Pakistan Journal of Engineering & Technology (Aug 2019)
Field Testing and Strength Evaluation of Khushhal Garh Rail cum Road Bridge
Abstract
Old age steel bridges mostly have various problems facing potentially catastrophic result. There is complex array of issues with the railway wrought iron bridges regarding their residual life. Road Cum Rail Bridge near Khushhal Garh is of wrought iron & crosses the River Indus. This bridge is 775 ft. long and consist of four deck truss spans i.e. a 303’-0” anchor arm, a 104’-8” east cantilever (Jand end) , a 261’-0” slung and a 104’-8” west cantilever span (Kohat end). The west cantilever is anchored deep into the rock by means of guys. The upper end of the guys is attached to the top boom while the lower end is connected to anchors of size 10’x 7’-6”x 4’. Roadway is supported on bottom booms of the trusses and railway track is on the top chords. The bridge was opened to traffic on 27th November, 1907. In the course of time this bridge showed some signs of distress, in December 2006, it was decided by the Pakistan Railways Authorities to carry out strength evaluation of this bridge. The task was awarded to a joint venture, Pakistan Railways Advisory and Consultancy Services (PRACS) and Multi-Dimensional Consultants (MDC, Lahore, to conduct field studies, carry out computed model analysis & suggest measures for the repair & rehabilitation of this bridge if required. For field testing, 30 strain gauges were installed at different critical locations of main members of truss. Tensile and compressive strain variation under standard test train were recorded and analyzed. Maximum tensile & compressive stresses in main members were assessed. 22.5 Ton axle group III engine were used with PR standard test train for the test. Stress range and number of loading cycles of the selected members were compared with Wohler Curves for residual fatigue life. On the basis of this comparison, it was concluded that bridge was safe under the loading given in Bridge Rules, 1971 Pakistan Railways & Pakistan Highways Code and residual life has been estimated.
