Chapter 21 — Quiz

B. Equipment selection is a schedule decision priced in dollars, not a rental decision. The machine determines production rate, production rate determines duration, and duration is money — at Northgate, $10,650 a calendar day of total exposure. Safety is a hard envelope around the decision rather than the decision itself, and the rental market is an input, not the driver.

B. Load × radius is an overturning moment about the tipping fulcrum. Double the radius and you double the moment from the same load, so the load must halve. At short radius the limit shifts to structural capacity — boom, hoist, and ropes — and in that region adding counterweight does not help, which is why charts flag structurally limited values.

C. Total suspended = 14,900 + 480 + 520 = 15,900 lb against a 15,600 lb gross chart value. You are 300 lb over — 102 percent of chart. Framed the other way, net capacity for the load is 15,600 − 480 − 520 = 14,600 lb against a 14,900 lb load. Options A and B are the classic error of comparing the bare load to the gross chart and forgetting the deductions.

C. Always round toward less capacity — the longer radius row and the longer boom column. Interpolation is not inherently wrong on charts that permit it, but interpolating in your favor is, and a textbook rule that always works is better than a judgment call made under schedule pressure. Software is a tool, not an authority.

C. Twelve days at daily is $13,800. Two weeks plus two days is $6,400 + $2,300 = $8,700 — very close, and it is the trap answer. The four-week rate at $8,900 costs $200 more than option B but keeps the machine on site for another 8 working days at no additional charge, eliminating a second delivery and pickup at $850 each if the work runs long, which on a 12-day estimate it usually does. The crossovers are roughly three days for the week and roughly three weeks for the month.

B. Trucks required = truck cycle time ÷ load time. At the moment the first truck returns, every other truck in the fleet has been loaded and dispatched, so the excavator never waits. Option C gives you trucks per hour, which is the correct formula for concrete delivery but not for a haul fleet, and multiplying it by cycle time in hours gets you to the same place.

C. On the chapter's Northgate numbers, one truck too many costs $13,101 in truck rent with no schedule effect. One truck too few costs $5,564 in fleet cost — less money — but adds roughly two calendar days on the critical path at $10,650 a day, for a total of $26,864. The folk rule is right, and it is right because of calendar, not because of hauling economics. The second reason is availability: at 92 percent truck availability, a nominal fleet of 13 puts an expected 11.96 on the ground.

B. In the chapter's worked example, a 15 percent rental discount pushed break-even from 1,372 hours to 4,235 — effectively eliminating the ownership case. Improving the repair reserve from 65 to 45 percent of depreciation pulled it down to 1,033. Purchase price, cost of capital, and residual all matter, but they move the answer far less than the two variables that are actually under your organization's control.

B. Out of service, the slewing brake is released so the jib turns with the wind instead of taking side load — that is how the machine survives a storm. So the airspace you must negotiate is defined by the out-of-service radius, twenty-four hours a day for the entire crane term, not by the working radius during a handful of picks. Aviation notice (option C) is a real and separate requirement, and it evaluates the crane's tip height, not the building height.

C. Every machine costs money to bring and money to take away, and demobilization is the one that disappears because it happens after everyone has stopped paying attention. Northgate's crawler mobilization and demobilization was $38,000 — 6.6 percent of the entire crane cost — and none of it appears on a rental rate sheet.

B. Placement rate = 620 ÷ 8 = 77.5 CY/hr. Trucks per hour = 77.5 ÷ 10 = 7.75 → 8 per hour. Cycle = 66 ÷ 60 = 1.1 hr. Trucks in rotation = 8 × 1.1 = 8.8 → 9 trucks. The mistake behind answer A is stopping at trucks-per-hour and never multiplying by the cycle.

C. $239 of a $22,460 total. Thirteen idle haul trucks were $7,410 of it and one critical-path calendar day was $10,650. The machine is never the number. The crew and the calendar waiting on it are the number — which is why a cheap, poorly maintained rental is not cheap.

False. The moment you suspend a load from a hook or jib rather than carrying it on forks, you have a machine with a load chart, a rated capacity that varies with boom extension and angle, and a rigging problem. If you hang a load from it, it gets a lift plan.

False. When the boom swings over a corner, one float can carry well over half the total — the chapter's example used 62 percent. Use the manufacturer's outrigger-load chart or lift-planning software. Dividing by four understates the worst float by a factor of two or more and is a straightforward way to punch a crane through the ground.

False. Unit price puts quantity risk on the owner and productivity and price risk on the contractor. The owner pays for cubic yards measured, at the bid unit price, regardless of how many hours it took you. That is exactly why the $116,550 in Case Study 2 was unrecoverable.

False. The loading tool is typically only 10 to 15 percent of the hourly fleet cost but 100 percent of the production rate. In the chapter's comparison, the smallest machine was cheapest per hour and per yard as a machine ($0.585/LCY) and the most expensive as a system ($5.75/LCY). Compare $/unit of production for the whole spread.

False. The operator and the lift director have unqualified authority to refuse a lift. No superintendent, project manager, or owner's representative overrides that, and no documentation makes it acceptable. Documenting an override does not distribute the responsibility; it records it.

False, or at least not without checking the contract. On a GMP or cost-plus job, the general conditions commonly define allowable equipment charges and cap owned-equipment rates by reference to a published schedule, the prevailing local rental rate, or actual cost plus a stated percentage, often with a limit that total charges not exceed the machine's fair market value. Beyond the contract question, a rate set well above true cost hides a profit center inside job costs and corrupts every cost report that uses it.

Concrete has a clock. When placement stops long enough that the leading edge takes initial set before fresh concrete arrives against it, the two placements never bond — that is a cold joint, and unlike a designed construction joint it has no keyway, no dowels, and no engineered load transfer across it. Repairing one means an engineer's evaluation, surface preparation, dowelling, and often epoxy injection, and it becomes a documented defect in the structure. The cheapest insurance is a backup pump — roughly $1,900 in mobilization and minimum against a $43,000 to $69,000 exposure — plus a written stop-point decision made before the pour starts rather than at 10:40 a.m. with eight trucks in the queue.

The four shapes are the rental invoice (actual outside dollars), the allocated internal rate (your own machine charged to the job), idle and standby (a machine on site not producing), and mobilization and demobilization. Coding idle and standby separately is what lets you distinguish a productivity problem — the operation is slow — from a utilization problem — the machine is waiting on somebody else. Those have completely different fixes, and a cost report that buries standby inside the working code shows you a variance with no cause. It also gives you contemporaneous evidence when standby was caused by an owner-directed change or a delay, which is the difference between a claim you can prove and one you cannot.

Probably not on those numbers alone, and the reasoning is that a $1,594 annual difference on a machine of this cost is inside the noise of every assumption in the analysis — residual value, repair reserve, and utilization forecast each move the answer by more than that. When the money is a genuine coin flip, decide it on what is not money: a machine available in twenty-four hours without a phone call, operators who know it, no return-condition disputes, and the ability to send it out at 5 a.m. on a Saturday.

What would change the answer is a structural change to one of the sensitivities: if you can negotiate a fleet discount with a rental house, the ownership case collapses entirely (break-even moves to 4,235 hours). If you can genuinely improve maintenance performance, it strengthens (break-even moves to 1,033). So the professional answer is: do not sell the machine, go negotiate the rental agreement and fix the shop, then re-run the analysis in twelve months with real telematics utilization instead of an estimate.

1. Get the cost codes and separate hours from dollars. Pull equipment hours against installed quantity, by activity, and look for whether standby is coded separately. Designed to find: whether this is a productivity variance, a utilization variance, or a rate variance. Right now nobody knows which.

2. Run a stopwatch study on the earthmoving cycle — forty cycles, element by element: spot, load, haul, dump and maneuver, return. Designed to find: where in the cycle the time actually went. "The machine's running good" almost always means the constraint has moved off the machine and nobody re-measured, which is the exact failure in Case Study 2.

3. Recompute the matched fleet from the measured cycle and compare it to the trucks actually on site. Designed to find: a fleet matched to a cycle that no longer exists.

4. Ask to see the pick schedule for tomorrow. If there is not one — or if it is built in the morning rather than the afternoon before — you have found several hundred dollars an hour of loss. At $621 per productive pick-hour, twenty minutes of daily indecision is $4,347 a month. Designed to find: whether crane time is being managed or merely consumed.

5. Walk the crane setup and read the current lift plan. Ground, mats, what is under them, radius, chart, deductions, percent of chart, and who signed it. Designed to find: whether the safety envelope is real or assumed. This one is not about the 14 percent.

The number on your desk by Friday: the measured truck cycle time, broken into its five elements. Everything else in the earthmoving diagnosis follows from it — the required fleet, the achievable production rate, the honest duration, and the real cost per cubic yard.

Credit also for: verifying rental terms and off-rent dates against the schedule; checking the mobilization and demobilization lines; and confirming that the crane's demobilization date leaves you a way to set rooftop equipment later.