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