Weather Radar Station On the Swiss Alps

5-1 Introduction

In 2012, the Federal Office of Meteorology and Climatology of Switzerland decided to install a well-equipped and advanced radar station on the Alps located at Pointe de la Plaine Morte Mountain. This weather station was equipped with advanced facilities and devices which determine the climate changes, heavy precipitations, snowfalls and blizzards, and similar atmospheric hazards with providing aerial and meteorological photos and performing precise data analyzing. The primary investigation of this project was before 2012, and once the initial studies had accomplished, the implementation began since May 2012. We were requested to take the responsibility of structure behavior control against the dynamic and seismic loads.

Figure 5-1 A picture of weather radar station on Alps– Switzerland

5-2 Structure Description

The considered place for implementing and installing the radar was in the Alps Mountains in the Pointe de la Plaine Morte region, located at Wallis State with a height of 3000 meters above the sea level. This region was completely virgin and natural, and neither driveway nor railway was available. The climatic condition of the region was frigid along with strong winds, blizzards, and heavy snowfalls. In such situation, the operating activities were feasible only in few warm seasons. Transferring the materials and transportation of workers and engineers was performing using helicopters. The concrete, armatures, the steel components, and other required facilities were transferred with helicopters, and the workers again were returned after eight hours working. Due to particular climate condition and impossibility of practical activities in most seasons of the year, the project implementing took two years to be completed.

Figure 5-2 The practical steps of the construction of the weather radar station – Alps mountains.

5-3 The Structure Specifications and Project Operation

The Structure of the station was designed cylindrical with a diameter of 4.68 meters and a height of 12.4 meters, made of concrete with a thickness of 25 centimeters. The body of the cylinder has included several openings. The architecture of this project was performed by a group of the most expert architects in Switzerland.

Once the preliminary project operation step and leveling the mountain area was done, the major project operation was started in August 2012. As it was mentioned, the construction was progressed only in summer; and because of interruption, the initial part of the project was completed in summer, 2013. The type of the structure foundation was a MAT foundation, and one of the challenging topics of the design was that whether or not it was required to anchor the MAT with the bedrock.

The first step of the radar and station was unveiled at 4th of July, 2013; then the implementation of steel façades of the structure was started. The main radar, the cap, and related equipment were installed, and some facilities were implemented in November 2013. In spring 2014, the first operation step of systems was performed, and hence after two years the process of installation and implementation of the weather radar station was finalized. Figure 5-2 shows the sequences of practical steps.

Figure 5-3 The 3-D finite element model of the cylinder and the foundation in ADINA program.

5-4 Analysis of Lateral Forces

According to seismic zonation maps of SIA, the site of the radar was located in a high seismic hazard zone. Thus, the seismic analysis was required to be performed. Moreover, the wind speed could reach up to 218 kilometers per hour in the 3000 meters height above the sea level. In such situation, the wind forces would have a decisive role in the design process.

One of the critical points in the structure design is the sensitivity to deformation and large lateral displacements against the wind and seismic loads; in other words, it is a stringent criterion in design.

As the cylinder of the station was placed on the bedrock and on a MAT, there was no concern for the vertical displacements. However, it was possible that the lateral wind or seismic load cause enlargement of uplift pressure, which is considered as a major challenging point of this design.

The analysis of structure’s seismic behavior at high altitude and in a severe weather condition (low temperature and high wind speed) as well, was the most exciting challenging section for us.

The installed facilities inside the station were sensitive to the vertical and horizontal displacements, and the radar displacements were limited to less than 10 millimeters. Based on the primary analysis we came to decide that the structure should anchor with the bedrock.

The body of the radar was designed as a cylinder with thickness of 25 centimeters. The steel trusses as superficies were installed surrounding the body to avoid the direct effect of climate factors on the body. The procedure of the truss installation is shown in Figure 5-2. The concrete was a suitable and safe material based on the geometry and situation of this structure.

Seismic analysis calculation of lateral wind load was conducted based on Standard SIA 260-262 and Swiss standards. The following finite element softwares were used: (see Figure 5-3)

  • ADINA, Ver 8.3, developed by Professor Bathe et al. at MIT, Cambridge.
  • CSI SAP 2000-Ver 15, and
  • CONAN, which was used to determine the soil springs stiffness.

The seismic analysis of the structure was calculated based on response spectrum method, and the earthquake spectrum was selected from the zonation documents of Switzerland. The maximum ground acceleration also was evaluated and calculated in that region.

The design values of the wind and temperature in the considered height were extracted from the different weather reports. The values of springs’ stiffness also were assumed based on initial data and calculations. As it was mentioned in previous projects, the accuracy and quality of the input data play a prominent role in analysis and in optimum design.

Figure 5-4 The magnified image of foundation uplift on the bedrock.

5-5 Hints

The obtained results from finite element analysis for the seismic and wind loads implied that the designed MAT was appropriate for the present structure, and the lateral displacements were in an acceptable range (less than 10 millimeters). However, it was required to anchor the MAT to the bedrock. The design of cylindrical structure also was rechecked, and it was found that the design was proper.

One of the particular points of this project was the seismic design at the height of 3000 meters above sea level. It is of note that the recorded data by accelerometers are related to ground level, and the transfer of the quake waves to the height of 3000 meters is a subject which still is vague for me. To solve this problem, it is necessary to conduct researches as a thesis or as field tests.

The present design and analysis was such an attractive challenging topic. It was my honor that I took the responsibility of one of the most distinctive structures in a severe weather and climate condition. In the following, a schematic of the station specifications is presented.