Ioannis Avramidis

Formulation of a generalized beam element on a two-parameter elastic foundation with semi-rigid connections and rigid offsets

A new, generalized Bernoulli/Timoshenko finite beam element on a two-parameter elastic foundation is presented. The element stiffness matrix is based on the exact solution of the differential equation governing displacements, and possesses the ability for an optional consideration of shear deformations, semi-rigid connections, and rigid offsets. In addition to the proposed stiffness matrix, equivalent element nodal load vectors are developed for handling the external uniform loading and linear temperature variations. The usefulness of the new element in the analysis of reinforced concrete or steel structures is documented by three numerical examples.

Concurrent Design Forces in Structures under Three-Component Orthotropic Seismic Excitation

According to the model of Penzien and Watabe, the three translational ground motion components on a specific point of the ground are statistically noncorrelated along a well-defined orthogonal system of axes p, w, and v, whose orientation remains reasonably stable over time during the strong motion phase of an earthquake. This orthotropic ground motion is described by three generally independent response spectra Sa, Sb, and Sc, respectively. The paper presents an antiseismic design procedure for structures according to the above seismic motion model. This design includes a) determination of the critical orientation of the seismic input, i.e., the orientation that gives the largest response, b) calculation of the maximum and the minimum values of any response quantity, and c) application of either the Extreme Stress Method or the Extreme Force Method for determining the most unfavorable combinations of several stress resultants (or sectional forces) acting concurrently at a specified section of a structural member.

Static Pushover Analysis Based on an Energy-Equivalent SDOF System

In this paper, a new energy-based pushover procedure is presented in order to achieve an approximate estimation of structural performance under strong earthquakes. The steps of the proposed methodology are quite similar to those of the well-known displacement modification method. However, the determination of the characteristics of the equivalent single-degree-of-freedom (E-SDOF) system is based on a different rational concept. Its main idea is to determine the E-SDOF system by equating the external work of the lateral loads acting on the multi-degree-of-freedom (MDOF) system under consideration to the strain energy of the E-SDOF system. After a brief outline of the theoretical background, a representative numerical example is given. Finally, the accuracy of the proposed method is evaluated by an extensive parametric study which shows that, in general, it provides better results compared to those produced by other similar procedures.

Evaluation of inelastic response of 3D single-story R/C frames under bi-directional excitation using different orientation schemes

The aim of the present paper is to evaluate by means of nonlinear dynamic analysis four different procedures for the selection of sectional forces needed for the design of R/C frames. For this purpose, a single-story building is designed using four different procedures to select the sets of internal forces needed for the calculation of longitudinal reinforcement. All the four procedures are based on the results of linear response history analysis. Nonlinear dynamic analyses under 16 bi-directional ground motions are performed for 4 different seismic intensity levels. The two horizontal accelerograms of each ground motion are applied along horizontal orthogonal axes forming with the structural axes several incident angles. The results of this study demonstrate that one of the investigated procedures that takes into account the critical seismic angle is more efficient for the design of R/C frame elements.

Evaluation of a multimode pushover procedure for asymmetric in plan buildings under biaxial seismic excitation

In this paper a recently developed multimode pushover procedure for the approximate estimation of structural performance of asymmetric in plan buildings under biaxial seismic excitation is evaluated. Its main idea is that the seismic response of an asymmetric multi-degree-of-freedom system with

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Fundamental Principles for the Design of Earthquake-Resistant Structures

N degrees of freedom under biaxial excitation can be related to the responses of