required locations for joining new cables and then stressing them for making up the loss of pre-stress. A new concrete block was constructed inside the box girder in which cables from either side were anchored in cross shape giving overlap. Transverse cables were also provided to take care of the bursting forces on account of longitudinal pre-stressing.
brackets fixed on the tilted silo and diagonally on the opposite side. The jacks were supported on the concrete jacket built around the silo in lower portion.
The concrete of the silo at 7 M. height was broken on the opposite side of the crack. Tilting the silo on the opposite side of the cracks by controlling carefully, lifting and lowering the jacks in stages of 100 mm. After bringing back the silo to its vertical alignment, concreting was done to the damaged portion. The outer jacket was integrated with existing silo. A pre-stressed concrete rig beam was provided on the top of the jacket.
After restoration, the silo is performing well.
9.
9.1 Khuni Nallah Bridge This bridge is on Jammu Srinagar Highway and is situated in the Himalayan terrain, which is prone to landslides. For providing safety to the bridge and traffic, a buffer system is provided on the hillside 13 M. from the bridge. (Photo No.9) The superstructure is a box girder constructed over 2 piers by free cantilever method and anchor spans. The cantilevers are 39.02 M. and 19.82 M. on Srinagar and Jammu side respectively. The anchor spans are 18.6 M. and 8.23 M. The central suspended span is 30.49 M. A mass of about 20 M3 of landslide fell on the valley side girder on Srinagar side pier. The impact was so big that the deck was punctured in an area of 6 M. x 3 M. besides damaging the pre-stressed cables of 12 φ 8 size. Out of 46 cables, 23 cables were completely sheared off and 9 cables were bent or exposed. Concrete was crushed and damaged severely. Suspenders and strands of the buffer system were also snapped.
Photo No. 9-Khuni Nallah Bridge – Damaged Girder
Accidental damage to the Structure
Traffic was restricted to one lane with speed restrictions. The subway nearby was opened to traffic. The following measures were taken to restore the integrity of the decking: Cutting all snapped and damaged cables at
The Bridge and Structural Engineer
Repairing damaged concrete.
Stressing and grouting of cables.
A load test was carried out for maximum flexural and shear effect as per IRC loading. The recovery of deflection measured at the tip of cantilever was excellent.
10. Corrosion of Pre-Stressing Steel 10.1 New Shorrock Mills at Nadiad For this textile unit, roof arrangement consists of prestressed concrete girders over which pre-cast RCC elements are supported. The PSC girders rest on RCC corbels. Humid air is circulated in the weaving section as per quality requirement. Over a period, this led to corrosion of reinforcement as well as pre-stressing steel. Number of RCC corbels has developed distress on account of loss of steel section. Spalling of concrete along the cable profile had taken place in PSC girders. (Photo No.10) Additional supports were provided to the corbels by fixing bolted steel brackets under RCC corbels. In addition to bolting, pre-stressing cables were used to fix the brackets firmly to the parent box girder. Strengthening of roof girders was done by external pre-stressing cables. Two cables were provided on either side of the girder. Cables of 1T15 were anchored Volume 45 Number 2 June 2015 7