10. GENERAL DESIGN PROCEDURES
Service Functions
Location
Surface & Subsurface Conditions
Infrastructure
Environmental Impact etc
Problem Definition
Constraints
• Material Availability
• Zoning Requirements
• Construction Expertise ...
Economy
Design It
Right the
First Time
12. 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
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.
16. ECIV 325 OBJECTIVE
FOCUS ON DESIGN OF COMPONENTS
Steel Structural Members
Tension Members
Compression Members (Columns)
Beams
Beam-Columns
Connections
17. Sructural Steel – Typical Composition
Element
Composition %
HPS
50W and 70W
HPS
100W
Mild 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 - -
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
21. Structural Steel - Properties
If Yield Point not Clearly Defined
0.2% Method
0.2% Strain
Draw line parallel to elastic part
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
27. Structural Steel - Characteristics
Buckling: Instability due to slenderness
28. 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
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
40-250 psf
32. 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 Variation
10 psf (45o slope) - 100 psf (North Main)
33. Rain Loads
More sever on flat roofs
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
• 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
Effects
Severe Effects on tall buildings & long flexible structures
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.
38. 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)
39. Design Loads
Real Life: Design loads difficult to predict
UNCERTAINTIES
DESIGN MUST ADDRESS OVERLOAD
