Introduction to Structural Engineering

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Introduction to Structural Engineering

• By Mr. Matthew D. Stockberger

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Outline

• Why such a Need for Structural Engineers
• Where it fits into the picture
• Objective of Structural Engineering
• Structural Engineering Process
• Types of loads
• Types of structures
• Load paths in structures
• Summary

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Why such a Need for Structural Engineers

• But why??? Next Slide Please

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Why such a Need for Structural Engineers

• The average road bridge is about 43 years old.
• These road bridges were only designed for a 50
  year life span
• Catch my drift???
• If not, they will need replaced and a rapid
  rate. Thus, we need your help.

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Structural Engineering is a sometimes
subcategorzied under Civil Engineering

• Civil Engineering is a composite of many specific
  disciplines.
• Waste Treatment
• Transportation
• Geotechnical
• Water Management
• Construction Management
• STRUCTURAL

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Waste Treatment Environmental.

• Wastewater treatment engineers are civil or
  environmental engineers trained to design or
  analyze water treatment plants.
• Water treatment plants are categorized as
  follows
• Sanitary waste treatment facilities,
• Industrial waste treatment facilities,
• Potable (drinking) water treatment facility.

Largest treatment basins in the USA
Link Visit Sewage World
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Transportation

• Transportation Engineers design and analyze
• Highways,
• Railways,
• Airports,
• Urban and Suburban Road Networks,
• Parking Lots, and
• Traffic Control Signal Systems.

Link Transportation at work
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Geotechnical Soil Mechanics

• Geotechnical Engineers analyze the subterranean
  rock and soil to determine its suitability to
  support extreme loads.
• Proper geotechnical engineering
  is essential for a safe and secure
  structure.

Link A bad engineering job
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Hydraulics Water Management

• Water management involves the use of
  hydrologic and hydraulic principles to
  design
• Drainage systems,
• Detention/retention ponds,
• Navigational waterways, and
• Flood control levees, dams, and lakes.

Link Hoover Dam
Link Flood Pictures
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Construction Management

• Construction managers
• Review contracts,
• Order materials,
• Hire and schedule sub-contractors.
• The job of a construction manager is to
• Provide quality control and insure project is
  completed on time and.
• Within budget.

Link Golden Gate Bridge Construction
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Structural Solid Mechanics

• Structural engineers design steel, concrete, or
  timber framed structures such as
• Tall buildings towers,
• Bridges,
• Dams,
• Retaining walls, foundations, .
• Stadiums.
• and other civil engineering works (bones)

Link Mackinack Bridge
Link Chesepeake Bay Bridge/Tunnel
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Objectives of Structural Engineering

• Structural engineering is the science and art of
  designing and making, with economy and elegance,
  buildings, bridges, frameworks, and other
  structures so that they can safely resist the
  forces to which they may be subjected.
• The Structural Engineer,
• Official Journal of the British Institute of
  Structural Engineers

Link Building Big Site
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U.S. Civil Engineering 150 years

• The twelve founders gathered at the Croton
  Aqueduct, New York,
  on November 5, 1852, to establish ASCE.

• The American Society of Civil Engineers, a
  pro-fessional organization representing more than
  123,000 civil engineers, celebrates its 150th
  anniversary in 2002.

Link ASCE History Site
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Engineering Design Process
Identify the problem (challenge) Explore
alternative solutions Research past
experience Brainstorm Preliminary design of most
promising solutions Analyze and design one or
more viable solutions Testing and evaluation of
solution Experimental testing (prototype) or
field tests Peer evaluation Build solution using
available resources (materials, equipment, labor)
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Design Process in Structural Engineering

• Determine types magnitudes of loads
• Determine structural context
• geometric and geological information
• cost / schedule / height/ etc. limitations
• Generate alternative structural systems
• Analyze one or more alternatives
• Select and perform detailed design
• Implement (usually done by contractor)

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Types of loads

• Dead loads
• Live loads
• Dynamic loads (e.g., trains, equipment)
• Wind loads
• Earthquake loads
• Thermal loads
• Settlement loads

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Dead Loads

• weight of the structure itself
• floors, beams, roofs, decks, beams/stringers,
  superstructure
• loads that are always there

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Live Loads

• People, furniture, equipment
• Loads that may move or change mass or weight
• Minimum design loadings are usually specified
  in the building code

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Load Example Live Load in Ballroom
Ballroom
Live Load 100 lb/ft2
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Dynamic Loads

• Moving loads (e.g. traffic)
• Impact loads
• Gusts of wind
• Loads due to cycling machinery

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Load Example Dynamic Load
HVAC
F
t
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Load Example Water in a dam
Water, ? density
h
p ?gh
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Earthquake Loads

• Structure loaded when base is shaken
• Response of structure is dependent on the
  frequency of motion
• When frequencies match with natural frequency of
  structure - resonance

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Load Example Earthquake Load
Earthquake Load
Earthquake Load
Base Motion
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Settlement
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Forces in Structural Elements
100 lb
Tension
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Forces in Structural Elements (cont.)
Torsion
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Some Types of Structures

• Arch
• Planar Truss
• Beam/Girder
• Braced Frame
• Rigid Frame
• Space Truss
• Cable Suspended Structure

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Arch
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Planar Truss
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Planar Truss
Truss
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Beam/Girder
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Cable Suspended Structure
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Cable Stayed Bridge
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Frames
Braced
Rigid
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Frames Continued
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Flat Plate
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Folded Plate
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Shells
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Load Paths in Structures

• Load Path is the term used to describe the path
  by which loads are transmitted to the foundations
• Different structures have different load paths
• Some structures have only one path
• Some have several (redundancy good)

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Load Path in Framed Structure
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Load Path in a Tied Arch
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Properties of Civil Engineering Materials
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Definition of Stress
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Definition of Strain
Strain DL / Lo Example Lo 10 in. DL 0.12
in. Strain 0.12 / 10 0.012 in./in. Strain
is dimensionless!! (same in English or SI units)
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Stress Strain Behavior of Elastic Mats.
Stress
E
E Modulus of Elasticity Stress / Strain
Strain
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Types of Stress-Strain Behavior
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Materials Used in Civil Engineering

• Stone and Masonry
• Metals
• Cast Iron
• Steel
• Aluminum
• Concrete
• Wood
• Fiber-Reinforced Plastics

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Engineering Properties of Materials

• Steel
• Maximum stress 40,000 120,000 lb/in2
• Maximum strain 0.2 0.4
• Modulus of elasticity 29,000,000 lb/in2
• Concrete
• Maximum stress 4,000 12,000 lb/in2
• Maximum strain 0.004
• Modulus of elasticity 3,600,000 6,200,000
  lb/in2
• Wood
• Values depend on wood grade. Below are some
  samples
• Tension stress 1300 lb/in2
• Compression stress 1500 lb/in2
• Modulus of elasticity 1,600,000 lb/in2

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Concrete Components

• Sand (Fine Aggregate)
• Gravel (Coarse Aggregate)
• Cement (Binder)
• Water
• Air

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Fiber-Reinforced Composites
Composite Laminate
Polyester
Polymer Matrix
Epoxy
Vinylester
Glass

• Functions of matrix
• Force transfer to fibers
• Compressive strength
• Chemical protection

Fiber Materials
Aramid (Kevlar)
Carbon

• Function of fibers
• Provide stiffness
• Tensile strength

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Important Structural Properties
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Engineering Properties of Structural Elements

• Strength
• Ability to withstand a given stress without
  failure
• Depends on type of material and type of force
  (tension or compression)

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Engineering Properties of Structural Elements

• Stiffness (Rigidity)
• Property related to deformation
• Stiffer structural elements deform less under the
  same applied load
• Stiffness depends on type of material (E),
  structural shape, and structural configuration
• Two main types
• Axial stiffness
• Bending stiffness

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Axial Stiffness
Stiffness T / DL Example T 100 lb DL
0.12 in. Stiffness 100 lb / 0.12 in. 833
lb/in.
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Bending Stiffness
Displacement
Force
Stiffness Force / Displacement Example Force
1,000 lb Displacement 0.5 in. Stiffness
1,000 lb / 0.5 in. 2,000 lb/in.
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Stiffness of Different Structural Shapes
Stiff
Stiffer
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Types of Structural Elements Bars and Cables
Bars can carry either tension or compression
Cables can only carry tension
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Types of Structural Elements Beams
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Providing Stability for Lateral Loads
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Concepts in Equilibrium
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Equilibrium of Forces (Statics)

• Forces are a type of quantity called vectors
• Defined by magnitude and direction
• Statement of equilibrium
• Net force at a point in a structure zero
  (summation of forces zero)
• Net force at a point is determined using a force
  polygon to account for magnitude and direction

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Summary

• Structural Engineering
• identifies loads to be resisted
• identifies alternatives for providing load paths
  (arch, truss, frame, ...)
• designs structure to provide safe and economical
  load paths (material, size, connections)
• to be economical and safe, we must be able to
  predict what forces are in structure.

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Related Web Sites
Click on picture

• Click sites below to visit Civil Engineering
  related web sites

Link Discover Engineering Online
Link National Engineering Week
Link West Point Bridge Designer
Link Engines of Our Ingenuity
Link Engineering Case Studies
Link Virtual Laboratory
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References

• http//www.ce.memphis.edu/1101/notes/course_intro/
  What_is_Civil_Engineering.pdf
• http//www.engr.colostate.edu/meroney/classes/eg3
  80/civil_engineering_ppt/civil_engineering.ppt
• https//www.umassk12.net/sess/Brena/Structures.ppt
  
• http//www.ce.cmu.edu/brownfields/nsf/sites/WASHL
  AND/LECT3.PPT