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Amazing Old Trestle (a Haupt Bridge)
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<p class="MsoNormal"><span style="font-family: verdana,geneva;"><span style="font-size: small;">I began this thread with a focus only on the gigantic / mysterious bridge and the haunting quality of the antique photograph of it.<span style="mso-spacerun: yes;"> </span>This led me to wonder about the nature of the structure supporting the bridge.<span style="mso-spacerun: yes;"> </span>Discovering that information led to wondering about the interesting timber trusses used for the twenty-five spans of this bridge, and wonder about the apparent redundancy of a box truss combined with an arch.<span style="mso-spacerun: yes;"> </span>This led to the discovery of the origin and identity of this unique truss design, which was pioneered by Pennsylvania Railroad bridge engineer, Herman Haupt.</span></span></p> <p class="MsoNormal"><span style="font-size: small;"><span style="font-family: verdana,geneva;"><span style="font-size: small;"> <o:p></o:p></span></span></span></p> <p class="MsoNormal"><span style="font-family: verdana,geneva;"><span style="font-size: small;">This truss design is an outgrowth of the timber lattice truss, which was a box truss reinforced by diagonal latticework bracing.<span style="mso-spacerun: yes;"> </span>Haupt was also a pioneer in the development of this lattice truss, but the structural shortcomings of the design led him to overcome the deficiency by the addition of an arch.<span style="mso-spacerun: yes;"> </span>However, the arch and the lattice truss do not simply add their strength together.<span style="mso-spacerun: yes;"> </span>Instead, the primary load-carrying element is the arch, and the lattice truss merely adds reinforcement to maintain the shape of the arch.<span style="mso-spacerun: yes;"> </span>So there is no redundancy between the box truss and the arch because they both have different functions.<span style="mso-spacerun: yes;"> </span>Fundamentally, for the arch to fail, it must buckle, so the lattice truss maintains the shape of the arch all along the arch’s length, thus preventing it from buckling.</span></span></p> <p class="MsoNormal"><span style="font-size: small;"><span style="font-family: verdana,geneva;"><span style="font-size: small;"> <o:p></o:p></span></span></span></p> <p class="MsoNormal"><span style="font-family: verdana,geneva;"><span style="font-size: small;">Here is a link to an excellent page of details on the Herman Haupt Bridge:</span></span></p> <p class="MsoNormal"><span style="font-size: small;"><span style="font-family: verdana,geneva;"><span style="font-size: small;"> <o:p></o:p></span></span></span></p> <p class="MsoNormal"><a href="http://www.trainweb.org/horseshoecurve-nrhs/Haupt.htm"><span style="font-family: verdana,geneva;"><span style="font-size: small;">http://www.trainweb.org/horseshoecurve-nrhs/Haupt.htm</span></span></a></p> <p class="MsoNormal"><span style="font-size: small;"><span style="font-family: verdana,geneva;"><span style="font-size: small;"> <o:p></o:p></span></span></span></p> <p class="MsoNormal"><span style="font-family: verdana,geneva;"><span style="font-size: small;">In the previous post, I noted the close relationship between the Haupt truss and the Burr truss.<span style="mso-spacerun: yes;"> </span>Here is a link that explores that relationship in detail.<span style="mso-spacerun: yes;"> </span>Interestingly, it mentions that the use of a combined arch and truss was viewed with particular contempt by many who did not understand it:</span></span></p> <p class="MsoNormal"><span style="font-size: small;"><span style="font-family: verdana,geneva;"><span style="font-size: small;"> <o:p></o:p></span></span></span></p> <p class="MsoNormal"><a href="http://mysite.du.edu/~jcalvert/tech/burr.htm"><span style="font-family: verdana,geneva;"><span style="font-size: small;">http://mysite.du.edu/~jcalvert/tech/burr.htm</span></span></a></p>
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