Bundesanstalt für Materialforschung und -prüfung

International Symposium (NDT-CE 2003)

Non-Destructive Testing in Civil Engineering 2003
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DEVELOPMENT OF INSPECTION SOFTWARE FOR DETERIORATED CONCRETE STRUCTURES

H. KANADA, Department of Civil Engineering, The University of Tokyo, Japan
H. YAMASHITA, Hazama Corporation, Japan
T. SHIMIZU, CTI Engineering Co, Ltd, Japan
T. UOMOTO, International Center for Urban Safety Engineering, Institute of Industrial Science, The University of Tokyo, Japan

ABSTRACT

This paper presents a summary of the system and the user interface of the inspection software developed for maintenance of concrete bridges. This system was developed with the concept that inexperienced engineers can easily diagnose and indicate necessities for the detailed inspections through a visual check. The software should also enable user to refer to many samples of deterioration patterns and to the structure types when clear diagnosis cannot be made. The causes and levels of deterioration are determined by the software, based on the data collected during the visual inspection.In this process, the inspection methods related to the causes already listed in the database are deduced automatically. Finally, the current condition and the result of diagnosis are stored part-by-part for each inspected structure so the history of inspection can also be traced.

KEYWORDS

Inspection software for deteriorated concrete structures, visual inspection, diagnosis, database

INTRODUCTION

In order to extend the lifespan of existing concrete structures, they must be inspected and tested periodically to detect any deterioration. The results should then be analyzed to determine its lifespan. If any signs of deterioration were found, the cause should be determined by this analysis. Using the information given by the analysis, the structure can be repaired and strengthened by applying appropriate reinforcement methods.

The market for maintenance and repairing existing structures in Europe and America accounts for approximately 30 to 50 percent of the entire construction market. These percentages are expected to increase further in the future. The current rate for this market in Japan is around 15% and it is expected to increase in the same manner as Europe and America [1].

The shortage of engineers with expertise and vast experience in maintenance has already posed a problem to the market. With the declining birthrate in Japan, this may lead to a reduction of overall number of engineers. Maintaining a large number of concrete structures with a decreasing number of engineers poses a challenge for the industry. Thus, a software for inspection of deteriorated concrete structures would prove to be a powerful tool for the maintenance engineers and authorities. At the present stage, inspection software for concrete bridges has been developed. The versions of the software for tunnels and piled piers are also ready for release. Unfortunately, these software are developed for domestic use, therefore, all documentations are provided in Japanese. English version are planned to be released in near future.

Handling of inspection data is one of the greatest concerns during maintenance due to the vast quantity of data. Furthermore, the maintenance engineer assigned to the concrete structure may be move to other department after inspection. In that case, inspection histories may not be completely transferred to successor. This software provides several useful functions in order to resolve this problem. For example, inspection histories, pictures, notes are stored into database when diagnosis result is derived, and diagnosis report is outputted as digital document. This report is believed to be useful for management body, and the consultants to be able to make suggestions for appropriate maintenance procedures.

DIAGNOSIS LOGIC OF SYSTEM

Fig 1: Summary of the diagnosis system for concrete bridges based visual inspection.

Figure 1 shows the summary of the diagnosis system. The salient features of the system are briefly discussed below. Inputted data from the user is stored into database through the interface, and it is also transferred to calculation sheets. The possible causes and the degree of deterioration are calculated with the sheets, and then the results are outputted and fed back into the database.

Fig 2: Supported structure types by the system.

Figure 2 shows a representation of how the different components of the superstructure and substructure can be inspected separately, and the data for each component stored. Figure 3 shows a simplified 'spread-sheet' showing the format for input of data, with the rows and columns showing the causes of deterioration and the inputted data, respectively. The numbers shown in an individual cell are determined based on general knowledge of concrete or trial diagnostic tests of this system on field. If the value of the cell on sheet is higher than other cells, current condition correlates with the corresponding cause of deterioration. It can be seen that the data needs to be input for the components A, B, C, D, E as shown. As can be seen, the details of different likely deterioration mechanisms (such as carbonation etc.), primary defects (such as drying shrinkage) and damage (such as over loading) have been given in different columns. Though the figure shows only the main girders (1/4 of span), the system has similar rows for other structural elements such as main girders (central part of span, vicinity of support), slabs, crossbeams (end or other than end). Figure 4 is a detailed view for the part highlighted in Figure 3, for the main girders (1/4 of span). Based on the data that is input during inspection, the column-wise sums are obtained, and the probable cause of deterioration, Pc, and, the level of deterioration, Pg, calculated as in the example discussed below.

Fig 3: Sample of calculation table for diagnosis (Prestressed concrete T-beam bridge).

(1)

where Pc is the possible value of cause of deterioration
A : subtotal of the values of environmental, accidental ,internal and construction conditions
B : subtotal of the values of structural deteriorations
C : subtotal of the values of deteriorations regarding cracks
D : subtotal of the values of deteriorations with cracks such as rust or free lime etc.
E : subtotal of the values of deteriorations other than cracks such as honeycombs, discoloration, gel or pop-out etc.

Fig 4: Detail view of calculation table for diagnosis (Prestressed concrete T-beam bridge).

Example : A part of Figure 4 has been highlighted to represent the condition in a particular span of a Prestressed concrete T-beam bridge.

  • Longirudinal direction of bridge, Crack + Rust + Free lime
  • Spalling, separation
  • Exposure, corrosion of steel

the value of C related to carbonation is 1.3, the value of D related to carbonation is 3.0. The values of Pc are calculated for each cause of deterioration by using all sub totals.

The degree of deterioration can be also evaluated by using similar calculation sheet.

(2)

Where Pg is the possible value of degree of deterioration
A : subtotal of the values of deteriorations regarding cracks
B : subtotal of the values of deteriorations with cracks such as rust or free lime etc.
C : subtotal of the values of deteriorations other than cracks
D : additional rate

If Pc is high, the possibility of the cause of deterioration is high.If Pg is high, the degree of deterioration is high.

FLOW OF INSPECTION SOFTWARE

Fig 5: shows the flow-chart of the diagnosis software.

For a start, a data file must be opened to record input data. If an inspection had previously been carried out, the recorded data can be modified and additional inspections can be conducted. Basic data such as the construction date, location of the structure, the traffic volume are considered for diagnosis. For example, information like the effect of use of sea sand or alkali reactive aggregate, chloride induced reinforcement corrosion, freezing and thawing or industrial damage can be determined from the location (user can easily select location from map), the construction location being divided into local municipality levels. The default values of environmental conditions or used materials are automatically designated when a location is selected. If necessary, the settings can be adjusted manually by the user.For assistance, hazard maps [2,3] for chloride induced reinforcement corrosion, dispersion of deicing agent, freezing and thawing damage, industrial area or use of sea sand and alkali-reactive aggregate can be referred by the user. The software also requires user to input accidental events after completion since they may affect the results of diagnosis.

Fig 6: Illustration of user interface for inputting data to superstructures and substructures.

Diagnosis data from visual inspection are inputted for each superstructure and substructure (Figure 6).

Fig 7: Input form of deterioration (Prestressed concrete T-beam bridge).

The number of spans, piers and abutments are determined from basic data of bridge, and active buttons are highlighted. Scroll bar is prepared for multi-span bridges, and it enables the user to select arbitrary superstructure or substructure. Since structural type may differ between spans, they should be selected independently. The input screen of deterioration is displayed once superstructure or substructure is selected. Input forms of deterioration are prepared for each structural type, and members are distinguished by using different colors (Figure 7). Figure 7 is a sample input form for a prestressed concrete T-beam bridge. In this case, the superstructure is divided laterally into 5 parts (Vicinity of support × 2, 1/4 of the span × 2 and the central part of the span), and divided longitudinally into 12 parts (Outside railing × 2, Wheel guard, Inside railing × 2, Undersurface of main girder × 3, Side of main girder × 3, Slab × 2), and input form for crossbeam (end × 2, others) is also prepared. Since the number of divisions is restricted to reduce input time, several options are available (such as an image capture or remark space) when detailed information is needed. In the case of multigirder bridges, inspection data is inputted separately into the database of outside main girder and inside main girder. At this time, inspection result of inside main girders and crossbeams are stored into one database together.The input form of actual condition will be displayed when inspection area is clicked (Figure 8). Present condition of members of concrete bridge should be inputted on the basis of information from visual check by inspector, and then the causes and levels of deterioration are estimated by the system. In the case of superstructures, the following deteriorated conditions are required for input to make the diagnosis.

  • Deteriorations regarding cracks
    The number of cracks, crack width, crack pattern, rust, free lime, crack intervals
  • Deteriorations other than cracks
    Spalling or separation of concrete, exposure or corrosion of reinforcement, fractures or pull-out of steel, honeycombs, discoloration of concrete, cold joints, gel, scaling, pop-out

Many samples (Pictures, illustrations) are prepared, so user can easily refer to accrual deterioration patterns by clicking the [References] button. This enables inexperienced inspectors to input, and eliminates differences among individual judgments. Stored image data corresponding to selected parts can be referred to from this screen. If the same conditions of deterioration are inputted in several parts,the initial input data can be copied to other members.

Fig 8: Input screen of Deterioration (Superstructure).

OUTPUT OF DIAGNOSIS RESULT

The estimated causes of deterioration from equation (1) are listed in order of descending priority (upper 5 causes), and deterioration levels, Pg are also evaluated. Figure 9 is the output screen for cause of deterioration, the bar chart in screen is obtained based on calculation sheet (Figure 3, 4). The first to fifth possible causes of deterioration can be displayed for each part, and cells instantaneously sort according to priority or category when upper and right side buttons are clicked. The option to display possibilities of deterioration causes for each part enables the user to check deterioration trend. The evaluated degree (4 levels) of deterioration is distinguished by using different colors (Figure 10). Some questions can be listed in order to confirm whether inputted data is correct or not. Actual cases related to estimated causes of arbitrary parts will be displayed.

Fig 9: Causes of deterioration (Prestressed concrete T-beam bridge). Fig 10: Evaluated deterioration levels (Prestressed concrete T-beam bridge).

Other options

  • Risk of injury to third parties
    Assessed risk of injury to third parties due to reasons such as spalling of concrete cover etc. can be outputted.
  • Suggestion for detailed inspection
    This software has the capability to suggest detailed inspections like concrete sampling or non destructive testing.

CONCLUSIONS

This paper describes a diagnostic method using an inspection software for deteriorated concrete bridges. This software would contribute to the maintenance system, and help engineers and authorities in maintenance procedures. For the future, some modifications will be made to improve the user interface or diagnosis logic. This system (with restricted capabilities) may also be accessed via internet,and the collected information from the users will be stored into a database. Accumulated data will then be utilized effectively.

ACKNOWLEDGMENT

This work was carried out jointly at Institute of Industrial Science, the University of Tokyo by 10 companies. The authors are grateful for supports from the following people: Dr. A. Moriwake (Toa Corporation), Mr. K. Kinoshita (CTI Engineering Corporation), Mr. O. Taniguchi (Penta-Ocean Construction Co.,Ltd), Dr. T. Nishikawa (Constec engineering, Co.), Mr. D. Sato (Constec engineering, Co.), Mr. K. Matsuyama (Nippon Koei Corporation), Mr. K. Hida (Chiyoda Engineering Consultants),Mr. T. Hikichi (Chiyoda Engineering Consultants Corporation), Mr. Y. Uno (Sato Kogyo Corporation), Mr. S. Abe (Zenitaka Corporation) and Mr. K. Kasai (Tobishima Corporation).

REFERENCES

  1. Uomoto T. , Diagnostic technology of concrete, Japan Concrete Institute, 2001 (In Japanese)
  2. Hazard map of freezing and thawing damage, Japanese Architectural Standard Specification "JASS 5 Reinforced Concrete Work", Architectural Institute of Japan, 1997 (In Japanese)
  3. Report of committee for research of alkali-aggregate reaction, Committee for research of alkali-aggregate reaction, Japan Concrete Institute, 1989 (In Japanese)
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