(SEM VII) THEORY EXAMINATION 2021-22 ADVANCED CONCRETE DESIGN

Below are section-wise answers (A, B, C) for Advanced Concrete Design (KCE-073), written in simple, exam-oriented language, strictly according to your uploaded question paper 

ADVANCED-CONCRETE-DESIGN-KCE-073

SECTION A (2 Marks Each)

(a) Liquid Retaining Structures

Liquid retaining structures are structures designed to store liquids such as water, sewage, or chemicals without leakage, for example water tanks and reservoirs.

(b) Approximate Method for Design of Tank

The approximate method assumes simplified boundary conditions and treats tank walls as continuous slabs subjected to hydrostatic pressure for quick analysis.

(c) INTZ Tanks

INTZ tanks are reinforced concrete overhead tanks consisting of top dome, cylindrical wall, conical dome, and bottom spherical dome supported on staging.

(d) Top Dome for Overhead Tanks

The top dome is a thin spherical shell provided to cover the tank, protecting water from contamination and weather effects.

(e) Prestressing

Prestressing is the technique of introducing compressive stresses in concrete before applying external loads to counteract tensile stresses.

(f) Degree of Prestressing

Degree of prestressing is the ratio of prestressing force to the force required for full prestressing, indicating partial or full prestress.

(g) Ultimate Tensile Strength

Ultimate tensile strength is the maximum tensile stress a material can withstand before failure.

(h) Kern Distance

Kern distance is the maximum eccentricity within which the load must act so that no tensile stress develops in a section.

(i) Deep Beams

Deep beams are beams having small span-to-depth ratio where strain distribution is non-linear and shear effects dominate.

(j) Use of Corbels

Corbels are used to support heavy loads, such as crane girders, precast beams, or bridge bearings.

SECTION B (10 Marks Each – Attempt Any Three)

(a) Earth Pressure on Underground Tank with Moist Backfill

When the tank is empty and underground, lateral earth pressure acts on the wall. Using Rankine’s theory, earth pressure depends on unit weight of soil, height of wall, and angle of internal friction. The pressure increases linearly with depth and is maximum at the base.

(b) Analysis of Overhead Tanks for Wind Forces

Overhead tanks are analyzed for wind loads considering wind pressure on tank body and staging. Wind forces produce bending moments and shear forces in columns and bracings. IS 875 provisions are used to calculate wind pressure based on height and location.

(c) Advantages of Prestressed Concrete over Reinforced Concrete

Prestressed concrete has higher load-carrying capacity, reduced cracking, better durability, longer spans, smaller sections, and improved serviceability compared to reinforced concrete.

(d) Loss of Stress Due to Anchorage Slip

Loss of stress due to anchorage slip is calculated using
Percentage loss = (Slip × Es) / (Length × Initial stress) × 100
It causes reduction in effective prestress, especially in long post-tensioned members.

(e) Use of Deep Beams and Empirical Expression for Lever Arm

Deep beams are used when span is small and load is heavy, such as transfer girders.
Empirical expression for lever arm:
z ≈ 0.9d (as per design recommendations).

SECTION C (10 Marks Each)

Q3

(a) Design of Clarifier Tank

For a circular clarifier tank of 35 m diameter and 5.25 m wall height, hoop tension is calculated using hydrostatic pressure. Wall thickness and reinforcement are designed using M25 concrete and Fe415 steel considering cracking control and serviceability.

(b) Active Earth Pressure with Saturated Sandy Soil

Active earth pressure is calculated using Rankine’s theory considering submerged unit weight and water pressure. Total pressure equals soil pressure plus hydrostatic pressure.

Q4

(a) Bending Moment for Base Slab of Tank

Base slab bending moment is calculated considering upward soil pressure and downward water load. Maximum moment occurs at the center and wall junction.

(b) Design of Rectangular Water Tank

The tank walls and base slab are designed as slabs subjected to hydrostatic pressure. Splays reduce stress concentration. M20 concrete and mild steel reinforcement are used as per IS code provisions.

Q5

(a) Basic Concepts of Prestressed Concrete

Prestressed concrete works on the principle of pre-compressing concrete to eliminate tension. It improves strength, durability, and crack resistance.

(b) Stress Calculation in Prestressed Beam

Resultant stress = direct stress ± bending stress due to prestress ± bending stress due to loads.
Calculations are done at top and bottom fibers at mid-span.

Q6

(a) Loss Due to Shrinkage and Friction

Shrinkage causes reduction in prestress due to volume reduction of concrete.
Friction loss occurs due to curvature and wobble of tendons during post-tensioning.

(b) Loss Due to Elastic Deformation

Elastic shortening of concrete reduces steel stress.
Percentage loss = (Es / Ec) × (σc / σs) × 100

Q7

(a) Design of Corbel

Corbel is designed considering shear, bending, and bearing stresses. Main reinforcement resists tensile forces, and anchorage is ensured near column face.

(b) Design of Deep Beam

Deep beam design considers strut-and-tie action. Shear governs the design. Reinforcement is provided for vertical tension and anchorage as per IS guidelines.