Abstract: Four-dimensional (4D) schedules have proven successful in planning with their visualization capabilities allowing for co-
ordination and time-space conflict detection. However, when considered in depth, internal aspects of 4D scheduling techniques have
not made significant advances from traditional two-dimensional (2D) scheduling. What is missing from 4D scheduling? Why has the in-
teraction between activities, their relationships, and three-dimensional (3D) components not been flexible and adaptive enough? In light of
these questions, this paper analyzes the current state of 4D scheduling. The missing element in 4D scheduling is found to be 4D relationships
(4DRs). A prototype of 4DRs has therefore been developed to improve 4D scheduling. Finally, guidance on the application of 4DRs in 4D
scheduling is presented to help the users come to a thorough understanding of its advantages and disadvantages and potential applications
DOI: 10.1061/(ASCE)CO.1943-7862.0001007. © 2015 American Society of Civil Engineers.
The term four-dimensional (4D) scheduling is used to refer to the generation of a schedule by linking three-dimensional (3D) com-
puter-aided design (CAD) model components with their corresponding schedule activities. The availability of 3D building
information models (BIMs) has recently overcome the technological challenge of producing 4D schedules, which involves the ability to recognize individual objects, their categories, associated materials, and relations between objects in terms of geometry and structure. Because of this, 4D schedules are already available for use in practice using a variety of commercial software. Speaking at the
Construction CPM Conference in 2014, Ben Nolan, a director with forensic analysis consulting firm Berkeley Research Group of
Florida, said that “in 35 years of construction work, I have not seen change happen so rapidly and [a technology] adopted so quickly as
I have with the adoption of 4D” (Joyce 2014). In terms of theory, several researchers already proposed an automated generation of 4D schedules based on 3D BIMs (Tauscher 2011; Kim et al. 2013).
However, 4D schedules are currently considered to be primarily for visualization, allowing managers to see, coordinate, and control what trades need to be where and when, to anticipate workplace conflicts, and to catch hidden flaws, which would not be possible with traditional schedules. In other applications, 3D models presented in a 4D schedule can also be used to automatically calculate quantities such as material and product items, or can be used for time calculation and resource capacities to establish the correct duration of work to complete an individual task or section. This in-tegration of 3D models in planning allows the internal content of an
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