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DESIGNING A 332 CROSSING TOWERUsing PLS-TOWER 11.16

By: George Watson, Consulting Engineer

CenterPoint Energyformerly Reliant Energy

formerly Houston Industries Inc.

formerly Houston Lighting & Power

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Small Service Area (2.5%)Big Electrical Load (25%)

Texas Peak Load for2010 was 66,000mw

CNP Peak Load for2010 was 16,100mw

(25% of Texas Total)

233 Substations

3800 Miles of T-Lines

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Typical Houston housewith 11 Car Garage

61,000 Square Feet on an 11 Acre Lot

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Ancient Tower Design Tools

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Early Stress Analysis

Graphical Method ofJoints

Many Assumptions toAllow Analysis

Multiple Load Cases

Very Time Consuming

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Calculator from 1973 ($2,000)

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1976 Tower Design on CDC 6600

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Tower hit by a barge of scrap

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PLS-TOWER Face Designation

The windward transverse face is that on which apositive transverse wind (in the positive Y-direction)would blow.

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Adjust Drag Factors

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Start with a basic geometry

Tower Baseis 27 x 18

All Redundants mustbe accounted for in

the Drag AreaCalculations, eitherby adding to themodel or adjusting

the factors

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Start with a basic geometry

Tower Baseis 27 x 18

Redundants addedand Leg Members

split

Crossing Diagonalsjoint added

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Start with a basic geometry

The 7 Joints shownare the Primary Joints

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Start with a basic geometry

The CrossingDiagonal Joints must

be re-calculated if theleg slope is changed

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Add Some Extensions

Add a 40 footExtension

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Add Some Extensions

Add a 20 footExtension

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Add Some Extensions

Add a 32 footExtension

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Add Some Extensions

Add 3 more32 foot

Extensions

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Add Some Extensions

Add another32 foot

Extension

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Add Some Extensions

Add a 48 footExtension

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The Final Starting Geometry

332-0 Tall

109.6 Wide

73.1 Deep

7 Primary Joints

214 Secondary Joints

384 Member Groups

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Evaluate Different Base Spreads

Change OneJoint

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Make the Base Wider

332-0 Tall

124.4 Wide

92.8 Deep

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Make the Base Narrower

332-0 Tall

75.1 Wide

53.3 Deep

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Use PLS-CADD Lite

Max Line Angle

Max Span

Min Line Angle

Min Span

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Generate Design Load Cases

Max Line Angle

Max Span

Min Line Angle

Min Span

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New Tower Version 11.16

Redundant Check and Design

Included Angle Check

Climbing Load Check and Design

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Evaluate the Best Leg Slope

The CrossingDiagonal Joints must

be re-calculated if theleg slope is changed

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Evaluate the Best Leg Slope

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Evaluate the Best Leg Slope

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Evaluate the Best Leg Slope

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Crossing Tower Statistics

Crossing Span is 1700

Anchor Span is 1200

Line Angle is 20

Wind Speed is 120 MPH

Wind on Structure accounts for 77% of FoundationLoad

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Observation

In the days prior to PLS-CADD and Tower, theseWhat-If permutations were not possible withoutmassive manpower and many weeks or months ofEngineering calculations.

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Questions?