Theory of Structure Sem 1

Structure in civil engineering

Arrangement of connected elements designed to resist loads and transfer them safely to the ground.

Examples of structures

Buildings, bridges, dams, towers, stadiums.

Main functions of a structure

Support loads, provide stability, offer shelter, and transfer loads to the ground.

Typical load transfer path in a building

Roof→Slab → Beam → Column → Foundation → Soil.

Structural system

An arrangement of elements working together to transfer all loads safely.

Key features of a load-bearing system

It uses thick walls to support loads, is suitable for small buildings, and provides less flexibility in planning.

Key features of a framed structure

It uses beams, columns, and slabs; allows flexible planning and large spans; and is suitable for modern buildings.

Main functions of a foundation

It transfers loads to the soil, prevents settlement, and provides stability.

Role of a column

A vertical member that carries loads from beams/slabs to the foundation; it mainly works in compression.

Main function of beams

Horizontal elements that support slabs and transfer loads to columns; they primarily resist bending.

Slab in structural terms

A flat, horizontal plate, usually made of concrete, forming floors or roofs and carrying loads to supporting beams or walls.

Difference between load-bearing and partition walls

Load-bearing walls support structural loads, while partition walls only divide spaces and do not carry structural loads.

Main function of a roof

It protects the building from weather and external elements.

Force

A push or pull acting on a body, measured in newtons (N).

Tensile force

A force that tends to elongate or stretch a material.

Compressive force

A force that shortens or compresses a material.

Shear force

A force that causes sliding of material parts relative to each other.

Torsional force

A twisting force causing rotation about an axis.

Dead loads

Permanent, fixed loads such as the self-weight of the structure, walls, and floors.

Live loads

Temporary or variable loads such as people, furniture, and vehicles.

Wind loads

Forces exerted by wind pressure, affecting mainly tall buildings and towers.

Seismic loads

Loads caused by earthquake ground motion.

Equilibrium in structures

A state where all forces and moments acting on a structure are balanced.

Moment

The turning effect of a force calculated as: Moment = Force × Perpendicular Distance.

Types of beams used in structures

Simply supported beam, cantilever beam, fixed beam, and continuous beam.

Truss

A framework of straight members forming triangular units, used for large spans in roofs and bridges.

Most stable geometric shape for trusses

Triangle.

Center of gravity (C.G.)

The point through which the entire weight of a body acts.

Factors increasing stability of a structure

A wider base, lower center of gravity, and proper load distribution.

Stress

Force per unit area; its SI unit is pascal (Pa) or N/m².

Strain

Relative deformation per unit length; it is dimensionless and has no units.

Neutral axis in a beam

The axis where there is no change in length under bending; it experiences neither tension nor compression.

How truss members mainly carry loads

Truss members mainly carry pure axial tension or compression.

Function of structural supports

They hold members in position and provide reactions to applied loads.

Structural safety

Ensured by proper design to withstand all applied loads and maintain equilibrium.

Roller support

A support that restrains vertical movement but allows horizontal movement and rotation; it provides one vertical reaction.

Hinged or pinned support

A support that prevents horizontal and vertical movement but allows rotation; it provides horizontal and vertical reactions.

Fixed support

A support that prevents horizontal movement, vertical movement, and rotation; it provides horizontal, vertical, and moment reactions.

Difference between King Post and Queen Post Truss

King Post Truss has one central vertical post and is suitable for smaller spans; Queen Post Truss has two vertical posts and is suitable for larger spans.

Typical span ranges of King Post and Queen Post Trusses

King Post: approximately 5–8 m; Queen Post: approximately 8–12 m or more.

Formulas for stress and strain

Stress = Force / Area (σ = F/A); Strain = Change in Length / Original Length (ε = ΔL/L).