Mechanical Engineering, bridge bearings, structural engineering Specialists In Structural Movement Control

Attachment:

Fixing holes are provided in the top and base members of the bearings.This enables a variety of fixing methods to be used.Standard fixings are designed to ensure the bearings can be removed as simply as possible.

 

Support and Installation:

Important - See pages 21 - 23 for Installation and Maintenance.If the bearings are to be installed on a steel spreader plate Ekspan must be notified. The overall height will be reduced by 3mm in these cases. 

 

Concrete stress:

Where suitable reinforcement of the concrete has been provided the allowable concrete stress is dependent on the relative dimensions of the bearing/structureinterface, the total support area and the characteristic strength of the concrete.The stress on the structure should therefore be checked to ensure that it is acceptable.At the Nominal Rating capacity tabulated the mean stress approaches 20N/mm2.

 

Design loads:

The designation of loadings varies depending on the design code employed.The tabulated load capacities list Nominal rating, at which load the base concrete stress is 20N/mm2 maximum. The working stress / serviceability limit statemaximum loads are determined by the allowable PTFE stresses. The ultimate limit state maximum load characteristics are determined by the strength characteristics of the bearing and incorporate the material and partial safety factors m and f3 as required by BS5400.The practice of stating working loads, or nominal loads is inappropriate for limit state designs. The SLS and ULS capacities represent design loadeffects, i.e. nominal loads to which ALL the appropriate factors have been applied. Factored loads must be provided to ensure correct bearing selection.

 

Rotation:

All the bearings can rotate at least 0.01 radians about any horizontal axis.The maximum for each bearing is shown in the tables.

 

Movement:

The dimensions for the 21K & 31K (Constrained) and 22K (Free) bearings are shown in the tables for the following movements -

 

Longitudinal

21 & 31K 100mm total

22K 100mm total

 

Transverse

21 & 31K NIL (see pages 14 & 16)

22K 20mm total

 

Movements in increments of 50mm total can be supplied. The top plate dimensions and the top plate fixing centres should be increased accordingly.

N.B. 21 & 31K bearings should not be used where movement is required at right angles to the constraints.The required movements should be specified in the part number as described below.The clearance between the constraints must not be used to accommodate any structural movement.

 

Bearing design loads:

Bearings should be selected to suit the appropriate design code.The maximum vertical and horizontal loads shown in the tables may be taken in combination.

 

Horizontal loading:

The 20K fixed bearing will resist a horizontal force acting in any direction.In order for the bearing to support the maximum horizontal loads stated in the tables, a minimum concurrent vertical load of 0.33 x the Nominal Vertical rating must be present.At ULS, the actual load combination may permit the use of a vertical load higher than that shown in the table.Where higher horizontal load capacities are required, the 30K series or a special bearing may be more appropriate.We will be pleased to advise.

 

Concrete stress:

Where suitable reinforcement of the concrete has been provided the allowable concrete stress is dependent on the relative dimensions of the bearing/structureinterface, the total support area, and the characteristic strength of the concrete.The stress on the structure should therefore be checked to ensure that it is acceptable.At the Nominal Rating capacity tabulated the mean stress approaches 20N/mm2.