A contractor will place 90-cubic yards of concrete for a housekeeping pad on the rooftop of a 36-ft tall building. Site conditions dictate that the safest and best method of placement is to use a crane and a 2-cubic-yard bucket. To perform the task efficiently, five Union laborers are needed - one at the concrete truck, three at the point of placement, and one on the portable internal vibrator. The wage rate for laborers is $22.00/hr (Union overtime rate is 1.5 times the wage rate after 8-hour day). Time needed for the operation is: Setup: 15-min; Cycle time consists of Load = 3-min., plus Swing, dump and return = 6-min. which allows a total cycle time = 9-min; Demobilize operation, 10-min. Supervision is done by the superintendent. Allow a 10% factor for inefficiencies during the cycle time. Crane rental cost is $1,800 per 8-hr day. The total labor cost per cubic yard for the concrete crane placement of the 90 cubic yards is most nearly:
Solution:
Identify (by underlining) relevant cost items and calculate summary quantities.
No. of cycles 90-CY/2-CY/Bucket = 45 cycles
Total cycle time 45-cycles x 9-min/cycle = 405 min
Inefficiency(labor,delays,etc.)10%of cycle time = 41-min
Setup and demobilize: Sub-total = 25 min
Total operation time: 405 + 41 + 25 = 471-min or 7.85-hrs
Amount of time needed (adjusted to workday) = 8 hr Laborers - five for 8 hours at $22.00/hr = $880.00
Total labor cost per 90-yd3 = $880.00
Cost per cubic yard $880/90-yd3 = $9.78/yd3