5.2 Development of Performance Measure for A Representative PA Bridge

5.2 Development of Performance Measure for A Representative PA Bridge Accurately predicting future performance of bridges is key to effective maintenance and rehabilitation decision making. One way to predict future performance of bridges and determine their remaining service life is to utilize deterioration models. In essence, relatively few indicators (such NBI Condition Rating and Elemental Condition States) have been adopted to determine the performance of bridge components. To that extent, the average performance of a typical bridge (similar to BEAST) in Pennsylvania is calculated based on the analysis of historical data available at the InfoBridge website (see Figure 39). To derive information for this representative bridge, the historical NBI deck condition ratings were analyzed for steel multi-girder bridges in PA (located in the Mid-Atlantic cluster) to mimic the structural characteristics of the BEAST specimen. As shown in Table 7, the average time-in-state (TIS) for each NBI condition rating (9 to 3) was separately estimated after proper levels of data cleaning. Two separate curves, one with the mean of TIS and one with the upper bound of TIS (mean + standard deviation) for each condition rating, were developed to define the region that the bridge performance will be most probably progressed in the perspective years. Figure 40 represents the performance of the deck component based on the deck condition rating. The two curves with light green color (one thick solid and one dashed) refer to the mean and upper predicted performance curves based on historical TIS data collected from PA bridges. At the same time, the figure represents the timing of BEAST data collection periods based on bridge age. The figure is instrumented with two vertical axes, where the left axis denotes the Deck Condition Rating and the right one is associated with the live-load traffic (ADTT). The dashed vertical lines refer to the scaled timing of data collection periods from BEAST. The skewed blue line depicts the increase of live load based on the data collection periods.

Figure 39. Distribution of multi-girder Steel Bridges in PA (color-coded based on deck condition)

Table 7. Average time-in-state (TIS) for each NBI condition rating Condition Rating TIS – Average TIS - Standard Deviation Performance Curve (TIS) Mean Upper Boundary

9 3.4 2.0 3.4 5.4

8 7 6 5 4 Total Life 7.7

6.4 7.7 14.0 10.7 7.1 10.7 17.8 8.0 5.8 8.0 13.8

6.0 4.3 6.0 10.3

4.4 3.1 4.4 7.5 40 69

Figure 40. Derivation of refined curve for the representative bridge based on BEAST visual inspection Given the space between the mean and upper performance curves is relatively large, potential exists for very high uncertainty in the reliability and accuracy of predictions of remaining service life in the BEAST experiment. Therefore, the condition rating acquired from the visual inspection reports conducted on the BEAST specimen were later used to refine the performance curve for realistic assessment. It shall be noted that the skewed blue line associated with the ADTT and scaling the time of data collection from BEAST was used to determine the scaled timing of visual inspection periods. The three datapoints shown with black (+) signs depict the scaled deck condition ratings derived from two rounds of visual inspection of the BEAST specimen. Reviewing Figure 40 reveals that the BEAST specimen has overperformed the representative PA bridge (with similar structural characteristics), however, it underperformed the upper boundary of the performance curve. To some degree, this observation ensures the reliability of the performance assessment and scaling of the BEAST experiment. The final