K Series Pot Bearings
The designs confirm, where appropriate, to the recommendations of British Department of Environment and of the Institute für Bautechnik, Berlin.
Standard 'K' series bearings are designed for PTFE pressures in accordance with BS 5400 which limits maximum pressure to 40 Mpa.
Standard 'K' series bearings are designed for a mean concrete seating pressure of 18,5 Mpa, resulting in a maximum edge pressure (due to horizontal load and rotation) of approximately 21 Mpa.
In the interests of economy and standardisation, designers are strongly strength (35 Mpa minimum) or an epoxy mortar beds to accept the standard plates for the appropriate concrete pressure, (see page 12), should be specified. The alternative solution of designing special bearings is not preferred.
Note on Application
There is a nominal mm transverse clearance between the guide bar and plate slot in unidirectional bearings. For this reason, horizontal load sharing between two or more bearings cannot be safely assumed if they are fixed to a common pier or abutment, and the full horizontal force should be assumed to act on one bearing only. In case of separate pier, however, their flexibility may be sufficient to permit load sharing between the bearings.
Where a fixed bearing and a unidirectional bearing are mounted on the same pier or abutment, the notes in par. 1 above should again be considered.
Fixed and unidirectional bearings with proportionately very high horizontal loads should be avoided, the preferred solution being the use of pin bearings and guide bearings where possible.
Unidirectional bearings should be used only where they serve an essential function. Excessive restraint of the structure should be avoided.
Provision should always be made for transverse shrinkage and thermal movement of the dark between bearings fixed to a common pier, if their centers are more than 2m part.
Standard Material Specifications
The tables list the standard range of 'K' series bearings, showing overall dimensions, load capacities, and fixing details. Standard drawings are available for each bearing listed, showing full dimensions and tolerances for designers wishing to check our calculations for approval purposes. Substantial economic advantages are to be gained by selecting bearings from this standard range.
HORIZONTAL LOAD CAPACITY
Normal horizontal load capacities of KB and KC type bearings are given in the tables. For KC type bearings, the values range from a maximum of 9% of the vertical load to 4% for large bearings. The range for KB type bearings is from 18% down to 4%. (See paragraph below on special bearings.)
The standard method of attachments is by anchor bars and bolts. This method is simple and adequate for most cases, and permits bearing removal / replacement with the minimum of jacking of the structure. Alternatively, the bearing may be recessed in an adaptor plate (see page 12) which is anchored to the concrete by ragbolts or the like. This system is sometimes regarded as being more convenient for installation. Adaptor plates may be required, in any event, if the permissible concrete seating pressure is below 17,5 Mpa and an epoxy mortar bed is not used. Anchor bolt and bar sizes shown in the tables for KB and KC type bearings are designed to accommodate the horizontal loads shown providing that at least 50% of the tabulated vertical load is acting simultaneously. If this condition is not met, larger anchor bolts and bars will be necessary (see paragraph on special bearings).
The tables show standard translations for each bearing size, in 50mm increments, and designers are urged to select one of these standards wherever possible (see paragraph below on special bearings).
N.B. presenting requirements, if applicable, should be stated clearly by the customer. If this information is not supplied, bearings will be supplied with top plates in the central position.
All the bearings can rotate at least 0.01 radians (0.57°) about any horizontal axis.
Where combinations of loads and/or movements are such that standard bearings cannot be used, special bearings are designed for each particular case. References to such bearings will always carry the suffix "SP" e.g. KC 1400 SP.
EXAMPLES ON SELECTION OF BEARINGS
Bearing required for: Maximum vertical Load : 3 300kN, Total longitudinal translation : 85mm, Total transverse translation : 10mm, Bearing code: KA 350/100/20
Bearing required for: Maximum vertical Load : 5 900kN, Maximum horizontal load : 450 kN, Total longitudinal translation : 130mm, Transverse translation : restrained, Bearing code : KC 600/150