Automated generation of workspace requirements of mobile crane operations to support conflict detection

Abstract

Modeling workspace requirements related to mobile crane operations could minimize delays associated with spatial conflicts and hazards on construction sites. To identify spatial conflicts related to crane operations, project engineers need to model and reason about spatio-temporal behaviors of cranes and coordinate them within a dynamic construction environment across time. Current approaches for identifying equipment-related spatial conflicts are based on discrete-event simulation of dynamic equipment motion. The accuracy of spatial conflicts detected using such approaches can be error-prone since it depends on a rate of time increment for the simulation to be set by the user. This paper presents an approach for generating workspaces that encapsulate spaces occupied by mobile cranes moving during an operation. It also discusses an assessment of the effectiveness of the approach in identifying spatial conflicts between mobile cranes and building components.

Introduction

Mobile cranes are widely used on construction sites for lifting materials. Compared to other types of construction equipment, mobile cranes typically occupy relatively large workspaces in three dimensions (3D) during an operation. When the workspace of a crane is not taken into account prior to its operation, the potential for spatial conflicts between the crane and other components (e.g., existing building facilities, temporary structures, and other construction equipment) located within the proximity of the crane increases [1], [2], [3]. Existences of such spatial conflicts can potentially result in work interruptions, productivity reductions, hazardous work conditions, and damages to existing structures [1], [2], [4], [5]. As reported by Occupational Safety and Health Administration (OSHA), 40% of the deaths involving cranes on construction sites from 1984 to 1994 were related to spatial conflicts [6]. These all suggest the need for modeling the workspace requirements of cranes so that project engineers and operators can be aware of possible spatial conflicts ahead of time and can accordingly take necessary preventive actions.

Space available for crane operations on construction sites is typically limited by facilities under construction and activities being executed concurrently and in close proximity [1]. Existing structures, such as electric lines and building structures, can have spatial conflicts with crane operations [2], [7]. To assess the availability of space on construction sites and to identify spatial conflicts, one needs to represent and reason about not only crane workspaces but also components that are expected to be in place at a given time of operation in three dimensions.

A major challenge in modeling workspace requirements of cranes stems from the fact that crane operation is dynamic. Although cranes are typically located at fixed places, some of their parts, such as their booms and hooks, move during an operation. These movements result in changes in the workspace requirements of cranes over time during a given operation. Hence, to identify crane-related spatial conflicts, one needs to account for the dynamic behavior of cranes and their parts and the corresponding changes in the workspace requirements over time.

Currently, commercially available visualization tools based on discrete-event simulation, such as Bentley Dynamic Animator [8], allow project engineers to model and visualize dynamic motion of equipment in conjunction with the evolution of constructions in three dimensions and over time. Within such systems, spatial configurations of pieces of equipment are modeled and visualized in four dimensions based on a set of user-defined information characterizing the motion of each part of equipment at discrete points in time. During simulation and visualization, such systems perform collision detection tests to identify possible spatial conflicts between pieces of equipment and building components at each incremental time step selected by a user.

Spatial conflicts detected using such simulation and visualization tools can be error-prone as the increment in discrete time steps of the visualization needs to be set properly by a user. If users select a very fine time increment, it will be possible to accurately identify possible spatial conflicts. However, a fine time increment could result in a large amount of time dedicated to visualization of construction operations. For example, in our experiment, we identified that when we selected a time increment as small as 1 s, we could identify all possible spatial conflicts that occur while a crane is lifting and placing a single component [2]. Visualizing this crane operation took approximately 1 min on an Intel Pentium 4 2.2 GHz computer, while the actual operation on the job site took 10 min. Since construction projects typically involve large quantities of building components and corresponding crane operations, visualization of operations and detection of related spatial conflicts throughout the entire construction period with fine time increments can become prohibitively time-consuming.

Instead of a fine time increment, a user may opt to use a coarse time increment for visualization of operations throughout the entire period of construction. For example, if the user selects a time increment as large as 1 day, visualizing construction operations of a project with a total duration of 5 months can take approximately 1 min on the same computer. However, with such a coarse time increment, it is likely that some potential spatial conflicts can be missed since a crane can perform multiple operations on a given day.

These all suggest that the accuracy of detected spatial conflicts be not rely mainly on a user-selected time increment of discrete-event simulation. This paper focuses on this need to model and identify possible spatial conflicts during an equipment operation without the reliance on a user-selected time increment. It presents an automated approach for generating workspace requirements of mobile cranes to enable automatic identification of spatial conflicts related to crane operations. It also describes the validation performed to assess the effectiveness of such an approach in detecting spatial conflicts related to mobile crane operations.