Impact of Variability on Construction Projects - Presentation

8/11/2019 Impact of Variability on Construction Projects - Presentation

1/39

Impact of variability

on engineering projects

Dr. Jos Humberto Lora ArcilaDean School of Engineering

n vers a u noma e uca n

Selected Topics in Construct ion

Civil Engineering August-December 2014


2/39

Engineering Projects

ngneerng proec s, suc as u ng cons ruc on,

involve a large number of specialty trades that

genera y wor n a con nung an repea ngsequence as they move from one floor (station x) to

ano er s a on y .

S

ecialt trades t icall work as subcontractors to

the general contractor and may include:

decking

formwork

mechanical

electrical

vertical transportation syst.

fire protection systems

concrete rb

concrete

plumbing

roofing

environmental controls

etc.


3/39


Gus Sestrup, superintendent with Turner

Construction, says these contractors work sequences

should be performed as a parade of trades.

Example parades are (Riley and Sanvido 1997) as follows:

. .,

erector); placing and securing deckingas well as welding

shear stud deckin contractor and

lacin reba rebar

contractor), then pouring and finishing concrete (concrete

contractor).


4/39

Structural Parade: e.g., erecting structural steel (steel

erector); placing and securing deckingas well as welding

shear studs (decking contractor); and placing rebar (rebar

contractor), then pouring and finishing concrete (concrete

.

https://www.youtube.com/watch?v=JNg3IY64uts


5/39


Overhead Work Parade: e.g., installing a HVAC system

(mechanical contractor), sprinkler system(fire protection

, ,

pipe (plumbing contractor).

Perimeter Enclosure Parade: e.g., building perimeter walls,

placing windows, installing flashing, and applyingsealants.

n er or n s es ara e: e.g., ns a ng wa s u s, rou ngelectrical conduit, placing insulation materials, hanging

, .


6/39


Trades involved in any of the previous parades are

comprised by workers with different skills and

perform at different levels of productivit .,

performance, such as:

accessibility to the working area

concentration of work

etc.


7/39


Te overall impact of the interaction of many different

trades, in the setting previously described, upon the

majority of engineering projects is usually namedvariability, or unreliability.

Many in construction deem variability as a necessary

. ,

construction management practice, particularly

.Let us then analyze and understand how variability

impacts on engineering projects.


8/39

Variability

Apt or liable to vary or change.

The extent to which data points in a statisticaldistribution, or data set, diverge from the average

or mean value.

Example:

The weigth of each person in this room.


9/39

Causes of variability,

in roduction rocesses:

Natural variability, which includes minor fluctuations in

process times due to differences in operators,machines and materials.

Random failures. Change of process.

. Reworks (due to bad quality).


10/39

Causes of variability,

in roduction rocesses:

Labor Measurements

ac nery nvronmen

Materials Methods

Output variability (characteristics of quality)


11/39

In many production systems, there are many

atributes which variabilit is of reat interest:

Physical Dimensions.

Process or execution times.

epa r mes or equ pmen a ure.

Quality Measures.

Temperatures.

. Etc., etc.


12/39

Variability and randomness

Variability is associated closely with randomness,

however these twoARE NOT IDENTICAL.

Perspectives on randomness

1)This is due to that we have imperfect (orincomplete) information, and systems appear to

behave randomly

VS.

.


13/39

Two types of variation

Controllable variation occurs as a direct result of

.

an om vara on s a resu o evens a are

beyond our immediate control.


14/39

Variabil ity is inevitable

Some degree of variability is natural.

Some degree of variability is caused by the way

work (or production processes) is administered.


15/39

Measures of variabil ity

To analyze variability effectively, we must first be

.

Variance, denoted 2, is an absolute measure of

Standard Deviation ( ), defined as the square

root of the variance.


16/39

However ...

... the measures of central tendency, such as

,

provide a complete view of a distribution.


17/39

For example:

means, but differ in the distribution of their data.

One could then say that:

Distribution B.


18/39

We must also consider:

Absolut variabilit

.

Relative variability


19/39


Let us take a brief survey on the implementation ofsome "engineering projects.

For example, what is the duration that you estimate to

.

Project My Estimatex m o concre e

Build a 10 m2 CMU wall

u a m x m e roomBuild a 60 m2 dwelling unit


20/39

Durations

Mix m3 of concrete

2

. .

Build a 4 m x 4 m bedroomBuild a 60 m2 dwellin unit

Build a building like this one

Normal Distribution


21/39

Let us performe a practical example:

An engineering project consisting in the production of.

Each artifact has 5 components.

Each component is produced by an individual.

Each engineer commits to produce5 components

per week.


22/39

Schematic design of a single artifact:

Component 5

Component 4

ng neer

Component 3

Component 2

Component 1


23/39

Components of a single artifact:


24/39

Finished artifact:


25/39

Artifacts:


26/39

Grouping of 5 artifacts:


27/39

Grouping of 10 artifacts:


28/39

But now we wonder

if each engineer is commited to produce the

components he/she is responsible for, with an

output of 5 components per week,

How long will take to each engineer to produce

What will be the total duration of the project?

I t f i bil it i i j t


29/39

15 20 25 30

Station:

100 1005 10

Impact of variability on eng ineering p rojects

Dr. Jos H. Lora Arcila

80

90 90

ution:

80

70

60

70

60

Distri

50 50

rtifactsinprocess

40

30

40

30

Accumulateda

20 20

10

5 10 15 20

10

0 025 30


30/39

Let us see how reality works:

Station

1Station

2Station

3Station

4Station

5

100

Supplier Buffer Buffer Buffer Buffer Finished

Parade of Trades


31/39

Instructions:

Integrate two teams of 5 Engineers.

Each team will determine whichEngineerwill beresponsible for each station (Stations 1 to 5).

One student will play theSupervisorrole, and anotherstudent will play the Supplierrole.

TheSu ervisor will rovide a co ofAnnex 1 to eachEngineer, and will provide the Supplierwith theengineering packages required for each team. The

required to produce 100 artifacts.

package.


32/39

Instructions (2):

In the correspondent boxes on Annex 1, each engineerwill write down the station number he/she is responsible

, .

Beginning with Station 1, each engineer should roll the

by the die.

Then, each engineer should assemble his/hercomponents to the artifacts in process.

Warning: Despite of the number indicated by the die,the number of produced components cannot exceed

manufacture.


33/39

Instructions (3):

The engineer in Station n will pass to the engineer inStation n+1 the number of artifacts in process indicated

, .

Each engineer should document (register) on Annex 1 the

engineer in Station n+1, and the number of artifacts in

rocess remainin in his/her buffer. Furthermore, shouldgraph the cumulative number of artifacts in processhe/she already passed to the engineer in Station n+1.

Repet the process as many times as needed, until eachengineer completes his/her share of 100 units.


34/39

Instructions (4):

Register the number of times required to complete 100units, and calculate the average number of units

.

No. of times to

produce 100

Averageper

Average= 100 / No. de times toproduce 100 artifacts

.


35/39

This slide is left blank to present the results of


36/39

Therefore, variability impacts on:

Longerproduction cycles

arger nven or es o wor n progress .

, , .

Lost of throughput.

roug pu : num er o wor un s comp e e y eproject duration.


37/39

Variability can be handled:

Reducing variation

- .

Using buffers (delays, inventories, storage).

- Resources: espace, time and others.

- .

Changing trades (size, composition) and tools to

compensate for variations, and to keep balanceamong production processes.


38/39

Thus, we could conclude than:

Variabilit is inherent to all roduction rocesses

and may have a major impact upon performance.

Therefore, the ability to measure, understand

engineering projects.


39/39

Recommended bibliography:

Tommelein, I.D., Riley, D. and Howell, G.A. (1999). Parade Game: Impact

of Work Flow Variability on Trade Performance. ASCE, Journal of

ons ruc on ng neer ng an anagemen , , - , ep c .

Alarcn, L.F and Ashley, D.B. (1999). Playing Games: Evaluating the

mpac o ean ro uc on raeges on roec os an c e ue. roc.

Seventh Annual Conference of the International Group for Lean

Construction, IGLC-7, 26-28 July, held in California, Berkeley, 12 pp

Mitropulos, P., Alves, T. and Wwalsh, K.D. (2014). Parade Plus: A

Simulation Game for Investigating and Teaching Strategies for Managing

Production Variability and Dependence. Proc. Construction ResearchCongress 2014,ASCE, 19-21 May, held in Atlanta, Georgia, 10 pp.

Impact of Variability on Construction Projects - Presentation

Documents

Transcript of Impact of Variability on Construction Projects - Presentation