Wind Load as per BNBC 2020

wind load as per BNBC 2020

Wind Load as per BNBC 2020

BNBC 2020 এ র wind load অংশটা আগের BNBC 2006 এর সাথে তেমন একটা মিল নেই। কিছুটা জটিল। বিল্ডিং এবং শেড এর জন্য আলাদা সিস্টেম। কোডের এই অংশটা সিভিল ইঞ্জিনিয়ারদের জন্য নিজে কোড পড়ে বুঝাটা খুব সহজ হবে না বলেই মনে হয়। এই শর্ট কোর্সটা অত্যন্ত চমৎকারভাবে wind load কে সহজ করা হয়েছে। ETABS model এ কিভাবে wind load parameters input দিতে হয় তাও এই কোর্সে আছে।

Wind load as per BNBC 2020 will be great for design engineers. The wind load portion of BNBC 2020 does not match the previous BNBC 2006. Somewhat complicated. Separate system for building and shed. This part of the code does not seem to be very easy for civil engineers to read and understand the code themselves. This short course is very nicely made easy to wind load. This course also covers how to input wind load parameters in ETABS model.

What you'll learn

  • Wind load design procedures
  • Characteristics of Wind
  • Wind speed variation with height
  • Pressure co-efficient
  • Basic Wind Speed
  • Exposure
  • Wind Load Calculation

Special Gift with The Course

Wind load calculation excel program

Prerequisite / Eligibility

  • BSc, MSc or PhD in Civil Engineering
  • Level 4 or 4th year student of bachelor’s in civil engineering
  • AMIEB students of IEB

Course Teacher

Professor Dr. Jahangir Alam, Department of Civil Engineering, BUET, Dhaka, Bangladesh

Brief Biography of Course Teacher

Education

  • PhD in Geotechnical Earthquake Engineering, the University of Tokyo, Japan, 2005
  • MSc in Civil and Geotechnical Engineering, BUET, Dhaka, Bangladesh, 2002
  • BSc in Civil Engineering, BUET, Dhaka, Bangladesh, 1998

Biography

Professor Dr. Engr. Md. Jahangir Alam is faculty member at the Department of Civil Engineering, BUET, Dhaka-1000, since 1999. He completed his PhD from University of Tokyo in Geotechnical Earthquake Engineering in 2005 as a Monbu-Kagaku-sho Scholar. He was research fellow in Ecole Centrale Paris in 2008. Professor Jahangir did his BSc in Civil Engg with major in Structure and MSc in Civil and Geotechnical Engineering from BUET.

Professor Jahangir has multidisciplinary research interests and has publications in international journals and conferences. His current research topics are “Risk Sensitive Land Use Planning of Mega City”, Physical and Numerical Modeling of Liquefaction Hazard, Mitigation against Seismic Liquefaction, Cyclic Behavior of Non-plastic silt, Reinforced Earth, Earthquake Resistant Foundation in Soft Soil, Climate Resilient Concrete, Climate Resilient Road.

Professor Jahangir was involved in many consultancy projects where he designed/checked high rise RCC buildings, Communication towers, Jetty, Shore Pile, Embankment, Container Terminal, Ground Improvement, Bridge Foundation etc. He supervised many MSc and PhD students. He was involved in pile load testing, pile integrity testing, concrete mix design and development of laboratory and field-testing equipment.

Professor Jahangir actively involved in National and International professional bodies. He is life member and was Treasurer of Bangladesh Society for Geotechnical Engineering (BSGE), which is Bangladesh Chapter of ISSMGE. He is life fellow of Institute of Engineers Bangladesh (IEB). He is life member of Bangladesh Earthquake Society (BES). He was Treasurer of Bangladesh Earthquake Society (BES).

Certificate of Attendance

Certificate of attendance will be awarded after completion of all video lessons and quizzes

Related Courses

  • Earthquake Load as per BNBC 2020
  • Seismic Detailing of RCC Structure as per BNBC 2020
  • Soils and Foundations as per BNBC 2020

Free Courses

  • Design Issues for Large Earth Structures: Stress, Deformation, FOS and Liquefaction
  • Webinar on Dynamic Analysis

Features of ourPROFESSORs.com

User Guide of ourPROFESSORs.com

Course Preview

BNBC intensive outline

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BNBC intensive outline

CONTENTS

  • BNBC Part 6, Chapter 1 – Definition and General Requirement
  • BNBC Part 6, Chapter 2 – Load (wind and earthquake load)
  • BNBC Part 6, Chapter 3 – Soils and Foundations
  • BNBC Part 6, Chapter 8 – Seismic Detailing of RCC Structures
  • Software implementation of wind load and earthquake load


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All documents of Wind load

Definitions and general requirements

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Definitions and general requirements, Part-1

DEFINITIONS AND GENERAL REQUIREMENTS OF BNBC 2017

Table of contents

1.0 Definitions

2.0 Wind Speed Definitions

3.0 BNBC, 2017: Basic wind speed V = v3s

4.0 Basic considerations

5.0 Structural systems

5.1 Basic Structural Systems

6.0 Dual system

7.0 Design for lateral loads

7.1 Design for Wind Load

7.2 Design for Earthquake Forces

7.3 Overturning Requirements


1.0 Definitions

  • Base shear: Total design lateral force or shear at the base of a structure.
  • Basic wind speed: Three-second gust speed at 10m above the mean ground level in terrain Exposure-B and associated with an annual probability of occurrence of 0.02.
  • Bearing wall system: A structural system without a complete vertical load carrying space frame.
  • Braced frame: An essentially vertical truss system of the concentric or eccentric type which is provided to resist lateral forces.
  • Building frame system: An essentially complete space frame which provides support for loads.
  • Concentric braced frame (CBF): A steel braced frame.
  • Bearing wall system: A structural system without a complete vertical load carrying space frame.
  • Collector: A member or element used to transfer lateral forces from a portion of a structure to the vertical elements of the lateral force resisting elements.
  • Dead load: The load due to the weight of all permanent structural and non-structural components of a building or a structure, such as walls, floors, roofs and fixed service equipment.
  • Diaphragm: A horizontal or nearly horizontal system acting to transmit lateral forces to the vertical resisting elements. The term “diaphragm” includes horizontal bracing systems.
  • Dual system: A combination of Moment Resisting Frames and Shear Walls of Braced Frames to resist lateral load.
  • Eccentric braced frame (EBF): An eccentric braced frame is a structural system that is designed primarily to resist wind and earthquake forces and some members in the braced frame are eccentrically placed.
  • Horizontal bracing system: A horizontal truss system that serves the same function as a floor or roof diaphragm.
  • Intermediate moment frame (IMF): A concrete moment resisting frame.
  • Live load: The load superimposed by the use and occupancy of a building.
  • Moment resisting frame: A frame in which member and joints are capable of resisting forces primarily by flexure.
  • Ordinary moment frame (OMF): A moment resisting frame not meeting special detailing requirements for ductile behavior.
  • Primary framing system: That part of the structural system assigned to resist lateral forces.
  • Shear wall: A wall designed to resist lateral forces parallel to the plane of the wall (sometimes referred to as a vertical diaphragm or a structural wall).
  • Slender buildings and structures : Buildings and structures having a height exceeding five times the least horizontal dimension, or having a fundamental natural frequency less than 1Hz. For those cases where the horizontal dimensions vary with height, the least horizontal dimension at mid height shall be used.
  • T > 1 s = flexible structure
  • T < 1 s = rigid structure
  • Soft story : A soft story is one in which the lateral stiffness is less than 70 percent of that in the story above or less than 80 percent of the average stiffness of the three storeys above.
  • Space frame: A three-dimensional structural system without bearing walls composed of members interconnected so as to function as a complete self-contained unit with or without the aid of horizontal diaphragms or floor bracing systems.
  • Special moment frame (SMF): A moment resisting frame specially detailes to provide ductile behavior.
  • Storey: The space between any two floor levels including the roof of a building. Storey-x is the storey below level x.
  • Storey shear, vx: The summation of design lateral forces above the storey under consideration.
  • Strength: The usable capacity of an element or a member to resist the load as prescribed in these provisions.
  • Terrain: The ground surface roughness condition when considering the size and arrangement of obstructions to the wind.
  • Three-second gust speed: The highest average wind speed over a 3 second duration at a height of 10 m. The three-second gust speed is derived using Durst’s model in terms of the mean wind speed and turbulence intensity.
  • Tower: A tall, slim vertical structure.
  • Weak storey: Storey in which the lateral is less than 80 percent of that of the storey above.

2.0 Wind Speed Definitions

  1. Three Second Gust, V3s :
  2. Wind speed averaged over a period of three seconds.
  3. Codes: BS CP3, BNBC 2017, ASCE 7-05
  4. Mean hourly, Vmean :
  5. Wind speed averaged over a period of an hour.
  6. Codes: BS8100 (tower code).
  7. Fastest Mile Wind, VFM :
  8. Average speed of a one mile long sample of wind crossing a fixed point.
  9. Codes: BNBC 1993, TIA-EIA-F

3.0 BNBC, 2017: Basic wind speed V = v3s

3-sec gust wind at a height of 10m above ground in a terrain Exposure B having a return period of 50 years.

Figure 10: Wind speed vs. time graph of a typical storm


4.0 Basic considerations

1 Building and Structure Occupancy Categories:


Nature of Occupancy: Buildings and other structures that represent a low hazard to human life in the event of failure, including, but not limited to:

  1. Agricultural facilities.
  2. Certain temporary facilities.
  3. Minor storage facilities

Occupancy Category - i


Nature of Occupancy: All buildings and other structures except those listed in Occupancy Categories I, III and IV.

Occupancy Category - ii


Nature of Occupancy: Buildings and other structures that represent a substantial hazard to human life in the event of failure, including, but not limited to:

  1. Buildings with more than 300 people.
  2. Buildings with day care facilities with a capacity greater than 150.
  3. Buildings with elementary school or secondary school facilities with a capacity greater than 250.
  4. Buildings with a capacity greater than 500 for colleges or adult education facilities.
  5. Healthcare facilities with a capacity of 50 or more resident patients, but not having   surgery or emergency Treatment facilities.
  6. Jails and detention facilities.

Occupancy Category - iii


Nature of Occupancy: Buildings and other structures designated as essential facilities, including, but not limited to:

  1. Hospitals, Fire, rescue, ambulance, and police stations and emergency vehicle garages.
  2. Designated earthquake, hurricane, or other emergency shelters, emergency preparedness, communication.
  3. Power generating stations, Ancillary structures, Electrical substation structures, Aviation control towers, air traffic control centers.

Occupancy Category - iv


2 Distribution of Horizontal Shear: 

The total lateral force shall be distributed to the various elements of the lateral force-resisting system in proportion to their rigidities considering the rigidity of the horizontal bracing systems or diaphragms.


3 Horizontal Torsional Moments: 

Structural systems and components shall be designed to sustain additional forces resulting from torsion due to eccentricity between the centre of application of the lateral forces and the centre of rigidity of the lateral force resisting system. Forces shall not be decreased due to torsional effects.


4 Stability Against Overturning and Sliding

Every building or structure shall be designed to resist the overturning and sliding effects caused by the lateral forces specified in this Chapter.


5 Anchorage: 

Anchorage of the roof to wall and columns, and of walls and columns to foundations, shall be provided to resist the uplift and sliding forces resulting from the application of the prescribed loads. 


5. Structural systems

5.1 Basic Structural Systems:

Moment resisting frame system: 

Moment resisting frames also provide resistance to lateral load primarily by flexural action of members, and may be classified as one of the following types:

  • Special Moment Frames (SMF).
  • Intermediate Moment Frames (IMF).
  • Ordinary Moment Frames (OMF).

BEARING WALL SYSTEMS (no frame)

  • Special reinforced concrete shear walls.
  • Ordinary reinforced concrete shear walls.
  • Ordinary reinforced masonry shear walls.
  • Ordinary plain masonry shear walls.

BUILDING FRAME SYSTEMS (with bracing or shear wall)

  • Steel eccentrically braced frames, moment resisting connections at columns away from links.
  • Steel eccentrically braced frames, non-moment-resisting, connections at columns away from links.
  • Special steel concentrically braced frames.
  • Ordinary steel concentrically braced frames.
  • Special reinforced concrete shear walls.
  • Ordinary reinforced concrete shear walls.
  • Ordinary reinforced masonry shear walls.
  • Ordinary plain masonry shear walls.

MOMENT RESISTING FRAME SYSTEMS (no shear wall)

  • Special steel moment frames
  • Intermediate steel moment frames
  • Ordinary steel moment frames
  • Special reinforced concrete moment frames
  • Intermediate reinforced concrete moment frames
  • Ordinary reinforced concrete moment frames

DUAL SYSTEMS: SPECIAL MOMENT FRAMES CAPABLE OF RESISTING AT LEAST 25% OF PRESCRIBED SEISMIC FORCES (with bracing or shear wall) 

  • Steel eccentrically braced frames
  • Special steel concentrically braced frames
  • Special reinforced concrete shear walls
  • Ordinary reinforced concrete shear walls

DUAL SYSTEMS: INTERMEDIATE MOMENT FRAMES CAPABLE OF RESISTING AT LEAST 25% OF PRESCRIBED SEISMIC FORCES (with bracing or shear wall)

  • Special steel concentrically braced frames.
  • Special reinforced concrete shear walls.
  • Ordinary reinforced masonry shear walls.
  • Ordinary reinforced concrete shear walls.

DUAL SHEAR WALL-FRAME SYSTEM:

ORDINARY REINFORCED CONCRETE MOMENT FRAMES AND ORDINARY REINFORCED CONCRETE SHEAR WALLS.

STEEL SYSTEMS NOT SPECIFICALLY DETAILED FOR SEISMIC RESISTANCE.


6.0 Dual system

1.      An essentially complete space frame provides support for gravity loads.

2.      Resistance to lateral forces is provided by moment-resisting frames capable of resisting at least 25 percent of the design base shear and rest (less than 75%) by shear walls (ASCE 12.2.5.1).

3.      The two subsystems (moment-resisting frames and shear walls) are designed to resist the design base shear in proportion to their relative rigidities (ASCE 12.2.5.1).


7.0 Design for lateral loads

7.1 Design for Wind Load:

a)     Direction of wind: Structural design for wind forces shall be based on assumption that wind may blow from any horizontal direction.

b)     Design considerations: Design wind load on the primary framing systems and components of a building or structure shall be determined on the basis of the specific procedures considering the basic wind speed, shape and size of the building, and the terrain exposure condition of the site.

For slender buildings and structures, dynamic response characteristics, such as fundamental natural frequency, shall be determined to estimate gust response coefficient. Load effects, such as forces, moments, and deflections etc. on various components of building due to wind shall be determined from static analysis of the structure.

c)      Shielding effect: Reductions in wind pressure on buildings and structures due to apparent direct shielding effects of the up wind obstructions, such as man-made constructions or natural terrain features, shall not be permitted. *****

d)     Dynamic effects: Dynamic wind forces such as that from along-wind vibrations caused by the dynamic wind-structure interaction effects. For other dynamic effects such as cross-wind or torsional responses as may be experienced by buildings or structures having unusual geometrical shapes, response characteristics, or site locations, structural design.

e)      Wind tunnel test: Properly conducted wind-tunnel tests shall be required for those buildings or structures having unusual geometric shapes, response characteristics, or site locations for which cross-wind response such as vortex shedding, galloping etc.

f)      Wind loads during construction: Buildings, structures and portions thereof under construction, and construction structures such as formwork, staging etc. shall be provided with adequate temporary bracings or other lateral supports to resist the wind load on them during the erection and construction phase. *****

g)     Height limits: Unless otherwise specified elsewhere in this Code, no height limits shall be imposed, in general, on the design and construction of buildings or structures to resist wind-induced forces.


a)     Direction of wind: Structural design for wind forces shall be based on assumption that wind may blow from any horizontal direction.

b)     Design considerations: Design wind load on the primary framing systems and components of a building or structure shall be determined on the basis of the specific procedures considering the basic wind speed, shape and size of the building, and the terrain exposure condition of the site.

For slender buildings and structures, dynamic response characteristics, such as fundamental natural frequency, shall be determined to estimate gust response coefficient. Load effects, such as forces, moments, and deflections etc. on various components of building due to wind shall be determined from static analysis of the structure.

c)      Shielding effect: Reductions in wind pressure on buildings and structures due to apparent direct shielding effects of the up wind obstructions, such as man-made constructions or natural terrain features, shall not be permitted. *****

d)     Dynamic effects: Dynamic wind forces such as that from along-wind vibrations caused by the dynamic wind-structure interaction effects. For other dynamic effects such as cross-wind or torsional responses as may be experienced by buildings or structures having unusual geometrical shapes, response characteristics, or site locations, structural design.

e)      Wind tunnel test: Properly conducted wind-tunnel tests shall be required for those buildings or structures having unusual geometric shapes, response characteristics, or site locations for which cross-wind response such as vortex shedding, galloping etc.

f)      Wind loads during construction: Buildings, structures and portions thereof under construction, and construction structures such as formwork, staging etc. shall be provided with adequate temporary bracings or other lateral supports to resist the wind load on them during the erection and construction phase. *****

g)     Height limits: Unless otherwise specified elsewhere in this Code, no height limits shall be imposed, in general, on the design and construction of buildings or structures to resist wind-induced forces.


7.2 Design for Earthquake Forces:

The seismic forces on structures shall be determined considering seismic zoning, site soil 

characteristics, structure importance, structural systems and configurations, height and dynamic

properties of the structure.

a)     Requirements for directional effects: The directions of application of seismic forces used in the design shall be those which will produce the most critical load effects. Earthquake forces act in both principal directions of the building simultaneously. *****

b)     Structural system and configuration requirements : Seismic design provisions impose the following limitations on the use of structural systems and configurations:

  • The structural system used shall satisfy requirements of the Seismic Design Category and height limitations.
  • Structures assigned to Seismic Design Category D having vertical irregularity Type shall not be permitted. Structures with such vertical irregularity may be permitted for Seismic Design Category B or C but shall not be over two stories or 9 m in height. *****
  • Structures having irregular features shall be designed in compliance with the additional requirements.
  • Special Structural Systems may be permitted if it can be demonstrated by analytical and test data to be equivalent, with regard to dynamic characteristics, lateral force resistance and energy absorption, to one of the structural systems for obtaining an equivalent R and Cd value for seismic design.


7.3 Overturning Requirements: **

Every structure shall be designed to resist the overturning effects caused by wind or earthquake forces as well other lateral forces like earth pressure, tidal surge etc. The overturning moment Mx at any storey level-x of a building shall be determined as:

Where,

Mx = Summation of {Fi(hi-hx)}

  • Hi,hx,hn = Height in metres at level- I, -x or -n respectively.
  •  Fi = Lateral force applied at level- i, I = 1 to n

At any level, the increment of overturning moment shall be distributed to the various resisting elements in the same manner as the distribution of horizontal shear. Overturning effects on every element shall be carried down to the foundation level.

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Definitions and general requirements, Part-2
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Definitions and general requirements, Part-3
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Definitions and general requirements, Part-4
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Definitions and general requirements, Part-5
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BNBC Quiz 1 : Definitions and general requirements
10 questions

Drift and deflection limits

1
Drift and deflection limits, Part-1

Drift and deflection limits


Table of Contents

1.0 Basic considerations

1.1 Serviceability: Deflection Limits a, b, c, h (Except earthquake load)

1.2 Control of Deflections

1.3 Serviceability:  Deflection limits

2.0 serviceability for lateral loads

2.1 Drift and Building Separation

2.2 Load Combination for Serviceability

2.3 Deflection due to creep

2.4 Drift due earthquake loading

2.5 Stiffness of frame members in analysis

2.6 Effective Stiffness for Determining Lateral Deflections

2.7 BNBC requirement of 1.4 times the cracked section for serviceability check

2.8 Input in Analysis (etabs)

2.9 Allowable Storey Drift Limit (Δa) for earthquake load

2.10 Separation between adjacent structures



1.0 Basic considerations

1.1 Serviceability: Deflection Limits a, b, c, h (Except earthquake load)

Construction

1 Roof members

  • Supporting plaster ceiling, L= L/360, Wf = L/360, Dg+Ld= L/240
  • Supporting non-plaster ceiling, L= L/240, Wf = L/240, Dg+Ld= L/180
  • Not supporting ceiling, L= L/180, Wf = L/180, Dg+Ld= L/120

2 Floor members , L= L/360, Dg+Ld= L/240

3 Exterior walls and interior partitions

  • With brittle finishes, Wf = L/240
  • With flexible finishes, Wf = L/120

4 Farm buildings, Dg+Ld= L/180

5 Greenhouses, Dg+Ld= L/120

Where, l,L,W and D stands for span of the member under consideration, live load, wind load and dead load respectively.


1.2 Control of Deflections

Minimum Thickness (h) of Nonprestressed beams or one-Way slabs Unless Deflections are calculated.

Member 1: Solid One- Way slabs (60 ksi)

  • Simply supported: L/20 , for fy>60 ksi multiply by (0.4+fy/700) MPa
  • One end continuous: L/24, for fy>60 ksi multiply by (0.4+fy/700) MPa
  • Both ends continuous: L/28, for fy>60 ksi multiply by (0.4+fy/100000) psi
  • Cantilever: L/10, for fy>60 ksi multiply by (0.4+fy/100000) psi

Member 2: Beams/Ribbed one-way slabs (60 ksi)

  • Simply supported: L/16, for fy>60 ksi multiply by (0.4+fy/700) MPa
  • One end continuous: L/18.5, for fy>60 ksi multiply by (0.4+fy/700) MPa
  • Both ends continuous: L/21, for fy>60 ksi multiply by (0.4+fy/100000) psi
  • Cantilever: L/8, for fy>60 ksi multiply by (0.4+fy/100000) psi


1.3 Serviceability:  Deflection limits :

1. Load deflecting :

  • For structural roofing and siding made of metal sheets, the total load deflection shall not exceed l/60.
  • For secondary roof structural members supporting formed metal roofing, the live load deflection shall not exceed l/150.
  • For secondary wall members supporting formed metal siding, the design wind load deflection shall not exceed l/90.
  • Interior partitions not exceeding 2m in height and flexible, folding and portable partitions are not governed by the provisions of this Section.

3. For cantilever members, I shall be taken as twice the length of the cantilever.******

4. The above deflections do not ensure against ponding. Roofs that do not have sufficient slope or camber to assure adequate drainage shall be investigated for ponding.

5. The wind load is permitted to be takes as 0.7 times the “component and cladding” loads for the purpose of determining deflection limits herein.*****

6. Deflection due to dead load shall include both instantaneous and long term effects.

7. For aluminum structural members or aluminum panels used in skylights and sloped glazing framing, roofs or walls of sunroom additions patio covers, not supporting edge of glass or aluminum sandwich panels, the total load deflection shall not exceed l/60.

8. For continuous aluminum structural members supporting edge of glass, the total load deflection shall not exceed l/175 for each glass lite or l/60 for for the entire length of the member, whichever is more stringent.

9. For aluminum sandwich panels used in roofs or walls of sunroom additions or patio covers, the total load deflection shall not exceed l/120.


2.0 Serviceability for lateral loads

2.1 Drift and Building Separation:

(a) Storey drift limitation :

Storey drift is the horizontal displacement of one level of a building or structure relative to the level above or below due to the design gravity (dead and live loads) or lateral forces (e.g. wind and earthquake loads). Calculated storey drift shall include both translational and torsional deflections and conform to the following requirements:

(I) Storey drift,  for lateral loads other than earthquake loads*, shall be limited as follows:

 < 0.005h   for T < 0.7 second

 < 0.004h   for T > 0.7 second *****

 < 0.0025h  for unreinforced masonry structures.

Where, h = height of the building or structure

 T = time period.

(ii) The drift limits set out in (i) above may be exceeded where it can be demonstrated that greater drift can be tolerated by both structural and nonstructural elements without affecting life safety.

(iii) For earthquake loads, the story drift,  shall be limited and given in ch. 2*


(b) Sway limitation:

The overall sway (horizontal deflection) at the top level of the building or structure due to wind loading shall be limited to 1/500 times of the total height of the building above ground.**


(c) Load combination

Load combination = 1.0 D + 0.5 L + 0.7 W

Lateral deflection at top level < h/500

This is not a criteria in ASCE-7-05

BNBC requirement of 1.4 times the cracked section for serviceability check


2.2 Load Combination for Serviceability

1. vertical deflection due to gravity load is: D+L [vertical and short term effect]

2. For serviceability limit states involving creep, settlement, or similar long-term or permanent effects, the suggested load combination is: D+0.5L [vertical and long term effect]

to account for long term creep effect, the immediate (e.g. elastic) deflection may be multiplied by a creep factor ranging from 1.5 to 2.0.

3. For serviceability limit state against lateral deflection of buildings and structures due to wind effect, the following combination shall be used: D+05L+0.7W [lateral and wind effect]

Due to its transient nature, wind load need not be considered in analyzing the effects of creep or other long-term actions. 


2.3 Deflection due to creep:

If the values are not obtained by a more comprehensive analysis, additional long-term deflection resulting from creep and shrinkage of flexural members (normal weight or lightweight concrete) shall be determined by multiplying the immediate deflection caused by the sustained load considered, by the factor λ△

where, ρ‘ shall be the value at midspan for simple and continuous spans, and at support for cantilevers. It shall be permitted to assume ξ, the time-dependent factor for sustained loads, to be equal to: 

λ△ =ξ/(1+50ρ‘)

ρ‘ is ratio of compression rebar As’/bd 

Table 3: Deflection due to creep (a)

5 years or more        2.0

12 months            1.4

6 months             1.2

3 months             1.0


Table 4:

1) Deflection due to creep in Sand and Hard Clay (b)

Isolated Foundations in Steel Structure:

  • Maximum Settlement : 50
  • Differential Settlement : 0.0033L
  • Angular Distortion : 1/300

Isolated Foundations in RCC Structure:

  • Maximum Settlement : 50
  • Differential Settlement : 0.0015L
  • Angular Distortion : 1/666

Notes: The values given in the Table may be taken only as a guide and the permissible total settlement, differential settlement and tilt (angular distortion) in each case should be decided as per requirements of the designer. 

L denotes the length of deflected part of wall/ raft or centre to centre distance between columns. 

H denotes the height of wall from foundation footing. 

* For intermediate ratios of L/H, the values can be interpolated


2.4 Drift due earthquake loading

δ x = Cd δxe / I

Δx = δx – δx-1


1.1 Stiffness of frame members in analysis

  1. Table 4-1 shows the range of values for the effective, cracked stiffness for each element based on the requirements of ACI 318 - 8.8.2. For beams cast monolithically with slabs, it is acceptable to include the effective flange width of ACI 318 - 8.12.
  2. More detailed analysis may be used to calculate the reduced stiffness based on the applied loading conditions.  For example, ASCE 41 recommends that the following (Table 4-2) Ie/Ig ratios be used with linear interpolation for intermediate axial loads.
  3. Note that for beams this produces Ie/Ig = 0.30. 
  4. When considering serviceability under wind loading, it is common to assume gross section properties for the beams, columns, and joints. *****

BNBC requirement of 1.4 times the cracked section for serviceability check


2.6 Effective Stiffness for Determining Lateral Deflections

Lateral deflections resulting from service lateral loads for reinforced concrete building systems shall be computed by either a linear analysis with member stiffness determined using 1.4 times the flexural stiffness defined in Sections 6.1.11.2 and 6.1.11.3 or by a more detailed analysis. Member properties shall not be taken greater than the gross section properties.


2.7 BNBC requirement of 1.4 times the cracked section for serviceability check

1.      Elastic second-order analysis

2.      Elastic second-order analysis shall consider section properties determined taking into account the influence of axial loads, the presence of cracked regions along the length of the member, and the effects of load duration

3.      It shall be permitted to use the following properties for the members in the structure:


Table 5: BNBC requirement of 1.4 times the cracked section for serviceability check

Value of I for:

  • Columns = 0.70 I
  • Shear Wall Uncracked = 0.70 I
  • Shear Wall Cracked = 0.35 I
  • Beams = 0.35 I
  • Flat plates & Flat Slabs = 0.25 I

Input in Analysis (ETABS) for Moment of Inertia I22 / I33

  • Columns = I22 = I33 = 0.70
  • Shear Wall Uncracked = modeled as shell – f11, f22 = 0.70
  • Shear Wall Cracked = modeled as shell – f11, f22 = 0.70
  • Beams = I22 = I33 = 0.35
  • Flat plates & Flat Slabs = modeled as membrane/shell – f11, f22, f12 = 0.25

BNBC requirement of 1.4 times the cracked section for serviceability check.


ACI 318 - 8.8.2

Table 7: Cracked stiffness modifiers.

Element le/lg

Beam 0.35-0.50

Column 0.50-0.70



ASCE 41

Table 8: Effective stiffness modifiers for columns.

Compression Due to Design Gravity Loads - le/lg

≥0.5Agf 'c 0.7

≥0.1Agf 'c 0.3



2.9 Allowable Storey Drift Limit (Δa) for earthquake load 

(a) Structures, other than masonry shear wall structures, 4 stories or less with interior walls, partitions, ceilings and exterior wall systems that have been designed to accommodate the story drifts.

  •  Occupancy Category i and ii = 0.025hsx
  •  Occupancy Category iii = 0.020hsx
  •  Occupancy Category iv = 0.015hsx

(b) Masonry cantilever shear wall structures :

  • Occupancy Category i and ii = 0.010hsx
  •  Occupancy Category iii = 0.010hsx
  •  Occupancy Category iv = 0.010hsx

(c) Other masonry shear wall structures :

  •  Occupancy Category i and ii = 0.007hsx
  •  Occupancy Category iii = 0.007hsx
  •  Occupancy Category iv = 0.007hsx

(d) All other structures :

  •   Occupancy Category i and ii = 0.020hsx
  •  Occupancy Category iii = 0.015hsx
  •  Occupancy Category iv = 0.010hsx

There shall be no drift limit for single-story structures with interior walls, partitions, ceilings, and exterior wall systems that have been designed to accommodate the storey drifts.


As per ASCE 7 Allowable story drift:

(a) Redundancy Factor ρ = 1.0

  •  Occupancy Category i and ii = 0.020hsx
  •  Occupancy Category iii = 0.015hsx
  •  Occupancy Category iv = 0.010hsx

(b) Redundancy Factor ρ = 1.3

  • Occupancy Category i and ii = 0.015hsx
  •  Occupancy Category iii = 0.012hsx
  •  Occupancy Category iv = 0.008hsx



2.10 Separation between adjacent structures

Buildings shall be protected from earthquake-induced pounding from adjacent structures or between structurally independent units of the same building maintaining safe distance between such structures as follows:

(i)        for buildings, or structurally independent units, that do not belong to the same property, the distance from the property line to the potential points of impact shall not be less than the computed maximum horizontal displacement (Sec 2.5.7.7) of the building at the corresponding level.

(ii)       for buildings, or structurally independent units, belonging to the same property, if the distance between them is not less than the square root of the sum- of the squares (SRSS) of the computed maximum horizontal displacements (Sec 2.5.7.7) of the two buildings or units at the corresponding level.

•      if the floor elevations of the building or independent unit under design are the same as those of the adjacent building or unit, the above referred minimum distance may be reduced by a factor of 0.7

2
Drift and deflection limits, Part-2
3
Drift and deflection limits, Part-3
4
Drift and deflection limits, Part-4
5
Drift and deflection limits, Part-5
6
Drift and deflection limits, Part-6
7
BNBC Quiz 2 : Drift and deflection limits
10 questions

Wind load

1
Wind load, Part-1

“WIND LOAD ON BUILDINGS & STRUCTURES”

( As per BNBC 2017 )




2.4 Wind Load


q 2.4.1 design wind loads determined using one of following procedures: 

Ø Method 1:       Simplified Procedure

Ø Method 2:       Analytical Procedure*****

Ø Method 3:       Wind Tunnel Procedure


Shielding

There shall be no reductions in velocity

pressure due to apparent shielding afforded by

buildings and other structures or terrain features.



Minimum Design Wind Loading

q For Main Wind-Force Resisting System: The design wind load

Ø     For enclosed or partially enclosed building   

ü  Ps ≥ 0.5 kN/m2

ü projected onto vertical plane normal to wind direction.

           

Ø For open buildings

ü Ps ≥ 0.5 kN/m2


q For Components and Cladding: The design wind load

•     Ps ≥ 0.5 kN/m2

•     acting in either direction normal to surface.



2.4.3 Method 2: Analytical Procedure


q Conditions:

Ø Building is regular-shaped

Ø Building does not have response characteristics making it subject to

•     across-wind loading

•     vortex shedding

•     instability due to galloping or flutter

•     does not have a site location for channeling effects



Laminar flow Vs.Turbulent flow


Wind induced oscillations


There are three forms of wind induced motion as follows:-

·        Galloping - Galloping is transverse oscillations of some structures due to the development of aerodynamic forces which are in phase with the motion.

·        Flutter - Flutter is unstable oscillatory motion of a structure due to coupling between aerodynamic force and elastic deformation of the structure. Perhaps the most common form is oscillatory motion due to combined bending and torsion. Long span suspension bridge decks or any member of a structure with large values of d/t ( where d is the depth of a structure or structural member parallel to wind stream and t is the least lateral dimension of a member ) are prone to low speed flutter.

·        3) Ovalling : This walled structures with open ends at one or both ends such as oil storage tanks and natural draught cooling towers in which the ratio of the diameter of minimum lateral dimension to the wall thickness is of the order of 100 or more, are prone to ovalling oscillations. These oscillations are characterized by periodic radial deformation of the hollow structure.



Method 2: Analytical Procedure


1.     basic wind speed (V) & wind directionality factor, Kd

2.     importance factor, I

3.     exposure category and velocity pressure exposure coefficient, Kz or Kh

4.     topographic factor, Kzt

5.     gust effect factor, G or Kf

6.     enclosure classification

7.     Internal pressure coefficient, G Cpi  

8.     External pressure coefficients, Cp  or GCpf , or force coefficients Cf ,

9.     Velocity pressure, qz or qh

10. Design wind load (P or F) determination



q  2.4.9.5 Velocity pressure  evaluated at height z:

q_z=0.000613*K_z K_zt K_d V^2 I ;  (kN/m2),V in m/s

Where

           K_d, wind directionality factor,

            K_z, velocity pressure exposure coefficient

            K_zt, topographic factor

           q_z ,velocity pressure at mean roof height h



Velocity Pressure:

           q_z=0.000613*K_z K_zt K_d V^2 I ;  (kN/m2)


Design Wind Load for:

Rigid Buildings of All Heights,    p=qGC_p-q_i (GC_pi )                (k N⁄m^2 )

Low-Rise Building (Rigid),          p=q_h [(GC_pf )-(GC_pi )]         (kN⁄m^2 )

Flexible Buildings,                          p=qG_f C_p-q_i (GC_pi )                (k N⁄m^2 )

Parapets,                                  p_p=q_p GC_pn                                   (kN⁄m^2 )

Components and cladding, p=q_h [(GC_p )-(GC_pi )] (k N⁄m^2 )    h≤18.3m

p=q(GC_p )-q_i (GC_pi ) (kN/m^2 )      h>18.3 m

 Design pressure for the MWFRSs of monoslope, pitched, or troughed roofs,

p=q_h GC_N



7. Design wind force for other structures, F=q_z GC_f A_f   (kN)            

  for windward walls evaluated at height above the ground

 for leeward walls, side walls, and roofs, evaluated at height

 for windward walls, side walls, leeward walls, and roofs of enclosed buildings and for negative internal pressure evaluation in partially enclosed buildings



Low-rise building?


Enclosed or partially enclosed buildings that comply with the following conditions

•     Mean roof height h less than or equal to 18.3 m.

•     Mean roof height h does not exceed least horizontal dimension.



Three Second Gust, V3s:

Wind speed averaged over a period of three seconds.

Codes: BS CP3, BNBC 2017, ASCE 7-05


Mean hourly, Vmean:

Wind speed averaged over a period of an hour.

Codes: BS8100 (tower code).


Fastest Mile Wind, VFM:

Average speed of a one mile long sample of wind crossing a fixed point.

Codes: BNBC 1993, TIA-EIA-F


BNBC, 2017: Basic wind speed V = V3s

3-sec gust wind at a height of 10m above ground in a terrain Exposure B having a return period of 50 years

Basic Wind Speed (V) map


Velocity Pressure:

q_z=0.000613*K_z K_zt K_d V^2 I (kN/m2)


* Tornadoes have not been considered in

developing the basic wind-speed distributions



Table 6.2.8: Wind Speed for some selected region in Bangladesh


Location         Basic Wind Speed (m/s)

Angarpota      47.8

Bagerhat         77.5

Bandarban      62.5

Barguna          80.0

Barisal 78.7

Bhola  69.5

Bogra 63.9

Brahmanbaria 56.7

Chandpur       50.6

Chapai Nawabganj     41.4

Chittagong     80.0

Chuadanga     61.9

Lalmonirhat    63.7

Madaripur      68.1

Magura           65.0

Manikganj      58.2

Meherpur        58.2

Maheshkhali   80.0

Moulavibazar 53.0

Munshiganj    57.1

Mymensingh  67.4

Naogaon         55.2

Narail 68.6

Narayanganj   61.1



Table 6.2.12: Wind directionality factor, Kd


Structure Type ------Directionality Factor K_d*

Buildings

 Main Wind Force Resisting System 0.85

 Components and Cladding   0.85

Arched Roofs 0.85

Chimneys, Tanks, and Similar   Structures  

  Square         0.90

  Hexagonal   0.95

  Round         0.95




Table: Importance Factor (accordingly)


Occupancy Category or Importance Class = --- i---ii---iii---iv

Non-Cyclone Prone Regions and Cyclone Prone Regions with V = 38-44 m/s = 0.87---1.0---1.15----1.15

Cyclone Prone Regions with V > 44 m/s = 0.77----1.00----1.15-----1.15



Exposure

q Surface roughness categories

Ø ground surface roughness within each 450 sector determined



q Surface Roughness A:

Ø  Urban and suburban areas,

Ø  wooded areas, or

Ø  closely spaced obstruction terrain

Ø  Mostly single family dwelling  



Exposure


q Surface Roughness B:

·        Open terrain with scattered obstructions

·        having heights generally less than 9.1 m.

·        includes flat open country,

·        grasslands and

·        all water surfaces in cyclone prone regions.




Exposure


q Surface Roughness C:

  •  Flat, unobstructed areas and

o  water surfaces outside cyclone prone regions

  •  smooth mud flats and salt flats



q Exposure categories:

q Exposure A:

·        Surface Roughness A

·        upwind direction prevail distance at least 792 m

·        20 times the height of the building



Exposure A:


q Exception: For buildings

·        mean roof height h ≤ 9.1 m

·        upwind distance may be reduced to 457 m




When H ≤ 9.1 m

Exposure


q Exposure B:

Ø Exposure B shall apply for all cases

•     where Exposures A or C do not apply




Exposure


q Exposure C:

Ø Surface Roughness C

Ø prevails in upwind direction for

•      distance ≥ 1,524 m 

•     20 times building height



Exposure


q Exposure C extend into downwind areas of Surface Roughness A or B

Ø for a distance of 200 m or

Ø 20 times height of the building,



q For site located in transition zone between exposure categories,

Ø category resulting in largest wind forces


q Exception: An intermediate exposure between preceding categories is:

Ø permitted in transition zone provided

Ø determined by rational analysis method

Ø defined in recognized literature.



q  Notes: Topographic factor       

                                               

o   For values of H/Lh, x/Lh and z/Lh other than those shown (previous slide)

·        linear interpolation is permitted


o   If H/Lh > 0.5 then assume H/Lh = 0.5 for

·        evaluating K1 and

·         substitute 2H for Lh for evaluating K2 and K3


o   Multipliers are based on assumption that

·        wind approaches hill or escarpment along the direction of maximum slope   



Gust Effect Factor


q Rigid structure ( T < 1 s)

Ø For rigid structures gust-effect factor shall be taken as 0.85

Ø or calculated by the formula:

G=0.925 (1+1.7g_Q I_z ̅ Q)/(1+1.7g_v I_z ̅ )         

I_z ̅ =c(10/z ̅ )^(1⁄6)   

Where,

I_z ̅ = the intensity of turbulence at height z ̅

z ̅ = equivalent height of structure as 0.6h, not less than z_min for heightsh.

g_Q and the value of g_v shall be taken as 3.4.



q Rigid structure ( T < 1 s)

Ø The background response Q is given by

Q=√(1/(1+0.63((B+h)/L_z ̅ )^0.63 ))"          


Where,

B, h are defined in Sec 2.1.4; and

L_z ̅ = integral length scale of turbulence at equivalent height L_z ̅ =l(z ̅/10)^ϵ ̅    

In which l and ∈ ̅ are constants



q Flexible or dynamically sensitive structures ( T > 1 s)


Ø For flexible or dynamically sensitive structures as

·        natural period greater than 1.0 second


the gust-effect factor shall be calculated by

G_f=0.925((1+1.7I_z ̅ √(g_Q^2 Q^2+g_R^2 R^2 ))/(1+1.7g_v I_z ̅ ))

The value of both  and   shall be taken as 3.4 and

g_R=√(2 ln(3600n_1) )+0.577/√(2 ln(3600n_1) )


           R, the resonant response factor, is given by                                                 

           R=√(1/β R_n R_h R_B (0.53+0.47R_L))                                     R_n=(7.47N_1)/(1+10.3N_1)^(5⁄3)

           N_1=(n_1 L_z ̅ )/V ̅_z ̅                                                                                 R_l=1/η-1/(2η^2 ) (1-e^(-2η) ) for η>0

R_l=1  for  η=0


·        n_1 = building natural frequency

·        R_l=R_h setting η=4.6 n_1 h/V ̅_z ̅

·        R_l=R_B setting η=4.6 n_1 B/V ̅_z ̅

·        R_l=R_L setting η=15.4  n_1 L/V ̅_z ̅

·        β = damping ratio, percent of critical

·        V ̅_z ̅ = mean hourly wind speed at height z ̅ (=0.6h) determined from Eq. 6.2.16.

·        V ̅_z ̅ =b ̅(z ̅/10)^∝ ̅ V [table 6.2.10]


Enclosure Classifications


q For purpose of determining internal pressure coefficients


Ø all buildings shall be classified as :

·        enclosed

·        partially enclosed

·        open



Enclosed building


o  A_o≤1.10A_oi

o  A_o≤0.37m^2  ≤ 0.01A_g 

o  A_oi/A_gi>0.20

o  A_o = total area of openings in a wall that receives positive external pressure (m2)

o  A_oi = sum of areas of openings in building envelope 

o  A_gi = sum of gross surface areas of building envelope not including A_g

o  A_g = the gross area of that wall in which A_o is identified (m2).



Partially enclosed building


  • A_o>1.10A_oi
  •  A_o>0.37m^2  >0.01A_g
  • A_oi/A_gi≤0.20
  • A_o = total area of openings in a wall that receives positive external pressure (m2)
  • A_oi = sum of areas of openings in building envelope 
  • A_gi = sum of gross surface areas of building envelope not including A_g



v Building envelope:

•     Cladding, roofing, exterior walls, glazing

•     door assemblies, window assemblies, skylight assemblies

•     other components enclosing the building.




Open building

           A_o≥0.8A_g 

where,

·         = total area of openings in wall that receives positive external pressure (m2)

·         = gross area of that wall in which  is identified (m2)



Velocity Pressure Exposure Coefficients, Kh  and Kz

For 4.57 m ≤ z zg        Kz = 2.01 (z/zg)2/α

For z < 4.57          Kz = 2.01 (4.57/zg)2/α

Note: z shall not be taken less than 9.1 m for rigid building in exposure A



Exposure----α--------z_g (m)

A------------7.0--------365.76

B------------9.5--------274.32

C------------11.5------213.36

Kz and Kh may be taken from Table 6.2.11 directly



Velocity Pressure:

q_z=0.000613*K_z K_zt K_d V^2 I ;  (kN/m2)


Design Wind Load for:


·       Rigid Buildings of All Heights,    p=qGC_p-q_i (GC_pi )                (k N⁄m^2 )

·       Low-Rise Building (Rigid),          p=q_h [(GC_pf )-(GC_pi )]         (kN⁄m^2 )

·       Flexible Buildings,                         p=qG_f C_p-q_i (GC_pi )                (k N⁄m^2 )

·       Parapets,                                 p_p=q_p GC_pn                                   (kN⁄m^2 )

·       Components and cladding, p=q_h [(GC_p )-(GC_pi )] (k N⁄m^2 )    h≤18.3m                        

p=q(GC_p )-q_i (GC_pi ) (kN/m^2 )      h>18.3 m

·       Design pressure for the MWFRS of monoslope, pitched, or troughed roof    p=q_h GC_N        

·       Design wind force for other structures, F=q_z GC_f A_f   (kN)            



Internal pressure coefficient, GCpi

Enclosure Classification---------------GCpi

Open Building ---------------------------0.00

Partially Enclosed Building------+0.55, -0.55

Enclosed Building------------------+0.18, -0.18

Notes:

1. Plus and minus signs signify pressures acting toward and away

   from the internal surfaces, respectively.

2. Values of GCpi shall be used with qz or qh as specified in Sec

    2.4.11.

3. Two cases shall be considered to determine the critical load

    requirements for the appropriate condition:

    (i) a positive value of GCpi applied to all internal surfaces

    (ii) a negative value of GCpi applied to all internal surfaces.



q  Reduction Factor for Large Volume Buildings,:

·        For a partially enclosed building

·        containing a single, unpartitioned large volume,

 

** internal pressure coefficient,  multiplied by reduction factor, :

(R_i=1.0    or,    R)_i=0.5(1+1/√(1+V_i/(6951A_og )))≤1.0


External Pressure Coefficient, Cp for wall


Roof Pressure Coefficients, Cp, for use with qh



Design Wind Loads on Enclosed and Partially Enclosed Buildings


·        Case 1. 

o  Full design wind pressure acting on the projected area perpendicular to each principal axis of the structure, considered separately along each principal axis.

·        Case 2. 

o  Three quarters of the design wind pressure acting on the projected area perpendicular to each principal axis of the structure in conjunction with a torsional moment as shown, considered separately for each principal axis. 

·        Case 3. 

§ Wind loading as defined in Case 1, but considered to act simultaneously at 75% of the specified value.

·        Case 4.  

o  Wind loading as defined in Case 2, but considered to act simultaneously at 75% of the specified value.


Notes:

·        Design wind pressures for windward and leeward faces shall be determined in accordance with the provisions of Sec 2.4.11 as applicable for building of all heights.

·        Diagrams show plan views of building.

·        Notation:

·        Pwx, PwY :  Windward face design pressure acting in the x, y principal axis, respectively.

·        PLX, PLY :              Leeward face design pressure acting in the x, y principal axis, respectively.

·        e(ex, ey):     Eccentricity for the x, y principal axis of the structure, respectively.

·        MT :          Torsional moment per unit height acting about a vertical axis of the building.




Low-rise shed (MWFRS)

H < 18.3 m

a = 10 percent of least horizontal dimension or 0.4h, whichever is smaller, but not less than either 4% of least horizontal dimension or 0.9 m.

h = Mean roof height, in meters, except that eave height shall be used for Θ  ≤ 10°.

Θ = Angle of plane of roof from horizontal, in degrees.



Enclosed, Partially Enclosed Buildings: Low-rise Walls & Roofs

combined gust &

external pressure

effect, GCpf



Enclosed, Partially Enclosed Buildings: Low-rise Walls & Roofs

combined gust &

external pressure

effect, GCpf




Enclosed, Partially Enclosed Buildings: Low-rise Walls & Roofs GCpf


Notes

·       For the design of the MWFRS providing lateral resistance in a direction parallel to a ridge line or for flat roofs, use θ = 0° and locate the zone 2/3 boundary at the mid-length of the building.

·       The roof pressure coefficient GCpf, when negative in Zone 2 or 2E, shall be applied in Zone 2/2E for a distance from the edge of roof equal to 0.5 times the horizontal dimension of the building parallel to the direction of the MWFRS being designed or 2.5 times the eave height, he, at the windward wall, whichever is less; the remainder of Zone 2/2E extending to the ridge line shall use the pressure coefficient GCpf for Zone 3/3E.


Notation:

·       a: 10 percent of least horizontal dimension or 0.4h, whichever is smaller, but not less than either 4% of least horizontal dimension or 0.9 m.

·       h: Mean roof height, in meters, except that eave height shall be used for θ ≤ 10°.

·       θ: Angle of plane of roof from horizontal, in degrees.



COMPONENT AND CLADDING FOR LOW RISE SHED

H < 18.3 M

Component and Cladding (h<18.3)

Internal pressure coefficient from figure 6.2.5



Note:

q Values of GCP for walls shall be reduced by 10% when θ ≤ 100.

Notations:

a: 10 percent of least horizontal dimension or 0.4h, whichever is smaller, but not less than either 4% of least horizontal dimension or 0.9m.

h: Mean roof height, in meters, except that eave height shall be used for Θ  ≤ 100.

Θ : Angle of plane of roof from horizontal, in degrees.



Special notes

v Critical Load Condition: Values of external and internal pressures shall be combined algebraically to determine the most critical load.

v Tributary Areas Greater than 65 m2: Component and cladding elements with tributary areas greater than 65 m2 shall be permitted to be designed using the provisions for MWFRSs.



Explanation of equations


Design wind pressure for MWFRS for rigid buildings of all height


q Main wind-force resisting systems (MWFRS)

Rigid Buildings of All Heights: Design wind pressures                       

p=qGC_p-q_i (GC_pi )  (k N⁄m^2 )                                

Where,

q=q_z  for windward walls evaluated at height z above ground

q=q_h  for leeward walls, side walls, roofs, evaluated at height h

q_i=q_h for windward walls, side walls, leeward walls, roofs etc

q_i=q_z for positive internal pressure in partially enclosed buildings

For positive internal pressure evaluation, q_i at height h=(q_i=q_h )

G= gust effect factor

C_p= external pressure coefficient

GC_pi= internal pressure coefficient

q and q_i shall be evaluated using exposure



Design wind pressure for MWFRS for low rise building (h<18.3m)


q Low-Rise Building: design wind pressures for the MWFRS


shall be determined by :

p=q_h [(GC_pf )-(GC_pi )] (kN⁄m^2 )                



Design wind pressure for MWFRS for flexible buildings of all height


q Flexible Buildings: Design wind pressures for MWFRS   

Ø shall be determined by:

     p=qG_f C_p-q_i (GC_pi ) (k N⁄m^2 )          

 Where,

 q, q_i, C_p, and GC_pi shown in previous section

G_f= gust effect factor



Design wind pressure at parapet


q Parapets: design wind pressure for effect of parapets:

p_p=q_p GC_pn  (kN⁄m^2 )

 Where,

p_p= Combined net pressure front and back parapet surfaces.

(Plus and minus signs signify net pressure direction)

q_p= Velocity pressure evaluated at top of parapet

GC_pn                        

= Combined net pressure coefficient

= +1.5 for windward parapet

= −1.0 for leeward parapet



Components and claddings for buildings with h<18.3 m


Components and claddings for buildings with h>18.3 m



FLOW CHART FOR WIND LOAD CALCULATION (MWFRS)



Summary


  • for building main structure, internal pressure is not needed
  •  for component and cladding design, internal and external both pressures are need to be considered
  •  for shed main structure, both external and internal pressure have to be applied
  •  for shed component and cladding, both external and internal pressure have to be applied


2
Wind load, Part-2
3
Wind load, Part-3
4
Wind load, Part-4
5
Wind load, Part-5
6
Wind load, Part-6
7
Wind load, Part-7
8
Wind load, Part-8
9
Wind load, Part-9
10
Wind load, Part-10
11
BNBC Quiz 5 : Wind load
31 questions

Wind load Examples

1
Wind load example-1, Part-1
2
Wind load example-1, Part-2
3
Wind load example-1, Part-3
4
Wind load example-1, Part-4
5
Wind load example-2, Part-1
6
Wind load example-2, Part-2
7
Wind load example-2, Part-3
8
Wind load example-2, Part-4
9
Wind load example-2, Part-5
10
Wind load example-2, Part-6
11
Wind load example-3, Part-1
12
Wind load example-3, Part-2
13
Wind load example-3, Part-3

Wind load input tutorial on Etabs as per BNBC 2017

1
Wind load input tutorial, Part-1
2
Wind load input tutorial, Part-2
3
Wind load input tutorial, Part-3
4
Wind load input tutorial, Part-4
5
5 out of 5
3 Ratings

Detailed Rating

Stars 5
3
Stars 4
0
Stars 3
0
Stars 2
0
Stars 1
0

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