Civil Engineering Reference
In-Depth Information
7 0.70 0.70 0.42 0.42 0.22 0.22
8 0.60 0.60 0.35 0.35 0.18 0.18
9 0.52 0.52 0.30 0.30 0.00 0.15
10 0.45 0.45 0.26 0.26 0.00 0.13
11 0.41 0.41 0.00 0.23 0.00 0.00
12 0.37 0.37 0.00 0.21 0.00 0.00
13 0.00 0.34 0.00 0.00 0.00 0.00
14 0.00 0.31 0.00 0.00 0.00 0.00
15 0.00 0.28 0.00 0.00 0.00 0.00
>15 0.00 0.00 0.00 0.00 0.00 0.00
From Waters et al. (1993). 75 cm = 30 in.
Because the operator must exercise significant control to load the reel, the calculation for
the destination is required. The most protective of the two RWL values is used to
estimate the job demands: the RWL for the destination is 6.4 kg, which is smaller than
the RWL at the origin (7.6 kg). According to the lifting index formulated below, RWL
may be multiplied by a factor of 3 which brings the load to about 20 kg.
Example 2: Product Packaging
In this example, products arrive via a conveyor at a rate of 1 per minute (PutzAnderson
and Waters, 1991). The worker packages the product in a cardboard box and then slides
the packaged box to a conveyor behind table B, as illustrated in Figure 10.6. The product
weighs 7 kg (16 1b), and the job is performed for an 8-hour shift. For this example,
assume that significant control of the object is not required at the destination. Workers
twist their bodies to pick up the product. Furthermore, assume that workers can flex the
fingers to the desired 90° angle to grasp the container. The job is performed for a normal
8-hour shift, including regular rest breaks.
Solution:
The task data are as follows:
H
(origin)
(destination)
V
(origin)
H
(destination)
F
Asymmetry
(origin)
Asymmetry
(destination)
Coupling
35 cm
33 cm
60 cm
100 cm
1/min
90°
0°
Fair
Since the worker can grasp the object with the fingers flexed at 90°, the couplings are
classified as “fair” (Waters et al., 1993). In this example, the RWL is only computed at
the origin of the lift, since significant control is not required at the destination.
For the origin:
RWL=23×HM×VM×DM×AM×FM×CM
= 23×(25/H)×(1-0.003|V−75|)×(0.82+4.5/D)×(1-0.0032A) × 0.75×0.95
= 23×(25/35)×(1-0.003|60-75|)×(0.82+4.5/40)×(1-0.0032×90) × 0.75×0.95
= 7.4 kg
Thus the recommended weight limit is 7.4 kg, which is about the same as the actual
product weight of 7 kg.
