1. Cranes
   • Crane & Crane Attachements
   • Cranes
   • Crane Problems:
   • Clamshell Figure
   • Hydraulic Backhoe Figure
   • Various Types of Machinery
   • Shovel Figures
   • Power shovels:
   • Example
   • Shovel Problem:
   • Dragline Figures
   • Draglines
   • Dragline Problem
   • Trucks & Wagons
   • Truck/Shovel Problem::
   • Example

Cranes

Crane & Crane Attachements

Cranes

~ tipping condition: overturning moment = stabilizing moment

~ rated loads < tipping loads at minimum stability direction:

• crawler-mounted 75% of the tipping loads

• rubber-tired 85% of the tipping loads

• outrigged 85% of the tipping loads

~ classifications:

• radius (ft) @ max. rated load & base boom length

• load weight (lb/100) @ 40-ft radius & 50-ft boom length

• Ex:Table 7-2, pg. 180, for 25-ton crane, pcsa class 12-88

· Note:base boom is 31.5 ft & safety factor is 85%

·Class12-88; @ 12-ft radius & 31.5-ft boom, lift 50,000 lb

· Class12-88; lift 8,800 lb @ 40-ft & 50-ft boom (nearest boom is 48 ft)

Working ranges of cranes (see Fig. 7-12, pg. 185, textbook)

~ high boom angle: lift crane

~ medium boom angle: clamshell

~ low boom angle: dragline

Crane Problems:

Crane Problem #1:

Can the tower crane, whose load chart is shown in Table 7-3 (pg 182, textbook) lift a 15,000-lb load at a radius of 142 ft? The crane has a L7 Jib and a two-part hoist. The slings that will be used for the pick weigh 400 lb.

Crane Problem #2:

Using the information in Figure 7-12 (pg 185, textbook) determine the minimum boom length that will permit the crane to lift a load which is 34 ft high to a position 114 ft above the surface on which the crane is operating. The length of the block, hook, and slings that are required to attach the hoist rope to the load is 26 ft. The location of the project will require the crane to pick up the load from a truck at a distance of 70 ft. from the center of rotation of the crane. Thus, the operating radius will be 70 ft.

Clamshell Figure

Hydraulic Backhoe Figure

Various Types of Machinery

Clamshells:

~ best suited to vertical lifts of loose material

~ buckets have teeth for hard digging

~ buckets have no teeth for rehandling material

~ capacity (see Table 8-6, pg. 203) is as:

• water-level

• plate-line

• heaped

~ productivity calculations figure:

• time per cycle (sec)

• cycles per hour

• volume per cycle (cy)

• operating factor

Hoes:

~type of power shovel (hoe, back hoe, back shovel or pull shovel)

~ very versatile: dig trench, place pipe, backfill with same hoe

~ excellent digging power

~ excellent accuracy for depth control

~ excellent for loading trucks

~productivity approaches power shovel output when digging at moderate depths

Loaders:

~front end loaders used for digging, scooping, lifting, carrying & dumping

~ used for backfilling, spreading & compacting

~ productivity calculations similar to clamshell (above)

Trenching machines:

~ wheel type (Fig. 8-25, pg. 230)

~ adder type (Fig. 8-26, pg. 231)

~fast digging with accurate trench width & depth when soil conditions allow their use

~ ladder machines can dig deeper than wheel machines

Earth & rock saws:

~carbide-tipped cutters rotate on a wheel to saw the hardest earth

Trap & belt loading:

~bulldozer pushes material into hopper (trap) which feeds a conveyor belt used to load trucks or scrapers

Shovel Figures

Power shovels:

~ excavate earth of all types and load trucks

~crawler-mounted shovel (Fig. 8-11, pg 205 & Fig. 8-12, pg 206, textbook) or wheel-mounted shovels

~ single-engine, self-propelled

~ non self-propelled, separate engine

~ sized by dipper size, struck cy (loose)

~ heaping the dipper will approximate sized cy = bcy

~ commercial sizes 3/8 cy to 2½ cy

Power shovel basic parts & digging action

Cable control vs. hydraulic control

Trend is toward hydraulic equipment (pg 217)

Shovel selection factors:

~ mobility & job conditions

~ equipment cost (crawler is less expensive)

~ production cost

Cost/cy factors

Job condition factors

Intelligent engineering can save "big bucks"

Shovel production:

Example

EXAMPLE: Shovel production: (also, see example on pg 215, textbook)

• 1½ cy shovel

• sand excavation

• average depth of cut, 10 ft

• swing angle, 75°

• job conditions, fair

• management conditions, excellent

• operating efficiency, 50 min./hr (average)

~ ideal output (bcy/60 min hr):

• 1½ cy shovel & sand material:

· 270 bcy/hr; 7.0 optimum depth of cut

~ swing-depth factor:

• % optimum depth & 75° swing:

~ job & management factor:

• for:

~ operating factor (O.F.):

• O.F = 50 min./60 min. = 0.83

~ estimated production:

= 270 bcy/hr × .95 × .72 × .83 = 153 bcy/hr

Shovel Problem: p. 210

A 5-cu yd shovel having a maximum digging height of 34 ft is being used to load poorly blasted rock. The face being worked is 12 ft high and the haul units can be positioned so that the swing angle is only 60°. What is the adjusted ideal production, if the ideal cycle time is 21 sec.?

Dragline Figures

Draglines

~ advantages:

•versatile digging positions, can excavate above & below machine level (whereas shovel can only excavate above)

• versatile mounting: crawler, wheel or truck

• long reach for digging & dumping

• high cycle speed

•can vary bucket size for machine tipping safety (Table 8-1, pg. 192)

~ disadvantages:

• digging action about 75-80% efficient as shovel

• less positive control (swinging, jerking, spilling)

• less lateral movement

~capacity is determined by size of the bucket and the combined weight of the bucket and its load

~do not use a bucket that is too large. The loaded bucket weight must be safe for the boom length & angle (see Example 8-2, pg 197, textbook)

~production rates:

• note similarity between power shovels & draglines

• ideal output at optimum depth of cut

· Table 8-3 dragline, pg 195, textbook

• depth of cut & angle of swing conversion factors

· Table 8-4 dragline, pg 196; Table 8-8 shovel , pg 210, textbook

• factors for job & management conditions

· shovel & dragline

• output of draglines (see pg. 191, textbook)

Dragline Problem

Dragline problem: p.242, see pages 189-197

Assume: 1)material to be handled has a loose weight of 90 lb/ft³

2)use 2 cu yd medium duty bucket

3)80-ft boom dragline at a 40° angle

4) maximum safe load = 8,600 lb

~The approximate weight of the bucket and its load:

•bucket (Table 8-5, pg 198, textbook) = 4,825 lb

•earth, 60 cu ft @ 90 lb per cu ft = 5,400 lb

- combined weight = 10,225 lb

- max. safe load = 8,600 lb

Trucks & Wagons

Truck characteristics:

~ high-speed hauling units

~ high-capacity load

~ low unit price hauling costs

~ afford planning flexibility

~ on-highway or off-highway models

Truck classification factors:

~ engine size (hp)

~ engine type (fuel)

~ no. of gears

~ no. of drive wheels a/o axles

~ dump method: rear, side

~ material hauled: rock, dirt, etc.

~ load capacity: tons, cy (struck or heaped)

Wagons are tractor towed and usually bottom dump:

~ large capacity

~ rapid dump

Production factors for trucks:

~ load capacity per trip (cy/trip)

~ trips per unit of time (trips/hr)

Truck wait time, if any, will generate the operating factor (see Ex. 9-2, pg. 246, textbook)

Balancing trucks with loader (excavator) is usually based on an ideal 60-min. hour so that capacity of excavator _ capacity of trucks/wagons:

~ rule-of-thumb:

Cost of hauling earth variables Peurifoy reviews:

~ size of truck (Table 9-1, pg. 248)

~ size of excavator (Table 9-2 & 9-3, pgs. 249-250)

~ effect of grade resistance

~ effect of rolling resistance

~ effect of altitude

Rated payload = mfg. rated max. load:

~ either volume (cy) or weight (tons) could control -- why?

~ actual payload may depend on material’s density

Cycle time includes:

~loading

~hauling

~dumping

~returning

~spotting & maneuvering

Loading time for trucks (ideal):

Ideal number of trucks required to balance with loader (excavator):

~ dependent on statistical average times

~ need to round up or down to whole trucks

Complex truck - excavator balance problems can be performed by computer simulation or by mathematical methods such as the theory of queues

Truck/Shovel Problem::

For power shovel used previously, select trucks:

haul with trucks = 25 bcy capacity

trip time (excluding loading time) = 15 min.

power shovel ideal production = 270 bcy/hr

swing – depth factor = .95

power shovel estimated production = 153 bcy/hr (our solution)

Note:100% loader efficiency includes swing-depth factor but does not include job & management factor or operating factor

•loader governs production _ 4 trucks, i.e., keep output at maximum production

•trucks govern production _ 3 trucks, i.e., shovel will wait some.

•with 4 trucks, estimated production is 153 bcy/hr

•with 3 trucks, estimated production reduces to:

153 bcy/hr × (3/3.6) = 128 bcy/hr

~goal is to minimize cost/unit produced (s/cy)

~need to optimize the total mix of production equipment and site conditions

For our problem should we use 3 or 4 trucks?

~need an economic evaluation for both 3 and 4 trucks to determine which gives the lowest $/cy.

Example:Using same power shovel, select between 10- & 15-cy trucks, if shovel costs are $40/hr and

•find size & number of trucks for minimum production costs

•for 10-cy truck, loading time = 2.4 min.

N = (2.4 + 13)/2.4 = 6.4, use 6 or 7

•for 15-cy truck, loading time = 3.5 min.

N = (3.5 + 15)/3.5 = 5.3, use 5 or 6

Truck Size (bcy)	Number of Trucks		Production (bcy/hr)	Cost $/hr	Unit Cost ($/bcy)
10	7		153	138	.902
10	6	(6/6.4)(153) =	143.4	124	.865	•Select
15	6		153	160	1.046
15	5	(5/5.3)(153) =	144.3	140	.970

Example

Trucks & Wagons Problems (from Chapter 9, textbook):

Given: • 3/4 cu yd shovel, excavating good common earth

• angle of swing: 90°

• no delays waiting for hauling unit

• shovel cycle time: 21 sec

• dipper and the trucks are operated at their heaped capacities = BCY

• the time for a truck travel cycle = traveling to the dump + dumping +

returning to the shovel = 6 minutes

Problem #1:Assume 3-cu yd trucks are used.

~How many dippers will it require to fill a truck?

~With a shovel cycle time of 21 sec, it will be necessary to provide a new truck how frequently?

~The min. (minimum) round-trip cycle time for a truck would be?

~ The min. number of trucks required to keep the shovel busy would be?

~The time required to load the minimum number of trucks required to keep the shovel busy would be?

~The lost time per truck cycle would be?

~This will produce an operating factor of?

Problem #2:Assume 6 cu yd trucks are used.

~How many dippers will it require to fill a truck?

~The time required to load a truck would be?

~The min. round-trip cycle time for a truck would be?

~The min. number of trucks required to keep the shovel busy would be?

~The time required to load the minimum number of trucks required to keep the shovel busy would be?

~The shovel will lose how much time in loading this min. number of trucks?

~The percentage of time lost would be?

~If one additional truck is used (minimum number of trucks + 1), the loading time would be?

~This will increase the round-trip cycle of each truck from to

~The lost time per truck cycle would be?

~This will result in a loss of % of the truck time, which is equivalent to an operating factor of 78.6 percent for the trucks.

Problem #3:Assume 15 cu yd trucks are used.

~How many dippers will it require to fill a truck?

~The time required to load a truck would be?

~The min. round-trip cycle for a truck would be?

~The min. number of trucks required to keep the shovel busy would be?

~Time required to load the min. number of trucks required to keep the shovel busy would be?

~The lost time per truck cycle would be?

~This would produce an operating factor of what % for the trucks?

Problem #4:Assume a 3/4-cu yd shovel, operating at 80% efficiency while it is excavating with no lost time waiting for trucks. Also assume shovel cycle time = 21 sec.

~Number of cycles per minute?

~Number of cycles per hour?

~Ideal output per hour?

~Output at 80% efficiency?

~Travel cycle for each truck?

~If 6 cu yd trucks are used, the ideal number of trucks would be?

~If three trucks are used, the output would be?

~Cost per hour for a truck and driver?

~Total cost per hour for trucks?

~Truck cost while loading?

~Truck cost per cu yd of earth loaded?

~The hauling cost per cu yd?

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