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Introduction to Steel Design

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Presentation on theme: "Introduction to Steel Design"— Presentation transcript:

1 Introduction to Steel Design
ECIV 325 Introduction to Steel Design Instructor Dr. Dimitris C. Rizos

2 Steel Structures

3 Steel Structures

4 Steel Structures


6 Steel Structures

7 Steel Structures

8 Steel Structures


Problem Definition Service Functions Location Surface & Subsurface Conditions Infrastructure Environmental Impact etc Constraints Material Availability Zoning Requirements Construction Expertise ...

11 General Design Procedures
Geometric/Architectural Design Altern. 1 Altern. 2 Altern. 3 ………. Altern. n Final Layout Floorplans Elevations etc

12 General Design Procedures
Preliminary Structural Design Altern. 1 Altern. 2 Altern. 3 ………. Altern. n 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 Select Alternative for Final Design

13 General Design Procedures
FINAL DESIGN Sizing of Members Design of Details Design Drawings* (Blueprints) Bill of Materials Total Cost *Design Drawings Complete and Easy to Read AISC: Detailing for Steel Construction Engineering for Steel Construction

14 Preliminary/Final Design
Define External Loads Safe Functional Economic Select New Sizes NO Estimate/Assume Initial Size of Structural Elements Calculate Self Weigth Structural Analysis Check Design (Codes & Specs) YES O.K.

15 Structural Design Safety Seviceability Economy Practicality

Steel Structural Members Tension Members Compression Members (Columns) Beams Beam-Columns Connections

17 Sructural Steel – Typical Composition
Element Composition % HPS 50W and 70W 100W Mild Steel A36 Carbon (C) 0.11 max 0.08 max Manganese (Mn) 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) 0.40 max Copper (Cu) 0.20 min (when specified) Nickel (Ni) - Chromium (Cr) Vanadium (V) Molybdenum (Mo) Aluminum (Al) Nitrogen (N)

18 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)

19 Structural Steel - Properties
Yield Point: Stress Fy at the elastic limit Ult. Tens. Str: Fu is the maximum stress developed in the inelastic zone

20 Structural Steel - Properties
Residual Strain: Permanent deformation after unloading

21 Structural Steel - Properties
If Yield Point not Clearly Defined 0.2% Method Draw line parallel to elastic part 0.2% Strain

22 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 ductility High toughness

23 Structural Steel - Characteristics
Maintenance: Susceptible to Corrosion when exposed to air and water Use paints, or weathering steels Fireproofing: Strength reduces with increased temperature - Fireproofing required

24 Structural Steel - Sections
Typical Hot Rolled Steel Shapes See AISC Manual PART 1 Section Properties and other shapes

25 Structural Steel - Sections
Typical Cold-Formed Light Gage Steel Shapes See LRFD Manual for other sections

26 Structural Steel - Sections
Built-Up Members

27 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 UNDERSTRENGTH

29 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

30 Design Loads - Types Dead Loads Live Loads Self Weight
Loads Permanantly Attached Walls Floor Roof Plumbing Fixtures etc Easier to determine but are not known a priori Live Loads Occupancy - Floor Loads Snow & Ice Rain Traffic Loads for Bridges Impact Loads Lateral Loads Wind Earthquakes Other

31 Occupancy - Floor Loads
Specified by building codes Check 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 Variation psf

32 Snow & Ice Depend On Typical Variation Account for Location
Slope of Roofs Typical Variation 10 psf (45o slope) psf (North Main) Account for Snow Drift Increased wind loads due to increased surface area of ice coated members

33 Rain Loads More sever on flat roofs Geometric Design for Draining
ponding Geometric Design for Draining Allow for 0.25 in/ft slope with good drainage facilities

34 Bridges - Traffic Loads
American Association of Highway and Transportation Officials AASHTO American Railway Engineering Association AREA Truck and Lane Load Impact Longitudinal

35 Lateral Loads - Wind Depend On Effects Reference geographic location
height above ground types of terrain including surrounding buildings percentage of openings Effects Severe Effects on tall buildings & long flexible structures Reference ASCE Wind Forces on Structures, Transactions ASCE 126 Uniform Building Code

36 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.

37 Other Loads Soil Pressures Hydrostatic Pressures Blast Thermal Forces Centrifugal Forces (trucks on curved bridges)

38 Specifications for Steel Railway Bridges (AREA 1980)
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 International Building Code International Code Council (formerly BOCA, ICBO, and SBCCI)

Design Loads Real Life: Design loads difficult to predict UNCERTAINTIES DESIGN MUST ADDRESS OVERLOAD

40 ASSIGNEMENT READING Chapter 1 Homework 1.5-3, 1.5-6

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