Surrounded by 22 glittering "Ribbon" curved glass curtain walls, it is elegant from a distance and magnificent from a close view... As the only new ice competition venue for the 2022 Beijing Winter Olympic Games, the "China scheme" is adopted for the design, technology, materials and manufacturing of the "ice ribbon" of the national speed skating hall. Among them, the team of Professor Luo Yaozhi, School of architectural engineering, Zhejiang University, and the teams of Professor Deng Hua and Professor Yuan Xingfei provided important technical support for the construction, operation and maintenance of "ice ribbon" super long-span cable net structure. Deploy sensing equipment to monitor the steel cable in real time The roof system of "ice ribbon" adopts hyperboloid saddle shaped single-layer cable net structure, which can be understood as being fastened by a large net woven by steel cables. Compared with the traditional rigid roof structure system, the flexible cable net roof reduces the steel consumption of the structure on the premise of meeting the structural function. "Since each steel cable weighs several tons, only through reasonable tensioning can it be woven into a net." On January 19, Professor Luo Yaozhi introduced to the reporter of science and Technology Daily that the stress state of these steel cables is very key in the construction process, and the slightest carelessness will affect the construction quality and safety. In order to find out the state of the steel cable, Luo Yaozhi's team installed the wireless sensor independently developed by Zhejiang University in the construction link for real-time monitoring and mechanical analysis. The "ice ribbon" roof structure is a saddle shaped cable net with a long span of 198 meters and a short span of 124 meters woven by 49 pairs of load-bearing cables and 30 pairs of stabilizing cables. How to arrange the sensor network to ensure that the sensor can work normally and stably for a long time after the cable network is raised to high altitude? From September 2018 to December 2020, Luo Yaozhi's team carried out data processing on the front line, always paying attention to each node of threading and weaving a large network, so as to provide decision support for the construction process. In the construction process of cable net, the construction party adopts the process of "assembling on the ground first and then lifting as a whole". However, due to the limitation of site space, the steel cable laid on the ground waiting for tensioning needs to be slightly arched to cross the "bottleneck". Without accurate data support, it is not easy to bend several tons of steel cables. "The on-site monitoring data can grasp the influence of bending on the steel cable in real time, which provides an important basis for on-site decision-making and command and safe construction." The construction party commented, "these wireless sensors are like a pair of eyes, staring at the whole process of project construction." Constructing cable net model to simulate accurate construction How to lift the cable net paved on the ground smoothly, which cables need to be tensioned to tighten the cable net after reaching the roof height, and how much error can be tolerated in the end... Sensitivity analysis is required during the construction of "ice ribbon". "The roof of the national speed skating hall has large span, many steel cables and complex internal force coordination, which requires the structure to be constructed with high precision." Deng Hua introduced that a huge tensioning force needs to be applied in the cable net, and it must ensure high-precision cooperation with the ring truss and curtain wall cable. The lifting steps of the cable net from the ground and the tensioning sequence of the steel cable will affect the final construction quality of the whole "ice ribbon". It is particularly critical to determine a safe, efficient and accurate cable net construction scheme. In order to solve the problem of roof construction, the team of professors Deng Hua and Yuan Xingfei carried out the key technology and model test research on the construction of long-span cable net roof structure of the national speed skating hall through a 12:1 scale model. The scale model test began in early June 2018 and lasted until the end of August. Based on a large number of numerical simulation results and test data, the joint team put forward systematic schemes and suggestions on the overall lifting, tensioning control, construction acceptance and pretension monitoring of the cable net, providing strong technical support for the high-precision construction of the "ice ribbon" long-span cable net roof structure. In addition, the team also applies load on the tensioned cable net through sandbags and other forms. "We hang different loads on the model to simulate the wind and snow environment and verify the strength and deformation resistance of the roof." Deng Hua said. Remote analysis and diagnosis based on rear platform Walking into the spatial structure health monitoring platform located in Zijingang Campus of Zhejiang University, the reporter saw that the status data from "ice ribbon" are processed in real time. It is understood that this monitoring system was independently developed and designed by Zhejiang University and has been applied to the operation monitoring of buildings such as the National Stadium "bird's nest" and Daxing International Airport as early as 2010. Professor Xu Xian, a member of Luo Yaozhi's team, said that the team monitored six categories of parameters such as stress, displacement, acceleration, temperature, wind pressure and cable force of the speed skating hall through the platform. The number of test points also reached more than 1000, the largest number of single building structure. "We will transform this system according to the specific needs of each project. We will also conduct intensive monitoring in the key links of construction and bad weather conditions." In addition to the monitoring of the "ice ribbon" roof, the team of Zhejiang University also carried out health monitoring of the under ice concrete in the speed skating hall. It is reported that the "ice ribbon" adopts the whole ice surface design, and the temperature difference on the ice surface can be controlled within 0.5 ℃, which puts forward higher requirements for the quality of concrete. How to monitor the stress of concrete under ice in service is a new topic for Luo Yaozhi's team. Therefore, the team developed the internal force and temperature monitoring technology of concrete structure under low temperature and harsh environment, and proposed the performance state evaluation method of concrete under ice during long-term service. Fu Wenwei, a 2017 direct doctoral student at the school of construction and engineering of Zhejiang University who deeply participated in the project, said: "in this great era, it is a rare opportunity in life to make a small contribution to the construction of the national speed skating hall through his own scientific research work." (Xinhua News Agency)