Review on Out of Plane Offset in Multistory Building

Abstract

As per latest statistics, India comes under more denser oriented in terms of living in populated countries and by analysis, it is directly proportional to the land shortage problem. To overcome this problem, now engineers make a structure taller in height and having more land coverage area with aesthetic view is the only option available since it provides more suitability in less space. Also, architectural point of buildings are very famous and client prefer this type of structure. The main problem is to stable the architectural building when there will be instability due to attractive building looks. In this study, various papers associated to this topic are intensively studied and have gone through deep analysis in which an enormous work is done in this field earlier. To make these buildings more stable, literature review has conducted that came to know the conclusive outcome which forms the research objectives of our further technical study.

Introduction

I. INTRODUCTION

The current trend is to follow financial customs to ensure cost-effective construction. However, this approach can make achieving structural stability a challenging task, as it requires the use of heavy sections that can increase costs. Meeting seismic safety requirements can also necessitate the addition of stiffness-resisting members and shear walls in modern tall structures. While these measures can help protect against earthquakes and stabilize the structure, they also increase the weight and base shear of the building due to the use of heavy reinforced concrete components.

A. Out of Plane Offset

In Vertical Elements, the context of multistoried buildings, the term "out of plane offset" typically refers to a horizontal displacement of a structural element (such as a column or beam) in a direction perpendicular to its axis, with respect to the adjacent structural elements.

This displacement can occur for a variety of reasons, such as due to design considerations, construction tolerances, or settlement of the building's foundation. However, if the out of plane offset is excessive, it can affect the stability and structural integrity of the building.

Therefore, it is important to carefully assess and control the out of plane offsets in multistoried buildings during the design and construction phases to ensure the safety and durability of the structure.

B. Suggestion Provided As Per Indian Standards

When vertical elements in a building are offset out-of-plane, it creates disruptions in the load path that can compromise the building's earthquake safety. This irregularity occurs when structural walls or frames are displaced from the plane of the building in any story along its height.

If the building is located in Seismic Zone II, specialized literature should be consulted to design the building. If the building is in Seismic Zones III, IV, or V, two conditions must be met: the lateral drift in the story with the offset and the stories below it must be less than 0.2 percent, and specialized literature should be referred to remove the out-of-plane offset irregularity.

II. REVIEW OF LITERATURE

This research project involved the analysis of multiple high-rise buildings using CSI ETABS software, while taking into account the effects of response spectrum analysis. The research work considered high-rise buildings of various shapes, including H-shaped, O-shaped, and C-shaped buildings. All three building shapes were constructed with different numbers of stories, including 12 and 16 stories. To conduct a thorough seismic analysis of the aforementioned buildings, the response spectrum method was employed. The response spectrum analysis revealed distinct variations in the seismic behavior of each building. Specifically, the H-shaped building demonstrated superior performance compared to the other building shapes. Additionally, the 12-story building exhibited more favorable results than the 16-story building. Despite the transfer of heavy masses, there was minimal lateral sway observed, as the maximum displacement varied only slightly. However, in the case of the 16-story L-shaped building, the maximum displacement was measured at 87.804 mm. Despite the transfer of heavy masses, the total quantity and cost of the 16-story building were minimally affected. In summary, the study concluded that bending moments and shear forces increased by a range of 1.17% to 1.84%. The O-shaped building showed the greatest variation in bending moments and shear forces, while the L-shaped building exhibited the highest displacement among the irregular shapes analyzed (H-shape, L-shape, and O-shape).( Krishna Prasad Chaudhary et. al.)

The IS-1893: 2002 (Part-I), a standard code in India, identifies several structural irregularities and recommends a specific analysis approach for such structures. This study focuses on the response of a 10-story plane frame to lateral loads, specifically examining the impact of mass and stiffness irregularities in the building's elevation. To introduce irregularities in the building, the properties of the members on a given floor are altered. The study considers floor-mass ratios ranging from 1 to 5 to induce mass irregularities, with such irregularities being introduced at the fourth and seventh storey levels. The study introduces stiffness irregularity by decreasing the stiffnesses of the fourth and fifth storeys to 50% of that found in other storeys of the base frame, and similar stiffness irregularity is applied to all storeys except the first. Additionally, the research examines the effects of floating columns and unusually tall first storeys on the building's dynamic response. The study draws conclusions on how the identified irregularities impact storey-shear forces, storey drifts, and beam deflections. The findings suggest that irregular structures, compared to their regular counterparts, exhibit a moderate increase in response quantities due to the mass and stiffness criteria outlined in the IS code. (Poonam et. al.)

The manner in which a multi-storey framed building responds to powerful earthquake movements is contingent upon the distribution of mass, stiffness, and strength in both the horizontal and vertical planes of the structure. Typically, in such buildings, damage resulting from seismic activity begins at points of structural vulnerability in the lateral load resisting frames. Discontinuities in stiffness, strength, or mass between adjacent storeys can sometimes create these weaknesses. Such discontinuities are often associated with abrupt changes in frame geometry along the height. A vertical geometric irregularity resulting from a sudden drop in height is a typical form of discontinuity. This study investigates the performance and behavior of a regular and a vertically geometrically irregular reinforced concrete (RCC) framed structure subjected to seismic motion. The project includes five types of building geometry: one regular frame and four irregular frames. The study compares the building configurations by height and bay, using building frames that are modeled and analyzed in the Staad.Pro V8i software. The analysis is done in accordance with IS 1893:2002 part (1), with seismic zone IV and medium soil strata being applied to all cases. Various seismic responses, including shear force, bending moment, storey drift, and storey displacement, are obtained, and the differences in these responses are observed at different heights. (Dileshwar Rana et. al.)

The aim of this study is to analyze the behavior of vertically irregular buildings using advanced software, such as ETABS, through Non-Linear Dynamic analysis. The analysis focuses on three different types of irregularities, namely mass, stiffness, and setback irregularities. The response of the irregular buildings is compared to that of a regular building by examining factors such as Base shear, Displacement, and Story Drift. Vertically irregular buildings, particularly those located in seismic zones, can be difficult to understand due to the potential torsion effects resulting from the misalignment of their centre of mass and centre of gravity. Studying the behavior of such buildings presents a challenging task for structural engineers. The results of this study can be used to design vertical irregular buildings that meet the required standards. (V. Shiva Kumar et. al.)

The population is growing at an unprecedented rate, necessitating the construction of high-rise buildings. To withstand earthquake forces, these buildings must be designed appropriately. Regular structures are characterized by uniform mass, stiffness, strength, and structural form, making their behavior predictable under earthquake forces. In contrast, irregular structures with mass irregularities, torsion irregularities, weak stories, and diaphragm discontinuities are unpredictable.

Mass irregularity, in particular, has a significant impact on a structure's response to seismic loads, especially when the seismic weight of a story is more than 200% of its adjacent story. This can be achieved by increasing the weight of some floors relative to others. The impact of irregularity varies depending on the structural model, irregularity location, and analysis method. In this thesis, ETABS software is used to analyze a regular building with uniform mass and four irregular buildings with varying masses for Base shear, Mode shapes, storey drift, story shear, and Torsion moment. Suitable codes are employed for analysis and design. (Darshan D. et. al.) With limited space available in urban areas for building construction, constructing buildings with irregularities has become a necessity. However, these irregularities can cause weakness in the mass, stiffness, and geometry of the structure, leading to failures during earthquakes.

Performance-based seismic analysis has become an essential tool for assessing large structures, verifying new designs, and evaluating existing structures to identify damage states for various ground motions. As structural engineers shift towards performance-based seismic design, static and dynamic analyses are needed for designing high-rise structures. This paper considers a building with vertical irregularities, specifically mass irregularity, by modeling the roof diaphragm as both rigid and semi-rigid. The analysis is performed using ETABS 2015 software and static nonlinear analysis called pushover analysis. The results show that as buildings become more vertically irregular, the storey shear increases compared to mass regular buildings, making mass regular structures perform better than mass irregular ones. (T.M.Prakash et. al.)

A column is typically a vertical structural member that transfers load from the superstructure to the foundation. However, in certain architectural designs or site conditions, a vertical element called a floating column may be used. At its lower level, a floating column rests on a horizontal member known as a beam, which in turn transfers the load to other columns below it. This design is often adopted in multi-story buildings to create open spaces on the ground floor for purposes like assembly halls or parking. To support the floating columns, transfer girders are used and they must be properly designed and detailed, especially in seismic zones. The column is considered a concentrated load on the beam and is typically assumed to be pinned at the base, resulting in a point load on the transfer beam.

To analyze such structures, STAAD Pro V8I software can be used. While floating columns are capable of bearing gravity loads, the transfer girders must be sufficiently dimensioned and stiff to minimize deflection. (Pratyush Malaviya et. al.) This research paper aims to compare the performance of reinforced concrete (RC) frame buildings with and without floating columns under seismic and normal loading conditions. Irregularities in buildings, such as floating columns, can result in poor performance during earthquakes. The study will analyze the effect of earthquake forces on different building models using response spectrum analysis. The objective is to determine which structure performs better under seismic and normal loading conditions. The results of the analysis, such as storey drifts, storey displacement, and amount of steel required, will be compared to reach a definitive conclusion regarding the superiority of the two structures. (Prof. Rupali Goud)

III. ACKNOWLEDGEMENTS

I, Abdullah Mev, M. Tech. Scholar, would like to thank Mr. Mayur Singi, Assistant Professor, Department of Civil Engineering, B.M. College of Technology, Indore (M. P.), India, for his valuable guidance from the commencement of the work up to the completion of the work along with his encouraging thoughts.

Conclusion

On reviewing the above literature work, the building analysis has now become more easy and stable so that one can do the analysis of simple as well as difficult building having complex architectural view. By doing the literature survey, it is found that no one have discussed the out of plane offset in multistoried building under seismic loading. Here we come at conclusion drawn by literature reviews that emphasizes the extract of the research work and the necessary outcomes drawn from the study are enlisted below: 1) Conduction of the study for out of plane multistoried building having vertical irregularities and check for the same for both the directions would be necessary for lateral effect calculation. 2) Different parameters of analysis should be checked and validate as per Indian Standards along within the limits. 3) Actual soil data should be taken for analysis that would be comparable with realistic structure already constructed at that site. 4) Seismic zonal analysis should be check to analyze the data for different seismic zones in dual structural configurations. 5) It is always necessary to check the lateral effects in the form of displacements and limits prescribed by Indian Standards in terms of the lateral drift. The main focus of this study is to check whether the out of plane structure is possible and need to find out the limits in actual soil condition that has going to be a major study for upcoming proposed work.

References

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Copyright

Copyright © 2023 Abdullah Mev, Prof. Mayur Singi, Prof. Dinesh Vishwakarma. 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.