Functions of Bearings for BridgesFunction of Bearings:Bridge bearings are used to transfer forces from thesuperstructure to the substructure, allowing the following types of movements of the superstructure: Translational movements Rotational movementsTypes of Bearings: Pin Roller Rocker Metal sliding bearings Knuckle Pinned Bearing Pot Bearings

1. Pin Bearing:A pin bearing is a type of fixed bearings that accommodates rotations through the use of a steel Translational movements are not allowed. The pin at the top is composed of upper and lower semi circularly recessed surfaces with a solid circular pin placed between. Usually, there are caps at both ends of the pin to keep the pin from sliding off the seats and to resist uplift loads if required. The upper plate is connected to the sole plate by either bolting or welding. The lower curved plate sits on the masonry plate.

2. Roller Type Bearings:AASHTO requires that expansion rollers be equipped with substantial side bars and be guided by gearing or other means to prevent lateral movement, skewing, and creeping (AASHTO 10.29.3)A general drawback to this type of bearing is its tendency to collect dust and debris.Longitudinal movements are allowedLateral Movements and Rotations are Restricted.

3. Rocker Type Bearing:A rocker bearing is a type of expansion bearing that comes in a great variety.It typically consists of a pin at the top that facilitates rotations, and a curved surface at the bottom that accommodates the translational movementsRocker and pin bearings are primarily used in steel bridges.

4. Sliding Bearings:A sliding bearing utilizes one plane metal plate sliding against another to accommodate translations. The sliding bearing surface produces a frictional force that is applied to the superstructure, substructure, and the bearing itself. To reduce this friction force, PTFE (polytetrafluoroethylene) is often used as a sliding lubricating material. PTFE is sometimes referred to as Teflon, named after a widely used brand of PTFE Sliding Bearings be used alone or more often used as a component in other types of bearings Pure sliding bearings can only be used when the rotations caused by the deflection at the supports are negligible. They are therefore limited to a span length of 15 m or less by ASHTTO [10.29.1.1]5. Knuckle Pinned Bearing:It is special form of Roller Bearing in which the Knuckle pin is provided for easy rocking. A knuckle pin is inserted between the top and bottom casting. The top casting is attached to the Bridge superstructure, while the bottom casting rests on a series of rollersKnuckle pin bearing can accommodate large movements and can accommodate sliding as well as rotational movement.

6. Pot Bearings:A POT BEARING consists of a shallow steel cylinder, or pot, on a vertical axis with a neoprene disk which is slightly thinner than the cylinder and fitted tightly inside.A steel piston fits inside the cylinder and bears on the neoprene.Flat brass rings are used to seal the rubber between the piston and the pot.The rubber behaves like a viscous fluid flowing as rotation may occur.

Types of LacingThere are five types of lacing, named asI. Single LacingII. Double LacingIII. BattensIV. Lacing BattensV. Perforated Lacing

These are to be used under different field conditions.Single and double lacings are the most common out of these types. The shapes of these five types are shown, whereas, single and double lacing are compared in detail regarding design of such lacing.Lacing usually consists of flat bars but may occasionally consist of angles,perforated plates, channels or other rolled sections.1-The lacing elements must be so placed that the individual parts being connect have slenderness values less than the governing slenderness ratio for the entire member. L/R ratio of the flange included between the lacing points must not exceed three-fourth the governing slenderness ratio or the member as a whole.2- In riveted construction the effective length denoted by a, of lacing bars for the determination of the permissible stress shall be taken as the length between the inner end rivets of bar for the single lacing and as 0.7 of the length for double lacingIn welded construction, the effective length shall be taken as the distance between the inner ends of effective weld lengths connecting the lacing bars to the main member elements for single lacing and 0.7 of this length for double lacing.3- The AISC column formulas are used to design the lacing in the usual manner. The additional lacing provisions are discussed in AISC-E62.4- Slenderness ratios are limited to 140 for single lacing and 200 for double lacing.5- Double lacing or single lacing are using angles should be used if the distance between connection lines between the lines of welds or fasteners in the flanges, denoted by s Is greater 380 mm.TypesLyLy/rs

Single lacing600A< 140< 380 mm

Double lacing4500.7a< 200>380 mm

6- Lacing is assumed to be a shearing force normal to the built-up member denoted by v equal to not less than 2% of the total compressive design strength of the member. This force should be equally divided into lacing elements at particular cross-section.7- Lacing bars may be under tension and compression alternately. However compression in bars is more critical and design is performed for it. If N is the number of parallel planes of lacing, shear on one lacing face will be Vv/N. For single lacing, component of axial compression should provide the required shear component.8- The Transverse Centre-to-Centre distance between the rivets or centroid of welds may easily be found from the known standard gage distances of the individual elements.9- The AISC-E62 specification states that the end tie plates shall have a thickness at least equal to 1/50 the distance between the connection lines of rivets, bolts, or welds shall have a length parallel to the axis of the main member at least equal to the distance between the connection lines. Intermediate plates can have half its length. The welding on each line connecting a tie plate must be not less than one-third the length of the plate. The spacing of the bolts in the direction of stress in tie plates must not be more than 6d and tie plates must be connected to each segment by at least three fasteners. The weld on each line must not be less than one-third the length of the plate. The longitudinal spacing of intermittent welds or fasteners at the plates must not exceed 150 mm.Thickness of the plate, t > s/50Minimum length of tie plate = s10- The slenderness ratio (L/r) of the flange between lacing points should not be more than three-fourth of the overall slenderness ratio of the main member.11- Flat bar for lacing should have the minimum width considering minimum edge clearance from Centre of rivets to all sides. bmin = (1.5d) x 2 = 3d12- Batten plate is defined as a rigidly connected plate element used to join two parallel components of a built-up sections. This is designed to transmit shear between the two components of the main bar.13- Double lacing bars shell be joined together at their intersections.

Steel Strucutes Connections

Welded ConnectionsThe welded connections are solid, non-detachable connections based on the principle of local melting of connected parts using heat or pressure.

Bolted ConnectionsBolted jointsare one of the most common elements inconstructionand machine design. They consist offastenersthat capture and join other parts, and are secured with the mating ofscrew threads.There are two main types of bolted joint designs: tension joints and shear joints.Riveted ConnectionsArivetis a permanent mechanicalfastener. Before being installed, a rivet consists of a smoothcylindricalshaft with a head on one end. The end opposite the head is called thetail. On installation the rivet is placed in a punched or drilled hole, and the tail isupset, orbucked(i.e., deformed), so that it expands to about 1.5 times the original shaft diameter, holding the rivet in place. In other words, pounding creates a new "head" on the other end by smashing the "tail" material flatter, resulting in a rivet that is roughly a dumbbell shape. To distinguish between the two ends of the rivet, the original head is called thefactory headand the deformed end is called theshop heador buck-tail.

Moment Resisting ConnectionsMoment-resistingframes are rectilinear assemblages of beams and columns, with the beams rigidlyconnectedto the columns. Resistance to lateral forces is provided primarily by rigid frame action-that is, by the development of bendingmomentand shear force in the frame members and joints.