This document discusses production flow strategies in the construction of tall buildings. It analyzes the Empire State Building's rapid construction timeline and compares strategies of work in process (WIP) accumulation versus WIP reduction using discrete event simulation modeling. The results show shorter cycle times, higher productivity, and shorter project durations when using a WIP reduction strategy that minimizes buffers and explicitly manages trade progression between floors. WIP accumulation leads to longer cycle times and durations due to increased variation from accumulated buffers.

1. PRODUCTION FLOW IN THE CONSTRUCTION
OF TALL BUILDINGS
Rafael Sacks1, Rebecca Partouche2
Associate Professor, Faculty of Civil and Env. Engineering, Technion – Israel Institute of Technology
Graduate Student, Faculty of Civil and Env. Engineering, Technion – Israel Institute of Technology
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Present: Trần Nguyễn Nhật Nam 1770716
Phạm Hoàng Nam 1770415

2. 1. MOTIVATION
The time required for construction of tall buildings, whether measured
per floor or per unit area built, increased consistently through most of
the 20th century despite the introduction of improved construction
technologies
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- More technologically complex ?
- Networks of subcontracting ?
Construction management has become focused on contract
management and the allocation of risk and less on explicit
management of the production system
 Buffers of time, work in process and materials to accumulate

3. 2. BACKGROUND INFORMATION
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From 1929 to 2008 , the Empire State Building represents an international
record in terms of the pace of construction
Possible reasons for this seeming contradiction.
1. The increasing number of building systems and their complexity
2. The prevailing economic conditions.
3. The variation and reliability of the design information.
The production system itself, particularly in the ways in which labor
resources are applied.

4. 2. BACKGROUND INFORMATION
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The model's primary purpose was to enable experimentation with different
management strategies, such as the 'WIP accumulation’ and 'WIP
minimization' strategy, the impact of design and other errors, and resource
constraints

5. 2. BACKGROUND INFORMATION
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IMPROVE
CONSTRUCTION FLOW
1 - Minimizing WIP
2 - Improving design
information quality
Difficult because their design and
production detailing is carried out
by numerous different people
Need intensive use of building
information modeling and
integration tools
focus on 1st strategy:
reduced WIP

6. 3. NEW METHODS
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The research method was to compare different strategies using a Discrete
Event Simulation Model. This tool is common in construction research
(Martinez and Ioannou 1999; Sacks et al. 2007; Tommelein 1998)
The measures for comparison are cycle times, overall crew productivity and
construction duration. Focus on Simulating WIP Accumulation vs. WIP
Reduction

7. 3. NEW METHODS
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Using ProModel
simulation software
(ProModel 2007)
Simulate
construction
of buildings
Five horizontal
space types
Three vertical
space types
Parking floors
Entrance floors
Typical office floors
Lobby elevatorspaces
on each floor
Roof space
Elevator
Technical shafts
in the core
Facades

8. 3. NEW METHODS
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All in all 116 distinct types of activities are modeled
The durations for the activities are stochastic, varying according to triangular
distributions defined by minimum, most common and maximum duration.
The durations are also corrected to account for the learning curve as each
team learns the best ways to perform each floor:
Corrected duration = Base duration ×
Maximum crew size
# workers available
× 1 +
Learning curve factor
# repetition s

9. 3. NEW METHODS
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Wip definition

10. 4. RESULTS
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Strategy
Average
Project
Duration
(months),
Resources Work flow
Maximum
number of
workers
needed
Labor
Capacity
Utilization
(%)
Floor Cycle Time for the finishes
(days)
Minimum Average Maximum Std. Dev.
WIP accumulation 29.9 101 90.6% 53 92 181 37%
No explicit strategy 28.7 98 89.9% 40 53 74 18%
WIP reduction 29.8 95 90.0% 37 50 76 17%
Table 1. Selected results for each of the strategies A to C (the number of workers made
available for each trade was the same for all.)

11. 4. SUMMARY
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The significant differences in the project outcomes resulting from
WIP accumulation vs. WIP reduction strategies.
In buildings that are highly uniform, as the Empire State Building
was, mass construction, with predetermined progress of trades from
floor to floor using fairly uniform production rates and carefully set
buffers can work well.
Their construction could be improved if managers were better versed
in the ‘physics’ of construction production systems

12. 4. SUMMARY
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But where buildings are more complex and variation in design and
production rates cannot be removed, as in the case of modern
buildings, project schedules that pre-determine the sequence of
progression of trades from space to space result in long cycle times
and long project durations.
This is exacerbated where trade subcontractors are allowed to
determine their own progression through a building and accumulate
buffers of WIP

13. 4. REFERENCES
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6. Martinez, J. C., and Ioannou, P. G. (1999). "General Purpose Systems for Effective Construction Simulation." Journal of Construction Engineering
and Management, ASCE, 125(4), 265-276.
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Proceedings of the 16th Annual Conference of the International Group for Lean Construction IGLC16, Manchester, UK.
8. ProModel. (2007). "ProModel." ProModel Corporation, Orem UT.
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12. Tauranac, J. (1995). The Empire State Building: The Making of a Landmark, Scribner, New-York.
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Construction Engineering and Management, 124(4), 279-288.
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