Preserving mankind's past from mother nature's quakes

Civil engineers are in a continuous search of non-destructive measurement techniques that can help to estimate structural condition. The high definition surveying (HDS) or laser scanning, from Leica Geosystems fulfils this need.

A joint research team comprised of members from UC Berkeley’s Structures Laboratory (a research lab specialising in full-scale structural testing and numerical analysis), Miyamoto International (an earthquake and structural engineering firm in the USA), Smart Scanning Solutions, LLC (a 3D scanning and modelling service provider in Uzbekistan) and BNZ (Leica Geosystems’ representative in Uzbekistan) has been deploying HDS reality management technology at heritage monuments along the historic Silk Road within Uzbekistan. Multiple monuments have been captured and analysed for earthquake susceptibility.

The beginning: assessment of natural decline

作为许多遗产纪念碑的代表性例子，选出了乌兹别克斯坦撒马尔罕的雷吉斯坦广场合奏团。合奏包括1417-1420的Ulugh Beg Madrasah，Sher-Dor Madrasah，1619-1636，Tilya-Kori Madrasah和Mosque，1646-1660，以及18世纪的Chorsu Domed Market。

Earthquakes, extreme seasonal temperatures, normal depreciation of the buildings and the economic crises of the 18th and 19th centuries have left the ensemble in a ruined condition. Structural repairs and straightening of the minarets had been conducted in 1923 and 1932; however, major restoration works were undertaken in recent years.

从70多个电视台扫描了该合奏，并带有Leica扫描仪。除了位于合奏中的所有古迹的全球尺寸外，扫描还捕获了纪念碑的所有细节：瓷砖形状和尺寸，它们在古迹中的整体位置，任何缺陷以及门廊的整体几何形状。为了达到点密度的细节，所有扫描的密度为2 mm x 2 mm。

The scan data produced extremely valuable results to be used in the decision making of further restoration strategies for the monument located in this earthquake-prone area of Central Asia. In generation of finite element models from the point cloud, Leica Cyclone software was used for surfaces with complex geometry.

“With the ScanStation's ability to achieve ultrahigh scan speeds, we were able to quickly collect the data needed for a thorough investigation of the monuments,” said Liliya Myagkova, Smart Scanning Solutions CEO. “AndCyclone’s simple registration enabled the team to process the point clouds for fast analysis.”

The point cloud of one of the leaning minarets provided answers to questions regarding the amount of incline in the structure. Based on the analysis of the point cloud, an estimate of 4.6 per cent of inclination was obtained. The original taper of the minaret is estimated as 2.3 per cent.

New expeditions and monitoring by laser scans

激光扫描探险被扩展到新城市。广泛的历史结构清单包括乌兹别克斯坦的许多城市：布哈拉，沙克里斯巴兹和塔什肯特。除此之外，扫描了撒马尔罕的更多历史结构。

Shakhrisyabz位于乌兹别克斯坦撒马尔坦以南约80公里处的乌兹别克斯坦南部。它曾经是中亚的主要城市，今天主要被称为14世纪Turco-Mongol Conqueror Timur的发源地。扫描的纪念碑，库克·古巴兹（Kuk Gumbaz）（蓝色圆顶）清真寺，来自帖木儿王朝时代，在联合国教科文组织世界遗产名单上。这座纪念碑建于1437年，几个世纪以来，经历了几项修复和加强工作。

历史悠久的纪念碑在13个站点扫描Leica扫描C10. Data registration was performed in Cyclone and error did not exceed 3 mm for all scans used in the final registration. The monument was scanned from outside, inside of the main hall, and inside of a stairway with a large crack between the portal and the main structure.

“With Uzbekistan’s extreme continental climate, the research team needed to ensure it could rely on the instruments. As the C10 can work in temperatures anywhere from -20 to +50 degrees Celsius, it was ideal for this project,” said Brian Quigley, BNZ director. “The full 360° x 270° field of view also ensured scanning the complex surfaces of the monuments would capture all features and make the process simpler for the researchers.”

纪念碑的点云进行调查omalies. The main portal was investigated for its inclination from a vertical plane passing through the bottom of both piers. The portal’s inclination increases from south to north with the maximum differential displacement of 0.6 m at the top north corner. To ensure this degree of inclination of the portal is not progressing, a periodic monitoring by laser scanning was recommended to be carried out. It was also advised to proceed with the installation of laser targets to increase accuracy of monitoring. The permanently installed targets provide a consistent comparison between point clouds collected at different times.

The geometry of the finite element model was generated from the point cloud. All major imperfections and existing reinforcements were included into the geometry of the model. Numerical modelling and subsequent analysis was conducted in specialist software SAP2000.

Since there is a very large variability in the material properties of masonry walls, material tests were conducted on a brick recovered from the site. The material properties were used within the software for accurate modelling.

The minaret was scanned at different times to check if the inclination is progressing over time. The first scans were conducted by theScanStation C10and the second point cloud was collected by the P-series ScanStation. The first scans were registered to the second scans in Cyclone. The inclinations are estimated as a vector at each elevation with directivity and value. The latter result uses the main advantage of the high-definition laser scanning that captures multiple points of the surface that cannot be obtained by other means.

Future research for more protection

The test projects won interest from, and collaboration with, the Uzbekistan authorities dealing with heritage buildings. This provided permissions for the additional heritage scanning along Uzbekistan's active seismic zones in Samarkand, Bukhara, Tashkent and Shakhrisyabz.

With HDS scanning combined with material testing, advanced calibrated models were produced, accounting for brick properties, current conditions, and previous structural reinforcements. Long-term monitoring is being strategised and conservation recommendations are being provided based on the research data, including the investigation of dampening devices at an active mosque with multiple structural concerns.

“激光扫描帮助我们捕捉结构另malies of historical artefacts so we can help protect them for future generations,” said Amir Gilani, Miyamoto International, Manager of Earthquake Engineering Department. “Without this advanced technology, it would be challenging to get the as-found geometry of historic structures with accuracy of few millimetres that is essential for structural analysis.”

In recognition of the team’s effort and value of the collected data, the point clouds were accepted into the CyArk 500 Challenge database, an international effort to catalogue and archive endangered cultural heritage.