A refined method for calculating wind load combinations on open-framed structures

SUMMARYWind loads are very important in the design of tall buildings as often the load combinations containing the wind load govern the design. As for reliability, however, because of the higher inherent uncertainty in the wind load in comparison to the gravity load, safety indices decrease as the ratio of wind load to gravity load increases. The safety indices in RC columns depend on the nominal wind to gravity load ratios. Due to the interaction between bending moment and axial force, a single ratio cannot be defined, because the eccentricity is not similar for wind and gravity loads. In this paper, the ratio of wind to gravity loads is considered separately for axial force and bending moments. Unlike conventional approach, here it is assumed that the wind and gravity loads' eccentricities are not equal, and the final load eccentricity used in either the design or the reliability analysis is a function of applied loads. The results demonstrate that the sensitivity of RC columns' safety indices to bending moment ratios is higher than that of axial force ratios. Furthermore, the variation of RC columns' safety indices with a low rebar percentage is very different from RC columns with high rebar percentages. Copyright © 2010 John Wiley & Sons, Ltd.

Open frame structures, such as those commonly found in industrial process facilities, are often densely occupied with process related equipment. This paper presents a method for estimating wind loads for high-solidity open frame structures that differs from current approaches, which accumulate wind load contributions from various individual structure components. The method considers the structure as a porous block of arbitrary plan dimension that is subject to wind from any direction. The proposed method compares favorably with wind tunnel test results for similar structures. The possibility of defining an upper bound force coefficient is also discussed.

Wind load is the wind pressure on the windward sides of structures (houses, cranes, masts, billboards, power line supports, etc.). There are many examples of plant accidents due to strong gusts of wind, which, for example, shows the importance of considering wind load when calculating structures. The purpose of the work is to assess the actual state of the billboard design and make suggestions for its improvement for normal further operation. The work gives the calculation expressions of maximum total wind load, stress and deflection in the metal rack. Computation of billboard rack possessing sufficient strength and rigidity is described. Calculation of the required minimum diameter of the billboard rack is considered. The graph of the change in the deflection depending on the diameter of the rack is described. The investigations allow calculation of billboards racks that can withstand large wind loads. Received in work expressions allow to calculate of maximum total wind load, stress and deflection in the metal rack. Based on this, it is possible to estimate the reliability of the billboard construction. The expressions, obtained in the work, allow calculating the minimum diameter of billboard racks, ensuring their reliability. KeywordsWindBillboardWind load

An analytical approach and numerical solution to determine coupled aeroelastic and hydroelastic response of floating offshore wind turbines of arbitrary shape to combined wind and wave loads is presented. The model considers simultaneously the aerodynamic and hydrodynamic loads on an FOWT and integrates these with finite element method for structural analysis due to the combined loads. The hydrodynamic and aerodynamic loads are determined based on the linear wave diffraction theory and steady blade element momentum method, respectively, and the solution is obtained in frequency domain. The structure may be fixed or floating, located in arbitrary water depth, and may host single or multiple wind towers. The model captures the complete translational and rotational motions of the body in three dimensions, and the elasticity of the blades, tower and the floating platform. To assess the performance of the model, rigid and elastic responses of a FOWT to combined wave and wind loads are computed and compared with available laboratory measurements and other theoretical approaches where possible, and overall very good agreement is observed. The model developed in this study addresses directly three shortcomings of existing approaches used for the analysis of FOWTs, namely (i) determination of the elastic responses of the entire structure including the floating platform, (ii) analysis of the motion and elastic response of FOWTs in frequency domain, and (iii) assessment of responses of FOWTs with single or multiple wind towers.

Service strength validation of wind-sensitive structures, including fatigue life evaluation

In coastal areas, large-span space steel net trusses experience structural deformation due to strong winds. Currently, the application of equivalent static wind load to the structure does not consider the influence of local forces. The local uneven force on the bars caused by the structural appearance is ignored, complicating the identification of local deformation in the net truss. Additionally, this simplification increases the difficulty in evaluating wind load-sensitive areas of the building. This paper introduces a novel method for calculating static equivalent wind load, considering the transmission relationship between the structural roofs appearance and the internal truss forces. Following the outlined methodology, wind load is precisely applied at nodes with diverse windward faces, taking into account the node area ratio. The paper also examines how varying standard wind load values affect mesh truss deformation under different wind angles. Results indicate that, at 0o, 90o, 180o, and 270o wind directions, wind load-sensitive areas are linked to roof shape and structural characteristics. Maximum displacement in the truss grid’s overall structure primarily occurs in the windward corner contact area. Network truss deformation linearly increases with the load standard. If the wind load exceeds 1.0 kN/m2, deformation is associated with the windward vertical plane’s area and steel column spacing, impacting overall structural safety.

Sotech is a leading manufacturer of bespoke rainscreen cladding and architectural façade systems, where aluminium cladding façade is of particular interest. Necessarily, the design of façade system is required to meet safety and stability requirements, which is conventionally the deformation due to wind load. However, it is questionable that the thermal load is normally neglected, particularly during an extremely hot weather. For the benefit of Sotech in terms of design reliability, it is important to factor in thermal load to acquire for comprehensive deformation results. Consequently, the aim of this study is to investigate how the aluminium cladding façade reacts to a combined loading, which is the combination of wind load and thermal load, using finite element analysis. In the model, the gravitational load will be considered, and the combination of wind loads up to 50 mph and thermal loads from -30°C to 35°C are applied to the aluminium cladding panel. Typically, the material is defined as aluminium alloy, which is easy to manufacture and has a high strength to weight ratio. The key finding is that addition of thermal load to wind load is not necessarily topping up the deformation, since there can be an effect of wind load being negated by thermal load. This study lays a foundation for Sotech to improve the design standard.

Sandwich panels composed of glass fiber–reinforced polymer (GFRP) skins and low-density polyurethane core are investigated for potential structural applications such as lightweight insulated roofing or cladding systems. Ten 1,220×318×78-mm panels, including three control specimens, were tested under high-cycle fatigue at maximum load levels of 45–70% of the ultimate static load. Fatigue tests were carried out to failure, thereby enabling the development of the complete fatigue life (S-N) curve and stiffness degradation. Digital imaging correlation was used to map shear deformations and showed that shear contributes about 90% of the deflection. Both static and fatigue failure modes were due to core shear failure. The study showed that fatigue threshold was 37% of the ultimate static capacity, and that to sustain at least 2 million cycles, service load should be limited to 45% of ultimate. The maximum design service live and snow loads, as well as wind load based on the most critical conditions in Canada, were all below the fatigue threshold of the panel. The panels had a strength safety factor of 2.1 relative to the factored maximum design live and snow load, and 6.5 relative to the factored maximum wind load. Deflection limits may govern for some service load conditions, but is not critical when only wind load considered. Stiffness degradation reached a maximum of 15–20%, but residual deflections upon unloading were insignificant.

The principle objective of this project is to analysis and design a multi-storeyed building [G + 10 (3-dimensional frame)] using SAP2000. The design involves load calculations manually and analyzing the whole structure by SAP2000. The design methods used in SAP2000 analysis are conforming to Indian Standard Code of Practice and features a state-of-the-art user inter face, visualization tools, powerful analysis and design engines with advanced finite element and dynamic analysis capabilities. From model generation, analysis and design to visualization and result verification. The project is designed in accordance with Indian codes, considering various loads such as Reinforced concrete (IS 456-2000), dead load (IS875-1987 part1), live load (IS875-1987 part2), wind load (IS875-1987 part3), seismic load (IS1893-2016 part1) and load combinations are considered as per the (IS875-1987 part-5) code books. The analysis considers seismic zone III and ensures safety by considering dead load, live load, seismic and wind forces, and balancing economy and safety. Structural design is crucial for Civil Engineers, and proper analysis can prevent structure failure and loss of life. Engineers analyze structures considering constraints like serviceability and deformability, following IS codes. Our project focuses on analyzing and designing superstructures like slabs, beams, and columns, considering dead load, live load, seismic and wind forces Response Spectrum Analysis and Shear Wall. The analysis parameters such as shear force, bending moment, and displacement. KEYWORDS: Response Spectrum Analysis, Shear Wall, SAP2000, Seismic and Wind loads.

基于A塔楼风洞试验数据，本文详细分析了风荷载特性与风致响应特征，得到了结构表面幕墙设计荷载、结构主体设计荷载以及结构加速度响应。结果表明：1) 周边建筑对风荷载分布影响较大，出现明显的干扰效应；2) 结构主体设计风荷载最大值发生在斜风向，如195˚和240˚。所得结果可为该塔楼风荷载设计提供依据。 Wind loads and wind responses of high-rise building are analyzed in detail, based on the wind tunnel test data of Tower-A. And then the design wind loads for curtain wall, structure subject, and wind induced acceleration response have been obtained. The results show that: 1) Significant interference effects by around buildings were found; 2) The maximum design wind loads for structure subject occurred on oblique wind direction, such as 195˚ and 240˚. The results are expected to be very useful for the wind load design of the Tower.

Achieving uniform reliability is a desired intent of design standards based on Load and Resistance Factor Design (LRFD) methodology. The design standard for offshore wind turbines, the IEC 61400-3 (IEC, 2009), also follows the LRFD. This standard is based on European experience and it may not necessarily represent offshore environment in the US waters, where several offshore wind farms are being planned. For these reasons, it is of interest to investigate factors that may influence the reliability of offshore wind turbines under various levels of wind and wave loads. We evaluate the reliability index, which is a measure of the probability of failure, for the ultimate limit state associated with the fore-aft tower bending moment at the mudline for offshore wind turbines with fixed support structures. We compare reliability index for various values of characteristic levels and coefficients of variation of wind and wave loads, as well as for various ratios of hydrodynamic to aerodynamic loads. These parameters represent different sites and turbine designs. Using the combined wind and wave load effect model for offshore wind turbines proposed by Tarp-Johansen (2005), we show that the range of reliability levels are reasonably uniform under various combinations of wind and wave loads. This meets the intent of codes based on the LRFD. Since large diameter monopile support structures tend to be dominated by inertia forces, while jacket support structures with smaller diameter members are often dominated by drag forces, we also employ a more general wave load formulation that models both drag and inertia forces. We include this wave load model in the combined wind and wave load effect model for offshore wind turbines, and estimate resulting reliability levels. Results show that dragonly case results in smaller estimates of reliability index than the inertia-only case. Moreover, for inertia-dominated cases, reliability levels are found to be even more uniform than those for drag-dominated case. Introduction Several design codes, including the IEC 61400-3 (IEC, 2009) standard for offshore wind turbines, are based on the Load and Resistance Factor Design (LRFD). Designs of an entire class of structures based on the LRFD methodology tend to have a uniform reliability. On the other hand, different designs in a class of structures may have quite different reliability levels if working stress design methodology is followed. LRFD is particularly useful for loads that exhibit considerable variability. Offshore wind turbines are influenced by wind as well as wave loads, both of which can exhibit significant variability. Therefore, it is of interest to understand influence of various factors on the reliability of offshore wind turbines under various levels of wind and wave loads. Understanding reliability levels is even more important for relatively new industries like offshore wind energy for which the design practice is still evolving. The first edition of IEC 61400-3, the Design Requirements for Offshore Wind Turbines (IEC, 2009), was issued only recently in 2009. This standard is based more on the European experience, where the offshore wind industry is about a decade old. Lately, there has been considerable interest in developing offshore wind farms in the US waters. Care has to be used in applying IEC standards in the US where offshore environment is quite different than that in Europe. The offshore oil and gas industry is quite mature in the US, and American standards for design of fixed-bottom offshore structures exist, such as API RP 2A-LRFD (API, 2003) and API RP 2A-WSD (API, 2005). However, these standards were not intended for wind turbines, which are active machines instead of passive structures, and for which loads on support structures are mainly dominated by aerodynamic loads.

ASCE 7 is moving toward adopting load requirements that are consistent with risk-informed design goals characteristic of performance-based engineering (PBE). ASCE 7-10 provided wind maps that correspond to return periods of 300, 700, and 1,700 years for Risk Categories I, II, and combined III/IV, respectively. The risk targets for Risk Categories III and IV buildings and other structures (designated as essential facilities) are different in PBE. The reliability analyses reported in this paper were conducted using updated wind load data to (1) confirm that the return periods already in ASCE 7-10 were also appropriate for risk-informed PBE, and (2) to determine a new risk-based return period for Risk Category IV. The use of data for wind directionality factor, Kd , which has become available from recent wind tunnel tests, revealed that reliabilities associated with wind load combinations for Risk Category II structures are, in fact, consistent with the reliabilities associated with the ASCE 7 gravity load combinations. This paper shows that the new wind maps in ASCE 7-16, which are based on return periods of 300, 700, 1,700, and 3,000 years for Risk Categories I, II, III, and IV, respectively), achieve the reliability targets in Section 1.3.1.3 of ASCE 7-16 for nonhurricane wind loads.

Reliability-based calibration of companion load combination factors by considering concurrent wind and ice loading for structural design

In the process of the structural design of the working and façade scaffolds, the self-weight of the elements, the service load and the wind load should be taken into account. The wind load on a covered façade scaffold is determined by many factors, including the wind velocity, the solidity ratio of the building’s façade, the geometric characteristics of the scaffold’ components and the type of cladding – netting or sheeting. The paper investigates the effects of wind loads on both types of façade scaffolding – with and without claddings. A computational finite element model was developed to study the specifics of the scaffoldings in the function of the nets permeability and the solidity ratio of the façade. Load combinations, according to the requirements in EN 12811-1, were considered to obtain the internal forces and stresses of the scaffold elements subject to wind actions. Based on the numerical analyses, it was found that the porosity and air permeability of the nets have a significant effect on the internal forces and stresses of the façade scaffolds elements, which also depend on the anchorage patterns and solidity ratio of the façade. In conclusion, recommendations are given regarding the application of specific structural schemes and anchoring patterns, depending on the permeability of the different façade scaffold nets.

The wind load acted on ship mast at different wind angles of large Reynolds number is numerically simulated in this paper. CFX software was used to analyze the trend of constant and fluctuating forces that the mast surface suffered at different Reynolds numbers.The vortex shedding strength of the wind load around the mast was also analyzed according to the trend of Strouhal number varing with the simulated Reynolds numbers. The results show that the wind angle has an important impact on the lift, drag, and vertical force of the mast. The vertical force of the inclined side wall on the mast can not be ignored,and the angle of direction wind has great impact on the Strouhal number at different Reynolds numbers.