civl 331 engineering design process

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CIVIL 331 1/2/2011

CIVL 331 Engineering Design Process 1/2/2011 page 1 of 24

Engineering Design Process

The engineering design process can be defined as a

decision making process using engineering sciences tomeet a desired, measurable goal.

If a product can be engineered with ninety percent of theperformance at fifty percent of the cost, that is good

engineering.

Simple designs to solve complex problems are the mostelegant and complexity for its own sake is unnecessary.


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Sequence of Design Process

1. Establish Functional Specification

2. Concept Design

3. Define Target Values for Functional Requirements

4. Preliminary Design & Analysis

5. Evaluate (o.k = cont., not o.k. = go back to 1. or 2.)

6. Final Design & Analysis


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Functional SpecificationSpecify loads dead, live, wind, seismic, other

Specify space/span requirementsSpecify deflection limits

Specify mechanical function, if any

Specify useful life, if required

Concept Design

Load versus Structural System

Understanding load path


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Structural Systems

Tension hangers, tension ties, tension rings

Compression columns, arches,

compression rings

Bending & Shear beams, trusses

Torsion box beams/columns,

grillage


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Example 1


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Example 2

Loads always flow through the stiffest path

Shorter load paths generally result in more efficient


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Free Body Diagram

A picture of the physical situation you are analyzing, whichdepicts all of the relevant forces acting on the structure of

interest.

Ra Rb

w


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Example 2

Ra Rb

w


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Important factors to consider in Engineering Design

Functionality

Safety

Cost

Aesthetics

MaterialsManufacturability

Method of Construction & Shipping

Maintainability


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Functional Requirements for Engineering Structures

Load carrying/resisting

Vibration/Deflection

Space/Span

Mechanical function(s)

Useful life (fatigue/corrosion)


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Typical Safety Requirements for Engineering Structures

Limit States Design

Codes and standards

Jurisdictional requirements


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Cost Considerations

Engineering cost

Material cost

Manufacturing cost

Shipping cost

Construction costLife cycle cost


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Aesthetics Considerations

Form and style

Environment


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Material Considerations

Strength

Stiffness

Weight

Cost

ManufacturabilityField construction: special process/equipment


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Manufacturability Considerations

Cut/Sheared

Formed

Rolled

Punched/Drilled

Bolted/NailedWelded

Tolerances and distortion


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Method of Construction & Shipping Considerations

Modular construction

Field welded versus field bolted

Max. weight and size for shipping

Crane reach and capacity

Special consideration for remote site


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Maintainability Considerations

Access for inspection and maintenance of mechanicalequipment

Fatigue

Corrosion

civl 331 engineering design process

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