Design of Buildings for Wind E-Book

Emil Simiu

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 507

Veröffentlichungsjahr: 2011

Beschreibung

ASCE 7 is the US standard for identifying minimum design loads for buildings and other structures.  ASCE 7 covers many load types, of which wind is one.  The purpose of this book is to provide structural and architectural engineers with the practical state-of-the-art knowledge and tools needed for designing and retrofitting buildings for wind loads. The book will also cover wind-induced loss estimation. This new edition include a guide to the thoroughly revised, 2010 version of the ASCE 7 Standard provisions for wind loads; incorporate major advances achieved in recent years in the design of tall buildings for wind; present material on retrofitting and loss estimation; and improve the presentation of the material to increase its usefulness to structural engineers.

Key features:

• New focus on tall buildings helps make the analysis and design guidance easier and less complex.
  
• Covers the new simplified design methods of ASCE 7-10, guiding designers to clearly understand the spirit and letter of the provisions and use the design methods with confidence and ease.
  
• Includes new coverage of retrofitting for wind load resistance and loss estimation from hurricane winds.
  
• Thoroughly revised and updated to conform with current practice and research.

Leseprobe

Table of Contents

Title Page

Copyright

Preface

Part I: Introduction

Chapter 1: Overview

Part II: Guide to the ASCE 7-10 Standard Provisions on Wind Loads

Chapter 2: ASCE 7-10 Wind Loading Provisions

2.1 Introduction

2.2 ASCE 7-10 Standard: An Overview

2.3 Organization of the Guide: Chapters 3 to 9

Chapter 3: Regular and Simplified Approach: Risk Category, Basic Wind Speed, Enclosure, Exposure, Topographic Factor

3.1 Risk Category (ASCE Table 1.5-1)

3.2 Basic Wind Speed V (ASCE Sect. 26.5, ASCE Figs. 26.5.-1a, b, c)

3.3 Enclosure Classification (ASCE Sects. 26.2 and 26.10)

3.4 Exposure Category (ASCE Sect. 26.7)

3.5 Topographic Factor Kzt (ASCE Sect. 26.8, ASCE Fig. 26.8-1)

Chapter 4: Regular Approach: Steps Common to All Buildings/Other Structures (MWFRS and C&C)

4.1 Introduction

4.2 Regular Approach: Steps Common to All Buildings and Other Structures (MWFRS and C&C)

Chapter 5: Regular Approach: Buildings, Parapets, Overhangs (“Directional” Procedure), MWFRS

5.1 Introduction

5.2 Regular Approach: Enclosed or Partially Enclosed Buildings of All Heights, MWFRS

5.3 Regular Approach: Roof Overhangs and Parapets, MWFRS

5.4 Regular Approach: Open Buildings with Monoslope, Pitched, or Troughed Free Roofs, MWFRS

Chapter 6: Regular Approach: Low-Rise Buildings, Parapets, Overhangs (“Envelope” Procedure), MWFRS

6.1 Net Pressures on Walls and Roof

6.2 Comparison Between Results Based on ASCE Sects. 27.4.1 and 28.4.1

6.3 Regular Approach: Parapets and Roof Overhangs, MWFRS

Chapter 7: Regular Approach: Structures Other than Buildings, MWFRS

7.1 Solid Freestanding Walls and Solid Signs

7.2 Open Signs, Lattice Frameworks, Trussed Towers

7.3 Chimneys, Tanks, Rooftop Equipment, and Similar Structures

7.4 Solid Attached Signs

7.5 Rooftop Structures and Equipment on Buildings

Chapter 8: Simplified Approach: Enclosed Simple Diaphragm Buildings, Parapets, Overhangs (MWFRS)

8.1 Simplified Approach: Class 1 Buildings, Walls and Roof, MWFRS

8.2 Simplified Approach: Parapets, MWFRS

8.3 Simplified Approach: Roof Overhangs, MWFRS

8.4 Simplified Approach: Class 2 Buildings, Walls and Roof, MWFRS

8.5 Simplified Approach: Simple Diaphragm Low-Rise Buildings, MWFRS

Chapter 9: Regular and Simplified Approaches: C&C

9.1 Introduction

9.2 Regular Approach

9.3 Simplified Approaches

Part III: Wind Engineering Fundamentals

Chapter 10: Atmospheric Circulations

10.1 Atmospheric Hydrodynamics

10.2 Windstorms

Chapter 11: The Atmospheric Boundary Layer

11.1 Wind Speeds and Averaging Times

11.2 Wind Speed Profiles

11.3 Atmospheric Turbulence

Chapter 12: Extreme Wind Speeds and Wind-Induced Effects

12.1 Wind Speed Data

12.2 Cumulative Distributions, Exceedance Probabilities, Mean Recurrence Intervals

12.3 Parametric Estimates of -Year Wind Speeds; Closed Form Estimators; Software

12.4 Probabilistic Estimates of Wind Effects Based on Nondirectional and Directional Wind Speed Data

12.5 Development of Directional Databases of Hurricane Wind Speeds

12.6 Development of Directional Databases of Non-Hurricane Wind Speeds

12.7 Non-Parametric Statistics, Application to One-Dimensional Time Series

12.8 Error Estimates

Chapter 13: Bluff Body Aerodynamics Basics; Aerodynamic Testing

13.1 Introduction

13.2 Bluff Body Aerodynamics

13.3 Aerodynamic Testing

13.4 Low-Frequency Turbulence and Aerodynamic Pressures on Residential Homes

Chapter 14: Structural Dynamics

14.1 Introduction

14.2 The Single-Degree-of Freedom Linear System

14.3 Continuously Distributed Linear Systems

14.4 Time Domain Solutions for Three-Dimensional Dynamic Response

Chapter 15: Aeroelasticity

15.1 Introduction

15.2 Vortex-Induced Oscillations

15.3 Galloping

15.4 Flutter

Chapter 16: Structural Reliability Under Wind Loading

16.1 Introduction

16.2 First-Order Second-Moment Approach, Load and Resistance Factors

16.3 Dependence of Wind Effects on Wind Directionality

16.4 Structural Strength Reserve

16.5 Design Criteria for Multi-Hazard Regions

16.6 Individual Uncertainties and Overall Uncertainty in the Estimation of Wind Effects

16.7 Calibration of Design MRIs in the Presence of Dynamic Effects or of Large Knowledge Uncertainties

Chapter 17: Loss Estimation

17.1 Introduction

17.2 Elements of Damage Estimation Procedures

17.3 Loss Estimation

Part IV: Wind Effects on Buildings

Chapter 18: Rigid Buildings

18.1 Introduction

18.2 Database-Assisted Design (DAD)

18.3 Wind Directionality Effects

18.4 Uncertainties in the Estimation of Wind Effects

Chapter 19: Tall Buildings

19.1 Introduction

19.2 High-Frequency Force Balance Approach (HFFB)

19.3 Aeroelastic Effects. Testing Based on Strain Measurements

19.4 Database-Assisted Design

19.5 Serviceability Requirements

19.6 Preliminary Estimates of Flexible Building Response

Part V: Appendices

Appendix A1: Random Processes

A1.1 Fourier Series and Fourier Integrals

A1.2 Parseval's Equality

A1.3 Spectral Density Function of a Random Stationary Signal

A1.4 Autocorrelation Function of a Random Stationary Signal

A1.5 Cross-Covariance Function, Co-Spectrum, Quadrature Spectrum, Coherence

A1.6 Mean Upcrossing and Outcrossing Rate for a Gaussian Process

A1.7 Probability Distribution of the Peak Value of a Normally Distributed Random Signal

A1.8 Probability Distribution of the Peak Value of a Non-Gaussian Random Signal

Appendix A2: Mean Wind Profiles and Atmospheric Boundary Layer Depth

A2.1 Equations of Balance of Momenta within the Atmospheric Boundary Layer

A2.2 The Turbulent Ekman Layer

Appendix A3: Spectra of Turbulent Velocity Fluctuations, Kolmogorov Hypotheses

Appendix A4: Wind Directionality Effects, Outcrossing and Sector-by-Sector Approaches

A4.1 Approach Based on the Outcrossing of the Limit-State Boundary

A4.2 The Sector-By-Sector Approach [18-10]

Appendix A5: Report on Estimation of Wind Effects on The World Trade Center Towers

References

Index

This book is printed on acid-free paper.

Copyright © 2011 by John Wiley & Sons, Inc. All rights reserved

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Library of Congress Cataloging-in-Publication Data:

Simiu, Emil.

Design of buildings for wind : a guide for ASCE 7-10 standard users and designers of special

structures / Emil Simiu. – 2nd ed.

p. cm.

Includes index.

Originally published under title: Design of buildings and bridges for wind. 2006.

ISBN 978-0-470-46492-2 (hardback); 978-1-118-07735-1 (ebk); 978-1-118-07736-8 (ebk); 978-1-118-07737-5 (ebk); 978-1-118-08613-1 (ebk); 978-1-118-08622-3 (ebk); 978-1-118-08623-0 (ebk)

1. Wind-pressure. 2. Buildings–Aerodynamics. 3. Bridges–Aerodynamics. 4. Wind resistant design. I. Simiu, Emil. Design of buildings and bridges for wind. II. Title.

TA654.5.S54 2011

624.1′75–dc23

2011013566

Preface

For most common types of structure, standard provisions on wind loads are in principle adequate for design purposes. The ASCE 7-10 Standard, among other standards, has incorporated a great deal of wind engineering knowledge accumulated within the last half-century. However, because the Standard has been developed by successive accretions, not always smoothly, its previous versions have been perceived by some practitioners as complicated and unwieldy. In an effort to respond to the demand for a clearer document, the ASCE 7-10 version of the Standard has been substantially expanded and revised. However, difficulties remain.

One of the main objectives of this book is to help the reader better understand the ASCE 7-10 Standard provisions for wind loads and apply them with confidence and ease. To this end, the book presents a guide to the Standard that explains the rationale of the provisions and illustrates their use through a large number of detailed numerical examples. Particular attention is given to the numerous changes made in the 2010 version of the ASCE Standard. Comparisons are presented between—or among—results of alternative provisions specified by the Standard for the same type of building. The comparisons show, for example, that for low-rise buildings, the so-called envelope procedure does not necessarily yield the lowest wind loads, as the Standard asserts. They also show that wind loads yielded by alternative regular methods, by regular and simplified methods, or by alternative simplified methods, can exhibit significant differences.

Wind loads and effects on special structures cannot in general be estimated by using standard provisions based on tables and plots. Rather, they need to be based on aerodynamic testing in the wind tunnel or larger facilities, and on information on the extreme wind speeds at the site. The Standard's provisions on the wind tunnel method are still vague and incomplete. In particular, they contain little or no material on dynamic analyses, the dependence of the response on wind directionality, and the calibration of the design mean recurrence intervals to account for larger-than-typical errors and uncertainties in the parameters that govern the wind-induced demand.

Some design offices have a policy of requiring wind effects estimates from more than one consultant. This is prudent, and justified by the fact that, owing to the lack of adequate standard provisions on the wind tunnel procedure, estimates by various laboratories can differ significantly. For example, recent estimates of the New York World Trade Center towers response to wind, performed by two well-known consultants, were found to differ by over 40%.

Consultant reports need, therefore, to be carefully scrutinized, and the need for transparency in their presentation cannot be overemphasized. The book includes as an appendix a report by Skidmore Owings & Merrill LLP, which presents a practitioner's perspective on the current state of the art in wind engineering and is a testimony to the need for transparent, traceable, and auditable procedures. Material presented in the book enables structural engineers to “ask the right questions,” scrutinize effectively wind engineers' contributions to the determination of wind effects, and determine wind effects efficiently and accurately on their own, just as structural engineers do for seismic effects. This requires the use by the structural engineer of aerodynamic or aeroelastic data supplied by the wind engineer in standard, electronic form, and of directional extreme wind speed data obtained from wind climatological consultants. The wind effects of interest include internal forces, demand-to-capacity indexes for individual member design, as well as deflections and accelerations needed to check serviceability requirements. The book describes in detail modern, effective, and transparent methods for estimating such wind effects for any specified mean recurrence interval.

Wind effects on individual members are functions of influence coefficients that differ from member to member. In the past, the lack of sufficiently powerful computer resources did not allow this dependence to be taken into account accurately. The capability to do so is now routinely available. It has created a bridge between the wind engineer and the structural engineer that makes it possible to integrate the wind and structural phases of structural design more clearly and accurately than was heretofore possible. Public domain database-assisted design software referenced in the book allows the effective implementation of this capability.

Until about two decades ago, the time domain solution of large systems of differential equations posed insurmountable computational problems, and dynamics calculations were performed by using the spectral (frequency domain) approach, which transforms the differential equations of motion into algebraic equations. This approach is not always transparent and intuitive, and in practice suppresses phase information needed to correctly add wind effects from various sources (e.g., from two perpendicular lateral motions). Computational capabilities and measurement technology developed in last two decades have made it possible to replace the frequency domain approach by the typically more effective time domain approach. The time domain approach, used in publicly available software referenced in the book, is not limited to the estimation of loads through the summation of pressures measured at large numbers of ports. Rather, in the integrated format known as database-assisted design, it can be directly and effectively applied to the design or checking of individual member strength, and can thus substantially improve structural design accuracy. In particular, the time domain approach eliminates the need for large numbers of cumbersome load combinations, based on guesswork—the method currently being used—and performs the requisite combinations through simple algebraic addition of time series of load effects. The improvements inherent in the use of time domain rather than frequency domain methods can be compared to those inherent in the calculation of structural response by finite element rather than by slide-rule based techniques.

The book contains material on structural reliability under wind loads that provides, among other matters, a perspective on the limitations of the Load and Resistance Factor Design (LRFD) approach, and a procedure for the calibration of design mean recurrence intervals. The calibration is required to ensure adequate safety levels if uncertainties in the determination of wind effects exceed typical uncertainties assumed in the ASCE 7 Standard. To date, the role of errors and uncertainties in the specification of design mean recurrence intervals has not been addressed by the ASCE 7 Standard provisions for the wind tunnel procedure, with the result that some designers and wind engineers resort to “magic numbers” that may be inadequate. For example, the same design mean recurrence interval is implied in the Standard for ordinary buildings and for tall buildings, whose response depends on dynamic parameters, including damping, which may exhibit large uncertainties. A reliability-based approach that takes into account such uncertainties can yield, for some tall buildings, longer mean recurrence intervals and hence larger wind effects than those specified in the ASCE Standard.

Structural reliability is also useful because it helps engineers design structures that do not consume more material and do not contain more embodied energy than necessary to ensure adequate safety levels. Inadequate safety levels can result in wind-induced losses, which are visible and costly. On the other hand, the cost of unnecessary materials—of “fat,” as opposed to “muscle”—is much less visible to the public eye, but is nonetheless real, in monetary, energy consumption, and carbon footprint terms.

The book addresses incipient efforts to estimate ultimate capacities under fluctuating wind loads, aimed to achieve designs that are safer, more economical, and less demanding of embodied energy than those based on linear methods of analysis. The book also addresses wind-induced loss estimation, a topic fraught with difficulties, owing to the nonlinearities typically associated with the analysis of failures. Finally, in response to requests by students and practitioners of wind engineering, a number of theoretical developments are considered in some detail, mostly in appendices. On the other hand, it was decided in consultation with the editor that material on bridges be limited in this edition to fundamentals only.

I wish to express my sincere appreciation to the following contributors, who capably performed and checked calculations for Part II of the book: Dr. Girma Bitsuamlak, Dr. Arindam Gan Chowdhury, who also thoroughly reviewed the entire manuscript, and Dr. DongHun Yeo. I also wish to thank Professor Elena Dragomirescu, Dr. Dat Duthinh, Professor Mircea D. Grigoriu, Dr. Franklin T. Lombardo, Professor Jean-Paul Pinelli, Mr. Workamaw Warsido and Dr. Richard N. Wright, who provided helpful comments, suggestions, and criticism, and Professor Yuko Tamura, who kindly facilitated access to Tokyo Polytechnic University's extensive aerodynamics databases. Last but not least, I am indebted to Robert L. Argentieri, Executive Editor; Daniel Magers, Editorial Assistant; Doug Salvemini, Production Editor; and Holly Wittenberg, the talented designer of the book's cover, all of John Wiley and Sons; as well as Devra Kunin, copyeditor; for their capable contributions and gracious help.

The views expressed in this book do not necessarily represent those of the U.S. government or any of its agencies.

I dedicate this book gratefully and lovingly to my wife.

Emil Simiu

Rockville, MD, USA

Part I

Introduction

Chapter 1

Overview

The purpose of this book is to provide structural engineers with the knowledge and tools required for the proficient design of buildings for wind loads. The book is concerned with both ordinary and special structures.

Ordinary structures are typically designed by using standard provisions for wind loads. Owing in part to their development by successive and more or less disorderly accretions, the wind loading provisions of the ASCE 7 Standard have become increasingly difficult to apply. In an effort to respond to the demand for a clearer document, the ASCE 7-10 version of the Standard has been substantially expanded and revised. Nevertheless, difficulties remain. A main objective of this book is to provide clear and detailed guidance to the use of the ASCE 7-10 Standard, including information on the fact that alternative procedures specified in the Standard for buildings of the same type may yield significantly different results.

The design of special structures typically requires the use of aerodynamic data obtained in ad hoc tests conducted in wind tunnel and/or large-scale testing facilities, and of extreme wind speed data. The requisite aerodynamic and wind speed data are reflected in wind engineering consultant reports. However, such reports do not—or do not yet—have to conform to uniform standards of practice. For this reason, response estimates for the same building can differ by more than 40%, depending upon the wind engineering laboratories providing them. It is therefore in the structural engineers' interest to be able to scrutinize and evaluate consultant reports effectively. This book provides the wind engineering knowledge and tools required to do so. The book also enables structural engineers to perform, independently, detailed estimates of wind-induced response for both strength and serviceability, much as structural engineers do for seismic response. The estimates must use extreme wind speed data and aerodynamic or aeroelastic data provided in standardized formats by wind engineering consultants. The data are first applied to a preliminary structural design. Iterations of the calculations are then performed until the design is satisfactory. Such calculations, based on clear and transparent algorithms, can be performed routinely and efficiently by using public domain software referenced in the book.

Response calculations must allow for appropriate safety margins that reflect uncertainties in the parameters governing the wind-induced demand. These safety margins were provided in earlier versions of the Standard in the form of wind load factors. The book documents the limitations and shortcomings of the Load and Resistance Factor Design (LRFD) approach, in which wind load factors are used. In the ASCE 7-10 Standard, wind load factors are nominally equal to unity; however, values larger than unity are implicit in design wind speeds with mean recurrence intervals longer than those specified in the Standard's earlier versions. However, for some special structures, those mean recurrence intervals may not be adequate. This is the case if the uncertainties in the parameters affecting the demand are larger than the typical uncertainties inherent in the Standard provisions for ordinary, rigid structures. In particular, if uncertainties in the dynamic effects are significant, a calibration procedure is needed to calculate safe mean recurrence intervals of the design wind effects. Such a procedure was developed at the express request of structural engineering practitioners (see Appendix A5), and is discussed in the book's chapter on structural reliability.

Part II of this book is devoted to the ASCE 7-10 Standard, and is divided into eight chapters (Chapters 2 through 9) concerned with (1) general requirements (i.e., risk categories, basic design wind speeds, terrain exposure, enclosure classification, directional factors, topographic factors), and (2) the determination of wind effects on main wind force resisting systems and on components and cladding, by regular or simplified approaches. Part II illustrates the Standard provisions by means of a large number of calculation examples.

Part III is devoted to fundamentals. Chapter 10 is concerned with atmospheric circulations and the features of various types of storm. Chapter 11 provides descriptions of the atmospheric boundary layer, including the description of the wind velocity dependence on height above the surface, and of the turbulence within the atmospheric surface layer. Chapter 12 considers extreme wind speeds and extreme wind effects, their statistical estimation by parametric and non-parametric methods, estimation errors, wind speed simulations, and the dependence of wind effects on wind directionality. Chapter 13 provides fundamental notions of bluff body aerodynamics, and discusses modeling laws and aerodynamic measurements in the wind tunnel and large-scale aerodynamic testing facilities. Chapter 14 presents fundamentals of structural dynamics under stochastic loads for the general case of buildings with non-coincident mass and elastic centers. Chapter 15 is concerned with aeroelastic effects. Chapter 16 presents (1) a critique of conventional structural reliability approaches known as Load and Resistance Factor Design, (2) material on mean recurrence intervals calibrations as functions of parameter uncertainties, (3) an introduction to strength reserves in a wind engineering context, and (4) an innovative approach to multi-hazard design, which shows that ASCE Standard provisions on the design of structures in regions with strong earthquakes and wind storms can be unsafe. Chapter 17 is an introduction to wind-induced loss estimation.

Part IV is concerned with the determination of wind effects on rigid and flexible buildings (Chapters 18 and 19, respectively), and discusses database-assisted design (DAD) concepts and procedures. Pressure records can be used for the calculation of wind loads, or can be part of the more elaborate DAD approach, which allows combinations of wind effects to be developed conveniently and rigorously, and provides integrated loading and design calculations in one fell swoop.

Part V contains appendixes. Appendix A1 concerns fundamentals of the theory of stochastic processes. Appendix A2 presents elements of the theory of mean wind profiles in the atmospheric boundary layer. Appendix A3 presents elements of the theory of turbulence in the atmospheric boundary layer. Appendix A4 provides a description and critique of two commonly used but typically unsatisfactory approaches to the wind directionality problem. Appendix A5 provides an authoritative view by a prominent structural engineering firm on some important aspects of the state of the art in wind engineering.

Part II

Guide to the ASCE 7-10 Standard Provisions on Wind Loads