FM 5-277 CHAPTER 5 ROLLER LAYOUT This chapter describes the longitudinal and lateral spacing of rocking rollers and plain rollers. The elevation o...
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FM 5-277




This chapter describes the longitudinal and lateral spacing of rocking rollers and plain rollers. The elevation of rollers and base plates, as well as a simple method of leveling and placing rollers, is discussed. LAYOUT OF ROCKING ROLLERS Establish the longitudinal location of the rocking rollers by the safety setback determined in the field design of the bridge. To determine the lateral spacing, place a rocking roller (Figure 5-1, page 58) on each side of the bridge 7 feet 5 inches (2.26 meters) from the centerline (Figure 5-2, page 58). This gives a constant value of 14 feet 10 inches (4.52 meters) between the centers of the rocking rollers. Most bridges are double- or tripletruss and need another set of rocking rollers (Figure 5-3, page 59) placed 1 foot 6 inches (.46 meter) out from each of the first set of rocking rollers (Figure 5-4, page 59). Rocking-roller templates have been made which help the proper 1-foot 6-inch (.46 meter) center-to-center spacing of the rocking rollers. On the interior side of these templates, smallangle iron lugs are attached to aid roller spacing. The edge-to-edge spacing of the rocking-roller templates (lug to lug) is 11 feet 6½ inches (3.51 meters) (Figure 5-4). The lugs are, however, frequently lost through use and the most accurate method of spacing the rollers is to use the 14-foot 10-inch (4.52 meters) constant. The Bailey bridge transom is manufactured with a small hole in its

center web and two dowel holes toward each end. These holes can be used to properly space the rocking rollers, as shown in Figure 5-5 (page 60). LAYOUT OF PLAIN ROLLERS To determine longitudinal spacing, place two or more plain rollers every 25 feet (7.6 meters) behind the rocking rollers to support the bridge during assembly and launching. Place temporarily an extra set of plain rollers (called construction rollers) 12½ feet (3.8 meters) behind the rocking rollers. The construction rollers aid in inserting the launching-nose links and provide clearance between the links and the ground. Remove these construction rollers after the links have passed over the rocking rollers. To determine lateral spacing, for single-story, single- and double-truss bridges, place two plain rollers one on each side of the centerline every 25 feet (7.6 meters). The center-to-center roller spacing is 14 feet 10 inches (4.52 meters) or 7 feet 5 inches (2.26 meters) each side of the centerline. Plain rollers are normally placed on plain-roller templates which increase the bearing area over the ground. These templates also aid in the lateral spacing of the rollers. The templates are equipped with angle iron lugs, like the rocking-roller templates. Place the template so the lugs face the centerline. The distance between lugs, then, is 11 feet 6½ inches (3.51 meters) (Figure 5-6, page 60).

For all other assembly types use four plain rollers every 25 feet (7.6 meters), two on each side of the centerline. Each plain roller consists of two small independent rollers. For triple-truss or multistory bridges, place the inside plain rollers so that the inside truss will rest upon the second small roller (Figure 5-7, page 60). The spacing between the centers of these small rollers, then, is 14 feet 10 inches (4.52 meters). Place the other set of plain rollers so that the second truss will rest on the first small rollers of this set (Figure 5-7). The distance between these trusses is 1 foot 6 inches (.46 meter). The third truss will rest on the outermost small roller. Plain-roller templates also aid in lateral spacing of the plain rollers for the triple-truss or multistory bridges. Use one template under each roller. Place two templates end to end on each side of the centerline, with the angle iron lugs of the inside templates facing center and the outside lugs facing away from center. When the spacing between the inside lugs is 10 feet 10% inches (3.31 meters), the plain rollers will be at the proper spacing (Figure 5-7). BASE PLATES Establish, by the type of grillage required, longitudinal spacing between the center of the rocking rollers and the center of the base plate. The grillage type is determined as described in Chapter 4. To establish lateral spacing, place the base plates under the trusses as shown in Figure 5-9 (page 61). 57

FM 5-277

Space the bearings on the base plates (under the trusses), as shown in Figures 5-8 (page 61) and 5-9. GRILLAGES Figures 4-5 through 4-11 show the size of the areas to be leveled off to accommodate the grillages. Take care that the rocking rollers and base plates are properly positioned when placed on the grillage. The grillage can be cribbed up or dug in as needed for leveling. ELEVATION OF ROLLERS AND BASE PLATES Set the base plates at an elevation to keep the slope of the ramp bays less than 10 to 1. Also, allow for the depth of wear tread. Set all rollers (both plain and rocking), except the construction rollers, so their tops are in the same horizontal plane. Normally this plane is level, but a slight inclination, not to exceed 30 to 1 slope along the line of the bridge, is permissible. Set the construction rollers 2 to 4 inches (5.1 to 10.1 centimeters) below the level of the other rollers. Placing the far-bank rocking rollers a few inches lower than the plane formed by near-bank rollers allows for near-bank settlement caused by bridge weight. PLACEMENT CONTROL LINES A simple method of leveling and placing rollers is the use of placement control lines. The bridge centerline is first placed and extended 25 feet (7.6 meters) on the far shore and the length of the bridge and launching nose on the near shore. Then position two placement control lines parallel to and 7 feet 58

FM 5-277

5 inches (2.26 meters) to either side of the centerline. Position the placement control lines level with the proposed plane of the rollers. Use line levels at several spots on the placement control lines to ensure that they are level. It is also important to ensure that the placement control lines are parallel to the centerline. The rollers can then be cribbed up or dug in as needed to bring their tops to the level of the placement control lines (Figure 5-10, page 62).


FM 5-277


FM 5-277


FM 5-277


This change supersedes page 62.