Design Of Economical Structures Research Articles

Analysing the Directional Dependence of Wind and Wave Interactions for Offshore Wind Turbines Using Environmental Contours

The structural design of offshore wind turbines is dominated by environmental conditions such as wind and waves, in addition to deadweight loads and loads from operation. Probabilistic combination approaches exist for the ultimate limit state (ULS) to estimate the simultaneous occurrence of extreme meteorological and oceanographic (metocean) environmental conditions at the site of an offshore wind turbine. The site-specific direction of action of the load parameters is mostly neglected in these approaches; the design of offshore wind turbines in the ULS is usually carried out for the most structurally unfavourable directional superposition of load parameters—which is not based on physical principles and wastes potential material savings. The reasons for different load parameters in different directions of action are the influences of nearby land masses and the topographic shape of the sea floor, atmospheric air circulation, and marine current systems. In this paper, wind and sea state data from the coastDat-2 WAM database are statistically analysed for two sites in the North Sea, common environmental contours are estimated using the example of significant wave height and wind speed, and the site-specific influence of the direction of the load parameters on the environmental contours are investigated. It is shown that, depending on the site under consideration, the direction of action can significantly influence the metocean environmental conditions and that direction-resolved probabilistic combination approaches can contribute to a safe and economic structural design of offshore wind turbines.

Elastic Critical Buckling Coefficients for Skew Plates of Steel Structures under Biaxial Normal Stress

In steel structures, skew thin steel plates serve as panel zones in structures spanning large spaces (e.g., warehouses and gymnasiums). Considerable research has been conducted on the shear buckling of panels due to seismic loads acting on a structure. Conversely, under snow or wind loads, the panel zone may experience compressive and tensile stresses simultaneously from two directions. Considering the economic preference for thin steel plates, evaluating the elastic critical local buckling stresses in the panel zone under biaxial normal stress may provide essential information to structural engineers. In this study, an elastic buckling analysis based on the energy method is performed to clarify the impact of panel geometry and boundary conditions on the elastic local buckling stresses of skew panel zones. As confirmed from the results, the local buckling stresses calculated using the energy method were consistent with those determined using finite element analysis. The findings indicate that a skew angle of up to 30° marginally affects the elastic buckling stress under uniaxial stress. Consequently, engineer-friendly design formulas were developed based on these findings. Comparisons with previous research demonstrated that the buckling loads reported were generally higher than those determined by finite element analysis. The study also established the correlation of the buckling stresses under biaxial stresses, which implied that the skew angle posed minimal influence on buckling stress for skew plates under biaxial stress. Additionally, a method for evaluating this correlation was presented. Engineers can utilize the provided design equations to more efficiently and accurately calculate buckling loads, facilitating a safer and more economical design of structures with skew plates.

Re-Design of the Structure of the Batang I Industrial Flats Worker Building Using the Precast Concrete Method

The Industrial Workers' Flats, located in the Batang Integrated Industrial Area, are supporting facilities workers use. The building was previously planned using conventional methods. In many cases, demands for fast and efficient construction work often occur, especially in the case of high-rise buildings. The need for multi-storey buildings encourages the need for an economical structural design that can be implemented quickly and efficiently without reducing the stiffness between the components of the building structure. From the explanation above, it is re-planned using the precast concrete method so that the work is neat, precise, and fast. In this planning, the SRPMK system is used. It needs good supervision in precast concrete, especially in joints, because precast joints are not as monolithic as conventional ones. It is necessary to develop precast technology to be more innovative in its use and easier to apply.

Numerical simulation of wave interaction with porous structures

The economical design of rubble mound structures namely breakwaters can be facilitated by means of an accurate simulation of interactions between the porous media and the passing currents and waves, to assure the safe economical design of these structures. Unlike most of the previous studies, the present study dealt with the development of a more realistic simulation by simultaneous consideration of the porous structure reshaping and the fluid flow interactions. To this end, the wave interactions with the porous media together with the breakwater deformation are modeled using a combination of FVM-VOF-DEM numerical methods. The flow in both the pure fluid and porous media were modeled using a new formulation of an Eulerian FVM-VOF method, while a Lagrangian DEM method with a new simple porosity adjustment was incorporated to simulate the deformation of the breakwater. The performance of the presented model is evaluated by comparing its results with those of laboratory measurements. The results indicate that the developed model can accurately simulate the free surface and the flow passing through the porous media; as well as the breakwater deformation.

Assessment of hysteretic damping in reinforced concrete structures using local hinge characteristics

Performance-based seismic engineering is nowadays adopted for economical design of structures to resist earthquakes and it requires nonlinear static pushover analysis to be performed. In this approach, the energy dissipation due to nonlinear behavior of the structures is taken into account by obtaining the equivalent viscous damping and this damping is evaluated from the global pushover curve of the structures. However, the global structural damping is basically due to energy dissipation at local joints of the structures deforming beyond yield rotation. This paper presents the methodology of estimating equivalent damping from the local hinge characteristics of the structures at element level by carrying out Pushover analysis of three structures viz 3D six storeyed, 2D two storeyed and a simple column RC structure. This damping is assessed by considering cumulative hysteretic energy dissipated at all the plastic hinges developed in the structures and is compared with that calculated based on formulations given in codes such as FEMA-440 and ATC-40. Damping agrees well with that given in FEMA-440, estimated from global pushover curve of structures for ductility value greater than 3. Also, nonlinear time history analysis is performed for all the structures to validate the structural performance.

A phase field modeling approach of cyclic fatigue crack growth

Phase field modeling of fracture has been in the focus of research for over a decade now. The field has gained attention properly due to its benefiting features for the numerical simulations even for complex crack problems. The framework was so far applied to quasi static and dynamic fracture for brittle as well as for ductile materials with isotropic and also with anisotropic fracture resistance. However, fracture due to cyclic mechanical fatigue, which is a very important phenomenon regarding a safe, durable and also economical design of structures, is considered only recently in terms of phase field modeling. While in first phase field models the material’s fracture toughness becomes degraded to simulate fatigue crack growth, we present an alternative method within this work, where the driving force for the fatigue mechanism increases due to cyclic loading. This new contribution is governed by the evolution of fatigue damage, which can be approximated by a linear law, namely the Miner’s rule, for damage accumulation. The proposed model is able to predict nucleation as well as growth of a fatigue crack. Furthermore, by an assessment of crack growth rates obtained from several numerical simulations by a conventional approach for the description of fatigue crack growth, it is shown that the presented model is able to predict realistic behavior.

Cost and time reduction of concrete slabs construction by selecting the most economical structural design

In construction industry, projects are usually completed in a budget more than what is estimated for, finished in a time more than the contracted time, not executed properly according to the specifications, and not constructed with the client satisfaction. The thing that causes lowering the profits of contractors, clients losing, time to market prolonging, and other consequences. Projects execution on or under the budgeted money requires valid practices, precise decisions, good strategies, and needs developing new techniques, such as cost reduction technique. Thus, this paper mainly aims to relieving part of the big concerns of those who specialized in construction media respecting construction cost overruns by determining the most economical structural design, which can be realized by studying, quantifying, analysing cost, and comparing a number of structural elements with different dimensions, different design combinations, and different materials proportions. Then, the optimum structural element, the element that meets the design requirements, comprises the least materials quantities, and costs least, was selected in case to achieve an economical construction.

Machine learning based stochastic dynamic analysis of functionally graded shells

This paper presents stochastic dynamic characterization of functionally graded shells based on an efficient Support Vector Machine assisted finite element (FE) approach. Different shell geometries such as cylindrical, spherical, elliptical paraboloid and hyperbolic paraboloid are investigated for the stochastic dynamic analysis. Monte Carlo Simulation is carried out in conjunction with the machine learning based FE computational framework for obtaining the complete probabilistic description of the natural frequencies. Here the coupled machine learning based FE model is found to reduce the computational time and cost significantly without compromising the accuracy of results. In the stochastic approach, both individual and compound effect of depth-wise source-uncertainty in material properties of FGM shells are considered taking into account the influences of different critical parameters such as the power-law exponent, temperature, thickness and variation of shell geometries. A moment-independent sensitivity analysis is carried out to enumerate the relative significance of different random input parameters considering depth-wise variation and collectively. The presented numerical results clearly indicate that it is imperative to take into account the relative stochastic deviations (including their probabilistic characterization) of the global dynamic characteristics for different shell geometries to ensure adequate safety and serviceability of the system while having an economical structural design.

Lightweight aggregate concrete produced with crushed stone sand as fine aggregate

Lightweight aggregate concrete mixtures incorporating 0, 10, 20, and 30 weight percent replacement of normal-weight aggregate with lightweight aggregate and crushed stone as fine aggregate were tested at 7, 28, 56, and 90 days for various strength and durability characteristics of hardened concrete. Test results indicated that compressive, flexural, and split tensile strengths and static modulus of elasticity of concrete mixtures reduced with an increase in the percent replacement of normal-weight aggregate with lightweight aggregate. Furthermore, the volume of permeable voids and hence moisture sorption in lightweight aggregate concrete reduced as the lightweight aggregate content was increased pointing at the enhanced durability of the lightweight aggregate concrete mixtures. A significant reduction in dry density of hardened concrete was recorded due to the inclusion of lightweight aggregate in concrete mixtures. Considering the strength and reduction in dry mass, 20 wt.% replacement of normal-weight aggregate with lightweight aggregate is considered to be an optimum level. Reduced density of lightweight aggregate concrete mixtures is viewed as a major source of economical design of structural members as the lower concrete density will result into a reduction of self-weight of the structural members, which will allow the economical structural design of such members with smaller cross-sections. Test results of this work also showed the viability of 100% replacement of desert sand with crushed stone sand as fine aggregate towards the production of lightweight aggregate concrete.

Effect of dynamic soil–structure interaction on the seismic response of bridges with elastomeric bearings

The influence of soil–structure interaction (SSI) on the responses of an isolated bridge structure, subjected to seismic excitation, is investigated. The study considers the laminated rubber bearing and the lead rubber bearing for the seismic isolation of the bridge. The specific objective of the study is to evaluate the performance of the isolators and to investigate the effect of SSI on the seismic performance of the isolated bridge. A significant variation in the responses and the performance of the isolators are observed when the SSI is considered. It is concluded that consideration of SSI can lead to a more realistic structural modeling and more economical design of structures.

Torsional Restraint Problem of Steel Cold-Formed Beams Restrained By Planar Members

The effect of continuous or discrete lateral and torsional restraints of metal thinwalled members along their spans can positively influence their buckling resistance and thus contribute to more economical structural design. The prevention of displacement and rotation of the cross-section results in stabilization of the member. The restraints can practically be provided e.g. by planar members of cladding supported by metal members (purlins, girts). The rate of stabilization of a member can be quantified using values of shear and rotational stiffness provided by the adjacent planar members. While the lateral restraint effected by certain shear stiffness can be often considered as sufficient, the complete torsional restraint can be safely considered in some practical cases only. Otherwise the values of the appropriate rotational stiffness provided by adjacent planar members may not be satisfactory to ensure full torsional restraint and only incomplete restraint is available. Its verification should be performed using theoretical and experimental analyses. The paper focuses on problem of steel thin-walled coldformed beams stabilized by planar members and investigates the effect of the magnitude of the rotational stiffness provided by the planar members on the resistance of the steel members. Cold-formed steel beams supporting planar members of cladding are considered. Full lateral restraint and incomplete torsional restraint are assumed. Numerical analyses performed using a finite element method software indicate considerable influence of the torsional restraint on the buckling resistance of a steel thin-walled member. Utilization of the torsional restraint in the frame of sizing of a stabilized beam can result in more efficient structural design. The paper quantifies this effect for some selected cases and summarizes results of numerical analysis.

Damage assessment for reinforced concrete frames subject to progressive collapse

Due to increasing threats from terrorism, progressive collapse modeling is gaining popularity with the objective of simulating the collapse process of the whole or partial structural system. In order to conduct an accurate progressive collapse modeling, one needs to identify damaged members and to trace the propagation of damage. Hence, good damage assessment criteria are vital to the modeling and analysis. Only with reliable damage assessment criteria, realistic collapse mechanisms of structures can be simulated. It can then provide useful guidance for a better and more economic structural design against progressive collapse. This paper presents a set of damage assessment criteria that can be easily implemented for progressive collapse analysis of reinforced concrete (RC) frames. Flexural, shear and axial damage criteria for RC members are separately proposed incorporating axial-shear-flexural interactions in the analysis. Three scaled moment-resisting RC frame tests were conducted to validate the proposed flexural and axial damage criteria. Three shear-dominant damaged tests were also modeled to assess the proposed shear damage criteria. The results obtained show that the proposed damage assessment criteria are effective and reliable for progressive collapse analysis of RC frames.

Pryout failure capacity of single headed stud anchors

Concrete pryout failure mode, which occurs for relatively short and stocky cast-in headed studs or post installed anchorages, has been investigated only to a limited extent in the past. The increasing use of such anchorages in engineering practice emphasizes the need to clarify the pryout failure mechanism and to formulate design rules that assure safe and economical structural design. Currently used design provisions are based mostly on analysing push off test data, which were focusing on composite beam design. The database (Jebara and Ožbolt in Vergleichsanalyse von Bemessungskonzepten fur Querbelastung und Scherversuche mit ruckwartigem Betonausbruch (pryout). (Literature review of design concepts for shear loaded tests with pryout failure), Internal Report/November 2011) including recently reported shear tests is lacking in pryout in-the-field tests with systematic variation of anchor embedment depth and diameter. In order to clarify the behaviour of cast-in headed studs and anchor bolts, shear tests were performed on single cast-in headed studs (Jebara and Ožbolt in Tragverhalten von angeschweistem gedrungenen Kopfbolzenverankerungen in der Flache unter Querlast, experimentelle Untersuchung, (Bearing mechanism of stocky studs in-the-field under shear load, experimental Investigation), Internal Report/November 2013). In the present article the experimental results, pryout failure mechanism and proposed pryout capacity equation for single anchor under pure shear load are presented, discussed and compared with current design formula.

A simulation-based method for reliability based design optimization problems with highly nonlinear constraints

Abstract Reliability-based design optimization (RBDO) is a topic of interest in the design of economical structures. It allows designers to effectively reach a balanced cost-safety configuration in the design of structures. In this study, a simulation-based method is presented for RBDO problems in which the design variables are treated as random variables. The method works by uniformly distributing samples in the design space and employing a feature that allows the designer to obtain the optimum design solution by performing only one simulation run. Moreover, the proposed feature also helps the designer to use the results of aforementioned run to provide multi-level design solutions when the arrangement of the design problem is changed. The robustness and accuracy of the method are examined by solving design problems with highly nonlinear constraints and comparing with the results of common RBDO methods. The results confirm the robustness of the method for highly nonlinear problems with different design arrangements.

Evaluation of the influence of design factors on the CO2 emissions and costs of reinforced concrete columns

Reinforced concrete (RC) is one of the structural materials that produce environmental pollution. The objective of this study is to present design guidelines for reducing CO2 emissions or costs associated with structural materials in the structural design phase of RC columns. After identifying the cross-sections of RC columns with the minimum CO2 emissions or costs while satisfying the structural design conditions via a parametric study, the influence of the design factors (i.e., concrete strength, steel reinforcement strength, cross-section size, and amount of steel reinforcement) on the CO2 emissions and costs of RC columns are investigated. The results confirm that increasing the strength and amount of steel reinforcements is efficient for sustainable design, whereas increasing the strength of the structural materials and the amount of concrete is efficient for economical structural design.

Structural performance and cost analysis of wind-induced vibration control schemes for a real super-tall building

To evaluate different energy dissipation systems used to control wind-induced vibrations of a 456 m super-tall building in fluctuating wind excitations, the finite element (FE) method was employed to simulate the dynamic responses of the building. A series of wind tunnel pressure tests were conducted on a 1:450 scale model to determine the wind forces acting on the super-tall building. A FE model was also constructed and mass, damping and stiffness matrices were subsequently formulated as an evaluation model for numerical analysis. The evaluation model was further simplified to a state reduced-order system using the state order reduction method. Three different vibration control schemes, namely a tuned mass damper (TMD) system, a system containing only nonlinear viscous dampers and a hybrid control system combining TMD and viscous dampers, were examined through simulations with respect to their effectiveness in reducing the accelerations at the top of the building. Furthermore, a cost evaluation was conducted to determine the most economical structural design and vibration control scheme. The results show that the wind-induced vibrations of the analysed building can be controlled effectively by all the three examined schemes, while the hybrid control scheme and the scheme containing only viscous dampers further reduce the wind-induced vibration to satisfy a more stringent criterion for a six-star hotel. In addition, the hybrid vibration control scheme is also the most cost-effective among the examined schemes.

Technical Analysis of Optimal Design for Building Structure Considering Cost Constraint of Project

Cost of building structure takes a large proportion of total construction investment. Investors also come to realize that different structural designs affect project cost, which means the higher demand for structural design institutes, because it requires structural designers to work out safe, suitable, perdurable and economic structural design by either meeting current design codes, or considering structure cost constraints and architectural design scheme. One way of controlling the structural engineering cost is to optimize the structural design. This article analyzes the factors which affect the structural costs and optimal design methods, and it discusses the relationship of structural material quantity and structural safety. This article aims to provide reference and guidance for structural designer’s optimization.

부재 종류에 따른 고강도 강재의 경제성 평가

현재 국내에서 생산되는 구조용 강재의 강도는 크게 5가지로 구분할 수 있다. 경제적인 구조설계를 하기 위하여 적절한 강도의 선정이 우선적으로 요구되는데 현재는 이와 관련된 기존 자료가 충분치 않은 상태이다. 최근, 국내에서 항복강도가 650MPa인 고강도 강재가 개발되어 구조용 강재의 강도 범위가 더 커졌기 때문에 부재 종류별 강재의 선택에 따른 경제성의 차이도 더 커졌을 것으로 예상된다. 본 논문에서는 경제적인 구조설계에 도움이 되도록, 항복강도 235MPa, 325MPa 및 650MPa 강재를 다양한 구조부재에 적용함으로서, 고강도 강재 적용에 따른 부재 종류별 경제성을 분석하였다. The structural steel produced in domestic is classified into 5 grades. For economic structural design, the structural engineers need to choose optimal steel grades for structural member types, but the related data is not sufficient. Recently, high strength steel with yield strength in 650MPa was developed in domestic. It provides structural engineers with the wider range of structural steel strength, which leads to the larger difference in economic evaluation. In this paper, the economic evaluation of high-strength steel in building structures is investigated, by applying structural steel with 235MPa, 325MPa and 650MPa in yield strength to various types of structural members, and can be used as basic data for economic structural design.

A micromechanically motivated finite element approach to the fracture toughness of silicon nitride

Abstract Silicon nitride is often used, when high fracture toughness and strength is needed. For a safe and economic structural design with this material, a prediction of its resistance against thermal and mechanical loads is important. The finite element method together with a continuum damage mechanics model allows for such calculations. The parameters of the suggested model have been adjusted to three-dimensional micromechanical finite element simulations, which include models for the microstructure, the thermoelasticity and the fracture. The material model is used for four-point bend test simulations. The results are compared to recent experiments.

Optimum structural modelling for tall buildings

SUMMARYIt is a common practice to model multi‐storey tall buildings as frame structures where the loads for structural design are supported by beams and columns. Intrinsically, the structural strength provided by the walls and slabs are neglected. As the building height increases, the effect of lateral loads on multi‐storey structures increases considerably. The consideration of walls and slabs in addition to the frame structure modelling shall theoretically lead to improved lateral stiffness. Thus, a more economic structural design of multi‐storey buildings can be achieved. In this research, modelling and structural analysis of a 61‐storey building have been performed to investigate the effect of considering the walls, slabs and wall openings in addition to frame structure modelling. Sophisticated finite element approach has been adopted to configure the models, and various analyses have been performed. Parameters, such as maximum roof displacement and natural frequencies, are chosen to evaluate the structural performance. It has been observed that the consideration of slabs alone with the frame modelling may have negligible improvement on structural performance. However, when the slabs are combined with walls in addition to frame modelling, significant improvement in structural performance can be achieved. Copyright © 2012 John Wiley & Sons, Ltd.