Suspended Steel Roof of the Archeological Site of the School of Aristotle

The structural design of the cable-suspended steel roof covering the archaeological site of the School of Aristotle in Athens, Greece is presented. The preliminary architectural proposal, which was awarded first prize in a competition organized by the Greek Ministry of Culture, provided for 65m span, arch-type main structures, each suspended by means of five suspension cables from a single pylon, stabilized by a pair of back-stay cables. Main arches were spaced at 11m and connected by means of purlins and bracing. The structural design concentrated on avoiding deviations from architectural requirements. Nevertheless, as a result of the vaulted shape of the roof, several cables were found to relax under service loads, thus the number, locations, cross-sections and prestressing of cables had to be re-evaluated. The present paper focuses on nonlinear analyses for understanding the behavior, predicting all possible failure mechanisms, and evaluating the ultimate strength of the roof by means of commercially available finite element software. Emphasis is placed on the role of flexural buckling of the pylon and lateral-torsional buckling of the main arch beam in the bearing capacity of these two members, both having complex geometry and varying cross-section, thus requiring a novel approach extending beyond code specifications. Failure dominated by either material yielding or instability is addressed, as well as interaction of failure modes. Steps include setting up an appropriate finite element model, obtaining critical buckling modes from linearized buckling analysis (LBA), and then using a linear combination of these modes as imperfection pattern for a geometrically and material nonlinear imperfection analysis (GMNIA). Equilibrium paths accompanied by snapshots of deformation and stress distribution at characteristic points are used to evaluate the analysis results, identify the dominant failure modes and optimize the structural performance

Numerical Analysis of Buried Steel Pipelines

Various alternative numerical analysis methods that are used to simulate the response of buried steel pipelines subjected to large imposed displacements triggered by seismic fault activation are presented. Due to the grave financial, social and environmental consequences of a potential pipeline leakage, damage or failure is a problem deserving special attention. Advanced nonlinear numerical simulations are the only way to handle with sufficient accuracy the complexity of the physical problem associated with the surrounding soil and the relevant pipeline-soil interaction. During preliminary design, however, reliable numerical models are required that demand minimum computational effort. In this paper alternative simulations of the problem making use of beam-type finite elements are presented and compared in terms of accuracy and computational cost. Comparisons are carried out regarding the types of finite elements, whether geometric nonlinearity is included or not

Progressive Collapse of Buildings

The progressive collapse of buildings is an important ongoing research topic in civil engineering [...

Artificial Time Histories of Wind ActionsFor Structural Analysis of Wind Turbines

A computational method for generating artificial time histories of wind loads on wind turbine towers is presented, based on wind turbine aerodynamics and a wind field model. First, the forces acting on the blades parallel and perpendicular to the rotor’s plane are calculated according to aerodynamics theory for given mean wind velocity. Due to the blades’ aerodynamic behavior the inflow wind velocity is transformed into the relative wind velocity, depending on the axial and tangential flow induction factors, the blades’ angular velocity and their radius. Then, the forces acting on the blades are calculated combining relative velocity with two-dimensional aerofoil coefficients depending on the blades’ geometry and crosssection. The flow induction factors are estimated by an iterative process taking into account the flow angle between the relative wind velocity and the rotor’s plane and the aerofoil coefficients. Next, the turbulence component of the wind is determined by the stochastic theory, in order to describe the total wind field model and compute more realistic wind induced actions on the blades. Each fluctuating component is modeled as Gaussian, stationary stochastic process with zero-mean value and is completely characterized by the correlation matrix in time domain or the power spectral density matrix in frequency domain. Wind time histories are simulated by the decomposition of the power spectral density matrix. Then, finite element models of the wind turbine tower are subjected to the load time histories derived above and dynamic analyses are performed. Ultimate objective of this research is to study fatigue at bolted and welded connections between adjacent parts of wind turbine towers and to investigate the importance of dynamic effects on local buckling of the tower shell

Membrane Action of Cladding Subjected to Blast Loading and Effects on the Supporting Structure

A recent blast design trend is to properly select cladding characteristics in order to limit blast consequences on its supporting structure. In this context, it is worth noting that cladding components may exhibit significant membrane action, and its effects may be decisive for the supporting structure. The main focus of the present study was to examine these effects through two-step dimensionless SDOF analyses, aimed at reaching conclusions that would be applicable to a large variety of cladding/supporting structure arrangements. The results of these analyses are presented by employing the dynamic load factor, representing the maximum supporting structure displacement. It was found that cladding membrane action has adverse effects over its supporting structure, as it does not allow for extensive plastic dissipation and leads to higher support reactions. On the contrary, insignificant membrane action leads to lower dynamic load factor for the supporting structure. Thus, membrane behavior should be activated only as a safety backup action in order to prevent cladding failure. A case study of a typical cladding/supporting structure is presented to demonstrate and verify the proposed two-step SDOF analyses and the obtained results

Progressive Collapse of Buildings

The progressive collapse of buildings is an important ongoing research topic in civil engineering [...

Nonlinear dynamic behavior of cable nets subjected to wind loading

The nonlinear dynamic behavior of saddle-form cable nets subjected to wind actions is studied. The pressure coefficients are obtained by adjusting the recommendations of Eurocode 1 regarding vaulted and duopitch roofs. Artificial wind velocity time-histories are numerically generated according to the geometry of the problem and the wind exposure (wind direction and terrain roughness). The importance of the consideration of the aerodynamic admittance and coherence is also investigated. Nonlinear dynamic analyses are conducted and the results are compared with the ones calculated by the equivalent static method proposed by Eurocode 1. Parametric analyses show that cable nets with small values of the non-dimensional parameter λ2 exhibit large oscillation amplitudes, while large differences between static and dynamic analyses are consistently noted, although both approaches take into account the geometric nonlinearity of the system. © 2017 Institution of Structural Engineer