a knowledge based expert system for design of berthing structures

Ocean Engineering 26 (1999) 653–673

A knowledge based expert system for design ofberthing structures

A.V. Ranga Rao, R. Sundaravadivelu*

Ocean Engineering Centre, I.I.T., Madras 600 036, India

Received 12 April 1997; accepted 12 November 1997

Abstract

Rapid growth in the water transport system demands the construction of more port andharbour structures. Berthing structures are constructed in ports and harbours to provide facili-ties such as berthing and mooring of vessels, loading and unloading of cargo and embarkingand disembarking of passengers. Quays, wharfs, piers, jetties and dolphins are the most widelyused berthing structures. The construction and maintenance of these structures are very expens-ive and, therefore, the most economical design should be adopted. These structures will bechecked against limit state of crack, which is important in respect to preventing corrosion. Aknowledge based expert system, KNOWBESTD, has been developed using LEVEL5 OBJECTfor the design of berthing structures. This paper describes the development of KNOWBESTDand illustrates the design of a typical berthing structure. 1998 Elsevier Science Ltd. Allrights reserved.

Keywords:Berthing; Design structure; Expert system

1. Introduction

Berthing structures are constructed in ports and harbours to provide facilities forberthing and mooring of vessels, loading and unloading of cargo and for embarkingand disembarking of passengers and vehicles. Berthing structures are classified asvertical face structures (vertical face type) and open piled structures (open type)

* Corresponding author.

0029-8018/99/$—see front matter 1998 Elsevier Science Ltd. All rights reserved.PII: S0029 -8018(98)00013-4

654 A.V. Ranga Rao, R. Sundaravadivelu /Ocean Engineering 26 (1999) 653–673

(Agerschou et al., 1983) (Fig. 1). Berthing structures are to be designed for berthingforce, mooring force, wave force, current force, seismic force, active earth pressureand differential water pressure, in addition to self-weight of the structure and liveload. Live load is due to rail, road, bulk unloaders, cranes, pipelines, conveyor trestle,etc. Berthing structures are to be analysed for different load combinations. The con-struction and maintenance of berthing structures are very expensive and, therefore,the most economic design should be adopted. Crack width is very important in thedesign of berthing structures, since these structures are constructed in marineenvironment.

Structural design is a complex process combining design knowledge and analyticaltechniques. Design of any structure involves three stages, i.e., conceptual design,preliminary design and detailed design. Analysis can be automated in an algorithmicfashion, i.e., a set of calculations performed following a predetermined sequence ofoperations done by traditional computer programs. But the process of structuraldesign cannot be reduced to a fixed set of mathematical operations because designis concerned with concepts, ideas, judgements and experience, all of which appearto be outside the range of traditional computer programming. Conceptual design islargely done in the mind and is characterised by a high degree of ambiguity withthe possibility of more than one acceptable solution. The designer uses his or herexperience to find the suitable solution. The desire to use a computer to aid ill-structured problems like design requires skillful manipulation of large quantities ofknowledge, in a trial and error fashion, starting with certain assumptions and hypoth-eses and revising them when necessary, until a solution is achieved. The whole pro-cess of problem solving requires symbolic computation, which can be achieved bya knowledge based expert system.

A KNOWledge based expert system for BErthing STructures Design(KNOWBESTD) has been developed for the economical design of berthing struc-tures, using LEVEL5 OBJECT (1990), with forward-chaining mechanism, using Pro-duction Rule Language.

2. Expert system shell

Several expert system shells such as RULEMASTER, VPEXPERT, M1,INSIGHT2, IITMRULE, etc. are available for development of an expert system. Theselection of a particular shell for a particular problem is a difficult task in any expertsystem development. The following points may be kept in mind while selecting anexpert system shell:

1. type of machine and operating system;2. type of control strategy and inference mechanism;3. user interface;4. availability of complex mathematical routines;5. ability to interface with external programs; and6. explanation facilities.

655A.V. Ranga Rao, R. Sundaravadivelu /Ocean Engineering 26 (1999) 653–673

Fig. 1. Various types of berthing structures.


LEVEL5 OBJECT (LEVEL5) is an application development environment thatcombines expert system technologies with object oriented programming, relationaldatabase models, hypertext capabilities and debugging tools. LEVEL5 provides aninteractive windows based user interface. Production Rule Language is used to createa LEVEL5 knowledge base, which contains class declarations, forward-chainingdemons, methods and displays. Objects in a knowledge base are created via classdeclarations. Class declarations define the structure of the objects contained in aknowledge base, for example, to hold and retain the application’s data values.Demons describe the operational logic, rules of thumb and cause-and-effect relation-ships, which are needed to make decisions and to fire certain events or actions duringexecution. Methods establish procedures for determining values, and displays areused to interact with end users by prompting for values and showing the output data.The structural breakdown of LEVEL5 objects used in KNOWBESTD is given inFig. 2.

3. Components of KNOWBESTD

The relation between various components of KNOWBESTD is shown in Fig. 3.

3.1. Knowledge acquisition

Knowledge acquisition is the process of obtaining information from various codes,books and experts familiar with the problem to be solved.

Fig. 2. Structural breakdown of LEVEL5 OBJECT in KNOWBESTD.


Fig. 3. Schematic view of KNOWBESTD.

The domain knowledge of KNOWBESTD, such as basic dimensions, clear cover,effective span, minimum grade of concrete, minimum grade of steel, minimum per-centage of reinforcement, placing of additional reinforcement, etc., is acquired fromcodal specifications and experts in the field of berthing structure design.

3.2. Knowledge base

Knowledge base is represented in the form of demons and facts that are structuredfor the purpose of consultation, using Production Rule Language.

The design procedures, as specified by Indian Standard Codes, depending on vari-ous end conditions, for designing structural members like slab, beam, pile and dia-phragm wall of berthing structures, form the knowledge base. Types of berthingstructures, various codal provisions and expert knowledge regarding basic dimen-sions, clear cover, effective span, minimum grade of concrete, minimum grade ofsteel, minimum percentage of reinforcement, placing of additional reinforcement,etc. are also included in the knowledge base.


3.3. Inference engine

An inference engine controls the selection of demons and methods from the knowl-edge base to derive a conclusion or fact. A forward-chaining mechanism is used fordeveloping KNOWBESTD.

Based on the type of berthing structure, the design of various structural membersof the berthing structure is considered. If open type berthing structure is selected,the user interface will display the structural members SLAB, BEAM and PILE. Ifvertical face type is selected, the user interface will display structural member DIA-PHRAGM WALL in addition to the above. Similarly, if long span to short spanratio of slab exceeds 2, then a message ‘Slab is designed as two way slab’ willappear on the screen for user information.

3.4. Explanation system

The knowledge base is used to explain the reasoning process to the user.Explanations of berthing structure types, procedures to design various structural

members of berthing structures, various codal provisions and experts commentsregarding design of berthing structures are included in the explanation system ofKNOWBESTD via the HELP button. Users can get explanations at any level ofexecution by using the HELP button provided at that level.

3.5. User interface

Windows based user interface is provided in the form of visual edit screens andmenus in which the user must enter the values of the required parameters at theappropriate field. The HELP button on each screen provides necessary help to theuser, related to the option on that screen. With the help of the GO BACK button,the user can return to the previous screen, with the help of the CONTINUE button,the user can continue to the next screen, and with the help of the EXIT button, theuser can exit the program at any stage.

4. KNOWBESTD

KNOWBESTD is a user friendly and menu driven knowledge based expert systemfor the design of berthing structures. The first screen of KNOWBESTD is given inFig. 4. By pressing the CONTINUE button of the first screen, the user will get adisplay of types of berthing structures (Fig. 5). By pressing the HELP button of thescreen shown in Fig. 5, the user will get a display about types of berthing structuresas shown in Fig. 6. The EXPLANATION button of this screen will display WHYand DEFAULT as shown in Fig. 7. WHY displays an explanation regarding whythe user has to select the type of berthing structure (Fig. 8). DEFAULT displays thedefault option, if any. Based on the type of berthing structure, it will display variousstructural members for design. Fig. 9 shows the type of members to be designed in


Fig. 4. First screen of KNOWBESTD.

Fig. 5. Type of berthing structure.


Fig. 6. Help for type of berthing structure.

Fig. 7. Explanation screen.


Fig. 8. Explanation regarding selection type of berthing structure.

Fig. 9. Structural members for vertical face type berthing structure.


case of vertical face type berthing structure; and Fig. 10 shows the type of membersto be designed in case of open type berthing structure. The design knowledge baseof KNOWBESTD is given in Table 1. Reinforced cement concrete of minimum M30grade and reinforcement of minimum Fe415 grade are used for berthing structures.A minimum cover of 40 mm for deck slab, 50 mm for beams, 65 mm for piles and65 mm for diaphragm wall is provided. A minimum of 8 mm diameter bars are usedfor shear/transverse/distribution reinforcement. For beams, where the depth of webexceeds 750 mm, side face reinforcement is provided along the two faces. The totalarea of such reinforcement will not be less than 0.1% of web area and will be distrib-uted equally on two faces at a spacing not exceeding 300 mm or web thickness,whichever is less (IS 456, 1978). The allowable crack width is considered as 0.004times the clear cover. The various end conditions considered in the KNOWBESTDare given in Table 2. The abstraction of design of berthing structures is given inFig. 11. The crack width,Cw, is calculated using the following formula:

Cw 53acrem

1 1 2Sacr 2 Cmin

D 2 x Dwhere

Fig. 10. Structural members for open type berthing structure.

663A.V. Ranga Rao, R. Sundaravadivelu /Ocean Engineering 26 (1999) 653–673T

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acr 5 distance from the point considered to the surface of the nearest longitudinalbar (Fig. 12);Cmin 5 minimum cover to the longitudinal bar;em 5 average strain at the level considered;D 5 overall depth of the member; andx 5 depth of the neutral axis.

The average strain at the level at which cracking is being considered is given by

em 5 e1 20.7btD(a9 2 x)

Ast(D 2 x)fs3 10−3

where

e1 5 the strain at the level being considered5(D 2 x)(d 2 x)

fsEs

;

bt 5 the width of the section at the centroid of the tension steel;a9 5 the distance from the compression face to the point of the crack;Ast 5 the area of tension steel;

fs 5 service stress in tension reinforcement5 0.58fyAst requiredAst provided

;

Es 5 modulus of elasticity of steel; andd 5 effective depth.

The above formulae shall be used, provided the strain in tension reinforcementdoes not exceed 0.8fy/Es. The negative value ofem indicates that the section isuncracked.

Fig. 12. Crack width in beams.


5. Case study

A case study has been carried out on a typical berthing structure to demonstratethe usefulness of the developed KNOWBESTD. The layout and cross-section aregiven in Figs. 13 and 14, respectively. The structure consists of a deck 10.7 m wideand 325 m long and is divided into 6 blocks. Blocks 1, 2, 3 and 4 are of size 10.73 60 m, while blocks 5 and 6 are of size 10.73 42.45 m. An expansion gap of20 mm is provided between two blocks. Vertical piles of 600 mm diameter in thefront and 900 mm diameter in the middle and rear rows are provided to support thedeck. The deck consists of a cast-in-situ RCC slab of 150 mm thick which is coveredby a weathering coat of an average 100 mm thick, with a slope of 1:300. The slabis supported by a series of precast secondary beams of size 3003 800 mm. Theprecast secondary beams have a flange of total 2366 mm width which acts as a formwork for the cast-in-situ slab. The precast beams are supported on cross-beams of500 3 1000 mm. The cross-beam transfers the loads to three piles spaced at 5 mintervals across the width. The front, middle and rear rows of pile are spaced longi-tudinally at 5 m c/c in blocks 5 and 6 and at 4.85 m c/c in blocks 1–4.

The analysis of the structure is carried out using Structural Analysis Program (SAPIV) by considering the fixity depth. The loads considered for analysis are earth press-ure, berthing force, mooring force and seismic force, in addition to self-weight andlive load, as shown in Table 3. The structure is analysed for various load combi-nations as per the codal provisions. The design forces and moments of various struc-tural members from the analysis for critical load combination are given in Table 4.

Fig. 13. Pile layout of a typical berthing structure.

Table 3Loads considered in the analysis using SAP IV

S. no. Load Value

1. Earth pressure 150 kN2. Berthing force 650 kN3. Bollard pull 120 kN4. Seismic force 63.6 kN5. Live load 30 kN/m2


Fig. 14. Cross-section on-XX.


Table 4Forces and moments on structural members for the critical load combination (dead load1 live load 1earth pressure1 seismic force)

Beam Pile

Bending moment Shear Front row Middle row Rear rowforce (kN)

Support Midspan Axial Bending Axial Bending Axial Bending(kNm) (kNm) force (kN) moment force (kN) moment force (kN) moment

(kNm) (kNm) (kNm)

1281.4 798 1118.6 863.2 79.8 1514.1 342.6 543.4 562.4

The designs of deck slab, cross-beam and rear row pile are carried out by KNOW-BESTD. M30 grade concrete and Fe415 grade steel are used in the design.

5.1. Design of deck slab

The deck slab of 150 mm thick is designed for self-weight, load due to 100 mm thickweathering coat and a live load of 30 kN/m2. A clear cover of 40 mm is provided forthe slab. The short span of slab is 2.336 m and long span is 5.00 m. Fig. 15 shows the

Fig. 15. Input for design of deck slab.


input given for slab design and Fig. 16 shows the reinforcement details given by KNOW-BESTD.

5.2. Design of cross-beam

A cross-beam of 5003 1000 mm is considered for the design. A clear cover of50 mm is provided for beam. The design is carried out for the moments and shearforce given in Table 4. Fig. 17 shows the input given for the design of cross-beamand Fig. 18 shows the reinforcement details given by KNOWBESTD.

5.3. Design of rear row pile

A pile of 900 mm diameter in the rear row is considered for the design. A clearcover of 75 mm is provided for pile. The design is carried out for the moment andaxial force given in Table 4. Fig. 19 shows the input given for design of rear rowpile and Fig. 20 shows the reinforcement details given by KNOWBESTD.

6. Conclusions

The knowledge based expert system KNOWBESTD is very useful for the designof berthing structures. In the absense of KNOWBESTD the user is forced to referto many codes and consult experts for an economical design.

Fig. 16. Reinforcement details of deck slab.


Fig. 17. Input for design of cross-beam.

Fig. 18. Reinforcement details of cross-beam.


Fig. 19. Input for design of pile.

Fig. 20. Reinforcement details of pile.


The expert system KNOWBESTD is user friendly and the knowledge base canbe expanded very easily wherever and whenever required. It not only saves time forthe design of various structural elements, but it also provides help and explanationsto the user whenever required.

References

Agerschou, H., Lundgren, H., Sorensen, T., Ernst, T., Korsgaard, J., Schmidt, L.R., Chi, W.K., 1983.Planning and Design of Ports and Marine Terminals. Wiley Interscience, New York.

IS 456, 1978. Indian Standard Code of Practice for Plain and Reinforced Concrete. Bureau of IndianStandards, New Delhi.

IS 4651 (Parts IV), 1989. Indian Standard Code of Practice for the Design of Port and Harbour Structures.Bureau of Indian Standards, New Delhi.

LEVEL5 OBJECT, 1990. User’s Guide for Microsoft Windows. Information Builders, New York.

a knowledge based expert system for design of berthing structures

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