Elastomeric bearings

Description and scope

Elastomeric bearings are deformable elements used to transfer loads from one part of the structure to another. With relatively low production costs and easy installation they are optimally used in bridge construction, building construction and industrial buildings. They can be reinforced (AEL) and unreinforced (NEL). AEL include reinforcement of high-strength sheet steel, which is heat vulcanization combined with layers of elastomeric material (hereinafter elastomers).

Steel plates are coated on all sides elastomer and thus protected against corrosion.
Elastomers are produced from synthetic Chloroprene rubber that is resistant to aging under the influence of atmospheric effects, which are usually present on the premises. Elastomeric bearings are manufactured according to the quality prescribed by the ISO standards and the proposal on the production, quality control and application of elastomeric bearings IGH - Zagreb.
They can be used at temperatures between - 30 ° C (243K) and +50 ° C (323K). Permitted short-term temperatures up to +70 ° C (343K).

Elastomeric bearings allow:

• simultaneous shifts in two perpendicular directions
• simultaneous rotation in three perpendicular planes
• download vertical (normal) load
• download horizontal load

Objects can generally lie only on elastomeric bearings without the use of fixed bearings.

Compared to conventional bearings with elastomeric bearings can achieve significant savings for the simple incorporation and cheap maintenance.

The shape and dimensions

Reinforced and unreinforced POLIROL elastomeric bearings in the floor plan are usually rectangular or round. According to special order they can be produced in other shapes.
Types with labels bearing shown in the CATALOG.
Reinforced POLIROL bearings are manufactured according to standard sizes shown in the CATALOG.
By special order they can be manufactured in other sizes, in this case the thickness of the layer, thickness of the elastomer and steel plates corresponds to the thickness nearest the surface of the small-size bearings.

Permitted loads and displacements

On elastomeric bearing during use can act normal force (Fz), shear forces (Hx, Hy) and bending moments (Mx, My).

Allowable stresses and displacements for various loads are given in the CATALOG.

Normal loads

POLIROL reinforced elastomeric bearings can take normal loads up to 4500 kN, according to the CATALOG. For intermediate are determine the allowable load based on the allowable pressure centric nearest smaller size bearing.

DAllowable normal pressures AEL standard formats are given in the CATALOG. Safety factor for normal load current is >10. With regard to safety against sliding is determined centric slightest pressure.

s_mind >3 N/mm2 for bearings up to 350 × 400 mm
s_mind >5 N/mm2 for bearings larger than 350 × 400 mm

or a minimum factor of safety against sliding where:

s_min - minimal pressure
f_min - minimum friction coefficient

for concrete compound - elastomer:

G_min - minimum shear modulus
tang_max - maximum shear strain

Shear loads and deformations

Allowable shear strain as follows:

tan g_d =0,7 for 0,1 a < T < 0,2 a
tan g_d =0,9 for 0,2 a < T < 0,3 a

u = horizontal displacement
T = thickness of the elastomer

Shear deformation in different directions to the vector sum. Shifts buildings parallel to the plane of the bearing is determined by the technical regulations.
Horizontal forces due to forced shear deformation bearings, if adversely affect static taken into account in the design of structures.
Horizontal forces due to forced shear deformations are:

H₁ = tan g₁ × A × G
A – bearing superficies
G – mthe shear modulus

Current shear deformation of the external loads are:
utotal shear strain must be:
tan g₁ + tan g₂ < tan g_d

AIf you are at low temperatures occur more shear deformation (eg due to moving load) performed a special test structures. It should be taken that the temperature of + 30 ° C size G = 2N = mm2 for elastomeric bearings hardness of 60 + 5 Shore.

Rotate

Rotate elastomeric bearings is determined on the basis of rotation of the structure. Allowable bearing swivel angles are given in the CATALOG, and for one layer of elastomer in the CATALOG. Criteria for determining the permissible rotation angles were determined on the basis of claims that the edges do not come to raise the beds, and the eccentric force is within the core cross-section.
For intermediate true swing angle allowed for the closest higher page bearing a standard format in an even layer of elastomer.
In steering bearings must be taken into account following the computational elements if adversely affect static.

For rectangular bearings

For round bearings

where:

a - page normal to the axis of rotation angle of rectangular bearing
b - sides parallel to the axis of rotation angle of rectangular bearing
D - diameter of the round bearing
t - thickness of elastomer
a - angle of rotation by a single layer of elastomer

Dimensioning

Building structures, based on elastomeric bearings should be regularly addressed as supple statically indeterminate systems, taking into account the characteristics of the deformable bearings, and bearing dimensions are determined by an iterative procedure flowchart sizing.
In the beginning, make an approximate calculation of the distribution of forces and deformations in the structure.
Based on the approximate calculation choosing the dimensions of elastomeric bearings and carried out a detailed static and dynamic analysis of the structure.

From static and dynamic design calculations we obtain the information for bearing dimensioning. Based on these data following parameters are determined and controlled by the: maximum pressure, safety skid, bearing height, stability, shear deformation, thickness reinforcement and rotation of bearing.
The presented procedure is repeated for selecting new dimension to the bearings and demanding the accuracy of the budget due to the new size of the forces and moments.

Embedding

To prevent unwanted bearings tension, surface of the bearing must be parallel to each other, straight and perpendicular to the result of the continuous load.. Therefore, as a rule, between the bearing and the lower part of the structure provides for leveling (eg mortar thickness of 2-3 cm). Contact bearing surfaces and structures should be horizontal or angled so that affected weight or constant load (eg earth pressure ) does not arise shear deformation of bearing.

Bearings should be set so there is no difficulty with replacing (prrdict the possibility of delamination of structural hydraulic presses).
RIt's not allowed to set two or more bearings, one after the other in the longitudinal direction at a construction palm.
Different sized bearings can not be placed next to each other because of unequal stiffness.

UUse of POLIROL elastomeric bearings along with other types of beds is allowed only if bearings of same type are used on single palm a single palm. Welding on the bearing plate with anchoring is not permitted . If the contact area above or below the bearing is damaged, it must be repaired so that the grouting on the other side of that bruises inserted pins and steel plate thickness min. 20 mm.. Once cured, remove the pins.
With appropriate safeguards needs to be ensured that the bearings do not come into contact with grease, solvents, etc., and especially not with stale oil.

Elements on the contact surfaces of the bearings should be designed and constructed to withstand the anticipated loads without damaging the local deformations. If during the installation of bearings require preset , presetting always need to be performed by manufacturer of bearings . presetting should be performed so that the bearings can no longer deform pre- function and so they are secured during transport . Bearings should be dimensioned so presetting should not be changed on the reconstruction area.
Subsequent changes are permitted under the responsibility of the manufacturer of bearings and perform by him or his knowledgeable experts.
Bearing parts due to the need presetting, to interconnect so that at the beginning of its operation are in the projected position and shape. Manufacturer of bearings must in that case give aids . If the bearings must be delivered in parts, on the reconstruction area must be done by bearing manufacturers experts, or a trained experts.