an integrated system for computer-aided design and construction of reinforced concrete buildings...

Automation in Construction 5 (1996) 323-341

An integrated system for computer-aided design and construction of reinforced concrete buildings using modular forms I

Mohammad Alfares aT * , Ali Seireg b

a Mechanical Engineertng Department, College of Engineering and Petroleum, Kuwait Uniuersity, P.O. Box 5969, Safat 13060, Kuwait b Mechanical Engineering Department, The Uniuersity of Wisconsin, Madison, 53706, USA

Abstract

The study reported in this paper investigates the feasibility of automating the on-site construction of reinforced concrete residential buildings. The basic construction tasks are identified, analyzed and modified with a view towards potential for automation. Emphasis is placed on developing modular forms that facilitate automation. The majority of work in the field of construction robotics has focused on the adaptation of existing industrial robots to automate traditional construction processes. This paper outlines a computer-aided construction system approach specially suited for integrating design and implementation by on-site robots. A Computer-Integrated Construction (CIC) system, similar to CIM, is developed that includes a CIC data-ba.se, a construction design system, a construction production/process planning system, and a robotics execution system. This approach is intended to minimize the redesign effort as well as the need for on-site manual work.

1. Introduction

Advanced technology is currently being intro-

duced in the construction industry and is expected to play an increasingly -important role in the next decade. To meet the challenges of the future, the industry is

looking towards the: use of advanced robotics and automation technology to develop high quality, efficient, safe, and economical construction facilities.

The remarkable progress of Computer-Integrated Manufacturing (CIM) and Automation in the manufacturing industry provides a good model for the construction industry to follow [ll. Good progress has been made in the automation of some construction activities at the work site. which focuses on

* Corresponding author.

’ Discussion is open until April 1997 (please submit your

discussion paper to the E!ditor of Construction Technologies and

Engineering, M.J. Skibniewski).

automating individual processes [2]. However, it is the integration and simplification of these activities, and approaching the problem from a total system viewpoint that is lacking in the construction industry and there is a growing trend to transfer the robotics

technology from advanced manufacturing to construction. It is necessary, however, to ensure that such transfer is compatible with the special needs of the construction industry [3].

The main objective of this paper is to investigate the development of an integrated computer-based system for the automation of on-site reinforced concrete construction and the employment of robotics within this system. An important part of the study is to explore solutions that have already found their way into the manufacturing industry and apply them with the necessary modifications to the complex construction environment. In contrast to manufacturing, decentralized work locations and on-site production activities are characteristics of construction pro-

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PII SO926-5805(96)00157-4

324 hf. Alfares, A. Seireg/Automation in Construction 5 (1996) 323-341

cesses. Construction is a labor intensive industry and reduced labor requirements could be an important benefit of automation. Automation could also help maintain construction quality by achieving a consis- tent output over time and by providing built-in inspection. Finally, an improvement in construction

safety could be a major benefit of automation. The methodology introduced in this paper pre-

sents the framework of a possible solution, within the limitations of the complex construction process, to the development of an Integrated-construction system [4]. Automating the construction processes and

integrating them into an overall process will, therefore, require identification and decomposition of system and subsystem activities using a hierarchical network of object-models that represent a building model. These models can be represented by a single structural unit called Modular Forms. Standardized forms can help reduce the complexity of the construction site activities, and enhance the technical feasibility of robotization and automation.

2. Computer-integrated construction methodology

Today, large Japanese construction firms are be- ginning to realize that it is beneficial to have a structured approach to the introduction of robotics and automation in construction. Current research in construction automation focuses on the introduction of Computer-Integrated Construction (CIC) [5-s]. CIC is defined as a strategy for linking existing and emerging technologies in order to optimize construc-

tion design, planning, management, engineering, contracting, construction, and maintenance [4]. The CIC model is divided into three major areas: (1) Integrated Design-Construction Planning, (2) The Factory Automation System, and (3) The On-Site Automation System. There are no comprehensive CIC systems fully developed yet for reinforced concrete structures, and much research is centered on the management of the planning processes for automating existing construction methods.

This paper introduces an approach which is based

Feed-kick --_-_-_

1 Sensory 1

Computer-Integrated Construction Informalions -MobiIc Robot I I Data-base I Execution Commands a I

r I I' I I I

'PI I II ’

T I

Physical & Graphical lnfonnations

Layour. Assembly,

and Diasscmbly Operation Sequences Informations

Trajectory Segments, ’ Types of Robots, and End-Effecters

1

Informalion I

Motion ‘& Control ’ Codes

I I

-Forms Geometry

-Connectivity Models

Construction L Design System

-Construction Sequences

-Assembly Sequences

-Disassembly Sequences

-Form Coding Operation

-Mobile Robot Selection

-Testing Ii -Simulation I

I Computer I

+ Program 8 Codes

I

-Cost & Time Optimization 1 -----_-_-_-_-_-_

-etc.. I

Robotics & Automation Process Planning Execution System

System

Fig. 1. Computer-integrated construction system outline for the on-site robotic construction system.

M. Al&ares, A. Seireg /Automation in Construction 5 (1996) 323-341 325

on the concept of Computer-Integrated Construction (CIC) with on-site automation. The on-site automation deals with reinforced concrete construction based on a prefabricated modular formwork system which is specially suited to purpose-designed robots. It is not intended in this study to introduce full automation for all types of construction. Only the construction activities that can feasibly be carried out with robots, such as formwork construction, which re- quires simple positioning, placement, and removal of

discrete components are investigated. Fig. 1 shows the outline of a proposed

Computer-Integrated Construction (CIC) system. Through this system, the construction planner would specify the required construction components (i.e., modular forms) using a computer simulation program. The construction process could be planned, rehearsed, modified, optimized, and checked in a systematic manner. The entire process of assembly

of the forms would then be documented as a full set of instructions to be used by on-site computer con- trolled machines (i.e., robots). The required parts (e.g., forms) and equipment (e.g., robots and end-ef- fectors) would be scheduled and retrieved just in time for use in the automated construction process.

The CIC system is implemented in a Microsoft Windows environment (i.e., menu-driven system) that allows the user to do the following:

0 Create and load a 3D computer model of construction compotrents for a project, into its data- base. Also, all the related information to both com-

ponents and construction machines are incorporated within the data-base.

0 Allow for easy modification within the con-

struction model. 0 Relate schedulied activities for optimum cost

and time of construction. 0 Give complete instructions to the robotics

system of when and lhow to assemble or disassemble construction componlents.

0 Create a custom simulation of any portion of the construction project.

The CIC system is formed by a library of three programs from which a symbolic or a graphical project model can be generated. These are: a design system, a process pl,anning system, and a construction robotics execution system. All systems are linked through a common graphical component-based data-

base which provides the paradigms necessary to

achieve such a knowledge-rich representation of a construction project.

2.1. The modular form-based construction system

In order to establish integration within CIC automation methodology, the first step is to identify and classify the types of design, processes, and tools

currently used, and how they can be automated and integrated into the total process [4,5]. There have been many attempts to make the construction processes match the requirements for automation [9-121.

These attempts tend to partially automate the on-site construction or transfer a number of on-site construction operations into the off-site, well-structured envi-

ronment of a prefabrication plant. While prefabrication of construction will improve the efficiency of present methods of construction and the operation of robots will in a large part resemble the well-structured factory conditions, a major problem in this

system is the lack of standardization for construction methods [2]. Also, it has been difficult to obtain the flexible construction output volume and satisfactory quality level that is projected by designers of this

method [9]. Despite these disadvantages, prefabrication of building components off-site and automating the remaining work on-site, can be another useful alternative to the full on-site automation method [ 131.

Modular forms can serve as the missing link between manufacturing and construction. The use of

these standard forms enables the designer to specify buildings of many shapes and sizes. Also, the forms can be designed to conform with the robot perfor-

mance characteristics and limitations (e.g., good capabilities in a series of simple and highly repetitive

work tasks, performed in serial or parallel sequences). This is done by using similar components, components within a modular dimensional system or the use of subassemblies common to different final assemblies. Also, the components are designed so that the way in which they can be assembled is standardized. This minimizes the chances of mismatching assemblies and subassemblies. The complex spatial nature of the building can be considerably simplified if the component assemblies obey a system of standard dimensional coordination. This simplifies not only the local operations of handling, mating, and

326 M. Alfares, A. Seireg/Automation in Construction 5 (1996) 323-341

fixing, but also the determination and updating of the spatial properties of the developed building. Also, the use of discrete components makes the design of an on-site automation system much simpler when the sizes, shapes, and attributes of the forms to be handled are more closely specified.

2.1.1. Design of the modular forms

Although, prefabricated forms are temporary

structures in concrete construction, they must be built to maintain the desired dimensions. They must also be built with sufficient strength to be self-supporting while bearing the concrete load that will be imposed upon them [ 14,151. Reusable prefabricated forms and forming systems have become increasingly important to concrete construction as a means of savitlg both material and labor cost through the efficiency of mass production. The proposed modular form systems for buildings are standardized pre-

fabricated forms, which are easy to handle and can be adapted to forming different structural members. They are classified as either a horizontal formwork system (i.e., for floor and ceiling) or a vertical formwork system (i.e., for columns and walls). Fig. 2 illustrates a classification of the modular formwork system developed in this study and the constructional details are illustrated in Appendix A.

There are some basic objectives in designing forms such as design for automatic assembly, modulariza- tion, standardization, strength, ease of dismantling, and reusability. Forms should also be designed to

simplify the task of the robots and end-effecters employed in the handling, assembling, and disassem-

MODULAR FORMS

------ZHorilontel Vertical

. . . . , / Redangular Circular Triangular

Wall Forms Column Forms

r-T+-rl l--kl-l

Flat Curved Corner T-shape Hinged Z-Sided Xided 3.Sided 4-Sided

Farm Form Form Form Form square Corner Form Form

I I Form FONtI

I ’ I Door Window FLlrlll Form

Fig. 2. Modular form classes.

dd-On Reinforcement Internal Panel

Fig. 3. Add-on reinforcement and two wall panels.

bling processes. An important feature in their design is preassembling the steel reinforcement inside the forms off-site, as shown in Fig. 3. The complex spatial nature of custom-designed buildings can be also simplified by the use of an appropriately de-

signed system of modular components [ 121. For the vertical modular form system, the design of the connectivity mechanism is based on the principle of male/female connections. Fig. 4 shows the male/female channel junction between two forms. Special features are introduced in designing the forms to ensure tight connection between them, to support

lateral loading, and to ease their assembly and disassembly. These are described in details in [4].

The horizontal modular forms have L-shaped junctions to prevent cement leakage. They are placed on automatically adjustable telescopic support frames

designed to be supported in pockets that are casted into the side walls. Fig. 5 shows detailed representation of the connectivity between horizontal forms. The reinforcement bars of horizontal forms are designed to automatically link with the reinforcement bars in other horizontal forms as well as those in the side walls which can help in establishing strong connectivity between the reinforcements. The design details of all forms are given in [4] and are outside the scope of this paper.

2.2. Data-base design and management within the CIC system

To make optimal use of the proposed automated building system, early participation of the customer

M. Alfares, A. Seireg/Automation in Construction 5 (1996) 323-341 327

with the design and construction engineers is necessary to improve the productivity of the entire process. A versatile data-base that stores design and engineering information, construction planning and management information as well as production infor-

mation, with all the necessary conditions and con- straints, is required to effectively link the different operating components. A data-base design is devel-

oped for modular form construction which defines a set of data structures and operations that can be used for storage and manipulation of data objects. There are different models and procedures for data-base design that can be applied to the proposed system [16]. There are also attempts to design data-base systems that integrate design and construction through the use of the CAD system which is linked to relational or objiect-oriented data-bases models [17-211. These systems lack the consideration of standardization of c80nstruction information and the

direct integration of robotics in the total system. The proposed CIC system is designed to incorpo-

rate a graphical component-based data-base. This data-base captures the geometric information and the necessary features of the modular form system for design and then uses this information to facilitate the automation of production planning and construction. The geometric description is only one element of the

total table of functions for the construction project model which is a computer representation of the

construction project structure. It contains form geometric and non geometric attributes, connectivity, dependencies, production and cost information, and access to robotics hardware systems. The first step after designing the modular forms is to code and classify them according to the Group Technology principle, as shown in Fig. 6. The next step is to store and link these forms to the data-base within the

computer memory. Accordingly, a 3D model that accurately represents these components (e.g., forms sub-assembly) along with their associated data (e.g., handling and fixing information, cost, assembly and disassembly processes, and materials) is built for

Male Junction

I

(b) Top View

Fig. 4. The male/female connectivity mechanism.

328 M. Alfares, A. Seireg /Automation in Construction 5 (1996) 323-341

supporting both storing and integration of design and construction data within the CIC data-base. A component, such as the inside and outside panels of forms and a reinforcement bar, is considered to be an

individual building element. In this 3D representation of the building structure, every individual build-

ing element is represented as an “object.” There- fore, the building itself is not an object but rather a

-

-

very large collection of individual objects or components. Also, in terms of the representation of construction design, all encounters with the 3D representation of the building occur in a computer environment. In other words, all manipulation and commu- nication of building construction will occur within

the CIC data-base. This will ensure consistency and integration of all information relative to the particu-

L I,-connection

- Concrete \V:1ll

- Outside I’ancl

Iiorizontal Madulm-

(I)) Top View

Fig. 5. Connectivity between horizontal modular forms.


lar building design. .Fig. 7a displays a 3D model of a In order to enhance the utility of the integrated

modular 4-Sided column form and its associated system, the physical structures are represented by data. Fig. 7b shows the type of stored and inputted 3-D solid models to be deployed within the data-base.

data within the CIC program structure. The use of modular forms provides the vehicle for

External Face Reinforcement Bars

CODE : 0001100 Position of Digit Characteristic Digit Represents

First There are two systems of modular forms, Vertical (0) or

Horizontal (I).

Second There are two types of vertical moduiar forms, Wall (0) or

Column (I).

Third There are five classes within the vertical wall forms, Flat (0),

Corner (1). T-shape (2). Hinged (3). Curved (4).

Fourth

Fifth

Height to width ratios, H/W = I, 2, 3, etc..

Connectivity Information, Male (0) Female (I), or

Combination (2).

Sixth Supporting Structure type, Foundation-Floor (0) Floor-

Floor (I), or Floor-Ceiling (2).

Seventh Special features, such as door opening (O), window (I). and casting-edge (2).

Fig. 6. A Hybrid Coding scheme for Modular Forms.

330 M. Alfares. A. Seireg/Automation in Construction 5 flY96) 323-341

(a)

&::::E& , . a : . :

I

LP . . 1.11. I

..I..

Top View

COMPONENT CODE # 0001130 COLUMN FORM

SUB-COMMPONENTS = ( 4 Panels, Reinforcement Bars)

* Shape = { 4-sided column form )

* Size = [ Length(l), Length(Z), Height ) * Location on Site = ( X-coordinate, Y-coordinate )

* Connectivity + Orientation = [ Female [X,-X], Male [Y,-Y] )

* Supporting Structure = ( FD-FL, FL-FL, FL-C )

* Form Material = { Aluminum, Composites )

MACHINE = ( Equipments, End-Effector, Work-Space )

(b) TYPO of Data 1 Hardware /Types of Hardware 1 lnout Data 1

I Stored Data

Design

Forms

Tools -Supporting Frame

-Vertical

-Horizontal

-Location on Site

-Form-Space

-Level #

-Element Codes

-Shape of Element

-Shape of Forms

- StrengthJTimelCost

-Connectivity of Forms

-Supporting Structure

- Soecial Features

-Location on Site -Orientation oo Site -Types of Supporting

-Level # Frames

Implementation

-Robot Crane

:e -Work-Spat

-Equipments

-Types of End-Effedors

-Processing Time per

Unit

I

Fig. 7. (a) A 3D model representation of 4-sided column form. (b) Stored and inputted dat within the CIC data base


integration. The modular form system, while provid-

ing an advanced medium for the accessing, retrieval, and presentation of construction project data, can be used to visualize and plan the different construction activities during the design phase. Due to the graphical and physical nature of these forms, they can be

represented as the basic entity within the data-base of the Computer-Integrated Construction system [4]. This will also increase the flexibility of graphical site representation, construction information consolida- tion, and design/construction integration.

2.3. The CIC program structure

Although there is considerable ongoing research

in CIC systems, there is, to the best of our knowledge, no published information on a fully integrated system for concrete building. The developed pro-

gram is structured around the specially developed data-base and its utilization in the design and implementation stages. The main objective of the data- base, as part of the total integrated system, is to achieve design-construction integration. This can be accomplished through the integration of a graphical component-based data-base with a menu-driven program structure [4]. This will provide a visual investigation and representation of site topology, forms

geometry, connectivity modules regarding the form work components, and robot and end-effector types. This information is then interfaced through a menu driven program to initiate the planning and execution of the construction processes.

The graphical CIC program structure is developed according to the standard “Windows” program user interface. The typical user interface includes dia- logue windows, pull-down menus, buttons, and fields. An application program code (written in C + + ) is composed of procedures or subroutines that correspond to each menu in the program. Fig. 8 shows an abstract model of the program structure within the CIC data-base. There are ten main menu options in the program. A brief description of the different options is provided in Appendix B.

This program stmcture serves as the core for the CIC system. Through the system, the designer can create spatial or volumetric models that act as “For- mwork” for the development of the component construction model. Once the’ components have been

Fig. 8. Program Structure for the CIC data-base.

defined, the spatial model could be eliminated because there now exists an accurate depiction of the surfaces that define the volume (e.g., concrete walls). Additionally, this description could be stored as a separate collection of components allowing the designer, at any stage, to add to or modify them interactively without the need to start from the be- ginning. This kind of representation of building projects and the flexibility within this representation, can enhance consistency of information, construction sequencing, critical path application, cost prediction,

and constructability. Three major types of output information that the

CIC program structure can supply to the designer,

are: 1.

2.

3.

3.

2D or 3D graphical representation for each construction stage. Detailed production or process plans that include optimum operation time and cost. Detailed robotic execution commands (e.g., tra- jectories, end-effector selection, etc.> for each construction stage.

Integrated construction design and implementation within the CIC system

The building realization process, within the CIC program structure, consists of three stages: conceptual design, implementation process, and modification process. The conceptual design is how to use the modular forms to design a specific building structure


(e.g., a wall) which satisfies the client’s requirements

and results in an accurate representation of the building. The implementation process will then generate sequences of construction operation and hardware requirements based on the design information. The designer can change or modify any step of the construction process through the modification procedure included in the program structure. All design, implementation, and modification stages are manipu-

lated and produced through the interactive CIC program structure.

3.1. Design procedure within the UC program struc-

ture

The proposed CIC program structure through the CIC data-base, can allow visual investigation of construction topology, form geometry, and connectivity requirements regarding the formwork compo-

nents [4]. This information is then interfaced with the implementation procedure to initiate planning and execution of the construction process. The first step for the designer is to create and name a new file using menu [“File”]. Assuming that both the foundation and the first floor are already constructed, the designer knows exactly the number of columns and their locations on site. Accordingly, the next step is to construct the vertical modular form components. First, the designer selects the menu [“Construct”] to start the selection sequences of “columns or walls”

and the level at which they will be constructed. At this step, the designer will start constructing the first column at level one of the building model. Following this, the designer selects the type of vertical modular form that is a column modular form. When this selection is made, the column forms table of elements, Fig. 9, will appear giving the designer the flexibility to select the exact type of column form,

Eile Construct implement Generate Modify Farms Tools Text Mew Yelp

Element Code

Shape Form

Supporting Structure :

~

Strength 1 Time Cost

Location on Site :

Connectivity of Forms :

Male [x,-x]

Female [x,y]

Size :

Male [x],Female I-x] &#

Top View

F-C -------j Levelttl Stage812

Fig. 9. ‘Column forms’ table of elements

hf. Alfares, A. Seireg / Automation in Construction 5 (19961323-341 333

File Construct L jmplement &.nerate Modify Forms Tools Text yew Help

Level ?J 1

X Stage # 13 -

Fig. 10. 3D view of the column modular form on location.

Eile construct lmplcmcnt Generate Modify Farms Tools Iext New Help -

Types of En&Effector :

Assembly Time per unit : (-G-)

- . . . . . . . . * . . . . . . . . . . . . .

Top View

Fig. 11. Robotic devices and types of end-effecters dialog box relative to placing column forms.

334 M. Alfares, A. Seireg/Automation in Construction 5 (IY%/ 323-341

location on site, size of the form, the supporting structure, connectivity types, and any special features (e.g., adding an edge-support). The selection of the designer can be done by clicking on the item to be chosen or by typing the input information in the dialog boxes. Once the designer finishes selecting and clicking on “OK”, the design process of the column form is completed as illustrated in Fig. 10.

This procedure can be repeated for other components to complete the construction process.

3.2. Construction implementation procedure within

the CIC program structure

Upon completion of each component design step, the designer can proceed to choose the robotic machines and end-effecters based on their attributes needed for the implementation process of the designed structure. Fig. 11 illustrates the final step within the CIC program structure to implement the placement of the forms needed for a corner column.

3.3. Construction modification procedure within the

CIC program structure

The CIC program structure allows the designer to modify any step at any level of the construction project. The designer can add or remove one or more modular forms or tools depending on the type of modification required. Also, the choice of different implementation devices can be changed, modified,

added, and removed according to the type of modification required. The original designs can be saved while the designer tests different scenarios of construction layouts. This gives the designer and the client the flexibility to visualize and analyze each construction layout to their satisfaction.

The construction process is divided into levels of construction (which correspond to the number of stories the building has). Each level has different stages of construction (e.g., the assembly of each modular form). The program structure includes a counter that indicates to the designer the current level and stage of the construction process. This allows the designer to retrieve the level and the stage where the modification procedure can be performed.

4. Integrated production/process planning within the CIC system

Designing a software program that is capable of automatically generating a construction process plan using design information is one of the major components in the CIC system [22]. A Computer-Aided Construction Planning system (CAPP) is designed

within the developed CIC system to automatically transform the modular formwork construction design and implementation processes into a well-structured data representation (i.e., knowledge). The data can then be readily transformed into graphical activity networks which allow the designer to evaluate and modify the activities, their precedence, estimated duration, and the required resources at any stage of the construction process. At the end of the design and implementation processes, the entire activity network can be assembled, displayed, and optimized after acceptance of the final plan by the designer and the construction engineer. The process planning can allocate combinations of construction components and resources to every level or stage of the building

project produced. The goal of the developed production planning program is to achieve the implementation of the different levels or stages according to the design specifications within the given time and in the most economical way. The system would allow the automatic evaluation of the graphical component- based representation of a construction project leading to the development of the optimum production/process planning.

4.1. Knowledge representation of the construction production /process planning

A modular construction project is composed of many repetitive activities. An activity has several attributes that are important for automatic planning; duration, cost, resources, and location. Also, the activities are divided into main events as follow: (1) Preliminary activities such as ground levelling, exca- vation, and foundation, (2) Structure works on a modular floor system, (3) Structure works on a modular wall system, and (4) Structure works on a modular ceiling system. Within the design and implementation processes of the CIC system, all activities are divided into discrete construction levels and

M. Alfares, A. Seireg/Automation in Construction 5 (1998 323-341 335

Table 1

‘Activity generator’ for design and implementation for any modu-

lar form

Activity “Activity Generator” and its knowledge

Transport-Type Form[Level, Stage]

( Type._Of_Robot = Crane or Transportation

Robot

Select a Form

(Menu #5))

Implement a Form

(Menu #2)

Work-Space = Internal or External

Site-Storage = [X,, U,]

Conslruction_Site = [X,, Y,]

Transportation_Time = T,

Transportation_Cost = C,

1

Place-Type Form[Level, Stage]

1 Type__Of_Robot = Mobile Assembly Robot

or

Crane Robot

Work-Space = Internal or External

Placing_Location = [X,, Yp]

Placing_Time = Tp

Placing_Cost = C,

1

stages, and most of these activities are dependent on their predecessors. Each level represents horizontal and vertical modular formwork. Within each level, the process of placing or removing a form or part of a form, placing or removing a supporting frame, or pouring concrete represents a single construction stage. Therefore, each construction activity of the building process describes the application of an Ac- tivity Generator which is a set of computer commands incorporated within the CAPP system that

generates the activity’s knowledge (e.g., type of activity, location, time, and cost) and its precedence network (i.e., a graphical representation of activity’s precedence). Table 1 represents a sample of the Activity Generator and its knowledge for designing and implementing the process (e.g., at any level and stage) of placing any modular forms in their location.

The process planning instructions generated automatically through the Activity Generator are also transformed into an activity network graphical representation similar to that used for Critical Path analysis. Both the Activity Generator and the graphical representation are the backbone of the Computer-

Aided Process Planning (CAPP) integrated within

the CIC system. The computer system can automatically generate the activity network at any stage of any level of the construction process. For example, the designer can, after completing the design and the implementation procedure of the current stage, select

the menu [“Generate”] and submenu [“Activity Network”], to view the network generated automatically by the CAPP. The designer has the option to

view the default level and stage (i.e., current level and stage), previous levels and stages, a range of

levels and stages, or the total construction levels and stages of the building process planning.

4.2. Cost and time analysis of the construction pro-

duction /process planning

In the developed program, the design process is

the input module that interfaces CAD and CAPP, and the implementation process is the input module that interfaces CAPP and Robotics Execution. To

analyze the automatic production and process planning activities, interactive planning between building elements and construction methods is to be per-

formed by comparing the given conditions and con- straints on design and implementation with the characteristics of the construction system. Also, time and cost simulation (and optimization) for several combinations of building designs and construction methods can be demonstrated to support the choice. Illustra-

tive examples of the program capabilities are given in [41.

4.2.1. Principle of ordering and scheduling among

construction activities

The overall objective of construction planning is

to execute the construction project as specified, with available resources, in the most efficient manner [23]. The system for planning and scheduling of construction activities described in this paper is for the specific domain of the modular formwork construction. It is an activity oriented rather than work or object oriented construction planning procedure. An activity is defined here as a repetitive construction of modular formwork performed at various locations in a building by a team of robotic machines. The three basic activities are: Transport, Place, Re- move.

336 M. Al&ares, A. Seireg /Automation in Construction 5 11996) 323-341

Focusing on activities enables dealing with groups based tools employing, for example, Critical Path of construction components instead of each compo- algorithms can help in analysing a plan since the nent. For example, the planner can choose to erect an definition of activities and their attributes and prede-

entire wall in one step instead of the individual wall cessors are provided to the CAPP system by the

forms that construct the wall. The repetitive nature of design and implementation processes. Figs. 12 and modular form construction allows considerable sav- 13 describe the least-constraint representation of

ing of effort when there is repetitive information and some stages of the construction plan for a single

processing work. room-single story building.

During or after the design and implementation

processes, the program structure will generate automatically the type of activities to be performed and their specific knowledge at any level and stage. Once the designer completes the design and implementation phases for each stage of the construction process, the CAPP system will allow the planner to

interactively study, analyze, and evaluate the interac- tion of the current stage with previous stages, each intermediate event, or the entire construction project. Using techniques similar to the traditional network-

The main focus when analysing any planning model is to study the following output parameters from each stage: (1) Utilization of selected automation resources, (2) Total transporting/placing/removing processing time, and (3) Total transporting/placing/removing processing Cost. Us- ing the activity network models, the designer can analyze the current design stage or the process up to this stage and evaluate the utilization of available resources, time, and cost to maximize the productivity levels.

/4

WF19

WFlB All Vertical

+ Forms Are In Place

Fig. 12. Activity network for placing all vertical modular forms. Where; [l] represents the process of transporting all vertical forms to

location [C,] represents the process of placing column fodi] in location. [WFi] represents the process of placing wall fodi] in location. [DWF,] represents the process of placing door form[i] in location. [WWF,] represents the process of placing window fodi] in location.

M. Alfares, A. Seireg / Automation in Construction 5 (1996) 323-341 337

4.2.2. Optimization of the construction production / process planning

Once the designer has completed the preliminary design and implementation of the building project model, the CAPP system will generate a strategy to optimize the construction process planning according

to the established output requirements of each level and stage. A common objective is to maximize the productivity while complying with the target time

and cost. The time to finish a project is usually specified by the customer and is constrained by the availability of resources. Also, in other instances the

desire of the customer may be to minimize the cost without any restriction on the finish time. In general, the objective of optimization of the construction planning is to minimize the cost for meeting a target

All Supporting

Frames And All

Horizontal Modular

Forms Are Placed

date of completion. This can be formulated by the following linear objective function:

U = Ctota, + k 1 - _T,,I,I , I ‘desired 1

where; Ctotal = the total cost calculated to complete the construction, Ttota, = the total time calculated to finish the construction., Tdesired = the time to

completion as desired by the designer or the customer. k = A weighting factor that reflects the optimization strategies of the designer and customer.

The planner can automatically generate the activity network at any stage for inspection and modifications by the designer or the construction engineer. At

the end of the design process the entire network can

I All Supporting Frames And

All Horizontal Modular

Frames Are Removed

All Outside

Panels Of The

Vertical Modular Forms

Are Removed

Fig. 13. Activity network for removing supporting frames, horizontal forms, and outside panels of the vertical forms with minimum number

of robot on location. Where; [13] represents the process of placing concrete mix in the Horizontal Forms (Stage # 13). [ 14-171 represents

the process of removing supporting frames. [18-251 represents the process of removing horizontal forms. [62-851 represents the process of

removing outside panels of both wall and column forms.

338 M. Alfares, A. Seireg /Automation in Construction 5 (1996) 323-341

be displayed and optimized after the acceptance by the designer and the construction engineer. The optimization scheme can also be performed at different instances of the construction process, such as stage, event, level or the entire construction process which makes the integrated system a dynamic process. The CAPP system will automatically find the critical

stage (e.g., the stage that takes a long time) and modify it by adding a parallel operation or rearrang- ing the order of operations.

5. Integrated robotic and automation within the CIC system

To generate the robot motion plan for a given task or activity, it is important to develop a scheme that

will translate the construction process plans to robot motion plans [4]. To accomplish this, a Computer- Aided Motion Planning (CAMP) system, illustrated in Fig. 14, is developed and integrated with the CIC system that translates the knowledge of the work environment and the construction process plans into robot motion plans knowledge. This knowledge can then be transferred to the construction robot system for execution of the specified construction task. The CAMP system consists of knowledge representation of the robot motion plans and automatic robot task

planner. Details of the developed system and sample illustrations of its capabilities are given in [4].

5.1. Knowledge representation of the robot motion

plans

One of CAMP’s important features is the ability to directly extract the necessary knowledge from both the design and implementation stages (e.g., CAD data) and process plans (e.g., CAPP data). This helps the CIC users by not having to model the construction components again in the robot execution world.

According to the “Activity Generator” commands that specify the activity-level of construction knowledge, it is important to generate a general

robot-level knowledge that the on-line robot motion planner can use to perform the construction tasks. To generate this knowledge, a Robot-Activity Genera- tor which is a set of computer commands is devel-

The CIC Data-Base

1

World Model

(CAD)

.

CAPP (Process

Sequences)

* c

Robot-Activity Generator

Automatic Robot

.

Task Planner

Speclflc Robot-Level Commands (Robot Dependent)

CAMP

Fig. 14. The Structure of the CAMP system.

oped. The next step is translating the robot-indepen- dent commands into a specific robot-level knowledge (i.e., robot-dependent commands) to actually

execute the construction tasks. Table 2 illustrates the

Table 2

‘Robot-activity generator’ for placing any modular form

Activity “Robot-activity generator” and its knowledge

[Macro-Level Motion]

( Translate-Mobile Assembly Robot

Orient-Mobile Assembly Robot

Level-Mobile Assembly Robot

Place-Type

Form[Level,Stage] ) [Macro-Level Motion]

I Grip-Type Form Pickup-Type Form

Position-Type Form

Release-Type Form

I


Robot-Activity Generator and its knowledge for manoeuvre the arm around the obstacle and return to placing any modular form in its designated location. the preprogrammed path.

5.2. Automatic robot task planner

6. Conclusion Automatic plannmg of construction robot tasks

involves the use of appropriate control strategies and

procedures to generate a sequence of actions (robot motion) to transport, place, or remove the modular forms. A rule-based automatic robot task planner

system contains a knowledge-base of production/process sequences, a data-base that includes a model representing the modular form state and the robot world model, and a rule interpreter that acts as a control mechanism for selecting the robot motion to be execmted. For manipulator robots, the motion planning problem with complete information has been thoroughly investigated in the literature [24-261. Due to the. special nature of the construction tasks, the main scheme in the motion planning and path generation for the proposed system is not to avoid obstacles, but to find the obstacle (e.g., the

modular form). Also, due to the shape and size of the modular form, it is important to consider the com- bined effect of the slhape and size of both the manipulator arm and the form when moving the form from its initial location ~to the assembly location while avoiding obstacles. The basic algorithm used to gen-

erate’ motion planning for the construction robot system integrates the construction design and implementation data generated by the CIC program structure and stored in the CIC data-base with existing motion planning algorithms [27-291. The algorithm represents a methodology of specifying the required manipulator motion plan according to the design data knowledge.

The framework of an integrated design, planning,

and implementation system which is developed for concrete buildings is presented in this paper. The central element is the standardized and reusable groups of modular forms which incorporate the reinforcement and can be easily assembled and disas- sembled by robotic devices. The object-oriented data-base, interactive graphic representation, automated production planning, and robotic execution makes it possible to simulate the entire construction process. It also allows the designer to modify and optimize the design interactively based on cost and

completion time to the satisfaction of the client before the actual implementation.

Although the developed approach is demonstrated by a relatively simple example, the approach can be readily expanded to deal with practical cases which are subject to established construction practice and codes.

Appendix A. Illustration of the different types of modular forms

A.1. Modular wall forms

A.2 Modular column forms A.3 Horizontal modular forms

Because of the difficult nature of the construction environment, some type of obstacle avoidance scheme or sensors should be incorporated within the algorithm to avoid unanticipated changes. There are several schemes for obstacle avoidance that can be incorporated in this algorithm [27,28]. A typical scheme uses sensor-based path planning for robot arms operating around unknown obstacles of arbi- trary shapes. Therefore, if an obstacle is introduced or discovered within the preprogrammed trajectory of the robot arm, the automatic task planner can invoke at any time the obstacle avoidance scheme to

Appendix B. The main menu options of the CIC program structure

Menu #0 File: This option is used to: - Open a new file or already existing file.

- Save a file. - Print a file. l Exit from the program.

Menu #1 Construct: This option is used to select which type of construction work is to be built and at


what level. There are three main types of construction works; Foundation, Horizontal (Floor or ceiling), and Vertical (Columns or Walls). Foundation work is considered as level #O, whereas for each piece of horizontal or vertical work, the user needs to select a

corresponding level number that depends on the number of stories a building has (i.e., two-story building will have floor level # one and two).

Menu #2 Implement: This option is used to select the implementation of construction work which consist of placing or removing forms, placing or removing the supporting frame, and pouring con-

crete. For each implementation, the user needs to selectone type of robot, one type of end-effector. Also, the user needs to select whether the robot will work internally or externally with respect to the building workspace. According to the selected information, the process (e.g., assembly) time per construction unit is calculated and presented.

Menu #3 Generate: This option is used to generate construction process plans (e.g., CPM plans) and robotics execution plans (e.g., robot trajectory).

Menu #4 Modify: This option is used to modify any stage at any level of the construction work that is related to adding or removing a form or a supporting frame. Also, the user can change or modify any robotic equipment or end-effector selections.

Menu #5 Forms: This option is used to select a horizontal or vertical type of form. For each type of form, the user needs to select the element code, the

type of supporting structure, connectivity of form, and size of form. Also, the user needs to input the location of the form on-site according to a specified reference coordinate.

Menu #6 Tools: This option is used to select the type of Supporting Frame. Additionally, the user needs to input the location and orientation of the supporting frame on site.

Menu #7 Text: This option is used to type in engineering (or personal) notes or documentation on the construction design plans.

Menu #8 View: This option is used to let the user select the viewing of the construction design plans. The user has the option to choose between 2D or 3D presentation.

Menu #9 Help: This option is used to give the user an interactive help command at any stage of the construction design.

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an integrated system for computer-aided design and construction of reinforced concrete buildings...

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