Bridge bearings

Elastomer bearings

Elastomer bearings are layered products, i. e. they alternate between an elastomer layer and a steel panel as reinforcement for the part.

The entirety is vulcanised to permanently attach the rebar with the elastomer layers.

The main component used in manufacture is polychloroprene rubber, reinforcement is made of enhanced quality steel type S355 J0.

The reinforced elastomer blocks are used in engineering structures to transfer reactions from vertical and horizontal loads to the support parts; they also provide freedom of deformation for stays and the walkway platform, which are a result of temperature changes.

Product description

Support for drive-on components of engineering structures: bridges, viaducts, pedestrian flyovers – is constructed in most cases through the use of flexible components. Elastomer bearings are such components. The load resistance is ensured by internal reinforcement with steel panels. These bearings are made of polychloroprene rubber or natural rubber.

Thanks to different types of bearings, it is possible to satisfy all that is required of them in engineering structures.

According to Polish Standard PN-EN 1337-3, structural elastomer bearings possess the CE mark, confirming the adherence to particular requirements of the indicated norm by the manufacturer, in this case the company Gumba GmbH. The CE mark issued to the elastomer structural bearings made by Gumba GmbH by MPA Stuttgart, a notified body within the European Union, unequivocally conforms the adherence to requirements of standard PN-EN 1337-3. This document permits the introduction of the bridge bearings onto the European market, including the Polish market.

Elastomer properties allow, to a certain degree, movement of the material itself and twisting by deformation. As compared to other bearing types, they have a certain particular advantage – in many cases one can forgo expensive structures with slip components. If the shift caused by the properties of the elastomer bearing is not sufficient for a particular case, the scope of functionality may be expanded.

Note:

As a result of errors during design and bearing selection, locking of the structure may occur, as well as pressure of the main structure on the abutments, and following that – cracking of front walls, head walls and lower plinths. Altering bearing dimensions also causes flaws, and as a result, it needlessly increases costs of construction and maintenance of the structure.

Every elastomer bearing has a vulcanised label describing the bearing, which contains the following information (image below):

CE certificate number

norm according to which the bearing was manufactured

manufacturer logo

bearing number

Bearing types

Considering the anchoring method, one can differentiate between four basic elastomer bearing types: type B(1), type C(2), type B/C(1/2) and type C-PSP(5).

Type B(1) – reinforced, non-anchored bearing, consisting of at least two steel reinforcement plates. Fulfilment of the condition of minimum load and friction prevents this bearing from slipping. Lack of anchoring eases replacement and servicing of these bearings.

Type B/C(1/2) – reinforced bearing with single-side anchoring. The vulcanised external rubber prevents this bearing from slipping, and forms the lower support surface of the part. The method of anchoring of the bearing may be freely configured: welded anchors, protective circular plates or threaded holes. For railway bridges, irrespective of the loads, type B/C(1/2) should always be used.

Type C(2) – reinforced bearing, anchored on both sides. The vulcanised external sheet steel (support surfaces) prevent this bearing from slipping. Similarly to the type described earlier, the method of anchoring of the bearing is freely selectable: welded anchors, protective circular plates or threaded holes. Replacement of this bearing type is quite complicated, and requires additional operations.

Type C-PSP(5) – reinforced bearing, anchored on both sides. Vulcanised external ribbed metal sheets (support surfaces) prevent this bearing from slipping. The replacement of this bearing type is quite complicated, and requires not only the grout under the bearing, but also the reinforced concrete part above the bearing, to be removed.

Standard Gumba bearing dimension tables

			Minimum pressure ≥ 3N/mm²			Minimum pressure < 3 N/mm²
			Typ B(1)			Typ C (2) i C (5)				Typ B/C (1/2)
Load N_z,k	Bearing dimensions a x b	Elastomer layer count n	Shift +/- e_x	Bearing height d	Elastomer thickness t	Shift +/- e_x	Bearing thickness Typ 2 d	Bearing thickness Typ 5 d	Elastomer thickness t	Shift +/- e_x	Bearing thickness d	Elastomer thickness t	Turn angle Ø
kN	mm	pcs.	mm			mm				mm			rad/1000
100 150	100×100 100×150	1	7	14	10	–	–	–	–	–	–	–	4
		2	11	21	15	7	42	32	10	9	31,5	12,5	8
		3	14	28	20	11	49	39	15	12	38,5	17,5	12
		4	16	35	25	14	56	46	20	15	45,5	22,5	16
		5	18	42	30	16	63	53	25	17	52,5	27,5	20
		6	–	–	–	18	70	60	30	–	–	–	24
300	150×200	1	7	14	10	–	–	–	–	–	–	–	3
		2	11	21	15	7	42	32	10	9	31,5	12,5	6
		3	14	28	20	11	49	39	15	12	38,5	17,5	9
		4	18	35	25	14	56	46	20	16	45,5	22,5	12
		5	21	42	30	18	63	53	25	19	52,5	27,5	15
		6	23	49	35	21	70	60	30	22	59,5	32,5	18
		7	25	56	40	23	77	67	35	24	66,5	37,2	21
		8	27	63	45	25	84	74	40	26	73,5	42,5	24
		9	28	70	50	27	91	81	45	28	80,5	47,5	27
		10	–	–	–	28	98	88	50	–	–	–	30
310 630 750 1000	ø200 200×250 200×300 200×400	1	9	19	13	–	–	–	–	–	–	–	3	4
		2	15	30	21	11	49	39	16	13	39,5	18,5	6	8
		3	20	41	29	17	60	50	24	19	50,5	26,5	9	12
		4	26	52	37	22	71	61	32	24	61,5	34,5	12	16
		5	30	63	45	28	82	72	40	29	72,5	42,5	15	20
		6	34	74	53	32	93	83	48	33	83,5	50,5	18	24
		7	36	85	61	35	104	94	56	36	94,5	58,5	21	28
		8	–	–	–	37	115	105	64	–	–	–	24	32

			Minimum pressure ≥ 3N/mm²			Minimum pressure < 3 N/mm²
			Typ B(1)			Typ C (2) i C (5)				Typ B/C (1/2)
Load N_z,k	Bearing dimensions a x b	Elastomer layer count n	Shift +/- e_x	Bearing height d	Elastomer thickness t	Shift +/- e_x	Bearing thickness Typ 2 d	Bearing thickness Typ 5 d	Elastomer thickness t	Shift +/- e_x	Bearing thickness d	Elastomer thickness t	Turn angle Ø
kN	mm	szt.	mm			mm				mm			rad/1000
600 1300	Ø250 250×400	1	9	19	13	–	–	–	–	–	–	–	3	4
		2	15	30	21	11	49	39	16	13	39,5	18,5	5	8
		3	20	41	29	17	60	50	24	19	50,5	26,5	8	12
		4	26	52	37	22	71	61	32	24	61,5	34,5	10	16
		5	32	63	45	28	82	72	40	30	72,5	42,5	13	20
		6	37	74	53	34	93	83	48	35	83,5	50,5	15	24
		7	40	85	61	38	104	94	56	39	94,5	58,5	18	28
		8	43	96	69	41	115	105	64	42	105,5	66,5	20	32
		9	46	107	77	44	126	116	72	45	116,5	74,5	23	36
		10	–	–	–	46	137	127	80	–	–	–	25	40
900 1800	Ø300 300×400	1	9	19	13	–	–	–	–	–	–	–	2	3
		2	15	30	21	11	49	39	16	13	39,5	18,5	4	6
		3	20	41	29	17	60	50	24	19	50,5	26,5	6	9
		4	26	52	37	22	71	61	32	24	61,5	34,5	8	12
		5	32	63	45	28	82	72	40	30	72,5	42,5	10	15
		6	37	74	53	34	93	83	48	35	83,5	50,5	12	18
		7	43	85	61	39	104	94	56	41	94,5	28,2	14	21
		8	46	96	69	44	115	105	64	45	105,5	66,5	16	24
		9	50	107	77	48	126	116	72	49	116,5	74,5	18	27
		10	52	118	85	51	137	127	80	52	127,5	82,5	20	30
		11	55	129	93	53	148	138	88	54	138,5	90,5	22	33
		12	–	–	–	56	159	149	96	–	–	–	24	36
1200	Ø350	1	11	24	16	–	–	–	–	–	–	–		4
		2	19	39	27	15	56	46	22	17	47,5	24,5		8
		3	27	54	38	23	71	61	33	25	62,5	33,5		12
		4	34	69	49	31	86	76	44	33	77,5	46,5		16
		5	42	84	60	39	101	91	55	40	92,5	57,5		20
		6	50	99	71	46	116	106	66	48	107,5	68,5		24
		7	55	114	82	52	131	121	77	53	122,5	79,5		28
		8	59	129	93	57	146	136	88	58	137,5	90,5		32
		9	63	144	104	61	161	151	99	62	152,5	101,5		36
		10	66	159	115	64	176	166	110	65	167,5	112,5		40

			Minimum pressure ≥ 5 N/mm²			Minimum pressure < 5 N/mm²
			Typ B(1)			Typ C (2) i C (5)				Typ B/C (1/2)
Load N_z,k	Bearing dimensions a x b	Elastomer layer count n	Shift +/- e_x	Bearing height d	Elastomer thickness t	Shift +/- e_x	Bearing thickness Typ 2 d	Bearing thickness Typ 5 d	Elastomer thickness t	Shift +/- e_x	Bearing thickness d	Elastomer thickness t	Turn angle Ø
kN	mm	pcs.	mm			mm				mm			rad/1000
2400	350×450	3	27	54	38	23	81	61	33	25	67,5	33,5	8
		4	34	69	49	31	96	76	44	33	82,5	46,5	10
		5	42	84	60	39	111	91	55	40	97,5	57,5	13
		6	50	99	71	46	126	106	66	48	112,5	68,5	15
		7	55	114	82	52	141	121	77	53	127,5	79,5	18
		8	59	129	93	57	156	136	88	58	142,5	90,5	20
		9	63	144	104	61	171	151	99	62	157,5	101,5	23
		10	66	159	115	64	186	166	110	65	172,5	112,5	25
1900 3000	Ø400 400×500	3	27	54	38	23	81	61	33	25	67,5	35,5	6	9
		4	34	69	49	31	96	76	44	33	82,5	46,5	8	12
		5	42	84	60	39	111	91	55	40	97,5	57,5	10	15
		6	50	99	71	46	126	106	66	48	112,5	68,5	12	18
		7	57	114	82	54	141	121	77	56	127,5	79,5	14	21
		8	62	129	93	60	156	136	88	61	142,5	90,5	16	24
		9	67	144	104	65	171	151	99	66	157,5	101,5	18	27
		10	70	159	115	69	186	166	110	70	175,5	112,5	20	30
		11	74	174	126	72	201	181	121	73	187,5	123,5	22	33
		12	–	–	–	75	216	196	132	–	–	–	24	36
2400 4050	Ø450 450×600	3	27	54	38	23	81	61	33	25	67,5	33,5	6	9
		4	34	69	49	31	96	76	44	33	82,5	46,5	8	12
		5	42	84	60	39	111	91	55	40	97,5	57,5	10	15
		6	50	99	71	46	126	106	66	48	112,5	68,5	12	18
		7	57	114	82	54	141	121	77	56	127,5	79,5	14	21
		8	65	129	93	62	156	136	88	63	142,5	90,5	16	24
		9	70	144	104	67	171	151	99	68	157,5	101,5	18	27
		10	74	159	115	72	186	166	110	73	172,5	112,5	20	30
		11	78	174	126	76	201	181	121	77	187,5	123,5	22	33
		12	82	189	137	80	216	196	132	81	202,5	134,5	24	36
		13	85	204	148	83	231	211	143	84	217,5	145,5	26	39

			Minimum pressure ≥ 5 N/mm²			Minimum pressure < 5 N/mm²
			Typ B(1)			Typ C (2) i C (5)				Typ B/C (1/2)
Load N_z,k	Bearing dimensions a x b	Elastomer layer count n	Shift +/- e_x	Bearing height d	Elastomer thickness t	Shift +/- e_x	Bearing thickness Typ 2 d	Bearing thickness Typ 5 d	Elastomer thickness t	Shift +/- e_x	Bearing thickness d	Elastomer thickness t	Turn angle Ø
kN	mm	pcs.	mm			mm				mm			rad/1000
2900 3600 4500	Ø 500 Ø 550 500×600	3	27	54	38	23	81	61	33	25	67,5	33,5	6	6
		4	34	69	49	31	96	76	44	33	82,5	46,5	8	8
		5	42	84	60	39	111	91	55	40	97,5	57,5	10	10
		6	50	99	71	46	126	106	66	48	112,5	68,5	12	12
		7	57	114	82	54	141	121	77	56	127,5	79,5	14	14
		8	65	129	93	62	156	136	88	63	142,5	90,5	16	16
		9	72	144	104	69	171	151	99	71	157,5	101,5	18	18
		10	77	159	115	75	186	166	110	76	172,5	112,5	20	20
		11	82	174	126	80	201	181	121	81	187,5	123,5	22	22
		12	86	189	137	84	216	196	132	85	202,5	134,5	24	24
		13	89	204	148	88	131	211	143	89	217,5	145,5	26	26
		14	93	219	159	91	146	226	154	92	232,5	156,5	28	28
		15	–	–	–	94	161	141	165	–	–	–	30	30
4100 5000 6300	Ø 600 Ø 650 600×700	3	35	70	50	32	95	75	45	33	82,5	47,5	6	6
		4	46	90	65	42	115	95	60	44	102,5	62,5	8	8
		5	56	110	80	53	135	115	75	54	122,5	77,5	10	10
		6	67	130	95	63	155	135	90	65	142,5	92,5	12	12
		7	77	150	110	74	175	155	105	75	162,5	107,5	14	14
		8	86	170	125	84	195	175	120	85	182,5	122,5	16	16
		9	93	190	140	91	215	195	135	92	202,5	137,5	18	18
		10	99	210	155	98	235	215	150	98	222,5	152,5	20	20
		11	105	230	170	103	255	235	165	104	242,5	167,5	22	22
		12	109	250	185	108	275	255	180	109	262,5	182,5	24	24
		13	113	270	200	112	295	275	195	113	282,5	197,5	26	26

			Minimum pressure ≥ 5 N/mm²			Minimum pressure < 5 N/mm²
			Typ B(1)			Typ C (2) i C (5)				Typ B/C (1/2)
Load N_z,k	Bearing dimensions a x b	Elastomer layer count n	Shift +/- e_x	Bearing height d	Elastomer thickness t	Shift +/- e_x	Bearing thickness Typ 2 d	Bearing thickness Typ 5 d	Elastomer thickness t	Shift +/- e_x	Bearing thickness d	Elastomer thickness t	Turn angle Ø
kN	mm	pcs.	mm			mm				mm			rad/1000
5800 6600 8400	Ø 700 Ø 750 700×800	3	35	70	50	32	95	75	45	33	82,5	47,5	6	6
		4	46	90	65	42	115	95	60	44	102,5	62,5	8	8
		5	56	110	80	53	135	115	75	54	122,5	77,5	10	10
		6	67	130	95	63	155	135	90	65	142,5	92,5	12	12
		7	77	150	110	74	175	155	105	75	162,5	107,5	14	14
		8	88	170	125	84	195	175	120	86	182,5	122,5	16	16
		9	98	190	140	95	215	195	135	96	202,5	137,5	18	18
		10	105	210	155	103	135	215	150	104	222,5	152,5	20	20
		11	112	230	170	110	255	235	165	111	242,5	167,5	22	22
		12	118	250	185	116	275	255	180	117	262,5	182,5	24	24
		13	123	270	200	121	295	275	195	122	282,5	197,5	26	26
		14	127	290	215	126	315	295	210	127	302,5	212,5	28	28
		15	131	310	230	130	335	315	225	131	322,5	227,5	30	30
7500 8500 9600	Ø 800 Ø 850 800×800	3	41	79	59	38	104	84	54	40	91,5	56,5	6	6
		4	54	102	77	50	127	107	72	52	114,5	74,5	8	8
		5	67	125	95	63	150	130	90	65	137,5	92,5	10	10
		6	79	148	113	76	173	153	108	77	160,5	110,5	12	12
		7	92	171	131	88	196	176	126	90	183,5	128,5	14	14
		8	104	194	149	101	219	199	144	103	206,5	146,5	16	16
		9	115	217	167	113	242	222	162	114	229,5	164,5	18	18
		10	124	240	185	122	265	245	180	123	252,5	182,5	20	20
		11	131	263	203	129	288	268	198	130	275,5	200,5	22	22
		12	138	286	221	136	311	291	216	137	298,5	218,5	24	24
		13	144	309	239	142	334	314	234	143	321,5	236,5	26	26
		14	149	332	257	147	357	337	252	148	344,5	254,5	28	28

			Minimum pressure ≥ 5 N/mm²			Minimum pressure < 5 N/mm²
			Typ B(1)			Typ C (2) i C (5)				Typ B/C (1/2)
Load N_z,k	Bearing dimensions a x b	Elastomer layer count n	Shift +/- e_x	Bearing height d	Elastomer thickness t	Shift +/- e_x	Bearing thickness Typ 2 d	Bearing thickness Typ 5 d	Elastomer thickness t	Shift +/- e_x	Bearing thickness d	Elastomer thickness t	Turn angle Ø
kN	mm	pcs.	mm			mm				mm			rad/1000
9500 12000	Ø 800 900×900	3	41	79	59	38	104	84	54	40	91,5	56,5	5	5
		4	54	102	77	50	127	107	72	52	114,5	74,5	6	6
		5	67	125	95	63	150	130	90	65	137,5	92,5	8	8
		6	79	148	113	76	173	153	108	77	160,5	110,5	9	9
		7	92	171	131	88	196	176	126	90	183,5	128,5	11	11
		8	104	194	149	101	219	199	144	103	206,5	146,5	12	12
		9	117	217	167	113	242	222	16	115	229,5	164,5	14	14
		10	128	240	185	126	265	245	180	127	252,5	182,5	15	15
		11	137	263	203	135	288	268	198	136	275,5	200,5	17	17
		12	145	286	221	143	311	291	216	144	298,5	218,5	18	18
		13	152	309	239	150	334	314	234	151	321,5	236,5	20	20
		14	158	332	257	156	357	337	252	157	344,5	254,5	21	21
		15	163	355	275	162	380	360	252	163	367,5	272,5	23	23
		16	168	378	293	167	403	383	270	391	390,5	290,5	24	24

The tables for reinforced elastomer bearings apply to standard-construction Gumba bearings. They apply to initial dimensions, which only allow a general and fast estimation of the bearing size. The values provided in them are characteristic values for the Serviceability Limit State (SLS). In order to conduct more precise dimensioning of the structural bearings, please contact our representatives in the retail branches, employees of the technical department or alternatively use the software available at the manufacturer’s website at www.gumba.de. The software allows optimum bearing selection. It includes only known bearing dimensions with layered structures according to Gumba standards and regular bearing dimensions according to norm EN 1337-3.

Calculation basis according to EN 1337-3.

Designing and manufacture of elastomer bearings is based on Polish Standard PN-EN 1337-3, which is harmonised with the Construction Directive 89/106/EEC. This norm covers i. e. reinforced elastomer bearings with a surface area of up to 1200 x 1200 mm2, used between temperature values between -25 °C and +50 °C.

Below, the recommended course of calculations, the expansion of which is found in the norm indicated earlier on, is presented.

Remarks and further hints concerning the presented calculation phases are found in standard PN-EN 1337.

For the calculation of values related to elastomer bearings, characteristic load values need to be applies. The proof takes place at the Ultimate Limit State (ULS) for joint deformation stemming from load and shift.

The table above contains information necessary to dimension bearings according to standard PN-EN 1337-3. The table also contains necessary shore conditions. It may serve the determination and description of structural bearing parameters designed for a particular structure.

Note:

According to Polish Standard PN-EN 1337-3, the bridge structure designer presents all necessary data allowing the selection of structural bearings for such a structure. It is not possible for the bearing manufacturer to calculate this data.

Elastomer bearing calculations

The bearings must correspond to the following requirements:
1. Maximum calculational deformation

At any given point of the bearing, the sum of deformations (Ɛt,d) caused by effects of calculational load (Ed) is given by the formula:

Ɛ_c,d – calculational deformation caused by compressive calculational loads

Ɛ_q,d – calculational shear deformation caused by calculational horizontal shifts

Ɛ_ɑ,d– calculational deformation caused by the calculational twist angle

K_L – load type coefficient

Calculational deformation caused by compressive calculational loads

N_z,d – vertical force calculational value

G – nominal value of the ordinary non-dilatational strain modulus for an elastomer bearing

A_r – reduced effective area of the elastomer bearing

A’- effective area of a reinforced bearing (surface area of reinforcement sheet steel)
A’ = a’·b’ (for cuboid bearings without openings)

a’ – effective width of reinforced bearing (reinforcement sheet width)

b’ – effective length of reinforced bearing (reinforcement sheet length)

v_x,d – maximum horizontal relative shift of a bearing part towards dimension a of the bearing caused by all effects of calculational load

v_y,d – maximum horizontal relative shift of a bearing part towards dimension b of the bearing caused by all effects of calculational load

S – shape coefficient

A’- effective area of a reinforced bearing (surface area of reinforcement sheet steel)
A’ = a’·b’ (for cuboid bearings without openings)

a’ – effective width of reinforced bearing (reinforcement sheet width)

b’ – effective length of reinforced bearing (reinforcement sheet length)

l_p – circumference of bearing without load

l_p=2·(a’+b’)

t_e – effective thickness of individual elastomer layer at compression

Calculational shear deformation caused by calculational horizontal shifts.

v_xy,d – maximum resultant horizontal relative shift of bearing part obtained from vector sum of v_x,d and v_y,d

T_q– total elastomer thickness at non-dilatational strain with upper and lower cover

Calculational deformation caused by calculational twist angle

a’ – effective width of reinforced bearing (reinforcement sheet width)

ɑ_a,d – turn angle about bearing width a

b’ – effective length of reinforced bearing (reinforcement sheet length)

ɑ_b,d – turn angle (if applicable) about bearing width b

t_i – individual elastomer layer thickness

2. Maximum extension pressure in reinforcement sheets

Reinforcement plate thickness

K_p – correction coefficient

K_p = 1,3

N_z,d – calculational value of vertical force

t₁, t₂ – elastomer thickness on both sides of metal sheet

K_h – extension pressure coefficient caused in the reinforcement steel sheet

K_h =1 (without openings)

K_h = 2 (with openings)

Ɣ_m – partial safety coefficient, Ɣm= 1,0

A_r – reduced effective elastomer bearing area

f_y – steel yield strength

3. Limit conditions

Twist limit condition

For reinforced bearings, the limit turn should not be reached when total vertical compression ∑Vz,d meets the following conditions:

For parallel wall bearings:

For circular bearings:

∑v_z,d – total vertical compression causing ɑ_a and ɑ_bN_z,d – vertical force calculational value

t_i – individual elastomer layer thickness

A’ – effective reinforced bearing area (surface area of reinforcement sheet steel)

G – nominal value of the ordinary non-dilatational strain modulus for an elastomer bearing

S₁ – thickest layers shape coefficient

E_b – volumetric strain modulus Eb = 2000 MPa

a’ – effective width of reinforced bearing (reinforcement sheet width)

ɑ_a,d – turn angle about bearing width a

b’ – effective length of reinforced bearing (reinforcement sheet length)

ɑ_b,d – turn angle (if applicable) about bearing width b

K_r,d – twist coefficient

K_r,d = 3

D’ – effective bearing diameter

ɑ_d – twist angle about diameter D of circular bearing

Dent stability

In reinforced elastomer bearings, the load should conform to the following formula:

N_z,d – vertical force calculational value

A_r – reduced effective area of the elastomer bearing

a’ – effective width of reinforced bearing (reinforcement sheet width)

G – nominal value of the ordinary non-dilatational strain modulus for an elastomer bearing

S₁ – thickest layers shape coefficient

T_e– sum total of all elastomer layers

No-slip condition

Non-anchored bearings must conform to the following formula:

and under fixed loads

N_xy,d – resultant force of all horizontal forces

N_z,d_min – minimum vertical calculational force related to Nxy,d

A_r – reduced effective area of the elastomer bearing

µ_e – friction coefficient according to the following formula:

K_f = 0,6 for concrete

K_f = 0,2 for all other surfaces including resin mortars and grout

σ_m – average load tension resulting from N_z,d_min

4. Forces, moments and deformations acting on structures

mutual contact surface pressure

All that is required is a test whether the average pressure on the surface does not exceed the base layer material strength.

result force of resistance against horizontal shift

A – total flat bearing area

G – nominal value of the ordinary non-dilatational strain modulus for an elastomer bearing

v_xy,d – maximum resultant horizontal relative shift of bearing part obtained from vector sum of v_x,d and v_y,dT_e – sum total of all elastomer layers

Rotation resistance

Parallel wall bearings

G – nominal value of the ordinary non-dilatational strain modulus for an elastomer bearing

ɑ – bearing angle of rotation

a’ – effective reinforced bearing width (reinforcement sheet width)

b’ – effective reinforced bearing length (reinforcement sheet length)

n – elastomer layer count

t_i – individual elastomer layer thickness

K_s– resistance moment coefficient

Circular bearings

G – nominal value of the ordinary non-dilatational strain modulus for an elastomer bearing

ɑ – bearing angle of rotation

D’ – effective bearing diameter

n – elastomer layer count

t_i– individual elastomer layer thickness

The Ks resistance moment coefficient is determined using the following table.

b/a	0,5	0,75	1	1,2	1,25	1,3	1,4	1,5
K_s	137	100	86,2	80,4	79,3	78,4	76,7	75,3
b/a	1,6	1,7	1,8	1,9	2	2,5	10	X
K_s	74,1	73,1	72,2	71,5	70,8	68,3	61,9	60

ASSEMBLY RECOMMENDATIONS

General information

Apart from co-operation with design agencies and contractors concerning selection and design of structural bearings, Betomax offers supervision, and, since 2010, also installation of structural bearings. We currently utilise two specialised teams of structural bearing installation specialists. Installation covers arrangement of the bearing on the support structure, levelling and adjusting the bearing with respect to axes, execution of formwork, grouting using low-contraction mortar and protecting the bearing after installation. Our teams are equipped with specialised tools required for correct bearing installation. they utilise the following measurement devices: high-precision levels, electronic levelling instruments, infra-red thermometers and power tools required at installation. The installation concludes with the issue of a bearing installation protocol transferred to the site contractor.

We co-operate with the largest construction companies operating in Poland, i. e. Skanska, Strabag, Polimex Mostostal, Budimex. We have participated in the construction of the first sections of Polish highway A1 and several sections of highway A2. For the installation of structural bearings, we adhere to the current standard PN-EN 1337-11, complying with the strictest EU requirements, as proven by the respect of our satisfied customers.

The installation of a bearing is preceded by creation of image documentation and its transfer to the construction site. After it is approved, preparatory works may commence. The first stage is the execution of lower plinths. The plinths are executed individually for every bearing, considering the hints included in assembly drawings transferred by Betomax. The plinth needs to be reinforced and covered by formwork up to an appropriate height. In case of anchored bearings equipped with studs, openings need to be left clear in the plinth. After appropriate concrete strength is reached, the installation of the bearing may commence. The part on which the grout shall be executed must be prepared accordingly. The bearings are arranged according to the axes indicated by the geodesic services. Then, the bearings are levelled, and their arrangement is checked and approved by a geodesic specialist. A further step is preparing the formwork, after which the grout may be executed. The grout is introduced in a manner ensuring removal of air from under the bearing, so as to avoid emergence of so-called air bubbles under the bearing. Depending on the grout type, after appropriate resistance strength is reached, the load bearing structure of the element may be executed. For transport and assembly, the bearings are protected by assembly securing screws, which must be removed when the structure starts transferring loads and working by itself.

Assembly work

1. Preparation of plinth surface by graining	2. Cleaning of lower plinth surface

3. Assignment of bearings	4. Layout and levelling of elastomer bearing

5. Grout execution	6. Securing the bearing

Structural bearing replacement

Extensive investments related to the construction of new road sections and engineering structures are currently carried out in Poland, along with repairs and upgrades of existing structures and roads. In case of existing structures, old, used-up bearings needs to be replaced with new products. Viaducts and bridges often rest on corroded roller bearings which do not work properly, with the entire structure at risk of failure. Betomax offers assistance in the selection of appropriate solutions and in the installation of new bearings. The first stage is designing appropriate bearings, which shall ensure the transfer of vertical loads, horizontal forces and thermal deformations of the existing structure. The above solutions must be accepted by the design office executing the site upgrade design. The replacement of the delivered bearings itself entails lifting the existing structure by hydraulic motors to an appropriate height, thus ensuring the space necessary for removal of the current bearings, in most cases by chiselling them away, and the installation of new bearings.

Professional evaluation of the condition of elastomer bearings requires to a great extent knowledge and experience, and must be conducted by qualified personnel. If divergences are found, consultations with the bearing manufacturer are recommended.

During the inspection of a bridge, structural bearings are also controlled. During an inspection, among others, the following factors are analysed:

elastomer bearing position

elastomer bearing contact area size with surrounding surfaces

quality of elastomer bearing surface (springing effects, cracks)

allowable horizontal shift

allowable rotation

slip surface quality

corrosion protection quality

Below may be found a few examples of upgrade works completed. Photographs provided by Other Montagen.

before

after

before

after

Bridge bearings

Hidroplasto Blog

joi, 31 august 2017

Protectie conducte

Protectie anticoroziva a tevilor

Bridge bearings

Bridge bearings

Elastomer bearings

ASSEMBLY RECOMMENDATIONS