Lecture 1 introduction What is structure design?

1. STRUCTURAL DESIGN I
STRUCTURAL MECHANICS
LECTURE 1

2. INTRODUCTION
• Structural mechanics, or the start of structural
design, is concerned with the study of forces and
how these act on a body, in our case – buildings.
• Each building component has weight which is a
load. This load is a downward acting force that
has to be transferred through various building
members to the earth. These members are slabs,
beams, columns etc.
• An economical structure is that in which the load
transfer is through the shortest distance.

3. Common Characteristics Of Structures
• Structures are designed to support various kinds of loads.
These are self weight of members, live loads on these,
snow loads, water/ earth loads, wind loads, seismic loads,
thermal loads, shrinkage loads and sometimes construction
loads etc.
• All the structural loads are transferred to the ground.
• At the support points structural members generate reaction
forces to resist the various loads.
• External loads and the reactions that resist these loads
produce different kinds of stresses in the structural
member.
• The structural members have to be strong enough to resist
all these external stresses.
• Structural members should not substantively deform under
their own or external applied loads.

4. Types of structures.
Schematic representation

9. • As the structural load is basically a force that
has to be resisted, structural design becomes
a study of forces that act on a structure, the
stresses such forces generate and the
selection and design of materials and forms
that can resist these forces.
• Hence, it becomes important to know the
contemporary use of force units.

10. UNITS OF FORCE
• The Newton is the unit of force derived in the SI
system.
• it is equal to the amount of net force required to
accelerate a mass of one kilogram at a rate of one
meter per second.
• In dimensional analysis, F=ma, multiplying m (kg) by
a (m/s2).
• The dimension for 1 Newton unit is therefore

11. • The dimension for 1 Newton unit can be seen as:
– 1 N is the force of Earth’s gravity on an object with a mass
of about 102 g (1⁄9.81 kg) (such as a small apple).
– On Earth's surface, a mass of 1 kg exerts a force of
approximately 9.8 N [down] (or 1.0 kilogram-force; 1
kgf=9.80665 N by definition). The approximation of 1 kg
corresponding to 10 N is sometimes used as a rule of
thumb in everyday life and in engineering.
– The force of Earth's gravity on a human being with a mass
of 70 kg is approximately 686 N.
– It is common to see forces expressed in kilo-newtons or
kN, where 1 kN = 1,000 N.

12. Classification of forces
1. According to the effect produced by the
force-
a) External force (Push or Pull)
b) Internal force (Resistance)
c) Active force (Cause a body to move or
change its shape)
d) Passive force (prevents the motion or
deformation of a body)

13. Contd.
2. According to the nature of force
a) Action and Reaction
b) Attraction and Repulsion
c) Pull and Push
3. According to the nature of stress produced in the
body-
a) Tensile force
b) Compressive force
c) Shear force

14. COMPOSITION OF FORCES
• Forces can be acting on a number of planes in different
situations but here the study will be limited to ‘co-planer’
system of forces i.e. forces that are acting on only one
plane as that is what is normally required in calculations
required for structures of common buildings.
• Forces can be represented graphically. Force has a value
and a direction so, a line on a scale with an arrow can
represent a force.
• Forces can be:
– Parallel forces
– Concurrent forces
– Non concurrent forces

15. Parallel Forces
Resultant
Concurrent Forces
Resultant
Non-concurrent Forces
Equilibrant

16. • Write a paper on “Structures in Architecture”.