Chapter 21 — Exercises

Work these with a pencil and a calculator, not from memory. Selected answers are in Appendix J; where a numeric answer appears here it is in a <details> block so you can check yourself after you commit to a number.

Difficulty legend: ⭐ basic · ⭐⭐ applied · ⭐⭐⭐ advanced judgment · ⭐⭐⭐⭐ extension and research

Part A — Conceptual Understanding ⭐

A1. State the five questions of the equipment decision framework in order, and explain in one sentence each why production comes before physical constraints, and physical constraints before money.

A2. Define, in plain language a first-week field engineer would understand: bank cubic yard, loose cubic yard, compacted cubic yard. Which one does a truck carry, and which one does an owner usually pay for?

A3. List the four components of ownership cost and the six or more components of operating cost for a machine. Which single component is most sensitive to the utilization you assume, and why?

A4. What is an internal rental rate, and name one specific consequence of setting it too high and one of setting it too low.

A5. A load chart gives a value of 18,600 lb at your radius and boom length. Name at least five things that may have to be subtracted from that number before you know what you can actually lift.

A6. Explain, using the idea of an overturning moment, why a crane's rated capacity falls as radius increases — and explain why adding counterweight does not always help.

A7. What is oversail, and why is the analysis fundamentally different for a freestanding hammerhead tower crane than for a mobile crane making four picks?

A8. Distinguish a bare rental, an operated-and-maintained rental, an operating lease, and a rental purchase option. For each, name the party that carries maintenance and downtime risk.

A9. Why is a stopped concrete pour a quality problem rather than merely a schedule problem? Name the defect and say what makes it structural.

A10. In a cost report, name the four different shapes equipment cost takes, and say which one is most commonly invisible and why that matters.

Part B — Applied Analysis ⭐⭐

B1. A superintendent tells you he is renting a skid steer "day by day so we stay flexible." The daily rate is $340, the weekly is $940, and the four-week is $2,600. He has used it 4 days this week and expects "another week or two." Diagnose the decision, compute the two crossover points, and tell him exactly what to do and what it saves.

B2. Your project's excavation cost code is running 18 percent over budget, but the quantity excavated is exactly on plan and the crew hours are on plan. Name the three most likely causes and say which one your cost-code structure should have caught before month 6.

B3. A subcontractor's proposed telehandler will lift a 3,100-lb bundle of curtain wall components at maximum forward reach from a slab-on-grade position. The subcontractor's foreman says "it's rated for five thousand." Explain, in the terms you would actually use in the coordination meeting, why that sentence is not an answer, and list the four things you would ask for.

B4. A rental house offers you a machine at a 22 percent discount if you sign a national account agreement covering all your projects. Your equipment manager objects because "we already own three of those." Frame the argument on both sides using the break-even analysis from §21.3.4, and state what data you would need to settle it.

B5. Your erector proposes to move the crane from setup position A (radius 82 ft, chart capacity 12,400 lb) to position B (radius 61 ft, chart capacity 18,900 lb) for the four heaviest picks. Moving the crane takes 3.5 hours including re-matting and re-leveling, and the crane costs $621 per productive hour. The alternative is upsizing to a machine that costs $9,200 more for the week. Which do you choose, and what would change your answer?

B6. On a job with a tower crane, four trades all want the hook between 6:30 and 9:00 a.m. Describe the management artifact that resolves this, who builds it, when, and what happens on the day it does not exist. Use the $621-per-productive-hour figure to put a price on the disorder.

B7. A ready-mix supplier confirms "540 yards on the fourteenth, no problem." Write the three follow-up questions you ask before you hang up, and explain what each one protects you from.

B8. Your fleet's telematics report shows an average of 34 percent idle time across eleven machines. Your equipment manager says that is normal. Assume the fleet averages 4.1 gal/hr working and roughly a third of that at idle, runs 9,600 engine hours a year in total, and diesel is $4.15/gal. Estimate the annual fuel cost of the idle time, then name two non-fuel costs idling also generates.

Part C — Calculations and Deliverables ⭐⭐–⭐⭐⭐

C1. Production, four ways. An excavator has a 3.5 CY bucket and a measured cycle time of 24 seconds. The material has a fill factor of 0.86 and you are planning at a 50-minute hour.

• (a) Compute production in LCY/hr.
• (b) The material has a 24 percent swell. Convert to BCY/hr.
• (c) The operation must move 58,000 BCY. How many productive hours, and how many work days at 9 hours?
• (d) Your estimator assumed a 60-minute hour. By what percentage did the estimate overstate production, and what does that do to the duration in (c)?

C2. Match the fleet. Using the excavator from C1 (376.1 LCY/hr): trucks hold 16 LCY; spot is 0.9 min; dump and maneuver is 2.2 min; the haul is 5.4 miles loaded at 21 mph and empty at 27 mph.

• (a) Load time per truck.
• (b) Total cycle time.
• (c) Trucks required.
• (d) If you can only get five-sixths of that fleet, what is your production rate and what is the percentage shortfall?

C3. Build the ownership cost. A wheel loader: delivered price $410,000; useful life 12,000 hours over 9 years; residual 22 percent; cost of capital 6.5 percent; insurance, tax and licenses 3.0 percent of average value; storage and inter-job transport $6,200 a year; assumed utilization 1,500 hr/yr. Operating: fuel 6.8 gal/hr at $4.15; DEF at 4 percent of fuel volume at $3.60; lubricants and filters at 15 percent of fuel cost; tires $28,000 over 4,500 hr; repairs at 60 percent of depreciation; ground engaging tools $0.95/hr; operator fully burdened $61.00/hr.

Build the full table and report: total ownership $/hr, total operating $/hr bare, and all-in $/hr with operator.

C4. Break-even utilization. Using the loader from C3: the same machine rents bare at $14,800 per four weeks (176 hr), with a 12 percent damage waiver and a 3 percent surcharge, plus $1,100 per delivery-and-pickup round trip. You would need 5 mobilizations a year. On a rental you still buy fuel, DEF, greasing and ground engaging tools, but not tires or repairs.

• (a) Fixed annual cost of owning.
• (b) Variable $/hr of owning.
• (c) Variable $/hr of renting.
• (d) Break-even hours per year.
• (e) At 1,500 hours a year, which is cheaper and by how much?

C5. Run a pick. A load weighs 19,800 lb. The main block and hook weigh 640 lb, the rigging weighs 810 lb, and there is no spreader bar. The required radius is 63 feet, and the boom length must be at least 88 feet to clear an existing building. Use the illustrative chart from §21.6 of the chapter. Your critical-lift threshold is 75 percent.

• (a) Total suspended weight.
• (b) The chart column and row you must use, and why.
• (c) Net capacity available for the load.
• (d) Does it work? Is it a critical lift?
• (e) If it does not work, what is the cheapest single change and what does it get you?

C6. Ground bearing. The crane in C5 has a gross weight with counterweight of 214,000 lb. Its outrigger-load chart shows a worst-case single outrigger at 58 percent during the swing. Floats are 30 in × 30 in. The geotechnical report gives an allowable bearing pressure of 3,000 psf on the compacted fill in the setup area.

• (a) Total weight during the pick (use the C5 suspended weight).
• (b) Worst outrigger load.
• (c) Pressure under the bare float.
• (d) Required mat area, and a practical square mat size.

C7. Plan the pour. You are placing a 780 CY mat foundation continuously. The finishing plan requires it be complete in 9 hours. Ready-mix trucks hold 11 CY. The plant is 9 miles out; the round-trip cycle including load, haul, queue, discharge, washout and return is 78 minutes. The plant's total batching capacity is 165 CY/hr.

• (a) Required placement rate.
• (b) Trucks per hour required.
• (c) Trucks in continuous rotation.
• (d) What percentage of the plant's capacity are you consuming, and what is the specific question you ask the dispatcher?
• (e) Write the two-sentence stop-point decision you will put in the pour plan.

Part D — Judgment and Ethics ⭐⭐⭐

D1. Your company's equipment division is losing money. The equipment manager proposes raising internal rates from $96/hr to $128/hr, arguing that the rental market supports it. You are the project executive. Work through what will actually happen over the following eighteen months, and propose an alternative. Then answer the harder question: on a GMP job, is raising the internal rate to a market rate honest? Where is the line, and what document decides it?

D2. A superintendent under schedule pressure asks a crane operator to make a pick at 96 percent of chart, arguing that "the chart has a safety factor built into it." Explain, in language you would use to that superintendent's face, why this reasoning fails. Then describe what your company's system should have in place so that the conversation never gets that far — and note who, other than the superintendent, has failed if it does.

D3. You discover that a subcontractor has been operating a rented excavator with a cracked rollover protective structure, taped over. Nobody has been hurt. The subcontractor is your best performer, is three days ahead, and the machine goes back to the rental house Friday. Walk through your obligations, your options, and the consequences of each. Name what you do in the next thirty minutes.

D4. A rental invoice arrives showing a machine on rent for eleven days that you know was on your site for four. Your project accountant says the vendor is a long-standing partner and it is probably a clerical error worth $2,100. Describe the professional handling — and then describe the version of this that is not a clerical error, and what you would look for to tell the difference.

D5. Your estimator's equipment number for a job is 14 percent below what your equipment plan says the work actually needs. Your VP of Operations wants to bid the lower number, arguing that "we'll manage it in the field." Make the case against in one page, using specific arithmetic from this chapter, and then say what you would do if you were overruled.

Part M — Mixed and Interleaved Practice ⭐⭐–⭐⭐⭐

M1. With Chapter 8 and Chapter 14. Northgate's mass excavation is on the critical path. Using the three-machine comparison in §21.4.2, select a loading tool, then write the two schedule activities it produces (excavation and export haul) with durations, and state what the choice does to the early start of the foundation package. Then answer: under what circumstance is the 11-work-day option not worth choosing?

M2. With Chapter 13 and Chapter 28. Design the equipment portion of a cost-code structure for a mid-size commercial building. Show at least eight codes, and demonstrate with a worked example how your structure lets you distinguish a productivity variance from a utilization variance from a rate variance. Explain why a single "equipment" code cannot.

M3. With Chapter 17 and Chapter 5. Build the crane-related row set for a permit and approval matrix on an urban site with a tower crane: every permit, approval, or private agreement you would need; the issuing party; an assumed lead time; the prerequisite; and what it gates. Include at least one item that is not issued by any government. Then write one paragraph on who — owner or contractor — should carry each, and what contract language decides it.

M4. With Chapter 20. The chapter uses a fully burdened operator rate of $58.50/hr. Build that number from the bottom: base wage, payroll taxes, insurance, fringe benefits, and any small tools or allowances. Then show how a 12 percent error in the burden calculation propagates into (a) the all-in machine rate, (b) the break-even utilization, and (c) the own-versus-rent decision.

M5. With Chapter 6. Write five risk-register entries for the equipment scope of a steel-framed building: the risk, its probability band, its impact in dollars and days, the owner of the response, the response itself, and the contingency you would carry. At least one entry must be a risk that is created by an equipment decision rather than merely encountered.

M6. With Chapter 19 and Chapter 24. Two subcontractors each want to bring their own aerial lifts to a floor with a posted construction-load limit. Describe the coordination and verification process you would run, name the documents you would collect, and write the two sentences you would put in the subcontract that make this the subcontractor's obligation rather than a favor you ask for.

Part E — Research and Extension ⭐⭐⭐⭐

E1. Get a real load chart. Find a published load chart for a real crane — manufacturers and rental houses publish them, and they are freely available. Pick a real machine and a real configuration. Then take the rooftop air handler problem from §21.6 of the chapter — 14,200 lb, 380 lb block, 640 lb rigging, 480 lb spreader, 74 ft radius, at least 96 ft of boom — and work it against the real chart. Note every difference between the real chart and the teaching table: the notes, the footnotes, the configuration matrix, the outrigger positions, the quadrant restrictions, the wire rope deductions, the "structural limit" markings. Write one page on what the teaching table left out and why those omissions matter.

E2. Price your own break-even. Pick one machine class. Get a real dealer purchase price, a real four-week rental rate from two different rental houses in your market, and a real fuel price. Build the full ownership and operating table from §21.2 and the break-even from §21.3.4. Then interview somebody who actually owns that machine class — a contractor, an equipment manager, a dealer rep — and ask them what their real annual utilization is. Compare it to your break-even. Write what you find, including the parts that surprised you.

E3. Find your jurisdiction's rules. Research three things for the jurisdiction where you work or intend to work: (a) whether a separate crane permit or engineered siting plan is required, and by whom; (b) whether the jurisdiction, the state, or a local air district imposes any engine emissions-tier requirement on off-road construction equipment, and on which projects; and (c) what the applicable minimum approach distances to energized power lines are for crane operations, and where the current authoritative text lives. Cite the actual issuing authority and the actual document in every case — and if you cannot find an authoritative source for one of them, say so, because that is also a finding.