Estimating-Durations-Activities-EDGE.pdf

cppe durations

1. Determining Activities' Duration in the
Construction Schedule

Muhammad Zubair
B.E., MS (UK), PMP

y rN EDGE

a Ga \s 9 SCHOOL OF

EN i Y || CONSTRUCTION
UMSS À MANAGEMENT

2. An Activity, Lag, or Event?

% An activity:
= Duration > 0, uses resource and has a budget
€ A lag:
= Duration > 0, does not use resource, does not have budget
% An event (or milestone):
= Duration = 0, does not use resource , does not have budget
= An event likely has a responsibility, i.e. someone responsible

Activities Duration Slide No. 2

3. Who Determines Durations?

4 % It is strongly recommended for the scheduler not to
assign durations without consulting with the teams
(crews / subcontractors) leaders.

% In the end, the project manager must take a careful
look at the schedule and approve it; perhaps with
some adjustments.

= This implies the approval of all team leaders and subs.

Activities Duration Slide No. 3

4. How are Durations Determined?

4 Several methods are used to determine durations,
ranging from objective / calculated to subjective /
guesstimated:

a. Calculations based on average past performance or expected
production for a worker or a crew.

8. Calculations based on given equipment production rate.

c. Estimation based on expert opinion.

o. Estimation based on comparing to numbers in a reference.
= With assumptions in all cases.

Activities Duration Slide No. 4

5. 1.

Source of Production Rates

Contractor’s own past records

= How close is the item considered to the one compared to?

. Ask crew leaders / subcontractors

Commercial databases such as RS Means or Spon's
price book

Internet

How reliable?

Activities Duration Slide No. 5

6. How are Durations Determined?

_1 $ Most importantly: Have all factors impacting the

production been considered?
a. In the “database”, and
8. The considered project and activity?

Activities Duration Slide No. 6

7. Productivity Numbers

@ When keeping a production rate in the database (or
importing it), some factors have to be considered:

1. Labor skill level. 9. Height (for masonry, painting,
2. Amount of resources allocated etc.)

3. Weather conditions 10. QA/QC and safety requirements
a. Design complexity 11. Work minutes / hour

s. Learning curves 12. Jobsite logistics and congestion
6. Fatigue 15. Any unexpected evets?

7. Multi-shift turnover 14. Does it represent “average

ir >
Soil condition (for excavation) production to you!

Activities Duration Slide No. 7

so

8. Productivity Numbers

% Now you have a “base” number as a reference, you
need to make proper adjustments based on the
current job situation.

= You can start with the same previous factors.
= For cost estimating purpose, there are other factors too.

Activities Duration Slide No. 8

9. Adjusting Numbers

Factors that have to do
with:
= The design of the project
= The climate / weather:
+ Temperature, humidity,
wind, precipitation,
visibility, lightning,
= Location / terrain /
elevation
= Jobsite congestion and
condition

Activities Duration

Workforce type and skill
level

Crew composition

Type and condition of
equipment and tools
used

Availability and readiness
of materials

Management style
Safety regulations

Slide No. 9

10. Importance of Durations Accuracy

. Knowing how long the crews are needed

4:

Calculating the cost of the activity

Determining the dates for dependent / succeeding
activities

Calculating the expected finish date for the project

So in general, the accuracy of activities’ duration
impacts both the time and cost aspects of the project.

‚Activities Duration Slide No. 10

11. Inaccurate Durations

% Impact of inaccurate durations

Delayed crews

Subcontractors conflicts

Wasted money

Shortage of materials / crews (if actual date is earlier)
Possible problems with cash flow

Disrupted plans and chaos

Impact on succeeding activities as well as the entire project

Activities Duration Slide No. 11

12. Items in the RS Means Database

Une Number Description Unit Crew Daily Output Labor Hours
312316421600 Excavating, bulk bank measure, 2-1/4 C.Y. capacity = 100 C.Y./hour, wheel mounted, excluding truck loading B.CY. — B1OT 800.00 0.015
312316421650 Excavating, bulk bank measure, 5 C.Y. capacity = 185 C.Y./hour, wheel mounted, excluding truck loading BCY. BOU 1480.00 0.008
312316421800 Excavating, bulk bank measure, 1/2 C.Y. = 30 C.Y./hour, hydraulic excavator, truck mounted, excluding truck loadin B.CY. B12) 240.00 0.067
312316421850 Excavating, bulk bank measure, 48" bucket, 1 CY. = 45 C.Y./hour, hydraulic excavator, truck mounted, exclud B.CY. B12K 360.00 0.044

Unit Crew Daily Out Labor Hour Bare Mater Bare LabcBare Equipn Bare Total Total OBP.

B.CY. BIOT 800.00 0.015 0.76 0.66 142 187
B.CY. BIOU 1480.00 0.008 041 066 107 135
B.CY. B12) 240.0 0.067 3.28 259 6.87 890

Activities Duration Slide No. 12

13. Items in the RS Means Database

Une Number Description Unit Crew Daily Output Labor Hours
312316421600 ‘Excavating, bulk bank measure, 2-1/4 C.Y. capacity = 100 C.Y./hour, wheel mounted, excluding truck loading B.C Y BOT 800.00 0.015
312316421650 Excavating, bulk bank measure, 5 GY. capacity = 185 C.Y./nour, wheel mounted, excluding truck loading E BIoU 1480.00 0.008
312316421800 Excavating, bulk bank measure, 1/2 C.Y. = 30 C.Y./hour, hydraulic excavator, truck mounted, exciudingrückloadin B.CY. B12) 240.09 0.067
312316421850 Excavating, bulk bank measure, 48" bucket, 1 CY. = 45 C.Y./hour, hydraulic excavator/ Truck mounted, exclud B.CY. B12K 0.044

Bare Incl.
Crew B-10T Hr. Daily Hr. Daily || Costs O8P

1 Equip. Oper. (medium) $55.10 $440.80 | $82.70 $661.60 $50.42

5 Laborer 41.05 16420 | 6210 24840

1 FE. Loader, W.M., 2.5 C.Y. 531.20 584.32 44.27

T2L.H,, Daly Totals $1136.20 $1494.32 || $94.68

Labor hours perday _ 12 _ 0.015

Labor hours per CY

Crew Production per day ~ 800

Activities Duration Slide No. 13

14. Line Number

031113350010 FORMS IN PLACE, ELEVATED SLABS

Description unit Crew

031113351000 | Flat plate, job-built plywood, to 15° high, 1 use sE a
—Q 031113351050 2use a
031113251100 3use a
031113351150 ause e
IL 031113351500 15' to 20' high ceilings, 4 use (a
031113351600 21' to 35' high ceilings, 4 use @
031113352000 Flatsleb, drop penels, job-built plywood, to 15' high, 1 use e
031113352050 2use SF e
031113352100 3 use SE a
031113352150 4use SE a

031113352250 15' to 20' high cej SE a 480.00 0.100

031113352350 20' to 35H ceilings, 4 use SE a 435.00 0.110

4,200 SF Elevated slab, 4 use, 18’ high

EN | a wre] Duration = 4200 / 495 = 8.5 x 9 days
Er an mu | ss zus | Labor hours = 4200 x 0.097 = 407.4, or
ELA, Daly Tos Fr] ET =6x8x8.5 = 408

‚Activities Duration Slide No. 14

15. Multi-Stage Activities

% Those activities performed by the same crew but with
different nature or location
= Wood framing
= Flooring
$ Those activities performed by different crews but
result in completion of same finished product
= Reinforced concrete items
4 Keep it as one activity or split it?
4 Use the KISS principle!

ad

Activities Duration Slide No. 15

16. Pictures from zum = A J l 1 |
CE Pl

| |
De No.16 à

17. Concrete Work

Picture from

18. Simplify...

4 4 In general, it is better to break the activity whenever
its portions are separated physically or by time.
= This simplifies all calculations: productivity, time, and money

= This also reduces the use of Start-to-Start (SS) and Finish-to-
Finish (FF) relationships and lags, which simplifies even more.

Activities Duration Slide No. 18

19. Intermittent Activities

_¢_@ Electrical work: one activity, 23 days

Electrical work [TRoUghAn o] [Finish]
|

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Days

4 Electrical work: two activities, 4, and 3 days
Electrical Rough-in DD]

Electrical Finish
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Days

Activities Duration Slide No. 19

20. Discontinuous Activities

$ It will be better to separate intermittent activities
when segments are separated by time periods

& This is better for control and many other scheduling
functions

© If not separated, it may skew the percent complete
and other dependent functions

Activities Duration Slide No. 20

21. P

Discontinuous Activities

Or
ply for —u
ermit, Lag, 89 days +
day Permit
issued

Activities Duration Slide No. 21

22. FS.

‘felationship:

17 days

65
relationship
with lag:
11 days

FS relationship

ith splitting:
11 days

A1

A2

Logic and Duration
|

af 23h al "sl el "7" 8] 9] 10] 11] "12| 13| 14/15) 16| 17] Days

Apap 8p 4b Sp er" 7p Bl 9] 10} 44-12-43} 14} 5)

Activities Duration Slide No. 22

23. Unplanned Stoppage

1% Excavation was planned for 7 continuous days (Case

A)
4 But a technical problem forced a 6-day pause (Case B)

= Importance of activity notes

À [Escavation ON

11--2|--:3|-:-4|-—5|-.-6|--—7

B Excavation

3]....2]...:31.:4|i...51...6]...:7].:8]:...9|. 10/.:11/..12]:13|

Activities Duration Slide No. 23

24. Multiple Crews

$ Multiple crews (2+)
LE crew #1]

= Crew #2

& Issues to be considered:
= Coordination
= Available space for work and safety
= Available equipment and maintenance
= Supervision, administration

Activities Duration Slide No. 24

25. Multiple Shifts

% Multiple shifts (2+)

Crew #2

4 Issues to be considered:

Coordination, turn-over

Supervision, administration

Night lighting, security, facilities, and services

Same equipment? Maintenance

Productivity may not be the same (different weather
conditions, visibility)

2nd (and 3") shift pay: Overtime?

Activities Duration Slide No. 25

26. Multiple Crews and Shifts

+ Multiple crews and shifts (2+)

4 Issues to be considered:

Crew #2A

= Coordination, turn-over

Crew #2B

Available space for work and safety
Available equipment and maintenance
Supervision, administration

2nd (and 3") shift pay: Overtime?

Activities Duration

Night lighting, security, facilities, and services
Productivity may not be the same for different shifts

Slide No. 26

27. Duration Adjustment

% For the excavation crew that has a recorded
production rate of 800 CY / day, assume that adverse
conditions results in 20% productivity reduction.

Description Unit _ Crew Daily Output Labor Hours

Excavating, bulk bank measure, 2-1/4 C.Y. capacity = 100 C.Y./hour, wheel mounted, excluding truck loading BEY. B10T 800.00 0.015

4 Calculate adiusted: Bare Mater Bare LabcBare Equipn Bare Total Total O&P
J : 0% 06 18 19

ı. Daily production
2. Labor hours / unit
3. Unit cost

‚Activities Duration Slide No. 27

28. Duration Adjustment

+ Adjusted daily production:

= 800 CY/day * (100% - 20%) = 640 CY / day
Adjusted labor hours per unit:

= 0.015 / (100% - 20%) = 0.01875 = 0.019

= Or Labor hours per day _ = = 0.01875 = 0.019

’ Crew Production per day ~ 64

4 Note that as one parameter increases, the other one
decreases, and vice versa

Activities Duration Slide No. 28

29. Let’s Not Forget...

1 $ The accurate estimation of crew production is important
to both estimating and scheduling

Crew Cost per day <———— Constant

4 Unit Price - ——— ———

Crew Production per day < Variable
Total Quantity <——— Constant

Crew Production per day < Variable

% Unit price and duration are inversely proportional to

$ Duration =

production rate

Activities Duration Slide No. 29

30. Activities with Variable (Non-
Linear) Production

4 There are several ways to deal with activities with
non-linear production:
1. If the productivity variation (non-linearity) is small, you can

ignore it. For example, installing concrete blocks for a 5' or 6’
wall.

2. Split the activity to homogeneous activities (each with
assumed linearity)

3. Use the software tools to divide the activity into steps and
distribute the resources per step

Activities Duration Slide No. 30

31. Duration Risk Management

% How do you account for risk in the project?
= At the activity level, i.e. part of the duration?

= At the entire project level, i.e. independent of activities’
duration? or

= Both?

Activities Duration Slide No. 31

32. Duration Risk
Allowance

Duration Uncertainty

Xp

>
Most Likely
Duration

Expected
Duration
11

Activities Duration

=.—>

1
Pessimistic
Duration
18

Slide No. 32

33. Time Contingency

1% It is not recommended to add extra time to activity
duration due to risk calculations, but the risk impact is
estimated for the entire path, and added within the
project but outside the activities.

= If added within the activity, it will be used no matter what.

= It will become the “norm” for next time.

= So keep the activities durations lean!

= Activity duration may still have little “fluff” due to rounding.

Activities Duration Slide No. 33

34. What If?

a © What if the start of the project was postponed for a

month or more?

Activities Duration Slide No. 34

35. Duration While Updating

® When updating the schedule, officially or unofficially,
certain activities will be off the track; ahead or behind.
= If the schedule variance is small, it can be dismissed as
normal and expected variation.
= If the schedule variance is major, you need to analyze and
pinpoint the cause:
A. Something went wrong with this activity,

B. Certain factors were not considered when estimating the
duration, or

C. The number in the database was inaccurate

Activities Duration Slide No. 35

36. Duration While Updating

$ Example: An excavation activity, 11,500 CY, using a
crew with an estimated production of 700 CY/day.
= Estimated duration = 11,500 / 700 = 16.43 x 17 days
= Five days later, 2,420 CY only were excavated:
+ Baseline % complete = 30.4%, Actual % complete = 21.0%
= If everything was normal, i.e. no unexpected problems, then
remaining duration must be corrected based on actual
production, 484 CY/day:
+ RD = 24-5 = 19 days, and WOT 17-5 = 12 days

Activities Duration Slide No. 36

37. Keep in Touch...

+ Any comments?
$ Any questions?
$ [email protected]

Activities Duration Slide No. 37