从大自然的地震中保存人类的过去

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.

开始：自然下降的评估

As a representative example of the many heritage monuments, the Registan Square ensemble in Samarkand, Uzbekistan was selected. The ensemble includes the Ulugh Beg Madrasah, 1417-1420, the Sher-Dor Madrasah, 1619-1636, the Tilya-Kori Madrasah and Mosque, 1646-1660, and the 18th century Chorsu domed market.

地震，极端的季节性温度，建筑物的正常折旧以及18世纪和19世纪的经济危机使整体处于破坏状态。1923年和1932年进行了结构维修和矫直宣礼塔；但是，近年来进行了重大的修复工作。

The ensemble was scanned from more than 70 stations with a Leica ScanStation. In addition to the global dimensions of all monuments located within the ensemble, the scans captured all details of the monuments: tile shape and dimensions, their overall locations in the monuments, any imperfections and the overall geometric shapes of the portals and facades. To achieve this level of detail in point density, all scans were conducted with a density of 2 mm by 2 mm.

扫描数据产生了极为有价值的结果，可用于决策中亚洲地震地区的纪念碑的进一步恢复策略。在从点云中生成有限元模型中，使用Leica Cyclone软件用于具有复杂几何形状的表面。

“随着ScanStation实现ultrahi的能力gh 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简单的注册使团队能够处理点云以进行快速分析。”

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

The laser scanning expeditions were expanded into new cities. An extensive list of historic structures included many cities of Uzbekistan: Bukhara, Shakhrisybaz and Tashkent. In addition to that, more historic structures in Samarkand were scanned.

Shakhrisyabz is located in southern Uzbekistan approximately 80 km south of Samarkand, Uzbekistan. Once a major city of Central Asia, it is primarily known today as the birthplace of 14th century Turco-Mongol conqueror Timur. The scanned monument, the Kuk Gumbaz (Blue Dome) Mosque, is from the Timurid Dynasty era and it is on the UNESCO World Heritage List. The monument was built in 1437 and over the centuries has undergone several restorations and reinforcement efforts.

The historic monument was scanned from 13 stations with aleica ScanStation 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.”

The monument’s point cloud was investigated for anomalies. 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.

由于砌体壁的材料特性有很大的变化，因此在从该地点回收的砖上进行了材料测试。该材料属性在软件中用于准确的建模。

在不同时间扫描尖塔，以检查倾斜度是否随着时间的推移而发展。第一个扫描是由ScanStation 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.

HDS扫描结合材料测试,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.

“激光扫描有助于我们捕获历史文物的结构异常，因此我们可以为子孙后代提供保护它们，”地震工程系经理宫本国际宫（Miyamoto International）说。“没有这种先进的技术，以几毫米的准确性来获得历史结构的基础几何形状，这对于结构分析至关重要。”

为了认识到团队收集的数据的努力和价值，点云被接受到Cyark 500挑战数据库中，这是一项国际努力，以分类和存档濒临灭绝的文化遗产。