2. INTRODUCTION TO DESIGN

6. SO WHAT IS A REINFORCED
CONCRETE?

7. WHAT IS REINFORCED CONCRETE?
• Principal materials used in many civil
engineering applications (buildings, retaining
walls, foundations, water retaining structures,
highways, bridges etc
• A composite material: reinforcing bars
embedded in concrete
• Concrete: high compressive strength, low
tensile strength

8. WHAT IS REINFORCED CONCRETE?
• Steel: high tensile strength, low compressive
strength
• Concrete + Steel:
• Economical structural material, strong in compression
& tension
• Concrete provides corrosion protection and fire
resistance

11. STRUCTURAL DESIGN?
• Process of determining
, selection of
and
determination of
for
the structure to be built
• Aim: ensure that the structure will perform
satisfactorily during its design life

12. STRUCTURAL DESIGN PURPOSES?
•
•
•
•
Fitness for purpose
Safety and reliability
Economy
Maintability

13. Fitness for purpose
• Arrangement of spaces, spans, ceiling height,
access and traffic flow must complement the
intended use.
• The structure should fit its environment and
be aesthetically pleasing

15. Safety and reliability
• Structure must be strong to safely support all
anticipated loadings
• Structure must not deflect, overturn, tilt,
vibrate or crack in a manner that impairs its
usefulness

20. Economy
• Overall cost of structure should not exceed
the client’s budget
• Designer should take into account: cost of
materials, buildability, construction time, cost
of temporary structures and maintenance
costs

22. Maintainability
• Structure should be designed to require a
minimum maintenance, can be maintained in
a simple fashion

23. Structural Elements
• Beams: horizontal members carrying lateral loads
• Slabs: horizontal plate elements carrying lateral loads
• Columns: vertical members carrying primarily axial
loads but generally subjected to axial load and moment
• Walls: vertical plate elements resisting vertical, lateral
or in-plane loads
• Foundations: pads or strips supported directly on the
ground that spread loads from columns or walls to the
ground
• Stairs: plate elements consists of a flight of steps,
usually with one or more landings provided between
the floor levels

24. Structural Elements

25. Structural Elements

26. Code of Practice
• document that gives recommendations for the
design and construction of structures
• Contains detailed requirements regarding
loads, stresses, strengths, design formulas and
methods of achieving the required
performance of complete structure

27. Code of Practice functions
• Ensure adequate structural safety
• Simplify the task of designer
• Codes ensure a measure of consistency among
different designers
• Have legal validity, in that they protect the
structural designers from any liability due to
structural failures that are caused by
inadequate supervision, faulty material and
construction

28. Eurocode
• EN 1990: Eurocode – Basis of structural design
• EN 1991: Eurocode 1 – actions on structures
• EN1992: Eurocode 2 – Design of concrete
structures

29. Creep
• General definition: the
or
of a solid material to
• occurs as a result of long-term exposure to high levels
of stress that are below the yield strength of the
material
• more severe in materials that are subjected to heat for
long periods, and near their melting point. Creep
always increases with temperature
• The rate of this deformation is a function of the
,
,
and the

30. Example: creep in cardboard
• a largely empty box was placed on a smaller box
• fuller boxes were placed on top of it
• Due to the weight, the portions of the empty box not sitting
on the lower box gradually crept downward

31. Concrete Creep
• Definition: Continuous deformation of a member
under sustained load
• Characteristics:
• The final deformation of member can be 3 – 4 times the
short term elastic deformation
• Deformation is roughly proportional to the intensity of
loading and to the inverse of concrete strength
• If load is removed, only instantaneous elastic deformation
will recover – the plastic deformation will not
• There is a redistribution of load between concrete and steel
present

33. Concrete Durability
• Influenced by:
i.
ii.
iii.
iv.
v.
Exposure conditions
The cement type
The concrete quality
The cover to the reinforcements
The width of any cracks

34. Specifications of materials (Concrete)
• The selection is governed by the strength
required – depends on the intensity of loading
and the form and size of structural member
• Concrete strength: measured by the crushing
strength of cubes or cylinders of concrete
made from the mix
• Identified by its class. Ie: C25/30 –
characteristic cylinder crushing strength (fck)
of 25N/mm2 and cube strength of 30N/mm2

35. Specifications of materials (Reinforcing
Steel)
• Grade 250 bars: hot-rolled mild-steel bars –
have smooth surface, bond with conrete is by
adhesion only
• High-yield Bars: Deformed bars, ribbed highyield steel bars may be classified as:
• Class A: used in mesh and fabric. Lowest ductility
cathegory
• Class B: commonly used for reinforcing bars
• Class C: high ductility, used in earthquake design

36. PRINCIPLES OF LIMIT STATE
DESIGN
INTRODUCTION TO DESIGN

37. Example

39. Limit State Design
• Design method in EC2 is based on limit state
principles
• Limit State: State of a structure which
represents the acceptable limit of an aspect of
structural behaviour
• Criterion for safe design is the structure
should not become unfit for use – not reach a
limit state during its intended life

40. Principle types of limit state
1. Ultimate Limit State
•
•
Deals with the strength and stability of the
structure under the maximum design load it is
expected to carry
No part or whole of the structure should
collapse, overturn or buckle under any
combination of design load

41. Principle types of limit state
1. Ultimate Limit State
•
Divided into the following categories
•
•
•
•
EQU – Loss of equilibrium of the structure
STR – Internal failure or excessive deformation of the
structure or structural members
GEO – failure due to excessive deformation of the
ground
FAT – fatigue failure of the structure or structural
members

42. Principle types of limit state
2. Serviceability Limit State
•
Deals with the conditions beyond which specified
service requirements are no longer met such as
excessive deflection and cracking
3. Other Limit States
•
May be reached including considerations of
durability, vibration, and fire resistance of
structures

43. Actions
•
•
•
EC2 terminology for loads and imposed
deformations
EC2 defines and action (F) as a force or load
applied to structure
Characteristic actions used in design and defined
in EC2 are as follows:
•
•
Characteristic permanent action Gk – Selfweight of
structure, finishing weight etc
Characteristic variable action Qk – people, furniture,
equipment etc

44. Design Actions
•
•
•
•
Design value of an action is obtained by
multiplying the characteristic actions Fk by partial
safety factor for actions γf
Fd = Fk x γ f
γf accounts for possible increases in load,
inaccurate assessment of the effect of loads,
inaccurate modelling of the load
Values of γf are given in EN 1990: Annex A1

45. Combination of Action
•
Permanent and Variable actions will occur in
different combinations. All must be considered to
determine the most critical design situation

46. MODE OF FAILURE IN SECTION
DURING LOADING
• Reinforcing steel can sustain very high tensile
strains, due to the ductile behavior of steel
• Concrete can accommodate compressive
strains which is much lower in comparison
• The final collapse of a normal beam at ULS is
usually cause by crushing of concrete in
compression
• Depending on the amount of RS provided,
flexural failure may occur in 3 ways:

47. 1. Balanced
• Concrete crushes & steel yields
simultaneously at ULS
• Compressive strain of concrete reaches
ultimate strain and the tensile strain of steel
reaches yield strain simultaneously
• Depth of neutral axis is equal to 0.617d

49. 2. under-reinforced
• Steel reinforcement yields before concrete
crushes
• Area of tension steel provided is less than the
area provided in balance section
• Depth of neutral axis is less than 0.617d
• Give ample prior warning of the impending
collapse

51. 3. over-reinforced
• Concrete fails in compression before steel
yields
• Area of tension steel provided is more than
the area provided in balance section
• Depth of neutral axis is greater than 0.617d
• Failure is sudden (without any sign of warning)
and brittle

53. REFERENCE
• REINFORCED CONCRETE DESIGN TO
EUROCODE 2, IR MOHAMAD SALLEH YASSIN
• REINFORCED CONCRETE DESIGN TO
EUROCODE 2, BILL MOSLEY, JOHN BUNGEY,
RAY HULSE