Time–frequency analysis of structural dynamic characteristics of tall buildings

This study focuses on the correlations between the structural dynamic properties and the instantaneous response characteristics of a 492-m high building during a typhoon. An instantaneous analysis framework is established based on a combined usage of both linear-phase filtering and time–frequency techniques. This analysis framework can separate each modal response contribution without phase distortions. Random decrement technique is used to estimate the modal damping ratios. It is found that beating phenomenon widely exists in the separated modal response contributions, and the damping ratios correlate with the modulation of phase and amplitude within the beating closely. When the beating amplitude comes close to zero, the instantaneous frequency fluctuates evidently. The more intensive this fluctuation is, the larger the damping ratio becomes. An empirical model is presented to formulate the variations of damping ratio and natural frequency of this building with the fluctuation intensity of the instantaneous frequency.     

Dynamic analysis of three-dimensional bridge–high-speed train interactions using a wheel–rail contact model

A formulation of three-dimensional dynamic interactions between a bridge and a high-speed train using wheel–rail interfaces has been developed. In the interface, contact loss is allowed, the vertical contact is represented by finite tensionless stiffness and the lateral contact is idealized by finite contact stiffness and creepage damping. Such stiffness and damping are nonlinearly dependent on normal contact force. The relative rotations of a wheelset to the rails about its vertical and longitudinal axes are included. Bridge eccentricities and deck displacement due to torsion are accounted for in bridge deck modeling. A numerical algorithm using separate integrations for bridges and trains, and iterations for interface compatibilities is established. A case study of a ten-car train passing over a two-span continuous bridge at various speeds and rail irregularity wavelength ranges is analyzed. The responses of the bridge, car-bodies and wheelsets are investigated for their behavior, acceptability and relations with the wavelengths. Analytical and numerical evaluations of resonant speeds are in good agreement, and the exit span vibration is more amplified than the entrance one at those speeds. The computed relative displacements of all wheelsets to the rail facilitate an explicit assessment for derailment risk.     

What can a bridge be? The wind and rain bridges of the Dong

Bridges are taken for granted in the modern world as utilitarian structures and if noticed at all are remarked upon mainly for the elegance of their engineering structures, but a mere couple of centuries ago many in Europe still had chapels in which prayers for a safe crossing could be said. In the Dong areas of south-west China, which remained remote until around two decades ago, the bridges are the principal monuments, elaborately roofed and decorated with shrines to various gods, built with pride and at great local cost. Our research began with the question of why so much trouble was taken over these bridges, and led on to how they were read by their users and builders, and what they were considered to mean. The consequent excursions into anthropological theory and traditional Chinese ideologies, which can only be briefly summarised in the following paper, revealed a rich and complex network of causes, fascinating in their multiplicity and interaction. The enquiry was pushed far beyond the bounds of traditional art history, engaging fundamental questions about the significance of architecture as a communicative and ritual medium in traditional oral-based cultures. At a more general level it also prompted a thought-provoking exploration of the similarities and differences between bridges metaphorical and bridges physical.     

Dynamic testing of a soil–steel composite railway bridge

Actual dynamic response of a long-span corrugated steel culvert railway bridge is studied. The bridge, which is a type of soil–steel composite structures, has a span of 11 m. Tests were carried out by measuring strains and displacements during passages of a locomotive at different speeds. Vertical ballast accelerations as well as the effects of braking forces were also measured. The tests showed that the speed has a large influence on the displacements, thrusts and moments. The measured dynamic displacements and thrusts are as much as 20% larger than the corresponding static response. This is greater than the values specified in bridge design codes. Dynamic amplification factors as high as 1.45 were obtained for the moments at the quarter point which is found to be much larger than the values for the crown point. This type of bridge structure is believed to be less sensitive to resonance from passing trains than other common bridge types, due to the high damping values obtained from the forced vibration tests.     

Influence of wind–waves energy transfer on the impulsive hydrodynamic loads acting on offshore wind turbines

This paper draws some preliminary considerations about the direct wind effects on the kinematics and dynamics of steep extreme waves propagating near offshore wind turbines. Most of the hydrodynamic load models currently employed in designing offshore wind turbines take into account only indirectly the role of the wind. In fact, once the sea severity upon a certain wind speed is established, the sea state is fully determined by means of the significant wave height and the peak spectral period. In contrast, recent experimental results show that the local wind strongly influences the evolution of steep waves. A wind–waves energy transfer model is here implemented in a fully nonlinear potential flow model for wave-propagation. First, the laboratory experimental evidences about the influence of the wind on the propagation of steep waves are confirmed numerically by simulating the 2D propagation of a Gaussian wave packet. Second, real environmental conditions are reproduced in the near field of an offshore wind turbine using linear–nonlinear potential flow models within a novel coupling strategy. Different wind-wave relative speeds are simulated attempting to quantify the influence of the wind on the wave propagation. Although a reliable evaluation of this influence is still an open issue, the importance of some physical parameters, such as the duration of the energy transfer, is highlighted.     

A survey of vehicle fires in Norwegian road tunnels 2008–2011

Norway is one of the countries that constructs most road tunnels, and there are well over 1000 in the country today. The aim of this study is to map the prevalence and describe the characteristics of vehicle fires in Norwegian road tunnels 2008–2011. The average number of fires in Norwegian road tunnels is 21.25 per year per 1000 tunnels, and the average number of smoke without fire (SWF) is 12.5 per year per 1000 tunnels. The study provides four main results. The first is that the fires generally did not involve harm to people. This has also been reported in previous Norwegian research. The second finding is that heavy vehicles are overrepresented in fires in Norwegian road tunnels. This is in line with international research. The third main finding is that the causes of road tunnel fires involving heavy and light vehicles are different. This is also in accordance with international research. The fourth important and unique finding of the study is that subsea road tunnels are overrepresented in the statistics of fires in Norwegian road tunnels.     

Anti-corrosion performance of bridge strands consisting of steel wires galvanised with zinc–aluminium alloy

Strands consisting of 19 parallel steel wires galvanised with zinc (Zn, 90%) and aluminium (Al, 10%) alloy were produced and accelerated corrosion tests were conducted, and the anti-corrosion performance was compared with the conventional strands galvanised with Zn. The strands were placed at a relative humidity (RH) of 60%, RH of 100% and the wet condition in the thermo-hygrostat at 40°C for 150 days. The mass loss due to corrosion of the strands galvanised with Zn–Al at an RH of 60% and 100% was small, and the strands had good corrosion resistance. The corroded mass of the strands at the wet condition was 15 times larger than that at RH of 100%. The strands galvanised with Zn–Al had lesser corrosion than those galvanised with Zn under the three environmental conditions. Corroded mass was larger in the surface wire, the inside wire and the centre wire in this order. The cross-sections of corroded strands were investigated by using a microscope and an electron probe micro-analyser showing that the corrosion product of Zn was porous and coarse. By contrast, the corrosion product of Zn–Al alloy was dense and hard to exfoliate from the steel layer. This difference made Zn–Al galvanised wire strands superior to Zn galvanised wire strands.     

Acceleration generation due to strain localization of saturated clay specimen based on dynamic soil–water coupled finite deformation analysis

In the conventional bifurcation and strain localization analyses of geomaterials, the inertia forces are generally ignored, based on the quasi-static equilibrium equation. Even though a great deal of literature exists on dynamic strain localization analyses, information on acceleration generation during the formation of shear bands has not been emphasized. Inspired by the acoustic emission phenomenon in laboratory tests and the seismic acceleration related to the slippage of faults, a dynamic soil–water coupled strain localization analysis is performed in the present paper on a saturated rectangular clay specimen subjected to constant cell pressure under plane strain conditions, employing the SYS Cam–clay model as the elasto-plastic constitutive model for the soil skeleton. An initial geometrical imperfection was introduced to the specimen to trigger one single shear band, and the following results were found: (1) Two types of oscillation occurred within the specimen during acceleration when the specimen was subjected to compression deformation at a constant rate, namely, (a) one caused by the sudden external compression and (b) the second induced by the formation of strain localization/a shear band. With the occurrence of the shear band, if, for example, the vertical rate was equivalent to about 10 cm/s, the accelerations that occurred within the specimen were in the order of several thousand gal, which is similar to those measured during earthquakes; (2) The effects of the time increment, the mesh division, the initial confining pressure, the OCR and the stress-control loading on the generated acceleration in (b) were investigated in detail. It was found that under stress control, even though the formation of the shear band was similar to that under displacement control, the induced acceleration behaved quite differently.     

Input–output analysis of the Chinese construction sector

The construction sector has played a key role in the Chinese economy, which has been experiencing a rapid growth for the past two decades. This development and growth are reviewed in a framework of input–output analysis. The national input–output table (IO table) was used to study the current input–output profile of the Chinese construction sector and the relationship between the construction sector and other sectors. The pull and push effect of the Chinese construction industry to the whole national economy has been estimated. It shows that the pull effect is much larger than the push effect. Furthermore, through the analysis of a series of four IO tables spanning over the last 10 years, it reveals that the pull and push effect of the Chinese construction industry are both getting larger and larger. This means the Chinese construction industry is becoming mature and is in great transition.     

Analysis of seismically-isolated two-block systems using a multi–rocking-body dynamic model

A novel multibody rocking model is developed to investigate the dynamic response of two stacked rigid blocks placed on a linear base isolation device. The model is used to investigate the dynamic response of a realistic statue-pedestal system subject to pulse-like ground motions. The analysis shows that, in general, base isolation increases the safety level of the rocking system. However, for large period pulses or small size blocks, the isolator can amplify the ground motion, resulting in a lower minimum overturning acceleration than for the nonisolated system. Further, the amplification or shock spectrum of a linear mass-dashpot-spring oscillator, was found to be the reciprocal of the minimum nondimensional overturning acceleration of the investigated rocking system. Novel rocking spectra are obtained by normalizing the frequency of the pulse by the frequency of the isolator. The analysis also demonstrates how the dynamic response of the two stacked blocks is equivalent to that of a single-block configuration coincident with the whole system assumed monolithic or the upper block alone, whichever is more slender.     

An input–output analysis of Thailand's construction sector

Three input–output (IO) tables compiled between 1995 and 2000 were used to examine the significance of the construction sector and its relationships with other sectors of the Thai economy. The pull and push effect of the Thai construction sector to the national economy indicated that the former is much larger than the latter. Additionally, the relatively high output multipliers and backward linkage indicators showed that the construction sector had the potential to trigger off production in many economic sectors linked to it. An aggregated sectoral analysis revealed the high dependence of construction on manufacturing followed by services. The findings also suggest that the trends of the profile of inputs and outputs are correlated to the economic conditions in Thailand at the time the IO tables were compiled. Finally, the results of employment analysis showed that although the share of construction sector in direct employment generation may not be very large, its economic importance lies in its direct and indirect contribution to employment through strong backward linkage effects. Consequently, when its backward linkages and output multiplier are considered together with the employment opportunities latent within it, then the construction sector could be a major contributor to the economic growth of Thailand.     

Correction of direction reduction factors of extreme wind speed considering the Ekman spiral in the wind load estimation of super high-rise buildings with heights of 400–800 m

The wind direction in the atmospheric boundary layer (ABL) twists with height due to the Coriolis force; this phenomenon is called the Ekman spiral. However, this phenomenon is generally not considered in the present wind load estimation of super high-rise buildings, which may lead to an incorrect estimation and affect the safety of structures. Therefore, this study considers and analyzes the influence of the Ekman spiral phenomenon in the wind direction reduction effect (WDRE) of the wind load of super high-rise buildings. First, this paper proposes an empirical fitting equation for the twisted wind direction angle for a height of 100–800 m according to the classical Ekman spiral theory model (CE model). Subsequently, on the basis of twisted wind, this paper proposes a method for the correction of the wind direction reduction factors (WDRFs) of strong winds considering the influence of the Ekman spiral phenomenon in the design wind load estimation of super high-rise buildings with heights of 400–800 m. A high-frequency balance force measurement test of a square-section super high-rise building model was performed to analyze the influence of the Ekman spiral phenomenon on the WDRE of the aerodynamic force and wind-induced response. Three Chinese cities (i.e., Beijing, Wuhan, and Kunming) are selected as case studies to illustrate the importance and necessity of the correction method. The results demonstrate that the proposed empirical fitting equation accurately determines the twisted wind direction angle at different latitudes and altitudes. Furthermore, estimating the design wind load while considering the WDRE and neglecting the influence of the Ekman spiral phenomenon may lead to a significant underestimation of the wind load of super high-rise buildings, rendering the designed building structure more dangerous.     

Design and simulation of a solar–wind–biogas hybrid system architecture using HOMER in India

The renewable energy sources are accompanied by certain constraints as reliability, availability and continuous generation. In India, biomass is considered as the second best suitable combination with other renewable energy sources. Both solar and wind are undependable renewable energies as they are unpredictable. Now the key to successful renewable energy harvesting lies in the selection of hybrid system architecture for power generation. In rural areas, light is usually unavailable and if it does, it is mostly an incandescent light used for household lighting instead of fluorescent. System reliability, economy and environmental issues are the three major issues for decentralised electrification. So, finding the best suited hybrid system configuration to overcome these constraints is the need of the hour. It is at this stage that HOMER comes into the picture. HOMER, abbreviated name of hybrid optimization model for electric renewable, successfully realises system configuration before its installation and works for on-grid, off-grid and stand-alone systems, which make it useful for rural to urban applications. It simulates and optimises the best suitable solution for a hybrid system and generates reports incorporating all the aspects in designing a system. Here, a typical hybrid system is considered and the implementation of HOMER software has been incorporated.     

A preliminary study of wind–solar hybrid systems potential in Jammu and Kashmir

ABSTRACT

This paper deals with the study of wind–solar hybrid systems in the region of Jammu and Kashmir. Due to scarcity of less renewable energy resources in the J&K region, National Institute of Wind Energy, Chennai had installed different wind monitoring stations to measure the wind data at different locations. The survey reveals that four districts (LEH, KARGIL, POONCH and REASI) are suitable for small wind–solar hybrid systems. BIDDA (REASI) and CHUSHUL (LEH) are the two sites for small wind farm development due to the highest wind speed (more than 7?m/s) and power density (more than 400?W/m²) at 100?m agl.     

Practical nonlinear analysis of steel–concrete composite frames using fiber–hinge method

A fiber–hinge beam–column element considering geometric and material nonlinearities is proposed for modeling steel–concrete composite structures. The second-order effects are taken into account in deriving the formulation of the element by the use of the stability functions. To simulate the inelastic behavior based on the concentrated plasticity approximation, the proposed element is divided into two end fiber–hinge segments and an interior elastic segment. The static condensation method is applied so that the element comprising of three segments is treated as one general element with twelve degrees of freedom. The mid-length cross-section of the end fiber segment is divided into many fibers of which the uniaxial material stress–strain relationship is monitored during analysis process. The proposed procedure is verified for accuracy and efficiency through comparisons to the results obtained by the ABAQUS structural analysis program and established results available from the literature and tests through a variety of numerical examples. The proposed procedure proves to be a reliable and efficient tool for daily use in engineering design of steel and steel–concrete composite structures.     

Effects of soil–pile interaction on the response of bridge pier to barge collision using energy distribution method

Abstract

In this paper, the effects of soil–structure interaction (SSI) on the response of a girder bridge pier is evaluated by assessing the energy distributions in the barge–pier collision system. The finite-element models of two example piers of St. George Island Causeway Bridge, which have different structural and geometrical characteristics, are developed in LS-DYNA software to simulate the barge–pier collision scenarios. By comparing the energy distribution results among the barge and pier components, it is obtained that barge bow component has greater value of the internal energy contribution than pier components in the barge collision with more stiff pier. While, in the barge collision with more flexible pier, the pier components including the pier structure, piles and SSI have more internal energy contributions than the barge component. In addition, From the comparison of energy absorbed by the pier structure between the cases with and without SSI, it is found that the effect of the substructure and its relevant SSI on the response of the more flexible pier affected by the produced large deformations and relative displacements of the pier substructure, is more than that of stiff pier which displaces with semi-rigid and global deflections.