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
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
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
제약 규명 : 속도가 가장 늦은 대원 D가 제약
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
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)
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
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
이스라엘의 물리학자 Eliyahu M. Goldratt 박사 : 친구의 가구공장에 대해 병목공정 중심의
생산일정계획 시행 → 생산성 3배 증가
조직의 목표를 달성하는데 제약이 되는 요인을 찾아 집중적으로 개선하고 조직내의 모든 의사결정을 집중적으로 개선하고 , 조직내의 모든 의사결정을 제약요인 위주로 수행함으로써 조직의 목표 달성
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
Traditional contingency buffering: Advances are wasted
Traditional contingency buffering: Advances are wasted, while delays are accumulated.
Student syndrome
Student syndrome
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
각 단계의 안전여유를 모음3 4
2
프로젝트 버퍼 반으로 줄임1
Feeding, Resource Buffer Feeding, Resource Buffer Feeding, Resource Buffer Feeding, Resource Buffer
A1 FB RB
3 4
1 2
프로젝트 버퍼Critical 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
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.
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.
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
프로젝트 관리 비용을 절감하고 고객의 Needs에 부응하는 신제품개발의 속도를 빠르게 한다
일반적인 제조시스템과 다른 특성을 갖는 프로젝트
생산에 대한 관리를 위해 TOC (Theory of Constraint) 를 적용
PERT/CPM과 같이 네트워크를 사용해 일정관리를 함
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
Technical Buffer: a buffer for securing technically required time (i.e.,
i ti f t i )assign a time for concrete curing).
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
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
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
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
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
Park, M. and Pena-mora, F. (2004) “Reliability Buffering for Construction Projects ”
Construction Projects
Chua, M. , Shen, L. and Bok, S. (2003) “Constraint-Based Planning with Integrated Production Scheduler over Internet ”
Ballard, G. (2000) “Phase Scheduling”, LCI White Paper
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
Goldratt, E. (1997) “Critical Chain”, A Business Novel
Goldratt, E. (2002) “It’s not Luck”, 동양문고
Park Young-min A Study in Schedule Management in Construction
Park, Young-min, A Study in Schedule Management in Construction Projects by CCPM 2004.10
Park, Young-min, A study on Instruduction of Critical Chain Project
CC C 2003
Mangement(CCPM) to Construction Projects, 2003
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
각 토너먼트는 7전 4선승제
American league 16개팀
National league 14개팀 : 총 30개팀 참가
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
Series가 Game 4에서 끝난다면…
G 5 6 7 h d l W t Game 5,6,7 schedule = Waste
현재의 Schedule은 Contingency Buffer를 가지고 있다.
History of World Series History of World Series History of World Series History of World Series
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
4 4Vs
4Vs
4Vs
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
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
각Activity의 성공 확률 75%, Delay 발생 확률 25%
4개의 Activity에서 반복시행되는 이항 분포 4개의 Activity에서 반복시행되는 이항 분포
Delay 발생 0 (0일) : 4C4 * (0.75)
4
* (0.25)0
= 32%Delay 발생 1 (3일) : 4C3 * (0.75)y ( ) ( )
3
* (0.25)( )1
= 42%Delay 발생 2 (6일) : 4C2 * (0.75)
2
* (0.25)2
= 21%Delay 발생 3 (9일) : 4C1 * (0.75)
1
* (0.25)3
= 5%95 %
Delay 발생 4 (12일): 4C0 * (0.75)
0
* (0.25)4
= 0.4%Schedule Schedule
Final
Total Buffer 12 days Needed Buffer
6 d 6 days
34 days 40 days 34 days