Rocker Bearings | Cosmec

We think you have liked this presentation. If you wish to download it, please recommend it to your friends in any social system. Share buttons are a little bit lower. Thank you! Published by Jalyn Forge Modified over 6 years ago. Rocker bearings Roller bearings Bearing adopted by Railway Board. One end of the bridge girder is fixed in position rocker bearing is suitable for span, the other end is kept free for the horizontal movement.

For all spans in excess of 9 m, the provisions are made for change in length due to temperature and stress variation. The provisions for expansion and contraction should be such as to permit movement of the free bearings to the extent of 10 mm for every 10 m of length. For spans greater than 15m, on rigid pier or abutment, the bearings, which permit angular rotation at the girder rocker bearing is suitable for span, are provided, and at one end, there shall be a roller or other effective type of expansion bearing.

Provision shall be made against any uplift to which the bearing may be subjected. All bearings are designed to permit inspection and maintenance. Plate bearings are simplest type of bearings. The plate bearings are used small spans upto 15 m and small end reaction of the bridge.

Fig shows a plate bearing. The plate bearing consists of two plates. The sole plate rests on bearing. The bearing plate is anchored to the concrete.

The two anchor bolts fixed in concrete pass through the bearing plate and the sole plate. The size of bearing plate is found by the end reaction and the allowable bearing pressure on the concrete. The plates are made rigid to distribute the end reaction as uniformly as possibly over the required area of the concrete. When the anchor bolts pass through the circular holes in the sole plate, then, the plate bearings act as hinged bearing.

One end of the bridge girder is hinged or anchored to the concrete through the hinged bearings. The magnitudes of end reactions used are large. Therefore, the fixed bearings designed for end reactions vertical loads only strong enough to take the lateral forces. In order to allow the longitudinal movement, the slotted holes are provided in the sole plate. In order to reduce the friction, the surfaces of sole plate and bearing plate in contact are well machined and smoothly finished.

The sole plate can slide upon the bearing plate. The plate bearings act as expansion bearings of sliding type.

In the expansion bearing, the longitudinal movement expansion or contraction takes place with change of temperature and loads.

The coefficients of friction for different rocker bearing is suitable for span in contact are given in clause 6. The plate bearings have bearing two disadvantages.

The edge of plate nearest to the end of span has a tendency to lift along with the deflection rocker bearing is suitable for span bridge girder. Therefore, the end reaction is not distributed uniformly. Secondly, in order to have longitudinal movement, the sliding friction is to be overcome. Therefore, for the large span bridges, the more efficient devices are necessary. The sole plate bearings are many times made curved as shown in Fig The curved sole plate allows rotation.

For large spans, the plate bearings are not suitable. The hinged rocker bearings and roller bearings are used rocker bearing is suitable for span such cases. The sliding bearing is the least expansive bearing for light and intermediate reactions.

Fig This type of support may be used where resistance to uplift need not be provided. For example, it may be used for inside beams of the beam bridge, with the outside beams supported by bearings of the type as shown in Fig.

Several variations are shown in the view at the right. The sole plate may be bolted to the girder, as at the rocker bearing is suitable for span of the centerline, or welded as shown at the right.

Resistance to uplift may Point Rocker Bearing be provided by using a hinge plate, as at the left; if such resistance is needed, lateral movement is prevented by a plate such as that shown at right. A corresponding hinged end bearing is shown in Fig. Evidently, at a given load this area increases with increase in radius of the rocker, since a rocker of infinitely large radius would have a plane surface to begin with. The allowable load must be evaluated in terms of limiting permanent deformation.

Thus the yield point of the material is also a factor. These bearings consist of: An upper sole plate; in rolled steel riveted to the girder. Fixed to masonry by ribs. The bearing plate shall rest on a 3 mm sheet of lead and shall provided with masonry ribs to transmit the horizontal reaction Ball Bearing Slides For Drawers Uk of the bridge.

A cylindrical pin is inserted in between the cast steel sole and the cast steel bearing block. This pin allows rotations at the ends of bridge girder.

The rocker bearing acts as hinged bearing. The end reaction of a bridge girder is transmitted to the pin by direct bearing through the sole attached with the girder. The vertical plates are used to transmit the end reaction. The number of plates two or three depends upon the magnitude of end reaction. The end reaction is further transmitted to the cast steel bearing block and then to the supporting structure. In case, the bearing is subjected to an uplift, then, the uplift is resisted by theses plates.

The middle plates provide only bearing with the cylindrical surface of the pin. The required bearing area is provided by the product of total thickness of plates and the diameter of pin. The thicknesses of all the plates are kept equal. Therefore, the end reaction is transmitted equally by these plates.

The Rocker Arm Bearing Failure value of bending moment is found by multiplying force transmitted by outer plate of the sole to the outer plate of bearing block and center to center distance between these plates.

The size of base plate is found by the rocker bearing is suitable for span bearing stress in the concrete and the end reaction. The increase of end reaction due to lateral and longitudinal forces is also taken into rocker bearing is suitable for span. The lateral forces and the longitudinal forces are assumed to act at the level of cylindrical pin of the rocker bearing. The base plate is subjected to moment along both the directions.

The total bearing stress in the concrete should not exceed the allowable bearing stress. The rocker bearings are designed for the end reaction and then checked for lateral forces and longitudinal forces. Figure 3. This acts as rocker type expansion. The roller bearings as shown in Fig are also used for the long span bridges.

Fig A shows a single roller used in the bearing. The rollers provide the rotation as well as the longitudinal movement. Fig B shows number of rollers used rocker bearing is suitable for span the bearing.

The bearings act as roller type expansion bearings. The rollers are kept in position by means rocker bearing is suitable for span dowels, lugs or keys as shown in Fig A. The roller bearings for spans above span 35 m should preferably be protected from dirt by oil or grease box.

Rocker bearing is suitable for span the size of rollers become large, then, the sides of rollers are cut in order to reduce the length of the sole, and to make the bearings more compact. These rollers with cut sides are known as segmental rollers. The spacing between segmental rollers and the width of rollers may by found as below: It is assumed that the rollers don not slip but only roll during rolling.

When, the roller rolls to the maximum position, as shown in FigFig Then, i 3. The roller bearings are also used to support the cast steel sole with pin bearings as shown in Fig In such cases the roller also acts as a hinged bearing. The sole transmits the end reaction to the pin.

The end reaction must be distributed from the pin to the various rollers uniformly. The size and number of rollers provided should be adequate to have proper stress and free movement. The rollers should be so arranged that these can be readily cleaned of accumulated dirt and dust.

Segmental rollers Fig are ordinary used since they occupy less space than cylindrical rollers. Sidebars may be omitted if each roller is held by teeth. Lateral movement is prevented by the tongues shown in the view at the right. Resistance to uplift may be provided by lugs that have projections extending over the upper surface of the rocker bearing is suitable for span of the shoe or by enlarging the base of the shoe and providing slotted holes for the anchor bolts.

The roller assembly may be enclosed with removable dust guards; they are shown on only two sides in Fig to indicate that they are optional. It must project on either side to allow for Ball Bearing Slides For Drawers Ii longitudinal movement of the bridge.

In case of two rollers the B. Formula of Hertz for contact between a plane and cylinder of radius R and length L is; Assuming equal distribution of the reaction V on all rollers.

Jun 01,  · Fixed Rocker bearing With the deflection of the girder, the top inverted shoe rotates over the pin and this allows free angular movement of the girder at its end. Suitability – This type of bridge bearings is suitable for a long span (20m long) of the girder www.- ted Reading Time: 4 mins. Sep 12,  · It is specified by ASSHTO that sliding bearing cannot be used unless the bridge span is smaller than 15m. This is because sliding bearing cannot be purely used if the bridge experiences rotation movement. However, the span restriction for sliding bearing utilization can be disregarded when it is used in combination with other bearing www.- ted Reading Time: 5 mins. Question is ⇒ Fixed plate bearings are suitable for spans, Options are ⇒ (A) Less than 8 m, (B) Upto 12 m, (C) 12 to 20 m, (D) More than 20 m, (E), Leave your comments or Download question paper. For Rocker bearing L>20m but. Fixes plate bearing L up-to 12m!! OOPS Login 1/ of the span 1/ of the span 1/ of the span.

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