THE PACK RIVER BRIDGE AS AN AREA 

 FIRE INTENSITY INDICATOR 



The Sundance Fire burned with extreme 

 intensity in many areas, as exhibited by rock 

 spalling and complete burnout of ground 

 fuels. The area where the fire crossed the Pack 

 River is a notable example. Here, the visitor is 

 awed by the coupled effects of high winds 

 and intense fire activity. Nearly all the large 

 trees — cedars and hemlocks — have been up- 

 rooted or broken and are lying charred among 

 the grey ash remains of ground fuels. Also, 

 the remains of the Pack River Bridge are mute 

 evidence of the fire's passing. There has been 

 much speculation about the intensity neces- 

 sary to result in the complete burnout of the 

 approach spans and distortion of the carbon 

 steel plates covering the deck runway. This 

 short study is intended to establish the rela- 

 tionship, if any, between fire intensity at the 

 bridge and in the surrounding area. 



Extent of Fire Damage 

 to the Bridge 



The bridge spans the Pack River in a nearly 

 north-south direction near the McCormick 



Creek inlet as shown on the foldout map. 

 Three connected segments make up the 

 bridge: the center span resting on two con- 

 crete piers in the stream bed and two ap- 

 proach spans resting on concrete footing on 

 the streambank. The design is shown in figure 

 28. The center span is 65 ft, long by 14 ft. 

 wide. Each approach span is approximately 

 24 ft. long by 14 ft. wide. The decks of the 

 approach spans are 6 inches thick, and are 

 made up of laminated 2- by 6-inch boards. 

 Strength is given to the deck by nine traverse 

 beams 8- by 20 inches by 24 feet, spaced 

 along the length of the span. Carbon steel 

 plates 5/16-inch thick were also placed on the 

 deck runways to provide traction and reduce 

 wear. The primary structural material used 

 was creosote-treated Douglas- fir. 



Fire damage to the bridge was confined 

 essentially to the approach spans; although 

 there was evidence of burning at each end of 

 the central span, the major portion of it was 

 unscorched by the 'surrounding fire activity. 

 Figure 17 (main text) shows the burnout of 

 the north approach span. Figures 29 and 30 

 show other views of the bridge. Notice the 

 unbumed paint on the central span shown in 

 figure 29. Figure 30 shows the complete burn- 



Figure 28. — Side elevation of Pack River Bridge. 



33 



