CREEP IN THE FUNDAMENTAL FREQUENCY AND STABILITY OF A SLENDER WOODEN COLUMN OF COMPOSITE SECTION

ABSTRACT Creep is a phenomenon that can occur in wooden structures since wood is a viscoelastic material. Creep may change the purely elastic parameters determined in wood characterization initial tests, as its behavior depends on the rheology of the material, even under a constant stress level. Mathematically, creep can be characterized by models in which the immediate elastic deformation is increased by a viscous deformation, resulting in a temporal function. For this reason, the calculation of the natural frequency of vibration and the stability verification of a slender column should include the reducing effects of stiffness both of axial force and creep. The first one can be considered through the geometrical portion and the second one by the introduction, in the conventional portion, of a variable elasticity modulus over time, obtained in relation to the adopted rheological model. A numerical simulation was performed to evaluate the aspects above, considering a bar compressed by a force at the free end equivalent to 10% of the Euler critical force, plus its own weight, adopting a rheological model with three parameters for the variation of the elasticity modulus. The results show differences of 60% and 50% for the frequency and elasticity modulus, besides defining the exact instant of column collapse in the case of its non-observance.</jats:p

Analytical and Mathematical Analysis of the Vibration of Structural Systems Considering Geometric Stiffness and Viscoelasticity

For a complete analysis of vibration, the stiffness of a structure must have two characteristics: one corresponding to conventional stiffness and the other to the geometric stiffness. Thus, the total stiffness takes form where the model to be used to represent any behavior of the material is introduced to the first part via the modulus of elasticity. The second is the geometric stiffness, through which it is possible to linearize a geometric nonlinear problem. To consider both aspects, a mathematical model based on the Rayleigh method has been elaborated. Two systems were numerically studied. First, the occurrence of resonance in the vibration of a prestressed reinforced concrete beam has been investigated. The results indicated resonant and non-resonant schemes between the natural frequency of the beam and the frequency of the engine. To the second system, the first natural frequency of a slender, 40-m-high concrete mobile phone mast, was calculated, and an evaluation of the structural collapse was performed. To the both systems, the cross section of reinforced concrete was treated by the theory for the homogenized section in order to consider the presence of the steel, and the viscoelasticity of the concrete was taken into account through a three-parameter rheological model

A Review Of Creep In Wood: Concepts Relevant To Develop Long-Term Behavior Predictions For Wood Structures

A review is presented of the effects of constant and transient moisture and temperature conditions on the time-dependent behavior of wood as a material and as a structural element. A rational approach towards the identification of long-term behavior of wooden structures is proposed. Utilizing the fact that wood is a combination of several polymers, polymer viscoelasticity concepts are suggested to enhance the predictive capabilities. A finite element procedure is outlined to indicate how design predictions can be made. Some attention is given to structures such as domes where creep of the wood could lead to structural instabilities

Prospect for new guidance in the design of FRP

Over the last twenty years, many innovative solutions have confirmed the usefulness of composite structures realized with FRPs (Fibre Reinforced Polymer or Plastic). The need of European standards for use of fibre-reinforced polymer composites in civil engineering was justified in 2007 in the JRC Report EUR 22864 EN. The new European technical rules will be developed using the existing organization of CEN/TC250. The present report has been worked out in the frame of CEN/TC250/WG4 activities. The report encompasses: • Part I, which introduces the policy framework and the CEN/TC250 initiative • Part II, which gives a prospect for CEN guidance for the design and verification of composite structures realized with FRPs The report presents scientific and technical background intended to stimulate debate and serves as a basis for further work to achieve a harmonized European view on the design and verification of such structures. This has been the main impulse to include the work item of the Fibre Reinforced Polymer Structures in the Mandate M/515 with high priority.JRC.G.4-European laboratory for structural assessmen

Paper structures

The examples of paper architecture presented in this chapter show the wide variety of materials and compositions used. The chosen examples are divided into two sections. The first section, entitled ‘The History of Paper in Architecture,’ embraces the projects realised from the late nineteenth century to the late 1980s. The examples provided in the ‘Case Studies’ section were assessed more thoroughly for their function, structural system, usable area, used material, connections and details of the structure (foundation, walls, roof), impregnation and lifespan. The chosen projects represent the most interesting solutions as far as structure and use of materials are concerned. Each of the examples described in this section presented an element of novelty in the world of paper architecture

Prospect for new guidance in the design of FRP : support to the implementation and further development of the Eurocode

Over the last twenty years, many innovative solutions have confirmed the usefulness of composite structures realized with FRPs (Fibre Reinforced Polymer or Plastic). The need of European standards for use of fibre-reinforced polymer composites in civil engineering was justified in 2007 in the JRC Report EUR 22864 EN. The new European technical rules will be developed using the existing organization of CEN/TC250. The present report has been worked out in the frame of CEN/TC250/WG4 activities. The report encompasses: • Part I, which introduces the policy framework and the CEN/TC250 initiative • Part II, which gives a prospect for CEN guidance for the design and verification of composite structures realized with FRPs The report presents scientific and technical background intended to stimulate debate and serves as a basis for further work to achieve a harmonized European view on the design and verification of such structures. This has been the main impulse to include the work item of the Fibre Reinforced Polymer Structures in the Mandate M/515 with high priority

Timber Engineering - Principles for Design

This comprehensive book provides in-depth knowledge and understanding of design rules according to Eurocode 5. It is based on the first edition of the STEP (Structural Timber Education Programme) series, which was prepared in 1995 by about 50 authors from 14 European countries. The present work updates and extends the STEP compilation and is aimed at students, structural engineers and other timber structure professionals

Timber Engineering - Principles for Design

This comprehensive book provides in-depth knowledge and understanding of design rules according to Eurocode 5. It is based on the first edition of the STEP (Structural Timber Education Programme) series, which was prepared in 1995 by about 50 authors from 14 European countries. The present work updates and extends the STEP compilation and is aimed at students, structural engineers and other timber structure professionals

Buildings and Structures under Extreme Loads II

Exceptional loads on buildings and structures are known to take origin and manifest from different causes, like natural hazards and possible high-strain dynamic effects, human-made attacks and impact issues for load-bearing components, possible accidents, and even unfavorable/extreme operational conditions. All these aspects can be critical for specific structural typologies and/or materials that are particularly sensitive to external conditions. In this regard, dedicated analysis methods and performance indicators are required for the design and maintenance under the expected lifetime. Typical issues and challenges can find huge efforts and clarification in research studies, which are able to address with experiments and/or numerical analyses the expected performance and capacity of a given structural system, with respect to demands. Accordingly, especially for existing structures or strategic buildings, the need for retrofit or mitigation of adverse effects suggests the definition of optimal and safe use of innovative materials, techniques, and procedures. This Special Issue follows the first successful edition and confirms the need of continuous research efforts in support of building design under extreme loads, with a list of original research papers focused on various key aspects of structural performance assessment for buildings and systems under exceptional design actions and operational conditions