File:Details of railroad truss-bridges (1910) (14780713333).jpg

Identifier: detailsofrailroa00jerv (find matches)
Title: Details of railroad truss-bridges
Year: 1910 (1910s)
Authors: Jervis, Paul
Subjects: Bridges Railroad bridges Truss bridges Theses
Publisher:
Contributing Library: University of Illinois Urbana-Champaign
Digitizing Sponsor: University of Illinois Urbana-Champaign

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These Knee-braces are fastened to thebottom flanges of the top strut and to the intermediate post. Theyare often composed of two angles placed bacK to bacK; and are sup-ported in the middle by means of a short angle,which is attached atthe upper end to the top chord, occasionally they are supported bya solid web plate. PORTAL BRACING.Many different types of portal bracing are used in throughtruss-bridges. This is probably due to the fact that the standard-ization of their details has been retarded by an effort on the partof the different designers to give the portal an artistic effect.The general tendency at present is to use as few members as possi-ble in the construction of the portal bracing. While some of ihemore complicated forms may be better from an aesthetic point ofview,they are less economical and often less effective than thesimpler types of bracing. The most efficient type of portal is shown in Fig.36. Inthis case a relatively low attachment to the end post can be secured
Text Appearing After Image:
Fig.38. Fig.39. 2*. This feature is desirable?since the stress transferred at the footof the Knee-brace causes considerable bending moment in the post. Inthis type of bracing the top strut and long diagonal are the onlymembers which carry stress. The other two members act merely asstiffeners. This type of portal is composed of angles,and they arefastened to the end post in three different ways; (l) they may beattached to upper flange only; (2) they may be attached to both up-per and lower flanges; or (3) they may be fastened to the centersof the end posts. The latter is the most common method of fasten-ing the portal bracing,and it has an advantage in that an eccentricconnection is avoided. The principal disadvantages of connectingthe portal bracing at the centers of the end post are that the riv-ets connecting it to the posts are in the tension; and further,anexpensive diaphragm Is necessary at the connection to transfer thestress equally to both sides of the posts. The first method

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