Analysis of Precision of Geodetic Instruments for Investigating Vertical Displacement of Structures Procedia Engineering 165 ( 2016 ) 906 – 917 1877 7058 © 2016 The Authors Published by Elsevier Ltd T[.]
Available online at www.sciencedirect.com ScienceDirect Procedia Engineering 165 (2016) 906 – 917 15th International scientific conference “Underground Urbanisation as a Prerequisite for Sustainable Development” Analysis of precision of geodetic instruments for investigating vertical displacement of structures Boštjan Kovačič a, Rok Kamnik a, Andrey Pustovgar b, Nikolai Vatin c,* a University of Maribor, Smetanova 17, Maribor, SI 2000, Slovenia Moscow State University of Civil Engineering, Yaroslavskoye Shosse 26, Moscow, 12933, Russia c Peter the Great St Petersburg Polytechnic University, Polytechnicheskaya 29, St Petersburg, 195251, Russia b Abstract This paper presents the analysis of preciseness and safety of different instruments for researching the vertical displacements of the objects in the space In Slovenia researching the objects by the test of pressure is obligatory for all structures, which are longer than 15 meters (JUS U.M1.046) Among all the methods we choose geodetic as well as non-geodetic ones There are many methods for researching the displacements, so we took limits to the instruments available to us On the Faculty of Civil Engineering, University of Maribor, Slovenia, used the level, total station, and inductive transducer and laser level The measures of displacements were made on the reinforced concrete plate, type PVP5 For the plate we calculated the foreseen displacements by the analytic as well as by the numeric method For analytic calculation we used the national regulations (Euro code 2) and for numeric part we used the programme Ocean For each instrument we calculated the standard deviation and the optimal accuracy, we checked the significance of results by the analysis of variances with one variable factor In this paper we described all the instruments for following the displacements and the working principles of instruments by which the research was made and the measurement errors The analysis of precise was made on the base of comparation between the results of foreseen displacements and the gained results of measurements The results of this research are gathered in a conclusion and give us the answer to the goals © 2016 2016The TheAuthors Authors Published by Elsevier © Published by Elsevier Ltd Ltd This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the scientific committee of the 15th International scientific conference “Underground (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under scientific committee of the 15th International scientific conference “Underground Urbanisation as a Urbanisation as aresponsibility Prerequisite of forthe Sustainable Development Prerequisite for Sustainable Development Keywords: innovative materials, accuracy of measurement results, analysis of preciseness, displacements; * Corresponding author Tel.: +7-921-964-37-62 E-mail address: vatin_ni@mail.ru 1877-7058 © 2016 The Authors Published by Elsevier Ltd This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of the 15th International scientific conference “Underground Urbanisation as a Prerequisite for Sustainable Development doi:10.1016/j.proeng.2016.11.800 Boštjan Kovačič et al / Procedia Engineering 165 (2016) 906 – 917 Introduction Experimental methods for investigating structures in their early phases were based on theoretic calculation that describes deformation growth and breakage under load With the development of numerical sciences and the increased surge of information science in the last 30 years, numerous home and foreign experts have taken up the analysis of displacements and deformations and published their results in articles and books Most of the authors analysed displacements and deformations, and fostered the upgrading of the compensation model for horizontal and vertical measurements [1-25] Among home authors, Marjanovič [1] deserves to be mentioned who describes non-geodetic methods for measuring linear displacements Methods for measuring displacements and deformations were presented also by Narobe in 1996 [2] In his article, he presents measurements performed with inductive transducers, classic theodolite and precision level All the results obtained were statistically processed, mathematical statistics thus forming a component part for the compensation of results The statistical processing of data based on the growth of the nil or alternative hypotheses and on different tests for checking significance, as well as on the class of error values was presented by Pelzer [3] An outstanding contribution to deformation measurement methods was made by Milev [4] in 1985 Welsch [5] made a schematic presentation of deformation analysis process of geodetic nets, which served as a basis for the creation of computer programs The same topic was studied also by Kapović, Narobe and Mastelić [6] from the Geodetic Faculty in Zagreb, and Breznikar [7], Vodopivec and Stopar [8] from the Faculty of Civil Engineering and Geodesy of the University in Ljubljana Their investigations focus on the calculation of precision measurements and errors in measuring structural displacements and deformations As evident from this survey, numerous experts worked on the analysis of displacements and deformations To repeat, the most notable contribution to the analysis of deformations was made by Welsch and Pelzer with coauthors They set the bases of deformation analysis and solved key problems in the stability of geodetic nets Measuring instruments According to standards in Slovenia, all vertical displacements during statically loading test must not exceed calculated values These values are calculated by static in statically calculation of constructions Calculations are made for all critical points on constructions These points are on structure typically: supporters and middle of the span (Figure 1) Vertical displacements are observed on these critical points At observations of vertical displacement, three different geodetically and one physical measurement methods are used to get better uncertainty Systematic errors can also be avoided when all methods are applied Fig.1 Measurement points on the bridge In geodetically measurements methods on traffic surface of a construction are used total station with precisely tripod, digital level with high accuracy and laser level with sensors In physically measurement method are used 907 908 Boštjan Kovačič et al / Procedia Engineering 165 (2016) 906 – 917 inductive transducers of displacement on the opposite surface of the traffic surface Sensors must stand on reference to the grounding, so they can be used on structure not higher than meters Most of constructions don't make us possible to set up the inductive displacement transducers because of height or unapproachability of the area In such cases the method of geodetic levelling and method of laser system are used, which enables us to determine vertical movements up to span of 300 meters Laser system is made of sensors, laser level, communication terminal and the program "Laser", which notice the movements Sensors and communication terminal are connected to coaxial cable RS-485, and the communication terminal is connected to the personal computer with the RS-232 cable The reference station used with laser system and classical geodetic instruments must be set up on a stabile ground and at the appropriate distance from the construction, so, that vibrations caused by overloading aren't transmitted to instruments To increase the accuracy of instruments, the reference station is set up to a pre-prepared massive tripod With a tripod the error of subsiding the instrument, which we could expect with the use of classical geodetic tripod, is avoided Geodetically prisms can also be set up to concrete squares (20x20x20 centimetres) to increase the accuracy of measurement Sensors can be fastened to classical tripod or directly to construction, which is also more reliable (Figure 2a,2b) Fig a) Position of geodetic instruments; b) The rotation level and sensors on the critical points Calculated movements 3.1 Analytical methods To enhance the accuracy of measurements and to be able to verify the results, predicted displacements should be calculated before measurements have been taken For an uncracked cross-section, with analytical methods, displacements can be computed with known methods of structural calculations More problems are encountered at cracked cross-sections where cracks occur due to low tensile strength of concrete This results in the reduction of inertial moment of average cross-section and thus in greater deformation As the location and the height of cracks are difficult to determine, due to properties of concrete, they are stated in different national codes Euro code (EC2) [10] has lately been applied most frequently C3 C2 Boštjan Kovačič et al / Procedia Engineering 165 (2016) 906 – 917 C1 P1=P/3 = 7.895/3 = 2.,632 kN 40 40 20 40 40 bp=1.60m ya L=4.18m yb Fig.3 Statically system 3.2 Numerical methods It is often the case in practical applications that the required geometry of plates cannot be obtained by analytical methods Therefore, different numerical methods are used which are based mainly on finite elements or finite differences As the calculation procedure is a long one, different computer programs are used One of them is Ocean [11] It allows the computation of cracked cross-sections in accordance to EC2 Fig.4 Simulation displacement in 4th step with program Ocean 3.3 Calculated results The obtained results with both methods are similar With analytically method we get in first three step linearly displacements while in the fourth step we observe a occurrence of steel cracked so because that the displacement in first step are greater and not linearly With another method we get the dissimilar movements, which are not linearly in separate steps This method are suitable to calculated a bigger constructions where is the expected displacements greater too 909 910 Boštjan Kovačič et al / Procedia Engineering 165 (2016) 906 – 917 3.4 Measuring results of experiments Considering mean values of individual instruments we obtain the following values in millimetres (Tabl 1, Graph 1) Table Measured and calculated values Instruments/ displacement [mm] Step Step Step Step Total station 0.4 0.9 1.3 1.8 Level 0.4 0.7 1.1 1.6 Inductive transducer 0.356 0.715 1.051 1.530 Rotation level 0.4 0.8 1.3 1.9 Calculated movements by EC2 0.3965 0.793 1.185 1.731 Calculated movements by Ocean 0.56 0.88 1.20 1.67 Graph Measured and calculated movements shown in graph It is evident from Graph 1, that correspondence with predicted displacements is the highest when measurements are performed with the level method, and the lowest when they are performed with the method of rotation level It is also evident from the graph that the inductive transducer gives the most balanced results, while the least balanced are obtained with the rotation level 911 Boštjan Kovačič et al / Procedia Engineering 165 (2016) 906 – 917 Calculation of results adequacy, accuracy and safety 4.1 Mathematically calculation of results adequacy For this we use the mathematically method of interpolated polynom of 3rd degree For each instrument the equation system are combine On the salvation of this system we execute an integrated comparison of results We think that the prime results of integrated salvation are these that are fulfil expectations of hypothesis ³ T x f x dx b a n (1) Where is: Tn(x) – theoretically method function (EC2 and Ocean) fn(x) – estimation of 3rd degree polynom for each instrument The results integrated comparison to EC2 has a minimum hypothesis values at the rotations level These results are similar like the obtained measurement results in Table 4.2 Calculation of uncertainties and standard deviations of displacements For all methods calculations of uncertainties and standard deviations were made Measured values were compared with calculated values of displacement [12] s >vv@ n 1 (2) Uncertainties for each method are in mm: Table 2: Calculated standard deviations for step 1, 2, and Method s – 1st step s– 2nd step s – 3rd step s – 4th step Total station 0.09 0.06 0.14 0.09 Level with micrometer 0.08 0.06 0.12 0.09 Rotating level 0.07 0.06 0.19 0.09 0.01 0.01 0.01 0.01 Inductive Transducer Graph Uncertainties in 3D graph 912 Boštjan Kovačič et al / Procedia Engineering 165 (2016) 906 – 917 The standard deviations are calculated for each instrument Results shown us that we measured in separate steps very precisely Only in third steps the results are a little bit greater so we can this ascribe to appearance of cracks All usage instruments are appropriate to measured micro displacement If the constructions permitted the inductive transducer setting up (height) that is expedience to used it 4.3 Calculated optimal measure accuracy of micro-displacement On the groundwork [6] the measurement procedure are determinate and optimal measurement accuracy are calculated for all used instruments On the bases of measured results the means values and standard deviations are calculated For this calculate we set two criterions: 1/20