H O W E T R U S S HISTORY, USE AND STRUCTURAL ANALYSIS 143 bridges - - PowerPoint PPT Presentation

H O W E T R U S S

HISTORY, USE AND STRUCTURAL ANALYSIS

H I S T O R Y

143 bridges are supported by the Howe

Truss Secondary only to the Burr Truss in populari- ty in the U.S.

15% of all covered bridges are Howe

Truss configurations. Originally patented by William

Howe with variations designed my

Harris, Stone and Thomas Pratt. Designs were based on stress anal-

ysis which was a first amongst early truss-

• es. Detailed diagrams accompanied

Howe’s patents. Its configuration was easy to as-

semble and had readily pre- fabricated components, leading

to its success.

1840 1850 1st patent

William Howe

• An all-timber

variation of the first Howe Truss

2nd patent

William Howe

• Incorporated

metal compo-

nents into the same design

3rd patent

William Howe

• Timber arch
• n the side similar to

Burr Truss

All-steel varia-

tions on Howe and Pratt’s Trusses became common- place.

Pratt Truss

• Parallel chords and vertical

struts in wood and ‘X’ in wrought iron diagonals

Harris & Stone

• Design similar modifications of

Howe’s Timber Truss

Cast Iron = compression members Wrought Iron = tension members

In a Howe truss, the vertical supports hold the tensile forces, while the diagonal supports dis- tribute the compression forces.

This configuration of diagonals and verticals allow the Howe truss to span a greater distance than

• ther trusses. In current practice 6.1m (20ft) to 61 m (200ft)

COMPRESSION & TENSION

Scissors Pitched Beam Flat

TRUSS CONFIGURATIONS

http://www.diracdelta.co.uk/science/source/t/r/truss/source.html#.Umadz_nrxPc http://www.coveredbridgesite.com/ny/truss.html http://www.northlandtrusssystems.com/roof_trusses.html

CONFIGURATIONS

TYPICAL USES

Railroad Bridges Roof Trusses Covered Bridges

GENERAL CONSTRUCTION

Joints for the Steel Truss

STEEL JOINTS

P I T C H E D M O D E L

B E A M M O D E L