Luciano Rodrigues Ornelas de Lima

Structural analysis of guyed steel telecommunication towers for radio antennas

The usual structural analysis models for telecommunication and transmission steel tower design tend to assume a simple truss behaviour where all the steel connections are considered hinged. Despite this fact, the most commonly used tower geometries possess structural mechanisms that could compromise the assumed structural behaviour. A possible explanation for the structure stability is related to the connections semi-rigid response instead of the initially assumed pinned behaviour. This paper proposes an alternative structural analysis modelling strategy for guyed steel towers design, considering all the actual structural forces and moments, by using three-dimensional beam and truss finite elements. Comparisons of the above mentioned design models with a third alternative, that models the main structure and the bracing system with 3D beam finite elements, are made for three existing guyed steel telecommunication towers (50m, 70m and 90m high). The comparisons are initially based on the towers static and dynamic structural behaviour later to be followed by a linear buckling analysis to determine the influence of the various modelling strategies on the tower stability behaviour. Keywords : telecommunication and transmission towers, guyed steel structures, spatial structures, structural analysis, computational modelling, modal analysis, stability analysis.

Numerical and Experimental Assessment of Stainless and Carbon Bolted Tensioned Members with Staggered Bolts

Current stainless steel design codes, like the Eurocode 3, part 1.4, (2006), are still largely based on analogies with carbon steel structural behavior. The net section rupture represents one of the ultimate limit states usually verified for structural elements submitted to normal tension stress. An investigation aiming to evaluate the tension capacity of carbon and stainless steel bolted structural elements was performed and in this article, the results are discussed and compared in terms of stress distribution, and force-displacement curves, among others. The result assessment was done by comparisons to the Eurocode 3 (2003) provisions for carbon and stainless steels. The investigation indicated that when stainless steel is used in certain structural engineering applications like joints under tension forces, the current design criteria based on deformation limits need to be re-evaluated, especially due to the differences in the yields for ultimate deformation and stress ratios.

Vibration Analysis of Long Span Joist Floors Submitted to Human Rhythmic Activities

In the last years, building structures are more and more becoming the modern landmarks of urban areas. Designers seem to continuously move the safety border, in order to increase slenderness and lightness of their structural systems. However, more and more steel and composite floors (steel-concrete) are carried out as light weight structures with low frequencies and low damping. These facts have generated very slender composite floors, sensitive to dynamic excitation, and consequently changed the serviceability and ultimate limit states associated to their design. The increasing incidence of building vibration problems due to human rhythmic activities led to a specific design criterion for rhythmic excitations to be addressed in structural design (Allen et al. 1985); (Almeida, 2008); (Almeida et al., 2008); (Bachmann & Ammann, 1987); (Faisca, 2003); (Ji & Ellis, 1994); (Langer, 2009); (Murray et al., 2003); (Silva et al., 2008). This was the main motivation for the development of a design methodology centred on the structural system dynamical response submitted to dynamic loads due to human activities. This paper investigated the dynamic behaviour of composite floors (steel-concrete) subjected to the human rhythmic activities. The dynamic loads were obtained through experimental tests conducted with individuals carrying out rhythmic and non-rhythmic activities such as stimulated and non-stimulated jumping and aerobics (Faisca, 2003). The description of the loads generated by human activities is not a simple task. The individual characteristics in which each individual perform the same activity and the existence of external excitation are relevant factors when the dynamic action is defined. Numerous investigations were made aiming to establish parameters to describe such dynamic loads (Allen et al. 1985); (Bachmann & Ammann, 1987); (Faisca, 2003); (Murray et al., 2003). The present investigation considered the dynamic loads, based on results achieved through a long series of experimental tests made with individuals carrying out rhythmic and nonrhythmic activities. This investigation described these dynamic loads, generated by human activities, such as jumps with and without stimulation, aerobics, soccer, rock concert audiences and dancing (Faisca, 2003).

Um sistema de laje mista para edificações residenciais usando perfis de chapa dobrada com corrugações

The composite steel-concrete system has been used in various major projects motivating the development of an efficient composite floor system using cold-formed steel sections with web corrugations. The system was based on previous investigations that involved the development of steel deck prototypes using various types of interlocking mechanisms in the concrete to steel deck interface. An ideal section evaluation was made to determine an efficient steel profile that presented a good mechanical adherence to the concrete interface while keeping a ductile behavior. Variables like weight, height, thickness and yield stress amongst others were investigated. An experimental program consisting of a full-scale composite slab test was executed to validate the proposed composite cold-formed system.

Non-Linear Dynamical Response of Steel Portal Frames with Semi-Rigid Connections

Traditionally, the steel portal frame design assumes that beam-to-column joints are rigid or pinned. Rigid joints, where no relative rotations occur between the connected members, transfer not only substantial bending moments, but also shear and axial forces. Alternatively, pinned joints are characterised by an almost free rotation movement between the connected elements preventing the bending moment transmission. Despite these facts, it is largely recognised that the great majority of joints does not exhibit such idealised behaviour. These joints, called semi-rigid, should be designed according to their actual structural behaviour. Considering all these facts one of the main objectives of this investigation is to propose a modelling strategy to represent the dynamical behaviour of semirigid joints under dynamic actions. The developed finite element model included geometric nonlinearities and considered the influence of non-linear and hysteretic joint stiffness. The updated Lagrangean formulation is used to model the geometric non-linearity. The mathematical model calibration was made based on comparisons to semi-rigid tests and other numerical models [1],[2] and proving to be in accordance to them. However, it must be emphasized that cautions should be taken on the direct use of the results in structural design. The main reasons for this affirmative are related to the occurrence of very important distortions due to the consideration of the semi-rigid joints geometric non-linearity effects on the steel portal frames dynamical response.

Numerical investigation of semi-rigid connection ultimate capacity

With the advances in computational analysis techniques and development of new design methods, new interests have arisen in structural engineering. In the last few years, with the increasing numbers of terrorist attacks, the study of robustness, progressive structural collapse and ultimate resistance of structures has grown exponentially, with various studies being published all over the world. In order to perform this study through computational analysis, it was necessary to develop a calibrated numerical model capable of representing the behaviour of structures in their final stage of resistance. This article presents an evaluation of semi-rigid connections through a numerical model considering the implementation of collapse and damage progression criteria calibrated against experimental tests. Afterwards, a parametric study was developed by varying the bolt diameters and endplate thickness of a flush endplate semi-rigid connection. The main parameters and criteria that rules the simulation of flush end-plate joints subject to damage were assessed, allowing that many different kind of studies with similar components could be performed, such as impact, explosion and column loss analysis. As an outcome, the bending moment-rotation curves of these connections are presented and it is shown that those with a larger bolt diameter were able to produce greater rotation, while an increase in the endplate thickness was able to provide a greater bending moment capacity.

Dual-Concentrically braced frames using high strength steel – Seismic response

The recent technological advances on steel production process allowed introducing in construction market steel grades with significantly high yield strength. These new materials are known as High Strength Steel (HSS). The use of these steel grades offers economical and mechanical benefits compared with mild carbon steel (MCS). Consequently, their use is constantly increasing especially for seismic applications that are the rational field to exploit the high performance of HSS, by means of the “dual-steel” concept, which combines the HSS with MCS in order to provide overstrength to non-dissipative element and ductility to dissipative ones, thus controlling the global frame behaviour into a ductile overall failure mode. In this paper, a comprehensive parametric study devoted to investigate the seismic performance of Eurocode 8 compliant dual-steel chevron Dual-Concentrically Braced Frames (DCBF) is presented and discussed. This structural typology is composed of two dissipative sub-systems acting in parallel, namely Moment Resisting Frames (MRFs) and Concentrically Braced Frames (CBFs). Static nonlinear pushover analyses were carried out in order to assess the seismic performance of the D-CBFs. The examined parameters cover both geometric and mechanical variables, as the type columns, span length, number of storeys and spectral shape. The analyses showed that the use of HSS in Eurocode 8 compliant D-CBFs is effective to avoid the damage in non-dissipative members. On the other hand, the use of HSS leads to design flexible members, especially for the braced-intercepted beams, resulting in poor performance of bracing members due to significant damage concentration. The economic evaluation shows that the use of HSS allows reducing the material consumptions and dropping the total constructional costs.

Finite Element Modelling

The objective of this chapter is to present the necessary steps for the development of numerical models based on finite element method and the main aspects related to results interpretation of numerical models used in steel and composite structures simulation. It should be once more emphasised that the present book was conceived from an idea where the most important aspects of numerical modelling are introduced, as computer simulations of practical cases of numerical experiments are presented. Initially, some aspects and general questions will be addressed to elucidate key points of numerical modelling planning to ensure the validity and reliability of the performed computer simulations. The numerical modelling described in this chapter is based on the finite element method, traditionally adopted by structural engineers to simulate complex problems that usually cannot be solved with the suitable accuracy with mechanical, or simple analytical models. In summary this chapter aimed to introduce the necessary steps for the correct design, implementation, and interpretation of numerical model results of using the finite element method for the simulation of the response of steel and composite structures. These ideas are discussed throughout a series of numerical simulations depicting nonlinear responses focusing on their main details and restrictions in terms of boundary conditions, major difficulties, solution strategies, and methods to overcome convergence difficulties.

Computational Intelligence Modelling

The development of new materials and faster computing processes opened new frontier for the conception and development of new and audacious designs that will set the trend for the future 21th century structures. Various methods, techniques, and procedures have been, and still are being, used to improve and design these structures like optimisation processes, numerical modelling systems involving non-linear finite element analysis, etc. Concurrently, the last decade of the 20th century has been related to a large improvement and development of the so-called Computational Intelligent Techniques. These techniques are computational systems that try to mimic human behaviour, such as perception, reasoning, learning, evolution, and adaptation. They involve Neural Networks, Genetic Algorithm, Fuzzy Logic, and Hybrid Intelligent Systems , such as Neuro-Fuzzy, Neuro-Genetic, and Fuzzy-Genetic models .

Structural analyses of reinforced tubular T-joints

The use of rolled hollow sections has been substantially boosted mainly due to the advantages associated with structural behavior and aesthetics, leading to an intense use in Europe, Southeast Asia, North America, Australia, and now, in Brazil due to the wider supply of these profiles. Therefore, it is important to investigate the structural behavior in order to provide an adequate structural design for the civil engineering community. Thus, this paper presents a parametric analysis of a reinforced T-joint focused on NBR 16239 provisions. Two types of reinforcement plates: Collar and Double were investigated. A wide set of numerical models has been defined varying the thickness of the reinforcing plate, chord and brace members and axial loads applied in the brace. The numerical models have been developed using ANSYS 12.0 software considering both geometrical and material non-linearity. Concerning the results, there was a slight gain of resistance when a double plate reinforcement was used, mainly for small displacement, due to large stiffness provided and a linear response up to the serviceability limit. In addition, Von Mises stress distribution confirmed the type A failure with chord yielding beginning at the upper chord surface. Comparing the numerical results with NBR 16239 provisions, an excessive conservatism was noted for this code. In fact, the Brazilian code only takes into account the reinforcement thickness in joint resistance. However, when the results provided by the new proposal where both thicknesses (chord and reinforcement) are considered, a more realistic assessment of the joint capacity is obtained.