GENERAL DESIGN PROCEDURES Service Functions Location Surface & Subsurface Conditions Infrastructure Environmental Impact etc Problem Definition Constraints Material Availability Zoning Requirements Construction Expertise...
General Design Procedures Geometric/Architectural Design Altern. 1Altern. 2Altern. 3Altern. n Final Layout Floorplans Elevations etc ……….
General Design Procedures Preliminary Structural Design Altern. 1Altern. 2Altern. 3Altern. 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 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
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.
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 % HPS 50W and 70W HPS 100W Mild Steel A36 Carbon (C)0.11 max0.08 max0.25-0.29 Manganese (Mn)1.10-1.350.90-1.501.20 max Phosphorus (P)0.020 max0.015 max0.04 max Sulfur (S)0.006 max0.005 max0.05 max Silicon (Si)0.30-0.500.40 max0.15-0.40 Copper (Cu)0.25-0.400.90-1.200.20 min (when specified) Nickel (Ni)0.25-0.400.65-1.00- Chromium (Cr)0.45-0.700.40-0.65- Vanadium (V)0.04-0.080.05-0.07- Molybdenum (Mo)0.02-0.080.40-0.65- 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 If Yield Point not Clearly Defined 0.2% 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 ductility High toughness
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
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 - 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
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 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
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
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 (45 o slope) - 100 psf (North Main)
Rain Loads More sever on flat roofs ponding Geometric Design for Draining Allow for 0.25 in/ft slope with good drainage facilities
Bridges - Traffic Loads American Association of Highway and Transportation Officials AASHTO American Railway Engineering Association AREA 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 Effects Severe 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 Pressures Hydrostatic Pressures Blast Thermal Forces Centrifugal 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 OVERLOAD