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TRANSPORT and ROAD RESEARCH LABORATORY

Department of the Environment Department of Transport

SUPPLEMENTARY REPORT 499

HIGH STRENGTH FRICTION GRIP BOLTED JOINTS - EFFECTS AFTER ONE YEAR OF WEATHERING UNDER LOAD

by

D S Moss

Any views expressed in this Report are not necessarily those of the Department of the Environment or of the Department of Transport

Bridge Design Division Structures Department

Transport and Road Research Laboratory Crowthorne, Berkshire

1979 ISSN 0305-1315

Abstract

1. Introduction

2. Programme of tests

3. Specimens

3.1 Specimen design

3.2 Surface treatment

3.2.1 Grit blasting

3.2.2 Metal spraying

3.2.3 Priming

3.3 Pre-assembly weathering

3.4 Bolts

3.5 Assembly

4. Exposure sites

4.1 Tinsley (industrial)

4.2 Eastney (marine)

5. Testing

5.1 Testing for slip factor (laboratory tests)

5.2 Continuous loading tests (field trials)

5.2.1 Test rig

5.2.2 Measurement of slip

6. Results

6.1 Slip factor

6.2 Slip of loaded joints

6.3 Bolt tension

7. Discussion of results

8. Conclusions

9. Future work

10. Acknowledgements

11. References

CONTENTS

Page

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3

3

3

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4

4

4

4

4

4

5

5

5

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6

6

6

6

7

7

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8

(C) CROWN COPYRIGHT 19 79 Extracts f rom the text may be reproduced, except for

commercial purposes, provMed the source is acknowledged

Ownership of the Transport Research Laboratory was transferred from the Department of Transport to a subsidiary of the Transport Research Foundation on 1 st April 1996.

This report has been reproduced by permission of the Controller of HMSO. Extracts from the text may be reproduced, except for commercial purposes, provided the source is acknowledged.

HIGH STRENGTH FRICTION GRIP BOLTED JOINTS - EFFECTS AFTER ONE YEAR OF WEATHERING UNDER LOAD

ABSTRACT

The first year of a five year study of the behaviour of high strength friction grip bolted joints under the combined action of continuous loading and weathering is reported.

The plies of specimen joints were given various surface treatments and were weathered before assembly. Some joints were tested for slip factor and the results compared with those of tests on joints having unweathered plies. Similar joints are now weathering under continuous loading, and slip is being monitored.

The slip factors of unprotected joints,particularly those made from weathering steel,were increased by pre-assembly weathering, but were reduced for joints having corrosion resistant treatments.

Slip has occurred in most of the loaded joints and the largest movements have taken place in the joints having corrosion resistant treatments containing zinc.

It is concluded that, when some corrosion resistant treatments are used on the interfaces of high strength friction grip bolted joints, the efficiency of the joint is impaired if the surfaces weather before assembly. It is recommended that, when these treatments are used, the interfaces should be protected to prevent weathering in the time between preparation of the surfaces and assembly of the joint.

1. INTRODUCTION

The effects of weathering on the performance of high strength friction grip (HSFG) bolted joints have been under

investigation at TRRL since 1969. In this work particular care was taken, when assembling the specimen joints, to

prevent contamination of the interfaces, in order that the effects of progressive corrosion occurring within the joint,

could be studied. The joints have been weathered in the unloaded state 1.

In practice however, HSFG bolted joints are used under different circumstances and the project described in

this report was started, in order to study the behaviour of joints assembled and used under conditions more approp-

riate to bridge construction. On site, the joint interfaces may not always be entirely free from contamination before

assembly and when it is put into service, the finished joint is required to transmit design loads between structural

members.

The possible condition of real joints, before assembly, was assessed from a survey of current practice in the

use of HSFG bolting by the construction industry. It was found that there was usually a delay between preparation

of the steel surfaces and final assembly of the joint. Delays of three months were common and much longer periods

of time sometimes elapsed. During this period the surfaces were not normally provided with temporary protection,

but if the joint interfaces were found to be contaminated, when inspected prior to assembly, they were wire

brushed to remove loose material.

In the work described in this report, the plies of specimen joints were given various surface treatments and

were exposed to aggressive environments, to produce interfaces in a condition, which could exist in practice. The

slip factors of joints having weathered and unweathered plies have been compared, and the slip of joints currently

being weathered under continuous loading, is being monitored. The results presented have been obtained during

the first year of the programme, which is planned to be of five years duration.

2. PROGRAMME OF TESTS

Seven sets of specimen joints were prepared, each set comprising three samples of each of five surface treatments.

One set was assembled immediately following completion of the surface treatment and the joints were tested for

slip factor* 24 hours later. The values obtained were used to derive the loads applied to the joints being weathered

under load.

The six remaining sets o f specimens were divided between two exposure sites, where the plies were weathered.

After weathering, the plies were returned to the laboratory, where the interfaces were wire brushed and the joints

assembled. One set from each exposure site was tested for slip factor and the remainder were returned to their

respective exposure sites, where one set is weathering in the unloaded state and the other under continuous loading

in specially designed test rigs.

In addition to the principal series of specimens described, joints were assembled from weathered plies using

proprietary load indicating washers. Three such specimens are being weathered at each site, in the unloaded state,

and will be used to assess whether or not moisture is able to penetrate the joint more easily when these washers

are used.

During weathering, measurements are being made of bolt tension, applied load and slip, and at the end of the

programme all the joints will be tested for slip factor.

3. SPECIMENS

3.1 Specimen design

The specimen is shown in Figure 1 and was a four bolt double lap joint, having dimensions based on the

recommendations o f BS 46042. The majority of the specimens were made from structural steel to BS 4360

Grade 50 B 3 and 13 made from weathering steel were included.

The tension plates were cut consecutively from the same bar to ensure matching cross-sections and all the

holes were drilled, using a jig to ensure alignment. All holes and cut ends were de-burred.

Slip factor = slip load

Number of effective interfaces x proof load of one bolt x number of bolts

and is defmed as the ratio o f the load, per effective interface, required to produce slip in a pure shear joint to

the nominal shank tension (ie proof load) induced in the bolt or bolts 2.

3.2 Surface treatment

The plies of the specimens were treated in one of the following ways:

(i) Grit blasted, with no corrosion resistant treatment.

(ii) Grit blasted, followed by zinc metal spray.

(iii) Grit blasted, followed by aluminium metal spray.

(iv) Grit blasted, followed by zinc rich silicate primer.

(v) Grit blasted weathering steel.

3.2.1 Grit blasting: All grit blasting was carried out in a direct pressure machine operating at an air pressure of

550 kN/m 2 and charged with G34 chilled iron grit. Each surface was blasted for a period of time which was 50 per

cent longer than that required to produce a bare steel surface having no visible contamination or discoloration. After

blast cleaning, the surfaces were dusted off using a compressed air jet.

3.2.2 Metal spraying: The sprayed metal coatings were applied immediately after blast cleaning, using a gas pistol

of the wire feed type. The thickness of application was based on the requirements of BS 25694 and was taken as

the mean of six local thickness measurements made on the joint interface area of each surface. The coating thick-

nesses and the relative positions of the surfaces in the specimens are shown in Tables 1,2 and 3.

3.2.3 Priming: The material used was a proprietary, two component zinc rich silicate primer, which was mixed

in accordance with the manufacturer's instructions and applied by brush, immediately after blast cleaning. After

curing, the coating thicknesses were measured and the values are included in Tables 1,2 and 3.

3.3 Pre-assembly weathering

The joint plies were weathered at one of two exposure sites for a period of 10 weeks, during which they were

mounted in wooden racks, with the plane of the joint surfaces vertical. After exposure, the plies were wire brushed

sufficiently to remove loose rust or other adherent material.

Manual wire brushing was employed, as better control was possible over the light action required to clean the

protected surfaces, and the burnished effect, sometimes produced by powered rotary brushes, was avoided.

3.4 Bolts

The bolts were M16 ISO metric high strength friction grip type to BS 4395: Part 25. They were modified to

make them load indicating by the method illustrated in Figure 2, which was the development of the system described

in reference 6. A steel reference rod was attached to the bot tom of a hole drilled axially in the plain part of the bolt

shank. The top surface of the bolt head and the free end of the rod were ground and lapped flat. Since the rod was

attached to the bolt by one end only, it remained unstressed under all conditions of bolt tension, hence the extension

of the bolt shank under load resulted in axial movement of the free end of the rod relative to the bolt head. This

movement was measured, using the gauge shown in the figure, and was related to tension by calibrating the bolt

against a load cell.

In order to preserve the bolt load calibrations, it was necessary for the bolts to remain within their elastic

range, when tensioned to the required load. Therefore higher grade bolts were used at the proof load of M16 general

grade bolts 7. The same type were used in the weathering steel specimens.

3.5 Assembly

The specimens were assembled using a jig to ensure the correct alignment of the plies and the longitudinal

position of the tension plates was adjusted so that slip would not be arrested prematurely by the bolts bearing on

the sides of the holes. Hardened washers were used only under the nuts.

The bolts were tensioned to 92.1 kN, as required by BS 4604: Part 12 using a torque multiplying device to

increase the tension smoothly. No attempt was made to rectify any subsequent relaxation of bolt tension and slip

factors were calculated using the initial bolt load.

After assembly, the specimens to be weathered under load were fitted with the datum pegs used in testing for

slip. The positions of the pegs are shown in Figures 3 and 4 and consisted of 1.5 mm diameter, stainless steel pins

driven into holes drilled in the plate edges.

The specimens were not given any protective treatment after assembly, with the exception of the bolt heads,

which were greased and fitted with caps, to prevent damage to the datum surfaces of the bolt load measuring system.

4. EXPOSURE SITES

The exposure sites were chosen to represent the extremes of industrial and marine environments in which a bridge

might be constructed.

4.1 Tinsley (industrial)

The site is situated near Sheffield, adjacent to an elevated section of the M1 motorway. The area has a high

density of heavy industrial installations, many of which are engaged in steel working.

4.2 Eastney (marine)

The marine site lies to the east of Portsmouth, at the entrance to Langstone Harbour in such a position that

there is sea on two sides. The arrangement of the site is shown in Plate 1, in which the loading rigs may be seen in

the front left hand corner of the compound, facing in an easterly direction.

5. TESTING

5.1 Testing for slip factor (laboratory tests)

The tests were carried out in accordance with the recommendations of BS 46042. The rate of loading was

set at 50 kN/min, and load and slip were recorded continuously by X-Y plotters. The slip load was taken as that

causing 0.1 mm displacement between adjacent points on the tension and cover plates measured in the direction of

loading. The slip load of a specimen was taken as the mean of the slip loads o f the two ends o f the specimen.

The slip loads of the specimens having unweathered plies were used to derive the working loads applied to

the joints weathering under continuous load. Three specimens o f each type were tested and the minimum value

of slip load used in the expression;

Working load = slip load

1.4 _ _ , where 1.4 is the load factor 2.

5.2 Continuous loading tests (field trials)

5.2.1 Test rig: The testing is shown in Figure 3 and Plate 2. The frame of the rig consisted o f a square section,

hollow steel column, having stiffened brackets welded to its ends. The specimen was tensioned between the

brackets, using a high tensile bolt to apply the load, which acted on the specimen through a stack o f disc springs.

The loadingbolt was made load indicating in the same way as those in the specimen, and by removing an adaptor

ring from the bolt load gauge, the instrument could be used to measure the tensile load on the specimen.

The reduction in the applied load resulting from slip in the specimen was approximate ly 2.3 kN for a total

slip of 0.2 mm, and the variation in load caused by temperature change was 3 kN over a temperature range o f

44°C.

The loading mechanism was fitted with safety screws to restrict its movement , should the loading bolt fail.

The moveable parts of the rigs were greased and enclosed in protective covers before being set up on the

exposure sites. On site the rigs were mounted on tubular steel frames, which suppor ted them at an angle o f approx-

imately 60 ° to the horizontal, with the centre o f the specimen about 1 m above the ground. The unloaded specimens

were supported in a similar attitude and position on side extensions o f the test rig frames.

There are 14 test rigs in service at each of the two exposure sites.

5.2.2 Measurement of slip: Slip in the loaded specimens was measured using the instrument shown in Figure 4.

The fixed knife edges in the base of the instrument were made to contact the datum pegs in the cover plates, as

shown in the figure, using the side plate and one peg to fix the transverse position. When posit ioned in this manner,

the central knife edge, which was formed in one end of a pivoted lever, made contact with the tension plate peg

under spring pressure. The other end of the lever controlled the position of the moving element o f a displacement

transducer, the electrical output of which was thus dependent on the relative longitudinal positions o f the da tum

pegs. The instrument was calibrated over a range o f known displacements, but as it was affected by temperature

change, slip was derived from the difference between readings taken on the specimens and on a reference block.

The reference consisted of a small steel block having in one surface the same arrangement o f pegs as in the specimens.

The displacement transducer was of the same type as that used in the bolt load gauge and a single display unit

served both instruments.

6. RESULTS

6.1 Slip factor

The slip factors of joints assembled from unweathered plies, with the minimum values obtained with each

surface treatment and the derived working loads, are given in Table 4. The slip factors of joints having weathered

plies are given in Table 5.

6.2 Slip o f loaded ioints

Table 6 gives the slip movements measured after one year and Table 7 gives the mean values of slip factor and

slip for each surface treatment.

6.3 Bolt tension

The mean bolt loads and relaxations after one year for each surface treatment in loaded and unloaded specimens

are given in Table 8.

7. DISCUSSION OF RESULTS

The slip factors of all joints having protective coatings were reduced by pre-assembly weathering, the greatest

reduction occurring in metal sprayed specimens weathered under industrial environmental conditions. The adverse

effects were not so marked on joints protected by the zinc silicate primer, on which the marine environment had a

marginally greater effect.

A possible reason for the reduction in slip factor of protected joints is that the mechanism of slip is changed by

weathering of the joint interfaces. Several unweathered surfaces were found to be partially welded, when the spec-

imens were dismantled after test, suggesting that the formation and subsequent rupture of small friction welded

areas during slip contributed to the slip resistance of the joint. No weathered plies were found to be welded after

test and it is possible that sufficient contamination remained on the faying surfaces, after wire brushing, to prevent

the intimate contact necessary for such welds to form, so reducing the slip factor.

In contrast, weathering of the plies before assembly had a beneficial effect on the slip factor of joints having

unprotected surfaces. For both Grade 50 B and weathering steel, the marine environment effected the greatest

improvement.

As the unprotected surfaces rusted during weathering, a rough surface texture was produced, particularly by

the marine environment. It is probable that the increased roughness of the surfaces allowed a greater measure of

interlocking of the surface peaks, hence greater force was required to shear the peaks and produce slip.

In all the slip factor tests on joints having weathered plies, the performance as defined by slip factor improves

but slip tended to develop more rapidly after initiation than in joints having unweathered plies.

All the specimens coated with zinc metal spray or zinc silicate primer have slipped under sustained load, but

it is suggested that part of the movement may be the result of creep of the zinc. Figure 5 shows the result of a

laboratory test on an unweathered zinc metal sprayed specimen. The specimen was loaded in the same type of

loading rig as described, but slip was monitored continuously. Slip was complete after approximately 50 hours

when the specimen was subjected to the same load as applied to the exposed specimens.

Aluminium metal sprayed specimens have not shown the same tendency to slip under load although the slip

factor was reduced by pre-assembly weathering. In four specimens no movement has been detected and in one,

movement has occurred at one end only. The remaining specimen has slipped at both ends by amounts comparable

with those measured in the zinc silicate primer treated specimens, but the reason for the different behaviour of this

specimen has not been established.

The unprotected Grade 50 B specimens have slipped at one end, with the exception of one joint, in which no

movement has been detected. No movement has occurred in any of the weathering steel specimens at either exposure

site.

The effect of the change in slip factor caused by pre-assembly weathering has been to change the load factor

applicable to loaded joints. For example, the working load of joints having zinc metal spray surface treatment was

181.8 kN, which was derived as shown in Section 5.1 from the slip loads of unweathered joints. Using the slip

loads of joints assembled from plies weathered at Tinsley in the same calculation reduces the working load to

152.4 kN, thus the specimen joints are working at 85 per cent of the real slip load and not 71 per cent. The other

surface treatments are similarly affected, but in the case of the unprotected joints, the load factor has been increased.

8. CONCLUSIONS

Test results obtained over the first year of a five year programme show that the slip factor of HSFG bolted joints

is reduced by pre~assembly weathering, when the joint interfaces are protected against corrosion by the treatments

described. The reduction in slip factor results in a reduced load factor, when this has been derived from tests on

unweathered joints, thus increasing the possibility of slip. The tendency to slip is aggravated by the creep properties

of zinc, when this metal forms the basis of the protective system.

It is recommended that when these surface treatments are used, the joint interfaces should be protected

from the environment during the period between preparation of the surfaces and assembly of the joint.

The performance of unprotected joints, particularly those made from weathering steel, was improved by

the pre-assembly weathering conditions applied, suggesting that industrial procedure is satisfactory under these

circumstances.

9. FUTURE WORK

The monitoring of slip, applied load and bolt tension will continue until 1982, when the specimens will be returned

to the laboratory for slip factor tests.

10. ACKNOWLEDGEMENTS

The work described in this report was carried out in the Bridge Design Division (Division Head: Dr G P Tilly) of

the Structures Department of TRRL. The author gratefully acknowledges the contribution made by

Mr B Mecklenburgh (TRRL Experimental Equipment Engineering) who designed the loading rig.

11. REFERENCES

1. MOSS, D S. Effects of two years weathering on high strength friction grip bolted joints. Department of the

Environment, TRRL Report SR 191 UC. Crowthorne, 1976 (Transport and Road Research Laboratory).

. BRITISH STANDARDS INSTITUTION. The use of high strength friction grip bolts in structural steelwork.

Part 1. General grade. British Standard BS 4604: Part 1 : 1970. London, 1970 (British Standards Institution).

. BRITISH STANDARDS INSTITUTION. Weldable structural steels. British Standard BS 4360. London,

1972 (British Standards Institution).

4. BRITISH STANDARDS INSTITUTION. Sprayed metal coatings. Part 1. Protection of iron and steel by

aluminium and zinc against atmospheric corrosion. British Standard BS 2569: Part 1 : 1964. London, 1964

(British Standards Institution).

. BRITISH STANDARDS INSTITUTION. High strength friction grip bolts. Metric series. Part 2. Higher grade

bolts and nuts and general grade washers. British Standard BS 4395: Part 2: 1969. London, 1969 (British

Standards Institution).

. MOSS, D S. A method of measuring the tensions in bolts. Ministry o f Transport, RRL Report LR 100.

Crowthorne, 1968 (Road Research Laboratory).

7. BRITISH STANDARDS INSTITUTION. High strength friction grip bolts. Metric series. Part 1. General grade.

British Standard BS 4395: Part 1 : 1969. London, 1969 (British Standards Institution).

T A B L E 1

Specimens assembled from unweathered plies Coating thickness and relative position in specimen

L . . . . . . . . . . . . . . . . . . . . . . . i t l

t2 t 3

L . . . . . . . . . . . I t . . . . . . . . . . . . . t4 t5

t6

Z inc Sil icate Primer Zinc Metal Spray A l u m i n i u m Metal Spray

[ Thickness mm ! Thickness mm I I t l [ tl

Spec. i t2 t3 Spec. t2 t3 No. t4 15 No. ] t4 t5

t6 t6 i

Thickness mm tl

S p e c . t2 t3 N o . t4 t5

t6

0.05 0.04

25 0.05

0.05

0.04 0.05

2 6 0 .04

0.06

0.04 0.06

2 7 0.04

0.05

0.13 0.05 0.21

4 7 0.06 0.21

0.14

0.18 0.09 0.14 0 .14 48 0.05 0.14 0.15

0.20

0.15 0.04 0.22 0.21

5 0 0.07 0.21 0 .20

0.14

0.21 0.20

69

0.20 0.15 0 .17 0 .20 0 .20

0 .18

0.19 0.14 0.14

70 0.16 0.13

0.15

0 .17 0 .20 0 .24

7 0 A 0.13 0 .14

0 .20

Tested 24 hours

after assembly

9

T A B L E 2

S p e c i m e n s e x p o s e d a t T i n s l e y

C o a t i n g t h i c k n e s s a n d r e l a t i v e p o s i t i o n i n s p e c i m e n

L . . . . . . . . . 'J t l

t2 t3 I I I

t4 t5 t6

I =

Zinc Silicate Primer

Thickness mm t l

Spec. t2 No. t4

t6

0.06

3 0.06 0.03

0.05

0.04 0.03

5 0.06

0.07

0.04 0.07

8 0.03

0.04

0.05 0.06

9 0.04

0.05

0.03 0.07

10 0.06

0.06

0.03 0.06

11 0.06

0.06

0.06

2 0.06 0.04

0.04

0.04 0.04

6 0.04

0.05

0.06 0.05

12 0.05

0.04

0.06 0.04

1 0.05

0.07

0.06 0.06

4 0.07

0.05

0.07

7 0.03 0.04

0.05

t3 t5

0.04 0.06

0.03 0.04

0.04 0.03

0.04 0.04

0.08 0.07

0.05 0.08

0.04 0.04

0.06 0.04

0.06 0.03

0.04i 0.05

0.04 0.04

0.03 0.05

Zinc Metal Spray

Spec. No.

29

30

33

32

34

36

28

31

35

Thickness mrn t l

t2 t3 Spec. t4 t5 No.

t6

0.18 0.20 0.14 0.20 0.18

0.16

0.16 0.18 0.18 0.13 0.22

0.13

0.17 0.19 0.15 0.16 0.11

0.18

0.13 0.15 0.16 0.15 0.17

0.13

0.17 0.15 0.14 0.14 0.12

0.16

0.13 0.13 0.17 0.13 0,17

0.13

0.15 0.15 0.19 0.15 0.17

0.14

0.14 0.15 0.18 0.13 0.13

0.14

0.17 0.15 0.16 0.14 0.17

0.18

Aluminium Metal Spray

Thickness mm tl

t2 t3 t4 t5

t6

0.18 0.17 0.15

52 0.20 0.17

0.14

0.20 0.17 0.18

55 0.18 0.20

0.17

0.14 0.18 0.18

58 0.21 0.18

0.14

53

54

59

51

56

57

0.18 0.13 0.20 0.12 0.19

0.18

0.20 0.19 0.18 0.16 0.15

0.16

0.18 0.13 0.14 0.17 0.13

0.19

0.16 0.12 0.15 0.14 0.13

0.16

0.20 0.19 0.16 0.14 0.17

0.19

0.19 0.19 0.17 0.18 0.19

0.18

Weathered plates

Specimens tested

24 hours after

assembly

Specimens exposed under load

Specimens exposed

unloaded

Specimens exposed

unloaded Fitted with

load indicating washers

1 0

T A B L E 3

S p e c i m e n s e x p o s e d a t E a s t n e y

C o a t i n g t h i c k n e s s a n d r e l a t i v e p o s i t i o n i n s p e c i m e n

[ . . . . . . . . . . . . . . . . . . ! t l

t2 t3

i - -2-- -_-_-_3 U.--g---.- t4 t 5

. . . . . . . . . L 6_ . . . . . . . . . . . I I

i

Zinc Silicate Primer Zinc Metal Spray Aluminium Metal Spray

Thickness mm tl

Spec. t2 t3 No. t4 t5

t6

0.07 0.05 0.04

14 0.04 0.04

0.06

0.04 0.04 0.04

17 O.O5 0.04

0.06

0.06 0.05 0.04

24 0.06 0.05

0.06

0.05 0.04 0.04

16 0.05 0.04

0.04

0 .O4 0.05 0.05

18 0.05 0.06

0.05

0.05 0.04 0.04

21 0.06 0.05

0.05

0.06 0.04 0.04

15 0.05 0.04

0.05

0.04 0.05 0.04

22 0.04 0.O5

0.04

0.06 0.05 0.05

23 0.06 0.04

0.06

0.05 0.03 0.04

13 0.04 0.04

0.04

0.04 0.04 0.04

19 0.05 0.05

0.05

0.07 0.05 0.04

20 0.04 0 .O4

0.03

Thickness mm Thickness mm tl t l

Spec. t2 t3 Spot . t2 t3 No. t4 t5 No. t4 t5

t6 t6

0.20 0.14 0.17 0.13 0.20 0.16

37 60 0.13 0.15 0.13 0.13

0.15 0.19

0.14 0.14 0.15 0.19 0.19 0.19 39 63 0.16 0.14 0.21 0.18

0.14 0.17

0.20 0.16 0.20 0.21 0.14 0.17

43 67 0.14 0.20 0.20 0.20

0.18 0.13

0.20 0.15 0.14 0.15 0.17 0.15

41 61 0.12 0.14 0.11 0.11

0.14 0.13

0.15 0.17

44 0.19 0.14 65 0.17 0.20 0.20 0.13 0.17 0.12

0.17 0.19

0.13 0.19

45 0.18 0.19 68 0.13 0.15 0.15 0.19 0.17 0.14

0.17 0.19

0.15 0.19 0.17 0.14 0.15 0.14 38 62 0.19 0.15 0.19 0.17

0.17 0.16

0.19 0.15

40 0.18 0.19 64 0.12 0.18 0.17 0.20 0.14 0.18

0.13 0.22

0.17 0.15 0.17 0.17 0.16 0.15

42 0.20 0.17 66 0.14 0.15

0.15 0.17

Weathered plates

Specimens tested

24 hours after

assembly

Specimens exposed under load

Specimens exposed

unloaded

Specimens exposed

unloaded Fitted with

load indicating washers

11

TABLE 4

Slip factors of specimens assembled from unweathered plies, and loads applied to specimens weathering under continuous load.

Surface Treatment

Grade 50 steel grit blasted unprotected

Weathering steel grit blasted unprotected

Zinc silicate primer

Zinc metal spray

Aluminium metal spray

Slip Factor

0.453 0.421 0.391

0.378 0.377 0.345

0.476 0.446 0.432

0.764 0.716 0.691

Min. value

0.391

0.345

0.432

0.691

0.766 0.700 0.612

0.612

Rig Load Setting kN

102.9

90.8

113.7

181.8

161.0

TABLE 5

Slip test results. Joint plies weathered before assembly of specimens.

Surface treatment


Weathering steel grit blasted unprotected


Zinc metal spray


Exposure site Tinsley i Eastney

Slip Factor

0.567 0.504 0.398

0.483 0.462

0.453 0.433 0.410

0.613 0.613 0.579

0.632 0.589 0.585

0.561 0.543 0.530

0.510 0.501

0.431 0.424 0.421

0.724 0.664 0.626

0.644 0.643 0.618

12

TABLE 6

Slip after weathering for 1 year under constant load

Surface Treatment


Grit blasted +

Zinc metal spray

Grit blasted +


Grit blasted +


Weathering steel grit blasted

Spec. No.

71 75 79

Tinsley

Slip mm Top Bottom

0.051 0 0.038 0

0 0.043

32 0.152 0.094 34 ! 0.028 0.127

I 36 t 0.091 0.076 !

53 54 59

9 10 11

C2 C6

}

I 0.038 0.064 I 0 o I

0 0

0.043 0.064 0.051 0.056 0.043 0.017

0 0 0 0

Spec. No.

80 83 85

41 44 45

61 65 68

16 18 21

C7 C12

[

Eastney r

Top

0 0.034

0

0.094 0.084 0.090

0.043 0.043 0.056

0 0

Slip mm Bot tom

0.039 0 0

0.025 0.081 0.068

0 0

0.035

0.041 0.053 0.064

0 0

TABLE 7

Mean slip movements and slip factors from specimens weathered at two sites

Surface Treatment


Grit blasted +

Zinc metal spray

Grit blasted +


Grit blasted +


Weathering steel Grit blasted only

Slip - m m

i Tinsley

0.044

0.095

0.017

0.046

0

Eastney

0.012

0.074

0.006

0.050

0

Slip Factor weathered plates

Tinsley ] Eastney

0.490 0.545

0.602 0.671

0.602 0.635

0.432 0.425

0.473 0.506

clean plates

0.422

0.724

0.693

0.451

0.367

13

TABLE 8

Mean bolt loads and relaxations after 1 year

Surface Treatment


Zinc metal spray


Grit blasted 50 B

Grit blasted weathering steel

Loaded Joints Bolt load - kN

Tinsley I Eastney

77 78

64 66

81 82

78 79

80 80

Relaxation % Tinsley I Eastney

16.4 15.2

30.5 28.3

12.1 10.9

15.3 14.1

13.1 13.0

Unloaded Joints Bolt load - kN

Tinsley [ Eastney

82 8O

72 71

88 87

76 75

79 80

Relaxation % Tinsley I Eastney

10.8 13.0

21.7 22.8

4.3 5.4

17.4 18.5

14.1 13.0

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(1248) Dd0536361 1,200 7 /79 H P L t d S o ' t o n G 1 9 1 5

PRINTED IN E N G L A N D

ABSTRACT

HIGH STRENGTH FRICTION GRIP BOLTED JOINTS - EFFECTS AFTER ONE YEAR OF WEATHERING UNDER LOAD: D S Moss: Department of the Environment Department of Transport, TRRL Supplementary Report 499: Crowthorne, 1979 (Transport and Road Research Laboratory). The first year of a five year study of the behaviour of high strength friction grip bolted joints under the combined action of continuous loading and weathering is reported.


The slip factors of unprotected joints, particularly those made from weathering steel, were increased by pre- assembly weathering, but were reduced for joints having corrosion resistant treatments.

Slip has occurred in most of the loaded joints and the largest movements have taken place in the joints having corrosion resistant treatments containing zinc.

• It is concluded that, when some corrosion resistant treatments are used on the interfaces of high strength friction grip bolted joints, the efficiency of the joint is impaired if the surfaces weather before assembly. It is recommended that, when these treatments are used, the interfaces should be protected to prevent weathering in the time between preparation of the surfaces and assembly of the joint.

ISSN 0305-1315

ABSTRACT

HIGH STRENGTH FRICTION GRIP BOLTED JOINTS - EFFECTS AFTER ONE YEAR OF WEATHERING UNDER LOAD: D S Moss: Department of the Environment Department of Transport, TRRL Supplementary Report 499: Crowthorne, 1979 (Transport and Road Research Laboratory). The first year of a five year study of the behaviour of high strength friction grip bolted joints under the combined action of continuous loading and weathering is reported.


The slip factors of unprotected joints, particularly those made from weathering steel, were increased by pre- assembly weathering, but were reduced for joints having corrosion resistant treatments.

Slip 1ms occurred in most of the loaded joints and the largest movements have taken place in the joints having corrosion resistant treatments containing zinc.

It is concluded that, when some corrosion resistant treatments are used on the interfaces of high strength friction grip bolted joints, the efficiency of the joint is impaired if the surfaces weather before assembly. It is recommended that, when these treatments are used, the interfaces should be protected to prevent weathering in the time between preparation of the surfaces and assembly of the joint.

ISSN 0305-13 l 5

TRANSPORT and ROAD RESEARCH LABORATORY Department of … · 2016-10-02 · The bolts were M16 ISO...

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Transcript of TRANSPORT and ROAD RESEARCH LABORATORY Department of … · 2016-10-02 · The bolts were M16 ISO...