Piles: Prefabricated, driven by hammer/vibrator. Displacement piles.

    2. Bored/Drilled Piles: Cast-in-situ. Non-displacement. Includes bored cast-in-situ, bored pre-cast.

    3. Screw Piles: Helical plates.

• Under-reamed Piles: Special bored piles with bulbs (under-reams) at the end of the shaft. Used in expansive soils (like black cotton soil) to resist uplift/swelling pressure.

  [!DIAGRAM] Search: "under-reamed pile sketch bulb".

• Advantages of Pile Foundations:

  • High load capacity.

  • Suitable for weak soils.

  • Resists lateral and uplift forces.

  • Can be installed in water.

• Disadvantages:

  • High cost.

  • Requires skilled supervision.

  • Noise/vibration (driven piles).

  • Difficult to inspect (cast-in-situ).

1.4 Special Foundations

• Caisson Foundation:

  • Definition: A watertight, retaining structure (usually RCC) constructed in situ, sunk by excavation inside it. Used for deep foundations in water or soft soil.

  • Types:

    1. Open Caisson: Open at top and bottom. Sunk by excavating inside.

    2. Pneumatic Caisson: Compressed air keeps water out. Workers work in dry chamber.

    3. Box Caisson: Prefabricated, closed at bottom, sunk by filling with ballast.

• Well Foundation:

  • Definition: A large-diameter, open-bottom, sinking structure, typically cylindrical (or double-D). Used for major bridges, docks, heavy waterfront structures.

  • Well-Shaped Foundation: Usually circular for uniform sinking resistance, but double-D or octagonal also used.

  • Elements/Parts:

    1. Well Curb: Bottom cutting edge (usually steel).

    2. Well Steining: Vertical wall (brick/RCC).

    3. Bottom Plug: Seals bottom after sinking.

    4. Top Plug: Supports pier/column.

    5. Sand Filling: Between plugs.

• Grillage Foundation:

  • Definition: A layered system of steel beams (I-sections) embedded in concrete, used to distribute heavy column loads to a larger area of soil. Acts as a flexible footing.

  • Types: Single-layer or multi-layer grillage.

  • Uses: For heavy columns (e.g., trestle, gantry, bridge piers) where a spread footing would be too large.

  [!DIAGRAM] Search: "well foundation parts diagram", "grillage foundation steel beams".

1.5 Foundation on Special Soils

• Causes of Frost Heave:

  1. Freezing of Water in Soil Pores: Water expands ~9% on freezing, causing upward movement.

  2. Ice Lens Formation: Water migrates to freezing front via capillary action, forming ice layers.

  3. Sensitive Soils: Silty sands, silts, clays with high water table are most susceptible.

• Precautions for Bearing Piles on Rock Surfaces:

  • Driven Piles:

    1. Driving to Refusal: Pile must be driven until very few blows per inch (e.g., <10 blows for last 25mm).

    2. Check for Rock: Confirm rock stratum by boreholes or test piles.

    3. Use of Pile Cap: To distribute load and prevent local crushing.

  • Cast-in-situ Piles:

    1. Boring Through Overburden: Use temporary casing to prevent caving.

    2. Cleaning Base: Remove all loose material, debris, and water from rock surface before concreting.

    3. Roughening Rock Surface: For better bond, rock may be roughened or grooved.

    4. Use of Rich Concrete: M20 or higher grade concrete at base for better contact.

2.0 FORMWORK (SHUTTERING) FOR CONCRETE

2.1 Introduction & Importance

• Definition: Temporary moulds to shape and support fresh concrete until it hardens and gains sufficient strength.

• Purpose: Gives desired shape, size, and finish to concrete member. Must be strong, rigid, and economical.

• Materials:

  • Timber: Most common, reusable but less durable.

  • Steel: Durable, strong, smooth finish, reusable 100+ times.

  • Plastic/FRP: Lightweight, corrosion-proof, good finish.

  • Aluminum: Lightweight, good for repetitive work.

2.2 Types & Techniques

• Stationary Formwork: Fixed in position until concrete hardens. Used for most building components (beams, columns, walls).

• Slip Form Construction:

  • Definition: A continuous moving formwork where concrete is poured continuously and the form is raised vertically as concrete sets.

  • Features:

    1. Continuous Operation: No construction joints.

    2. Hydraulic Jacks: Used to lift the form.

    3. High Speed: Suitable for towers, silos, cores.

    4. Requires: Careful concrete mix design, vibration, and supervision.

• Comparison:

  | Feature | Stationary Formwork | Slip Formwork | | :--- | :--- | :--- | | Joints | Construction joints every lift | No vertical joints (continuous) | | Speed | Slower (cycle time) | Very fast | | Labor | More (assembly/disassembly) | Less (continuous) | | Finish | Good (if good form) | Excellent (smooth, uniform) | | Suitability | General buildings | Towers, cores, tanks |

2.3 Design & Material Considerations

• Design Considerations:

  1. Loads: Dead load (concrete + formwork), Live load (workers, equipment), Impact/Vibration.

  2. Stability: Against overturning, bulging, buckling.

  3. Ease of Stripping: Should be easy to dismantle without damage.

  4. Joint Tightness: Prevent leakage (grout loss).

  5. Surface Finish: Material choice affects concrete finish.

• Steel vs. Timber Formwork:

  | Merits of Steel | Demerits of Steel | | :--- | :--- | | High strength & stiffness | High initial cost | | Reusable 100+ times | Heavy, needs crane | | Smooth, durable finish | Can rust if not maintained | | Resistant to fire/termite | Storage space needed | | Uniform size possible | |

• Plastic Formwork:

  • Applications: Complex shapes, curved surfaces, architectural concrete.

  • Advantages: Lightweight, corrosion-proof, excellent finish, easy handling.

  • Limitations: Lower strength than steel, can deform under high pressure, limited reuse (~50-100 times).

2.4 Stripping & Removal

• Steps:

  1. Check Concrete Strength: Must reach minimum stripping strength (usually > 1.2 N/mm² for vertical forms, > 70% design strength for beams/slabs).

  2. Remove Props/Supports: Start from top for slabs, sides for beams.

  3. Dismantle in Reverse Order: Of assembly. Do not pry against concrete.

  4. Clean & Repair: Immediately clean forms, repair damages, apply release agent for next use.

• Safety & Efficiency:

  • Safety: Use proper wedges, avoid dropping forms, guard edges.

  • Efficiency: Sequence stripping to avoid overloading remaining props. Inspect forms before reuse.

3.0 MASONRY

3.1 General Principles & Construction

• Principles: Level, Plumb, Uniform Joints, Proper Bonding.

• Procedures:

  1. Layout: Establish reference lines and benchmarks.

  2. Bonding: Overlap of bricks in successive courses to tie the wall together.

  3. Levelling: Use spirit level for each course.

• Essential Elements: Headers, Stretchers, Bed Joints, Perpends, Arches, Lintels.

3.2 Types of Masonry

• Brick Masonry:

  • Types of Bricks: Common Burnt Clay, Fly Ash Clay, Concrete, Sand-lime, Engineering.

  • Efflorescence: White, powdery deposit of soluble salts on brick surface.

    • Cause: Water dissolves salts in brick/mortar; evaporation leaves salts.

    • Classification (IS 3495):

      • Slight (10% area): Minor, acceptable.

      • Moderate (50% area): Noticeable.

      • Heavy (>50% area): Significant, unacceptable.

      • Severe (with powdering/flaking): Very serious.

• Stone Masonry:

  • Characteristics of Stones: Hard, Durable, Tough, Fire-resistant, Low porosity.

  • Methods of Testing: Abrasion, Impact, Acid, Water Absorption, Freezing & Thawing.

  • Types of Stones: Granite, Basalt, Limestone, Sandstone, Marble, Slate.

• Rubble Masonry: Stones not dressed. Coursed (layers) or Uncoursed (random).

• Ashlar Masonry: Stones finely dressed (smooth faces). Ashlar fine, Ashlar rough, Ashlar chamfered.

• Composite Masonry: Two different materials combined, e.g., brick back-up with stone facing.

3.3 Bonds in Brickwork

• Header Bond: Headers (brick ends) visible on face. Every course is headers. Used for thick walls (>1.5 bricks). Stronger in transverse direction.

• Stretcher Bond: Stretchers (long faces) visible on face. Every alternate course has headers. Used for half-brick thick walls (partition). Most common.

• [!TIP] Header bond requires more bricks and is for thicker walls; Stretcher bond for thin walls.

3.4 Special Construction Features

• Corner Reinforcement in Earthquake Zones:

  • Vertical Bars: 2-4 bars (10-12mm dia) in both faces of wall at corners, extending from footing to roof.

  • Horizontal Bars: 2 bars (6-8mm) at every lintel/sill level and every 1-2m vertically.

  • Anchorage: Bars must be anchored into columns/cores with hooks.

• Seismic Stone Masonry (Codal):

  • IS 15971 (2007): Use dressed stones, through stones every 0.5-1m, limestone/dolomite mortar, no rounded boulders, max stone size 300mm.

  • Bands: Reinforced concrete bands at lintel, sill, roof levels.

• Construction Joints:

  • Need: When concreting is interrupted (end of day, equipment breakdown). Prevents cold joints (weak planes).

  • Types:

    1. Vertical Joint (Longitudinal): Along length.

    2. Horizontal Joint (Transverse): Across width.

  • Provision: Keyed or shear key to transfer shear.

4.0 BUILDING ELEMENTS & COMPONENTS

4.1 Stairs, Ladders & Ramps

• Essential Elements of Stair:

  1. Tread: Horizontal step surface.

  2. Riser: Vertical distance between treads.

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

  4. Waist/Slab: Slab supporting the stair.

  5. Newel Post: Vertical post at ends/landing.

  6. Baluster/Handrail: Safety support.

• Types of Stairs (with Cross-sections):

  1. Straight Run: Single flight. Cross-section: Rectangular.

  2. Dog-legged: Two flights with 180° turn. Cross-section: L-shaped.

  3. Quarter-turn: 90° turn.

  4. Spiral/Circular: Around a central newel.

• Definitions:

  • Ladder: Inclined, vertical-rung structure for short vertical access (e.g., loft). No treads.

  • Lift/Elevator: Powered, enclosed cabin for vertical transport of people/goods.

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

4.2 Doors, Windows & Ventilators

• Technical Terms in Doors:

  • Leaf: The swinging panel.

  • Frame: Fixed structure holding leaf.

  • Stile: Vertical edge of leaf.

  • Rail: Horizontal edge of leaf (top, bottom, lock, meeting).

  • Casing/Architrave: Trim around frame.

  • Sill/Threshold: Bottom member.

  • Lintel/Head: Top member.

• Factors for Size/Location/Orientation:

  1. Function: Privacy, light, ventilation.

  2. Room Size & Furniture: Clear opening for movement.

  3. Orientation: Windows on windward side for ventilation; doors for access.

  4. Daylighting: Windows placed to maximize natural light (north for uniform light in northern hemisphere).

  5. Privacy: Bedrooms/bathrooms away from public view.

• Principles of Passive Ventilation & Daylighting:

  • Cross-Ventilation: Inlet (low) & outlet (high) openings on opposite walls.

  • Stack Effect: Warm air rises, exits high openings, drawing in cool air from low openings.

  • Daylighting: Window-to-wall ratio, sill height, glazing type.

• Factors for Selection of Windows:

  1. Climate: Ventilation needs.

  2. View & Aesthetics.

  3. Security.

  4. Maintenance.

• Types of Windows: Fixed, Sliding, Casement, Awning, Hopper, Bay, Dormer.

• Repair Techniques for Doors:

  1. Binding/Sticking: Plane edges, check hinges.

  2. Sagging: Adjust/replace hinges, add support.

  3. Drafty/Draughty: Add weatherstripping, adjust latch.

  4. Damaged Finish: Scrape, sand, refinish.

4.3 Floors & Flooring

• Definitions:

  • Floor Finish: Topmost layer (e.g., tile, wood, marble) providing wearing surface.

  • Wall Cladding: External/internal facing (e.g., stone, brick veneer) for protection/aesthetics.

• Common Floor Finishing Materials: Marble, Granite, Terrazzo, Wood, Vinyl, Ceramic Tile, Concrete, Brick.

• Types of Floors:

  1. Ground Floor: On soil (requires subgrade preparation).

  2. Upper Floor: Supported on beams/joists.

  3. Suspended Floor: Not on ground (air gap below).

  4. Floating Floor: Not bonded to subfloor (acoustic).

• Characteristics of Ground Floorings:

  | Material | Advantages | Limitations | | :--- | :--- | :--- | | Brick | Cheap, durable | Hard, uneven | | Concrete | Strong, cheap | Rough, cold | | Marble | Aesthetic, durable | Expensive, slippery | | Terrazzo | Durable, seamless | Skilled labor, costly |

• Construction Method:

  • Marble Flooring:

    1. Prepare screed bed (1:4 cement:sand).

    2. Apply mortar bed (1:3) for bonding.

    3. Lay marble slabs with wet mortar or adhesive.

    4. Grout joints, polish surface.

  • Terrazzo Flooring:

    1. Underbed: Concrete slab.

    2. Divider strips: Metal/plastic to create panels.

    3. Place terrazzo mix (marble chips + cement/marble dust).

    4. Grind & polish after curing (using terrazzo grinder).

4.4 Roofs

• Importance: Provides shelter, weatherproofing, insulation, structural top.

• Pitched Roof:

  • Definition: Sloping roof (slope > 10°).

  • Sketch: Show common rafters (inclined members), purlins (horizontal supports on rafters), roof covering (tiles, sheets).

  • Advantages: Good drainage, attic space, aesthetic.

  • Disadvantages: More material & labor, complex geometry.

• Bengal Terrace Roof:

  • Construction Procedure:

    1. Brick Edges (Kani): Around periphery.

    2. Brick Flat Arches: On main beams/joists.

    3. Brickwork in CM 1:6: Over arches in diagonal pattern.

    4. Lime Concrete (1:2:3): Over brickwork, sloped for drainage.

    5. Terracing: Brickbat + lime mortar or concrete for waterproofing.

  [!DIAGRAM] Search: "Bengal terrace roof construction section".

• Technical Terms:

  • Common Rafters: Inclined members supporting roof covering.

  • Purlins: Horizontal members on rafters, supporting roofing sheets/tiles.

5.0 DAMPNESS, EFFLORESCENCE & PREVENTION

5.1 Dampness in Buildings

• Definition: Unwanted moisture in building structure or interior.

• Effects:

  • Health: Mold, fungi, respiratory problems.

  • Structure: Corrosion of steel, spalling of concrete, decay of timber.

  • Aesthetics: Staining, peeling paint, efflorescence.

  • Insulation: Reduces thermal resistance.

• Causes:

  1. Rain Penetration: Defective roof, parapet, joints.

  2. Capillary Action: From ground (rising damp).

  3. Condensation: Warm moist air on cold surfaces.

  4. Leakage: Pipes, tanks, drains.

  5. Construction Moisture: In new concrete/mortar.

• Methods of Damp Prevention (Damp Proofing):

  1. Damp Proof Course (DPC): Horizontal/vertical barrier.

  2. Waterproofing: Membranes, coatings (for roofs, tanks).

  3. Cavity Walls: Air gap prevents moisture transfer.

  4. Grading & Drains: Slope away from building, gutters.

  5. Ventilation: Reduce condensation.

• Damp Proof Course (DPC):

  • Definition: Continuous layer of impervious material in walls/floors to stop capillary rise.

  • Types:

    1. Horizontal DPC: At plinth level, window sills.

    2. Vertical DPC: At external wall junctions, around pipes.

    3. Materials: Bituminous felt, HDPE sheet, Mastic asphalt, Cement concrete (1:2:4) with waterproofing admixture.

5.2 Efflorescence in Bricks

• Meaning: White, crystalline salt deposits on brick/mortar surface due to migration of soluble salts.

• Classification (IS 3495): Same as in 3.2: Slight, Moderate, Heavy, Severe.

6.0 EARTHQUAKE-RESISTANT CONSTRUCTION

6.1 Planning & Design Principles

• Importance: Life safety in seismic zones (India: Zones II-V). Prevents sudden collapse.

• Key Planning Factors:

  1. Symmetry & Regularity: Simple, symmetric plan & elevation. Avoid re-entrant corners (L, T, U shapes).

  2. Aspect Ratio: Height-to-width ratio should be limited.

  3. Torsional Resistance: Center of mass ≈ center of stiffness.

  4. Soft Stories: Avoid large openings/openings at ground floor (parking).

  5. Ductility: Design for energy dissipation.

• How Protection is Achieved:

  1. Proper Sizing & Detailing of members.

  2. Adequate Connections (beam-column, wall-roof).

  3. Use of Ductile Materials (steel, reinforced concrete).

  4. Base Isolation or Energy Dissipating Devices.

6.2 Construction Techniques & Details

• Beams & Columns:

  • Columns: Tie all longitudinal bars with lateral ties (stirrups) at max 150mm c/c in end 1/4 length. Closed ties with 135° hooks.

  • Beams: Reinforcement should be anchored into columns. Stirrups throughout, closer at ends.

• Base Isolation:

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

  • Purpose: Increase fundamental period, reduce acceleration transmitted to structure.

  • Components:

    1. Isolators: Lead-rubber bearings (LRB), Friction Pendulum bearings (FPB).

    2. Bearings: Support vertical loads, allow horizontal displacement.

    3. Damping Devices: Viscous dampers to absorb energy.

  • Construction: Isolators placed between foundation and superstructure. Requires special detailing for utility connections.

6.3 Retrofitting

• Definition: Modification/upgrading of existing structure to meet current code/seismic demands.

• Global Retrofitting: Entire structure upgraded (e.g., adding shear walls, braced frames).

• Local Retrofitting: Specific elements strengthened (e.g., column jacketing, beam strengthening, foundation underpinning).

• Repair Actions for Architectural Shape:

  1. Assess Damage.

  2. Remove damaged material.

  3. Reinforce with steel plates, FRP wraps, or concrete jackets.

  4. Restore original shape using formwork and patch repair.

7.0 TEMPORARY CONSTRUCTION & STRUCTURES

7.1 Introduction & Importance

• Purpose: Support construction activities until permanent structure is complete.

• Importance: Worker safety, access, material storage, stability during construction.

7.2 Types with Sketches & Features

• Scaffolding:

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

  • Types:

    1. Single Scaffolding: One row of standards, putlogs in wall. For masonry.

    2. Double Scaffolding: Two rows of standards, independent. For painting, repairs.

    3. Steel Scaffolding: Tube & clamp or modular systems. Strong, reusable.

    4. Suspended Scaffolding: Hanging from roof/beam. For façade work.

  [!DIAGRAM] Search: "single scaffolding sketch", "double scaffolding sketch".

• Shoring:

  • Definition: Temporary supports to prevent collapse of unsafe structure or during excavation.

  • Types: Raking, Flying, Dead, Hydraulic.

• Underpinning:

  • Definition: Strengthening/repairing foundation of existing building by extending depth or replacing it.

  • Methods:

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

    2. Pile Underpinning: Piles installed alongside/under existing footing.

    3. Jack Underpinning: Hydraulic jacks lift structure while new foundation built.

    4. Needle/Grouting: Needle beams support wall, grout below.

• Construction Features:

  • Stability: Base width ≥ 1/4 height, tied to structure.

  • Load Capacity: Designed for live + dead loads.

  • Access: Safe ladders/stairs.

  • Inspection: Daily checks.

8.0 BUILDING MATERIALS (SPECIFIC TOPICS)

8.1 Paints

• Constituents:

  1. Pigment: Provides color & opacity (e.g., TiO₂, ochre).

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

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

  4. Filler/Extender: Bulk, texture (e.g., whiting, talc).

  5. Additives: Driers, anti-fungals, UV stabilizers.

• Desirable Properties:

  • Good coverage, durability, adhesion.

  • Resistant to weathering, cracking, peeling.

  • Easy application, quick drying.

  • Aesthetic appeal, color retention.

• Types of Paints:

  • Oil Paints: Linseed oil binder. Durable, glossy.

  • Water Paints (Distempers): Emulsion binder. Cheap, matte.

  • Cement Paints: Cement binder. For masonry.

  • Enamels: Varnish binder. Hard, glossy.

  • Bituminous Paints: Bitumen binder. For corrosion protection.

  • Synthetic Resin Paints: Polyurethane, epoxy. High performance.

8.2 Surface Finishes for Masonry Walls

• White Washing: Lime + water (sometimes chuna). Temporary, cheap, for interior/exterior. 2-3 coats.

• Colour Washing: White wash + pigment. Slightly more durable.

• Distempering: Binder (glue, casein) + chalk + pigment. Better finish than white wash, for interior.

• Plastering: Mortar (cement/lime/sand) applied to masonry for smooth, protective surface.

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

8.3 Bricks & Blocks

• Efflorescence: Covered in 5.2.

• Hollow Concrete Blocks:

  • Definition: Concrete blocks with cavities (holes). Lightweight, good insulation.

  • Advantages: Faster construction, less mortar, thermal/sound insulation.

  • Uses: Partition walls, infill walls.

9.0 PREFABRICATION & MODERN METHODS

• Definition: Manufacturing building components (walls, slabs, rooms) in factory under controlled conditions, then transporting & assembling on site.

• Advantages:

  • Speed: Parallel work, faster completion.

  • Quality: Controlled environment, better finish.

  • Less Waste: Precise cutting.

  • Weather Independent.

  • Less Site Labor.

• Disadvantages:

  • High Initial Cost: Factory, molds, transport.

  • Transport Limitations: Size/weight restrictions.

  • Design Rigidity: Changes difficult after production.

  • Skilled Assembly Required: Precise alignment.

  • Storage Space on site needed.