Fundamentals of Structural Members Working in Bending

1. Lecture 8. Fundamentals of Structural Members Working in Bending

P R E PA R E D B Y: S .
N I Y E T B AY

2. Fundamentals of Structural Members Working in Bending

• A beam is a structural element that primarily
Fundamentals of
Structural
Members Working
in Bending
works in bending and transfers loads to
supports.
• Main functions of beams:
• carry loads from floors and roofs;
• transfer loads to columns, walls, or other
supports;
• ensure structural stability and stiffness.
• Typical applications of beams:
• floor systems in buildings
• roof structures
• working platforms
• bridge structures
• Span of beams:
• in buildings typically up to 24 m
• for larger spans other structures are used:
• trusses
• arches
• frames

3. Types and Materials of Beams

Common materials used for beams:
Steel beams
rolled sections
welded sections
Reinforced concrete beams
cast-in-place (monolithic)
precast beams
Timber beams
solid wood beams
glued laminated timber (glulam)
Beam elements depending on structural function:
purlins
girders
lintels
pile caps / grillage beams
Classification according to structural system:
simply supported beams
continuous beams
cantilever beams
A beam supported by two supports is called a
simply supported beam.

4. Loads Acting on Beams

• Loads applied to beams can be classified as:
• 1. Concentrated loads
• applied at a specific point
• example: column load, equipment load
• 2. Distributed loads
• applied along the length of the beam
• the most common type in building structures
• Uniformly Distributed Load (UDL)
Loads Acting on
Beams
Usually denoted as q (kN/m).
• Sources of distributed loads:
• floor slabs
• roof structures
• walls resting on beams
• permanent and variable loads
• For structural analysis, beams are often
simplified as rectangular cross-section
elements.
• Typical cross-section parameters:
• b — width of the beam
• h — height of the beam

5. Beam Deformation Under Bending

• When a beam is subjected to bending:
• 1. The beam axis becomes curved
The initially straight axis changes shape under load.
2. Fibers experience different stresses
Upper fibers → compression
Lower fibers → tension
3. Neutral axis
a layer inside the beam where no longitudinal strain occurs
the length of this layer remains unchanged during bending
Maximum deflection (fmax)
Occurs approximately at the mid-span of a simply supported
beam under uniform load.
Understanding beam deformation is essential for:
structural safety
serviceability
accurate design of structural members.

6. Internal Forces in a Beam

• From the viewpoint of structural statics, internal forces arise in
any cross-section of a beam.
The main internal forces are:
1. Bending Moment —