1、| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | BRITISH STANDARD BS 7941-1:1999 Incorporat
2、ing Amendment No. 1 ICS 93.080.20 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW Methods for measuring the skid resistance of pavement surfaces Part 1: Side-way force coefficient routine investigation machineThis British Standard, having been prepared under the direction of t
3、he Sector Committee for Building and Civil Engineering, was published under the authority of the Standards Committee and comes into effect on 15 October 1999 BSI 12-1999 The following BSI references relate to the work on this standard: Committee reference B/510/5 Draft for comment ISBN 0 580 33028 1
4、 BS 7941-1:1999 Amendments issued since publication Amd. No. Date Comments 10783 December 1999 Indicated by a sideline Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Building and Civil Engineering Sector Policy and Strategy Committee (B
5、/-) to Technical Committee B/510, upon which the following bodies were represented: County Surveyors Society Department of the Environment, Transport and the Regions Represented by the Building Research Establishment Institution of Civil Engineers Quarry Products Association Road Surface Dressing As
6、sociation Society of Chemical Industry The following bodies were also represented in the drafting of the standard, through subcommittees and panels: BAA Plc Brick Development Association Britpave Department of the Environment, Transport and the Regions Highways Agency Ministry of Defence The BSI cop
7、yright notice displayed on some pages of the document indicates when the page concerned was last issued. Sidelining, where it appears in this document, indicates the most recent changes by amendment on the page concerned.BS 7941-1:1999 BSI 12-1999 i Contents Page Committees responsible Inside front
8、cover Foreword ii 1 Scope 1 2 References 1 3 Definitions 1 4 Safety 1 5 Principle 2 6 Test equipment 2 7 Calibration 3 8 Test procedure 3 9 Test report 3 Annex A (normative) Dynamic calibration check 4 Annex B (normative) Dynamic calibration check 4 Annex C (informative) Report format 5 Annex D (inf
9、ormative) Precision of data 5 Table 1 Static calibration 3ii BSI 12-1999 BS 7941-1:1999 Foreword This British Standard has been prepared under the direction of the Sector Committee for Building and Civil Engineering by Subcommittee B/510/5, Surface characteristics. Part 2 of this British Standard gi
10、ves a method for measuring surface skid resistance using a braked wheel fixed slip device. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not
11、of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 5 and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued. BSI 12-1999 1 BS 7941-1:199
12、9 | 1 Scope This British Standard describes a method for determining the wet-road skid resistance of a surface using the sideway-force coefficient routine investigation machine (SCRIM). The method provides a measure of the wet-road skid resistance properties of a bound surface by measurement of side
13、way-force coefficient at controlled speed. The method has been developed for use on roads but is also applicable to other paved areas such as airport runways. 2 References The following normative documents contain provisions that, through reference in this text, constitute provisions of this British
14、 Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. For undated references, the latest edition of the publication referred to applies. BS 903-A8:1990, Physical testing of rubber Method of determination of rebound resilience. 3 Definitio
15、ns 3.1 skid resistance property of a trafficked surface that limits relative movement between the surface and the part of a vehicle tyre in contact with the surface 3.2 wet road skid resistance property of a trafficked surface that limits relative movement between the surface and the part of a vehic
16、le tyre in contact with the surface, when lubricated with a controlled film of water NOTE 1 Factors that contribute to skid resistance include the tyre pressure, contact area, tread pattern, and rubber composition; the alignment, texture, surface contamination, and characteristics of the road surfac
17、e; the vehicle speed; and the weather conditions. NOTE 2 Skid resistance is not a constant value. It varies with time, climate and traffic. 3.3 bound surface top layer or wearing course of a road with the aggregates secured permanently in place NOTE Aggregates are commonly secured in place by bitume
18、n or cement. 3.4 sideway-force coefficient (SFC) ratio between the vertical force and sideway-force normal to a test wheel maintained in a controlled slipping condition NOTE The controlled slipping condition is achieved by mounting a freely rotating test wheel with its vertical plane at an angle to
19、the longitudinal plane of the test vehicle. When the vehicle is in motion, the test wheel slides or slips in the forward direction. SFC values depend upon the type of equipment and the way in which it is used. 3.5 subsection length of road for which SCRIM records one SR NOTE A subsection can be 5 m,
20、 10 m or 20 m. 3.6 test section length of road between defined points (e.g. location references, specific features, or measured distances) 3.7 test length number of test sections over which a continuous sequence of measurements is made 3.8 SCRIM reading (SR) measurement recorded by SCRIM for a singl
21、e subsection NOTE A SCRIM reading is expressed as a positive integer equal to 1003 the SFC. 3.9 corrected data SCRIM readings altered to represent standardized conditions NOTE Corrected data should be prefixed “corrected” and an indication given of the type of correction (e.g. “speed-corrected SR”).
22、 3.10 SCRIM coefficient (SC) corrected data multiplied by the index of SFC (see 3.12) applicable to the SCRIM during the test NOTE SCRIM coefficients are expressed as decimal fractions to two places. 3.11 index of SFC ratio (expressed as a percentage) of values of SFC obtained from a current calibra
23、ted item of test equipment to values of SFC obtained from the equipment at TRL during the period 1963-1972 used to derive information on which to base proposals for specification NOTE The present index of SFC is 78 % and is valid for all UK SCRIM machines in current use. 3.12 theoretical water film
24、thickness theoretical thickness of a water film between a measuring tyre and a test surface, assuming the surface has zero texture depth 4 Safety NOTE When measuring skid resistance on trafficked roads the SCRIM may operate at speeds different to normal road speeds and as a result may create a hazar
25、d to other road users. Safety measures shall be in place to maintain safe working practice in accordance with current regulations, and to ensure the safety of other road users. NOTE Testing should not be carried out if there is a risk of water freezing on the road.2 BSI 12-1999 BS 7941-1:1999 5 Prin
26、ciple A freely rotating wheel fitted with a pneumatic, smooth rubber tyre, mounted mid-machine in line with the nearside wheeltrack and angled at 208 to the direction of travel of the vehicle, is applied to the road surface under a known vertical load. A controlled flow of water wets the road surfac
27、e immediately in front of the test wheel, so that when the vehicle moves forward, the test wheel slides in the forward direction along the surface. The force generated by the resistance to sliding is related to the wet road skid resistance of the surface and measurement of this sideways component gi
28、ves the SR. The SCRIM reading is affected by the speed of the test vehicle. Testing should be carried out at a specified speed. 6 Test equipment 6.1 SCRIM test equipment The SCRIM test equipment shall include the following features: a) test wheel assembly; b) water supply and flow control mechanism;
29、 c) electronic recorder and measurement control system. NOTE A machine conforming to the general characteristics of the SCRIM designed by the Transport Research Laboratory should be used for the tests. SCRIM test equipment has been built onto a number of different vehicle chassis and functions indep
30、endently of vehicle choice. 6.2 Test wheel assembly Mount the test wheel assembly on a frame within the wheel-base of the vehicle. Attach two vertical shafts to the frame and locate the test wheel assembly in the appropriate wheelpath. The assembly shall be free to move vertically when the test whee
31、l is in contact with the surface (to minimize the effects of vehicle chassis movements). The test wheel assembly shall comprise a back plate for location on the vertical shafts, a swinging arm, hub, test wheel and tyre, electrical load-cell, and single damper/spring suspension unit. The mass of the
32、test wheel assembly shall provide a static vertical load of (200 2) N. Fix the vertical plane of the test wheel at to the line of the chassis. (20 )8 20.5 +1.0 NOTE This angle is the “slip angle”. A mechanism shall be provided for raising and lowering the test wheel assembly to and from the ground.
33、6.3 Test tyre The test tyre shall be tubed, pneumatic, natural rubber, (3.00/20) in, smooth treaded. The tyre resilience shall be in the range 40 % to 49 % as measured by the Lupke test (see BS 903-A8:1990). Inflate the tyre to (3.5 0.2) kg/cm 2 , measured at ambient temperature. Test for at least 2
34、 km with a new SCRIM test tyre before results are recorded. Discard the test tyre when it loses 6 mm in diameter (3.0 mm tyre wear), or if otherwise damaged. Date stamp all tyres and store vertically in a cool dry environment away from direct sunlight. Do not use a tyre that is more than 2 years old
35、. 6.4 Water supply and flow control The pattern and flow of water shall be controlled by a manually set control valve and fan shaped nozzle. The manual control valve shall include an indicator that allows the water flow to be adjusted depending on test speed. To prevent accidental dry testing, a sep
36、arate valve shall be provided that turns on the water supply before the tyre touches the ground. The valve shall remain open so that water continues to flow until the tyre has completely lost contact with the ground when the test wheel assembly is raised. The point where the centre of the jet of wat
37、er strikes the level surface shall be (400 50) mm in front of the centre line of the test wheel along the direction of the line of travel, and within 75 mm either side, with the wheel parked on the ground. Set the water control valve to provide the theoretical water film thickness at 50 km/h. The wa
38、ter shall be free from salt, emulsified oils or suspended solids. The theoretical water film thickness for the SCRIM test shall be 2 mm. NOTE For testing at speeds up to 50 km/h, if the average water flow, measured over the discharge of a full tank, is (0.95 0.19) l/s, then the theoretical water fil
39、m thickness can be achieved. If higher speed testing (55 to 65) km/h is undertaken, the average water flow should be (1.20 0.24) l/s. 6.5 Measurement control system The measurement control system shall enable the operator to raise and lower the test wheel and ensure that the water supply valve is op
40、ened or closed as required. It shall ensure that water flow commences before the wheel touches the road surface and ceases after the wheel is raised. 6.6 Electronic recorder An electronic recorder shall be provided, able to measure the sideways force and distance travelled. The electronic recorder s
41、hall display the speed, SR, and length for the subsection and the distance travelled from a predetermined reference point. The recorder shall be able to accurately record automatic or manual input reference points. BSI 12-1999 3 BS 7941-1:1999 7 Calibration 7.1 Static calibration Static calibration
42、shall be carried out using a “rolling trolley calibration rig”, in accordance with the manufacturers instructions, not more than 24 h before commencement of measurements. Before carrying out a static calibration, check that the the test wheel assembly moves freely by lowering the tyre to the road. N
43、OTE It should be possible to create an oscillatory movement by lifting and then lowering the back-plate. If this is not possible, the reason should be investigated or the manufacturer consulted. Static calibration shall conform to Table 1. Table 1 Static calibration Horizontal load applied in line w
44、ith test wheel axle Recorder output kg 00 t o 2 20 8 to 12 40 18 to 22 60 29 to 31 80 39 to 41 100 49 to 51 120 59 to 61 140 69 to 71 160 78 to 82 180 88 to 92 200 98 to 102 7.2 Dynamic calibration check Carry out a dynamic calibration check, in accordance with annex A, at least once per week during
45、 periods of SCRIM operation and after repairs/servicing to the measuring equipment. NOTE 1 A dynamic calibration check should also be carried out if there is any reason to suspect the validity of the test results. NOTE 2 For use on UK trunk roads, SCRIM machines should be checked at least annually i
46、n a correlation exercise with other SCRIM machines. 7.3 Distance calibration Carry out a distance calibration, in accordance with annex B, at intervals not exceeding 3 months, or if the vehicle rear tyres are changed, or if a malfunction is suspected. 8 Test procedure 8.1 Prior to testing Prior to t
47、esting check the measurement tyre for pressure and wear. Inspect the water flow system for: position of nozzle; appropriate flow rate on the water control valve; obstruction or damage to the system. 8.2 Testing On the approach to a test length, lower the wheel and allow it to run on the surface, to
48、bring it to stable operating temperature (run for approximately 0.5 km). Running the wheel to stable operating temperature is not required if less than 15 min elapse after completion of a previous test length. Adjust the vehicle speed to the speed specified for the test length and start the recorder
49、. NOTE 1 On some machines the required length for the subsections should be selected prior to starting the recorder. Continue with the test, maintaining the specified test speed and entering reference codes at the appropriate locations. NOTE 2 Usually the equipment should follow the nearside wheeltrack or the path taken by normal vehicular flow (in particular the path taken by heavy goods vehicles). During the test the operator should monitor speed, test line and recorded values. The operator can also insert codes to indicate a deviation from the tes
