ECIV 325 Introduction to Steel Design Instructor Dr. Dimitris C. Rizos [email protected].
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Transcript of ECIV 325 Introduction to Steel Design Instructor Dr. Dimitris C. Rizos [email protected].
Steel Structures
Steel Structures
Steel Structures
Steel Structures
Steel Structures
Steel Structures
GENERAL DESIGN PROCEDURES
Service Functions
LocationSurface & Subsurface ConditionsInfrastructureEnvironmental Impact etc
Problem Definition
Constraints• Material Availability• Zoning Requirements• Construction Expertise ...
Economy
Design It Right the First Time
General Design Procedures
Geometric/Architectural Design
Altern. 1 Altern. 2 Altern. 3 Altern. n
Final LayoutFloorplans
Elevations etc
Economy
……….
Design It Right the First Time
Alternate Use
General Design Procedures
Preliminary Structural Design
Altern. 1 Altern. 2 Altern. 3 Altern. n
Select Alternative for Final Design
……….
Prliminary Design: Location and arrangement of load bearing elements, columns, beams, footings etc., Sizing of structural elements for safety and serviceability
Architectural Constraints - Simplicity & Duplication - Fabrication & Construction Procedures
Economy: Add preliminary $ value to each design
General Design Procedures
FINAL DESIGNSizing of MembersDesign of Details
Design Drawings* (Blueprints)Bill of Materials
Total Cost
*Design Drawings Complete and Easy to Read
AISC: Detailing for Steel ConstructionEngineering for Steel Construction
Preliminary/Final Design
Define External Loads
Safe FunctionalEconomic
Select New Sizes
NO
Estimate/Assume Initial Size of Structural Elements
Calculate Self Weigth
Structural Analysis
Check Design (Codes & Specs)
YES
O.K.
Structural Design
Safety
Seviceability
Economy
Practicality
ECIV 325 OBJECTIVE
FOCUS ON DESIGN OF COMPONENTS
Steel Structural Members
Tension Members
Compression Members (Columns)
Beams
Beam-Columns
Connections
Sructural Steel – Typical Composition
Element
Composition %
HPS50W and 70W
HPS
100WMild Steel A36
Carbon (C) 0.11 max 0.08 max 0.25-0.29
Manganese (Mn) 1.10-1.35 0.90-1.50 1.20 max
Phosphorus (P) 0.020 max 0.015 max 0.04 max
Sulfur (S) 0.006 max 0.005 max 0.05 max
Silicon (Si) 0.30-0.50 0.40 max 0.15-0.40
Copper (Cu) 0.25-0.40 0.90-1.20 0.20 min (when specified)
Nickel (Ni) 0.25-0.40 0.65-1.00 -
Chromium (Cr) 0.45-0.70 0.40-0.65 -
Vanadium (V) 0.04-0.08 0.05-0.07 -
Molybdenum (Mo) 0.02-0.08 0.40-0.65 -
Aluminum (Al) 0.01-0.04 - -
Nitrogen (N) 0.015 max - -
Structural Steel - Properties
Elastic Limit:Transition from elastic to inelastic behavior
Yield Point:Stress Fy at the elastic limit
Elastic Modulus: Slope of elastic part of curve E~29,000 ksi (200,000 Mpa)
Structural Steel - Properties
Yield Point:Stress Fy at the elastic limit
Ult. Tens. Str: Fu is the maximum stress developed in the inelastic zone
Structural Steel - Properties
Residual Strain:Permanent deformation after unloading
Structural Steel - Properties
If Yield Point not Clearly Defined0.2% Method
0.2% Strain
Draw line parallel to elastic part
Structural Steel - Characteristics
Elasticity: Ability of metal to return to its original shape after loading and subsequent unloading
Fatigue: Cycling loading and unloading stresses material above its endurance limit and leads to failure
Ductility: Deformation without fracture beyond the elastic limit (ineleastic behavior)High Ductility
Toughness: Combination of strength and ductilityHigh toughness
Structural Steel - Characteristics
Maintenance: Susceptible to Corrosion when exposed to air and waterUse paints, or weathering steels
Fireproofing: Strength reduces with increased temperature - Fireproofing required
Structural Steel - Sections
Typical Hot Rolled Steel Shapes
See AISC Manual PART 1 Section Properties and other shapes
Structural Steel - Sections
Typical Cold-Formed Light Gage Steel Shapes
See LRFD Manual for other sections
Structural Steel - Sections
Built-Up Members
Structural Steel - Characteristics
Buckling: Instability due to slenderness
Structural Steel
Idealized Case: Material Properties - Uniaxial Cases
Real Life: Multiaxial scenarios determine material strength
UNCERTAINTIES
DESIGN MUST ADDRESS UNDERSTRENGTHDESIGN MUST ADDRESS UNDERSTRENGTH
Design Loads
Most important and difficult task is the accurate estimation of loads applied to a structure over its life
Second most difficult is to determine load combinations
Design Loads - Types
Dead Loads
Self WeightLoads Permanantly Attached
WallsFloorRoofPlumbingFixtures etc
Easier to determine but are not known a priori
Live Loads
Occupancy - Floor LoadsSnow & IceRainTraffic Loads for BridgesImpact LoadsLateral Loads
WindEarthquakes
Other
Occupancy - Floor Loads
Specified by building codesCheck Local (state) specs and requirements
In the absence of any available codes refer to:ASCE Standard 7 Minimum Design Loads for Buildings and Other Structures SEI/ASCE 7-05
Typical Variation40-250 psf
Snow & Ice
Depend On• Location• Slope of Roofs
Account for• Snow Drift• Increased wind loads due to increased surface area of ice coated
members
Typical Variation10 psf (45o slope) - 100 psf (North Main)
Rain Loads
More sever on flat roofsponding
Geometric Design for DrainingAllow for 0.25 in/ft slope with good drainage facilities
Bridges - Traffic Loads
American Association of Highway and Transportation OfficialsAASHTO
American Railway Engineering AssociationAREA
• Truck and Lane Load• Impact• Longitudinal
Lateral Loads - Wind
Depend On• geographic location• height above ground• types of terrain including surrounding buildings• percentage of openings
Reference• ASCE Wind Forces on Structures, Transactions ASCE 126• Uniform Building Code
EffectsSevere Effects on tall buildings & long flexible structures
Lateral Loads - Earthquakes
Depend On• geographic location - area seismicity• soil conditions• dynamic properties and characteristics of structure
Analysis & Design• Dynamic• Equiv. Static :Horizontal Loads associated to the mass of the structure• Bracing, Special Connections, Design for Shear etc.
Other Loads
Soil PressuresHydrostatic PressuresBlastThermal ForcesCentrifugal Forces (trucks on curved bridges)
Loads - References
ASCE Minimum design loads for buildings and other structures SEI/ASCE 7-05 NY
Specifications for Steel Railway Bridges (AREA 1980)
Standard Specifications for Highway Bridges (AASHTO)
ICC IBC-2006 2006 International Building Code International Code Council (formerly BOCA, ICBO, and SBCCI)
Design Loads
Real Life: Design loads difficult to predict
UNCERTAINTIES
DESIGN MUST ADDRESS OVERLOADDESIGN MUST ADDRESS OVERLOAD
ASSIGNEMENT
• READING– Chapter 1
• Homework– 1.5-3, 1.5-6
