Essay on Bridge Inspection

To ensure that a bridge is in good condition and working properly it should be checked consistently for any faults. This giant structure contains deck of the bridge, approach slab, joints and railings. This can be further divided into small structural elements like bearings, beams, soffits, wing walls, abutment, cap and pile. During biennial inspection different critical areas are accounted for like rusting, joint movements, efflorescence staining and spalling. Snooper truck is needed for reaching tricky areas of the bridge which are hard to reach. Inspection and checking come with huge costs and delay cost due to traffic jam during inspection. There is also the risk of worker being injured in such high risk’s situations.

            To understand the primary causes of differential settlement at the bridge approach slabs, in depth studies were performed in the last decade (Briaud et al. 1997; Horvath 2005; Kramer and Sajer 1991; Puppala et al. 2009). Poor soil compaction, soil erosion, water infiltration beneath the 46 pavement, development of voids, and settlement of backfill material due to excessive overburden pressure are key factors of differential settlement at the bridge approach slabs. To evaluate and mitigate this problem several techniques such as excavation and replacement of fill material, deep soil mixing (DMS) columns, geosynthetic reinforcement, mechanically stabilized earth (MSE) wall, lightweight EPS Geofoam replacement, effective drainage and erosion control methods were recommended  (Abu-Hejleh et al. 2006; Bartlett et al. 2000; Dupont and Allen 2002; Farnsworth et al. 2008; Horvath 2005; Hsi 2008; Jutkofsky et al. 2000; Negussey and Stuedlein 2003; Newman et al. 2009; Puppala et al. 2008; Seo 2005; Stark et al. 2004; Tadros and Benak 1989; Wahls 1990; White et al. 2007). Extensive monitoring programs are required to certify performance of rehabilitated bridge structures. Structural health monitoring and performance evaluation are two main factors that ultimately shows the true picture of bridge infrastructure project. The two most used methods for monitoring infrastructure performance are Visual evidence and in-situ instrumentation.

            The most basic form of forensic survey is visual inspection. This approach helps If you want visual evidence of the condition of the infrastructure quickly. On the other hand, quantifying settlement or any other pavement distress using visual surveys depends on the operator’s observation. Examining bridge deck and its underneath requires two kind of inspections. There are multiple kinds of equipment available to inspect bridge deck. The most commonly used survey that can quantify the settlements at a bridge infrastructure is total station survey. A total station survey incorporates change in elevation levels with respect to different time periods. One of the non-destructive methods is Ground Penetrating Radar (GPR) which can replicate subsurface profile (Gehrig et al. 2004). This method is useful in determining the distress in pavement infrastructure and in detecting voids as demonstrated by researchers. In-situ instrumentation is another effective technique which includes horizontal inclinometers. The device that is used for monitoring distortions of surfaces or subsurface in a direction perpendicular to the axis of a flexible plastic casing by means of passing a probe through the casing is 48 an inclinometer. Horizontal inclinometer is used for measurement of the settlement and heave under the storage tanks, dams, and embankments typically (Archeewa 2010). There are seven parts that make a horizontal inclinometer. These parts include inclinometer casing, horizontal probe, pull-cap, pull cable, dead-end pulley, control cable and readout. These measurements are obtained at limited locations and does not represent the performance of the entire infrastructure. Due to this there is a chance of failure at any location despite using these methods. Now a day’s inspection techniques include many practices to reach the unreachable areas of the bridge. The platforms that help in inspecting the under-bridge elements include Aerial work platforms (AWP) such as snooper trucks, lifts, or bucket-trucks. There are some drawbacks of using AWP’s which include high mobilization costs, unsafe conditions for inspector and traffic delay costs arising out due to lane closures. Proper training is required for the inspector to be able to access rope. Lower equipment and traffic delay are also highly dangerous for the inspector (Wells et al. 2017).

            There are new remote sensing based technologies that are introduced that can help in monitoring the performance of bridge infrastructure. Light detection and ranging (LiDAR) technology is being used to monitor the performance of rehabilitated bridge infrastructure which is currently used by University of Texas Arlington research team located in Johnson County, Texas (Shafikhani et al. 2017) The LiDAR works by emitting laser light from the scanner and projects it onto the material surface via a rotating mirror, which then captures the reflected laser beam pulses from the surface. A “Point Cloud” is generated in 3D space in which each set of point contains data. Physical features of target points such as distance, colour and reflective intensity can be recorded by (Aggarwal 2004; Campbell and Wynne 2011). determining the unabsorbed wavelengths of laser light at each point on the surface. For instance, in total displacement vector of target point settlement or heave would be the vertical component.

UAV Applications in Bridge Studies- Case Study

            Metni and Hamel (2007) examined bridges using UAV systems and introduced strategy for autonomous flight using orientation limits (Metni and Hamel 2007). Michigan Tech Research Institute (MTRI) joined hands with Michigan DOT (MDOT) and used five different UAV platforms to examine two bridges, two pump stations, two traffic sites and roadway asset site. In figure 2-24a it describes the function of the rotary type UAV (Bergen Tazer 800 hexacopter), accompanied by Micchigan Tech Research Institute (MTRI) with a camera attached for effective aerial surveillance of pavements and bridges. Figure 2-24b also shows the captured high-resolution image from a Tazer 800 UAV equipped with a Nikon D800 DSLR camera (Brooks et al. 2015). Using a bergen Hexacopter paired with optical and thermal sensors they captured 89 high resolution pavements.

            Figure 2-25 Aerial Bridge Deck Inspection (a) Bridge Condition Data Collection using Bergen Hexacopter (b) Stereoscopic imagery (Brooks et al. 2015) MTRI also showed the credibility of using a rotary wing, DJI Phantom 2 for aerial surveys in challenging areas, such as the locations which are hard to reach like under bridges and in tight spaces (Brooks et al. 2015). In hard to reach areas DJI Phantom Vision 2 UAV was used with a camera (with the ability to take pictures and record videos to micro SD cards with a real time video link of up to 900 feet). It was used create photogenic inventories of sites which are in tight spaces. Structural defects are found in this manner by analysing the results of UAV (Brooks et al. 2015). Condition of Bridge (a) Bridge selected for UAV Assessment, and 9b) A High-Resolution Image Showing Spalling and Cracking (Brooks et al. 2015. UAV played a big part in reducing the cost of inspection. Using UAV MDOT managed to save around $4000 which is estimated to be 90% of the cost invested in standard procedures (Asphalt Institute 2016). Bridge Deck Inspection was made a lot easier with the use of this updated technology. It also considered the safety of the personnel and mitigated the risks. The spaces that were hard to reach can be inspected thoroughly for any rusting and cracking (Asphalt Institute 2016).