Inelastic Analysis of Mdof Systems Damaged by Earthquakes, Posteriorly Subjected to Wind Load

This paper deals with the analysis of the inelastic response of buildings originally damaged by earthquakes and subjected to earthquake aftershock and wind loading. The overall aim is to establish the effect of wind actions on structural stability. To that end, one four-story bare frame benchmarked by the European Laboratory for Structural Assessment, is subject to various levels of winds and earthquake joint load while monitoring changes on the ductility demand. In this paper is shown that the combined action of strong winds and earthquakes, however its low probability of occurrence, would cause a decrease of strength reduction factors and considerably increase the ductility demand of damaged infrastructure hence inducing additional risks that would otherwise remain unquantified. The paper examines the non-linear performance of Multi-degree of freedom systems subject to various levels of winds and earthquake load and deals with the estimation of strength reduction factors. This is a relatively unexplored area of research which builds on past developments whereby inelastic performance of buildings has been discussed. It also links to various other paths of development such as structural reliability, forensic and control systems engineering. Doi: 10.28991/cej-2021-03091675 Full Text: PDF

Seismic Design of Offshore Structures under Simplified Pulse-Like Earthquakes

Oil and gas offshore structures are essential infrastructures which are subjected to several categories of environmental loads such as wave and wind actions. These loads commonly designate the structural design of offshore platforms. Additionally, several offshore platforms are founded in earthquake-prone areas and the design of them is intensely affected by seismic ground motions. To be sure, various investigations have studied the earthquake response of offshore structures under the action of far-field seismic events. However, the inelastic behavior of platforms under the action of simple pulses has not been examined yet, where the latter loads can successfully simulate near-fault earthquakes. This work investigates, for the first time to our knowledge, the dynamic inelastic response of offshore platforms subjected to triangular, exponential, sinusoidal, and rectangular pulses. Thus, three-dimensional offshore structures are examined also considering the dynamic soil-pile-platform interaction effects, satisfying all the pertinent provisions of European Codes and taking into account geometric and material nonlinearities as well as the effects of the different angles of incidence of seismic waves on the overall/global response of offshore platforms.

STORY VERTICAL POST-COMPRESSION FOR TIMBER BUILDINGS: A NEW SYSTEM FOR SEISMIC IMPROVEMENT OF CLT WALLS

A new constructive system for multi-story timber building with CLT panels is described. A vertical post-compression of each story allows avoiding the use of traditional joints, as hold-downs and angle brackets. Reducing the number of joint elements, the new constructive system may be faster than the traditional one. The story vertical post-compression allows to improve a shear-type behavior of each story with better performances of the CLT panels. Numerical studies on a single panel and a fivestory building are made performing pushover static equivalent nonlinear analyses. These studies show as the new system allows better performances, in the case of horizontal actions, in comparison to the traditional constructive use of CLT panels. Thus, the new system is very suitable, for timber buildings, in areas prone to seismic actions and wind actions.

Análise simplificada do efeito de ações sísmicas em edifícios de concreto armado dimensionados pela norma brasileira

<p class="Normal1">Earthquakes are natural events, caused mainly due to the relative movement between tectonic plates (interplate earthquakes) and in faults between rocky blocks (intra-plate earthquakes), or induced by human activity. It is possible to observe a relation between the regions located in areas with greater seismicity and the areas that are close to several intraplate failures and shale gas reserves in Brazil. According to NBR 15421/2006, this condition results in a map of seismic accelerations characteristic of the design. Such accelerations can be used to estimate equivalent horizontal loads. However, it is not usual to consider these effects in the design of reinforced concrete buildings. Therefore, this work aims to evaluate the global stability of reinforced concrete buildings with different bracing systems, subject to seismic accelerations provided for in NBR 15421/2006. Initially, the global stability was verified considering the wind and vertical actions by the γz coefficient. Therefore, all the frames analysed in this paper behaved as non-sway structures (γz ≤ 1,10). Then the wind actions were replaced by seismic ones since it is improbable that both phenomena occur simultaneously. Finally, global stability was re-evaluated by means of the γz coefficient. Therewith, it was observed that all the buildings analysed started to behave as structures of mobile nodes (γz &gt; 1,10), that is, susceptible to the second-order global effects.</p>

Consideration of Wind Loads in Fitness for Service Assessment of Storage Tanks

Wind actions are important to consider when performing fitness for service assessment on storage tanks with damage. Tank design codes typically have rules where a design wind velocity is used to determine required dimensions and spacing of wind girders, and a uniform wind pressure is used to evaluate tank anchorage for uplift and overturning due to wind actions. These rules are of little use in a fitness for service assessment of localized damage, as the actual distribution of wind pressure on the wall and roof of a cylindrical tank is far from constant, and a better evaluation of the wind pressure distribution is desired when performing a level 3 fitness for service assessment. API 579/ASME FFS-1 provides no direct guidance relating to the application of wind loading but refers to the American Society of Civil Engineers Standard ASCE/SEI 7. Other international codes relating to wind loads, such as Eurocode EN-1991-1-4 and Australia/New Zealand Standard AS/NZS 1170.2 also contain guidance for the evaluation of wind actions on cylindrical tanks. This paper will present a review of these international codes by comparing their guidance for wind actions on cylindrical tanks, with specific emphasis on how this may affect a level 3 fitness for service assessment of a damaged storage tank.

WIND LOADS ON ROOFING SYSTEM AND PHOTOVOLTAIC SYSTEM INSTALLED PARALLEL TO FLAT ROOF

Mechanically-attached waterproofing system has become popular in Japan. Being vulnerable to wind actions, especially to suctions, this roofing system is often damaged by strong winds. Similarly, photovoltaic (PV) systems installed on flat roofs are often damaged by strong winds, because the PV panels are subjected to large wind forces in an adverse wind. In order to reduce such damage to both systems, the authors propose to install the PV panels parallel to the flat roof with gaps between them, which may reduce the net wind forces on the PV panels due to the effect of pressure equalization. In addition, the wind pressures acting on the waterproofing system will decrease significantly. The present paper investigates the validity of the above-mentioned idea. The wind pressures underneath the PV panels, called ‘layer pressures’, are evaluated by a numerical simulation using the unsteady Bernoulli equation together with the time history of external pressures measured at many locations on the rooftop of a flat-roofed building model in a turbulent boundary layer. The results clearly indicate a significant reduction of wind forces acting on the PV panels as well as on the waterproofing system. The use of PV panels for reducing the wind pressures on waterproofing system is quite effective to the corner region of the roof, where very large suctions are induced in a diagonal wind.

Robotic complex for inspection of the outer surface of the aircraft in its parking lot

Through-flight inspection of the outer surface of the aircraft is necessary to identify possible damage to the surface of the aircraft caused by metal fatigue, lightning, birds collision, etc. The article discusses the method of robotic inspection of the outer surface of the aircraft in its open air parking area. The robotic complex (RC) consists of an unmanned ground vehicle (UGV) and an unmanned aerial vehicle (UAV) interconnected by a tether mechanism (TM). The algorithm of the RC functioning is presented. The main attention is paid to the formation of the TM control and the features of its work, ensuring the prevention of collisions of UAV with aircraft during extreme wind actions on UAV. The study of the most critical mode of the complex operation under extreme wind actions on an unmanned aerial vehicle is carried out. The results of modeling the typical process of the RC operation in an abnormal conditions of extreme wind exposure to UAV are presented.