In the design of concrete columns, it is important to provide some nominal flexural ductility even for structures not subjected to earthquake attack. Currently, the nominal flexural ductility is provided by imposing empirical deemed-to-satisfy rules, which limit the minimum size and maximum spacing of the confining reinforcement. However, these existing empirical rules have the major shortcoming that the actual level of flexural ductility provided is not consistent, being generally lower at higher concrete strength or higher axial load level. Hence, for high-strength concrete columns subjected to high axial loads, these existing rules are unsafe. Herein, the combined effects of concrete strength, axial load level, confining pressure and longitudinal steel ratio on the flexural ductility are evaluated using nonlinear moment-curvature analysis. Based on the numerical results, a new design method that provides a consistent level of nominal flexural ductility by imposing an upper limit to the axial load level or a lower limit to the confining pressure is developed. Lastly, two formulas and one design chart for direct evaluation of the maximum axial load level and minimum confining pressure are produced.

Maximum axial load level and minimum confinement for limited ductility design of high-strength concrete columns

Flexural Strength and Deformability Design of Reinforced Concrete Beams

A preliminary performance-based seismic design methodology is proposed. The top yield displacement of the system is computed from these of the components, which are assumed constant. Besides, a simple procedure to evaluate the top yield displacement of frames is developed. Seismic demands are represented in the form of yield point spectra. The methodology is general, conceptually transparent, uses simple calculations based on first principles and is applicable to asymmetric systems. To consider a specific situation two earthquake levels, occasional and rare are considered. The advantage of an arbitrary assignment of strength to the different components to reduce eccentricities and improved the torsional response of the system is addressed. The methodology is applied to an asymmetric five story building, and the results are verified by push-over analysis and non linear dynamic analysis.

Preliminary design and inelastic assessment of earthquake-resistant structural systems

In the design of earthquake resistant reinforced concrete (RC) structures, both flexural strength and deformability need to be considered. However, in almost all existing RC design codes, the design of flexural strength and deformability of RC beams are separated and independent on each other. Therefore, the pros and cons of using high-performance materials on the flexural performance of RC beams are not revealed. From the theoretical results obtained in a previous study on flexural deformability of RC beams, it is seen that the critical design factors such as degree of reinforcement, concrete/steel yield strength and confining pressure would simultaneously affect the flexural strength and deformability. To study the effects of these factors, the previous theoretical results are presented in various charts plotting flexural strength against deformability. Using these charts, a "concurrent flexural strength and deformability design" that would allow structural engineers to consider simultaneously both strength and deformability requirements is developed. For application in real construction practice where concrete strength is usually prescribed, a simpler method of determining the maximum and minimum limits of degree of reinforcement for a particular pair of strength and deformability demand is proposed. Numerical examples are presented to illustrate the application of both design methods.

Concurrent flexural strength and deformability design of high-performance concrete beams

Displacement-based methods are recognized as appropriate approaches to reach the goals of performance-based seismic design method. In the direct displacement-based seismic design method, the seismic yield displacement is applied as one of the important design parameters. In this paper, a new relation is suggested to determine the lateral displacement pattern at first yielding of eccentrically braced frame systems subjected to earthquake ground motions. This relation considers the influence of various structural features of frames. It is developed from the results of several nonlinear dynamic analyses containing 30 eccentrically braced frames under 15 far-field and near-field earthquake ground motions. Then, the results of these analyses are processed by nonlinear regression analysis in order to establish the most effective parameters on the yield displacement pattern of the  frames. As a result, a comparison between the suggested yield displacement pattern and nonlinear dynamic analyses showed the efficiency and advantages of the suggested approach.

https://www.ije.ir/article_93864_c649d157f50bf09a3204b026e9a18602.pdf

Seismic Yield Displacement Profile in Steel Eccentrically Braced Frames

A two-level displacement-based design procedure is developed. To obtain the displacement demands, elastic spectra for occasional earthquakes and inelastic spectra for rare earthquakes are used. Minimum global stiffness and strength to be supplied to the structure are based on specified maximum permissible drift limits and on the condition that the structure responds within the elastic range for occasional earthquakes. The performance of the structure may be assessed by an inelastic push-over analysis to the required displacement and the evaluation of damage indices. The approach is applied to the design of a five-story reinforced concrete coupled wall structure located in the most hazardous seismic region of Argentina. The inelastic dynamic response of the structure subjected to real and artificially generated acceleration time histories is also analyzed. Finally, advantages and limitations of the proposed procedure from the conceptual point of view and practical application are discussed.

Inelastic displacement-based design approach of R/C building structures in seismic regions

En este trabajo se estudia, utilizando analisis no lineal estatico y dinamico, el comportamiento de diversos sistemas de tabiques sismorresistentes disenados con los mismos requisitos establecidos en desplazamientos Se consideran diversos parametros de la respuesta, de interes para evaluar el desempeno correspondiente, efectos torsionales y la interaccion entre tabiques de distinta longitud Para el analisis dinamico no lineal se aplican treinta acelerogramas compatibles con la microzonificacion sismica del Gran Mendoza, obteniendo para cada parametro el valor medio mas un desvio estandar Los resultados contribuyen a comprender aspectos del comportamiento de los sistemas de tabiques sismorresistentes, siendo utiles para su diseno basado en desplazamientos

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Alejandro Giuliano

Papers

Preliminary design and inelastic assessment of earthquake-resistant structural systems

Inelastic displacement-based design approach of R/C building structures in seismic regions

Análisis del Comportamiento No Lineal de Sistemas de Tabiques Sismorresistentes