Structural Analysis

A Unified Classical and Matrix Approach, Seventh Edition

Amin Ghali, A. Neville, T. Brown

• Editorial: CRC Press
• Año: 2017
• ISBN:
  9781351971546
• Edición: 7
• Categoría: Technology & Engineering
• Categoría: Construction & Architectural Engineering

This comprehensive textbook combines classical and matrix-based methods of structural analysis and develops them concurrently. It is widely used by civil and structural engineering lecturers and students because of its clear and thorough style and content. The text is used for undergraduate and graduate courses and serves as reference in structural engineering practice. With its six translations, the book is used internationally, independent of codes of practice and regardless of the adopted system of units.

Now in its seventh edition:

• the introductory background material has been reworked and enhanced
• throughout, and particularly in early chapters, explanatory notes, new examples and problems are inserted for more clarity., along with 160 examples and 430 problems with solutions.
• dynamic analysis of structures, and applications to vibration and earthquake problems, are presented in new sections and in two new chapters
• the companion website provides an enlarged set of 16 computer programs to assist in teaching and learning linear and nonlinear structural analysis. The source code, an executable file, input example(s) and a brief manual are provided for each program.

Chapter 1

Structural analysis modeling ^*

1.1INTRODUCTION

This book may be used by readers familiar with basic structural analysis and also by those with no previous knowledge beyond elementary mechanics. It is mainly for the benefit of people in the second category that Chapter 1 is included. It will present a general picture of the analysis but, inevitably, it will use some concepts that are fully explained only in later chapters. Readers may therefore find it useful, after studying Chapter 2 and possibly even Chapter 3, to reread Chapter 1.

The purpose of structures, other than aircraft, ships and floating structures, is to transfer applied loads to the ground. The structures themselves may be constructed specifically to carry loads (for example, floors or bridges) or their main purpose may be to give protection from the weather (for instance, walls or roofs). Even in this case, there are loads (such as self-weight of the roofs and also wind forces acting on them) that need to be transferred to the ground.

Before a structure can be designed in a rational manner, it is essential to establish the loads on various parts of the structure. These loads will determine the stresses and their resultants (internal forces) at a given section of a structural element. These stresses or internal forces have to be within desired limits in order to ensure safety and to avoid excessive deformations. To determine the stresses (forces/unit area), the geometrical and material properties must be known. These properties influence the self-weight of the structure, which may be more or less than originally assumed. Hence, iteration in analysis may be required during the design process. However, consideration of this is a matter for a book on design.

The usual procedure is to idealize the structure by one-, two-, or three-dimensional elements. The lower the number of dimensions considered, the simpler the analysis. Thus, beams and columns, as well as members of trusses and frames, are considered as one-dimensional; in other words, they are represented by straight lines. The same applies to strips of plates and slabs. One-dimensional analysis can also be used for some curvilinear structures, such as arches or cables, and also certain shells. Idealization of structures by an assemblage of finite elements, considered in Chapter 17, is sometimes necessary.

Idealization is applied not only to members and elements but also to their connections to supports. We assume the structural connection to the supports to be free to rotate, and then treat the supports as hinges, or to be fully restrained, that is, built-in or encastré. In reality, perfect hinges rarely exist, if only because of friction and also because nonstructural members such as partitions restrain free rotation. At the other extreme, a fully built-in condition does not recognize imperfections in construction or loosening owing to temperature cycling.

Once the analysis has been completed, members and their connections are designed: the designer must be fully conscious of the difference between the idealized structure and the actual outcome of construction.

The structural idealization transforms the structural analysis problem into a mathematical problem that can be solved by computer or by hand, using a calculator. The model is analyzed for the effects of loads and applied deformations, including the self-weight of the structure, superimposed stationary loads or machinery, live loads such as rain or snow, moving loads, dynamic forces caused by wind or earthquake, and the effects of temperature as well as volumetric change of the material (e.g. shrinkage of concrete). This chapter explains the type of results that can be obtained by the different types of models.

Other topics discussed in this introductory chapter are: transmission (load path) of forces to the supports and the resulting stresses and deformations; axial forces in truss members; bending moments and shear forces in beams; axial and shear forces, and bending moments in frames; arches; the role of ties in arches; sketching of deflected shapes and bending moment diagrams; and hand checks on computer results.

1.2TYPES OF STRUCTURES

Structures come in all shapes and sizes, but their primary function is to carry loads. The form of the structure, and the shape and size of its members are usually selected to suit this load-carrying function, but the structural forces can also be dictated by the function of the system of which the structure is part. In some cases, the form of the structure is dictated by architectural considerations.

The simplest structural form, the beam, is used to bridge a gap. The function of the bridge in Figure 1.1 is to allow traffic and people to cross the river: the load-carrying function is accomplished by transferring the weight applied to the bridge deck to its supports.

Figure 1.1Highway bridge.

A similar function is provided by the arch, one of the oldest structural forms. Roman arches (Figure 1.2a) have existed for some 2000 years and are still in use today. In addition to bridges, the arch is also used in buildings to support roofs. Arches have developed...