Plastic Analysis And Design Of Steel Structures
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Thoroughly revised throughout, Ductile Design of Steel Structures, Second Edition, reflects the latest plastic and seismic design provisions and standards from the American Institute of Steel Construction (AISC) and the Canadian Standard Association (CSA). The book covers steel material, cross-section, component, and system response for applications in plastic and seismic design, and provides practical guidance on how to incorporate these principles into structural design.
Three new chapters address buckling-restrained braced frame design, steel plate shear wall design, and hysteretic energy dissipating systems and design strategies. Eight other chapters have been extensively revised and expanded, including a chapter presenting the basic seismic design philosophy to determine seismic loads. Self-study problems at the end of each chapter help reinforce the concepts presented. Written by experts in earthquake-resistant design who are active in the development of seismic guidelines, this is an invaluable resource for students and professionals involved in earthquake engineering or other areas related to the analysis and design of steel structures.
Plastic deformations represent material properties that require a nonlinear analysis. Utilize RFEM together with the RF-MAT NL add-on module to consider elastic-plastic material behavior in the analysis. In addition to the yield condition according to von Mises, the approaches according to Tresca, Drucker-Prager, and Mohr-Coulomb are available as strain hypotheses. For ductile materials such as steel, we recommend the plasticity theory according to von Mises. For the general spatial stress state, it is as follows:
With the help of nonlinear material models, it is also possible to determine redistribution effects in the model that result, for example, from the formation of plastic hinges. For plastic effects, results with large deformations - especially according to the large deformation analysis - have to be evaluated with caution.
The plastic design of steel structures has several advantages over the elastic design, of which the most important are simplified procedures, savings in the cost, and more realistic representation of the actual behavior of steel structures [1.1]. These advantages are due to the fact that the plastic design fully uses the important property of steel called ductility. This chapter will focus on the effects of ductility of the steel on the behavior of steel structures and show the benefits of the plastic methods that are derived from this property. To demonstrate the benefits of ductility, we will present two examples: first a hot-rolled section with residual stresses and second a plate with a hole. For both examples, the material is idealized to have an elastic-perfectly plastic stress-strain behavior as shown in Fig. 1.4.
In other words, if yield point is attained at a single point, it does not mean a state of collapse of the member. Due to plastic deformations and strain hardening of the material particles which were less stressed will be brought into action, so that the structure actually is able to resist greater loads. In modern designs the above principle is followed and the method of design on this principle is called collapse method of design or plastic design.
Plastic method adopts the ultimate strength as the criterion for design. The method therefore takes into account the behaviour of a member as it is stressed beyond the yield stress, in the inelastic or plastic range. Ultimate loads which cause the collapse are determined by multiplying the working loads by a load factor. In plastic designs importance is given to resistances to bending caused by loads when the members are in the plastic range.
Plastic designs consider the capacity of members to continue offering resistance even after reaching the yield stress. This has been possible due to the unique property of ductility possessed by steel. A steel member is capable of absorbing considerable deformation, beyond the limit of elasticity without fracture or collapse. The capacity of the member to have this reserve strength after reaching the yield stress has been recognized and taken into account in plastic designs.
CE 59200 - Plastic Design Of Steel Structures Credit Hours: 3.00. Ultimate load capacity of steel structures; methods of analysis for structures in the plastic range; plastic design of continuous beams, frames, and connections. Typically offered Fall Spring.Credits: 3.00
Portal frames are generally low-rise structures, comprising columns and horizontal or pitched rafters, connected by moment-resisting connections. Resistance to lateral and vertical actions is provided by the rigidity of the connections and the bending stiffness of the members, which is increased by a suitable haunch or deepening of the rafter sections. This form of continuous frame structure is stable in its plane and provides a clear span that is unobstructed by bracing.Portal frames are very common, in fact 50% of constructional steel used in the UK is in portal frame construction. They are very efficient for enclosing large volumes, therefore they are often used for industrial, storage, retail and commercial applications as well as for agricultural purposes.This article describes the anatomy and various types of portal frame and key design considerations.
Rafters may be fabricated from cellular beams for aesthetic reasons or when providing long spans. Where transport limitations impose requirement for splices, they should be carefully detailed, to preserve the architectural features.The sections used cannot develop plastic hinges at a cross-section, so only elastic design is used.
The term plastic analysis is used to cover both rigid-plastic and elastic-plastic analysis. Plastic analysis commonly results in a more economical frame because it allows relatively large redistribution of bending moments throughout the frame, due to plastic hinge rotations. These plastic hinge rotations occur at sections where the bending moment reaches the plastic moment or resistance of the cross-section at loads below the full ULS loading.
The figure shows typical positions where plastic hinges form in a portal frame. Two hinges lead to a collapse, but in the illustrated example, due to symmetry, designers need to consider all possible hinge locations.
A typical bending moment diagram resulting from an elastic analysis of a frame with pinned bases is shown the figure below. In this case, the maximum moment (at the eaves) is higher than that calculated from a plastic analysis. Both the column and haunch have to be designed for these large bending moments.
Where deflections (SLS) govern design, there may be no advantage in using plastic analysis for the ULS. If stiffer sections are selected in order to control deflections, it is quite possible that no plastic hinges form and the frame remains elastic at ULS.
For either plastic analysis of frames, or elastic analysis of frames, the choice of first-order analysis or second-order analysis depends on the in plane flexibility of the frame, characterised by the calculation of the αcr factor.
Whether the frame is designed plastically or elastically, a torsional restraint should always be provided at the underside of the haunch. This may be from a side rail positioned at that level, or by some other means. Additional torsional restraints may be required between the underside of the haunch and the column base because the side rails are attached to the (outer) tension flange; unless restraints are provided the inner compression flange is unrestrained. A side rail that is not continuous (for example, interrupted by industrial doors) cannot be relied upon to provide adequate restraint. The column section may need to be increased if intermediate restraints to the compression flange cannot be provided.
Restraint to the inner flanges of rafters or columns is often most conveniently formed by diagonal struts from the purlins or sheeting rails to small plates welded to the inner flange and web. Pressed steel flat ties are commonly used. Where restraint is only possible from one side, the restraint must be able to carry compression. In these locations angle sections of minimum size 40 40 mm must be used. The stay and its connections should be designed to resist a force equal to 2.5% of the maximum force in the column or rafter compression flange between adjacent restraints.
The earlier use of elastic design method does not take into account the strength of the material beyond the elastic stress. Therefore, the structure designed according to this method will be heavier than that designed by plastic method. In this method of plastic design of structures, the ultimate load rather than the yield load is considered as the design criteria.
Plastic analysis is defined as the analysis in which the criterion for the design of structures is the ultimate load. Actually, the ultimate load is found from the strength of steel in plastic range. This method of analysis is quite rapid and has rational approach for analysis of structure. It controls the economy regarding to weight of steel since the sections required by this method are smaller than those required by the method of elastic analysis. Plastic analysis has its applications in the analysis and design of indeterminate structures.
INTRODUCTION TO PLASTIC ANALYSIS Plastic design method has its main application in the analysis and design of statically indeterminate framed structures.In plastic design of a structure, the ultimate load rather than the yield stress is regarded as the design criterion. The term plastic has occurred due to the fact that the ultimate load is found from the strength of steel in the plastic range.
This method is rapid and provides a rational approach for the analysis of the structure. Plastic design method has its main application in the analysis and design of Statically Indeterminate Structures. In the analysis of structures by plastic theory, the following conditions must be satisfied (i)Equilibrium Condition 59ce067264