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Paper CIBW99-0074-06Theme : Measurement and quantitative analysis

DYNAMIC SURVEYING AS A MEANS TO ENSURE

STRUCTURAL SAFETY

Gheorghe M.T. Radulescu1, Ovidiu Stefan2 and Adrian Traian G. Radulescu3

1Prof. Dr. Eng. Mat. North UniversityBaia Mare 430083, Romania

2Vicemajor, Dr. Eng., Baia Mare Municipality, Baia Mare 430083, Romania3Eng. North University

Baia Mare 430083, RomaniaCorrespond to: [email protected]

Abstract. Construction safety cannot be conceived except by ensuring a careful geometricmonitoring in static, cvasistatic or cinematic regime of the execution and time behavior of the performedstructures. Among special structures (bridges, dams, very tall buildings) this aspect is in the center ofattention. In this way, new methods have appeared for ensuring the geometry, taking into account theperturbing factors from among which, the main one is the action of the wind. Situated at the borderbetween structural safety meteorology surveying, the new domain is therefore an interdisciplinaryone. Therefore, an axis should be identified, by which this domain should be defined and developed. Wewould call this axis the dynamic surveying axis.

The purpose of the paper is to present this new chapter of surveying and its role in structural safety.The research subject was initiated 20 years ago, when the new concept appeared and was developed,

and it was called verticality. In this paper we present the aspects that have been solved until now, andwhat else should be done such that this new concept would become a concept on its own.

The main results were:

1. Identifying the danger that some cumulated forces represent for structural safety. The examplespresented here are forces coupling as result of non-uniform sunlight and wind.

2. Illustrating the concept of the manager system in coordinating the geometry for executing thestructures under stress.

3. Defining the components of Dynamic Surveying and thus creating the platform for developingthis new concept.

The conclusions of the paper will emphasize the fact that Dynamic Surveying, though it has a verystrong interdisciplinary character, represents a development of classic surveying methods in the cinematicspace and therefore should be considered a distinct and separate chapter.

The safety of the inhabitants of a very tall building, of the people that use a very long bridge, cannot be accomplished except by the existence of safe structures, the role of Dynamic Surveying beingdefinitive.

It should be mentioned that Dynamic Surveying has a decisive role, both during the execution of

constructions, and after that, during the monitoring of their time behavior, which is a basic component ofstructural safety.

Key Words: dynamic surveying, performed structures, verticality, very tall building.

1. OUTLINING THE OBJECT OF STUDY OF DYNAMIC TOPOGRAPHY

Recreating the optimal design cycle of special reinforced concrete and metal structures in a certain space:in-situ behavior under the action of some stresses that are variable in time (wind, temperature,exploitation), implies monitoring them in dynamic regime (figure 1).

Among the applications of Topography in the field of special structures (figure 2), the dynamic part refers to the study, recording and processing of the characteristic parameters of the externalinfluences, as well as of the geometry of structures, under the action of variations of certain stresses in ashort period of time (at most 24 hours).
mailto:[email protected]:[email protected]


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For special structures, the behavior at temperature variations is part of dynamic analysis, implyinga diurnal variation of the geometry, therefore implying measurable parameters using classical means.Also, the behavior under the action of wind or under load is part of dynamic analysis, generating avariation of the geometry, with optimal periods for data collecting between 0.01-1 s. In this case, theclassical operating means of topography are not operable.

Figure 1. Recreating the optimal design cycle of special reinforced concrete and metal structures

Figure 2. Involving topographic measurements in the application of construction projects

2. STRUCTURES IN DYNAMIC REGIME

The stresses that operate on construction structures have a continuous character, if the inertia forces havesizes comparable to the intensity of the action that generates the phenomenon. Thus, the action of someequipment and industrial devices, earthquakes, temperature variations, and wind leads to the productionof some phenomena of dynamic behavior, described by equations having the following form:

d=Df (1)where:

d the main unknown of the problem it is usually a displacement system, subjected to somelimit constraints;

A better possibility

Technical economical studies

Studies on modelsDesign

Execution

In situstudies

Topographic survey

Comparativestudies

Execution Topographic survey

Topographic tracing

Survey of geometry

Time behavior

Behavior at variations in time

Behavior under the action of wind

Execution project

Static problem

Dynamic problem

Finitestructure


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D system of mathematical operations;f the constant term, corresponding to the action taken into consideration, which could contain the

initial conditions, too.

3. METROLOGICAL OUTLINING

Studying the variation of some geometric variables (Xi, Yi) or (Di, i) depending on time and on the parameters of the stress (direction, orientation, speed) requires the methodological approach of thephenomenon. Thus, the metrology of geometric variables, the metrology of time, and the characteristicsof the environment are involved directly, and the metrology of electrical variables is involved indirectly.In this case, taking into account the double mission of metrology: to pretend some performance from theproducer of the measuring devices, and to ensure the user (beneficiary) of this performance thefollowing question rises Shall we start with the method, going towards the devices, or, having a series ofinstruments, shall we adapt the methods?. In figure 3, the inter-relations device structure environment operator will be methodologically.

The connections are determined by the two possibilities of recording the dynamic parameters: 1)without having direct contact with the structure; and 2) the instruments are assembled directly on thestructure. The models of topographic survey (theodolite), photogrammetric survey, recorded on film orvideo belong to the first category. The unconventional methods, used for monitoring the structures, the

instruments and techniques that have to be included in the sphere of topography, belong to the secondcategory. The basic condition of recording, which is taken into account, requires: to ensure the uniformityof measurements with respect to the accepted precision.

Figure 3. The inter-relations device structure environment operator

In this case, the metrological principle no variable is perfectly constant in time is very true,because it needs to place the information of measurement into the specified category (figure 4).

Figure 4. The metrological principle no variable is perfectly constant in time. Outlining topographicmeasurements in variable regime

In this case, the functionsx(t),y(t) of the variablesx,y, depending on the time twill be measured. Inthe case of measuring through points, series of the measured variables will be obtained, which willform the flow of information Q:

Q = n I (2)where:

Measuring

Constant

Variable

Non-stationary

Stationary

Periodical

Non-periodical

Sinusoidal

Non-sinusoidal

Environment

Device

Operator

Standard

Device

Structure


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n is the number of pieces of information per time unit;I the primary information.

We can obtain n = 30 inf/min, Ibeing of geometric nature: angle or distance, one of each piece ofinformation.

The equations of the exit variables (figure 5) will have the following general form (3):),...,;,...,;,...,( 11 qpnii ccvvxxy = (3)

where:yi exit variables;xi measured variables;vi influence variables;ci device instructions.

, 1, ,pi n iii i n i

i n i p

ff f f y x x x i m

x x v v

= + + + = K (4)

where:i

i

x

f

represent the useful sensibilities of the measuring device, and must have exact values, as

stable in time as possible, generating the device errors, andi

p

f

v

represent the parasitic sensibilities of

the measuring device, determined and situated within certain limits, if possible.The exit variables can be referred to the operator or to a technical system for processing and

recording.

Figure 5. The exit-input elements in the process of topographic measurement in dynamic regime

When choosing measuring devices, the following elements should be taken into account: therequired precision, the existing perturbations, the necessary measuring speed, the length of ameasurement, the environmental and location conditions, the simplicity, the volume, and the cost. Ofcourse, here we are referring to such a measuring system, which allows measuring a series of variablesbased on a software measuring program. Now, there are numerous methods available, and there existreal manager systems for monitoring the behavior of structures under the action of some dynamic

stresses.In the case of measurements that are variable in time (dynamically stressed structures), the notion ofdynamic error becomes apparent. Concretely, in dynamic regime, the exit variable does not respect

InfluencevariablesEnvironmentOperatorT

emperatureExperienceWindDisp

ositionHumidityTirednessPressu

rePreoccupationImpuritiesTime

budget

InstructionsCoarseRefined X

Y X Y

MeasuringdeviceTheodolite

ExitinformationLinearAngular

X Y x

y

MeasuringvariablesLinearAngular X

Y X Y

n: measurands;

m: exit variables;p: influence variables;q: instructions;


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completely the variation of the input variable. Among the causes of this phenomenon, we can mention:the inertia of the mechanical parts of the device, the reactive components from the circuits of theelectrical part.

In the end, the data should be presented separately, and also cumulated, because an unfavorablesuperposition of the effects can lead to the production of a discontinuity in the behavior of the structure(mathematically called catastrophe), even though each cause is within design limits.

4. NEW TECHNIQUES, DEVICES, MANAGER SYSTEMS FOR MONITORING THE

STRUCTURES IN DYMANIC REGIME

In order to punctually or continuously record the response of real structures to various stresses, especiallywind, earthquakes, or different exploitation conditions, the following types of instruments have beencreated: classical scanners, or laser scanners, video systems, RTK-GPS systems, sensors, stamps,pendulums, laser levels, inclinometers, accelerometers, and generally, expert or manager systems formonitoring the structures.

A large part of them are creations of companies that produce geo-topographic devices, especiallyLeica and Trimble, but it should be mentioned that there are new companies, which are specialized inmonitoring the structures in continuous dynamic regime or which produce instruments for this activity,and which have nothing in common with the field of topography.

4.1. Sensor Systems

4.1.1. Typical New Sensors

Typical New Sensors that monitor the geometry and deformations of bridges are: linear variabledisplacement transducers (LVDT a distance measuring device), vibrating wire strain gauges, foil straingauges (set up in quarter, half, or full bridge strain configurations), inclinometers, crack and joint sensors,tilt sensors, piezo-resistive accelerometers, piezoelectric accelerometers, capacitive accelerometers,borehole accelerometers, servo force balance accelerometers and total stations. The effort focuses on thedesign and development of a self-displacement measurement device and a wireless data communicationsystem. The diagnosis techniques will include finite-element modeling of the suspension bridge,modeling and measurement of strong wind, earthquakes and traffic loadings, analysis of the ambient

vibration data through the use of the technique to eliminate the use of an exciter, a global damagediagnosis technique to identify and characterize the damage, and selection of sensors and techniques todetect localized damage and defects. The News concept of monitoring bridges combines on-siteinspections of the building by static and/or dynamic measurements with Finite-Element calculations andre-measurements at specific times. Typically, we conduct a detailed basic measurement to determine themodal parameters and static properties of the bridge. The optimization process is used to calibrate a FE-model representing the realistic dynamic behavior. These surveys show that it is already possible toevaluate the condition of the bridge and to calculate realistic reliability indices based on vibrationmeasurements. In principle, bridge-monitoring systems can be operated on a periodic or continuous base:

Periodical testing: measuring the vibration behavior is carried out at specific time intervals.Sensor location should be in accordance with the initial measurement.

Continuous monitoring: sensors are installed permanently to the bridge, providing a continuousflow of data concerning the condition of the bridge.

4.1.2. Sensor Network

A significantly new challenge in research is the need to integrate multiple sensor streams to develop localand global health-state indicator variables that need to be queried and monitored by the system. Theindicators may be defined as user-specified aggregates (or other functions) over instantaneous values ofseveral data streams, covering one or more sensors.

The sensor network may consist of a dense array of heterogeneous sensors (e.g., strain gauges,accelerometers, cameras, potentiometers, , etc.). In addition, the network must be easy to deploy,should be scalable allowing for progressive deployment over time, and must allow for local processingand filtering of data, remote data collection, accessibility and control. Communicating with sensors haslong been limited either to wired connections or to expensive, proprietary wireless communication

protocols. Using a ubiquitous and inexpensive wireless communication technology to create Fixed SensorArea Networks (FSANs) will accelerate the extensive deployment of sensor technology.


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4.1.3. The Cambridge Monitoring System (CMS)

The Cambridge Monitoring System (CMS) is a new, ultrasonic-based monitoring system primarily usedfor concrete structures, but with possible application to structures made of other materials, too.Cambridge Ultrasonics has successfully developed an R&D prototype system that works well.

What CMS provides:

- Regular, automated inspection of chosen locations on the structure at a frequency chosen by theoperator (for a network of 100 sensors the inspection period could be as frequent as 50 times aday per sensor).

- Uses injected ultrasound (not acoustic emission) with advanced pattern recognition signalprocessing to reject operational noise.

- Uses advanced decision-making algorithms to decide if any change has happened at a testlocation.

- Combines results from more than one test location to give a result for any part of the structureor the whole structure in the form of a probability of significant structural change.

- Presents warnings in various forms: CAD representation of the structure showing locations ofchange, e-mail message or similar to a central control, audible warning, etc.

Benefits of using a CMS system:- Improves safety of operating concrete structures.

- Helps make better use of repair budgets by directing inspection or repair to where most changeis happening.- Extends working life of older structures particularly beyond the normal working life.- Low annual running costs an automated system does not need a full-time operator.- Provides audit trail of any structural change in the event of litigation relating to integrity.A network of intelligent, CMS sensors is attached to the structure to be monitored and connected by

cable or radio back to an Archive PC. Each sensor injects a known pattern of waves into the part of thestructure to which it is attached and each sensor collects echo-waves back from the interior of thestructure. CMS is not an acoustic monitoring system, which is a passive monitoring system and which ispotentially very sensitive to operational noise.

4.2. 3D Scanner

The 3D Scanner is an advanced surveying instrument that uses high-speed laser and video to capture vastamounts of coordinate and image data. The office software is part of an integrated 3D scanning field andoffice software suite for surveyors and engineers. Taking advantage of the rich point cloud data providedby the 3D Scanner, RealWorks Survey manipulates and manages large scan files to produce dramatic andcompelling 2D and 3D deliverables. The software also supports data collected using GPS and total stationtechniques, so you can coordinate and combine data from a surveying job in one project file for anIntegrated Surveying solution.

Therefore, if benchmarks are assembled on the surveyed structure, these can be monitored incontinuous regime, 24/7, recording the displacements of the bridge, under load or under the action ofwind or non-uniform sunlight.

4.3. Digital & Electronic Levels

Digital and electronic levels create a new standard for leveling on construction sites. They are easy to use,take measurements two times faster and minimize human error, and the application programs on boardfurther enhance leveling work.

One of the most precise methods for monitoring the time behavior of structures is the middlegeometric leveling, digital and electronic levels allowing the increase of the precision of recording smalldisplacements in time.

4.4. GeoMoS Monitoring Software

GeoMoS consists of a Monitor and Analyzer application. Monitor is the real-time application ofGeoMoS, responsible for data collection and online measurement control, limit checks, status messagingand measurement cycle control. Analyzer is the analysis application of GeoMoS, responsible foranalyzing and reporting of the measured data, plus editing and post-processing of data where required.Data and results can be viewed numerically or graphically and exported in various standard numericaland graphical formats. Connection of different sensors (e.g. TPS, GPS, meteorological sensors, geo-


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technical sensors) is handled by a LEICA Sensor Manager component, which also provides an interfacefor sensor configuration.

Sensor Connections: Total Stations, GPS Sensors: Leica GPS System, Tilt Sensors, Meteorologicalsensors (e.g. temperature, pressure), Geo-technical sensors (e.g. extensometers), Sensors from othermanufacturers.

Software Features: Supports a project concept for periodic monitoring projects, System can be

remotely accessed and configured, Scalable configurations from single station to multi-stationconfigurations, Large database support with multi-user access (SQL-Server), Multiple number ofmeasurement stations connected to the system, Parallel use of several sensors (TPS, GPS, meteorologicaland geo-technical sensors), Automatic data dispatching and synchronization using cable, radio link, LAN,WAN or Internet, Long distance measurement capability (up to 5 km), Meteorological network modelingover measurement area, Powerful Analyzer, Toolbox for visual and alphanumeric analysis, Editing andPost-processing throughout data history, Powerful status message management (e.g. limit exceeded,power failure, burglary), Status messages via E-mail or Digital I/O Interfaces, Import/Export to othersystems (ASCII, DGN, WMF, standard Excel formats), Automatic Backup and Archive.

Applications: Deformation Measurements (e.g. dams, tunnels, volcanoes, bridges and high-rise buildings), Landslide and Settlement Detection (e.g. mining), Automated Surveys (e.g. continuous,automated measurements).

4.5. The Campbell System for Monitoring Structures

The versatile capabilities of Campbell Scientific data acquisition systems make them ideal for structuraland seismic monitoring. These data-loggers have been used in applications ranging from simple beamfatigue analysis, to structural mechanics research, to continuous monitoring of large, complex structures.

Highway overpasses, roads, buildings, retaining walls, bridges, and amusement park rides are thetypes of structures for which our systems provide remote, unattended, and portable monitoring. Thesedata acquisition systems make reliable structural measurements, even in harsh environments.

System Benefits: Onboard, programmable, excitation is provided for ratiometric bridgemeasurements. Systems provide triggered output with pre-trigger data capture capability. Most sensorsand communications options can be used, allowing systems to be customized to meet exact needs.Systems operate reliably in harsh environments. Scan rates range from a few hours to 100,000 times persecond. Systems can report conditions by calling out to pagers, radios, or phones. Systems support long-

term, unattended data storage and transfer. Pick-and-click software facilitates programming.Monitoring and Control: The versatility of systems allows them to be customized for each

application. We offer a range of data-loggers from the most basic system with just a few channels, toexpandable systems that measure hundreds of channels. Scan rates can be programmed from a few hoursto 100,000 times per second, depending on the data-logger model. Measurement types, recordingintervals, and processing algorithms, are also programmable. Data-loggers not only provide advancedmeasurement capabilities, but can also control external devices.

The configurable data-logger models, the CR9000X and CR9000XC, allow customizing a systemwith the channel types that best fit your application. The number and type of channels on most of ourdata-loggers are expandable using multiplexers and other measurement peripherals.

4.6. Using the GPS Technology for Monitoring Structures

It should be specified that the first use of GPSs in engineering was for monitoring bridges, in the 80, andthe development of professional GPSs was possible precisely because of these applications. Thesubsequent applications were for monitoring very tall buildings, and the execution and monitoring of thetime behavior of the Petronas and Taipei 101 buildings was accomplished using this technology.

The Global Positioning System (GPS) is used for many purposes in surveying and geodesy, such as:cadastral surveys, engineering surveys or intercontinental coordinate frames. The main characteristics ofthe GPS technology of geodesic class are: the signal code and phase in general 2 frequencies, accuracy of0.001 to 0.1 m, and approximate costs of 20-50000 .

The technology is simple and easy to use. Therefore, the GPS antenna is assembled on themonitored structure, recording the position, in continuous regime, through coordinates in the WGS1984worldwide system, then trans-calculating it in the national system and then, for simplification, into a localsystem. The displacements, oscillations, and displacement speed, hence, all the parameters that define thetime behavior of the structure under the action of wind or exploitation, are established comparing atvarious moments the coordinates of the axis of the antenna.


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5. CONCLUSIONS

In order to ensure safety in constructions in case of spectacular structural works, the surveying methodsbecame compulsory. Therefore, dynamical surveying has appeared as a new chapter of surveying, whichplays an important role in monitoring the geometry of the structure in kinematical conditions: the actionof wind or non-uniform sunlight, both during execution and during the process of monitoring the time

behavior. We consider that the main cause of the non-correlation between the lately increasing concernstowards computation to stability and the continuous happening of accidents, malfunctions, catastrophes ofthe structures is the lack of sufficient data regarding the in-situ behavior of the designed and executedstructures under various combinations of stresses. Precisely here, generally the Surveying, and especiallyits new chapter, the Dynamic Surveying, have the possibility to connect the broken chain of optimaldesign in the field of construction structures.

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