Viva Voce Questions – Architectural Building Construction and Materials

1. Prestressing Concepts & Systems

1. Differentiate between reinforcement bars (rebar) and tendons used in structural systems.
2. Explain the method of anchoring and application of tensile force in tendons for:
   • Pre-tensioning system
   • Post-tensioning system
3. What is the role of tendon ducts in a post-tensioning system?
4. How are tendons protected after the application of tension to ensure long-term retention of prestress?
5. Define and explain:
   • Prestressed concrete
   • Pre-tensioning
   • Post-tensioning

2. Concrete Materials & Composite Systems

1. Differentiate between ferrocement and reinforced cement concrete (RCC) in terms of composition, behavior, and applications.
2. What are the minimum and maximum thickness limits of ferrocement elements?
   How do these differ from typical RCC sections?

3. Precast Construction & Structural Connections

1. Give practical examples of precast post-tensioned structures in everyday life.
2. Explain the connection detail for fixing a precast beam over a precast column.

4. Glazing & Building Materials

1. Which types of glass are suitable for soundproofing applications? Explain their properties.
2. What type of rubber is used in dry glazing systems? State its function.
3. What type of silicone is used in wet glazing systems? Mention its properties and applications.

Viva Voce Answer

1. Prestressing Concepts & Systems

Prestressing improves load capacity, crack resistance, and span efficiency by introducing pre-compression in concrete.

Q1. Difference between Rebar and Tendon

Aspect	Rebar (Reinforcement Bar)	Tendon
Function	Resists tensile stress after cracking	Applies compressive force to concrete
Material	Mild steel / High-Yield Strength Deformed (HYSD) bars	High tensile steel strands/wires
Usage	RCC structures	Prestressed concrete
Stress condition	Passive (no initial stress) It only takes up stress once the concrete begins to deflect or crack under load.	Active (pre-applied stress) It is intentionally stressed to induce permanent compression in the concrete before service loads are applied.
Timing	Acts after load is applied	Stressed before or after casting
Surface	Usually ribbed or deformed to improve bonding with concrete.	Can be smooth wires, twisted strands, or threaded bars.
Strength	Lower yield strength (typically 250–500 MPa).	Much higher ultimate strength (typically 1500–1800 MPa).

Key Point:
Rebar is passive reinforcement, while tendon is active reinforcement.

Q2. Anchoring & Application of Tensile Force

(a) Pre-Tensioning System

• Steel tendons are stretched before concrete is cast.
• Anchored at external abutments (fixed supports).
• Concrete is poured around stretched tendons.
• After gaining strength, tendons are released, transferring stress to concrete via bond.

Example: Precast beams, Railway sleepers.

(b) Post-Tensioning System

• Tendons are placed inside ducts within concrete.
• After concrete hardens, tendons are stressed using hydraulic jacks.
• Force is locked using anchorage devices (anchor heads + wedges).

Key Difference:

• Pre-tension → stress transferred by bond
• Post-tension → stress held by anchorage system

Q3. Role of Tendon Ducts in Post-Tensioning

• Provide path/space for tendon placement
• Prevent direct bonding with concrete (in unbonded system)
• Allow movement during stressing
• Facilitate grouting (in bonded system)
• Protect tendon from corrosion

Q4. Protection of Tendons After Tensioning

To ensure stress is not lost:

• Grouting (cement slurry): fills ducts → prevents corrosion + bonds tendon
• Grease + sheathing (in unbonded systems): acts as protective layer
• Anchorage sealing: caps to protect exposed ends
• Corrosion-resistant materials: HDPE sheathing, epoxy coating

Goal: Prevent corrosion + slippage, ensuring long-term prestress retention.

Q5. Definitions

Prestressed Concrete

Concrete in which internal compressive stresses are induced before external loads, to counteract tensile stresses.

Pre-Tensioning

• Tendons are stressed before casting concrete
• Stress transferred through bond

Post-Tensioning

• Tendons are stressed after concrete hardens
• Stress transferred through anchorage system

2. Concrete Materials & Composite Systems

Ferrocement is ideal for thin shell structures, whereas RCC is used for heavy load-bearing structural elements.

Q1. Difference between Ferrocement and Reinforced Cement Concrete (RCC)

Aspect	Ferrocement	RCC (Reinforced Cement Concrete)
Composition	Cement mortar + closely spaced wire mesh	Concrete (cement + sand + aggregate) + steel bars
Reinforcement	Fine wire mesh (chicken mesh, welded mesh)	Steel rebars (main bars + stirrups)
Thickness	Very thin sections	Comparatively thicker sections
Strength behavior	High tensile resistance due to mesh distribution	High compressive strength, tensile handled by rebars
Weight	Lightweight	Heavier
Construction	No need for heavy formwork	Requires proper shuttering/formwork
Crack control	Better crack distribution (fine cracks)	Cracks are wider but fewer
Applications	Water tanks, shells, boats, roofing panels	Beams, columns, slabs, foundations

Key Point:
Ferrocement is a thin, lightweight composite, while RCC is a conventional structural material for load-bearing elements.

Q2. Thickness of Ferrocement vs RCC

Ferrocement Thickness

• Minimum: ~10 mm
• Maximum: ~40–50 mm

(Depends on number of mesh layers and application)

RCC Thickness (Typical Ranges)

• Slabs: 100 mm – 200 mm
• Beams: 230 mm and above
• Columns: 230 mm and above

Difference in Thickness Behavior

• Ferrocement:
  • Thin sections possible due to uniform distribution of reinforcement
  • Suitable for lightweight and curved forms
• RCC:
  • Requires greater thickness for strength and cover to reinforcement
  • Used for primary structural members

Key Concept Explanation

• Ferrocement behaves like a composite material with distributed reinforcement, giving:
  • Better crack control
  • High surface strength
• RCC behaves like a frame structural system, where:
  • Concrete resists compression
  • Steel bars resist tension

3. Precast Construction & Structural Connections

Precast connections must ensure load transfer, stability, and ease of erection, while accommodating tolerances and movement.

Q1. Examples of Precast Post-Tensioned Structures in Everyday Life

Common Examples:

• Precast bridge girders (flyovers, highway bridges)
• Metro rail viaduct segments
• Parking structures (multi-level parking slabs)
• Precast floor slabs in commercial buildings
• Railway sleepers (mostly pre-tensioned, but concept related)

Key Idea:
Precast + prestressing allows long spans, faster construction, and better quality control.

Q2. Connection Detail: Fixing Precast Beam over Precast Column

Common Methods:

1. Bearing Connection (Simple Support)

• Beam rests on column corbel / bracket
• Neoprene / rubber pad provided for:
  • Load distribution
  • Vibration absorption

Sketch idea:
Draw column → small projection (corbel) → beam resting on pad.

2. Dowel Bar Connection

• Steel dowel bars project from column
• Matching holes in beam
• Filled with grout after placement

Purpose: Prevents lateral movement.

3. Pocket / Socket Connection

• Beam end inserted into pocket in column
• Gap filled with non-shrink grout

4. Welded Connection (Steel Plate)

• Embedded steel plates in beam & column
• Plates are welded on site

5. Post-Tensioned Connection

• Tendons pass through beam-column joint
• Stressed after erection → creates rigid connection

4. Glazing & Building Materials

Dry glazing uses rubber gaskets (EPDM), while wet glazing uses structural silicone sealants like DOWSIL 995 Silicone Structural Sealant for bonding and sealing.

Q1. Which types of glass are suitable for soundproofing? Explain.

Types of Soundproof Glass:

• Laminated Glass (Acoustic Glass)
• Double Glazed Units (DGU / Insulated Glass Units)
• Triple Glazing (for high-performance spaces)

Explanation:

• Laminated Glass:
  • Consists of two or more glass layers with PVB (Polyvinyl Butyral) interlayer
  • The interlayer absorbs sound vibrations, reducing noise transmission
• Double Glazing:
  • Two glass panes separated by air or gas gap
  • The gap acts as a sound barrier
• Best Performance:
  Combination of laminated + double glazing

Applications: Studios, hospitals, conference rooms, buildings near highways/airports

Q2. Type of Rubber Used in Dry Glazing

Material Used:

• EPDM Rubber (Ethylene Propylene Diene Monomer)

Function:

• Acts as a gasket between glass and frame
• Provides:
  • Airtight seal
  • Watertight seal
  • Shock absorption
  • Prevents glass-to-metal contact

Key Property:
Weather-resistant, flexible, durable

Q3. Type of Silicone Used in Wet Glazing

Material Used:

• Structural Silicone Sealant like DOWSIL 995 Silicone
• (Usually neutral cure silicone)

Properties:

• High adhesion strength
• Flexible (accommodates movement)
• Resistant to UV, weather, and temperature
• Long-lasting durability

Function:

• Bonds glass to frame
• Acts as sealant + structural support (in structural glazing systems)

Difference: Dry Glazing vs Wet Glazing

Aspect	Dry Glazing	Wet Glazing
Material	Rubber gaskets (EPDM)	Silicone sealant
Method	Mechanical fixing	Chemical bonding
Installation	Faster, cleaner	Requires curing time
Flexibility	Replaceable	Permanent fixing
Usage	Windows, curtain walls	Structural glazing