Research And Control On Failure Modes Of Multi-storey Masonry Structure

Masonry structure has been one of the the most widely used forms in China for a long time. Due to its own limitations of Material properties, compared with concrete and steel structures, poor seismic performance led so heavy damage in Wenchuan and other previous earthquakes. Lots of earthquake damage phenomena show that: on one hand, masonry structure designed in strict accordance with specifications could meet the seismic requirements; on the other, it is still difficult to achieve the expected and controlled structure failure modes.For the current seismic problems of masonry structure,extensive researches are carried out in this article: much in-depth investigations and researches about failures modes of of multi-story masonry structure have been done by the author during the two years after the Wenchuan earthquake; The stress state and the distribution of masonry walls under seismic force are analyzed with MSC.MARC finite element simulation software;The inadequacies and shortcomings in our design specifications are proved; A large numbers of mechanical properties tests are carried out under various stress;The technical indicators and main factors of various failure modes are discussed through finite element quantitative analysis under seismic force;More reasonable stress analysis theory and seismic capacity design method of masonry structure are demonstrated; The reasonable failure modes and control methods are established.The main research achievement are presented as follows:According to the general laws of the earthquake damage phenomenon,three typical kinds of failure modes(window belly wall,window pier wall and mixed of the two)and damage distributions are proposed;The causes of of three different failure modes are omparatively analyzed and the structure failure mechanisms produced by various earthquake damage are scientifically explained; More reasonable failure modes are advanced to ensure the structural integrity and seismic energy dissipation.The stress state and the distribution of window belly wall and window pier wall under earthquake are revealed with the simulation methods and mechanics analysis(the stress states could be demonstrated with the biaxial tension-compression stress units by different stress ratio and the angle of the mortar joint); It is established the the corresponding function of the relationship between principal stress unit(shown by Mohr’s circle) and the plane stress state within the wall. Uniform strength failure envelope and the plane stress failure criterions under various stress conditions are put forward. For failure modes of window belly wall and window pier wall, the specific function expressions are given.By referring the characteristics of Wall-frame, the forces analysis model of multi-story masonry structure is built up and the improved method of calculating the internal forces is certained. Considerring the current design standards, Seismic capacity design methods of masonry structure are proposed and the seismic design expressions of window belly wall and window pier wall are set up. The ratio ψ is determined as the main controlling factor of different damage patterns,according which the conditions for the occurrence of the expected failure modes are put forward. The control methods of multi-story masonry structure failure modes are illustrated from the view of theoretical design and construction measures.The study value of the article is shown in follow aspects: it is provided information and reference for the tests of biaxial stress state and the finite element simulation of the masonry structure; Effective datas could be used to fulfill the strength theory and failure criterion of masonry structure;It makes up for the lack of our seismic calculation theory in current masonry codes and provides theoretical supports to satisfy the requirements of multi-seismic defense lines; In additional,several cost-effective and technological reinforcement measures are shown to guide the reconstruction of masonry structures in the dsaster area after the earthquake.