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*I-84 [#cba17078] **1.Field of application [#s979745a] >Interstate Route 84,eastbound and westbound, spans the Housatonic River between Newtown and Southbury, Connecticut. The eastbound structure, built in 1953, is riveted construction and contains no cracking. The westbound structure which is bolted and welded construction opened in 1978. **2.Circumstances of repair [#d6023602] >Fatigue cracks were found in the girder web gap of both the bracket and floorbeam connections after 6 years of service. **3.Types of structure [#tad86cb4] >The structure consists of main girders, floorbeams, cantilever brackets, stringers. The plan and elevation views are shown in [[figure 1>#fig1]]. At the floorbeam-main girder connection, the floorbeam web is bolted to a connection plate which is fillet welded to the main girder web. Directly opposite the floorbeam-main girder connection, the cantilever bracket web is bolted to a connection plate which is fillet welded to the main girder web([[Fig.2>#fig2]]). The main girder web is slotted for a tie plate which is bolted to the floorbeam flange and the cantilever bracket flange, to frame through. >Lateral cross bracing exists between the two main girders. >The Westbound structural steel of the girder flanges is ASTM A588, all other steel is ASTM A36. &br; CENTER:&aname(fig1);&attachref(i84_ht62.gif);&br; &br; CENTER:Fig.1 Plan and elevation of I-84 over Housatonic River. &br; CENTER:&aname(fig2);&attachref(i84_ht61.gif);&br; &br; CENTER:Fig.2 Schematic of bracket, floorbeam, and main girder. &br; **4.Details of loading [#t35be752] >Fluctuating loads due to vehicles live load. **5.Description of damage [#d92ed5e4] >Fatigue cracks were found in vertical gaps of the connection plates along the fillet weld toe which attached the floorbeam and cantilever bracket webs to the main girder web ([[Fig.3>#fig3]]) and in the horizontal gaps along the web fillet weld toe which attached floorbeam web to floorbeam flange and bracket web to bracket flange. &br; >Causes of fatigue crack were as follows: -The structural flexibility of floor system resulted in a differential displacement between the floor system and the girders. --(The longitudinal movement of the tie plate which was caused by the differential displacement.) --(The longitudinal movement of the connection plate (out-of-plane displacement ) and the floorbeam flange.) &br; CENTER:&aname(fig3);&attachref(i84_ht63.gif);&br; &br; CENTER:Fig.3 Cracks along fillet weld toes. &br; **6.Repair method applied [#n244c181] -The horizontal web gap --1984-- 19mm hole-drilling at the crack tips. -The vertical gap --1984-- 19mm hole-drilling at the crack tips. Remove the top bolts of the floorbeam and bracket connection plates ([[Fig.4>#fig4]]). --1985-- Remove two additional bolts from the connection plates and Remove 305mm of the connection plate ([[Fig.5>#fig5]]). --1987-- Peening for several inches from the flame cut connection plate end at the weld toe of the floorbeam and bracket connection plates. -Other --1985 Bracing was accomplished in the main girder compression flange([[Fig.6>#fig6]]). >Final retrofit is [[figure 7>#fig7]]. &br; CENTER:&aname(fig4);&attachref(i84_ht63.gif);&br; &br; CENTER:Fig.4 1984 retrofit procedure for weld toe cracks.&br; &br; CENTER:&aname(fig5);&attachref(i84_ht64.gif);&br; &br; CENTER:Fig.5 1985 retrofit procedure for slot enlargement, connection plate partial removal, and 1987 peen.&br; &br; CENTER:&aname(fig6);&attachref(i84_ht65.gif);&br; &br; CENTER:Fig.6 1985 retrofit of compression flange.&br; &br; CENTER:&aname(fig7);&attachref(i84_ht66.gif);&br; &br; CENTER:&aname(fig8);&attachref(i84_ht67.gif);&br; &br; CENTER:Fig.7 Cut connection plate and original welds remaining on girder.&br; &br; &br;
