*Lehigh Canal and River Br. [#l987ee92]
**1.Field of application [#z65ce600]
>The Lehigh Canal and River Bridge on US-22 carries traffic over the Lehigh Canal and River near Bethlehem, Pennsylvania.
**2.Circumstances of repair [#j715a0f2]
>Fatigue cracks were found in the tie plates in the spring of 1972 after 19 years of service. All of the tie plates were replaced between 1977 and 1978.During site inspections in 1987 and 1988, cracking was not observed in the tie plates. However cracking was found in the floorbeam and the cantilever bracket webs at the top web copes. Therefore, repair was required.
**3.Types of structure [#p48a4aef]
>Each structure is continuous for three spans and is composed of multiple longitudinal stringers, two longitudinal girders, transverse floorbeams, transverse cantilever brackets and lateral bracing. The framing plan and girder elevation views are shown in [[figure 1>#fig1]],[[2>#fig2]].A typical cross section is shown in [[figure 3>#fig3]]. The reinforced concrete deck is noncomposite construction and is supported by the stringers which are supported by the floorbeams and the cantilever brackets. The floorbeam and bracket webs are riveted to connection angles which are riveted to the girder web. The top flange of the floorbeam and bracket are connected with the tie plate ([[Fig.4>#fig4]]). The structural steel was ASTM A36.
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CENTER:Fig.1 Framing plan and girder elevation view.
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CENTER:Fig.2 Stringer, floorbeam, girder, and lateral bracing connections.
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CENTER:Fig.3 Typical cross section.
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CENTER:Fig.4 Plan view of 1953 tie plates.
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**4.Details of loading [#n1c91946]
>Fluctuating loads due to vehicles live load.
**5.Description of damage [#c2a69cd1]
>Fatigue cracks were found in the tie plates ([[Fig.5>#fig5]]) and the floorbeam and bracket webs at the top cope. Causes of fatigue crack were as follows:
>In case of the tie plates.
-Out-of-plane bending of the tie plates resulted from horizontal differential movement between the girders and the floorbeams and brackets ([[Fig.6>#fig6]]).
-Remainder of tack welds used to connect the tie plate to the bracket flange during fabrication.
>In case of the floorbeam and bracket webs at the top cope.
-Out-of-plane bending resulted from horizontal differential movement between the girders and the floorbeams and brackets.
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CENTER:Fig.5 Crack of the tie plate originated from tack weld.
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CENTER:Fig.6 In-plane-bending in the tie plate and out-of-plane bending of the tie plate.
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**6.Repair method applied [#x54e6f20]
-In case of the tie plates.
>All of the tie plates were replaced ([[Fig.7>#fig7]]) and these retrofits were effective.
-In case of the floorbeam and bracket webs at the top cope.
>Retrofit holes were drilled in the webs at the crack tips. However, the measured stress range at the retrofit hole edge was sufficient to reinitiate fatigue cracking. Removing the top 180mm of the outstanding legs of the connection angles was recommended ([[Fig.8>#fig8]]).
>However, this procedure which was tried on two floorbeams in Nov.1988 did not reduce the cyclic stress to a satisfactory level. Therefore, the trial retrofit suggested to remove 254mm lengths of angle. This had not been executed until 1989 ([[Fig.9>#fig9]]).
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CENTER:Fig.7 Detail of the tie plate replaced.&br;
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CENTER:Fig.8 Suggested 1988 retrofit procedures.&br;
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CENTER:Fig.9 Suggested 1989 retrofit procedures.&br;
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