Structural systems in high rise building and analysis methods
- 1. HIGH RISE BUILDINGS AND METHODS OF ANALYSIS BY: D P Nithin
- 2. CONTENTS: INTRODUCTION EVOLUTION OF HIGH RISE BUILDINGS DEMANDS AND CHALLENGES GENERAL REQUIREMENTS OF HIGH RISE BUILDINGS LOADS ACTING ON HIGH RISE BUILDING STRUCTURAL SYSTEMS STABILITY ANALYSIS OF TALL BUILDINGS DISCUSSION REFERENCES
- 3. INTRODUCTION: Definition of High Rise Building by different bodies Emporis standards- A multi storey structure between 35-100 meters tall or building of unknown height from 12-39 floors . Skyscraper is a multi-story building whose architectural height is at least 100m(300 ft). For buildings above a height of 300m(984 ft) termed as Super tall . While skyscrapers reaching beyond 600m (1969 ft) are classified as mega tall. INDIAN STANDARDS As per NBC, structure having height more than 15m (5 storey) is called high rise As per BMC, high rise is above 24m. As per NMMC(2006), high rise is above 16m height.
- 4. EVOLUTION OF THE HIGH RISE BUILDINGS.
- 5. Fig2 Home Insurance Building ,Chicago Fig3.Ingalls Building,Chicago Fig4.Burj Khalifa, Dubai
- 6. Fig5.World One Tower, Mumbai Fig6.Mantri Pinnacle
- 7. DEMANDS FOR HIGH RISE BUILDINGS. High rise buildings are becoming more prominent these days due to following reasons • Scarcity of land • Greater demand for the business and residential space • Economic growth • Innovations in structural systems. • They have technical and economical advantage in the areas of high population density. CHALLENGES: • Underlying soil having geotechnical risk factors such as bay mud. • Problems of Elevators and HVAC systems. • Challenges to fire fighters during emergency
- 8. GENERAL REQUIREMENTS FOR HIGH RISE BUILDINGS (IS 16700-2017) 1. ELEVATION • Height Limit for Structural Systems • Slenderness ratio (Ht/Bt)
- 9. • Aerodynamic effects: Elevation profile, facade features of the building and plan, shape of the building shall be such as to attract minimum wind drag effects. 2.PLAN • Plan geometry: The plan shall be rectangular (including square) or elliptical (including circular) • Plan aspect ratio(Lt/Bt) should not exceed 5 3.STOREY STIFFNESS AND STRENGTH: • Lateral translational stiffness of any storey shall not be less than 70% percent of the storey above. • Lateral translational strength of any storey shall not be less than that of the storey above. Lt Bt
- 10. 4.DEFORMATION: • Lateral Drift: Limited to H/500. • For earth quake load (factored load combinations)-hi/250 5.FLOOR SYSTEM: • For precast floor systems a minimum screed of 75mm (seismic zone3,4,5) and 50mm (Zone 2). • Openings in floor diaphragm shall not be permitted along any floor edge. Unless perimeter are shown to have stability and adequate strength. • Maximum area of opening in any floor shall not exceed 30% of the plan area of diaphragm 6.MATERIALS: • The minimum grade of concrete shall be M30. • Ultimate strength of reinforcement shouldn’t exceed (1.25 characteristic yield strength/0.2 percent proof stress) • No lapping of bars shall be allowed in RC Columns and walls, when diameter of bar is 16mm or higher as per IS 16172
- 11. LOADS ACTING ON THE TALL BUILDING: 1.Gravity Loads: • Dead Loads • Live Loads • Snow Loads 2.Lateral Loads: • Wind Loads • Seismic Loads 3.Other Loads: • Impact loads • Blast Loads
- 12. STRUCTURAL SYSTEMS IN HIGH RISE BUILDINGS: The Classification of the structural System was introduced in 1969 by Fazlur Khan.
- 13. 1.BRACED FRAME STRUCTURAL SYSTEM: • Braced Frames are considered as vertical trusses resisting lateral loads, primarily diagonal members that together with the girders, form the web of the vertical truss and columns acts as a chords.
- 14. 1.BRACED FRAME STRUCTURAL SYSTEM: • Bracing members eliminate bending in beams and columns. • It is majorly used in steel construction • This system is suitable for multi-story building in low to mid height range. • Efficient and economical for enhancing the lateral stiffness. • This system permits the use of slender members in the building. An outstanding advantage of braced frame is that ,it can be repetitive with obvious economy in design and fabrication. However, it might obstruct internal planning. Fig. John Hancock Tower (241m)
- 15. 2.RIGID FRAME STRUCTURAL SYSTEM • In Rigid Frame Structures, beams and columns are constructed monolithically to withstand moments imposed due to loads. • The lateral stiffness of a rigid frame depends on the bending stiffness of the columns, girders and connections in-plane Rigid End cap
- 16. 2.RIGID FRAME STRUCTURAL SYSTEM • It is suitable for reinforced concrete buildings. • Members of the rigid frame system withstand bending moment, shear force, and axial force • 20-25 storey buildings can be constructed. • One of the advantages of rigid frame is the planning and fitting of windows due to open rectangular arrangement. • Advantages of rigid frame include ease of construction ,labor can learn construction skills easily • A disadvantage is that the self weight is resisted by the action from rigid frames.
- 17. 3.SHEAR WALL SYSTEM: • It is a continuous vertical wall constructed from reinforced concrete or masonry wall. • Shear walls withstand both gravity and lateral loads and it acts as narrow deep cantilever beam. • Commonly constructed as core of the buildings. • It is highly suitable for bracing tall structure either RC or steel structure.This is because shear walls have substantial in plane stiffness and strength • Shear wall can economical up to 35 stories. • Shear walls need not to be symmetrical in plan,but Symmetry is preferred in order to avoid torsional effects .
- 18. 4.CORE AND OUTRIGGER STRUCTURAL SYSTEM a. Outriggers are rigid horizontal structures designed to improve building overturning stiffness and strength by connecting the core or spine to closely spaced outer columns. b. The central core contains shear wall or braced frames. c. Outrigger systems functions by tying together two structural systems (core system and perimeter system) and render the building to behave nearly as composite cantilever. d. Practically, Outrigger systems are used for buildings up to 70 stories. e. Not only does the outrigger system decline building deformations resulting from the overturning moments but also greater efficiency is achieved in resisting forces.
- 20. 5. TUBE STRUCTURAL SYSTEM: • This system consists of exterior columns and beams that create rigid frame, and interior part of the system which is simple frame designed to support gravity loads. • The building behaves like equivalent hollow tube. • It is substantially economic and needs half of the materials required for the construction of ordinary framed buildings. • Lateral loads are resisted by various connections, rigid or semi rigid, supplemented where necessary by bracing and truss element. Fig. Types of Tube system
- 21. Advantages of Tube Structural System • Offers some clear advantage from material standpoint. • Allows greater flexibility in planning of interior space since all the columns and lateral systems is concentrated on the perimeter of structure . • This allows column free space in the interior. • Wind resisting system since located on the perimeter of the building means that maximum advantage is taken of the total width of the building to resist overturning moment.
- 22. Dewitt Chestnut Fig. Framed Tube Structures
- 23. Trussed Tube System Fig.Bank of China, Hong Kong Bundled Tube System Fig. Willis tower
- 24. 6.BUTTRESSED CORE • The buttresses core permits a dramatic increase in height. • Its design employs conventional materials and construction techniques. • The system consists of a tripod shaped structure in which strong central core anchors three building wings. • It is stable system in which each wings is buttressed by other two. • The central core provides the torsional resistance for the building while the wings provide shear resistance and increase the moment of inertia. • Example –Burj Khalifa.
- 25. DIFFERENT TYPE OF ANALYSIS FOR THE TALL BUILDINGS 1.LINEAR STATIC ANALYSIS: • Also known as Equivalent Static method. • Based on formulas given in the code of practice (IS 1893 Part 1-2016) Determination of storey shear and moment Determination of lateral forces in each floor Determination of Design base shear Vb Determination of Fundamental natural period Calculation of Lumped weight/Seismic weight
- 26. LIMITATIONS: • High seismic zones and height of the structure • Buildings having higher modes of vibration than the fundamental mode
- 27. PUSH OVER ANALYSIS : • Non linear static analysis. • Used to estimate the strength and drift capacity of existing structure and the seismic demand for this structure subjected to selected earthquake. • It is an analysis in which, a mathematical model incorporates the nonlinear load-deformation characteristics of individual components and elements of the building which shall be subjected to increasing lateral loads representing inertia forces in an earthquake until a ‘target displacement’ is exceeded. Target displacement can be calculated by: a. Displacement Coefficient Method (DCM) b. Capacity Spectrum Method (CSM)
- 28. Response characteristics that can be obtained from the pushover analysis are Estimates of force and displacement capacities of the structure. Sequences of the failure of elements and the consequent effect on the overall structural stability. Identification of the critical regions, where the inelastic deformations are expected to be high and identification of strength irregularities of the building.
- 29. RESPONSE SPECTRUM METHOD • It is a linear dynamic analysis . • In this approach multiple mode shapes of the building are taken into account. • For each mode, a response is read from the design spectrum, based on the modal frequency and the modal mass. • They are then combined to provide an estimate of the total response of the structure using modal combination methods. • Buildings with plan irregularities and with vertical irregularities cannot be modeled for dynamic analysis by this method. • Methods: 1.Absolute Sum method. 2.Square root sum of squares. 3.Complete quadratic combination
- 30. This method is used for the following: 1. Regular building: • Greater than 40m in height and zone 4 and 5. • Greater than 90m in height and zone 2 and 3. 2. Irregular buildings • All frame buildings higher than 12m in zone 4 and 5 . • Greater than 40m in zone 2 and 3. Response vs time
- 31. TIME HISTORY ANALYSIS • It is a Non Linear Dynamic Analysis. • Also known as Time History Analysis(THA) • To perform such an analysis, a representative earthquake time history is required for a structure being evaluated. • In this method, the mathematical model of the building is subjected to accelerations from earthquake record. • The method consists of a step- by- step direct integration over a time interval.
- 32. Fig. Time History analysis
- 33. DISCUSSION: • New improved structural systems and new materials in the future can lead us to even greater heights and more stable building. • Structural System should be selected such that the system would efficiently resist the combination of loading that the structure is subjected to. • The building weight, and thus the vertical load to be supported by the foundation can be substantial. • Static analysis is not sufficient for high rise building its necessary to provide dynamic analysis because of specific & non linear distribution of forces. • Time history analysis should be performed as it predicts the structural response more accurately than other two methods based on damage assessment of building. • Nonlinear relationship between force and displacement in multi-storey building structures may be determined easy enough with the application of nonlinear static pushover analysis.
- 34. REFERENCES: 1. Prof. S .Vijaya Bhaskar Reddy, M.Eadukondalu. Study of Lateral Structural Systems in Tall Buildings, International Journal of Applied Engineering Research, Volume 13, 2018 2. Mohd Zeeshan, Ahsan Khan. The Stability of High Rise Buildings, International Journal of Advance research in Science and Engineering, Volume 7, October 2018 3.Sule Yılmaz Erten, Semiha Kartal, A Comparative Study on Structural Analysis of High-Rise Buildings, International Journal of Scientific Research and Innovative Technology, Volume 5, No 5, Dec 2018. 4. Christian Sandelin, Evgenij Budajev. The Stabilization of High rise buildings- An evaluation of the tubed mega frame structure. Uppsala University, Dec 2013. 5. Erik Hallebrand and Wilhelm Jakobsson. Structural design of High rise buildings, Department of construction Science. Lund's University, 2016. 6.IS Code- IS 1893(Part 1):2016, IS 16700-2017.
- 35. THANK YOU