(SEM VI) THEORY EXAMINATION 2017-18 DESIGN OF CONCRETE STRUCTURE II

Design of Concrete Structure–II (NCE-601)

Complete Section-Wise Explanation – B.Tech Semester VI

Introduction to the Subject
 

Design of Concrete Structure–II is an advanced structural engineering subject that deals with the design of special reinforced concrete structures beyond basic beams and slabs. It focuses on elements that are widely used in real projects such as flat slabs, footings, water tanks, retaining walls, culverts, and prestressed concrete members.
 

This paper is strongly application-oriented and expects students to:

Apply IS 456:2000 provisions

Assume missing data intelligently

Follow step-by-step design procedures

Present calculations neatly with proper checks

The question paper is divided into three sections: A, B, and C.

SECTION A – Conceptual Clarity & Definitions

Pattern:
Attempt all questions
10 questions × 2 marks = 20 marks

Nature of Section A

Section A checks whether your fundamental concepts and definitions are clear. Answers must be short, but technically correct. This section is easy to score if definitions are remembered properly.

Explanation of Section A Topics

Limitations of Flat Slab
Flat slabs are economical for large column spacing, but they suffer from problems like punching shear near columns, difficulty in handling heavy concentrated loads, and limitations in resisting lateral loads such as earthquakes.

Column Head
A column head is a flared or enlarged portion at the top of a column in a flat slab system. It helps reduce punching shear and negative bending moments.

Shallow Foundation vs Deep Foundation
Shallow foundations transfer loads to soil near the ground surface, while deep foundations transfer loads to deeper, stronger soil strata through piles or piers.

Depth of Foundation Calculation
This question tests soil mechanics fundamentals. Depth of foundation is calculated using Rankine’s formula considering safe bearing capacity, unit weight of soil, and angle of repose.

Culvert
A culvert is a structure that allows water to pass under a road, railway, or embankment. It may be slab type, box type, or pipe culvert.

Types of Retaining Walls
Retaining walls include gravity walls, cantilever retaining walls, counterfort retaining walls, and buttressed retaining walls.

Overhead Tank vs Underground Tank
Overhead tanks are elevated and subjected mainly to hoop tension and bending due to water pressure, while underground tanks are supported by soil pressure and have different stress conditions.

Intze Tank
An Intze tank is a special type of elevated water tank consisting of a cylindrical wall, conical dome, and spherical bottom dome, designed to reduce bending moments.

Creep
Creep is the time-dependent increase in strain under sustained load, leading to long-term deformation in concrete.

Anchorage
Anchorage refers to the length of reinforcement required beyond a critical section to develop full strength of the steel.

SECTION B – Design-Oriented Long Questions

Pattern:
Attempt any three questions
3 × 10 marks = 30 marks

Nature of Section B

Section B is the core design section. Questions require systematic design steps, assumptions as per IS codes, and clear presentation. Marks are awarded for method as much as for the final answer.
 

Explanation of Section B Questions

Design of Flat Slab Interior Panel
 

This question involves designing an interior panel of a flat slab supported on columns. You must calculate slab thickness, check deflection control, compute bending moments using direct design method, design reinforcement in column strip and middle strip, and finally design the drop panel.
 

RCC Footing with Axial Load and Moment

Here, the footing is subjected to both vertical load and bending moment. The task is to determine plan dimensions such that soil pressure remains within safe bearing capacity, followed by checks for bending, shear, and punching shear.
 

Design of Slab Culvert

This problem is based on bridge engineering concepts. The slab culvert must be designed for Class AA tracked vehicle loading, including impact factor, dead load, live load, and wearing coat. Reinforcement design is done based on maximum bending moment and shear force.
 

Design of Circular Water Tank

This question tests liquid retaining structure concepts. Since the tank rests on ground with wall restrained at base, hoop tension and bending moments are calculated. Crack control is critical, and working stress method principles are followed.
 

Losses in Prestressing

This is a theory question where losses such as elastic shortening, creep, shrinkage, relaxation of steel, friction loss, and anchorage slip are explained.
 

SECTION C – Advanced Design & Theory

Pattern:
Attempt any one part from each question
5 questions × 10 marks = 50 marks

This section carries the maximum weightage and decides overall performance.

Question 3 – Flat Slab Design & Analysis

Design of Flat Slab Without Drop and Column Head
This design is more critical due to higher punching shear. You must carefully calculate slab thickness, design bending reinforcement, and check shear safety.

Methods of Analysis of Flat Slab
This theory part explains methods like Direct Design Method and Equivalent Frame Method. You must explain assumptions, applicability, and steps of any one method.

Question 4 – Curved Beam / Square Footing

Design of Curved Beam under Combined Forces
This is a complex design involving bending moment, torsion, and shear. Reinforcement is designed as per IS 456 torsion provisions, combining equivalent bending and shear.

Design of Square Footing
This problem focuses on uniform thickness footing design under axial load. Checks include bending moment, one-way shear, and punching shear.

Question 5 – Water Tank & Intze Tank

Design of Square Water Tank
The tank is open at top with walls fixed at base. Design includes wall thickness, bending moments, hoop tension, and reinforcement detailing.

Design of Intze Tank Dimensions
This is a planning-based problem where dimensions of different components are calculated to meet required capacity, considering geometric relationships.

Question 6 – Retaining Wall

Design of Cantilever Retaining Wall
This is a very important question. You must calculate earth pressure using Rankine’s theory, design stem, heel, and toe slabs, and check stability against overturning, sliding, and bearing pressure.

Design Principles of Cantilever Retaining Wall
This theory explains load action, pressure distribution, stability checks, and reinforcement philosophy.

Question 7 – Prestressed Concrete

Assumptions in Prestressed Concrete Design
This theory question explains stress distribution, material behavior, and serviceability assumptions.

Load Balancing Cable Profile
This numerical involves calculating parabolic cable profile, eccentricity, and stress at top and bottom fibers under prestressing force.