Backrest Strength Test For Type I And II Chair

- Apr 14, 2018 -

Backrest Strength Test - Static - Type l , II  


5.1 Applicability This backrest strength test shall be performed on Type I and II chairs.  For chairs with tilt locks, locking the chair changes the chair type (See Section 4) and must also be tested according to Section 6 in the upright locked position.  An additional chair may be used for the Section 6 testing.   Note: This test does not apply to chairs with backrest height less than 200 mm (7.9 in.). 

 

5.2 Purpose of Test  The purpose of this test is to evaluate the ability of the chair to withstand stresses such as those caused by the user exerting a rearward force on the backrest of the chair. 

 

5.3 Test Setup 5.3.1 The chair shall be placed on a test platform in an upright position and the base shall be restrained from movement, but shall not restrict movement of the backrest or arms of the chair.  Figure 5f shows one acceptable method of restraining the chair.  Note: For this test, the test platform may be placed at an angle to facilitate testing/load application. 5.3.2 If adjustable features are available, all adjustments shall be set at normal use conditions, except for height-adjustable pivoting backrests which shall have the pivot point set at its maximum height or 406 mm (16.0 in.) whichever is less. 5.3.3 After making the above adjustments, determine points 406 mm (16 in.) and 452 mm (17.8 in.) above the seat.  (See Figure 5a and Section 3.5).  Mark these points on the vertical centerline of the backrest.   a) If the top of the load-bearing structure/surface of the backrest is greater than or equal to 452 mm (17.8 in.) above the seat, position the center of the form-fitting device (See Definition 2.10) 406 mm (16 in.) above the seat.  (See Figure 5b).   b) If the top of the load-bearing structure/surface of the backrest is less than 452 mm (17.8 in.) above the seat, position the top of the form-fitting device even with the top of the load-bearing structure/surface.  (See Figure 5c).  c) If the unit has a pivoting backrest that stops at a position less than or equal to 20 degrees rearward (See Figures 5d and 5e), position the form-fitting device as directed in a) or b).  If the unit has a pivoting backrest that stops at a position greater than 20 degrees rearward of the backrest, position the center of the form-fitting device at the height of the pivoting point.  (See Figures  5d and 5e). 


5.3.4 Attach a loading device (front push or back pull) to the horizontal center of the backrest as determined above.  With the backrest at its back stop position, apply a force that is initially 70 degrees ± 10 degrees to the plane of the backrest. (See Figures 5f and 5g). The force is not intended to be maintained at 70 degrees ± 10 degrees throughout the loading of the backrest.  If applying the load with a cable and pulley system, the cable must initially be a minimum of 762 mm (30 in.) in length from the attachment point to the pulley.   Note: Where the design of the chair does not allow the transfer of force(s) from the formfitting device to the load-bearing structure/surface, then a bridging device 38 mm to 102 mm (1.5 in. to 4 in.) in height may be used to span the width of the loadbearing structure/surface.  For backrests with complex or varying contours, the plane of the backrest may be defined by the front of the CMD upright.    

 

5.4 Test Procedures 5.4.1 Functional Load   a) A force of 667 N (150 lbf.) shall be applied to the backrest at the backstop position for one (1) minute.  If the backrest/tilt lock mechanism will not accept the load due to gradual slipping of the adjustment mechanism during the load application, set the backrest to its most rearward (stopped) position, then apply the specified load(s). b) Remove the load.  5.4.2 Proof Load a) A force of 1001 N (225 lbf.) shall be applied to the backrest at the backstop position for one (1) minute.  If the backrest/tilt lock mechanism will not accept the load due to gradual slipping of the adjustment mechanism during the load application, set the backrest to its most rearward (stopped) position, then apply the specified load(s).  b) Remove the load. 

 

5.5 Acceptance Level 5.5.1 Functional Load There shall be no loss of serviceability to the chair. 5.5.2 Proof Load There shall be no sudden and major change in the structural integrity of the chair.  Loss of serviceability is acceptable. 

 

 

 


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