Ingenieurvermessung 2004 14th International Conference on Engineering Surveying Zuerich, 15. – 19. Maerz 2004

Monitoring of old building in Ljubljana – Slovenia

Božo Koler, University of Ljubljana, Faculty of Civil and Geodetic Engineering

Aleš Breznikar, University of Ljubljana, Faculty of Civil and Geodetic Engineering

Summary This study shows the results of monitoring of old building in Ljubljana (Slovenia). Visible deformations on building (cracks on the walls, problems with casements and folds) appear when the reconstruction works on building in vicinity began. For determination of vertical movement we stabilized four benchmarks in the building and connected them in leveling loop.

1 Introduction According to the order by the object owners, where the object is situated in the center of Ljubljana we discovered vertical movements of this object. In the object visible deformations (cracks) appeared because of the renovation work on the neighboring object. To establish the vertical movements of the object and not the so-called own movements of the benchmarks, that are not connected with the vertical movements of the object, we have to reach for the stabilization of the benchmarks the suitable connection between the basis, in which the benchmark is built and the material from which the benchmark is made of. For the

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stabilization of benchmarks we used the two-component glue, with which we got a strong connection between the benchmark and the object.

Picture 4: Benchmark stabilized from the front side of the object We connected the new stabilized and existed benchmarks of the city levelling networks with the levelling network. With that loop we gained:

1. An additional control for single measurements, that we made and in this way we can close the levelling network.

2. Measured height differences can be adjusted as a free network. 3. On the basis of the adjusted above sea-level of the benchmarks, that we get with a

single measurement and assessment of accuracy of the determined above sea-level, we get a chance for a qualitative estimation of the stability or unstability of benchmarks, that is a consequence of the eventual vertical movements.

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Picture 2: View on the object from the front and the backside

2 Measurements of the leveling network We measured the levelling network (see picture 3) seven times. Four measurements were done from June to October 2002, the other three during March and July 2003. We included in the leveling network (see sketch below):

1. The new stabilized benchmarks (FGG1, FGG2, FGG3 and FGG4). 2. The existed benchmarks of the 1st levelling network of Ljubljana (5764, 100, 19-4). 3. Points stabilized on the object, which is renovated (R10 and R11).

Picture3: A sketch of the levelling network

FGG1FGG2

FGG3FGG4

R10R11

5764

100

19-4

Cankarjev dom

232527

19 15

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3 Instrument and equipment The measurement of the described levelling network was carried out with the digital level Leica Na 3000 enabling automatic recording of readings from coded invar levelling staff. Level is one of the most precise instruments in the world and it is intended for levelling the 1st order-levelling network, observing the deformation measurements and for the engineer surveying. At the measurements we used calibrated invar precise levelling staff. We measured also the temperature of the invar with the contact thermometer.

4 Adjustment of the leveling loop and assessment of accuracy

We adjusted the levelling loop as a free net with the software VIM 8, which was made at the Faculty of Civil and Geodetic Engineering (Ljubljana, Slovenia). The measured height differences are adjusted according to the method of adjustment of indirect observations. The criteria for assessment of accuracy are mean errors. In precision levelling the accuracy can be assessed according to different criteria. The following assessments of accuracy have been made for the levelling loop:

a) Assessment of accuracy on the basis of discrepancies of levelling lines (σL)b) Assessment of accuracy on the basis of closing a levelling loop (σZ)c) Assessment based on corrections of measured height differences after adjustment

(σ0)

From the table 1 we can see that all calculated standard deviations of the measurements are lower than 1mm/km. These values are within the expected ones considering the accuracy stated by the manufacturer of the levelling instrument used for the measurements.

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The results of standard deviations calculated according to the above-mentioned criteria are the following: Standard Number and date of the measurement Deviation

(mm) 1

18.6.02 2

26.6.02 3

3.09.02 4

21.10.02 5

16.04.03 6

22.05.03 7

03.07.03

σL ± 0,21 ± 0,42 ± 0,42 ± 0,64 ± 0,66 ± 0,42 ± 0,47σZ ± 0,52 ± 0,12 ± 0,44 ± 0,34 ± 0,67 ± 0,38 ± 0,69σ0 ± 0,75 ± 0,19 ± 0,61 ± 0,48 ± 0,93 ± 0,53 ± 1,00

Table 1 5 Vertical movements of the benchmarks in the area of old building The results of the deformation analysis for periodical measurements in which unstable object points are determinate are given in the table 2.

Vertical movement (mm) between periodical measurements (unstable)Benchmark 1-5 1-6 1-7 2-3 2-4 2-5 2-6 2-7 3-6 3-7

5764 -1.9 2,5 2,2 1,4 1,4 2,4 3,1 4,3 1,3 1,2

19-4 1,9 1,5 2,0 0,3 0,6 1,3 2,4 3,6 2,1 1,5

100 0,2 0,5 0,7 ±0,0 ±0,0 0,2 1,2 2,6 0,5 0,7

R10 -0,8 -0,7 -0,3 -0,3 -0,2 -0,8 -0,7 1,6 -0,4 ±0,0

R11 -1,6 -1,7 -2,1 -0,7 -0,5 -1,5 -1,1 -1,9 -1,1 -1,3

FGG1 0,5 0,4 0,5 0,2 0,1 0,4 1,0 2,2 1,1 0,2

FGG2 -1,9 -1,9 -2,3 -0,5 -0,3 -1,6 -0,9 -1,8 -1,1 -1,4

FGG3 1,0 0,8 0,6 0,2 -0,1 0,8 1,3 2,2 1,4 0,2

FGG4 -1,9 2,1 -2,2 -0,8 -1,0 -1,8 -0,7 0,1 0,2 -1,3Table2 Vertical movements of benchmarks

A deformation analysis was done with a Hannover method. After the adjustment of free network the deformation analysis was done in following steps:

1. The test of homogeneity of two epoch networks accuracy. 2. The global congruency test for the points stability between two measurements.

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3. The test for stability of reference points, if the reference point is found to be unstable then it is classified as object point.

4. Test of vertical displacements of object points. Al these test are included in the computer program DAH and were done with level of test significance α = 5 % (T. Ambrožič).

6 Conclusion On the basis of made measurements we can conclude, that the object has moved vertically. From the table 2 we can see, that the points FGG2 and FGG4, which are stabilized in the corner of the object, and are closer to the object that is renovated, were sunk. From the table 2 we can see, that the vertical movements for benchmarks FGG2 and FGG4 with the comparison from the first (18.6.2003) and the last measurements (3.7.2003) are relatively high, because these movements happened in a period little longer than a year. Benchmarks that are built in the opposite corners (FGG1 and FGG3) were lifted and were stable almost between all periodical measurements.

Reference: AMBROŽIČ, T. [1996]: Stability Estimation of Points in a Geodetic Network. Masterwork,

University of Ljubljana, Faculty of Civil and Geodetic Engineering, Slovenia

Address: University of Ljubljana Faculty of Civil and Geodetic Engineering Assist.Prof. Dr. Božo Koler Jamova 2 1000 Ljubljana Slovenia bkoler@fgg.uni-lj.si

University of Ljubljana Faculty of Civil and Geodetic Engineering Assist.Prof. Dr. Aleš Breznikar Jamova 2 1000 Ljubljana Slovenia abreznik@fgg.uni-lj.si

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