One major reason that hinders the implementation of process improvement principles in the construction industry is the lack of a powerful formalism to model and analyze the existing and new workflow processes. This paper proposes a framework which is based on the use of Petri nets for modeling and analyzing workflow processes in construction. The paper starts with an overview of current developments in the Petri nets theory. The paper then presents an example to demonstrate how to use the Petri net based framework to assist important steps of process improvement.
The paper describes the application of non-linear structural analysis methods to address archaeological questions concerning the reconstruction of the ancient city of Pompeii after a major earthquake that occurred 17 yr prior to the famous eruption of Mt. Vesuvius in 79 AD. It presents preliminary findings in an effort to develop an approach to modelling the two-way out-of-plane behavior of unreinforced masonry walls, including comparison studies with published analytic and experimental results for one-way loaded walls, plus a trial analysis for a two-way span condition. The approach requires the application of computationally intensive non-linear analysis techniques, since the linear analysis methods used in conventional design and education are inadequate to model the behavior of unreinforced masonry. Developing an understanding of the two-way behavior of unreinforced masonry has implications not only for archaeological investigation of ancient structures, but also for modern renovation of historic structures.
Learning architectural concepts through the study of precedents is a common activity in design studio. Traditionally, an instructor presents a design concept by showing selected examples using slides, photographs, drawings, texts and verbal analyses. This method relies on a linear mode of conveying design knowledge and is time bound. It emphasizes information retention and recall of facts rather than an understanding of information. If information on architectural precedents are represented digitally in a system designed to promote understanding of the material rather than just presentation of facts, then some disadvantages of the traditional method may be overcome and additional advantages may be achieved. This paper describes a computer-assisted lesson system designed to represent architectural concepts related to spatial composition in design by using graphic images and text and reports on its development, implementation and testing. The system relies on many characteristics, such as accessibility, interactivity, flexibility, rapid feedback, etc., which are known to foster effective concept learning. The paper also evaluates the viability and effectiveness of this system from a technological and logistical viewpoint as well as from a concept learning viewpoint, and concludes with a discussion on other potential applications.
It is suggested that expert systems storing the design knowledge of particular offices in terms of stylistic and construction practice provide a means to take considerably more advantage of information technology than currently. The form of the knowledge stored by such expert systems is a building representation in the form of rules stating how components are placed in three-dimensional space relative to each other. By describing how Frank Lloyd Wright designed his Usonian houses it is demonstrated that the proposed approach is very much in the spirit of distinguished architectural practice. To illustrate this idea, a system for assembling three-dimensional architectural details is presented with particular emphasis on the nature of the rules and the form of the building components created by the rules to assemble typical details. The nature of the rules, which are a three-dimensional adaptation of Stiny's shape grammars, is described. In particular, it is shown how the rules themselves are structured into different classes, what the nature of these classes is and how specific rules can be obtained from more general rules. The rules embody a firm's collective design experience in detailing. As a conclusion, an overview is given of architectural practice using rule-based representations.
In the paper, the design and method of operation of a robot cell for the assembly of rebar cages for beams and columns is described. The input elements are pre-manufactured rebars, and the output consists of rebar cages. Inside the robot cell, assembly is performed by robots equipped with tools for grasping the rebars, tools for bending the stirrups, and tools for welding the stirrups to the longitudinal bars. Various mechanisms for supplying the robots with rebars and supporting them during the assembly process have also been designed. Because of the specific nature of the assembly process, where robots have to successfully avoid various obstacles, mass-produced robots cannot be used for the assembly of rebar cages. For this reason, special robot configurations have to be designed. The robot cell described in this paper is at present at the design stage. It was modelled and simulated using the program WORKSPACE 3 for robot simulation, which makes it possible to study, optimise, and design in detail the proposed robot systems. The figures in the paper describing how such a system works have also been taken from this simulation.
Graders are used for ground grading or levelling. The desired profile is achieved by passing the machine over the ground surface with appropriately positioned grader blade. Grading errors are caused mainly by vertical displacements of grader front wheels. These displacements, despite a considerable wheel base of the grader, are transferred through the frame onto the grade blade. Moreover the quality of surface levelling is also influenced by the compliancies of the ground, the chassis and the blade suspension system. In the paper a blade stabilization system is proposed. The blade adjustment system with hydraulically driven mechanism is controlled using position signals from the selected points of the machine.
During the course of a design project numerous design decisions are made, usually with little attention paid to documenting them or keeping track of them. Systematic documentation and representation of design decisions can not only be invaluable in learning from past design experiences, but can also be good tools in teaching architectural design. By using abstraction and analogy to analyze a design precedent, a problem/sub-problem hierarchy can be built where similarities and differences between the precedent problem and the target problem, goals, constraints and solutions are identified for each level of the hierarchy. Each one of these can be represented as objects in an object oriented programming environment, allowing the construction of a hierarchic structure. This model was incorporated into a computer assisted learning system called 'DesignRep' which was created by using Toolbook® (Asymetrix) object oriented development environment.
There are in excess of 20 million acres of bomb and artillery ranges under the control of the Department of Defense (DoD). Each year some 800,000 to 2,000,000 km are turned over to civilian (private or commercial) use. Some of this land is contaminated with buried unexploded ordnance (UXO). These UXOs present a safety hazard and raise many environmental concerns. In addition to inaccurate locating, one of the most difficult aspects for the operator of an excavator is the inability to see the target ordnance while it is covered with soil and debris. This paper presents a system which is mounted to the arm of an excavator and is capable of detecting a buried UXO located in the path of an excavator's bucket. Also, the system is able to determine the precise location of the ordnance relative to the excavator's bucket. This information will allow the operator not only to avoid striking the ordnance during the digging operation, but also to expose the object by removing the soil around it. This technology is also capable of locating small UXO which can be buried within the spoil material. This technology has the potential to result in savings of millions of dollars in operating costs and prevent the damage or loss of equipment.