Exercise: 1) Construct static demonstration models of the Howe, Pratt, and Warren truss

                   bridges.  Do destructive testing of the models.  Graph your results.

               2)  Advanced - Test the holding strength of the pinge joint.  Use this value to

                    predict the maximum loads and specific mode of failure of the models based

                    on a computer static analysis. Compare actual and predicted values.

               3) More advanced - Using the load results from 1) compute the maximum tensile

                   stress experienced by any member of a model using manual static analysis

                   techniques. Compare this with the pinge joint test results of 2).


Note:  The forgoing model analyses are only meant to show general relationships between

applied loads, spans, weights of structures, structural geometries, etc.  Real bridges will

have significantly different structural characteristics than these models exhibit due to the

types of materials used, their structural properties and dimensions, specific design details,

applications, etc.


The truss bridges discussed so far have all been "through" truss designs where the bridge

traffic passes under the cross braced portal opening and between the trusses.  Two other

basic designs carry their traffic differently - the deck truss and pony truss bridges.

Deck truss bridge
The deck truss bridge carries the traffic on top of its truss structure.  As a result the top chord

is subject to compressive stresses mainly while the bottom chord experiences mainly tensile

stresses.  That is, opposite that of the through truss designs.





click image to enlarge

a) Howe

b) Pratt

c) Warren


Fig. 178 - Howe, Pratt, and Warren deck truss bridges  (static demonstration models)




Fig. 179 - Warren deck truss bridge ►


(scale visualization model)

click image to enlarge




Pony truss bridge


The pony truss carries the traffic between trusses that are

not cross braced with a portal.


◄  Fig. 180 - Pony truss bridge  (visualization model)


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Page 111 - Building stability - Deck and Pony truss bridges

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