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*King Street Bridge [#p6543ae9]

**1.Field of application [#v0138ede]

>King street Bridge across the River Yarra at Melbourne between two earlier crossing points, Spencer Bridge and Queen Bridge, Australia ([[Fig1>#fig1]],[[2>#fig2]]). 

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CENTER:Fig.1 Bridge area.
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CENTER:Fig.2 King street Bridge, looking south. 
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**2.Circumstances of repair [#bdc9fba8]

>The main bridge was completed on 12 April 1961. On the morning of 10 July, 1962, that is to say one of the coldest days of the Melbourne, winter-the temperature was 30 F-, one span collapsed. 

**3.Types of structure [#w312ece8]

>The bridge consists of two 2,300-ft-long and is of welded, deck-girder, suspended-span construction, with spans up to 160 ft. The cross section is shown in [[figure 3>#fig3]]. The superstructure consisted of reinforced concrete decking cast in site. The steel used conforms closely with British Standard Specification 968. ( Steel conforming to BSS 968 has a minimum yield point of 55,000 psi and an allowable basic design stress of 26,000 psi in normally used in Australia.)

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CENTER:Fig.3 Cross section. 
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**4.Details of loading [#l84a6473]

>Fluctuating loads due to vehicles live load. 

>One span collapsed under the load of s semi-trailer vehicle with a total weight of 47tons; a load within the permissible limits for the bridge.  

**5.Description of damage [#hc95510c]

>The collapsed span was made up of four 100 ft long suspended girders, and each girder fractured at a point 16 ft from the northern end of the span. The structure sagged 18 in. Inch-wide cracks spread acrossed the deck. 

>The cause of the failure was given as brittle fracture, at a point on each girder where a change in flange section occurred. The night temperature contributed to the collapse. The flanges of the girders were thickened locally by welded-on cover plates ([[Fig.4>#fig4]]), and each fracture was at the point of termination of one of these cover plates ([[Fig.5>#fig5]]). The cover plates were welded manually. 

>Under bead cracking was observed in welds at ends of tension-flange cover plates. It was suggested that the cause of the cracks might have been due to a lack of preheating at these points or to the presence of excess hydrogen or inadequate precautions for the difficulties of welding. 

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CENTER:Fig.4 Flange of a girder with cover plate. 
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CENTER:Fig.5 Clack and fracture location.
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**6.Repair method applied [#qa581c40]

>The recommended repair was to pre-stress the girders with steel cables or other devices within the depth of the present structure so that flanges liable to cracking under tension would be subjected to compressive stresses. 

**Reference [#ff51a569]
>'''Engineering News Record,'''Sept., 20, 1962.

>'''Engineering,''' Sept., 21, 1962.

>Nishimura T. and Miki C., Fracture of Steel Bridges Caused by Tensile Stress, '''J. Japanese SCE,'''      Nov., 1975. (In Japanese)
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