Building Damage Investigations And Analysis Of Wenchuan Earthquake In Longnan Area

A violent earthquake with the seismic intensity of 8.0 occured in May 12 2008, known as Wenchuan earthquake in Sichuan Province, China.This earthquake caused a large number of buildings destroyed in Longnan region. Based on the earthquake seismic investigations of Longnan buildings, the failure characteristics of the masonry buildings and reinforced concrete frame structures are summarized, the damage of typical Longnan frame building and seismic influencing factors are discussed and analyzed. Two kinds of structural types of earthquake experiences for two kinds of structures are concluded as below:1) Vertical walls, horizontal walls and the staircase walls of masonry buildings cracked generally, mainly due to the weak foundation and its structural integrity is not good. Reparation of these cracks is very difficult. Measures should be adoped to reduce seismic cracks of wall, such as developing the lightweight and high strength masonry materials, improving the strength of mortar, strengthening its connection to the structure to ensure the construction quality.2) To further enhance the integrity and anti-collapsed capacity of masonry building, the use of prefabricated panels shold be strictly restricted, especially in the building of vertical load-bearing walls and large span; the existing seismic concepts and principles of strict Implementation of seismic codes should be obeyed, especially for the measures to ring beam and columns.3) The asymmetry of Infilled wall layout resulted in non-coincidence of structural rigid centre and centre of mass, a dramatic turn was induced under earthquake; non-even of Infilled wall along the vertical layout of frame structure yielded discontinuous of vertical stiffness and weak floors that were bad to building seismic properties. Therefore, the infill walls of the frame structure should be layouted symmetrically and should be vertical continuous throughly.4) Most of infill walls made up with brittle materials, and the mortar properties can not be guaranteed, while the connections between walls and main structure are not steady. So infilled walls suffered serious damage under the earthquake, and the wall material and connection measures of the frame structures sholud be seriously considered.Finally, a typical frame structure in Longnan region was adoped for nonlinear analysis with Perform-3D. Material modeling, seismic response spectra and time history analyses of nonlinear response and influence of infilled walls on the structure were conducted. The study shows that the irrational filled wall layout, the lateral stiffness of the structure will be larger and the natural period will be smaller. Under rare earthquake, compared to the same input ground motion case, the maximum horizontal displacement and layer drift angle at all levels of the structure considered the impact of the infilied walls appears smaller than the pure frame.