The BIM Matrix (part 2)

In the previous example, I have shown how to get the quantities for concrete, not including labor or other cost associated with the quantities.

In the pre-design stage, it is important to estimate all the "unknowns" or "unknown variables" as close as possible, therefore the IPD process is very useful. The MacLeamy Curve shows how IPD could potentially help your project finish on time and on budget.

These unknown variables can be calculated simply by using previously bid jobs, and substituting those variables into today's conditions. But the more unknown variables exist, the more equations are required to solve the problem. Here is a simple problem with 3 unknown factors (X, Y, Z), where any of these variables can be any real number, and 3 equations required to solve the problem.

$X + $Y = $Z

$X + $Y = $Z

$X + $Y = $Z

Very simple, three unknowns, three equations.

Well, as shown in part 1, knowing some properties or information about the equation, such as cost of materials (X variable) can help us estimate the other two variables (Y and Z) and narrow down the cost. This example can be used as:

1. equation 1 is simply the cost of material + labor = estimated cost ( labor used from source A)
2. equation 2 is the cost of material + labor = estimated cost (labor rates from source B)
3. equation 3 is the cost of material + labor = estimated cost (labor rates from source C)

As the project keeps growing through other design phases, these unknown factors will keep growing and growing, going from three unknown factors with three equations, to 20 unknown factors, therefore requiring 20 equations. Estimating all unknown factors can be challenging, but can be manageable using the matrix. Below is an example of the cost factor matrix (i.e. for concrete) and all the properties to the material "concrete" can be adjusted or accounted for using the simple matrix. Properties can be added or deleted for different type of material, therefore increasing or decreasing the number of unknown factors.

The BIM Matrix (part 1)

Today I want to show an example of detailing. In VD&C, too much detailing is as useless as too little detailing. In the preliminary design phase when trying to figure out quantities, a good baseline is essential to good planing.

Now, I would like to show an example of the theory.

In the example shown below, I have modeled a space, 120 ft x 100 ft, with 3 levels and a roof.

The materials used:

• level 1 has a 12" generic concrete pad, 12000 CF
• levels 2 and 3 have a 3" LW concrete on 2" metal deck, 5000 CF per floor

The concrete quantities yield a total volumeof 22,000 CF.

The area of the slab yields a total volume of 60,000 SF, which includes the area of the concrete slab and the area of the metal decking for the 2nd and 3rd floors.

As seen in the schedule below, all the different parameters are shown (i.e. area, family and type, etc) and the total quantities of the area. What is not indicated in the schedule is a description of the slab for the 2nd and 3rd levels.

How do we make this schedule more essential or efficient? Well, let's modify the model with the following:

• add a slab edge to all floors, which will change our concrete quantities,
• see how the slab edge will change our cost for the concrete volumes,
• and customize the schedule for export to excel and make it more effective.

Let us estimate that 4000 psi concrete is at about $70.00 per cubic yard.

Because Revit families are dependable on the same type, giving our LW concrete the unit cost will change all the elements of type LW concrete. Instead, we will create calculated values and name it TOTAL COST per CY. Revit has calculated a total dollar amount of 57037 so far for our material, that is not including labor or other associated cost.

So, if you are asking yourself "how is this a BIM Matrix", well read part 2.