Pushover Analysis of Structures Subjected to Combined Actions of Earthquake and Wind

Abstract

This paper puts forward a framework to investigate the structural performance of buildings subject to the combined action of earthquakes and wind. The study uses a pushover analysis to determine strength capacities of low- and medium-rise concrete structures to compare versus their strength, as inferred from the Indian code for seismic design. The analysis addresses soil-structure interactions through the scrutiny of fixed-base and flexible- base conditions of three soil types ranging between dense and soft. The parametric study covers micro me- topological winds whose mean value spans between 0.5 m/s and 20 m/s. The simulated multi-load scenarios induce ductility levels going from 1 to 6 to totalize 288 case studies. The proposed framework reveals that consideration of earthquake and wind simultaneous effects could modify performance levels used for design through enhancing ductility demands. This evidences that, under current design recommendations, structures located in earthquake prone areas susceptible to unexpected levels of damage.

Introduction

I. INTRODUCTION

Composite construction is a generic term to describe any building construction involving multiple dissimilar materials. Composite construction is often used in building aircraft, watercraft, and building construction.

There are several reasons to use composite materials including increased strength, aesthetics, and environmental sustainability. In developing countries like India, most of the building structures fall under the category of low-rise building. So, these conventional Reinforced cement concrete and pure sectional steel construction prove to be convenient and economical in nature hence widely used all around. But when it comes to the need for vertical growth of building due to lack of land space area and rapid growth of population, medium high-rise building emerges as a solution to full - fill this need. The combination of steel and reinforced concrete, thereby utilizing the unique characteristics of the two materials, generally results in structures of greater economy and safety than either material alone could achieve. Because of this, engineers have been continually interested in finding practical and effective ways of joining the materials, in developing new design concepts, and in establishing requirements for satisfactory performance. In the recent years, very significant advances have been made in all these areas, thus leading to a widespread use of combined steel and concrete elements in construction of buildings, bridges, nuclear power plants, and other types of engineering structures. The paper is an attempt to study the behavior of reinforced concrete, steel and composite structure under the effect of seismic loading. The parameters considered are base shear, displacement and story drift.

grade “C30”. The yield and ultimate strengths of longitudinal and transverse rebar were set to be 335 MPa and 455 MPa, respectively. The dead load considered in the analysis included self-weight of structural members, additional 1.7 kN/m2 due to floor finishes, and 8.5 kN/m acting along each beam to represent light ductile partitions and external facades. The live load was set as 2.0 kN/m2. All loads are in agreement with the Code provisions. In this study, three-dimensional models of framed structures were modelled for the pushover analysis in SAP2000 version 20 The structural design addressed material properties and load configurations that are relevant to seismic-resisting structures. Beams and columns performed as nonlinear frame elements with lumped plasticity, hence could develop plastic hinges at both ends. We used the default-hinge properties provided by the program and assign the PMM hinges for columns and M3 hinges for beams as recommended. Most design codes characterize soil types based on the shear wave velocity Cs. This study investigates three types of soil, as classified by the IS :1893 PARET I. These are types A, B and C, whose basic properties appear in Table 1. Impedance functions associated with rigid massless foundations controlled the simulated soil- structure interaction whereas the soil physical properties worked as a lumped parameter system at foundation level through them constitute a capacity spectrum. The demand of strength against earth- quake ground motions come from the local elastic response spectra of acceleration. There is also a transformation process here, according to which the diagram showing spectral acceleration versus period be- comes the Acceleration-Displacement Response Spectrum (ADRS). It follows that the intersection of the capacity spectrum and the demand spectrum provides an estimation of the inelastic performance of the structure.

III. CAPACITY CURVE

The pushover analysis, as applied herein, induced a monotonically increasing displacement-controlled lateral load pattern, in the presence of constant gravity load, until an ultimate condition appeared. The applied lateral loads relate to accelerations that the structure would experience during ground shakings. Under incrementally increasing loading, some structural members may yield sequentially. Consequently, parameterization with stiffness coefficients. The stiffness of the idealized springs representing the soil-flexibility are highly sensitive to the size of their footing. Therefore, their dimensions either reflect the ultimate or serviceability limit state, as specified in the relevant Code of Practice. From this derives that the footings underlying each column have dimensions of 4 m × 4 m, and that satisfies all the re- querulents. The three translational springs located at the base of the ground floor columns, two in principal horizontal and one in the vertical di- rection, together with rotational springs about these mutually perpendicular axes, simulate soil-flexibility (Fig. 1(b)). The boundary element method and experimental tests were in use to calibrate the properties of springs as these were hypothetically resting on homo- generous elastic half- space. The modelling technique, mapped from Gazeta’s and reflected in the set of equations listed in Table 2, is shared practice to dealing with soil-structure interaction - see for ex- ample hence considered suitable for the purpose of this investigation. Its main features account dependability of spring stiffness on mechanical characteristics of the soil material that supports the structure as well as on the dimensions of the foundation. In addition, the mechanical characteristics of the foundation soil medium translate

into an effective shear modulus G and Poisson’s ratio. Here the effective shear modulus G relates to the initial shear modulus go. Although the foundation embedment depth did not influence the estimation of stiffness for springs, it did feed in to computing the bearing capacity of the simulated soil-flexibility. According to Bowles he depth of the foundation has little influence on the bearing capacity of springs; hence its consideration seems confined to cases where controlled construction conditions do exist. As pointed out bent he structural stiffness changes past the yield point, de- noted as B in Fig.2 This figure also illustrates the acceptance criteria as defined by ATC-40. That criterion defines specific performance thresholds such as Immediate Occupancy (IO), Life Safety (LS) and Collapse Prevention (CP), corresponding to 10%, 60%, and 90% of plastic hinge deformation capacity, respectively. Thus, the two in- ventilated structures were subject to gravitational forces and the in- cemental lateral loading. The latter increased step-by-step in the nonlinear static analysis, keeping displacements under control via target tip node displacements of 4% with respect to the total height of the structure, as specified in ATC-40. This process included P-delta effects to defining total forces acting on structural members hence the respective deformations.

References

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Copyright

Copyright © 2023 Mr. Naman Kumar Rai, Prof. Anubhav Rai. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.