BS 4875-3:1985 download.Strength and stability of furniture Part 3 : Methods for determination of strength of settees.
1 Scope
This Part of BS 4875 describes methods for determination of strength of the structure of all types of settees. and other articles such as benches with seats for from two to four persons.
BS 4875-3 does not apply to chairs or stools which are covered by BS 4875-1. It does not apply to multiple seating units for stadium seating as the loads applied are not representative of this type of use.
NOTE I Tests carried out according to the requirements of BS 4875-3 are intended to demonstrate the ability of the item to give satisfactory service in its intended environment. It should be understood that such tests do not ensure that structural failure will not eventually occur as a result of habitual mis-use or after an excessively long period of service.
NOTE 2 The titles of the publications referred to in this standard are listed on the inside back cover.
2 Principle
2.1 General
The principle is to determine the strength of the structure of an article of furniture by applying to various parts loads or forces simulating normal functional use, as well as acceptable mis-use, according to a graded scale of severity (see Appendix A).
The interrelation of the tests is shown in Table I and a summary is given in Table 2.
The sequence as a whole determines the following:
a) static strength and initial damage; b) fatigue strength and damage propagation;
c) ability to withstand acceptable mis-use and demonstration of sufficient residual strength.
The severity of loading is graded by varying the number of applications or the magnitude of forces applied.
2.2 Static tests
The principle of static tests is to assess the static strength of the article under the high levels of loading that only occasionally occur.
2.3 Fatigue tests
The principle of fatigue tests is to assess the strength of the component parts of the article under the repeated operations, movement, or applications of loads occurring during daily use.
2.4 Impact tests
The principle of impact tests is to assess the impact strength of the article under the rapid rates of loading that only occasionally occur.
5.13 Double back loading pad2, a pad consisting of two rigid rectangular objects 200 mm high
and 250 mm wide, whose faces are curved across the width of the pad with a convex cylindrical curvature of 450 mm radius and with a 12 mm radius on all front edges. The distance between the pads shall be adjustable so that the centres can be sited over the back loading positions on each seat.
6 Determination of seat and back
loading points
6.1 General
If the number of seats in the article is not obvious divide the total seat length (in mm) by 600 mm and round to the nearest whole number to determine the number of seats. Divide the total seat length into
seats of equal length. Mark the position of each of the seat(s).
6.2 Settees
Position the template (5.3) with its load applied at the seat loading point on the centreline of the seat as far towards the rear as possible. Adjust its position by pushing the back loading portion into the back, so levering the seat portion forward until the shape of the template correlates with that of the seat
(see Figure 3). Mark the required loading points from the template. Repeat the procedure on the other seats.
6.3 Benches
Set up the template (5.3) at angle of 90° with the aid of the mark as shown in Figure 3. Place on the bench as shown in Figure 2. Mark the required loading
point from the template.
7 Procedures
7.1 Test 1: seat and back static load tests
7.1.1 Test la. seat static load test. Carry out the test at the following positions (see Figure 9):
a) on each seat for articles with two seats;
b) on one end seat and the centre seat for articles with three seats:
c) on one end seat and one of the centre seats for articles with four seats.
During the test load the other seat(s) that is not
being tested with a force of 750 N applied through the smaller seat loading pad (5.6).
7.7 Test 7: back and arm impact tests
7.7.1 Test 7a. back impact test. Place the article with its front feet prevented by stops from moving forward. Strike the centre of the top outside of the back, or, when there is no back, the centre of the seat front edge with the impact hammer (5.11) horizontally. Drop the impact hammer through the appropriate vertical height (or angle) given in Table 2 at the following back positions:
a) at both positions for articles with two seats; b) at one end position and one centre position for articles with three seats;
c) at one end position and one centre position for articles with four seats.
Repeat the procedure 10 times.
If the article has wings, rearrange the position of the article and repeat the test with the impact hammer hitting the outside of the top of one wing at right angles to the surface and in the position most likely to cause failure.
7.7.2 Test 7b. arm impact test. Carry out this test in the same manner as for the back impact test except apply the impact in an inward direction to the outside face of one arm at the position most likely to cause failure (see Figure 16). Place the stops against the feet on the opposite side of the article to the arm being tested.
7.8 Test 8: drop test
Lift up the article at one end and then allow to fall freely from the appropriate height specified in Table 2 so that the impacting feet or castors strike the floor (5.12) (see Figure 17).
8 Interpretation of results
Each article shall be considered to have passed the tests at the appropriate test level if no defects are observed (see clause 4), if a backforce of not less than 410 N was used in 7.1.2 and if the requirements of the appropriate product specification are met.
9 Test report
The test report shall include the following particulars:
a) the number of BS 4875-3;
b) details of the article of seating tested;
c) the test level that the article has been tested against;
d) details of any defects observed before the tests;
e) details of any defects observed after the tests;
f) if required:
i) any damage which does not impair the function of the article;
ii) the magnitude of any non-standard forces used. see 7.1. 7.4 and 7.5:
g) the moisture content, if emergency tests have been carried out, see 3.3:
h) the test result, pass or fail;
i) details of any deviation from the test procedures.