(SEM V) THEORY EXAMINATION 2022-23 ADVANCED CONCRETE DESIGN

ADVANCED CONCRETE DESIGN (KCE073)

B.Tech SEM V – Complete Solved Question Paper (2022–23)

SECTION A

Attempt all questions in brief (2 × 10 = 20 Marks)

(a) Important factors considered while designing an RCC tank

While designing an RCC tank, the important factors include type of tank (ground, underground, or elevated), capacity of storage, water pressure, crack control, impermeability, durability, exposure conditions, seismic effects, and construction method.

(b) Define conical dome

A conical dome is a sloping roof structure shaped like a cone, generally provided at the bottom of tanks such as Intze tanks to facilitate easy drainage and reduce bending stresses.

(c) Define sliding joint with figure for tanks

A sliding joint is a flexible joint provided between the tank wall and base slab to allow free movement due to temperature variation and settlement, thereby reducing stress concentration.
(👉 In exam, draw neat sketch showing wall, base slab, and sliding joint)

(d) Loads acting on bottom conical dome in Intze tank

The loads include self-weight of the dome, hydrostatic pressure of water, load from cylindrical wall, and sometimes live load during maintenance.

(e) IS 3370:2009 (Part 2) – where it is used?

IS 3370:2009 (Part 2) is used for design of reinforced concrete structures for storage of liquids, particularly for stress and strength considerations.

(f) Define circular prestressing

Circular prestressing is a method in which prestressing force is applied circumferentially in circular tanks to counteract hoop tension caused by water pressure.

(g) What is load balancing concept?

Load balancing is a prestressing concept in which the prestressing force counteracts the applied external loads, thereby reducing bending moments and tensile stresses in concrete.

(h) Why high-strength concrete is needed for prestressing?

High-strength concrete is required because prestressing induces high compressive stresses, and stronger concrete helps resist cracking, creep, and long-term losses.

(i) Types of tensioning devices used in prestressed concrete

The devices include hydraulic jacks, wedges, anchorage blocks, and stressing heads.

(j) Advantages of prestressed concrete

Prestressed concrete provides higher load-carrying capacity, reduced cracking, longer span lengths, improved durability, and economical use of materials.

SECTION B

Attempt any THREE (10 × 3 = 30 Marks)

(a) Design of circular tank with flexible base (Outline Answer)

Given capacity = 10,00,000 litres (1000 m³)                       Depth of water = 6 m
Concrete = M25, Steel = Fe415

Steps:                                                                                  Calculate diameter using volume formula

Determine hoop tension due to water pressure                Design circumferential reinforcement

Provide minimum vertical reinforcement                           Check crack width as per IS 3370

Draw neat sketch showing tank wall and flexible base

( In exam, show step-wise calculations and sketch)

(b) Design of spherical cover dome and ring girder (Outline)

Given diameter = 6 m, rise = 1 m

Steps:                                                                                   Calculate radius of dome

Compute dead load and live load                                       Determine meridional thrust

Design thickness of dome                                                   Design ring girder for hoop tension

( Always draw dome and ring girder sketch)

(c) Loss of prestress due to elastic shortening

In pretensioned members, elastic shortening causes loss in all tendons simultaneously.
In post-tensioned members, loss is smaller because tendons are stressed sequentially.
Hence, elastic shortening loss is more significant in pretensioned members.

(d) Short notes

(i) Freyssinet System of Prestressing
It uses high-tensile steel wires anchored by conical wedges and applies prestress using hydraulic jacks.

(ii) Losses in prestress
Losses occur due to elastic shortening, creep, shrinkage, relaxation of steel, friction, and anchorage slip.

(e) Pretensioned beam loss calculation (Conceptual Answer)

Losses considered:                                                            Elastic shortening

Creep                                                                                Shrinkage

Relaxation

Using IS 1343:1980 formulas, calculate individual losses and sum them to obtain total prestress loss.

( In exam, write formulas clearly and show substitutions)

SECTION C

Q3

(a) Definitions for elevated water tank components

Top Dome: Roof structure protecting water from contamination
Top Ring Beam: Circular beam supporting dome and resisting horizontal thrust
Cylindrical Wall: Vertical wall storing water and resisting hoop tension

(b) Design of rectangular water tank (Approximate method)

Tank size = 2 m × 5 m × 3 m

Steps:                                                                                   Calculate water pressure on walls

Design long and short walls                                                Provide base slab reinforcement

Check crack control                                                             Draw plan and section

Q4

(a) Factors considered while designing RCC tank

Factors include water tightness, crack control, durability, exposure condition, temperature effects, and construction joints.

(b) Conditions for underground tank wall design

Walls are designed considering earth pressure, water pressure, uplift pressure, and combination of soil-water interaction.

Q5

(a) Prestressing transforming concrete into elastic material

Prestressing introduces compressive stress in concrete, preventing tensile cracking and making concrete behave elastically even under service loads.

(b) Percentage loss of prestress (Outline)

Losses due to creep, shrinkage, and relaxation are calculated using standard IS formulas, and percentage loss is obtained by dividing total loss by initial prestress.

Q6

(a) Stress distribution in prestressed beam

At initial stage, stresses are due to prestress only.
At final stage, stresses are due to prestress plus external loads.
( Draw stress diagrams at top and bottom fibres)

(b) Maximum bending moment without tension

Condition: No tension at soffit
Use stress equation:
σ = P/A ± M/Z
Solve for M when tensile stress = 0.

Q7

(a) Methods of post-tensioning

Methods include Freyssinet system, Magnel-Blaton system, Gifford-Udall system, and Lee-McCall system.

(b) Loss of stress due to friction in parabolic tendon

Loss is calculated using formula:
σx = σ₀ e⁻(µθ + kx)
Substitute given values to find stress loss at mid-span.