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13 Alternative 5--Data Collection Software Efficient data collection is important in a flood monitoring situation. The objective of this work was to develop a Windows-based software to automate the data collection process. Ideally, the software would not only automate the data collection process, but also provide immediate access to the results, which could include a cross section plot or bathy- metric map. PROTOTYPE DEVELOPMENT AND LIMITED TESTING Minnesota Boom Original Design Figure 2. Minnesota DOT winch mounted on bed of truck. Minnesota DOT developed an innovative boom and sound- ing weight system for scour depth measurements using a boom Minnesota DOT was using. This particular crane was capable truck and a custom-fabricated winch setup. The use of a boom of extending to 40 ft (12 m). and winch to deploy a sounding weight is not a new concept This design allowed adding the sounding weight capability and has been used extensively for stream gaging measure- to the truck without modifying the articulated crane, which is ments for many years. More recently, various boom and winch used for other purposes when it is not being used for scour configurations have been used for measuring scour depths at inspections. This design also facilitated installing and remov- bridges. In some cases, these were custom-fabricated devices; ing the winch, as necessary, and using the same winch setup in other cases, they were standard stream gaging boom and on various trucks. Although this was a relatively simple adap- winches (technically called sounding reels in stream gaging tation of a standard deployment concept, it simplified building work), as shown in Figure 1. and adapting sounding reel capability on any available boom The Minnesota DOT setup was unique in that the winch was and could be readily adapted to both articulated and non- not mounted on the boom itself. This has been the traditional articulated (straight) booms or cranes. The following para- approach for stream gaging operations and also has been com- graphs describe the design and construction of the Minnesota monly used in bridge scour measurements. Instead, the winch DOT winch in greater detail. was mounted on a frame that was attached to the truck bed To document the design of the Minnesota DOT winch, a trip (Figure 2). The winch could swivel and tilt to allow the cable was made to the DOT office in Mankato, Minnesota, where the to follow the movement of the articulated arm crane that boom was fabricated. Pictures and measurements were taken to document the device. Discussions were also held with the bridge inspection crew that developed the device to obtain sug- gested improvements to the design, based on experience to date. Generally, the device as built has performed quite ade- quately, and only minor changes to the design were suggested by the inspection crew. The winch used was an X3 SuperwinchTM (Figure 3), with the cable routed through a Hykon ReelTM wire rope length counter (Figure 4). The X3 winch has a 1.6 hp motor and 50 ft (15 m) of 7/32 inch (5.5 mm) wire rope with power in and out and freespooling capability. The rated line pull is 4,000 lbs (1,814 kgs) on a single line. The Hykon Reel is made by Hykon Manufacturing Company and can accommodate flex wire from 1 /64 in (0.4 mm) to 7/8 in (22 mm) and wire rope to 1/2 in (13 mm). A guide was fabricated at the outlet of the wire rope counter to better control the cable and to direct it toward the pulley at the end of the boom. The frame for the winch and wire rope Figure 1. USGS type stream gaging crane being used for counter was custom fabricated and included a place to attach scour monitoring. a safety chain to the truck bed.

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14 Figure 3. Close-up of Superwinch Model X-3TM. Figure 5. Pulley at end of articulated crane. One of the suggestions for improvement by Minnesota been the lift on the nose created by the cable and the difficulty DOT was to make sure that the frame can tilt adequately to pre- in controlling the position of the float. The dual winch con- vent excessive rubbing of the cable through the guide, which cept eliminates the lift problem when implemented with an can result in premature failure of the winch cable. The cable articulated arm that can get a cable further out in front of the was routed through a pulley at the end of the crane (Figure 5). float and will provide more directional control. Deployment Another suggestion was to include a swivel on the pulley to pre- by hand is convenient during normal flow conditions, but can vent twisting of the cable. Figure 6 is a dimensioned drawing be difficult under flood flow. of the winch, as built by Minnesota DOT. The concept, illustrated in Figure 7, may allow better posi- tioning control and the ability to drift the float under the bridge, when compared to a single cable operation. A single cable sus- Modifications to Original Design pension through the pulley on the end of the crane can still be used, similar to that in the Minnesota application, or the dual One of the modifications developed under this project was cable concept as illustrated. the use of a dual winch approach to allow more controlled oper- Other modifications concentrated on (1) the individual com- ation in certain cable-suspended applications, such as when ponents used in the design and (2) the mounting concept. In using a sonar device deployed in a floating platform. Part of general, heavier duty components were used, both in terms of the problem with floating platforms deployed by hand has the winch and the wire rope counter, and the framework was built using heavier steel. Figure 8 shows the modified winch assembly. More consideration also was given to balance and to pro- viding a smooth operation as the winches follow the motion of the boom. This combined with the desire to operate two winches resulted in the post mounting concept shown in Fig- ure 9, compared to the bed mounting concept used in the orig- inal Minnesota device. The post allows each winch to swivel independently. This feature, combined with the ability to tilt up or down, allows the winches to track the movement of the crane. The final modification related to the readout from the wire rope counter. Initially, a speedometer cable was used to relocate the mechanical readouts of the wire rope counters to the instrument box on the flatbed. Subsequently, these were replaced by pulse counters that allowed electronic readout and input to the data collection software program. This task also included consideration of a non-articulated Figure 4. Close-up of Hykon--ReelTM with guide added crane on a pickup truck, such as the one shown in Figure 10, at the outlet of the reel. which has a 15 ft (4.5 m) reach and sells for about $5,500.

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15 H Figure 6. Dimensioned drawing of Minnesota style winch.

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16 Figure 7. Two winch concept for cable suspended operations. Given the reach of an articulated arm, and the value of han- dling larger sounding weights with larger winches, a smaller device on a pickup, while feasible, may not be attractive for flood monitoring applications. Interphase Scanning Sonar The Interphase TwinscopeTM (Figure 11) is a forward- scanning sonar using a proprietary phased array acoustic tech- Figure 9. Winch system on the truck. nology. An acoustic array is a group of piezoelectric ceramic elements precisely sized and spaced. Each element can send ferent phasing of the signals applied or received by each ele- and receive acoustic pulses, similar to conventional single- ment. Depending on signal phasing, acoustic beams can be element depth sounders. However, when all elements in the directed in an almost unlimited number of directions. array are sending or receiving acoustic energy at the same time, The TwinscopeTM uses a 16-element array and can steer the entire array behaves like a single larger element with one the acoustic beam in any of 90 different directions in either important difference: the ability of the array to concentrate its the horizontal or vertical direction. Conventional fixed-beam acoustic energy in different directions, depending on the dif- sonar technology would require 180 different elements to duplicate this capability, and the resulting transducer would be too large and costly for practical use. Given that the acoustic Figure 10. Application of winch concept on a non- Figure 8. Modified winch design. articulated crane.

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17 ing was conducted at a pump station intake on the lake sup- plying water for some of the outdoor flumes and in the sump under the indoor laboratory. The pump station on the lake has a large platform on piles supporting the pump and its intake. However, the number of piles and cross bracing prevented getting a clearly identifiable return of a single pile on the screen. The testing in the sump adjacent to one of the pump intakes provided a clearer picture, because the transducer was seeing only the pipe for the pump intake extending down into the water, but the screen image was complicated by multiple returns from the various walls and partitions of the concrete- lined sump (Figure 13). A field test of the TwinscopeTM was conducted in Alabama. For testing purposes, a special bracket was fabricated to allow the TwinscopeTM transducer to be mounted on the crane (Fig- ure 14). Figure 15 shows the transducer positioned in the water Figure 11. Interphase TwinscopeTM sonar. upstream of the pile. This test was inconclusive. Based on sub- sequent discussions with the manufacturer, it was concluded beam is steered electronically, with no moving parts, it can that there must be at least 10 ft (3 m) of water for this device quickly scan and rescan a large area. Phased array technology to work--a situation that did not exist at this bridge. No addi- also allows the user to adjust beam width, which is not possi- ble with conventional fixed-beam sonar. In the TwinscopeTM array, 8 of the 16 elements are used to scan vertically, from straight ahead to straight under the boat, and the other 8 are used to scan forward from side-to- side. In horizontal mode, the side-to-side sweeping action of the scanning beam is up to 45 degrees on either side of the boat, angled downward at about 20 degrees. The cone angle of the TwinscopeTM is approximately 12 degrees, so in ver- tical mode, a forward scan to 1,000 feet in front of the boat would see targets across a 210-foot width (105 feet on either side of center). Initial testing of the TwinscopeTM was conducted at the Hydraulics Laboratory at Colorado State University (CSU). The transducer was mounted in a pontoon float for testing, and positioned with an extendable pole (Figure 12). Test- Figure 13. Horizontal scan showing multiple reflections. Figure 12. Pontoon float with transducer adjacent to Figure 14. Mounting the TwinscopeTM transducer for pump intake in the CSU Hydraulics Laboratory. field testing.

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18 The recommended Effer crane was model 28/3S. This crane has a maximum reach of 30.3 ft (9.2 m) with a lift- ing capacity at this distance of 650 lbs. The base price for this crane is $10,000, with an installation cost of $3,500. This crane could also be installed on a Ford F-450 truck or equivalent. The cost for this truck new is $31,800 plus $4,000 for a flatbed. Therefore, the total cost for this crane, new truck, flat bed, and installation would be approxi- mately $49,300. The recommended Jabco crane was model 705/3S. This crane has a maximum reach of 32.6 ft (9.9 m) with a lift- ing capacity at this distance of 880 lbs. The base price for this crane is $16,000, with an installation cost of $3,500. This crane could also be installed on a Ford F-450 truck or equivalent. The cost for this truck new is $31,800 plus $4,000 for a flatbed. Therefore, the total cost for this Figure 15. Positioning the TwinscopeTM transducer crane, new truck, flat bed, and installation would be upstream of a pile. approximately $55,300. The recommended National Crane was model N-50. This crane has a maximum reach of 40 ft (12.2 m) with a lift- tional testing of the TwinscopeTM was conducted; however, ing capacity at this distance of 700 lbs. The base price for under the proper conditions, the TwinscopeTM should provide this crane is $20,500, with an installation cost of $8,500. a graphical perspective of conditions approaching a pier and This crane is larger and heavier than the others and would might be a useful addition to the instruments used by a bridge require a slightly larger truck, such as a Ford F-500 or inspection crew during scour monitoring. equivalent. The cost for this truck new is $33,700, plus $4,000 for a flatbed. The total cost for this crane, new truck, flat bed, and installation would be approximately Articulated Arm $66,700. Crane Research Based on this information, the cost for the crane and instal- lation, excluding the truck cost, varies from $13,500 to Articulated arm cranes are also known as knuckle boom or $29,000, with the Effer crane being the lowest and the folding cranes. There are various manufacturers of articulated National Crane being the highest. Although there was some arm cranes. The first step in the investigation of feasible alter- difference in reach and lifting capacity, that alone did not natives for use in a scour monitoring application was to con- seem to explain the wide range of cost. tact various dealers across the country to obtain specific When asked about the range in price, the National Crane design and cost information. This was accomplished through representative suggested that the other cranes being considered web browsing, telephone conversations, and review of litera- were all manufactured in Europe and were not built to as strin- ture provided by the dealers and/or manufacturers. Based on gent safety standards as cranes manufactured in the United this research, four major crane manufacturers were consid- States. The opinion of the Jabco representative was that the ered: Palfinger, Effer, Jabco, and National. For each manu- foreign companies have more background and experience in facturer, a specific model was selected that could be used for the design and manufacture of knuckle boom cranes. It was his scour monitoring applications and preliminary cost informa- observation that they have had to deal with narrow streets and tion (2001 data) was researched. The results of that research limited access issues for years, where knuckle boom cranes are as follows: can be particularly useful over straight arm cranes. Addition- ally, he indicated that many of the European cranes are made The recommended Palfinger crane was model PK 4501 C. of high alloy steel and, as a result, there is less structural steel, This crane has a maximum reach of 36 ft (11.0 m) with and therefore, less cost. The additional weight of the crane, a lifting capacity at this distance of 600 lbs. The base such as the National Crane, also required the use of a larger price for this crane is $14,500, with an installation truck, as discussed above. cost of $1,800. This crane could be installed on a Ford F-450 truck or equivalent. The cost for this truck new is Crane Selected for Purchase $31,800 plus $4,000 for a flatbed. Therefore, the total cost for this crane, new truck, flat bed, and installation These issues entered into the decision for the type of crane would be approximately $51,000. selected for this project, with the desire to work with a smaller

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19 crane that could be mounted on a smaller truck. This criteria TABLE 1 Crane and truck cost information was to improve maneuverability, as well as to minimize lane Cost ($) closure and traffic control issues. Additionally, as a research Item (excluding tax, project, it was important to have a dealer and manufacturer who licensing, etc.) Palfinger 4501C Crane 14,553 were willing to be helpful and responsive to unique requests as Installation, including PTO pump 1,500 it related to equipment application outside the normal range 10-foot truck bed, installed 1,500 of use. Based on all these issues, a Palfinger 4501C crane was 2001 Ford F-450 25,550 purchased (Figure 16). The final cost breakdown for the crane Subtotal-base cost for truck and crane 43,103 Kinshofer Hydraulic Rotator 3,600 and truck are provided in Table 1. Tool boxes, beacon lights, etc 2,000 Total Cost (estimated as of 12/31/01) 48,703 Mounting the Crane on the Truck Modifications to the Rotator The most common location for a crane is immediately behind the cab of the truck. An alternative location is at the The ability to provide pan and tilt operations at the end of back of the truck, behind the rear axle. A rear mount puts more the crane was considered a valuable feature for positioning load at the back of the truck and can cause weight distribution instrumentation. Pan operation could be accommodated using problems if the truck is also carrying substantial weight on the a standard hydraulic rotator, often used with construction flat bed. The rear mount provides better clearance around the equipment on the end of a crane (Figure 18). Most rotators truck, because the cab is not in the way. For purposes of scour are designed for 360-degree, continuous rotation at a fairly monitoring, with no substantial weight being transported on high speed. Continuous rotation for scour monitoring applica- the truck bed, a rear mount seemed advantageous. tions was not desirable, given that the operator might acciden- Based on the reach of the PK4501C crane, mounted with an tally tear off cables connected to transducers, and high-speed offset to the center of the truck, the PK4501C has the capabil- operation would complicate precise positioning and could ity to reach 21.25 ft (6.5 m) below the bridge deck when the result in possible impact damage when in close proximity to truck is a maximum of 35 in (0.3 m) from the edge of the the bridge. bridge. This reach is to the end of the crane, prior to adding any In the past, rotators with a 270-degree rotation were avail- extensions for sensor mounting. Figure 17 summarizes the able; however, most construction operations require full rota- geometric capabilities of this crane when mounted on a Ford tion and the limited rotation devices are no longer available. F-450 truck. After working with engineers at the crane manufacturer, it was concluded that the only economical solution was to use flow restrictors in the hydraulic lines to slow down the motion and to use some type of limit switch or indicator as part of the position-sensing device to control overrotation. 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 19). 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, building the workstation area for the computer and instruments, and relocating the hydraulic controls to the flatbed. The hydraulic controls for an articulated Figure 16. Palfinger PK4501C crane. crane are typically located next to the crane, allowing operator

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20 Figure 17. Reach below the bridge deck with the PK4501C crane on a Ford F-450 truck. access while standing on the road (Figure 20). Some models, visibility of river conditions for the operator. To reach over the including the Palfinger 4501C, have dual controls allowing side of the bridge, it will be necessary to position the truck as operation from either side of the truck. close to the edge of the bridge as possible, which may restrict After reviewing the truck and crane operation, it was con- access for the operator on the bridge side of the vehicle. Access cluded that it would be better to relocate the controls from the from the opposite side, when the crane is equipped with dual standard location for reasons of safety and to provide better controls, would still be feasible, but visibility to the water sur-

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21 Figure 20. Hydraulic controls in typical location allowing operation from roadway. Tracking the Position of the Crane Figure 18. Standard rotator (prior to modifications to Various sensors were installed on the truck and crane to allow tilt). 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 does not provide face would be limited from that location and roadside safety any positioning information without the addition of other would be a concern. sensors to track the movement of the crane. Therefore, a crit- Moving the control valves up onto the flatbed eliminated the ical part of the articulated crane research was to develop a access and safety issues related to operation from the road sur- methodology to track the location of the end of the crane face and greatly improved the visibility to the water surface for in a real-time mode as the crane was being operated. It was the operator. The controls were moved to a position at the back also necessary to define the position of the truck on the of the flatbed, a workstation was fabricated on the flatbed to bridge deck. provide a shelter for the computer, and a seat was installed on Initially, 10-turn potentiometers with various gearing the bed (Figure 21). arrangements were used to measure the azimuth of the crane Figure 19. Rotator after modifications to provide tilt Figure 21. Instrument shelter for computer and relocated capability. hydraulic controls.

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22 and the rotator. However, these were not as robust as needed, and alternative methods were investigated. Subsequently, the potentiometer for the azimuth measurement was replaced with a 50 in. (125 cm) linear environmentally sealed draw wire. The draw wire was routed around a 15-in. (38-cm)-diameter circu- lar plate mounted near the base of the crane (Figure 22). The draw wire 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. This solution was not feasible for the rotator, and no other alternatives were identified. Therefore, the 10-turn potentiometer was retained. Tilt meters were used to measure the deflection angle of the crane arm and the rotator arm. The tilt meter for the crane arm was mounted inside the instrument box attached to the end of the crane (Figure 23). 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) envi- ronmentally sealed draw wire was used to measure the linear extension of the arm (Figure 24). Tilt data for the crane and rotator, the azimuth of the rota- tor, and the linear extension of the arm are transmitted by a wireless modem from an instrument box at the end of the crane that also transmits sonar data. The data are pre-processed with a Campbell CR10 data logger prior to transmission to the com- puter on the truck (Figure 23). An acoustic stage sensor was used to measure the distance to the water surface (Figure 25). A second CR10 mounted in the instrument shelter on the truck bed was used to process truck data, which included the azimuth of the crane, winch Figure 23. Tiltmeter installed in the instrument box at the data, the distance to the water surface, and the distance trav- end of the crane. eled across the bridge deck. A computer with two serial ports was used to process the data from each data logger, sent as serial data strings. Knowing allowed geometrically calculating the position in space of the the rotation of the crane and the rotator, the deflection angles of end of the rotator relative to the center pivot of the crane where the crane arm and rotator, and the extension of the crane arm it was mounted to the truck bed. 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 information necessary to locate the scour mea- Figure 22. Attachment for crane azimuth measurement Figure 24. Draw wire used to measure linear extension of using draw wire. crane.

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23 Based on simplicity, cost, and accuracy, this system was purchased and installed on the truck. However, this meter caused a fault in the truck anti-lock braking system and was also found to be difficult to interface with the data collection program being developed. Therefore, it was replaced with a standard surveying measuring wheel attached to the back of the truck (Figure 26). The only limitation of standard survey wheels is that they use a mechanical counter and do not have any electronic output capability. To provide a serial data string, pulse counters were added to the wheel to register electroni- cally the distance traveled. Scour Measurement Devices As developed, the instrumented, articulated crane could be Figure 25. Acoustic stage sensor used to measure used to position various scour measurement devices, both distance to the water surface. directly from the end of the crane and from cable-suspended methods using the winches. Sonar could be deployed off the end of the crane, or as a cable-suspended operation, while surements accurately. Initially, the use of low-cost GPS was direct probing was possible off the end of the crane. considered, but that approach was not found to be feasible (see To provide sonar measurement capability, a sonar instru- below). Given that the truck would always be positioned as ment with all the electronics built into the transducer head was close to the curbline or barrier rail as possible, and given that selected (Figure 27). The sonar outputs a serial data string of the bearing of the bridge is a known quantity, the only real depth and temperature that was connected to the Campbell location information necessary was the distance the truck had CR10 data logger and transmitted by the wireless modem (as been driven across the bridge, and the elevation of the truck. shown in Figure 23). This eliminated having to route any elec- The elevation of the truck could be established from the tronic cables for the sonar from the water surface to the bridge elevation of the bridge deck, as given on bridge plans, and deck. the height of the truck bed above the bridge deck. There- Given the desire to operate at flood conditions with high fore, the primary field measurement necessary to locate the velocities, a streamlined probe was built to position the sonar truck was simply the distance the truck had traveled across transducer directly in the water using the articulated arm. The the bridge deck. probe was fabricated from a section of helicopter blade and Various methods were considered to establish the distance proved to be very stable when placed in high-velocity flow traveled. To be useful, the measurement device had to be during field trials. The streamlined probe eliminated the vor- accurate, simple to use, and able to output a serial data string. tex shedding problems of a simple cylinder-shaped rod ex- Laser measuring devices were considered because of their posed to high-velocity flow. high accuracy and simplicity. However, because the laser must hit a target at the end of the bridge, there was concern about reflecting off the wrong target and the potential difficulties of getting a measurement when the bridge had a horizontal or vertical curve. Electronic distance meters are available for installation on vehicles used for various highway survey projects (e.g., mea- sure guard rails, pole or sign signing, and estimate pavement areas). For example, the NitestarTM system computes the dis- tance traveled by attaching to the speed sensor in the vehicle's transmission. This device has a calibration feature that can be used to account for change in tire size because of wear and under or over inflation of tires and is accurate to 30 cm over 1.6 km (1 ft per mile). It has RS-232 output capabilities that allow it to record data into a computer, which can be viewed by Nitestar software or by user-defined software. The cost of this unit with the appropriate installation kit was approxi- Figure 26. Surveyors wheel mounted to rear bumper of mately $700 dollars. truck.

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24 Figure 27. Sonar transducer with all electronics built into the transducer head. The initial design for the streamlined probe had a rigid Figure 29. Modified streamlined probe with swivel mount to the rotator, requiring the operator to turn the rotator capability and longer extension. as the crane angle changed, in order to keep the fin aligned with the current (Figure 28). This design was modified to allow the crane could reach below the bridge deck (21.25 ft or 6.5 m) the fin to swivel and track the current on its own; however, the and the length of the rotator mounting bracket (1.5 ft or axis of rotation was too far back on the fin and it would not 0.46 m), the crane could reach nearly 30 ft (9.1 m) below the track the current in low-velocity situations. A third version bridge deck for a sonar measurement. was built with the rotation point moved forward, as well as To provide physical probing capability, an extendable rod being built with a longer extension that provide more reach was fabricated. The rod extensions were built with 125 mm with the crane arm and less chance of submerging the rotator stainless steel, Schedule 80 pipe in 1.5 m lengths, allowing and instrument box at the end of the crane (Figure 29). The a total length up to 4.5 m. Threaded unions allow individ- length of the extension was 80 in (2 m). Given the distance ual sections to be connected to create the longer extensions. Using the articulated crane for physical probing is most appropriate in a gravel/cobble bed or to evaluate riprap con- ditions, because the strength of the crane hydraulics makes it difficult to know exactly when a soft channel bottom is reached. Cable-suspended operations were possible using the two Minnesota-style winches described above. Using a single- or dual-winch approach, traditional sounding weight measure- ments can be made. The dual-winch approach reduces the size of the weight necessary, because 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. A kneeboard with a wireless sonar was also developed that Figure 28. Streamlined probe. could be deployed from either a rigid framework attached to

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25 the rotator or as a cable-suspended operation. The sonar with the electronics built into the transducer was used and a small PVC enclosure fabricated for the kneeboard to hold the battery and wireless modem (Figure 30). Several versions of the frame- work for deployment off the end of the crane were fabricated, with the version shown in Figure 30 working the best. It was difficult at times to get the kneeboard positioned on the water surface, but, once in place, it could be readily moved forward and backward under the bridge, and, within limits, side to side using the rotator (Figure 31). This arrangement facilitated measurements under the bridge deck when direct measure- ment with the arm, or cable suspended weights, was not pos- sible. An accurate location of the sonar measurement could be calculated knowing the position of the end of the rotator, the length of the framework, the distance to the water surface, and the angle of the rotator. Figure 31. Kneeboard positioned under the bridge. Cable-suspended operations with a sonar installed in a sounding weight were also tested. A 4 ft (1.2 m) hanger bar for up to the bridge deck and greatly enhanced cable-suspended the sounding weight was built with a PVC pipe enclosure to operations using a sonar device. A standard 75-lb sounding house the battery and wireless modem at the top (Figure 32). weight was used, with a hole machined in the bottom for the This eliminated routing the sonar cable from the water surface transducer. 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 might adversely affect the sonar measurement. Therefore, the transducer was not mounted flush with the flat bottom, but allowed to protrude and a shim was fabricated to transition the flow more smoothly off the nose of the sounding weight (Figure 33). High-Load Casters 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 Figure 30. Kneeboard with wireless sonar being deployed with a rigid frame. Figure 32. Sounding weight with wireless sonar.

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26 Figure 35. Final design for castor system. ation, but was time-consuming; during a flood situation, the time to mobilize and deploy prior to making measurements can be critical. Therefore, an alternative design was developed based on an arm that could be lowered under the outrigger foot pad. The Figure 33. Sonar mounted in bottom of sounding weight wheel was permanently attached to the arm, with the arm pro- with shim to transition flow off the nose. viding the lateral support necessary after the outrigger was lowered onto the castor (Figure 35). This design was not quite as rigid as the turnbuckle approach, because the outrigger allow truck movement when the crane arm is extended. To could move around slightly on the plate, depending on how high the truck was raised, but the method worked and was very permit this type of operation with this crane, high-load casters quick to set up. were fabricated and installed on the outriggers. The castors worked well, but the lateral loading during transit was strain- ing the outriggers. This problem was initially solved by build- Low-Cost GPS ing heavy-duty turnbuckles to create a strut between the truck frame and the caster (Figure 34). This created a very rigid sup- Available GPS Receivers port system, but the turnbuckle had to be removed to raise Research on low-cost GPS receivers was completed to the outrigger, and the castor needed to be removed for transit evaluate their ability to provide position information for the given the clearance to roadway. This was not a difficult oper- truck and/or other related scour measurement technologies. Although GPS technology can provide accurate position infor- mation and has been used in scour measurement applications, its high cost and lack of ease of use limits its widespread appli- cation. For example, GPS receivers used for land surveying applications are very accurate, but cost $20,000 or more and require specialized training. Therefore, the objective of this task was to research current GPS products that could provide sub-meter accuracy and were affordable and easy to use. The testing was not intended to be comprehensive, covering all available manufacturers and models, but rather was limited to a small sample of available products that could give an idea of the capability of receivers in the $5,000 to $8,000 range. Units in this price range are typ- ically used for precision farming, forestry, or utility-related geographic information system (GIS) applications, when the accuracy of a survey grade system is not necessary. This grade of GPS receiver can typically provide meter or sub-meter Figure 34. Turnbuckle to stabilize the hydraulic jacks for accuracy using a differential correction signal from a satellite the crane. or beacon receiver.

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27 The simplicity of the GPS system was important, given that The Leica GS 5+TM is a compact receiver/antenna com- inspection and/or maintenance crews might not have GPS bination where the receiver is housed inside the antenna experience. To be valuable in a flood response context, the casing. The unit consists of a 10 cm by 15 cm receiver/ GPS system must also be able to report a real-time position antenna with a power and data cable. Once the power is on site and not require post-processing of the GPS data to get turned on to the receiver, a NEMA string is output to the correct coordinates. data collector in the WGS-84 datum. This system was Lower cost GPS systems range from basic handheld re- mainly designed with GIS in mind and a GIS software ceivers using a WAAS (Wide Area Augmentation System) package and data logger is an available option. The GS correction only, to more advance receivers using a satellite or 5+TM includes a 12-channel GPS receiver and a 2-channel beacon correction. Systems using WAAS are easy to operate USCG beacon receiver that will provide accuracy of and cost-effective, but cannot achieve the sub-meter accuracy. 1 to 2 meters. This unit sells for about $2,500. Typical examples of the variety of lower cost GPS receivers The Leica GS50TM is the next step in the LeicaTM line of on the market in 2001 were as follows: GPS receivers. This receiver can receive either beacon or satellite differential corrections with an accuracy of The Garmin GPSMAP 176TM is typical of low-cost, recre- 1 meter or less. The GS 50TM receiver can collect and ational style GPS receivers. It is a 12-channel WAAS- store post-process data which, when processed, will in- enabled GPS receiver under $200. This receiver has a crease the accuracy slightly. This system is operated using display screen on which built-in base maps of the United a LeicaTM data logger which enables it to change parame- States can be viewed. Data (NEMA String) can be output ters, monitor performance, or store data. The antenna has to a computer by way of an RS232 cable. This receiver is built-in multipath mitigation and carrier phase smoothing. cost-effective, but is unable to give a high degree of accu- A data string can also be output to a laptop using in-house racy. Using the WAAS system as a differential correc- software. Cost of the receiver and data logger are approx- tion, an accuracy of 3 to 5 meters is attainable, and when imately $9,500. the receiver is operating autonomously, an accuracy of approximately 15 meters can be obtained. This receiver was not considered for testing and is identified only to provide insight on the capabilities and limitations of very Test Plan low-cost differentially corrected GPS. The receivers tested were the Trimble Pathfinder Pro XR The Trimble Pathfinder Pro XRSTM is a 12-channel, and the Leica GS 50. The Leica GPS system was available on differential beacon and satellite receiver. This receiver loan from a local survey supplier. The Trimble system was can receive a WAAS signal, Coast Guard (USCG) bea- demonstrated by a Trimble representative. The differential con, and OmniStarTM signals. The Pathfinder Pro XRSTM correction signal for each receiver was a Coast Guard bea- receiver is equipped with multipath rejection technol- con located in Whitney, Nebraska, about 400 kilometers (250 ogy in the antenna to remove multipath signals in reflec- tive environments. When using the Omni star or Coast miles) away. Representatives from both companies indicated Guard beacon, submeter accuracy can be achieved. Data that the accuracy would be about 30 centimeters better if the can be output onto a Trimble data logger or PC using receiver was close to the beacon signal. They also indi- TrimbleTM or other software to record data. The cost of cated that correction using a satellite system (e.g., OmniStar) this receiver without any additional add-on software is would provide comparable results. approximately $5,500. A testing grid was set up on a local bridge to test the accu- The Starlink Invicta 210STM is a 10-channel GPS re- racy and repeatability of these two GPS systems. Temporary ceiver that can receive differential correction from USCG, control points were marked on the bridge deck and in the Canadian, or IALA beacon signals. Satellite differen- channel (Figure 36). Some points in the channel were located tial correction is also available using the OmniStarTM where trees, the bridge deck, and high channel banks created subscription-based service. This system is designed to be less-than-ideal conditions. The objective was to see if the low- mounted out of the way with no setup required to collect cost receivers could overcome these obstructions and how data. A front display provides the user with access to long it would take to get a fixed solution. menu screens for configuring the receiver and/or viewing Accurate coordinates for all points in the test grid were satellite performance. When the power is turned on, the established using a survey grade GPS system and available receiver broadcasts the position via a NEMA string in permanent bench marks on the bridge (Table 2). The control WGS-84 geographic coordinates. A laptop and user- survey was also based on a nearby National Geodetic Survey defined software are required to view or save position control point, in the Geographic Coordinate System, NAD 83. data. No post-process data are collected. Accuracy with A Larimer County control point located approximately one- either the USCG beacon or OmniStarTM system would be quarter of a mile from the bridge was checked to verify the 1 meter or less. This system costs approximately $4,500. accuracy of the control survey.

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28 Figure 36. Control grid for GPS testing. Each temporary control point was then revisited using the in geosynchronous orbit, suggesting that the satellite coverage Leica GS50 and the Trimble Pathfinder XR system. The should not change with time, there are issues related to the time GS50 was available twice, allowing measurements on two dif- of measurement. ferent days with this system. Therefore, the test plan allowed GPS satellite orbits consist of 24 satellites that orbit the testing different equipment at different locations on different earth twice in a 24-hour period. The satellites orbit the earth in days. The potential differences from one day to the next six orbital planes with four satellites in each plane. Although were a concern, given that satellite coverage may be less than their orbit is described as geosynchronous, it is not exactly ideal on one day or even at different times of a given day. geosynchronous and there are times of the day when satellite Although the GPS satellite constellation is described as being coverage for a given area is better than for other times of the TABLE 2 Control network Pt. Number Pt. Description Northing (m) Easting (m) Elevation (m) 101 NE Corner of Bridge 441901.28 954463.60 1496.6 102 NW Corner of Bridge 441901.96 954395.69 1496.6 103 SW Corner of Bridge 441879.11 954395.49 1496.5 104 SW Rebar 441878.44 954396.30 1496.6 105 Painted Rock 441876.96 954403.95 1493.7 106 Rebar in Channel 441873.22 954422.49 1491.3 107 SE Corner of Bridge 441878.44 954463.40 1496.6 108 Painted Rock 441872.27 954454.03 1493.2 162 County Control Point 441859.73 955474.99 1490.7

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29 day. Satellite almanacs are available to view the satellite orbits and plan what times of day will have the best coverage in a given area. For instance, Figure 37 from an almanac program shows the view of the Northern Colorado sky at 12:00 p.m., during which 12 satellites are in view. Figure 38 shows the same view of the sky, but at 4:00 p.m. when only 5 satellites are visible. Because of this, most GPS surveyors in northern Colorado avoid working late in the afternoon when the cover- age is not optimal. Note that when the horizon is clear of obstructions, the GPS receiver will be able to see enough satellites to get an accurate solution at all times of the day, but the solution may be more accurate or faster when more satellites are in view. When working around bridges, problems can occur during low satellite count when part of the sky is blocked off by veg- etation or the bridge structure, causing the GPS receiver to lose sight of key satellites that are part of the real-time solu- tion. A quality real-time solution takes a minimum of four satellites to compute an accurate coordinate. If enough satel- lites are not visible to the receiver, the surveyor would have to wait until the satellite orbit has changed to include enough satellites that are unobstructed. Another factor that affects the Figure 38. Satellites available at 4:00 p.m. as viewed ability of the GPS receiver to get a quality real-time solution looking up at the satellite orbits from Fort Collins, is the location of the satellites in the sky. Satellites that are Colorado. orbiting low on the horizon or directly above the receiver usually cannot be used in calculating a solution. Satellite location is important when obstructions are present and has Test Results an effect on the GPS solution. Test results are shown in Tables 3 and 4. The measured horizontal value was typically within 3 feet (1 meter) of the control survey coordinate. Figure 39 shows the scatter of the measured data around the control point. The vertical elevations, as expected, were not as accurate. Repeatability of the hori- zontal result was a problem when the measurements collected during different tests were compared. The error between iden- tical points taken during different tests was as high as 10 feet (3 meters). Careful review of the plotted points in Figure 39 indicates that satellite coverage was not the cause of the observed errors. The best satellite coverage and the most available satellites occurred during the Leica Test #2, but these results are not sig- nificantly different from those of Leica Test #1, or the Trim- ble test, both of which occurred at a time of day when the satellite coverage was marginal. The influence of the bridge and/or tree cover was also not significant in the accuracy or repeatability of the measure- ments. Points 103 and 107 were on the bridge deck with little overhead interference, yet results at these points were not sig- nificantly better than points influenced by the bridge (Points 105 and 106) or tree conditions (Points 104 or 108). The most noticeable effect of the bridge and tree cover, as well as time Figure 37. Satellites available at 12:00 p.m. as viewed of day, was a longer solution time to arrive at a coordinate when looking up at the satellite orbits from Fort Collins, conditions were not optimal. Therefore, these results suggest Colorado. that a lower-cost, sub-meter-grade GPS receiver, as commonly

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30 TABLE 3a Leica Test #1: September 26, 2001, 3:00 p.m. Pt. Number Pt. Description Northing (m) Easting (m) Elevation (m) 103 SW Corner of Bridge 441879.11 954395.13 1480.5 *103-a SW Corner of Bridge 441877.76 954395.30 1482.1 *103-b SW Corner of Bridge 441878.22 954395.36 1482.1 104 SW Rebar 441878.40 954396.15 1480.5 105 Painted Rock 441875.78 954403.21 1477.8 106 Rebar in Channel 441875.88 954421.76 1475.7 107 SE Corner of Bridge 441877.95 954463.36 1480.3 *107-a SE Corner of Bridge 441880.11 954461.22 1481.2 *107-b SE Corner of Bridge 441877.12 954462.75 1482.7 *107-c SE Corner of Bridge 441877.25 954462.78 1481.9 *107-d SE Corner of Bridge 441877.52 954462.96 1482.1 108 Painted Rock 441871.24 954453.47 1479.0 *For comparison, the same point was revisited approximately 10 minutes later. TABLE 3b Leica Test #2: October 2, 2001, 10:00 a.m. Pt. Number Pt. Description Northing (m) Easting (m) Elevation (m) 103 SW Corner of Bridge 441879.99 954396.03 1482.0 103-a SW Corner of Bridge 441879.93 954395.75 1483.1 103-b SW Corner of Bridge 441879.75 954395.72 1482.6 104 SW Rebar 441879.20 954396.18 1482.8 105 Painted Rock 441877.95 954404.41 1478.9 106 Rebar in Channel 441874.56 954422.33 1476.9 107 SE Corner of Bridge 441879.26 954463.51 1482.0 107-a SE Corner of Bridge 441878.89 954463.51 1483.1 107-b SE Corner of Bridge 441878.98 954463.48 1483.0 108 Painted Rock 441873.25 954454.15 1479.2 162 County Control Point 441860.18 955475.69 1472.7 *For comparison, the same point was revisited approximately 10 minutes later. used in precision farming, forestry, or utility-related work, all had the same general WindowsTM layout. The primary dif- cannot provide the level of accuracy and repeatability needed ference was the different geometric calculations necessary for for scour-related measurements. position, depending on which deployment method and sensors were being used. Data Collection Software Four programs were created: one for direct sonar measure- ments with the articulated arm, one for use with the kneeboard Extensive effort was put into creating a software package deployed on a rigid frame, one for direct probing, and one for to automate the data collection process with the articulated cable-suspended operations. All programs produce an x,y,z arm. Data collection and processing occurred with a laptop data file that can be read by CAESAR (Cataloging and Expert computer equipped with two serial ports, one for the boom Evaluation of Scour Risk and River Stability) or any other data and one for the truck data, as sent by the two Campbell program such as AutoCad or Microstation. The x dimension CR10 data loggers. defined the vertical direction, including the measured scour Different programs were required, depending on the deploy- depth. The y dimension was the distance out from the bridge, ment method. The programs were written in Visual Basic and and the z dimension was the location along the bridge deck. TABLE 4 Trimble #1: October 5, 2001, 3:00 p.m. Pt. Number Pt. Description Northing (m) Easting (m) Elevation (m) 103 SW Corner of Bridge 441879.31 954395.54 *103-a SW Corner of Bridge 441881.15 954395.27 *103-b SW Corner of Bridge 441880.29 954395.22 104 SW Rebar 441878.97 954396.85 105 Painted Rock 441879.20 954403.81 106 Rebar in Channel 441874.39 954422.83 107 SE Corner of Bridge 441878.66 954463.20 *107-a SE Corner of Bridge 441878.75 954463.92 *107-b SE Corner of Bridge 441879.85 954463.64 *For comparison, the same point was revisited approximately 10 minutes later.

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31 Figure 39. Error in the measured data at each control point. The program for direct sonar measurements and the one for coordinates, as defined by the profile line for the bridge. the kneeboard deployment on a rigid frame were fully devel- The profile line is a station-elevation line on the bridge oped and tested. The program for direct probing and the one plans, typically along the centerline of the bridge deck. for cable-suspended operations were prototype versions, with This same datum is also used for other dimensions on the only limited field testing. plans, such as pier locations and pile tip elevations. Pro- The sensors on the truck define position data relative to viding the scour measurement results in bridge coordi- the rotational pivot of the crane. This coordinate system nates, facilitates rapid review and evaluation of bridge was defined as the "truck" coordinate system. Within the integrity, and was considered an important aspect of soft- software, these coordinates were converted to "bridge" ware development.