Evaluation of Structural Irregularities in H-Shaped RC High-Rise Building

Evaluation of Structural Irregularities in H-Shaped RC High-Rise Building

Krishnendu M S

Student, M. Tech Structural Engineering: Department of Civil Engineering, Rajadhani Institute of Engineering and Technology Kerala, India

Sreelekshmi S

Assistant professor Department of Civil Engineering, Rajadhani Institute of Engineering and Technology Kerala, India

Abstract – Structural irregularities play an important role in the seismic response of Reinforced Concrete (RC) buildings, mostly in structures with complex geometries like H, T, U, I and L-Shaped plans. This study analyses Earthquake response of a G+7 H-shaped RC structure using Building Information Modelling (BIM) and ETABS. The model is created in Revit Structure and perform seismic analysis in ETABS based on seismic code IS 1893:2016 provisions. Type of structural irregularities such as Plan and vertical irregularities are identified and evaluated manually based on the code-based requirements. Various parameters like storey stiffness, displacement, drift and shear are evaluated. This investigation highlights the effect of irregularities on Response under seismic loading and the importance of proper evaluation during the design stage.

Keywords – Structural Irregularity; H-Shaped Building; Seismic Analysis; RC Buildings; ETABS; BIM; IS 1893:2016

1. INTRODUCTION

   Earthquakes create dynamic forces that can seriously affect building stability, and have the potential for causing great damages in RC Buildings. The Structural response to earthquakes of a RC structure during seismic forces depends on its overall shape, size and geometry, in addition to how the earthquake forces are carried out to the ground. Modern construction practices widely adopt asymmetrical structural configuration to fulfill architectural and functional requirements. Buildings with T, I, L, U And H-Shaped configurations commonly used in modern construction, but they can cause significant structural irregularities which affects the Earthquake performance. Seismic code IS 1893:2016 is used to detect the structural irregularities. As per the guidelines given in IS 1893:2016, structural irregularities are grouped into plan and vertical types based on their behavior during seismic events, which can lead to uneven force distribution and torsional effects during earthquakes. These effects may increase the risk of damage and reduce structural stability of the building. Such irregular structures can be accurately modelled and analyzed by using BIM and ETABS. This study aims to evaluate the reaction to earthquake forces of a G+7 H- Shaped RC building and to find the irregularities based on IS 1893 guidelines. The seismic forces developed at different floor level levels in a building need to be brought down along the height to the ground by the shortest path, any deviation or uneven load distribution results in poor performance of the building.

   Moreover, the existence of structural irregularities can mostly change the dynamic characteristics of a building, such as its natural frequency, mode shapes, and damping behavior. These changes can affect the seismic responses, particularly in higher modes, and leading to uneven concentration of stresses in critical regions like beam-column joints and re-entrant corners. So, proper design considerations, such as the inclusion of shear walls, bracings, and sufficient stiffness distribution, can help in mitigating these harmful effects. Therefore, a detailed seismic analysis considering codal provisions is essential for the safety, serviceability, and resilience of irregular RC structures under earthquake loading.

   1. CHALLENGES CAUSED BY STRUCTURAL IRREGULARITIES
      • Uneven load distribution
      • Torsional effects
      • Uneven stress concentrations
      • Increased seismic vulnerability
      • Complex design and analysis
      • Difficulties in construction
      • Higher cost and maintenance
2. OBJECTIVES
   • To generate a G+7 H-shaped RC building using Revit Structure.
   • To investigate the behavior of the structure using ETABS software under different load conditions
   • To identify plan and vertical irregularities based on IS 1893:2016 code provisions.
   • To study the building responses such as storey displacement, drift, stiffness, and base shear.
   • To study the effect of structural irregularities on Earthquake analysis
   • To understand the importance of proper structural design in irregular buildings.
3. METHODOLOGY

   Chart 1: Methodology Workflow

   The H-shaped G+7 RC building is model is created using Autodesk Revit. Structural elements like beams, columns, slabs, and structural level levels are accurately defined.

   Fig 1: Plan layout of H-shaped structure

   Table 1: H-shaped RC building model details

   Particulars	Data
   Type of structure	H-Shaped RCC building
   Number of stories	8
   Height of one floor	3m
   Total height of the building	21.7m
   Shape & Size of column	Rectangular 450X450
   Shape & Size of beams	Rectangular 350X350
   Length & Width of the building	27 m x 27m

   Fig 2: 3D plan layout

   Table 2: Material Properties

   Particulars	Data
   Grade of concrete	M30
   Grade of steel	Fe500
   Grade of Rebar steel	Fe450
   Modulus of elasticity, E	210000Mpa
   Poissons ratio	0.3

   Table 3: Load patterns as per IS 1893:2016

   Load Cases
   Dead load	DL
   Live load	LL
   Earthquake in X direction	EQ X
   Earthquake in Y direction	EQ Y

4. RESULTS

Structural analysis is performed to determine how the building responds to the assigned load cases. The software calculates forces, displacements, shear, drifts and other important parameters.

Fig 4: Axial force diagram for the building

Table 4: Auto Lateral Load under EQ X

Fig 5: Shear force diagram for the building

Fig 6: Bending moment diagram for the building

Fig 7: Auto Lateral Load under EQ X condition

Fig 8: Auto Lateral Load under EQ Y condition

Table 5: Auto Lateral Load under EQ Y

Fig 9: Storey Shear under EQ-X Load Conditions

Fig 12: Storey Displacement under EQ-Y Load Conditions

Fig 10: Storey Shear under EQ-Y Load Conditions

Fig 13: Storey Drift under EQ-X Load Conditions

Fig 11: Storey Displacement under EQ-X Load Conditions

Fig 14: Storey Drift under EQ-Y Load Conditions

Fig 15: Storey Stiffness under EQ-X Load Conditions

Fig 16: Storey Stiffness under EQ-Y Load Conditions

Fig 17: Storey Overturning Moment under EQ-X Load Conditions

Fig 18: Storey Overturning Moment under EQ-Y Load Conditions

Structural analysis is performed to determine, how the building responds to the assigned load cases. The software calculates forces, stiffness, displacements, shear, drifts and other important parameters.

Table 6: Plan Irregularity detection

Table 7: Vertical Irregularity detection

CONCLUSION

The behavior during earthquakes of the G+7 H-shaped RC building shows that plan irregularities, such as torsional irregularity and re-entrant corner irregularity are present. However, there are no significant vertical irregularities in the structure.

These plan irregularities can affect vulnerably of the buildings seismic performance during land shakes and to uneven force distribution. Therefore, it is very important to properly analyze and design to ensure the structural safety and improved seismic resilience.

FUTURE SCOPE

• Different seismic zones and soil conditions can be considered for a better comparison.
• Automation of code guidelines can be implemented for faster irregularity detection.

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