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Application of Seismic Isolation Technology in Consolidation of Masonry Structures

 1.Overview 

According to”Seismic Damage Analysis of Wenchuan Earthquake [J]”, this paper divides the earthquake disasters of masonry structure into six situations, including basic intact, minor damage, moderate damage, serious damage, partial collapse and collapse. This paper points out that the buildings which have good design, fine construction and good-quality masonry structure based on the seismic code of Tangshan Earthquake, performs well in Wenchuan Earthquake. The masonry structures have been consolidated based on the norms and the good quality of the masonry structure stands the racket of earthquakes.

Figure 1                                             Figure 2                                             Figure 3

Figure 1 The teaching building of Nanba Town Primary school collapsed.

Figure 2 The right wing of teaching building in Yinghua secondary school collapsed. (The left wing is the frame structure.)

Figure 3 The vertical load-bearing walls and brick column of teaching building in junior high school at Jiangyin Garden Road are severely damaged.

2.Analytical Methods

This paper focuses on the analytical results of numerical calculation and shaking table tests on the isolated structure.

2.1.Numerical Calculation

“Code for Seismic Design of Buildings” announced that there are two seismic analysis methods, including equivalent base shear methods and time history analysis. Both methods can be achieved by simplifying calculations and large-scale finite element software such as SAP2000, or by self-made software.

According to”Numerical Simulation Analysis of Seismic Isolation and Reinforcement of Existing Multilayer Masonry Structure [J]”, the structural finite element software SAP2000 is used to simulate the masonry structure. It can be seen that the structural period becomes longer using isolation devices from the comparison. The results of time history analysis show that seismic isolation devices can greatly reduce the acceleration peak of the structure.

When using large-scale finite element software, the selecting of bearing elements and wall elements and the simplification of the upper structure and other aspects need in-depth study.

2.2.Shaking Table Tests 

Through studying the shaking table tests of the whole structure, we can directly obtain the structural dynamic characteristics and the response of the structure under earthquake action. Due to the limitation of the table size and the energy input itself, the scale model is usually used. According to “Numerical simulation analysis of seismic isolation of multi-story masonry structures [J]”, this paper mainly describes the do’s and don’ts that the scale model needed, taking a teaching building using masonry structure as example.

The isolation structure of the shaking table tests are little in China, the experimental researches of shaking table tests in the future should be appropriate to increase.

3.Engineering Practice

It is supposed that the upper part above the isolation layer and the lower part under the isolation layer are all rigid layers which need to be guaranteed in the construction practise. But there is little practical engineering for the transformation of existing buildings, because its construction methods have not yet complete and the main difficulty in the construction is how to set the isolation layer, in other words , is how to detach the upper structure from the foundation.

According to”Retrofit of Masonry Structure Using Base Isolation Technology [J]”, this paper takes a reconstruction project referring to scientific experimental building of a middle school in Gansu Province as example. The reconstruction project sets rigid bottom plates and sandwich beams as rigid layers. And the project provides sufficient support to the rubber bearings and lead rubber bearings by putting sandwich beams under the bearings. Figure 4-8 are the photos of isolation reinforcement.

Figure 4                              Figure 5                                   Figure 6

Figure 7                                  Figure 8 

Figure 4 Anchorage through the sandwich beam 

Figure 5 Tie the steel of the sandwich beam

Figure 6 Tie the bottom steel of the first floor 

Figure 7 Details about lead rubber bearing

Figure 8 Construction of isolation layer is completed.

4.Conclusion

This paper mainly describes the application of seismic isolation technique in the strengthening middle and primary school buildings in masonry structures. It summarizes the theory and engineering practice after Wenchuan Earthquake through analytical methods and engineering practice, which can provide some reference for future design and construction.

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