SECM/13/139 DEVELOPMENT OF A BRIDGE ASSESSMENT TOOL TO IDENTIFY CURRENT CONDITION OF REINFORCED CONCRETE AND PRE-STRESSED CONCRETE BRIDGES

Transcription

1 Special Session on Structural Health Monitoring, 4 th International Conference on Structural Engineering and Construction Management 2013, Kandy, Sri Lanka, 13 th, 14 th & 1 th December 2013 SECM/13/13 DEVELOPMENT OF A BRIDGE ASSESSMENT TOOL TO IDENTIFY CURRENT CONDITION OF REINFORCED CONCRETE AND PRE-STRESSED CONCRETE BRIDGES Kariyawasam K.K.G.D.D.L 1, Hemapala U.B.H.U 1, De Silva Sudhira 2 and De Silva Subashi 2 Department of Civil and Environmental Engineering, Faculty of Engineering, University of Ruhuna, Hapugala, Galle, Sri Lanka kdinushika@yahoo.com 1, sudhira@cee.ruh.ac.lk 2 3 and subashi@cee.ruh.ac.lk Abstract Sri Lanka has many reinforced concrete (RC) and pre stressed concrete (PC) bridges along the coastal region. The bridges along the coastal region have high risk of initiating corrosion, compared with the bridges in country side, due to high concentration of chloride iron and carbon dioxide in the surrounding area. The corrosion can cause to deteriorate the bridges. As a result, the bridges along the coastal region do not often achieve their design life. Unsafe structural elements can lead for the severe disasters and it may cause even death of people. Therefore, the bridges must repair, strengthen or replace at an appropriate time. Objective of this study is to develop a bridge assessment tool, which can be used to identify current condition of RC and PC bridges. Unsafe structural elements were identified through visual inspections and assessments. The current conditions of thirteen bridges in the coastal region from Matara to Bentara were assessed by using non-destructive tests: rebound hammer test, cover meter test and ultrasonic pulse velocity test. In addition, thirteen bridges were visually inspected and current conditions of several elements were recorded. A rating system was applied to define a soundness score for bridges. An assessment tool to identify current condition state and to predict required maintenance level was developed using field measurements and is discussed in this paper. Keywords: Corrosion, Current condition, Repairing method, Non-distractive test, Bridge management system 1.0 Introduction Bridges are lifelines of a nation s infrastructure and massive investments are being made in the highway sector year after year. During the last fifty years, day by day, there were a significant increase of number of reinforced concrete (RC) bridges and pre-stressed concrete (PC) bridges all over the country, especially in highway sector. Currently, major infrastructure projects are being made by the government to improve public transportation system. Deterioration of the bridges due to chloride attack is a significant problem in Sri Lanka. When considering reinforced and pre-stressed bridges, bridges are rapidly corroded along the coastal region compare with those in the country side. As expected, this is because in the coastal region the chloride iron and carbon dioxide concentrations are very high.the chloride process initiates with the penetration of aggressive materials (chloride iron and carbon dioxide) in to concrete. When the steel reinforcement bars corrode, it creates expansive stresses, which cause for cracking and reinforced exposures. Then corrosion process is accelerating by 7

2 entering water, oxygen and chloride ions easily. Corrosion process causes the reduction of service life (Jerzy, 1). Figure 1: Reinforced exposures (deck soffit) Due to high construction cost and replacement cost, maximum utilization of service period is essential for bridges. Therefore, the bridges must be repaired, replaced or strengthened with time to time. Unsafe structural elements can lead for the severe disasters and it may cause death of several people. Unsafe structural elements can only be identified through time-to-time inspections and assessments. The bridge management systems, which are developed, based on the bridge structural engineering, mechanism of disease detection and geographic information systems, offers economic and technical convenience for the supervision and maintenance of a bridge. All Bridge Management Systems rely primarily on Inventory data and Inspection data.inspection data needs to be updated on a regular basis. Most bridge management systems in the world rely on visual inspections as their primary data source to determine the condition of a bridge. Periodic bridge inspection systems are required to obtain better safety for existing structures, it is necessary to assess the current performance of the existing structures (Elbehairy et al (2007)). Then replacement or repairing can be determined based on the inspected or predicted results. The purpose of the bridge management system (BMS) is assuring the safety of the bridge by using current condition and repairing method. Objectives of this study are To evaluate current condition state of bridge using non-destructive testing and apply a rating system to define a soundness score for bridge To develop bridge assessment tool to identify current condition state and introduce possible repairing methods 2.0 Methodology 2.1Current Condition Assessment The current conditions of existing reinforced concrete (RC) and pre-stressed concrete (PC) bridges were assessed by using non-destructive tests. Ultrasonic pulse velocity test, rebound hammer test and cover meter test were used as the non-destructive tests. A detailed inspection sheet was prepared for recording the visual inspection details. Inspections were carried out for thirteen bridges located along the coastal belt from Bentara to Matara. When conducting all the visual inspection detailing and non-

3 destructive tests, the element area was divided in to 1m 2 grid areas and measuring was done area wise to increase the accuracy of inspection details. The structural condition and performance were predicted based on soundness score. The soundness score of a structural element depends on the current condition of the structural element and element significant factor. The current conditions of the structural elements were rated according to National Bridge Inventory (NBI) specifications. Then, the NBI rating system was applied to define a soundness score for the critical elements (Equation 1). The bridges were categorized as bridges with piers and bridges without piers for the purpose of applying element significant factor in calculating soundness score. Element Soundness score value(ess) = Element Significant Factor Rating value (1) Then the overall Soundness value for bridge was calculated according to Equation 2. Overall Soundness score value (OSS) = Element Soundness score value (2) Four elements (Barrier & footway, abutment, deck and piers) were selected as critical elements in a bridge. Element Significant Factor (ESF) was assigned based on their priority defined by Rashidi and Gibson (2011) (Table 2). Table 1: Element significant factor (Rashidi and Gibson, 2011) Element Element significant factor (ESF) Barrier, Footway 1 Abutment 2 Deck 3 Piers 4 The current condition and the required level of treatment of bridges without piers and bridges with piers were predicted based on the calculated overall soundness score value and comparing them with the values published in a previous study (Pradeep et al, 2010) (Tables 2 and 3). Table 2: Bridge soundness score values and treatment requirement for bridges without piers (Pradeep et al,2010) Bridge soundness score Treatment requirement 4-4 No treatment required Simple maintenance techniques required (Patching Repair) 3-24 Special maintenance techniques required (Cathodic protection) Immediate maintenance techniques required (Retrofitting Techniques) 11> Replacement

4 Table 3: Bridge soundness score values and treatment requirement for bridges with piers (Pradeep et al, 2010) Bridge soundness score Treatment requirement 0-0 No treatment required 7-60 Simple maintenance techniques required (Patching Repair) -40 Special maintenance techniques required (Cathodic protection) 3-20 Immediate maintenance techniques required (Retrofitting Techniques) 1> Replacement Visual Inspection When conducting visual inspection, initially, element of the bridge which is expected to inspect was divided in to 1m 2 grid areas. Then visual defects (i.e., concrete stains, radial cracks, spalling and reinforced exposure) in the bridge were recorded in visual inspection sheet area wisely. Also bridge information such as bridge number, bridge name, location, bridge type, road name were recorded in bridge information sheet. Reinforced exposures and spalling area were considered as most significant factors that would be the critical indicator of the condition of bridge Non-Destructive Test Method (a)ultrasonic pulse velocity (b) Trance meter and receiver (c) Rebound hammer receiver (d) Cover meter (e) Crack gauge Figure 2: Non-destructive test instruments Non-destructive tests were also carried out area wisely, similar to the visual inspections. 0

5 Ultrasonic pulse velocity test Initially, the trance-meter and receiver were kept at 0.3 m distance away (Figure 2(b)) and then travelling time to the pulse was measured (Figure 2(a)). Pulse velocity was calculated by using known distance and time. Rebound hammer test Rebound hammer test was carried out by pressing rebound tip on the concrete surface (Figure 2(c)). When tip was compressed on concrete surface, it rebounds and shows rebound number and the related compressive strength of concrete. Compressive strength value for the rebound number was also determined by referring the graph given with the equipment. Cover meter test When the instrument (Figure 2(d)) was kept to the concrete surface, the device produces a magnetic field and locates the reinforcing steel. To locate the exact position of reinforcement bar, cover meter was moved along the surface until the bar coincides with the cross hair in the instrument. Then it was digitally measured the bar size and the depth of cover. Crack width measurements Crack width was measured by using crack gauge (Figure 2(e)). Most significant crack type was selected as the crack type of element. 2.2 Development of bridge management system (BMS) The procedure of developing BMS is shown in Figure 3. BMS application was developed by using Netbeans 6. and MySQL.2. The MySQL.2, the most popular Open Source SQL database management system, which is developed, distributed, and supported by Oracle Corporation, was used as a database to store input parameters, rating values, element significant factors, which were needed for calculations. Netbeans 6. was used to develop bridge management system. Netbeans 6. is a modular, standards-based integrated development environment (IDE), written in the Java programming language. The Netbeans project consists of a full-featured open source IDE written in the Java programming language and a rich client application platform, which can be used as a generic framework to build any kind of application. All the important parameters (i.e. element significant factors, rating values) were stored at the database and these parameters were dynamically loaded to the application for calculations. Bridge number,bridge name, location, bridge type, road name, number of spans,distance from the beach, number of lanes, surrounding temperature,date of construction and date of inspection were considered as bridge information. Figure 4 shows the bridge information-entering window. 1

6 Start Step 1: Logging to the tool by authorize person Logging False Exit Step 2: Entering bridge information True Bridge Information (Refer Figure 4) Next Add Add Step 3: Entering area Area Calculations (Refer Figure ) (Length and Width) Next Step 4: Entering non- Non-distractive Test Results Add distractive test results, crack details and Next Add visual inspection details Crack Details Next Visual Inspection Details Add Step : Calculations Element Significant Factors (Refer table 1) Of Elements and Ratings (Refer2.2.4) Database OSS Current Condition Repairing Method (Refer Tables 2 and 3) Figure 3: Procedure of developing BMS tool 2

7 Bridge Information Figure4: Bridge information entering window Area Calculation Dividing the selected element area into 1m 2 pieces is called as area calculations. It is important when entering inspection and non-destructive test results to enhance the accuracy of output of BMS. Figure shows the Area calculation window. Non-Distractive Test Result Entering Figure : Area calculation window After performing the area calculations, inspection data (as in three categories) were entered into the system area wisely. Inspection data were divided in to three categories: parameters obtained from non-distractive test, crack details, and information gathered from visual inspection. Parameters obtained from non-destructive methods were compressive strength, pulse velocity, reinforcement bar diameter and clear cover. Crack type, crack width, crack length and crack depth were considered as crack details. As the information gathered from visual inspection, vegetation cover, surface staining and bleed marks, reinforcement exposures, spalling were considered. Data entering window was used to enter the above data in to BMS. All the input data were stored in the database (Figure 6) 3

8 Figure 6: Stored data table in database Evaluation of the Current Condition State in BMS Table 4: Condition state ratings Rating values Condition Compressive strength (N/mm 2 ) Pulse Velocity km/s Crack Description Crack width (mm) Spalling R/F Exposures Excellent >=4 >4.0 No cracks 0 No No Very good 40-4 >4.0 Minor transverse cracks with no deterioratio n <1 No No 7 Good Sealable bridge cracks 1-2 No No 6 Satisfactory Excessive number of open cracks in bridge 2-3 No Less than 0% of the area is deteriorated. Rebar exposed. Fair condition Excessive cracking >3 % element area Less than 0% of the area is deteriorated. Rebar exposed 4 Poor condition Measurable structural cracks >3 <% element area More than 0% of the area is deteriorated. Rebar 4

9 exposed Serious condition Critical condition Imminent failure condition Failed conditions > < > < > >4.0 large structural cracks Numerous large structural cracks may be present. Full depth failure Extensive full depth failure >3 >3 >3 >3 <% element area <% element area <% element area <% element area More than 60% of the area is deteriorated. Rebar exposed. More than 60% of the area is deteriorated. Rebar exposed. More than 60% of the area is deteriorated. Rebar exposed. More than 60% of the area is deteriorated. Rebar exposed. A rating value for each element was determined by considering initial rating values (i.e., R1 to R6).Initially rating values (R1 to R6) were calculated based on the structural properties obtained from non-destructive tests. Rating value, R1, was assigned based on the average strength value as listed in Table 4. This method has also been used in a previous study by Pradeep et al (2010). The average strength of the element was calculated according to the Eq (3). Average Strength = Area Strength per area Total Area (3) Rating value,r2, was determined by comparing the average pulse velocity and the values listed in Table 4 (National Bridge Inventory US, 1).The average pulse velocity of each element was calculated according to Eq (4), by substituting the average pulse velocity measured in each 1m 2 area by using Rebound Hammer test.. Area Average pulse velocity per area Average pulse velocity = (4) Total Area

10 Rating value, R3, was determined by comparing the crack type and the details of the cracks listed in Table 4 (National Bridge Inventory US, 1). Most significant crack width was selected as a crack width of element. By comparing these values with the crack width listed in Table 4, rating value, R4, was determined. A similar method to determine R4 rating was used, in a previous study (Colorado Department of Transportation-BMS/Points Bridge Inspection Manual) Rating values, R and R6, were determined by comparing the reinforced exposures and spalling, respectively, by comparing the values obtained from the visual inspection, and the values recommended by the National Bridge Inventory US, (1) (Table 4) Average of R1, R2, R3, R4, R, and R6 was determined and considered as element rating value. The element soundness score value and overall soundness score value of the bridge were calculated according to the Equations 1 and 2. The required level of treatment was c determined according to the overall soundness values as shown in Tables 2 and Results and Discussion 3.1 Current condition assessment Collected bridge information details of inspected bridges along Benthota Matara (A2 road) such as bridge no, location, bridge type, number of spans, distance from the beach, number of lanes are shown in Table. Table : Bridge information No Bridge no Location Bridge type Number of spans Distance from the beach (m) Number of lanes 1 13/4 Matara /1 Mirissa With 3 14/2 Mirissa piers 4 41/ Weligama /4 Weligama /1 Ahangama /1 Benthota / Benthota /2 Koggala Without Mahamodara piers Gintota /2 Gintota Ambalangoda The average value of compressive strength and pulse velocity, significant crack type and width of element and reinforcement exposure and spalling area determined from are wise measurements collected from non-destructive tests are shown in Tables 6,7, and, for piers, deck, abutment, barrier (and footway), respectively. 6

11 No Spalling Table 6: Non-destructive and visual inspection details for Piers R/f exposures Crack type and width Pulse velocity (km/s) Compressive strength (N/mm 2 ) Seable bridge crack (1.2mm width > > Excessive number of open cracks in bridge (2.2 mm width) No cracks Minor transverse cracks with no - - deterioration( width<1) No cracks Minor transverse cracks with no deterioration( width<1) No Spalling Table 7: Non-destructive and visual inspection details for Deck R/f exposures Crack type and width Pulse velocity (km/s) Compressive strength (N/mm 2 ) > > Minor transverse cracks with > no deterioration( width<1) > > > Seable bridge crack (1.2mm >4.0 7 width - 43 Seable bridge crack (1.2mm >4.0 0 width Excessive number of open cracks in bridge (2.2 mm width) Minor transverse cracks with >4.0 0 no deterioration( width<1) Development of tool The developed BMS tool is capable in calculating overall soundness score value according to the parameters entered into the system. BMS gives the current condition and the repairing method based on overall soundness score value as shown in Tables 2 and 3. The developed bridge management system was validated by comparing output of BMS with the current condition assessment. When validating BMS, the bridges, whose current conditions were known, were compared with the current 7

12 condition determined from BMS (Tables 10 and 11).It was found that BMS gives the equal condition (100% equal level of treatment). The rating values and for each element and overall soundness score for each of bridges with piers and bridges without piers are presented in Tables 12 and 13, respectively. In addition, in these tables Required level of treatment is also summarized. Table : Non-destructive and visual inspection details for Abutment No Spalling R/f exposures Crack type and width Pulse velocity (km/s) Compressive strength (N/mm 2 ) > >4.0 Minor transverse cracks with no > deterioration( width<1) > > > Seable bridge crack (1.2mm width) > Excessive number of open cracks in bridge (2.2 mm width) No cracks Minor transverse cracks with no > deterioration( width<1) No cracks Table : Non-destructive and visual inspection details for Barrier/ Footway No Spalling R/f exposures Crack type and width Pulse velocity (km/s) Compressive strength (N/mm 2 ) > >4.0 Minor transverse cracks with no > deterioration( width<1) > > > Seable bridge crack (1.2mm width) > Excessive number of open cracks in bridge (2.2 mm width) No cracks Minor transverse cracks with no > deterioration( width<1) No cracks 3.3 2

13 Table 10: Rating values of each element for bridges without piers determined from developed BMS tool Bridge no Bridge element rating value Deck Abutment Barrier R1 R2 R3 R4 R R6 R1 R2 R3 R4 R R6 R1 R2 R3 R4 R R Table 11: Rating values of each element for bridges with piers determined from BMS Bridge no R1 7 R2 7 Pier R3 R R R6 6 R1 7 Bridge element rating value Barrier Abutment R2 R3 R4 R R6 R1 R2 R3 R4 R R6 7 R1 7 R2 7 Deck R3 R R R6 2

14 Table 12: Average rating value of each element, overall soundness score and required level of treatment for bridges without piers Bridge no Average rating value Deck Abutment Barrier OSS Required level of treatment No repairing Table 13: Average rating value of each element and overall soundness score of each element for bridges with piers Bridge no Average rating value Piers Deck Abutment Barrier OSS Required level of treatment Simple maintenance Simple maintenance Special maintenance No repairing Simple maintenance No repairing No repairing 4.0 Conclusions Unsafe structural elements were identified through inspections and assessments. Bridge management system was developed by using Netbeans software developer to identify current condition and repairing method of RC and PC bridges, without performing manual calculations. The current conditions of reinforced concrete (RC) and pre-stressed concrete (PC) bridges located in the coastal region from Bentara to Matara were evaluated by using non-destructive tests: ultrasonic pulse velocity test, rebound hammer test and cover meter test. In addition, crack type, crack width, crack length and crack depth, vegetation cover, surface staining and bleed marks, reinforcement exposures area, spalling area, were measured through visual inspections. Soundness score value was defined by considering collected inspection details. The structural condition and repairing method can be predicted from the developed Bridge Management System (BMS) based on overall soundness score. Reference Colorado Department of Transportation., BMS/Points Bridge Inspection Manual, Colorado Dept. of Transportation, Denver, USA,1. 100

15 Elbehairy H., Bridge Management System with Integrated Life Cycle Cost Optimization, University of Waterloo, Ontario, Canada, Jerzy Z., Modeling the Time to Corrosion Initiation for Concretes with Mineral Admixtures and/or Corrosion Inhibitors in Chloride-Laden Environments, Virginia Polytechnic Institute and State, University, Blacksburg, Virginia, 1. Pushpakumara, B. H. J., Sudhira De Silva and Subashi De Silva, G. H. M. J., Condition Assessment and Service Life Prediction of Reinforced Concrete Brides Exposed to Chloride Environment, Proceedings of the Second Annual Sessions,Society of Structural Engineers,Sri Lanka (SSE- SL),pp63-70,2012. Rashidi, M. and Gibson, P., Proposal of a Methodology for Bridge Condition Assessment, Proceedings of the Australasian Transport Research Forum, September 2 - September 30, Adelaide, Australia, Pradeep, L., Sudhira De Silva and Nawarathna,C (2010), Structural Assessment of Reinforced Concrete Bridge Structures Exposed to Chloride Environment, International Conference on Sustainable Built Environment (ICSBE-2010),Kandy, December 13- December 14, 2010, pp40-47,2010. Chase. S.B., Small E.P. and Nutakor C., An In-Depth Analysis of the National Bridge Inventory Database Utilizing Data Mining, GIS and Advanced Statistical Methods, TRB Transportation Research Circular 4, C-6,1. 101