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A-1 APPENDIX A USERS MANUAL A-2 CHAPTER 1 System Description Description, A-2 Major Components, A-2 A-3 CHAPTER 2 Fabrication Introduction, A-3 Crane and Truck, A-3 Instrumentation to Monitor Crane Position, A-4 Scour Measurement Devices, A-8 A-12 CHAPTER 3 Application Guidelines FHWA Scour Monitoring Guidance, A-12 Application of the Articulated Arm Truck, A-12 A-15 CHAPTER 4 Operational Guidelines Data Collection, A-15 Typical Sequence of Events to Collect Data, A-16 A-19 CHAPTER 5 Troubleshooting, Maintenance, and Servicing Troubleshooting, A-19 Maintenance and Servicing, A-19 A-20 CHAPTER 6 Enhancements CONTENTS
CHAPTER 1 SYSTEM DESCRIPTION DESCRIPTION The articulated arm truck described in this document was the result of research conducted under NCHRP Project 21-07, Development of Portable Scour Monitoring Equipment. The research concentrated on developing a truck-mounted articu- lated crane to quickly and safely position various measurement devices. The use of a crane for scour monitoring provided a solid platform for deployment, even under flood flow condi- tions, that could be instrumented to allow precise measurement of the movement of the crane. NCHRP Report 515 provides detailed findings from this research project and the interpreta- tion and appraisal of information developed from detailed field testing. The articulated arm truck was designed using readily avail- able components whenever possible. These components and pieces were also designed to be a bolt-on installation, so that the articulated arm truck could be readily used for other pur- poses outside of the flood season. In fact, many transportation agencies already have articulated arm trucks that could be retrofitted for scour monitoring work based on the design con- cepts developed through this research. The articulated arm truck can be used in various ways to collect scour data. Once in the water, the crane can be rotated in an arc to collect sonar data on a continuous basis upstream of the pier. The truck can also be driven across the bridge with the crane extended to collect a cross-section profile quickly. Traditional cable-suspended techniques can be used with the crane when working off higher bridges. Figure A1 illustrates the application of the articulated arm truck on a bridge during a scour measurement. The articulated arm truck provides improved deployment, positioning and data collection procedures for portable scour monitoring work, particularly under adverse conditions. These measurements can be completed from a variety of bridge geo- metries (e.g., limited clearance, overhanging geometry, and high bridges) using a truck that is affordable and maneuver- able. The data collection process is automated, and the scour data are presented in the bridge coordinate system, thereby allowing rapid evaluation of scour criticality. Overall, the abil- ity to make portable scour measurements during flood flow conditions has been substantially improved through develop- ment of the articulated arm truck. MAJOR COMPONENTS The articulated arm truck consists of four major compo- nents: a truck with an articulated arm crane; instrumentation A-2 to monitor the position of the crane in space; instrumentation to measure scour depth; and, computer software to collect, process, and present the results. The articulated arm truck consists of a standard knuckle boom or folding crane typical of the construction industry. The crane was mounted on a Ford F-450 truck chassis. Various tool boxes and storage compartments were added to the flatbed truck to store instrumentation used to collect data. In order to evaluate the potential risk associated with a mea- sured scour depth, it is necessary to know the location of the measurement, particularly relative to the bridge foundation. Therefore, various sensors are used to track the movement of the articulated arm in space, so that the location of the end of the crane is always known. Scour measurements are completed based on both sonar and physical probing methods. Sonar methods were developed around a new, wireless sonar that eliminates the need for any cables from the transducer to the bridge deck. Physical prob- ing methods were based on a simple rod at the end of the crane, the location of which is known in space by the sensors used to track crane movement. Comprehensive data collection software programs were developed to facilitate the use of the articulated arm, provid- ing the inspector with immediate access to the data collected. Collection of position and scour data is automated, and a data file is written that allows subsequent plotting of the channel section or scour hole bathymetry. Figure A1. Articulated arm truck making a scour measurement.
A-3 CHAPTER 2 FABRICATION INTRODUCTION The articulated arm truck was designed around readily avail- able parts and components to facilitate design, operation, and maintenance, and to control cost. However, some special fab- rication and machine shop work was necessary, and the sensors and instrumentation required custom design and construction. The purpose of this chapter is to provide detailed infor- mation on the components used and the fabrication required to develop the articulated arm truck that resulted from NCHRP Project 21-07. Adequate information is provided to allow a competent shop to build a similar articulated arm truck. To facilitate building the truck, a list of suppliers used is provided in Appendix A, although similar products would also be available from other sources. Given that much of the fabrication and construction is specific to the truck and crane selected, some of the information and details provided would need to be adapted for the specific equipment selected or available for use. CRANE AND TRUCK Crane Selection The cranes commonly used in the construction industry typ- ically are designed to handle large weight but with limited extension. In contrast, for scour monitoring the crane needed to reach long distances, without having to manage much weight or force. It was also desirable to work with a smaller crane that could be mounted on a smaller truck. These criteria were devel- oped in part to improve maneuverability and in part to mini- mize lane closure and traffic control issues. For research and development, a Palfinger PK4501C crane was used (Figure A2). This crane has a 600 lb (270 kg) lift at 36 ft (11 m) and was small enough to be mounted on a Ford F-450 truck chassis. A larger crane with more lift would be acceptable, as long as it also had a long reach. The long reach is necessary to be able to work off of higher bridges. Based on the reach of the PK4501C crane, mounted with an offset to the center of the truck, the PK4501C can reach 21.25 ft (6.5 m) below the bridge deck when the truck is a maximum of 35 in (0.3 m) from the edge of the bridge. This reach is to the end of the crane, prior to adding any extensions for sensor mounting. Figure A3 summarizes the geometric capabilities of this crane when mounted on a Ford F-450 truck. Cranes with similar capabilities are also available from other manufacturers. Crane Mounting Location The most common location for a crane is immediately behind the cab of the truck. An alternative location is at the back of the truck, behind the rear axle. A rear mount puts more load at the back of the truck and can cause weight dis- tribution problems if the truck is also carrying substantial weight on the flat bed. The advantage of the rear mount is the better clearance around the truck, because the cab is not in the way. For purposes of scour monitoring, with no substan- tial weight being transported on the truck bed, a rear mount seemed advantageous (Figure A4). However, mounting behind the cab would be acceptable, particularly if that loca- tion is more desirable for other lifting operations that the truck might be used for when not being used for scour monitoring. High-Load Castors Data collection with the crane extended was desirable for measuring a channel cross section. Many under-bridge inspec- tion trucks have counterweights and/or high-load castors to allow truck movement when the crane arm is extended. To permit this type of operation with this crane, a castor design was developed based on an arm that could be lowered under the outrigger foot pad. The castor was a 10 in. (25.4 cm) urethane wheel with a 4,200 lb capacity at 6 mph. The wheel was permanently attached to the arm, with the arm providing the lateral support necessary after the outrigger was lowered onto the castor. When not in use, the arm was raised and bolted to the truck frame, and a safety chain was attached. Figure A5 shows the castor system and its dimensions. The smaller truck chassis used in the research did minimize the cost of the vehicle itself, however, a larger truck also offers advantages. The F-450 used in the research was not large enough to handle even the lightweight crane selected without hydraulic stabilizers. As an alternative, a larger truck chassis might be able to handle the lightweight crane selected for the research without the outriggers and the additional cost and complication of the castor system. Modifications to the Rotator The ability to provide pan and tilt operations at the end of the crane was considered a valuable feature for positioning instrumentation. Pan operation could be accommodated using
A-4 Figure A2. Palfinger PK4501C Crane. a standard hydraulic rotator, often used with construction equipment on the end of a crane. The rotator used was a Kinshofer Liftall Model KM 04 F (Figure A6). Most rotators are designed for 360-degree, continuous rota- tion at a fairly high speed. Continuous rotation for scour mon- itoring applications was not desirable, given that the operator might accidentally tear off cables connected to transducers, and high-speed operation would complicate precise position- ing and could result in possible impact damage when in close proximity to the bridge. To solve this problem, flow restric- tors were used in the hydraulic lines to slow the motion. The movement of the rotator was tracked with a 10-turn poten- tiometer, with a readout on the computer software to prevent overrotation. Mounting the 10-turn potentiometer to the rotator, without drilling into the rotator housing, required fabricating a special mounting bracket. The bracket was made of aluminum and designed as a compression fitting around the perimeter of the rotator. The potentiometer was mounted in this bracket and measured rotation by a sprocket attached to the shaft of the rotator (Figure A7). Standard rotators are also designed to hang from the crane on a pin connection, so that the rotator is always positioned vertically, regardless of the angle of the crane arm. Therefore, providing tilt capability required modifications and special fabrication. An additional hydraulic cylinder and custom- fabricated brackets were added to the rotator to provide the tilt action (Figure 7). The tilt was designed to provide about 35 degrees toward the bridge and about 10 degrees away from the bridge, when the crane is positioned vertically over the bridge rail. The mounting bracket for the rotator was attached to the end of the crane, which extended the reach of the crane by 1.5 ft (0.46 m). Modifications to the Truck Flat Bed The modifications to the truck bed included adding ladders on both sides to facilitate access, adding toolboxes and storage compartments, building the workstation area for the computer and instruments, and relocating the hydraulic controls to the flatbed. Figure A8 shows the tool boxes and sizes that were added to both sides of the truck. These boxes provided ample storage room for all the equipment and sensors necessary. The hydraulic controls for an articulated crane typically are located next to the crane, thereby allowing operator ac- cess while standing on the road. Some models, including the Palfinger PK4501C, have dual controls allowing operation from either side of the truck. These controls were removed and relocated to the flatbed to improve safety and to provide bet- ter visibility of river conditions for the operator. The controls were moved to a position at the back of the flatbed, a work- station was fabricated on the flatbed to provide a shelter for the computer, and a seat was installed on the bed (Figure A9). Other equipment added included safety equipment. A dual- bulb yellow warning light was installed at the top-center of the truck rack behind the cab (i.e., Code 3 Inc., 420 Beacon Warn- ing Light SAE W397W5-1 98). A second single-bulb warning light was installed on a post on the back left (driverâs side) of the truck bed (i.e., Whelen Strobe Model 2012 series). A large 12-volt battery was installed in a steel box at the back of the truck, with a with a battery isolator to allow recharging from the engine alternator. This battery was used to power a 1000- watt invertor (i.e., Vector Model VEC049) in the instrument shelter and the winches used for cable-suspended work. INSTRUMENTATION TO MONITOR CRANE POSITION Various sensors were installed on the truck and crane to allow geometric calculation of the position of the end of the rotator. An articulated crane provides a very stable platform to deploy scour measurement devices, but it does not provide any positioning information without the addition of other sensors to track the movement of the crane. The sensors used included various devices to measure tilt angles and linear displacement. Sensors were required both at the end of the crane and on the truck itself, requiring two instrument boxes. The instru- ment boxes contain the power supplies, electronics necessary to operate each sensor, and a data logger to receive sensor data. An instrument box mounted at the end of the crane was used for the crane-end sensors and was designed to be removable for transit. The instrument shelter mounted on the bed of the truck, designed to hold the computer, was used for the sensors on the truck itself. Crane Rotation The rotation of the crane was measured with a 50 in. (125 cm) linear environmentally sealed draw wire (i.e., Unimeasure
A-5 Figure A3. Reach below the bridge deck with the PK4501C crane on a Ford F-450 truck. Inc., Model HX-P510-50-E3). The draw wire was routed around a 15-in (38-cm)-diameter circular plate mounted near the base of the crane (Figure A10). The circular plate was made from ultra-high-molecular-weight (UHMW) polyeth- ylene. The draw wire housing was permanently mounted to a bracket on the truck bed, and a groove on the edge of the plate kept the draw wire in place as the crane rotated. Crane Deflection Angle and Extension Tilt meters were used to measure the deflection angle of the crane arm and the rotator arm (i.e., Cline Labs, Inc., Elec- tronic Clinometer). The tilt meter for the crane arm was mounted inside the instrument box attached to the end of the crane (Figure A11). The tilt meter for the rotator arm was
attached directly to the support bracket fabricated to allow tilt- ing the rotator (as described above). A 400 in (10 m) environmentally sealed draw wire (i.e., UniMeasure Inc., Model HX-P510-400-E1) was used to measure the linear extension of the arm. The draw wire was mounted to the instrument box at the end of the crane and attached to a fixed mount near the top of the crane by a light- weight chain (Figure A12). Tilt data for the crane and rotator, the azimuth of the rota- tor, and the linear extension of the arm were transmitted by a MaxStream radio modem from an instrument box at the end of the crane that also transmits sonar data. The data were pre- processed with a Campbell CR10 data logger prior to trans- mission to the computer on the truck (Figure A11). Tracking the Position of the Truck on the Bridge Deck Tracking the position of the truck on the bridge deck was the last piece of geometric information necessary to locate the scour measurements accurately. Given that the truck would always be positioned as close to the curb line or barrier rail as A-6 possible, and given that the bearing of the bridge is a known quantity, the only real location information necessary was the distance the truck had been driven across the bridge and the ele- vation of the truck. The elevation of the truck could be estab- lished from the elevation of the bridge deck, as given on bridge plans, and the height of the truck bed above the bridge deck. Therefore, the primary field measurement necessary to locate the truck was simply the distance the truck had traveled across the bridge deck. This was accomplished with a standard survey measuring wheel attached to the back of the truck (Fig- ure A13). Pulse counters were added to the wheel and con- nected to the Campbell CR10 data logger to register the distance traveled electronically. Figure A4. PK4501C crane mounted on the back of a F450 truck. Figure A5. Castor system. Figure A6. Standard rotator (prior to modifications to allow tilt). Figure A7. Rotator after modifications to provide tilt.
Water Surface Elevation An acoustic stage sensor (i.e., STI Automation Sensors, Inc., Model U550-PV-CP-3N-ARR2-AK-H2) was used to measure the distance to the water surface (Figure A14). The stage sensor was mounted on an extendable arm to allow it to be positioned beyond the bridge rail with a clear view of the water. Position Calculation The Campbell CR10 data logger at the end of the crane col- lected the tilt data for the crane and rotator, the azimuth of the rotator, and the linear extension of the arm. These data were transmitted by the wireless radio modem to the computer on the bed of the truck. A second Campbell CR10 data logger at the computer workstation on the truck collected the data on crane rotation, distance traveled, and water surface elevation. Figure A15 shows the inside of the computer workstation with A-7 Figure A9. Instrument shelter for computer and relocated hydraulic controls. Figure A10. Draw wire attachment to base of crane. Figure A11. Instrument box at the end of the crane. Figure A8. Truck bed and toolbox dimensions. the wireless modem receiving data from the end of the crane, the Campbell data logger for the truck data, the voltage con- vertor for the acoustic stage sensor, and the DC-AC invertor. A laptop computer would be placed on the foam inside the instrument box for data collection and processing. The com- puter must have two serial ports to process the information from each data logger, sent as serial data strings. A PCMCIA serial card was used to provide the second serial port. Geo-
A-8 metric calculation of the position of the crane was predicated on keeping the top arm of the crane horizontal, because this provided the reference point for all calculations. Knowing the rotation of the crane and the rotator, the deflection angle of the vertical arm of the crane, the deflection angle of the rotator, and the extension of the crane arm allowed calculation of the position of the end of the rotator relative to the center pivot of the crane where it mounted to the truck bed. With the truck position defined on the bridge deck, the location of the crane in space could be completely described. SCOUR MEASUREMENT DEVICES As developed, the instrumented, articulated crane could be used to position various scour measurement devices, both directly from the end of the crane and from cable-suspended methods using the winches. Sonar could be deployed from the end of the crane or as a cable-suspended operation, while direct probing was possible off the end of the crane. Streamlined Sonar Probe To provide sonar measurement capability, a sonar instru- ment with embedded microelectronics was selected (Fig- ure A16). With the transducer element and signal processor in the transducer head, a separate readout device was not neces- sary. The signal from the depth transducer was processed inside the sensor and directly output as a serial data string of depth and temperature. The serial data output of the sonar was connected to the same Campbell CR10 data logger used at the end of the crane to collect position information. Given that information from this data logger was transmitted by the wireless modem (as shown in Figure A11), this eliminated having to route any electronic cables for the sonar from the water surface to the bridge deck. The sonar used was manufactured by Airmar Technology, Inc., and was an 8-degree, 200-kHz transducer. Given the desire to operate at flood conditions with high velocities, a streamlined probe was built to position the sonar Figure A15. Inside view of instrument shelter on truck bed. Figure A12. Draw wire to measure the extension of the crane. Figure A13. Surveyorâs wheel attached to back of truck. Figure A14. Acoustic stage sensor.
transducer directly in the water using the articulated arm. The probe was fabricated from a section of helicopter blade (Fig- ure A17) and proved to be very stable when placed in high- velocity flow during field trials. The streamlined probe eliminated the vortex shedding problems of a simple cylinder- shaped rod exposed to high-velocity flow. Helicopter blades are generally available from helicopter service companies who must routinely replace the blades or blades are available as a result of damage to a portion of the blade during use. Although various sizes and shapes are used on helicopters, the actual dimensions used when fabricating a sonar probe are not crit- ical. For example, the blade used for research was 1.75 ft (0.53 m) long; however, any given helicopter blade would per- form in a similar manner by improving the flow streamlines around the sonar transducer. A-9 The fin on the streamlined probe could freely rotate, which allowed the fin to follow the current, no matter what horizon- tal angle the crane was positioned in. The fin was attached to an 80 in. (2 m) by 2 in. (125 mm) Schedule 80 stainless steel pipe. Given the distance the crane could reach below the bridge deck (21.25 ft or 6.5 m) and the length of the rotator mounting bracket (1.5 ft or 0.46 m), the crane could reach nearly 30 ft (9.1 m) below the bridge deck for a sonar measurement. Physical Probing To provide physical probing capability, an extendable rod was fabricated. The rod extensions were built with 2 in (125 mm) stainless steel, Schedule 80 pipe in 5 ft (1.5 m) lengths, allowing a total length up to 15 ft (4.5 m). Threaded unions were machined to allow individual sections to be screwed together to create the longer extensions. Using the articulated crane for physical probing is most appropriate in a gravel/cobble bed or to evaluate riprap conditions, given that the strength of the crane hydraulics makes it difficult to know exactly when the channel bottom is reached. Kneeboard on Rigid Frame A kneeboard with a wireless sonar was also developed that could be deployed from either a rigid framework attached to the rotator or as a cable-suspended operation. The sonar with the electronics built into the transducer was used, and a small enclosure was fabricated (from 6-in. PVC pipe) for the knee- board to hold the battery and radio modem (Figure A18). It was difficult at times to get the kneeboard positioned on the water surface, but, once in place, it could be readily moved for- ward and backward under the bridge, and, within limits, side to side using the rotator. This arrangement facilitated mea- surements under the bridge deck when direct measurement with the arm or cable-suspended weights was not possible. An accurate location of the sonar measurement could be calcu- lated knowing the position of the end of the rotator, the length of the kneeboard framework, the distance to the water sur- face, and the angle of the rotator. Cable-Suspended Operations Winch System Minnesota DOT developed an innovative boom and sound- ing weight system for scour depth measurements using a boom truck and a custom-fabricated winch setup. What was unique about the Minnesota DOT setup is that the winch was not mounted on the boom itself, which is the traditional approach for stream gaging. Instead, the winch was mounted on a frame attached to the truck bed (Figure A19). The winch could swivel and tilt to allow the cable to follow the movement of the articulated arm crane that Minnesota DOT was using. This design allowed the sounding weight capability to be added to the truck without modifying the articulated crane, Figure A16. Sonar transducer with all electronics built into the transducer head. Figure A17. Streamlined sonar probe.
which is used for other purposes when it is not being used for scour inspections. It also facilitated installing and removing the winch, as necessary, and using the same winch setup on various trucks. A-10 Building on this concept, a dual-winch approach was devel- oped to allow more controlled operation in certain cable- suspended applications, such as when using a sonar deployed in a floating platform. Part of the problem with floating plat- forms deployed by hand or with a single winch has been the lift on the nose created by the cable and the difficulty in con- trolling the position of the float. The dual-winch concept elim- inates the lift problem when implemented with an articulated arm that can get a cable further front of the float and will pro- vide more directional control. The concept, illustrated in Figure A20, allows better posi- tioning control and the ability to drift the float under the bridge, when compared with a single-cable operation. A single-cable suspension through the pulley on the end of the crane can still be used, similar to the Minnesota application, or the dual-cable concept as illustrated. The winches used were Warn Model M6000, a medium- duty, compact winch with a rated line pull of 6000 lb (Warn Part Number 45880). The winch has a 4.8-hp motor and 80 ft (15 m) of 5/16 inch (8 mm) wire rope with power in and out and freespooling capability. The winch cable was replaced with standard stream gaging sounding reel cable, which is smaller and more flexible. The cable was routed through a Wemco Model 700 wire rope meter to measure the cable length played out. The mechanical readouts of the wire rope counters were replaced by pulse counters that allowed electronic readout and input to the data collection software program. The winch and wire rope meter were mounted on a tilting bracket with a collar for a post mounting (Figure A21). The post was mounted vertically at the back of the truck. The col- lars slide over the post with brass washers and spacers so each winch setup can rotate freely (Figure A22). With the ability to rotate and the tilt up and down, the winches could track any movement of the crane. Sounding Weight Using a single- or dual-winch approach, traditional sounding weight measurements can be made. The dual-winch approach Figure A19. Minnesota style winch. Figure A20. Dual winch concept. Figure A18. Kneeboard with wireless sonar (note PVC instrument enclosure where transducer and radio modem are located).
reduces the size of the weight necessary, given that the winch running through the end of the crane can be used to limit the movement under the bridge deck. Although the weight is not a concern, given the ability of the crane and the winches to handle very large weight, it does allow better control over the position of the sounding weight. Sounding Weight with Sonar Cable-suspended operations are also possible with a wire- less sonar installed in a sounding weight. A 4 ft (1.2 m) hanger bar for the sounding weight was built with a 4 in (10 cm) PVC pipe enclosure to house the battery and wireless modem at the top (Figure A23). This eliminated the need to route the sonar cable from the water surface up to the bridge deck and greatly enhanced cable-suspended operations using a sonar device. A standard 75-lb sounding weight was used, with a hole A-11 machined in the bottom for the transducer. The mounting hole for the transducer was placed just ahead and as close as possible, to the bolt hole for the hanger bar, in order to main- tain sounding weight balance. Standard sounding weights are designed with a flat bottom so they will sit upright without rolling. Under high-velocity flow, this can create a separation zone off the bottom that may adversely affect sonar measurement. Therefore, the transducer was not mounted flush with the flat bottom, but allowed to pro- trude and a shim was fabricated to transition the flow more smoothly off the nose of the sounding weight (Figure A24). Figure A21. Winch and wire rope counter on mounting bracket. Figure A22. Post mounting design for dual winches. Figure A23. Wireless sonar in a sounding weight. Figure A24. Shim on bottom of sounding weight.
CHAPTER 3 APPLICATION GUIDELINES FHWA SCOUR MONITORING GUIDANCE Approximately 584,000 bridges in the National Bridge Inventory (NBI) are built over streams. Many of these bridges span alluvial streams that are continually adjusting their beds and banks. Many of these bridges will experience problems with scour and stream instability during their useful lives. Scour and stream instability problems have always threat- ened the safety of the U.S. highway system. The National Bridge Inspection Standards (NBIS) require bridge owners to maintain a bridge inspection program (23 CFR 650, Subpart C) that includes procedures for underwater inspection. A national scour evaluation program as an integral part of the NBIS was established in 1988 by FHWA Technical Advisory T5140.20, superseded in 1991 by Technical Advisory T5140.23. Technical Advisory T5140.23 specifies that a plan of action should be developed for each bridge identified as scour critical in Item 113 of the NBIS. The two primary components of the plan of action are instructions regarding the type and frequency of inspections to be made at the bridges and a schedule for the timely design and construction of scour countermeasures. The purpose of the plan of action is to provide for the safety of the traveling public and to minimize the potential for bridge failure by prescribing site-specific actions that will be taken at the bridge to correct the scour problem. The inspection requirements in a plan of action typically will include recom- mendations for scour monitoring during and after floods. APPLICATION OF THE ARTICULATED ARM TRUCK General The type and frequency of inspection work called for in the plan of action can vary dramatically depending on the sever- ity of the scour problem and the risk involved to the traveling public. For example, a bridge rated scour critical by calcula- tions, but having relatively deep piles in an erosion-resistant material and having been in place for many years with no sign of scour, might be adequately addressed through the regular inspection cycle and after major flood events. Alternatively, a bridge found to be scour critical by inspection (e.g., during an underwater inspection that finds a substantial scour hole undermining the foundation) would be of greater concern and would require a more aggressive inspection plan. A-12 In either case, the application of portable scour monitoring devices, such as the articulated arm truck, during and after a flood, could be a key element of a scour monitoring program developed as part of the plan of action for a scour-critical bridge. The articulated arm truck provides a stable platform for deploying various scour instruments. The size of the truck and the automated data collection system facilitate flood measurements by allowing detailed data to be collected in a short time. The articulated arm truck is not a replacement for conven- tional scour monitoring methods, but is a supplement to those methods, designed specifically for work under adverse flood conditions. One of the most common conventional scour mon- itoring methods is the use of a lead line measurement from fixed locations across the bridge. The lead line approach is simple and can provide fast results without the complexity of the artic- ulated arm. However, a lead-line measurement is extremely difficult under the severe conditions encountered during a major flood event. High-velocity flow alone can make a lead line mea- surement infeasible, or at best, very difficult and inaccurate. Another difference between the truck and conventional methods in widespread use is the large amount of data that can be collected with the truck in a relatively short time. Conven- tional methods generally only produce point measurements at defined locations across the bridge, which may or may not be adequate to evaluate scour criticality. Although the truck can provide the same data, its real bene- fit and value occurs when more data are necessary or desirable to define the scour problem and such data must be collected under the adverse conditions of an extreme flood event. Using the articulated arm truck is somewhat analogous to completing a hydrographic survey, where a large amount of data is col- lected and used to create a bathymetric map. Working from the bridge deck, the truck can provide numerous data points that can be used for various contouring and mapping work products. Therefore, it is important to recognize that the articulated arm truck was designed for a specific application, that being flood flow conditions, and it may not be the best tool for all sit- uations. At lower flow conditions, or when fewer data can ade- quately address the problem, other methods may be preferable. With the number of sensors, the data loggers, and the com- puter data collection methods, the truck is a more complicated device than most conventional scour monitoring methods.
Proper use of the articulated arm truck will require training and a certain aptitude to operate and maintain. Therefore, the integration of the articulated arm truck into a state scour inspection program might be based on a single truck and a crew specifically trained in its use. In larger states, or states with more scour-critical bridges to monitor during and after floods, several trucks and trained crews might be necessary. These same crews might also be doing 2-year inspections or lower flood event monitoring with more conventional methods, but when a big flood occurs, they are the only ones who are trained and ready to operate the truck. Similar to all scour monitoring methods, the truck has advan- tages and limitations. Recognizing and remembering what these are will facilitate successful application of the articulated arm truck in a scour monitoring program. The articulated arm truck should be viewed as another tool in the inspectorsâ tool- box for scour monitoring, and for any given job, the right tool or combination of tools must be applied. Advantages of the Articulated Arm Truck High-Velocity Flow A major advantage of the articulated arm truck is the ability to make measurements in high-velocity flow. When the water surface is within 30 ft (9.1 m) of the bridge deck, the stream- lined sonar probe can be directly inserted into the water, pro- viding a very stable measurement with very reliable positioning data. This measurement has been completed in velocities in excess of 10 fps, and, based on those results, even higher veloc- ities could be measured. The combination of a strong, stable mechanical arm and a streamlined probe provided very suc- cessful results in high-velocity conditions. High-Sediment and Air Entrainment Conditions Flood conditions often produce large suspended sediment loading, which can complicate measurements with some sen- sors, particularly sonar. Part of the success in high-sediment conditions is minimizing other factors that can complicate a sonar measurement, including separation zones and high air entrainment. The streamlined probe that was developed min- imized these effects by reducing turbulence induced by the probe and streamlining the flow over the transducer. The streamlined probe also positioned the transducer about 12 in. (30 cm) under water for the measurement, which eliminated those surface interference issues typical of a floating deploy- ment where the transducer is skimming the surface. Limited Clearance Limited clearance conditions often exist during floods because of high stage conditions. This reduces the clearance A-13 under the bridge, which can complicate scour measurements. The crane can be articulated such that direct measurements can be made from a water level just below the bridge deck down to about 30 ft (9.1 m). Pressure Flow When flow is so high that the low-chord of the bridge is underwater, the use of floating deployments for pier scour measurement is virtually eliminated. However, under these conditions, the crane is still feasible and, within certain physical limits, could be articulated into position under- water. Another concern is that, under pressure flow, the velocity is typically accelerated from free surface condi- tions, and more turbulence exists. The overall stability of the articulated crane and the strength of the crane hydraulics would facilitate making measurements in such adverse flow conditions. Overhanging Bridge Geometry Overhanging bridge geometry often complicates scour mea- surement. With the ability to tilt the rotator, the crane could be articulated slightly to allow some positioning under the bridge deck. Greater ability to work under the bridge is avail- able through the rigid frame deployment of the kneeboard. The framework allows pushing the kneeboard under the bridge deck up to 10 ft (3 m) and can be rotated side-to-side with the rotator. Field testing revealed that it can be difficult to get the kneeboard positioned on the water and ready to push under the bridge. Therefore, although the use of the frame- work is somewhat problematic and is more difficult to use than a direct sonar measurement with the streamlined probe, this deployment method works and does allow data collec- tion under the bridge. High Bridges High bridges where the water surface is well below the bridge deck can create difficult measuring situations. Not only is the height of the bridge an issue, but at such loca- tions there can often be significant wind blowing through the bridge opening. The limit of the articulated crane under a direct measurement is 30 ft (9.1 m); therefore, high bridges typically require a cable-suspended approach. The dual- winch concept on a post mounting provides versatility in the measurement approach. One of the problems of a single- winch deployment is the drift under the bridge and/or the effects of wind on the cable or the deployment platform. The dual-winch approach allows a second cable and better control of the location of the deployment platform. With any cable-suspended operation, particularly on high bridges, the ability to track the position of the sensor accurately is lost. Therefore, the positional accuracy will always be better
with the direct measurements made with the streamlined probe or the physical probe. Easily Used and Affordable Although the articulated arm truck is a specialized measure- ment device, it was designed to be affordable and relatively ease to use and maintain. The truck was designed around commercially available, âoff-the-shelfâ products, whenever possible, to avoid special fabrication requirements. These com- ponents and pieces were also designed to be a bolt-on installa- tion, so that the articulated arm truck could be readily used for other purposes outside of the flood season. The combined cost of the truck and crane was about $50,000 prior to adding instru- mentation. Allowing $25,000 for instrumentation and fabrica- tion, the total cost for the scour monitoring truck is about $75,000. The Windows-based data collection software program makes the system relatively easy to use. The data are reported in station-elevation format to allow immediate comparison of the results with information on the bridge plans. Easily Transportable The articulated arm truck was designed around the small- est truck chassis possible, in part to control cost and in part to provide maneuverability and to minimize the traffic con- trol requirements. The latter issues are important when oper- ating in a flood-response mode, given that the inspection crew needs to collect data as efficiently as possible and get to as many bridges as they can in a short time. An F-450 truck chas- sis is not much bigger than a full-sized pickup, and, therefore, the articulated arm truck as developed was easily transportable and maneuverable. Accuracy The desired accuracy of a scour measurement is typically +/â12 in. (30 cm). Most sonar devices meet this criterion, and so as it relates to the articulated arm truck, this criterion was more critical for the positioning system. Individually, the accu- racy of each sensor is much better than the required accuracy. The combined accuracy of the entire system, including the software calculations to reduce the data, was well within +/â12 in (30 cm). Ultimately, what controls the accuracy of the system is the deflection in the crane. At full extension and in high-flow conditions, some bending was observed in the crane arm. Additionally, bouncing of the crane, either during an arc measurement or while driving across the bridge deck when making a cross-section measurement, caused some mea- surements to be in error by more than +/â12 inches. There- fore, although the articulated arm truck can provide the A-14 desired accuracy, these limits may be exceeded if proper and careful application procedures are not followed. Limitations of the Articulated Arm Truck Floating Debris The accumulation of floating debris is a common problem on the upstream side of a bridge. Trees, logs, and branches are trapped by the piers and gradually may create a large debris jam. Such debris complicate the measurement process and also can increase the scour that occurs. The use of the articu- lated arm could increase the opportunity for success under these conditions when it is possible to position the end of the crane upstream of the debris pile and point the sonar under the debris. However, debris accumulations often have substantial depth, sometimes accumulating down to the channel bed; this would limit success even if the crane could be positioned at the upstream edge of the debris pile. Alternatively, the physical probe that was developed, consisting of a 2-in. (5-cm) stainless steel pipe, might be forced through a debris pile using the crane hydraulics. However, once through the debris, the same crane hydraulics would make it difficult to detect the channel bottom. With- out developing some type of sensor at the end of the physi- cal probe to detect the channel bottom, this is not a practical solution. Therefore, debris continue to be a serious problem compli- cating scour measurements. The articulated arm may improve the potential for a successful measurement in a few cases, but overall, this problem has not been resolved. Ice Accumulation Ice accumulation creates problems similar to those of debris accumulation by creating a physical obstacle to measurement and by potentially increasing the scour that occurs. Similar to the conclusions stated in the debris discussion, the articulated arm truck has not resolved this problem. System Complexity The sensors selected for monitoring the position of the truck and crane movement were fairly simple, robust, and easy to replace. The computer program was designed with a calibration menu to allow easy zeroing of any new sen- sor, should one need to be replaced. However, as with any automated system that relies heavily on sensors, data loggers, and computers, the system requires that opera- tors have an aptitude for electronics and computers and some training so as to be able to operate and maintain the system.
A-15 CHAPTER 4 OPERATIONAL GUIDELINES DATA COLLECTION Software Programs Extensive effort was put into creating a software package to automate the data collection process with the articulated arm. Data collection and processing occurred with a laptop com- puter equipped with two serial ports: one for the boom data and one for the truck data, as sent by the two Campbell CR10 data loggers. Different programs were required depending on the deploy- ment method. The programs were written in Visual Basic and all had the same general Windows⢠layout. The primary dif- ference was the different geometric calculations necessary for position, depending on which deployment method and sensors were being used. Four programs were created: one for direct sonar measure- ments with the articulated arm; one for use with the kneeboard deployed on a rigid frame; one for direct probing; and one for cable-suspended operations. All programs produce an x,y,z data file that can read by CAESAR (Cataloging and Expert Evaluation of Scour Risk and River Stability) or any other program such as AutoCad or Microstation when contouring capability is desired. The x dimension defined the vertical direction, including the measured scour depth. The y dimen- sion was the distance out from the bridge, and the z dimension was the location along the bridge deck. Coordinate System The sensors on the truck define position data relative to the rotational pivot of the crane. This coordinate system was defined as the âtruckâ coordinate system. Within the software, these coordinates were converted to âbridgeâ coordinates, as defined by the profile line for the bridge. The profile line is a station-elevation line on the bridge plans, typically along the centerline of the bridge deck. This same information is also used for other dimensions on the plans, such as pier locations and pile tip elevations. Providing the scour measurement results in bridge coordinates facilitates rapid review and eval- uation of bridge integrity and was considered an important aspect of software development. To convert from truck coordinates to bridge coordinates required inputting the profile line into the program before beginning data collection. The program was designed to allow this to occur before arriving at the bridge or it could be done after setting up on the bridge. It was also necessary to mea- sure the horizontal and vertical offsets of the truck relative to the profile line. A chisel mark on the rear bumper of the truck was used as the point of reference, and both the dis- tance from the pavement to that mark and the horizontal distance from the profile line were measured and entered into the program. The vertical offset was manually cor- rected for the cross slope of the pavement (typically 2 per- cent) when entering that distance. With this information, the computer program automatically calculated and reported results in bridge coordinates. Methods of Data Collection The software for sonar measurements with the crane allows point measurements or continuous recording. Continuous recording can occur as the crane is either driven across the bridge or with the truck in a stationary position and sweeping the crane in an arc. The crane sensors are measuring once per second, and so the amount of data collected in a continuous mode depends on how fast the truck is moving during a cross- section measurement or how fast the crane is swept in an arc- based measurement. Physical Probing Physical probing with the stainless steel pipe attached to the rotator provides point x,y,z data. The method works best to locate the profile of riprap that might be place around a pier or in a gravel/cobble bed. Otherwise, the crane hydraulics limit accurate definition of the water/sediment interface. Given the positional information available on the crane, this method pro- vides very accurate point data and data points can be collected in a short time. Cross-Section Measurement When driving a cross section, the truck needs to move slowly for safety reasons and to avoid bouncing the crane, which causes erroneous readings from the tilt sensors. This
may require feathering the clutch on a manual transmission. The truck should be positioned to avoid running the wheels or the castors over any bridge grates, which might bounce the crane and/or result in breaking the grate. The driver needs to maintain a straight line, which may require observers walk- ing ahead and/or behind the truck. An observer should also be watching the river for floating debris and to make sure that the sonar does not lift out of the water or go too deep with changes in roadway profile. Cross-section data collected while driving the truck across the bridge can be plotted in any x-y plotting program. Multiple passes can be driven to col- lect several lines of data that could be used to map a larger upstream approach area. Sweeping Arc Measurement Similarly, when sweeping arcs with the crane from a sta- tionary location, the crane operator needs to swing the crane slowly. The usual pattern is to start with the crane at a right angle and swing a short arc immediately in front of the pier, with each successive arc getting larger and col- lecting data farther in front of the pier. The data collected during this measurement can all be written to one file, paus- ing the data collection as the crane is re-positioned for the next arc. The resulting x,y,z data collected by sweeping multiple arcs with the truck in a stationary position can be used to develop detailed bathymetric plots of the scour hole and approach conditions. Kneeboard Measurement Collecting data with the kneeboard on a rigid frame pro- vides additional point measurements under the bridge that can be used alone or in combination with other data to map addi- tional area. Once the kneeboard is in position, the crane can be used to pull it forward or backward, and the rotator can be used to swing small arcs side-to-side. During all these motions, the position of the kneeboard is being calculated and, at the end of the measurement, an x,y,z data file is written. Cable-Suspended Measurement Cable-suspended methods can be used with a traditional sounding weight, the modified sounding weight with the sonar, or a cable-suspended version of the kneeboard. The cable dis- placement is measured by a pulse counter and recorded by the computer program. Using any cable-suspended method limits the positional data and would be used primarily to locate a potential problem quickly, but not to provide enough data to map the potential problem in any detail. A-16 Typical Results Figure A25 illustrates typical results available with the articulated arm truck. At this bridge a cross section was taken, and arc measurements at two piers were completed, all on the upstream side of the bridge. The x,y,z data col- lected from these measurements along with bridge plan information were used in Microstation to create the plots shown in Figure 25. The top drawing shows the limits of the cross-section data collected, and the arcs that were taken at Piers 3 and 4. The middle part of the figure shows the cross section plotted, and at the bottom of the figure are the con- tour plots developed for each pier. TYPICAL SEQUENCE OF EVENTS TO COLLECT DATA The most common and perhaps the best application of the articulated arm truck is to collect data with the streamlined sonar probe. This provides the best positional data and the most rapid data collection. It can be used for cross-sectionâor arc-based measurements under both low-flow and flood flow conditions. As an illustration of the setup and data collection procedures when using the articulated arm truck, the follow- ing paragraphs describe the typical sequence of events that would occur when collecting such data. Before driving onto the bridge: 1. Mount the instrument box at the end of the crane. Do not install the battery yet. 2. Connect the chain for the draw wire measuring crane extension. 3. Connect the wire from the rotator tilt sensor to the instrument box CR10. 4. With the truck engine running, engage the PTO in the cab to power the crane hydraulics. Leave the truck running with the parking brake set. 5. Remove the bolt holding the crane in place during trans- port and, with the crane hydraulics, lift the crane off the transport block. Rotate slightly to position the crane over the center of the cab. Extend the crane out over the cab and lower down to the pavement in front of the truck to facilitate attaching the streamlined sonar probe. This operation can be done without placing the outriggers on the ground, provided the crane is kept over the cen- ter of the truck and not rotated side-to-side. NEVER ROTATE THE CRANE SIDE-TO-SIDE WITHOUT THE OUTRIGGERS ON THE GROUND. 6. Bolt on the streamlined sonar probe to the end of the rotator on the instrument box. 7. Connect the sonar cable to the terminal block con- nector. 8. Install the battery in the instrument box. The crane- end system, including all sensors, the CR10 data log- ger, and the modem, is now active and transmitting
Figure A25. Typical results obtained with the articulated arm.
data (i.e., sonar, tilt angles and crane extension) once per second. 9. Install the surveyorâs wheel on the back of the truck. Place in the up position (wheel not on the roadway), and pin the wheel to prevent freewheeling. 10. Install the acoustic stage sensor in the mounting bracket and connect the wire harness. Do not extend out off the side of the truck until positioned on the bridge. 11. Place the computer in the instrument shelter, plug in the power supply to the invertor, and turn on the invertor. 12. Connect the wireless modem to one serial port on the computer, and the truck CR10 to the other serial port. 13. Turn on the power switch controlling the wireless modem and the power convertor for the acoustic stage sensor. 14. Boot-up the computer and execute the data collection program. 15. If the station-elevation file for the profile line has not been created, do this before pulling onto the bridge deck. The profile line is a reference line on the bridge plans, typically along the centerline of the bridge. 16. Raise the end of the crane and fully retract the crane to position it over the cab. It does not need to be put back in the transport block. 17. The truck is now ready to drive onto the bridge. Make sure appropriate traffic control is in place. 18. Drive the truck to the starting station, positioned as close to the curb line or barrier rail as possible. 19. Extend the acoustic stage sensor over the bridge rail. Make sure it is far enough out for a clear shot of the water surface. 20. Lower the outriggers. For a cross-section measurement, the outriggers should be lowered onto the castors. For a stationary measurement at a given pier, the castors do not need to be used. 21. Level the truck bed using a bubble level. 22. Extend the crane out over the bridge rail, and articu- late into a 90-degree position. 23. Re-level the truck bed and then position the crane top arm in a horizontal position. This arm must be A-18 maintained in a horizontal position for all measure- ments. 24. Measure the vertical distance from the pavement to the chisel mark, and the horizontal distance from the pro- file line (typically the centerline) shown on the bridge plans. Enter this information in the program. Account for the cross slope drop from the profile line to the chisel mark when entering the vertical offset. 25. Lower the sonar into the water. 26. Check the program and make sure all sensors are responding. 27. Data collection can now begin. Collect data: 28. If a cross section measurement is being completed, articulate the crane to the desired location and lower the survey wheel. Click the start button on the pro- gram and drive slowly across the bridge. Monitor the position of the sonar in the water, and raise or lower the crane as necessary with the changes in the roadway profile. The position of the crane is being tracked continuously, and the program will compensate for any changes in crane position necessary as the cross section is being driven. 29. If the truck is positioned at a pier and the crane will be used to sweep arcs in front of the pier, rotate the crane until the arm bumps the side of the bridge. Click the start button and slowly rotate the crane until you bump the other side. Pause the program, reposition the crane, click the start button, and sweep a second arc back the other direction. Continue the process sweeping multiple arcs until all data have been collected. 30. Monitor the crane position graphic and the scour depth graphic as data are being collected to watch for any anomalies. 31. After all data collection is complete, for either the cross section or the multiple arcs, click the finish button to write a permanent data file with the x,y,z data in bridge coordinates.
A-19 CHAPTER 5 TROUBLESHOOTING, MAINTENANCE, AND SERVICING TROUBLESHOOTING Problem When the data collection program is started, no data appear from the data box at the end of the crane. Solution 1. Make sure the power switch in the instrument box is on. 2. Check the serial port connection on the computer, and make sure the communications protocol is correct. 3. Check the battery voltage in the instrument box at the end of the crane. If the voltage is low (i.e., less than 11 volts), replace the battery with a charged battery. 4. Close the data collection program and reboot the com- puter. 5. If data are still not appearing, exit the program and use MS Windows Hyperlink⢠to see if data are being sent and received. Problem When the data collection program is started, no data appear from the truck-based sensors. Solution 1. Make sure the power switch in the instrument box is on. 2. Check the serial port connection on the computer, and make sure the communications protocol is correct. 3. Close the data collection program and reboot the com- puter. 4. If data are still not appearing, exit the program and use MS Windows Hyperlink⢠to see if data are being sent and received. Problem Data are being transmitted, but the raw angle and/or dis- tance data appear in error. Solution 1. Use an inclining bubble level to determine angles and check against the program results. 2. If there are discrepancies, set the crane in the calibra- tion position. The calibration position is when the crane is fully retracted and articulated at a right angle over the bridge deck. 3. Check the truck bed and crane top arm to ensure they are still level. 4. Check the crane and rotator angles with an inclining bub- ble level. The crane should be set at 90 degrees, and the rotator arm should be parallel to the crane (180 degrees). 5. Run the calibration program. MAINTENANCE AND SERVICING Maintenance and servicing relate primarily to the truck and crane. Standard maintenance for the truck and the spe- cific manufacturer recommendations for the crane should be followed. The instrumentation for the positioning and depth require minimal maintenance; servicing a broken sensor typically would involve replacing the defective sensor with new one. Typically, the cost of the sensors is small, and there are no user-serviceable parts.
CHAPTER 6 ENHANCEMENTS Although the articulated arm truck is fully functional, improvements could be made to the device. Sensor-related improvements include work on both the kneeboard and phys- ical probe concepts. Work is needed on the rigid frame version of the kneeboard to improve the deployment and stability of the device. A sensor at the end of the physical probe would be beneficial to help identify the water sediment interface when working in softer bed materials. The calculation of the location of the end of the crane based on assorted tilt and displacement sensors, along with A-20 a surveyorâs wheel to locate the truck on the bridge deck. This system worked well, but created a system of multiple components that required a certain electronic aptitude to operate and maintain. A simpler positioning system involv- ing fewer components would be preferable, if the required accuracy can be maintained. For example, as GPS technol- ogy continues to become more cost-effective and user- friendly, an alternate positioning system based on GPS may be feasible.
