ASSESSMENT OF SEISMIC INPUT ENERGY BY MEANS OF NEW DEFINITION AND THE APPLICATION TO EARTHQUAKE RESISTANT DESIGN

A methodology for assessing the seismic input energy into structure (building) from earthquake (or seismic) excitation is proposed. The procedure is based on the energy balance of the structure and employs the earthquake intensity characteristic known as the specific energy density (SED) to estimate the maximum input energy. This energy is evaluated for the portion of earthquake record (accelerogram) where strong ground motion occurs (the interval between 5-95% accumulations of the Arias intensity). Comparison of the proposed approach in this paper and other proposals for assessing seismic input energy as a basis for energy-based seismic design methodology is presented. Since a critical condition to realize an energy-based seismic design is that the structure should have a rational relationship between damage/energy absorbed, the procedure establishes a relation between the seismic input energy into structure and strain, total cyclic displacement and low cycle fatigue. Seismic input energy obtained using this procedure is compared with results from other methods for assessment of seismic input energy. The procedure can useful especially, at the initial stage of design to provide the desired ductility to structure since it allows for evaluating the maximum input energy into structural system from any seismic excitation without recourse to dynamic analysis

On estimating the reduction factor of bridge piers

Estimating the reduction factor for calculating massive reinforced concrete bridge piers was made. For this purpose a quasi-static “force-displacement” diagram was built up using the ANSYS software. This diagram has the form of a bilinear one, and the character of the bilinearity depends on the diameter of the reinforcing bars insignificantly. The percentage of reinforcement affects only the moment when all reinforcement bars begin to flow. The reinforcement flow takes place in the displacement interval from 3 to 5 cm. The collapse will occur when the reaction of the bearing part goes beyond the pier cross-section at pier displacements from 5 to 20 cm. Using “force-displacement” diagram, the behavior of the single-mass model with a bilinear deformation diagram and the limit displacement of 20 cm was analyzed. Then, it became possible to obtain for each accelerogram the limit elastic displacement and the limit position of the point corresponding to the maximum structure displacement during structure oscillations. It was done using real accelerograms of earthquakes with intensity 9 on the MSK scale without normalizing their amplitudes. In this case, long-period accelerograms had smaller peak accelerations, but resulted in greater plastic deformations. As a result, no evident dependence of plastic deformation on the input spectral composition was found and the value of reduction factor K1 turned out to be 0.25-0.27. However, it is shown that this reduction factor cannot be used to make transition from seismic loads obtained on the basis of time-history analysis by accelerograms to design loads