Definition

It is any concrete structure, strengthened or reinforced by steel, FRP or otherwise desirable materials for higher load-carrying strength

How?

• Concrete: good in compression
• Steel / FRP: good in tension
• Reinforced concrete: Concrete + Steel

How to begin concrete design?

Sequential & iterative decision making process:

• Project Planning
• Stage I: General
• Stage II: Detailed

Project Planning

• Where
• When

• Why, the structure is to be built

Taking proper account of various activities:

• Design
• Construction
• Operations
• Maintenance
• Repair
• Demolition
• Replacement

Stage I: General

General Decisions:

• Type of structure
• Structural layout
• Geometry
• Construction materials

Stage II: Detailed

Detailed Design:

• Estimation of loads
• Analysis of structure
• Proportion of various components
• Adjustments where necessary

Design Objectives

• Adequate strength
• Serviceability under working loads
• Economy

Strength

• Consider ALL possible load combinations, taking the worst only
• Consider ALL possible ways for failure to occur
• Design & proportion accordingly - ductility

Economy

• Design cost
• Material cost
• Construction cost
• Repair
• Maintenance
• Insurance
• Demolition

Methods of Design

• Working Stress Method
• Ultimate Strength Design
• Limit State Design
• Probabilistic Design

Limit State

When a structure is rendered unfit for use for its designated function by one or more causes, it is said to have entered a Limit State.

Ultimate Limit State

• Stability or collapse
• Strength
• Stiffness
• Robustness
• Special hazard

Serviceability Limit State

• Deflection
• Cracking
• Vibration
• Fatigue
• Durability
• Fire resistance

Others

• Lightning
• Special requirements specific to the structure

Purpose of Design

• Ensure the structure being designed will not reach a limit state in its expected working life & conditions
• Some limit states are inapplicable
• Some can be satisfied with proper detailing
• Usual approach: Pick most critical limit state, satisfy it & check the rest

Fundamentals

For a simply-supported beam:

• Fundamentals principles
• Analysis at collapse, M_u
• Design of sections for flexure

• Methods:

1. Rectangular-parabolic stress block
2. Equivalent rectangular stress block
3. BS 8110 design charts

• Sections:

1. Singly-reinforced
2. Doubly-reinforced
3. Flanged

• Column interaction: N-M diagram
• Shear
• Torsion
• Reinforcement detailing
• Bond

Member Design

• General: loads, ULS & SLS
• Design procedure
• Deflection & cracking
• Anchorage & curtailment of bars

• Elastic analysis
• Approximate method

• Types: 1-way, 2-way
• Design of 1-way slabs
• Design of 2-way slabs

• General
• Classification
• Moments & forces in columns
• Design considerations
• Design of short columns

• Assumptions
• Size
• Design for axial load & bending
• Design for shear: vertical & punching