Keywords: accessibility issues, workspace congestion, simulation prototype, virtual environment, manual maneuvering, path-correcting stratagems, workspace allocations.

Accessibility issues form an integral component of constructability problems that commonly plague Civil Engineering projects. Construction materials, equipment such as pressure boilers and building components such as precast columns and beams all have to be moved from one point to another during various stages of the construction process. However, this flow is often hindered, or in some cases, even completely blockaded, by various factors such as workspace congestion due to concurrent proximate construction activities [3], sequencing problems inherent in the original project schedule, having to carry out the aforesaid movement operation in a confined space etc. The problem is exacerbated by the inherent difficulty of detecting such time-space conflicts during the pre-planning stage of the project [1]. Non-accessibility is an issue of major concern to the construction industry because they result in unnecessary delays, or in severe instances, even work stoppages.

In order to counter this pressing problem, this study proposes a prototype computer simulation program that can be used as a tool for analyzing and potentially solving problems arising out of having to keep the circulation of movement alive in the hectic environs of a cluttered and busy job-site. Upon detection of an accessibility-related conflict, either during field operations or during the pre-planning stage of the project, the prototype can be used to simulate a virtual three-dimensional model recreating the site conditions at the instant of the conflict. The target equipment/component of the movement operation can then be manually maneuvered in this virtual environment so that the user can personally evaluate whether an alternative solution to what was originally planned for in the project schedule can be found to resolve the accessibility issue.

In particular, the paper describes two features which have been developed and incorporated into the prototype to enhance its capabilities and help enable it to achieve the useful objective aforementioned. These are: (1) path-correcting strategies; and (2) finite workspace elements.

During the manual maneuvering stage by the user, it is very likely that the path traced out would have encountered some collisions with obstacles along the way. The path-correcting stratagems integrated into the prototype searches through the output file containing information pertaining to the user-limned route, identify any conflict instances, and automatically corrects for these using geometry-based routines. The transformation (e.g. translation, rotation, or both) carried out by the user which resulted in the clash and its corresponding counterpart which moved the object clear of the predicament are both taken into account in determining the type of correction that would be made to the path. Once all the necessary "repairs" have been completed, the collision-free course is played back to the user for analysis and for ascertaining its aptness for application to the real-life situation.

Finite Workspace Elements allow more accurate and precise modeling of workspaces proximate to the object in which machinery and/or manpower for effecting the transport operation can be deployed. Traditional modus operandi is to pre-specify a movement strategy together with the equipment/component of interest, which could be quantified, for instance, by the specification of minimum path width and height requirements [2] or by the determination of turn envelopes for the transport vehicle assigned [4]. However, this method is restrictive because it takes the focus away from the "transportee" and hauls the "transporter" into the movement equation. The undesirable consequence of this is that due to the increased aggregate bulk, potentially promising paths within the control volume of the job-site that would otherwise have been admissible are ruled out, thus resulting in a reduced solution space. Finite Workspace Elements resolve this issue by precluding the need for the pre-specification of a transport strategy prior to the mapping out of a feasible route for the object of interest. Workspace allocations next to the object are modeled by extrusion volumes from the faces of a bounding box of the object, with each extrusion volume further subdivided into finer individual elements. By not rendering those elements which have been detected to have collided with environmental artifacts, the volume and shape of the workspaces available next to the object can be relayed to the user at all times. This allows the user to plan in retrospect the transport strategy after a through route for the object in the job-site has been found, thus maintaining the object as the pith of the operation and opening up the solution space in its allowance for more flexibility in the choice of the accompanying movement plan.

1

Akinci B., Fischer M., Levitt R. and Carlson R. "Formalization and Automation of Time-Space Conflict Analysis", Journal of Computing in Civil Engineering, 16(2), 124-134, 2002. doi:10.1061/(ASCE)0887-3801(2002)16:2(124)

2

Guo, S.J. "Identification and Resolution of Work Space Conflicts in Building Construction", Journal of Construction Engineering and Management, 128(4), 287-295, 2002. doi:10.1061/(ASCE)0733-9364(2002)128:4(287)

3

Riley, D.R. and Sanvido, E.S. "Space Planning Method for Multistory Building Construction", Journal of Construction Engineering and Management, 123(2), 171-180, 1997. doi:10.1061/(ASCE)0733-9364(1997)123:2(171)

4

Varghese, K. and O'Connor, J.T. "Routing Large Vehicles on Industrial Construction Sites", Journal of Construction Engineering and Management, 121(1), 1-12, 1995. doi:10.1061/(ASCE)0733-9364(1995)121:1(1)

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