DESIGN AND PLASTIC ANALYSIS OF STEEL STRUCTURES TEXTBOOK BY CIVILENGGFORALL FREE DOWNLOAD PDF

CONTENTS OF THE BOOK

1. Structural Analysis – Stiffness Method

Introduction
Degrees of Freedom and Indeterminacy
Statically Indeterminate Structures—Direct Stiffness Method
Member Stiffness Matrix
Coordinates Transformation
Member Stiffness Matrix in Global Coordinate System
Assembly of Structure Stiffness Matrix
Load Vector
Methods of Solution
Calculation of Member Forces
Treatment of Internal Loads
Treatment of Pins
Temperature Effects

2. Plastic Behaviour of Structures

Introduction
Elastic and Plastic Behaviour of Steel
Moment–Curvature Relationship in an Elastic–Plastic Range
Plastic Hinge
Plastic Design Concept
Comparison of Linear Elastic and Plastic Designs
Limit States Design
Overview of Design Codes for Plastic Design
Limitations of Plastic Design Method
Plastic Flow Rule and Elastoplastic Analysis
General Elastoplastic Analysis of Structures
Reduced Plastic Moment Capacity Due to Force Interaction
Concept of Yield Surface
Yield Surface and Plastic Flow Rule
Derivation of General Elastoplastic Stiffness Matrices
Elastoplastic Stiffness Matrices for Sections
Stiffness Matrix and Elastoplastic Analysis
Modified End Actions
Linearized Yield Surface

4. Incremental Elastoplastic Analysis—Hinge by Hinge Method

Introduction
Use of Computers for Elastoplastic Analysis
Use of Spreadsheet for Automated Analysis
Calculation of Design Actions and Deflections
Effect of Force Interaction on Plastic Collapse
Plastic Hinge Unloading
Distributed Loads in Elastoplastic Analysis

5. Manual Methods of Plastic Analysis

Introduction
Theorems of Plasticity
Mechanism Method
Statical Method
Uniformly Distributed Loads (UDL)
Continuous Beams and Frames
Calculation of Member Forces at Collapse
Effect of Axial Force on Plastic Collapse Load

6. Limit Analysis by Linear Programming

Introduction
Limit Analysis Theorems as Constrained Optimization
Spreadsheet Solution of Simple Limit Analysis
General Description of the Discrete Plane Frame
A Simple MATLAB Implementation for Static Limit Analysis
A Note on Optimal Plastic Design of Frames

7. Factors Affecting Plastic Collapse

Introduction
Plastic Rotation Capacity
Effect of Settlement
Effect of High Temperature
Second-Order Effects

8. Design Consideration

Introduction
Serviceability Limit State Requirements
Ultimate Limit State Requirements

Degrees of Freedom and Indeterminacy

Plastic analysis is used to obtain the behaviour of a structure at collapse. As the structure approaches its collapse state when the loads are increasing, the structure becomes increasingly flexible in its stiffness. Its flexibility at any stage of loading is related to the degree of statical indeterminacy, which keeps decreasing as plastic hinges occur with the increasing loads. This section aims to describe a method to distinguish between determinate and indeterminate structures by examining the degrees of freedom of structural frames.

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The number of degrees of freedom of a structure denotes the independent movements of the structural members at the joints, including the supports. Hence, it is an indication of the size of the structural problem. The degrees of freedom of a structure are counted in relation to a reference coordinate system. External loads are applied to a structure causing movements at various locations. For frames, these locations are usually defined at the joints for calculation purposes. Thus, the maximum number of independent displacements, including both rotational and translational movements at the joints, is equal to the number of degrees of freedom of the structure. To identify the number of degrees of freedom of a structure, each independent displacement is assigned a number, called the freedom code, in ascending order in the global coordinate system of the structure

Plastic Design Concept

Plastic design makes use of the reserve strength beyond the elastic state of the structure. The structure’s reserve strength, which allows structural members to be loaded without failure when their maximum bending capacity is reached, is utilized through the elastic–plastic state when the loading is increasing. As a result, a more economical design due to material saving can be achieved when using the plastic design method. Plastic design can be viewed as a means whereby the ability of moment redistribution of steel structures is utilized when the structures are loaded beyond their elastic state. It may be noted that in adopting a bilinear moment–curvature relationship for steel, the beneficial effect of strain hardening of the material is ignored. Thus, as far as plastic analysis is concerned, the theoretical plastic collapse load is always less than the true load and the resulting design is always slightly conservative.

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Comparison of Linear Elastic and Plastic Designs

For elastic design, each of the members in the structure must have a design bending moment capacity (ΦMs) greater than the design moment (M*) obtained from an elastic analysis. The bending moment capacity, calculated by including the appropriate capacity factor f and other design considerations, is often used to represent the plastic moment Mp in plastic analysis. Under the design loading, if one of the members meets the design requirement such that ΦMs = M*, the first plastic hinge occurs exactly at the design load level along the elastic design curve. In most cases, the choice of the section for elastic design leads to ΦMs > M* so that the first plastic hinge of the structure always occurs at a load level above the design loading. In contrast, plastic design requires that the last plastic hinge occurs at or above the design load level. It is clear that if both elastic and plastic designs satisfy the same design loading, the plastic design method requires a lighter structure with smaller member size by utilizing the reserve strength of the structure. It is noted that for a structure with a high degree of statical indeterminacy, the reserve strength is large. Therefore, the benefit of using plastic design is greater for structures with high degrees of statical indeterminacy. However, for determinate structures that require only one plastic hinge to induce a collapse, there is no difference between elastic and plastic design methods.

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Limit States Design

Limit states design (LSD), also termed load and resistance factor design (LRFD) in the United States, is based on realistic loading conditions and material properties as opposed to allowable stress design (ASD), which is mainly based on prescribed loading and stress limits. Although the linear elastic design method can be applied to both LSD and ASD, only the latter is truly elastic. While linear elastic analysis is performed using the linear load–displacement relationship, elastic bending theory is applied to ASD for stress calculation, whereas for LSD, plastic bending theory is used for moment capacity calculation of the section. For steel structures, two major limit states need to be considered for general design: the ultimate limit state and the serviceability limit state. There are other limit states that may need special treatment and are usually classified under “accidental loadings” in design codes. In the present context, only ultimate and serviceability limit states are dealt with.

DESIGN AND PLASTIC ANALYSIS OF STEEL STRUCTURES TEXTBOOK BY CIVILENGGFORALL PDF

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