Ch 1 - Intro to Steel Structure
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Transcript of Ch 1 - Intro to Steel Structure
CE 411 - Steel Structures
Fall Semester 2014
Eiffel Tower - Paris Engineer A. Baseer AwanMS (Structures)
[email protected], SCEE
National University of Sciences & Technology
Steel Construction
Intro to Steel Structure
World Tallest StructuresCE 411 - Engr. A.Baseer Awan
Steel Construction
Intro to Steel Structure
Willis (Sear) Tower CE 411 - Engr. A.Baseer Awan
• World’s most famous steel building
• Chicago, IL
• Tallest building when constructed in the1970s
• 108 storey
• Height of 442 m
• Ranked 8 in the tallest buildings
• Architects Skidmore, Owings &Merrill (SOM)
• Architect Bruce Graham and StructuralEngineer Fazl-ur-Rahman Khan
• Tube Structure
• Innovative design was structurally efficientand economic
Steel Construction
Intro to Steel Structure
Willis (Sear) Tower CE 411 - Engr. A.Baseer Awan
Steel Construction
Intro to Steel Structure
Burj KhalifaCE 411 - Engr. A.Baseer Awan
• World’s most famous steel building
• Dubai, UAE
• Construction kicked off in 2004 andofficially opened in 2010
• 163 floors
• Height of 829.8 m
• Ranked world tallest building
• Architects Skidmore, Owings &Merrill (SOM)
• Architect Adrian Smith and StructuralEngineer Bill Baker
• Tube Structure
• Innovative design was structurally efficientand economic
Steel Construction
Intro to Steel Structure
Burj KhalifaCE 411 - Engr. A.Baseer Awan
Structural Design
Intro to Steel Structure
General Introduction Structural design is a systematic & iterative process that involves:
1) Identification of intended use & occupancy of a structure – by owner
2) Development of architectural plans & layout – by architect
• Conceptual design
3) Identification of structural framework – by engineer
4) Estimation of structural loads depending on use & occupancy
• Preliminary design
5) Analysis of the structure to determine member & connection design forces
• Final design
CE 411 - Engr. A.Baseer Awan
Structural Design
Intro to Steel Structure
General Introduction
6) Design of structural members & connections
• Detailed design
7) Verification of design
8) Fabrication & Erection – by steel fabricator & contractor
• Off-site fabrication in shop
9) Inspection & Approval – by state building official
• Meets code requirements
CE 411 - Engr. A.Baseer Awan
Structural Design
Intro to Steel Structure
Primary Responsibilities:
• Owner - primary responsibility is deciding the use &occupancy, & approving the arch. plans of the building -funding
• Architect - primary responsibility is ensuring that thearchitectural plan of the building interior is appropriate forthe intended use & the overall building is aestheticallypleasing.
• Engineer – primary responsibility is ensuring the safety &serviceability of the structure, i.e., designing the building tocarry the loads safely & meets performance requirementsunder Serviceability Limit State.
CE 411 - Engr. A.Baseer Awan
Structural Design
Intro to Steel Structure
Primary Responsibilities:
• Fabricator – primary responsibility is ensuring that thedesigned members & connections are fabricatedeconomically in the shop or field as required.
• Contractor/Erector - primary responsibility is ensuring thatthe members & connections are economically assembled(erected) in the field to build the structure.
• State Building Official – primary responsibility is ensuringthat the built structure satisfies the appropriate buildingcodes accepted by the Govt.
CE 411 - Engr. A.Baseer Awan
Structural Design
Intro to Steel Structure
Conceptually, from an engineering standpoint, the parameters that can be
varied (somewhat) are:
• The material of construction
• The structural framing plan.
The choices for material include:
• Steel
• Reinforced concrete
• Steel-concrete composite construction.
The choices for structural framing plan include:
• Moment resisting frames (MRF).
• Braced frames.
• Dual frames
• Shear wall frames, and so on.
The engineer can also innovate a new structural framing plan for a particular
structure if required. CE 411 - Engr. A.Baseer Awan
Structural Design
Intro to Steel Structure
• All viable material + framing plan alternatives must be considered &
designed to compare the individual material + fabrication / erection costs to
identify the most efficient & economical design for the structure.
• For each material + framing plan alternative considered, designing the
structure consists of designing the individual structural components, i.e., the
members & the connections, of the framing plan.
• This course CE 411 focuses on the design of individual structural
components. The material of construction will be limited to steel, & the
structural framing plans will be limited to braced frames & moment
resisting frames.
CE 411 - Engr. A.Baseer Awan
Structural Design
Intro to Steel Structure
• Determination of dimensions and selection of cross sections.
• The design process is a loop:
CE 411 - Engr. A.Baseer Awan
Structural Design
Intro to Steel Structure
• Optimal structural design shall achieve balance between the following
requirements:
CE 411 - Engr. A.Baseer Awan
Structural Design
Intro to Steel Structure
Roles and Responsibilities of the Structural Steel Designer
Arrange and proportion the members of the structures, using engineer’s
intuition and sound engineering principles, so that they can be practically
erected, have sufficient strength (safe), and are economical.
• Practicality: Ensure structures can be fabricated and erected without
problems
• Safety & serviceability: Ensure structures can safely support the loads.
Ensure deflections and vibrations are controlled for occupants comfort.
• Cost: Minimize costs without sacrifice of strength (consider labor costs in
fabrication and erection (60%), not just material costs (25%))
CE 411 - Engr. A.Baseer Awan
Basic Structural Shapes
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Steel Structure
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Steel Structure
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Steel Structure
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Steel Structure
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Steel Structure
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Steel Structure
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Steel Structure
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Steel Structure
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Steel Structure
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Structural Framework
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Structural Framework
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Structural Framework
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Structural Framework
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Structural Framework
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Structural Framework
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Structural Framework
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Structural Framework
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Structural Framework
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Structural Framework
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Structural Framework
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Structural Framework
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Structural Framework
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Structural Framework
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Structural Framework
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Structural Framework
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Structural Framework
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Structural Framework
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Structural Framework
Intro to Steel Structure
The building structure must be designed to carry or resist the loads that areapplied to it over its design-life. The building structure will be subjected to loadsthat have been categorized as follows:
• Dead Loads (D): are permanent loads acting on the structure. These includethe self-weight of structural & non-structural components. They are usuallygravity loads.
• Live Loads (L): are non-permanent loads acting on the structure due to its use& occupancy. The magnitude & location of live loads changes frequently overthe design life. Hence, they cannot be estimated with the same accuracy asdead loads.
• Wind Loads (W): are in the form of pressure or suction on the exteriorsurfaces of the building. They cause horizontal lateral loads (forces) on thestructure, which can be critical for tall buildings. Wind loads also cause uplift oflight roof systems.
CE 411 - Engr. A.Baseer Awan
Structural Framework
Intro to Steel Structure
Snow Loads (S): are vertical gravity loads due to snow, which are subjected to
variability due to seasons & drift.
Roof Live Load (Lr): are live loads on the roof caused during the design life by
planters, people, or by workers, equipment, & materials during maintenance.
Values of structural loads are given in the publication ASCE 7-05: Minimum
Design Loads for Buildings & Other Structures.
The first phase of structural design consists of estimating the loads acting on
the structure. This is done using the load values & combinations presented in
ASCE 7-05 as explained in the following sub-sections.
• Gravity loads – D, L, R, S
• Lateral Loads – W, E
CE 411 - Engr. A.Baseer Awan
Design Specifications
Intro to Steel Structure
It gives specific guidance for the design of Structural members and
connections
Periodically revised and updated
Structural Steel specification publishers
AISC (American Institute of Steel Construction)
Specifications for design of Structural Steel buildings and
connections
AASHTO (American Association of state Highway and Transportation
Officials)
Design of highway bridges and related structures. It provides for all
structural members used in bridges incl, steel, RC and timber
AREMA (American Railway Engineering and Maint-of-way Association)
Design of railway bridges and related structures. Formally AREA
AISI (American Iron and Steel Institute)
Deals with cold-formed steel
CE 411 - Engr. A.Baseer Awan
Structural Steel
Intro to Steel Structure
Iron was used for small tools in 4000 BC
Wrought iron (produced by heating ore in fire)
In late 18th and early 19th , wrought iron was used in bridges
Steel is an alloy of iron (Fe) and carbon (C) with few impurities
In 1874, first structural steel railroad bridge was Eads bridge in St. Louis
Missouri
In 1884, first building with steel frame was completed in Chicago
Stress, f =P/A
Strain , Ɛ= ∆L/L
CE 411 - Engr. A.Baseer Awan
Structural Steel
Intro to Steel Structure
Iron was used for small tools in 4000 BC
Wrought iron (produced by heating ore in fire)
In late 18th and early 19th , wrought iron was used in bridges
Steel is an alloy of iron (Fe) and carbon (C) with few impurities
In 1874, first structural steel railroad bridge was Eads bridge in St. Louis
Missouri
In 1884, first building with steel frame was completed in Chicago
Stress, f =P/A
Strain , Ɛ= ∆L/L
CE 411 - Engr. A.Baseer Awan
Structural Steel – Stress Strain Relationship
Intro to Steel Structure
Linear relationship up to proportional limit
(Hooke’s Law)
Yield Plateau or Plastic Range
Strain hardening begins at a
strain 12 times strain at yielding
Maximum value of Stress is reached
X-sec is reduced (Poisson effect)
Original cross-sec is used to compute
stress (Engineering Stress)
CE 411 - Engr. A.Baseer Awan
Structural Steel – Stress Strain Relationship
Intro to Steel Structure
Ductile Behavior of Steel
e= (Lf – Lo/ Lo) x 100
Elastic Limit
Yielding Stress (Fy)
Ultimate Stress (Fu)
Young Modulus or Modulus of Elasticity
E = 29, 000 ksi
Strain Hardening is when a metal is strained
beyond the yield point. An increasing stress is
required to produce additional plastic
deformation and the metal apparently becomes
stronger and more difficult to deformCE 411 - Engr. A.Baseer Awan
Structural Steel – Stress Strain Relationship
Intro to Steel Structure
High Strength Steel
Less ductile
Residual Strain
A strain 0f 0.002 is usually selected
to find yield stress
0.2% offset Method
CE 411 - Engr. A.Baseer Awan
Properties of Steel
Intro to Steel Structure
Properties of steel incl strength & ductility are determined by its chemical
composition
Steel is an alloy of iron and carbon
Other components are Copper, Manganese, Nickel, Chromium, Silicon etc
Plain carbon Steel (less than 1% carbon)
Low Alloy Steel (less than 5% carbon)
High Alloy Steel (High %of components added to iron and carbon)
ASTM (American Society for Testing and Materials)
develops standards for defining materials in term of composition,
properties and performance
CE 411 - Engr. A.Baseer Awan
Properties of Steel
Intro to Steel Structure
Most commonly used ASTM A36 or A36 (in short)
Yield Stress, Fy =36ksi
Tensile Strength, Fu=58 to 80 ksi
A36 is classified as plain carbon steel
Carbon: 0.26%
Phosphorous: 0.04%
Sulfur: 0.05%
Other commonly used structural steel are
ASTM A572 Grade 50
ASTM A992
CE 411 - Engr. A.Baseer Awan
Standard Cross-Sectional Shapes
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Standard Cross-Sectional Shapes
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan
Standard Cross-Sectional Shapes
Intro to Steel Structure
CE 411 - Engr. A.Baseer Awan