Analysis of Diaphragm Seismic Design Forces in Two 5-Story Miniature Steel Frame Buildings Tested in Shaking Table

Abstract eng:
The use of precast buildings is important for solving the housing problem in Latin America. Precast buildings are also used for other purposes, such as commercial malls, industrial and office buildings. Precast and prestressed floor systems offer significant advantages in many of the construction phases of a building, among which are: manufacturing time, reduced shoring system and they can be used in combination with any structural system such as concrete, steel or masonry. However, the use of precast structures has not been extensive, mainly due to the limited dissemination on the latest developments regarding the seismic design of diaphragms, lack of unified seismic design procedures and comprehensive regulations for precast floor systems. With cast-in-place reinforced concrete buildings there are also cases where the floor system would need especial detailing to resist seismic actions, such as for example floor systems with openings for elevators or stairs. Although every building has a type of floor system, little attention had been given to the criteria for evaluating and resisting in-plane diaphragm forces. However, that changed as a result of the 1994 Northridge earthquake in California. The collapses of some precast structures in this earthquake suggested that they were due to floor system failures. Most of these cases were parking buildings with a structural system based on the combination of perimetrical seismic resisting reinforced concrete walls, and precast concrete frames, primarily designed to resist gravity loads. This research presents the results of analytical and experimental studies of two miniature 5-story steel buildings tested on the shaking table of the National University of Mexico in order to review the seismic behavior of rigid floor systems in buildings, considering the effect of in-plane diaphragm forces. The results of shaking table tests are compared with results from inelastic analysis as well as with those using code provisions. This paper reviews different procedures for the analysis of diaphragm seismic design forces. A procedure for defining in-plane floor forces for use in design of building diaphragms is proposed in this study. Results using this procedure showed acceptable agreement with measured inertial forces.

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