When an earthquake strikes, can a bridge hold up? A test can be conducted first in a national key laboratory of structural dynamics for bridge engineering.

Located at Nan'an District, such a lab has carried out the following tests: the seismic isolation bridge vibration table test of Hong Kong-Zhuhai-Macao Bridge, which is the longest sea bridge in the world; the tensile bending fatigue test of the stay cable of the Su-Tong Yangtze River Highway Bridge, which is the super-large bridge project with the largest construction scale, and the most complex comprehensive construction conditions in the history of bridge construction in China, etc.

World's first large seismic simulation test array system

The world's first large seismic simulation test array system with two arrays was built in Chongqing in 2002, according to Tang Guangwu, director of the laboratory.

Tang continued, seismic resistance is crucial for civil engineering, especially large bridges, which are usually designed for a service life of 100 years. Therefore, it is of utmost importance for them to pass a seismic test.

"In order to find out the weak points in structural design, the array system simulates seismic waves and the real situation when an earthquake happens," said Tang.

"The lab pioneered the mode of array operation and track movement in the world," Tang pointed to the rectangular system and explained.

Each array, with a deadweight of 20 tons, can carry a bridge model of up to 70 tons; the actuators refer to the arm-like levers around the array; the array can simulate the tremendous power of an earthquake when the hydraulic oil system beneath is activated.

Tang added, a long-span bridge model will be placed on the two arrays with tracks between them, which can vibrate in three axial directions and six degrees of freedom. "Simply speaking, it can translate, rotate, or tilt like a seesaw," he said.

How strong earthquakes can the array system simulate?

According to Tang, the peak acceleration of the Wenchuan earthquake was about 1g, while the maximum of the system can reach 3g.

"This provides the necessary conditions for seismic test studies of long-span structures, which makes possible for those on some fundamental problems of seismic dynamics of long-span structures," Tang said.

On one side of the array system lies a transparent 1:60 model of the Mingzhuwan Bridge with the main span, side truss arches, piers, and even stay cables.

"The test model was made of organic glass through numerical control," said Liu Haiming, a laboratory staff member. In order to meet similar conditions, the model was fitted with lead and various sensors to obtain test data in 2016.

At the later stage of the test, researchers also conducted a lot of data analyses and guided the project's construction to ensure safe engineering.

"The seismic isolation bridge vibration table test of the Hong Kong-Zhuhai-Macao Bridge was also completed here," Tang emphasized.

Seismic mitigation and isolation technologies were introduced for the 55-kilometer bridge, the longest sea bridge with seismic faults.

In April 2012, the laboratory successfully carried out the quasi-static test of a single pier, the vibration table model test of the whole bridge for the comparison of the seismic mitigation and isolation, and anti-seismic performance of a single pier, as well as the uniform or non-uniform excitation tests of the multi-span model for the seismic mitigation and isolation, and anti-seismic performance of double vibration table.