Grouping response method for equivalent static wind loads based on a modified LRC method

Wind loading is one of the most important loads for controlling the design of large-span roof structures. Equivalent static wind loads, which can generally aim at determining a specific response, are widely used by structural designers. A method for equivalent static wind loads applicable to multi-responses is proposed in this paper. A modified load- response-correlation （LRC） method corresponding to a particular peak response is presented, and the similarity algorithm implemented for the group response is described. The main idea of the algorithm is that two responses can be put into one group if the value of one response is close to that of the other response, when the structure is subjected to equivalent static wind loads aiming at the other response. Based on the modified LRC, the grouping response method is put forward to construct equivalent static wind loading. This technique can simultaneously reproduce peak responses for some grouped responses. To verify its computational accuracy, the method is applied to an actual large-span roof structure. Calculation results show that when the similarity of responses in the same group is high, equivalent static wind loads with high accuracy and reasonable magnitude of equivalent static wind distribution can be achieved.

Study on semi-active control of mega-sub controlled structure by MR damper subject to random wind loads

The recently proposed mega-sub controlled structure （MSCS）, a new type of structure associated with the design and construction of super-tall buildings, has attracted the attention of designers for use in enhancing the control effectiveness in mega-frame buildings. In this paper, a dynamic equation and method to assemble parameter matrixes for a mega-sub controlled structure under random wind loads is presented. Semi-active control using magnetorheological dampers for the MSCS under random wind loads is investigated, and is compared with a corresponding system without dampers. A parametric study of the relative stiffness ratio and relative mass ratio between the mega-frame and the substructures, as well as the additional column stiffness ratio that influences the response control effectiveness of the MSCS, is discussed. The studies reveal, for the first time, that different control mechanisms exist. The results indicate that the proposed structure employing semi-active control can offer an effective control mechanism. Guidelines for selecting parameters are provided based on the analytical study.

Application of artificial neural networks in optimal tuning of tuned mass dampers implemented in high-rise buildings subjected to wind load

High-rise buildings are usually considered as flexible structures with low inherent damping. Therefore, these kinds of buildings are susceptible to wind-induced vibration. Tuned Mass Damper（TMD） can be used as an effective device to mitigate excessive vibrations. In this study, Artificial Neural Networks is used to find optimal mechanical properties of TMD for high-rise buildings subjected to wind load. The patterns obtained from structural analysis of different multi degree of freedom（MDF） systems are used for training neural networks. In order to obtain these patterns, structural models of some systems with 10 to 80 degrees-of-freedoms are built in MATLAB/SIMULINK program. Finally, the optimal properties of TMD are determined based on the objective of maximum displacement response reduction. The Auto-Regressive model is used to simulate the wind load. In this way, the uncertainties related to wind loading can be taken into account in neural network’s outputs. After training the neural network, it becomes possible to set the frequency and TMD mass ratio as inputs and get the optimal TMD frequency and damping ratio as outputs. As a case study, a benchmark 76-story office building is considered and the presented procedure is used to obtain optimal characteristics of the TMD for the building.

Measurements of Wind Loads on Side-by-Side Semi-Submersibles in A Wind Tunnel

The multi-body system has been a popular form for offshore operations in terms of high efficiency.The wind effects are crucial which directly affect the relative positions of floating bodies and operating security.In this study,the aerodynamic characteristics for two coupled semi-submersibles were analyzed in a wind tunnel to fill the gaps in literature related to the wind sheltering on offshore platforms.The influences of separation distance were also investigated.According to the results,substantial shielding effects were observed and wind forces on the shielded vessel decreased dramatically:a reduction in the transverse force could be up to 74%.Moreover,the longitudinal wind load was amplified by the platform abreast in a side-by-side configuration.As expected,the interference level became more pronounced with a decreasing separation distance.For cases in which wind interaction decayed rapidly with distance,logarithmic functions were preferable for describing the relationship between them.Whereas linear fitting was reasonable for the transverse wind force when there was still evident sheltering at a quite large distance.The length of shielding area was another important factor that there was approximately a linear relationship between it and the shielding level for two platforms in close proximity at various wind attack angles.Based on the two parameters,a preliminary wind loads estimation method considering shielding effects was proposed.This approach can aid the industry to have a qualitative assessment of wind sheltering especially at early stages.

Study on longitudinal wind load calculation method of cables for cable-stayed bridge

Along with the expanding of span of cable-stayed bridge,wind load becomes a more and more important controlling factor for bridge the design.A very large proportion of the wind load acting on cables has exceeded that acting on deck.There was not any detailed prescript in Chinese code for calculation of longitudinal wind load on cables due to lack of theoretical research and experiment,and conservative simplified calculation was adopted during design,which leads to conservative and uneconomical design of structures.To resolve this problem,cable force experiment was carried out during the design of Sutong Bridge.By comparing with international research results,the calculation formula of longitudinal wind drag coefficient for cables was advanced to fill the blank of bridge wind resistant code of China,and has already been adopted in the Highway Bridge Wind Resistant Design Code(JTG/T D60-01-2004)with great significance for bridge engineering.

Effects of sudden change in wind loads on running performance of trains on a highway-railway one-story bridge in crosswinds

To investigate the effects of sudden change in wind loads on the running performance of trains on the bridge in crosswinds,a highway-railway one-story bridge was taken as the research object.Aerodynamic coefficients of the train and the bridge were measured in a series of train-bridge system segment models through wind tunnel tests when two trains passed each other on the bridge and when a train entered and left the wind barrier section of the bridge.Based on the improved SIMPACK and ANSYS rigid-flexible coupling simulation method,a wind-double train-track-bridge system coupled vibration model was established.The dynamic responses of the train were analyzed under the effects of sudden change in wind loads caused by two trains passing each other and a train entering and leaving the wind barrier section of the bridge.The results show that the effects of sudden wind load change caused by the trains passing each other had less effects on the running safety of the leeward-side train than the wind shielding effect caused by the windward-side train in the wind speed range of 10−25 m/s.With the decrease in the porosity of wind barriers,the effects of the sudden wind load change played an increasingly important role in the running safety and comfort of the train.With the increase in wind speed,the lateral response of the train increased obviously because of the effects of sudden wind load change,which affects both the lateral running stability and the comfort of the train.

Discussion on Key Points of Wind Load of Jack-up Unit

The anti-overturning ability and structure safety of jack-up unit in in-place condition are often affected by environment loads, especially wind load. According to the MODU rule, the projected area method is used for calculating the wind load. However, the calculated results are conservative and not good for structure optimization design. In this paper, a 400 ft jack-up is studied as an example. Based on the wind tunnel test and numerical simulation method, some key points of wind load calculation, such as shielding effect, lift effect and shape coefficient of component, are discussed. The study shows that the points mentioned above, which are ignored in the MODU rule calculation, result in the conservative result.

Fracture Analysis for Torsion Problems of a Gravity Platform Column with Cracks Under Wind Load

Ocean platforms are subjected to a variety of environment loads, such as those from winds, waves, currents, etc. In this study, the torsion problems of a gravity platform column with cracks under wind load were investigated. The colmnn was assumed to be a composite cylinder. Therefore the torsion fracture problem of a composite cylinder was considered, and new boundary integral equations for the Saint-Venant torsion problem of a composite cylinder with curvilinear cracks were derived. The problem was re- duced to solving the boundary integral equations on every boundary. By using the new boundary element method, the torsion prob- lem of the gravity platform colunm with a straight crack under various wind loads was calculated. The obtained results were com- pared with those obtained for a torsion problem of the same column without cracks to prove the applicability of the present method. The comparison showed that the detrimental effect of cracks in a column should be considered in marine engineering.

Non-stationary Buffeting Response Analysis of Long Span Suspension Bridge Under Strong Wind Loading

The non-stationary buffeting response of long span suspension bridge in time domain under strong wind loading is computed. Modeling method for generating non-stationary fluctuating winds with probabilistic model for non-stationary strong wind fields is first presented. Non-stationary wind forces induced by strong winds on bridge deck and tower are then given a brief introduction. Finally,Non-stationary buffeting response of Pulite Bridge in China,a long span suspension bridge,is computed by using ANSYS software under four working conditions with different combination of time-varying mean wind and time-varying variance. The case study further confirms that it is necessity of considering non-stationary buffeting response for long span suspension bridge under strong wind loading,rather than only stationary buffeting response.

A Review of the Calculation Methods of Lifting Capacity in Wind Loads on Ocean Platforms

Wind load is a control load that affects the safety of structures in the design of ocean platforms. It has not only direct and powerful effects that may cause structure resonance but also has indirect effects causing waves or currents in the ocean. By analyzing the domestic and international norms, this study presents a review of calculation methods of wind load on ocean platforms, which belongs to large-scale non-entity structure used in the open sea while surrounding wind has no fixed direction. Current computations according to the norms are not accurate, which even not takes the force of the wind against the surface perpendicular to the structure into consideration. Additionally, this study also introduces and compares the lift model of platforms based on different theories, such as vortex-excitation and vibration, engineering structure dynamics, gas flow pressure theory, analyzing their applicability, advantages, and disadvantages. This paper analyzes the limitations and applicable conditions of the existing calculation method itself, such as the lift model is suitable for the existence of stable vortex wake;the calculation method of the structural dynamics of marine engineering must be combined with the wind tunnel test and consider the mistakes caused by the position relationship;the numerical simulation method is accurate but tedious. This study provides an insight into the calculation methods of lift in designing ocean platforms, including the finite element method for simulating fluid force and updating formulas in Chinese norms.

General Expression of LRC Method in Estimation of Bridge’s Equivalent Static Wind Load

According to the relationship between load and response, the equivalent static wind load(ESWL) of a structure can be estimated by load-response correlation(LRC) method, which can be accurately used to estimate the background ESWL of a structure. The derivation of the classical expression of LRC formula is based on a specific command response at a critical position, and the ESWL distribution has only one form in this case. In this paper, a general expression of LRC formula is derived based on a specific command response at all positions. For the general expression, ESWLs can be expressed by load-response correlation coefficients, response-response correlation coefficients, RMS values of the fluctuating wind loads, and peak factor in the form of matrices. By comparing the expressions of LRC method, it was found that the classical expression was only one form of the general one. The general expression which introduces the response-response correlation coefficients provided more options for structural engineers to estimate ESWLs and offered further insights into the LRC method. Finally, a cable-stayed bridge, a rigid three span continuous girder bridge, and a suspension bridge were used to verify the correctness of the general expression of LRC method.

Collapse and Reinforcement of Pipe-Framed Greenhouse under Static Wind Loading

The present paper investigates the collapse process of a pipe-framed greenhouse under static wind loading based on a non-linear finite element analysis.The purpose is to establish a more reasonable wind resistant design method for such structures.The structures are so flexible that the fluid-structure interaction(FSI)is considered in the analysis.In practice,iterative analyses of the structure’s response and the wind pressure distribution on the deformed structure are made.The wind direction is normal to the ridge.Computational fluid dynamics(CFD)analysis with a RANS turbulence model is used for evaluating the time-averaged wind pressure coefficient distribution on the structure.Both the geometric and the material non-linearity are considered in the structural analysis.The collapse behavior obtained is consistent with the practical one often observed in damage investigations.Based on the results,discussion is made of the validity of the current design guideline commonly used in Japan.The same analysis is carried out for various reinforced models.The effect of each reinforcement method on the improvement of wind resistance of the structure is investigated on the basis of the allowable stress and deformation limits specified in the current design guideline.

Autogeneration of Wind Loads on Buildings

in desisncede, some design knowledse about wind load on buildinss, i. e. ,wind load coefficient of building shape μs, is diasraniniatically prescribed.Wind pressure on a building surface partly depends on the shapo of the surfaceand the dimension of the building. This part of desisn knowledge can not bedirectly used in CAD systems.It must be prucesaed in order to autogenerate thewind load on a building for the niechanical analysis of the building structure.The article presents the formalization of design knowledge about wind load onbuildings. A mathematical model for the plane seonietrical contour of buildingstructure is established. The map relationship between the shape, dimension ofbuilding and wind load coefficient of building shape is numerically depicted.Therefore, the autogeneration of wind load on building structure isaccomplished. The data structure and algorithm related to the accomplishmentare also described in details.

Structural performance of flexible freeform panelssubjected to wind loads

An increased number of hurricanes and tornadoes have been recorded worldwide in the last decade,while research efforts to reduce wind-related damage to structures become essential.Freeform architecture,which focuses on generating complex curved shapes including streamlined shapes,has recently gained interest.This study focuses on investigating the potential of kerf panels,which have unique flexibility depending on the cut patterns and densities,to generate complex shapes for facades and their performance under wind loads.To investigate the kerf panel's potential capacity against wind loads,static and dynamic analyses were conducted for two kerf panel types with different cut densities and pre-deformed shapes.It was observed that although solid panels result in smaller displacement amplitudes,stresses,and strains in some cases,the kerf panels allow for global and local cell deformations resulting in stress reduction in various locations with the potential to reduce damage due to overstress in structures.For the predeformed kerf panels,it was observed that both the overall stress and strain responses in kerf cut arrangements were lower than those of the flat-shaped panels.This study shows the promise of the use of kerf panels in achieving both design flexibility and performance demands when exposed to service loadings.Considering that this newly proposed architectural configuration(design paradigm)for facades could revolutionize structural engineering by pushing complex freeform shapes to a standard practice that intertwines aesthetic arguments,building performance requirements,and material design considerations has the potential for significant practical applications.

Experimental study of wind loads on gable roofs of low-rise buildings with overhangs

Gable roofs with overhangs （eaves） are the common constructions of low-rise buildings on the southeastern coast of China, and they were vulnerable to typhoons from experience. The wind pressure distributions on gable roofs of low-rise buildings are investigated by a series of wind tunnel tests which consist of 99 test cases with various roof pitches, height-depth ratios and width-depth ratios. The block pressure coefficients and worst negative （block） pressure coefficients on different roof regions of low-rise buildings are proposed for the main structure and building envelope, respectively. The effects of roof pitch, height-depth ratio, and width-depth ratio on the pressure coefficients of each region are analyzed in detail. In addition, the pressure coefficients on the roofs for the main structure and building envelope are fitted according to roof pitch, height-depth ratio and width-depth ratio of the low-rise building. Meanwhile, the rationality of the fitting formulas is verified by comparing the fitting results with the codes of different countries. Lastly, the block pressure coefficients and worst negative pressure coefficients are recommended to guide the design of low-rise buildings in typhoon area and act as references for the future＇s modification of wind load codes.

Across-wind loads and effects of super-tall buildings and structures

Across-wind loads and effects have become increasingly important factors in the structural design of super-tall buildings and structures with increasing height. Across-wind loads and effects of tall buildings and structures are believed to be excited by inflow turbulence, wake, and inflow-structure interaction, which are very complicated. Although researchers have been focusing on the problem for over 30 years, the database of across-wind loads and effects and the computation methods of equivalent static wind loads have not yet been developed, most countries having no related rules in the load codes. Research results on the across-wind effects of tall buildings and structures mainly involve the determination of across-wind aerodynamic forces and across-wind aerodynamic damping, development of their databases, theoretical methods of equivalent static wind loads, and so on. In this paper we first review the current research on across-wind loads and effects of super-tall buildings and structures both at home and abroad. Then we present the results of our study. Finally, we illustrate a case study in which our research results are applied to a typical super-tall structure.

Numerical simulation of non-Gaussian wind load

Compared with Gaussian wind loads, there is a higher probability of strong suction fluctuations occurrence for non-Gaussian wind pressures. These instantaneous and intermittent fluctuations are the initial cause of local damage to roof structures, par- ticularly at the edges and comers of long-span roofs. Thus, comparative errors would occur if a Gaussian model is used to de- scribe a non-Gaussian wind load, and structural security would not be guaranteed. This paper presents a simplified method based on the inverse fast Fourier transform （IFFT）, in which the amplitude spectrum is established via a target power spectrum. Also, the phase spectrum is constructed by introducing the exponential peak generation （EPG） model. Finally, a random pro- cess can be generated via IFFT that meets the specified power spectral density （PSD）, skewness and kurtosis. In contrast to a wind tunnel experiment, this method can avoid the coupled relation between the non-Gaussian and the power spectrum char- acteristics, and lead to the desired computational efficiency. Its fitting accuracy is not affected by phase spectrum. Moreover, the fitting precision of the kurtosis and PSD parameters can be guaranteed. In a few cases, the fitting precision of the skewness parameter is fairly poor, but kurtosis is more important than skewness in the description of the non-Gaussian characteristics. Above all, this algorithm is simple and stable and would be an effective method to simulate a non-Gaussian signal.

Comparison and harmonization of building wind loading codes among the Asia-Pacific Economies

This paper reviews wind loading codes and standards in the Asia-Pacific Region,in particular in the 15 countries and areas.A general description of wind loading model is given as a famous wind loading chain described by four variables including velocity pressure,exposure factor,pressure coefficient,and gust response factor.Through the APEC-WW Workshops and the extensive calculations for three examples of low,medium and high rise buildings,these four important variables of wind loads are evaluated and compared with statistical parameters,mean values and coefficients of variation.The main results of the comparison show some differences among the 15 economies,and the reasons and further incorporation are discussed and suggested.

Collapse fragility assessment of steel roof framings with force limiting devices under transient wind loading

Steel structural frame is a popular structural form to cover large-span roof space and under high winds.Either part of the roof enclosure or the entire roof structure can be lifted off a building,particularly for low sloped roofs subject to wind-induced suction force.Collapse of roof could cause severe economic loss and poses safety risk to residents in the building.The buckling of members in a steel roof frame structure,which may lead to progressive collapse,may be dynamic in nature.This paper presents a fragility analysis of the collapse of steel roof frame structures under combined static and transient wind loading.Uncertainties associated with wind load change rate and member imperfections are taken into account in this study.A numerical example based on a Steel Joist Institute(SJI)K series joist was used to demonstrate the use of force limiting devices for collapse risk mitigation.For the presented fragility assessment of steel roof collapse,a Monte Carlo method combined with response surface approach was adopted,which greatly reduces the computation time and makes the Monte Carlo simulation feasible for probabilistic collapse analysis of steel roof frame structures.

Effects of corner modifications on wind loads and local pressures on walls of tall buildings

In this study, the aerodynamic characteristics of tall buildings with corner modifications (e.g., local wind force coefficients, mean pressure distributions, normalized power spectrum density, and extreme local pressure) were examined. Wind tunnel experiments were conducted to measure the wind pressures on building models with different heights and recessed corners of different ratios. At a wind direction of a = 0° (i.e., wind blowing on the front of a building), corner modifications effectively reduced wind forces in all cases. Specifically, small corner modification ratios reduced wind forces more effectively than their larger counterparts. However, corner modifications resulted in extreme local pressure on building surfaces. In addition, for small corner modification ratios, the probability of extreme local pressure occurring at a = 0° was high. This probability was also high for large corner modification ratios at a = 15° (i.e., wind blowing slightly obliquely on the front of a building) because wind blowing obliquely creates substantial vortex shedding on one side surface and extreme negative pressure over one building side surface. Results of computational fluid dynamic modeling were adopted to determine details of the aerodynamic characteristics of tall buildings with corner modifications.