From crane hook time to total project cost
A worked Global Variables example of Case Study A from the Commercial Building Estimating white paper: choosing a formwork set count for a 20 storey office tower when a shared tower crane and time related preliminaries are priced in the same chain, rather than left implicit in a flat floor rate.
This worked example applies the dependency graph principle from Section 2 of the white paper to the Case Study A scenario in Section 3: a 20 storey tower, a system formwork set costing $220,000, and a single tower crane shared across trades. It is a fixed illustration of that case study rather than a fully parameterised template; floor count, base cycle and the 1–6 set sweep are held constant so the demonstration stays aligned with the published white-paper figures. The hero worksheet is Total Project Cost & Optimizer: it does not price a single scenario, it evaluates all six candidate formwork set counts and returns the cheapest. That worksheet does not compute programme duration or preliminaries itself, it calls a Programme & Preliminaries Cost worksheet. That worksheet does not compute floor cycle time itself, it calls a Floor Cycle Time worksheet, the one place the crane hook time trade off from Section 3.2 is actually modelled. Every table and the chart below are drawn from the same live Global Variables; changing one changes all of them.
Interactive Global Variables
The best control is not N. N = 1…6 is a discrete sweep the model already computes. What demonstrates Global Variables is changing CHTB_GV, DPR_GV or FSC_GV once and watching the entire six-row sweep, chart, hero total and optimum recalculate together.
Adjust any slider. The scenario table, chart, hero box, cascade rates and optimizer all re-evaluate from the same single source of truth. No downstream figure is re-keyed by hand.
At current CHTB = 2.45 days: formwork binds for N = 2, 3, 4; crane binds for N = 5, 6.
The hero resource: Total Project Cost & Optimizer
Everything else in this worked example exists to feed this one worksheet. It evaluates the combined cost of formwork capital and time related preliminaries for every candidate set count from 1 to 6, then selects the minimum. At the current optimum the combined cost and programme duration update live as you move the Global Variables above.
The chain, crane budget to total cost
Reading top to bottom: each card is a full Global Variables worksheet in its own right, and the line joining it to the card below is a resource reference, not a copied number. Change the formwork set cost or the daily preliminaries rate and the whole optimizer recalculates, including which set count wins. Click any card to jump to its full build up.
The hero also multiplies Formwork_Sets by the Formwork Set Cost global variable directly to get capital cost, a straight line calculation that does not need its own worksheet. The full chain is evaluated six times, once for each candidate set count from 1 to 6, before the hero picks the minimum.
Zooming into the hero: capital vs. preliminaries, at the optimum
The optimum splits into two competing costs: the capital tied up in formwork sets, and the time related preliminaries that a slower cycle keeps accruing. The balance point moves when you change any of the Global Variables above.
Scenario results, every column a live formula output
Every cell in this table, and every point on the chart beneath it, is computed in the browser from the same Global Variables controlled by the sliders: CHTB_GV, NF_GV, DPR_GV and FSC_GV, plus the fixed operations and base cycle constants shown in the Floor Cycle Time tab. Nothing here is typed in twice; change a Global Variable and the table, the chart, and the hero all move together.
| Formwork sets | Days / floor | Programme | Capital cost | Preliminaries | Total cost |
|---|---|---|---|---|---|
| 1 | 15.10 | 302 days | $220,000 | $5,587,925 | $5,807,925 |
| 2 | 8.63 | 173 days | $440,000 | $3,193,100 | $3,633,100 |
| 3 | 6.47 | 129 days | $660,000 | $2,394,825 | $3,054,825 |
| 4 (optimum) | 5.39 | 108 days | $880,000 | $1,995,688 | $2,875,688 |
| 5 | 4.80 | 96 days | $1,100,000 | $1,776,162 | $2,876,162 |
| 6 | 4.80 | 96 days | $1,320,000 | $1,776,162 | $3,096,162 |
Trade off: capital vs. time related preliminaries
The model evaluates COMB(N) = N·FSC_GV + T_floor(N)·NF_GV·DPR_GV for N = 1 to 6. Adding sets raises capital (rust) but shortens the programme, cutting time related preliminaries (navy). The combined total is U shaped. The optimum marker moves as you change the Global Variables.
T_floor(N) = [FIX + MAX(BC/N, CHTB_GV)] × HD (N ≥ 2)N = 1: a non-pipelined boundary case. The MAX() bottleneck is skipped, but fixed operations still apply.
N = 2 to 4: formwork is typically the bottleneck; days per floor falls as sets are added.
N = 5 to 6: when CHTB binds, the curve flattens rather than continuing to fall.
Optimum: the model evaluates all six totals and keeps the smallest. Changing DPR_GV, FSC_GV or CHTB_GV moves the whole curve.
The full build up, worksheet by worksheet
Each tab below is one Global Variables worksheet, the same three worksheets shown in the chain above, in the same order. Each is worked in full for the current optimum. A resource line highlighted in blue is a pointer to another worksheet rather than a hardcoded figure.
Every row below is a full evaluation of the same worksheet chain with Formwork_Sets set to a different value, the same six rows as the scenario table above. This worksheet asks which of those six evaluations is cheapest.
| Description | Unit | Variable | Equation | Value | Amount |
|---|---|---|---|---|---|
| Candidate total costs, from the scenario sweep | |||||
| N = 1 | $ | – | CAP(1)+PC(1) | 5,807,925.00 | – |
| N = 2 | $ | – | CAP(2)+PC(2) | 3,633,100.00 | – |
| N = 3 | $ | – | CAP(3)+PC(3) | 3,054,825.00 | – |
| N = 4 | $ | – | CAP(4)+PC(4) | 2,875,687.50 | – |
| N = 5 | $ | – | CAP(5)+PC(5) | 2,876,161.88 | – |
| N = 6 | $ | – | CAP(6)+PC(6) | 3,096,161.88 | – |
| Optimizer | |||||
| Optimum total cost | $ | OPT | MIN(5807925, 3633100, 3054825, 2875688, 2876162, 3096162) | 2,875,687.50 | – |
| Optimum formwork sets | No. | – | lookup, N where Total = [OPT] | 4 | – |
| Optimum total project cost | $2,875,688 (N = 4) | ||||
Dynamic recalculation: crane hook time budget raised for sharing
Section 3.7 of the white paper describes a mid tender design change: a neighbouring tower is confirmed to share the same crane corridor, cutting the dedicated crane allocation to a 60% share. Because the model uses MAX() to resolve the bottleneck, a tighter crane share has to raise CHTB_GV, not lower it. Use the Play button above to animate the change from the dedicated baseline (2.45 days) to the shared allocation (4.08 days ≈ 2.45 / 0.6). One Global Variable, three layers down, changes once; the six-candidate sweep and the optimum answer recalculate in one pass.
CHTB_GV → 2.45 days (dedicated) → 4.08 days (60% shared corridor)
| Metric | Baseline, dedicated crane | Current / revised |
|---|---|---|
| Optimal formwork sets | 4 sets | 4 sets |
| Days / floor at optimum | 5.4 days | 5.4 days |
| Programme duration | 108 days | 108 days |
| Total project cost | $2.88M | $2.88M |
At the published baseline the optimum moves from 4 sets to 3 when the corridor is shared, and the target total cost rises, because one global variable, three layers down in the dependency graph, changed once. Nobody re-modelled the project or re-keyed a single downstream figure; both totals are the same worksheet chain, evaluated with different Global Variable values.
Reading the variable codes
Each bracketed code is a live pointer into its own worksheet, not a copied figure. CHTB_GV, NF_GV, DPR_GV and FSC_GV are global variables, shared with every other worksheet in the project that references them, not just this chain.
NFormwork_Sets, the project variable this whole chain is swept across, from 1 to 6 sets. N = 1 is a boundary case, see the Floor Cycle Time tab.BC / TFCBase cycle for a single set (BC, 12.00 days), and the raw formwork turnaround it implies at N sets in circulation (TFC), before the crane constraint is applied.CHTB_GVCrane hook time budget, the shared tower crane's dedicated allocation. A global variable; raise it when the corridor is shared (Section 3.7 animation).FCT / PDEffective days per floor (FCT) from the Floor Cycle Time worksheet, extended across the tower by the number of floors to give Programme Duration (PD).NF_GVNumber of floors, 20 for this tower. A global variable, reused anywhere else in the project that needs the floor count.DPR_GV / FSC_GVDaily preliminaries rate (DPR_GV) and formwork set cost (FSC_GV), the two global variables that convert programme duration and set count into dollars.MAX(...)Binding constraint function. Returns the larger of its arguments; the cycle cannot finish faster than either the formwork turnaround or the crane allocation allows.CAPFormwork capital cost: N × FSC_GV. The cost of the sets in circulation for a given candidate.PCPreliminaries cost: programme duration × DPR_GV. Time-related site costs for the full tower programme.OPTOptimum total cost: the minimum of the six candidate COMB(N) values evaluated by the hero optimizer worksheet.COMB(N)Combined cost for a given set count: CAP(N) + PC(N) = N·FSC_GV + T_floor(N)·NF_GV·DPR_GV.HDHeight decay multiplier: average of (1 + 0.015 × FloorNo / 2) over floors 1‥NF_GV. Applied to the base floor cycle so crane travel time lengthens with height rather than remaining flat.- Single tower crane, shared across formwork, steel and facade trades, one pour per level, matching the assumption check in Section 3.2 of the white paper.
- N = 1 is treated as a distinct, non-concurrent baseline: the MAX() bottleneck comparison is skipped, but fixed operations still apply, so base days = FIX + BC rather than BC alone.
- Zero / negative guards are applied: N ≤ 0 and NF_GV ≤ 0 return safe zero values rather than NaN or division-by-zero.
- Height-indexed cycle-time decay is modelled. Effective floor cycle is multiplied by the average of (1 + 0.015 × FloorNo / 2) over floors 1‥NF_GV.
- No allowance for a transfer or podium floor, or a first/last floor with materially different access conditions beyond the average height factor above.
- No waste or write-off allowance on formwork capital; each set is priced once for the life of the job.
- Figures are illustrative, constructed to demonstrate the calculation structure in Case Study A, not a cost schedule for any project.
Why this matters beyond one scenario
The formwork set cost and the daily preliminaries rate in this chain are exactly the kind of assumption a flat floor rate hides entirely. Here they are named, visible rows driven by Global Variables: revise either one, or the crane sharing arrangement, and the optimum set count and total cost recalculate immediately, with no need to re-run a separate scenario spreadsheet six times by hand.
Scale that from one formwork strategy decision to a full high-rise estimate with hundreds of resources, and the same pattern repeats: a single shared constraint, whether it is a crane, a crew, or a site access route, flows from one worksheet straight through to every dependent line item built on it.
Figures shown are illustrative, constructed to demonstrate the calculation structure described in Case Study A of the Commercial Building Estimating white paper, and are not a cost schedule for any project. Companion worked example to Section 3, using the same set cost and preliminaries rate published in Sections 3.4–3.7. Height-indexed cycle decay is an extension beyond the flat model in the white paper; the optimum set count remains 4 under the published baseline parameters.