Buffer Management Buffer Management

Buffer Management Buffer Management

4013.407Construction Technology

Moonseo Park

Assistant Professor PhD Assistant Professor, PhD

39동 433 Phone 880-5848, Fax 871-5518

E-mail: mspark@snu.ac.kr Department of Architecture

College of Engineeringg g g Seoul National University

Discussion Discussion Discussion Discussion

ƒ 행진 대열의 예 : 관리되지 않을 경우 아래 대열의 전체 속도 (생산성) 는 2k /h 이하이고 대열전체의 전체 속도 (생산성) 는 2km/h 이하이고 대열전체의 간격 (재고) 은 갈수록 벌어진다 .

A B C D E F

A B C D E F

2 km/h 3 km/h

5 km/h 4 km/h 4 km/h

3 km/h

ƒ 문제

대열의 전체속도를 향상시키는 방법은 ?

대열의 전체속도를 향상시키는 방법은 ?

대열의 간격을 벌어지지 않게 할 수 있는 방법은 ?

Question 1 :

Question 1 :대열 대열 전체속도 전체속도 제고 제고

Q :

Q :대열 대열 전체속 전체속 제 제

ƒ 제약 규명 : 속도가 가장 늦은 대원 D가 제약

ƒ 제약의 최대한 활용 : 대원 D의 가속 방안 모색

Ex) 속도가 빠른 대원 B나 F가 D의 짐을 들어줌

Question 2 :

Question 2 : 대열 대열 간격의 간격의 관리 관리

대원의 재배치 : 제약(대원 D)을 선두에 세움

Q :

Q : 대열 대열 간격의 간격의 관리 관리

A B C D E F

A B C D E F

2 km/h 3 km/h

5 km/h 4 km/h 4 km/h

3 km/h

⇒ But, 건축 공정에는 적용 불가능

북치기

북치기 (DRUM) (DRUM) ( ( ) )

속도가 가장 늦은 대원 , 즉 제약자원인 대원 D가 자신의 페이스에 맞추어 북 (Drum) 을 치면 다른 대원들이 그 속도에 맞추어 행진함

A B C D E F

2 km/h 3 km/h

5 km/h 4 km/h 4 km/h

3 km/h

제약 = Drum

줄로

줄로 묶기 묶기 (ROPE) (ROPE) 줄

줄 묶기 묶기 ( ( ) )

선두 대원과 대원 D를 줄 (Rope) 로 묶어 간격이 벌어지는 현상을 방지함

A B C D E F

2 km/h 3 km/h

5 km/h 4 km/h 4 km/h

3 km/h

Rope

줄이

줄이 너무 너무 짧으면 짧으면? ? 줄이

줄이 너무 너무 짧 면 짧 면? ?

대원 D 앞의 대원 A, B, C 중에서 하나만 문제가 생겨도 대원 D가 영향을 받고 따라서 전체 행렬의 속도가

늦어짐

A B C D E F

2 km/h 3 km/h

5 km/h 4 km/h 4 km/h

3 km/h

Rope

줄의 길이에 여유를 둔다

A B C D E F

2 km/h 3 km/h

5 km/h 4 km/h 4 km/h

3 km/h

느슨한 Rope 슨한 Rope

느슨한 줄의 결과는 ? 버퍼 (Buffer)

간격= 버퍼

A B C D E F

2 km/h 3 km/h

5 km/h 4 km/h 4 km/h

3 km/h

TOC d C i i l Ch i

TOC and Critical Chain

Buffer Buffer Buffer Buffer

ƒ Buffers operate to provide a cushion or shield against the

negative impact of disruptions and variability ^(H ll t l 1993 B ll d

negative impact of disruptions and variability (Howell et al. 1993, Ballard and Howell 1995)

ƒ When buffers are used correctly they not only provide shielding, but they provide the ability to efficiently respond to variable but they provide the ability to efficiently respond to variable

conditions thereby enhancing overall performance

(Horman, 2000)

T f b ff

ƒ Type of buffers

Product Operating Contingencies Inventories Time Workflow

architecture capacity

Highly Relatively

responsive unresponsive

Expense is incurred regardless of whether used Expense more easily recovered

regardless of whether used (converted to other things for

other benefit) if not used Source: Horman, 2000

TOC (Theory

TOC (Theory of Constraint) of Constraint) 의 의 배경 배경 TOC (Theory

TOC (Theory of Constraint) of Constraint) 의 의 배경 배경

시간이 경쟁력이다 시간이 경쟁력이다

※ 시대별 경쟁요소의 변화 (IBM사의 자료)

TOC

TOC ^(Theory (Theory of Constraint) of Constraint) 의 의 등장 등장 및 및 발전 발전 TOC

TOC ^(Theory (Theory of Constraint) of Constraint) 의 의 등장 등장 및 및 발전 발전

ƒ 이스라엘의 물리학자 Eliyahu M. Goldratt 박사 : 친구의 가구공장에 대해 병목공정 중심의

생산일정계획 시행 → 생산성 3배 증가

ƒ 조직의 목표를 달성하는데 제약이 되는 요인을 찾아 집중적으로 개선하고 조직내의 모든 의사결정을 집중적으로 개선하고 , 조직내의 모든 의사결정을 제약요인 위주로 수행함으로써 조직의 목표 달성

ƒ 조직의 성과를 저해하는 제약요인을 찾아 집중적으로

개선함으로써 최소의 비용으로 최대의 경영개선 실현

개선함으로써 최소의 비용으로 최대의 경영개선 실현

COLC

COLC (Cost Of Long Cycle Time) (Cost Of Long Cycle Time) 빙산 빙산

COLC

COLC (Cost Of Long Cycle Time) (Cost Of Long Cycle Time) 빙산 빙산

재고비용 납기지연비용

자금회전률 하락 자금회전률 하락 고객이탈 및 신뢰상실

신제품 출시기간 증가

경쟁력 상실

TOC

TOC (Theory (Theory of Constraint) of Constraint) 경영전략 경영전략 TOC

TOC (Theory (Theory of Constraint) of Constraint) 경영전략 경영전략

재고의 감소

짧은 리드타임 재고의 감소

짧은 리드타임

재고비용 감소

금융비용 감소

불량 감소 프로세스

효율 향상 고객 만족

납기 준수 시장점유율

증가

더 낮은 원가 더 높은 수익

$

이러한 결과를

어떻게 달성할 것인가?

$

Buffering Strategies from

Buffering Strategies from TOC TOC Buffering Strategies from

Buffering Strategies from TOC TOC

ƒ Traditional contingency buffering: Advances are wasted

ƒ Traditional contingency buffering: Advances are wasted, while delays are accumulated.

ƒ Student syndrome

ƒ Student syndrome

ƒ Parkinson ’s law

작업예상시간 준수확률 분포

Project Buffer Project Buffer Project Buffer Project Buffer

Activity 4 Activity

3 Activity

2 Activity

1

3 4 2

1

3 4

1 2

3 4

2

1

Feeding, Resource Buffer Feeding, Resource Buffer Feeding, Resource Buffer Feeding, Resource Buffer

A1 FB RB

3 4

1 2

Critical Path

B1 B2 FB B1 B2 FB

FB: Feeding Buffer RB: Resource Buffer

Souce:Park, young-min, A study on Schedule Management in Construction Projects by CCPM

ƒ Project buffer

The Project Buffer is the buffer at the end of the Critical Chain. It The Project Buffer is the buffer at the end of the Critical Chain. It determines the project completion date, and is the tool used by management and resources to make certain project decisions.

ƒ Feeding buffers

Feeding buffers are time buffers placed in project chains (paths) that tie in to the critical chain Their purpose is to help insure that that tie in to the critical chain. Their purpose is to help insure that the successor task on the critical chain has all of its inputs with about a 50% probability.

ƒ Resource buffer

The resource buffer is a flag to alert resources planned to work on the Critical Chain that their task is coming up to be worked on

the Critical Chain that their task is coming up to be worked on.

Critical Chain Critical Chain Critical Chain Critical Chain

ƒ 프로젝트 관리 비용을 절감하고 고객의 Needs에 부응하는 신제품개발의 속도를 빠르게 한다

ƒ 일반적인 제조시스템과 다른 특성을 갖는 프로젝트

생산에 대한 관리를 위해 TOC (Theory of Constraint) 를 적용

ƒ PERT/CPM과 같이 네트워크를 사용해 일정관리를 함

ƒ 적용 분야 : 선박 생산과 같은 대규모 제조, 건설

프로젝트 등에 대한 생산관리

The Characteristic of Buffer management The Characteristic of Buffer management The Characteristic of Buffer management The Characteristic of Buffer management

여유시간이 각 작업에 분배되지 않고, 중요한 위치에 모아져 사용된다.

작업시작을 가능한 늦추어 제공재고를 줄이면서도 프로젝트 완성을 늦추지 않는다.

작업 선후관계뿐 아니라 자원제약 려된다

작업 선후관계뿐 아니라 자원제약도 고려된다.

많은 버퍼이든 적은 버퍼이든 건설공사에서 다양한 문제의 원인이 될 수 있다

다양한 문제의 원인이 될 수 있다.

운영비용없이 프로젝트 기간을 짧게 할 수 있다.

PERE/CPM vs CCPM(Buffer) PERE/CPM vs CCPM(Buffer) PERE/CPM vs CCPM(Buffer) PERE/CPM vs CCPM(Buffer)

PERT/CPM CCPM

주공정 Critical Path Critical Chain

시간의 종속성 고려 고려

시간의 종속성 고려 고려

자원의 종속성

이론적으로 고려되지

않음(현장에서 임의적으로 고려)

고려 고려)

작업개시시간 EST사용 LST사용

불확실 상황의 대비 고려하지 않음 고려

불확실 상황의 대비 고려하지 않음 고려

Control Point

세부공정 각각에 대한 세부적 진도관리.(적당한 기준점 존재하지 않음)

버퍼의 소모에 따른

개략적인 진도 관리 가능 존재하지 않음)

신뢰성

50년 이상 현장에서

사용됨(일정 및 예산에 대한 준수율은 극히 떨어짐)

아직 국내 건설 현장에서 사용된적 없음.(검증이 필요)

준수율은 극히 떨어짐) 필요)

R li bili B ff i

Reliability Buffering

Buffering Practices So Far Buffering Practices So Far Buffering Practices So Far Buffering Practices So Far

ƒ Technical Buffer: a buffer for securing technically required time (i.e.,

assign a time for concrete curing).

ƒ Contingency Buffer: a buffer for guaranteeing the schedule performance.

Level Scheduled by Buffering Lower Subcontractors

S bdi i i

Adding some contingency to i di id l ti iti t or Subdivisions individual activities to

guarantee the schedule performance of each individual activityy Higher General

Contractors or Project

Given precedence

relationships, adding some contingency to the

j

Managers g y

preceding activity to avoid subsequent schedule

disruptions in the

succeeding activity

succeeding activity.

Contingency Buffer Is Mostly Inefficient Contingency Buffer Is Mostly Inefficient

ƒ Lack of Characteristics

g y y

g y y

Normally, Conceived as Being Positioned at the End of the Activity Duration.

Characterized as Nothing More Than Some More Ti M ki It Diffi lt t L t d Utili th Time, Making It Difficult to Locate and Utilize the Buffer.

As a Result, Contingency Buffer Is Not So Helpful to

Protect the Schedule Performance, Often Creating

a Rubber Band Duration.

Contingency Buffer Is Mostly Inefficient Contingency Buffer Is Mostly Inefficient Contingency Buffer Is Mostly Inefficient Contingency Buffer Is Mostly Inefficient

ƒ Inefficient Sizingg

Normally, Decided Based on Individual Experiences and Assigned in a Uniform Way.

Often Duplicated by Different Project Functions.

As a Result, the Traditional Contingency Buffer May g y y Not Be Efficient in Protecting the Project Schedule Performance, Resulting in an Unnecessary Resource Idl Ti

Idle Time.

Reliability Buffering Reliability Buffering y y g g

“Aggressively Protect the Project

“Aggressively Protect the Project Schedule Performance by Pooling, Re-

Sizing, Re-Locating, and Re-

Characterizing the Contingency Buffer”

Characterizing the Contingency Buffer

Reliability

Reliability Buffering yy Buffering Steps gg Steps p p

Contingency Buffers Are Fed Explicitly or Taking off Contingency Buffers from Individual

Re-Sizing based on the Simulation of Construction Re-Characterizing as a Time to Find Upstream Contingency Buffers Are Fed Explicitly or Implicitly in Individual Activities

Taking off Contingency Buffers from Individual Activities and Making a Buffer Pool

Re Sizing based on the Simulation of Construction Performance and Putting in front of the

Downstream Duration

g p

Changes and to Ramp up Resources for the Downstream Work

Contingency Buffer Contingency Buffer Contingency Buffer

Activity A

Contingency Buffers

Taking off

& PoolingTaking off

& Pooling Taking off

& Pooling

Activity B

Activity C

Re-Sizing & Re-Locating Re-Sizing & Re-Locating

Re-Sizing, Re-Locating, &

Re-Characterizing

Re-Sizing, Re-Locating, &

Re-Characterizing

Activity C Reliability Buffer

Path Pool Buffer

Reliability Buffering Reliability Buffering Reliability Buffering Reliability Buffering

ƒ Reliability Buffering Process

Taking off contingency buffer and pooling them (in traditional buffering) (CUTTING)

Re-sizing the contingency buffer or introducing a new buffer

Re sizing the contingency buffer or introducing a new buffer (RE-SIZING)

Putting the re-sized for newly introduced buffer between at the beginning of the succeeding activity duration (PUTTING))

Characterizing buffer as a time to ramp up necessary

resources for the successor activity and to find problematic resources for the successor activity and to find problematic predecessor work that would impact the successor activity in progress (CHARACTERIZING)

Using the remaining schedule contingencies in the buffer

Using the remaining schedule contingencies in the buffer pool as a path pool buffer for the project (POOLING)

Dynamically updating and size of buffers during construction

Dynamic Buffering Dynamic Buffering y y g g

ƒ Dynamically Update the Initially Sized and L t d B ff d i th P j t E l ti

Located Buffer during the Project Evolution.

A Construction Project Evolves throughout the Project

A Construction Project Evolves throughout the Project Duration, during Which the Characteristics of a

Construction System Continuously Change.

By Estimating Construction Characteristics and

Dynamically Utilizing the Information in Buffering, It Is

Possible to Minimize the Impact of Upstream Schedule

Possible to Minimize the Impact of Upstream Schedule

Disruptions and to Benefit from Schedule Advances

Achieved in the Upstream Work, If Any.

Dynamic Buffering Dynamic Buffering y y g g

As the Buffer Size and Location Continuously Change during Construction, Initial Precedence Relationships May Change

Conditions Precedence

Relationships

Conditions Precedence

Relationships

Conditions Precedence

Relationships

Di = Df FS 0 Di = Df FS (-Li) Di = Df FS (Li)

Di > Df FS 0 Di > Df Df FS (-Li) Di > Df Df FS (Li)

B f B f Bf

Di B i B i

Di B i Di

Df

Descriptions Without Lags/Leads With Leads With Lags

FS Initial

Updated

Di < Df Df FS (-(Df -Di)) Di < Df Df FS (-(Li+Df -Di)) Di < Df Df FS (Li-(Df -Di))

B f B f B f

Di = Df FF 0 Di = Df Di FF (-Li) Di = Df Di FF (Li)

Di > Df FF 0 Di > Df FF (-Li) Di > Df FF (Li)

B Sf = B Si+(B i-B f ) B Sf = B Si+(B i-B f ) B Sf = B Si+(B i-B f )

-(Di-Df ) -(Di-Df ) -(Di-Df )

B i

Df

B i B i

Di

Df Df

BSi

BSf Bf

BSi

BSf Bf

BSi

BSf B

Initial Updated FF

Di < Df FF 0 Di < Df Df FF (-Li) Di < Df Df FF (Li)

B Sf = B Si-(B f -B i) B Sf = B Si-(B f -B i) B Sf = B Si-(B f -B i)

+(Df -Di) +(Df -Di) +(Df -Di)

Di = Df SS 0 Di = Df SS (Li)

Di > Df Df SS 0 Di > Df Df SS (Li)

B f B f

B i Di Df

B i

Di Di

B f BSf

BSf

S

BSf

S

BSf

B f B f

SS Initial

Updated Not applicable by

definition of reliability buffer

Di < Df Df SS 0 Di < Df Df SS (Li)

B f B f

Di = Df Di SF (-Li)

Di > Df SF (-Li)

B i

Df Di

Di

BSi

SF Initial

Not applicable by Not applicable by

Reference Reference Reference Reference

ƒ Park, M. and Pena-mora, F. (2004) “Reliability Buffering for Construction Projects ”

Construction Projects

ƒ Chua, M. , Shen, L. and Bok, S. (2003) “Constraint-Based Planning with Integrated Production Scheduler over Internet ”

ƒ Ballard, G. (2000) “Phase Scheduling”, LCI White Paper

ƒ Ballard, G. (2000) “The Last Planner System of Production Control”

G ld E (1997) “C i i l Ch i ” A B i N l

ƒ Goldratt, E. (1997) “Critical Chain”, A Business Novel

ƒ Goldratt, E. (2002) “It’s not Luck”, 동양문고

ƒ Park Young-min A Study in Schedule Management in Construction

ƒ Park, Young-min, A Study in Schedule Management in Construction Projects by CCPM 2004.10

ƒ Park, Young-min, A study on Instruduction of Critical Chain Project

CC C 2003

Mangement(CCPM) to Construction Projects, 2003

ƒ Kim, young, Application of CCPM to Construction Project, 2003-09

2005 MLB Division Series

2005 MLB Division Series

2005 MLB Division Series

2005 MLB Division Series

“ F th k f h it ft

“ …For the sake of charity after World Series we plan the tournaments which all the

teams would be included… but there’s a big problem… more than 50 days...cold 5 y

weather…snow…”

“ l l th bl ”

“…please solve the problem….”

Bud Selig MLB Commissioner

Requirements Requirements Requirements Requirements

ƒ 각 토너먼트는 7전 4선승제

ƒ American league 16개팀

National league 14개팀 : 총 30개팀 참가

ƒ 최종 결승전 일정은 전세계 생방송을 위해 90%이상의 정확도

요구

Series Schedule Series Schedule Series Schedule Series Schedule

G G G G G G G

Game 1

Game

2 이동 Game

3

Game 4

Game

5 이동 Game

6

Game

7 휴식

10 days

Tournaments Tournaments

10 days

A i

10 days

American League 16 teams

National League 14 teams

8 4 2 1 win 1 2 4 7

10 days 10 days

10 days

10 days

현재 소요일정 5 ( ) 10 d 50 d

10 days

현재 소요일정 : 5 (steps) * 10 days = 50 days 11월 1일 시작, 결승전 12월 11일 예정

Hints Hints Hints Hints

ƒ Series가 Game 4에서 끝난다면…

G 5 6 7 h d l W t Game 5,6,7 schedule = Waste

ƒ 현재의 Schedule은 Contingency Buffer를 가지고 있다.

History of World Series History of World Series History of World Series History of World Series

ƒ Series 전적

4 vs 0 : 16 (21.1%)

4 vs 1 : 21 (27.6%)

4 vs 2 : 19 (25.0%)

4 vs 3 : 20 (26.3%)

Analysis Analysis Analysis Analysis

Mean value Resulted value Probability

Mean value

50% Contingency Buffer

Vs

Vs

Vs

Vs

0 1 2 3

4 5 6 8 9 10

New Series Schedule New Series Schedule New Series Schedule New Series Schedule

G G G G G G G G

If necessary Game

1

Game

2 이동 Game

3

Game 4

Game

5 이동 Game

6

Game

7 휴식

Game 6

10 days 7 days

ƒ Probability : 75%

Schedule Schedule

Step 1

3 days

Step 1

Step 2

S 3

Step 3

Semi

Final

Total Buffer 12 days

40 days

Needed Buffer

Needed Buffer = 6 days

Needed Buffer Needed Buffer

각

A ti it 의 성공 확률 75% D l 발생 확률 25%

= 6 days

ƒ

Activity의 성공 확률 75%, Delay 발생 확률 25%

ƒ 4개의 Activity에서 반복시행되는 이항 분포 4개의 Activity에서 반복시행되는 이항 분포

Delay 발생 0 (0일) : 4C4 * (0.75)

⁴

⁰

Delay 발생 1 (3일) : 4C3 * (0.75)y ( ) ( )

³

¹

Delay 발생 2 (6일) : 4C2 * (0.75)

²

²

Delay 발생 3 (9일) : 4C1 * (0.75)

¹

³

95 %

Delay 발생 4 (12일): 4C0 * (0.75)

⁰

⁴

Schedule Schedule

Final

Total Buffer 12 days Needed Buffer

6 d 6 days

34 days 40 days 34 days

“ Th k B t i it ll ibl ?”

“ Thanks… But is it really possible?”

“ Hmm…..” Hmm…..

“Hmm…..”

“Hmm…..we don’t know”

Bud Selig MLB Commissioner