Abstract
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.
Highlights
The transition to multi-level designing of seismic structures is taking place in earthquake engineering
As can be seen from the figure, there is no explicit dependence of the coefficient on the prevailing input period found in [5]. This is due to the fact that in [5] the accelerograms are normalized to peak ground accelerations (PGA) = 4 m/sec2
Its estimation is based on reducing the seismic load in the elastic system to a certain design level in accordance with the formula (3)
Summary
The transition to multi-level designing of seismic structures is taking place in earthquake engineering. In this connection, the notion of the reduction factor is used to relate the results of elastic calculations with those of inelastic ones. The notion of the reduction factor is used to relate the results of elastic calculations with those of inelastic ones This factor is designated as K1 in the Russian Federation Guidelines in use In a lot of studies the coefficient K1 is regarded as the ratio of elastic displacements to the maximum calculated displacements of the elastoplastic system in timehistory calculating using earthquake accelerograms In this case, the value of K1 depends essentially on the input type. The values of PGA depend significantly on the prevailing period of excitation, which is discussed in detail in literature [9,10,11]
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