Statics of structures | Structural design
Chapter 1: Introduction
Structure: organized system
For structures, the following is important:
1. The structural systems used
2. The structural materials that make these systems
3. The forces acting on the structure
4. The load-bearing subsurface the structure is placed upon
History
First man-made structures: made of timber, natural stone, bricks pressure-
based systems
In Egypt: almost no timber sun-dried clay was used as load-bearing wall.
Architects needed to span larger areas flooring structures using wooden
beams, arches, domes and pillars
Pillars
Doric: architecturally and structurally simple
Corinthian: has pillar base (to ensure smooth force transition to
foundation)
Ionic: has pillar base
Architraves: monolithic stone beams, span of 6 metres
Gothic style (13th century): flying buttresses, heavy buttresses avoid tensile
stresses (as result of horizontal forces) in pillars
In 18th and 19th century: iron and steel new construction materials avoid both
tensile and compressive stresses
Structural systems
,Structural materials
Natural materials: stone and timber
- Used as building material for centuries
- Characteristics well-known by craftsmen
- Variable quality/signifcant deflects: careful selection using high material
safety factors
Artifcial produced materials: steel and aluminium alloys
- Produced under controlled conditions in factories
- Production process subjected to various inspections and tests
- Consistent material: lower material safety factors
New materials: fbre reinforced composites
- Fully fabricated materials
- Around for a short while behaviour not fully understood high material
safety factors
Old materials: wrought iron and cast iron
- Used to be applied in structures, now replaced by steel
Steel
- Iron + Carbon + other additives
- Properties: relative strength, cheap, ductile and possibility to weld it
Concrete
- Ingredients: cement, fne aggregates, coarse aggregates, water
- Ratio gravel:sand:cement 4:2:1
- Properties: brittle material, tensile strength 10% of compressive strength
Timber
- Hardwood and softwood
- Properties: anisotropic material properties in diferent directions vary
Masonry
- Properties: can take minor tension stresses
- Bricks: made of clay and water, shaped and baked in ovens
, - Natural stone: expensive building material
- Concrete blocks: cheap building material, made as solid hollow blocks
- Calcium silicate blocks: mixture of sand, cement, lime and water, then
placed in autoclave (oven)
Aluminium
- Made from bauxite
- Properties: lightweight, strong, corrosion resisting
- Pure aluminium too soft add 5% other materials (magnesium, silicon)
Fibre reinforced composites:
- Fibres: glass fbres, carbon fbres
- As matrix used: polyester, vinyl ester, epoxy
Stress-weight-ratio (SWR): strength/volumetric weight
Structural safety
Load acting on structure must be smaller than resistance of structure
Load: also included deformations, expansion and shrinkage due to temperature
changes
Efect of loads: expressed in internal moments and forces, normal and shear
forces, deformation
Structure is safe if it meets the requirements:
Design load Sd
Characteristic load Sk
Load factor γ s
Design strength Rd
Characteristic strength Rk
Safety factor γ m
Design strength R=A*fy
A= cross section of bar
fy = yield stress of material
Design load
For beam supporting roof: snow load
needs to be taken into account in
load combination
Reliability classes: partial safety factors
