Statistical Modeling for Construction Estimating

Cross-topic of statistical-modeling and construction-estimating.

TALK

This note should discuss the application of modeling in estimating, including what is already common practice (e.g. average run lengths), as well as the potential for more robust models.

Models are useful where information is limited, and where more precise methods would be suboptimal¹.

Specific examples should generally be relegated to linked notes.

This note may contain common objections and arguments disputing them, but the reader should be assumed not to be especially skeptical.

Bayesian Takeoff

User Story

Frank is estimating a 20-story high rise and notices that their are roughly, but not exactly, the same number of receptacles in the corridors of levels 2 to 19. Frank starts a new takeoff for duplex receptacles, typical of levels 2 to 19. He counts and inputs quantities for 3 levels, each adjusts the prior to calculate the expected quantity for all 18 levels.

Stochastic Branch Takeoff

generate a BOM from point loads distributed in a space.

- x: 302.84
  y: 2364.47
  kW: 5.3
  voltage: 277
  phases: 1
...

determine relative impact of factors

allowable voltage drop

Methods

[!cite] Reddit u/mightofmerchants !spatial-sampling.gif

Poisson disc sampling
Delunay triangulation
Voronoi diagrams

%% TODO: link paper on procedural generation of single family homes %%

Average Distance Given Area

Holding area constant, average taxicab distance between points varies greatly with the aspect ratio of the space. Weighted by a probability distribution an average length and confidence could be given for any known area.

sigmoid-functions

Maximum area per floor is sometimes capped by ibc-construction-types or ibc-occupancy-classifications, either directly (see ibc_ch05, ibc_ch09), or by maximum travel distance (see ibc_ch10). Stairwells are expensive. There are usually only 2 or 3.

see risk-management-for-construction-estimating. ↩︎

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