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Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
Introduction to Civil/Structural Introduction to Civil/Structural EngineeringEngineering
Franklin Moon, Ph.D.Franklin Moon, Ph.D.
Assistant ProfessorAssistant Professor
Department of Civil, Architectural, andDepartment of Civil, Architectural, andEnvironmental EngineeringEnvironmental Engineering
Drexel UniversityDrexel University
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
ObjectivesObjectives
Provide an introduction to EngineeringProvide an introduction to EngineeringIntroduce the mechanics of ‘Spanning Introduce the mechanics of ‘Spanning Across’ (the ‘science’ side of engineering)Across’ (the ‘science’ side of engineering)Introduce the concept of Introduce the concept of PrestressedPrestressedConcrete (the ‘creative’ side of Concrete (the ‘creative’ side of engineering)engineering)Provide insight into the scale (overall size, Provide insight into the scale (overall size, forces, etc.) of Structural Engineeringforces, etc.) of Structural Engineering
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
Engineering versus Applied ScienceEngineering versus Applied Science
What is the goal of Engineering?What is the goal of Engineering?Create structures, machines, processes, and Create structures, machines, processes, and
networks networks To make things that previously did To make things that previously did not existnot exist
What is the goal of Science?What is the goal of Science?Explain natural systems Explain natural systems To discover things that To discover things that
have long existedhave long existed
Billington, D.P. (1983) “The tower and the bridge,” Basic Books, Inc., Publishers, New York
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
History of (Civil) EngineeringHistory of (Civil) Engineering
Military Engineering(mid-1600s)
Civil Engineering
1775 1775 -- King Louis XV authorized a King Louis XV authorized a School of Bridges and HighwaysSchool of Bridges and Highways
1794 1794 -- Napoleon developed Napoleon developed EcoleEcolePolytechniquePolytechnique
1835 1835 –– First class of US civil First class of US civil engineers graduatesengineers graduates
ShelterTransportationWater
3 keys to civilization
Structural Engineering
Transportation Engineering
Environmental Engineering
Water Resource Engineering
Architectural Engineering
Geotechnical Engineering
Grayson, L.P. (1993) “The Making of an Engineer: An Illustrated History of Engineering Education in the United States and Canada”
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
Challenges of Structural EngineeringChallenges of Structural EngineeringBuilding UpBuilding Up Spanning AcrossSpanning Across
Taipei 101 (1667 ft)(www.ErikInfoBase.com) Akashi Kaikyo (6,527 ft)
(www.pbs.org)
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
Spanning AcrossSpanning Across
LR1 R2
R3
Truck weight subjects bridge to both BENDING and SHEAR
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
Bending (Flexural) DeformationBending (Flexural) DeformationL - ∆L
L + ∆L
Top gets shorter (squeezed in compression)
Bottom gets longer (stretched in tension)
R1 R2
R3
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
L - ∆L
L + ∆L
C = compressive force
T = tension force
d = distance between T and C
R1 R2
R3
Bending MechanicsBending Mechanics
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
C
T
d
Apply the principle of equilibrium (statics) to solve for the internal forces
ΣFx = 0 ( [+])
-C + T = 0
C = T
R1
o
ΣMo = 0 ( [+])
-Cd + M = 0
M = Cd
or
M = Td
Bending MechanicsBending Mechanics
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
L - ∆L
L + ∆L
Cracks perpendicular to tension
Crushes perpendicular to compression
T T
CC
Bending FailuresBending Failures
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
Shear (Racking) DeformationShear (Racking) Deformation
L
R1 R2
R3Diagonal ‘strut’ gets shorter (squeezed in compression)
Diagonal ‘tie’ gets longer (stretched in tension)
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
Shear MechanicsShear Mechanics
R1R2
R3
L
V= internal shear force
V= internal shear force
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
Apply the principle of equilibrium (statics) to solve for the internal forces
ΣFy = 0 ( [+])
2V - P = 0
V = 0.5P
V= internal shear force
V= internal shear force
P
Shear MechanicsShear Mechanics
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
Shear FailureShear Failure
L
R1 R2
R3
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
PrestressedPrestressed Concrete BridgesConcrete BridgesAttributes of PC Girder BridgesAttributes of PC Girder Bridges
PrefabricatedPrefabricated--Minimal erection timeMinimal erection time--Short traffic interruptionShort traffic interruption--Good quality controlGood quality control--Transportation issuesTransportation issues
Typical Span Lengths ~150 ftTypical Span Lengths ~150 ft
Typical Girder Spacing ~8 ftTypical Girder Spacing ~8 ft
Good DurabilityGood Durability
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
Introduction to Prestressed ConcreteIntroduction to Prestressed Concrete
MotivationMotivation -- Concrete is “strong” in Concrete is “strong” in compression and “weak” in tensioncompression and “weak” in tension
GoalGoal –– Introduce “internal” forces into the Introduce “internal” forces into the concrete to keep the concrete in concrete to keep the concrete in compression under “everyday loads”compression under “everyday loads”
--Delays crackingDelays cracking--Improved durabilityImproved durability
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
Step 1 – Stretch the steel tendonsLs
Ls + ∆Ls
Jacking force
Introduction to PC: Method of ConstructionIntroduction to PC: Method of Construction
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
Introduction to PC: Method of ConstructionIntroduction to PC: Method of Construction
Step 2 – Cast concrete around the steel tendons and wait until the concrete cures (hardens)
Ls + ∆Ls
Jacking force Lc
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
Step 3 – Remove the jacking force
Ls + ∆Ls - ∆Lj = Ls + ∆L’s
Lc - ∆Lj
Steel contracts by Lj Steel remains in tension
Concrete is placed into compression
Introduction to PC: Method of ConstructionIntroduction to PC: Method of Construction
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
Validation of ConceptValidation of Concept
Canfield, S. and L. Kahn (2005) - School of Civil and Environmental Engineering, Georgia Institute of Technology
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
Test SetupTest SetupTest 1
Bending Force
Shear Force
Canfield, S. and L. Kahn (2005) - School of Civil and Environmental Engineering, Georgia Institute of Technology
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
Bending BehaviorBending Behavior
Mid-span displacement
Force
T = tension force in steel
C = Compressive force in concrete
dd
Canfield, S. and L. Kahn (2005) - School of Civil and Environmental Engineering, Georgia Institute of Technology
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
Flexure and Shear CracksFlexure and Shear Cracks
Bending cracks Shear
cracks
Centerline of point load
Canfield, S. and L. Kahn (2005) - School of Civil and Environmental Engineering, Georgia Institute of Technology
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
Structural FailureStructural Failure
Canfield, S. and L. Kahn (2005) - School of Civil and Environmental Engineering, Georgia Institute of Technology
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
PostPost--Processing ResultsProcessing ResultsLoad-Deflection Plot for the Type IV Girder
0
100
200
300
400
500
600
700
0 2 4 6 8 10 12 14 16 18
String Potentiometer Deflection (in.)
Load
(kip
s)
Cracking Test Ulitimate Test
First Visible cracks at 363 kips
Ultimate load = 592 kips
Canfield, S. and L. Kahn (2005) - School of Civil and Environmental Engineering, Georgia Institute of Technology
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
Structural FailureStructural Failure
Canfield, S. and L. Kahn (2005) - School of Civil and Environmental Engineering, Georgia Institute of Technology
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
Structural FailureStructural Failure
Canfield, S. and L. Kahn (2005) - School of Civil and Environmental Engineering, Georgia Institute of Technology
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
Structural FailureStructural Failure
Canfield, S. and L. Kahn (2005) - School of Civil and Environmental Engineering, Georgia Institute of Technology
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
Scale of Structural EngineeringScale of Structural Engineering592,000 lb
~4.0 ft.
Weight ~ 1000lb
~2.5 ft.
Weight ~ 1000lb
Canfield, S. and L. Kahn (2005) - School of Civil and Environmental Engineering, Georgia Institute of Technology
Drexel UniversityDepartment of Civil, Architectural and
Environmental Engineering 21 February 2006
Scale of Structural EngineeringScale of Structural Engineering592,000 lb
~1480 ft.
Weight ~ 592,000 lb
~1453 ft.
Canfield, S. and L. Kahn (2005) - School of Civil and Environmental Engineering, Georgia Institute of Technology