Design Capacity Research Articles

Evaluation of Link Overstrength Factor for the Seismic Design of Eccentrically Braced Frames

In eccentrically braced frames (EBFs), inelastic behavior is only permitted in the links. All members, except for the links, are designed according to the capacity design concept by using the link overstrength factor, Ω, so that they remain elastic even when the links develop their ultimate strength (including the strain-hardening effect). AISC 341 specifies that the Ω factor of link members must be 1.25 for beam and brace design and 1.1 for column design. In this study, the relevance of the current Ω factor was investigated. A total of 471 K-braced EBF systems with various conditions were designed using a multi-objective optimization technique, and nonlinear dynamic analyses were performed to evaluate the Ω factor. The results indicate that it is reasonable to use the current Ω factor for the design of beam outside link and brace; however, it leads to an overestimation of axial force in columns, especially in the lower stories of tall buildings. From the analysis results, a new Ω factor equation for column design was proposed. It was demonstrated that the structural quantities of 15-story frames designed using the proposed equation decreased by an average of 19% compared to those designed using the current Ω factor.

Retrofitting Techniques: A Comprehensive Review

The need of improving the structural performance of old constructed structures has grown significantly as a result to increasing concerns over deteriorating infrastructure, changing building codes and natural calamities. Retrofitting is one of the best processes to make an existing building safe against future coming earthquakes or other environmental forces. Retrofitting is the process of adding new features to older buildings, bridges and many other structures. It aims to strengthen the structure, to satisfy the load carrying capacity of structure and seismic design. This paper includes study of research papers published in past years related to various methods of retrofitting such as seismic retrofitting, retrofitting by glass fibers, retrofitting by chemicals such as epoxy resin and many other methods. Structures lose their strength in some years, some structures are important in view of public, social or any historical. Retrofitting helps to increase the strength, resistivity and lifespan of structure. Key Words: Retrofitting, Strength, Safety.

Performance-based design of strip foundation considering the full effect of ground improvement

Ground improvement is an effective way to improve the bearing capacity of a shallow foundation. However, the benefit of reducing uncertainties in soil parameters for shallow foundation design is rarely recognized. This study investigated the full effect of rapid impact compaction (RIC) on a strip foundation design. The finite difference method coupled Monte Carlo simulation were used to calculate the failure probability and the required width of the strip foundation, where the friction angle of soil was treated as a random variable. The results show that the foundation width reduces by 48.5% when considering the full effect of RIC, and a significant part of the reduction came from the decrease in the uncertainty of friction angle. Although the adopted relationship between the friction angle and tip resistance of cone penetration test affects the designed width of the foundation, the full effect of ground improvement contributed by the uncertainty reduction of soil parameters is still significant. The implication of the present study provides a basis for the performance-based bearing capacity design of shallow foundations.

Numerical and experimental investigation on angle multiple slit bolted connections for precast wall panels

Flat Multiple Slit Devices (MSDs) have been introduced in steel constructions located in earthquake-prone areas as compact hysteretic dampers connected to braces, and were further proposed to be employed also in other structural typologies, including aligned precast concrete walls. Nevertheless, similar angle connections needed for horizontal joints of orthogonal walls are not tackled in literature. The shape of MSDs, obtained by selective weakening by removing part of the steel area of flat plates, may allow to attain a highly ductile and stable dissipative behaviour, given local plate buckling is avoided, protecting the bolted joints through capacity design. Laser cutting as an alternative to mechanical milling introduces the possibility to easily optimise the shape of the slits in order to attain better performance under laterally imposed cyclic load. This paper analyses the application of right-angle-bent MSDs for the horizontal connection between orthogonal precast walls typical of panel structures with rigid diaphragms. In particular, bolted angle plates with hourglass-shaped multiple slits obtained after laser cutting are investigated numerically via non-linear finite shell elements and experimentally with original cyclic tests. The effect of the aspect ratio of the plate and of the restraint condition, possibly affecting the performance under imposed shear deformation due to the presence of the bent corner, is investigated by parametric analysis. Finally, general design rules and recommendations are presented.

Seismic behavior of hybrid post-tensioned special steel moment frames

Generally, conventional moment-resisting frames are prone to substantial residual displacements. To overcome this disadvantage, self-centering systems were introduced. Post-tensioned self-centering (PTSC) moment-resisting systems are a variation of conventional moment-resisting systems that drastically reduce the large residual displacements of the moment frames. However, one of the uncommon drawbacks identified in PTSC systems is their low energy dissipation. This study aims to compensate for this by innovatively combining conventional self-centering systems with special moment-resisting frames (SMRF) in various formats to retain the advantages of both systems. Another disadvantage of PTSC systems is the high cost and complexity of the structural design procedure required to maintain an elastic response in the framing beam-column elements. To address this issue, a practical and cost-effective design procedure was proposed. The study also included the influence of different dual SMRF-PTSC frame actions and base column connection types. A set of 35 structures comprising 4, 8, 12, and 16-story buildings were considered for nonlinear static/dynamic analysis and seismic response assessment. The nonlinear static analyses were carried out in a cyclic format due to the self-centering characteristics of the system. Additionally, 22 far-field records per FEMA P695 were chosen for the time history analyses. The results show that structures equipped with post-tensioned self-centering connections (PTSC) designed according to the proposed procedure are successful in drastically decreasing residual drifts. However, the total elimination of residual drifts relies on providing a self-centering connection for the base level columns and considering an overstrength factor for the base level columns' moment capacity design. The proposed value in this investigation was derived as 5, which significantly strengthens the base level columns while resulting in an overall notably cost-efficient PTSC-equipped frame. In the case of dual frames, the conventional SMRF spans should not exceed the number of PTSC-equipped spans, as doing so will diminish the self-centering characteristics of the lateral system.

Features and prospects of the Russian civil aircraft industry development under sanctions pressure from Western countries

The specifics and prospects of development of the Russian civil aircraft industry under sanctions pressure from Western countries have been considered. The study analyzes secondary data from open sources. The main provisions and conclusions of the work are as follows. The United States of America and its European satellites have imposed comprehensive sanctions against Russian air carriers, including a ban on aircraft deliveries. Lessors who owned foreign airplanes made demands for their return, and foreign registrars suspended airworthiness certificates for domestic airplanes. Western sanctions against Russian airlines have caused significant damage to Russia, but have also become a serious stimulus for the domestic aviation industry development. Significant time and investment will be required to resolve the problems encountered. Russia has the necessary potential to restore the aviation industry and ensure safe passenger and cargo transportation in the required volume. The country is currently working systematically to revitalize the industry, implementing advanced developments and establishing serial production of a wide range of civil aircraft. The success of the domestic aviation industry development depends mainly on the state’s efforts, as it has the access to almost all production and design capacities. In addition, effective measures are needed to influence the air transportation industry in order to balance the supply and demand for aircraft.

Seismic behaviour and design of a tall mixed reinforced concrete–steel structure supporting an oil refinery reactor

AbstractThis study investigates the seismic behaviour of a special mixed reinforced concrete-steel structure that supports an oil refinery reactor. The structure is 64.90 m tall and consists of three parts: (a) a reinforced concrete frame basement; (b) a steel braced frame that supports the oil reactor and (c) the steel reactor itself. A three-dimensional model of the structure is created to perform static non-linear (pushover) analyses in order to obtain the capacity curves and understand the overall inelastic behavior of the structure. The results of the pushover analyses reveal that the structure exhibits similar inelastic behavior in both horizontal directions and satisfies the capacity design principles. The structure exhibits limited ductility considering the fact that has been designed with a behavior factor of q = 1.5 and primary damages are expected mainly in concrete members. Subsequently, dynamic non-linear time-history (NLTH) analyses are performed utilizing the three translational components of three seismic motions recorded during past earthquakes. These results involve: (i) the maximum values for displacements, accelerations and base shears; (ii) the maximum stresses at critical points of the oil refining reactor and (iii) the formation of plastic hinges at columns, beams and braces of the structure. Contrary to pushover analyses, NLTH analyses revealed the development of plastic hinges, hence seismic damage, that do not follow the desirable formation pattern. Moreover, the accelerations and displacements observed are expected to cause failure of the piping and mechanical equipment, while local failure of the high-stress areas of the shell of the reactor may be possible. Localized strengthening might be necessary to avoid repair works and downtime after such seismic event.

Collaborative Design Capacity for Enactment Framework: An Analytic Tool for Conceptualizing Pedagogical Design Capacity Within Social Context

ABSTRACTThis study examines an urban middle school teacher design team's capacity for creating integrated science, technology, engineering, and mathematics curricula. Using Brown's pedagogical design capacity (PDC) theory, which highlights interactions between personal and curricular resources, this paper introduces an extended framework that includes social interactions as key influences on teachers' design abilities. Findings show that individual teachers' spontaneous curriculum modifications were adopted by the team, becoming collective resources for ongoing redesign and improving their design capacity. Teachers effectively used each other as resources to address unexpected challenges in integrating science, engineering, and mathematics concepts. Three types of social interactions were identified as collaborative resources: (i) Storytelling: sharing experiences to make abstract concepts actionable for curriculum development; (ii) Protocols: structured methods to address curricular problems related to integration; and (iii) Assessment “for” curriculum redesign: using assessment tools to inform and improve the curriculum. The Collective Design Capacity for Enactment framework is introduced to describe PDC within a social context, highlighting the importance of social interactions in bridging curriculum use and development, thus extending the literature on PDC.

An universal energy-matching design and regulation method for combined cooling, heating, and power (CCHP) systems in different scenarios

In this study, the impact of the coupling matching mechanism between the systems and the users on the energy-saving characteristics of the systems was analyzed based on a universal representation and computation method to identify the energy saving potential of the systems. The physical model was detailed derived for the relationship between the load supply and user demands under different capacity design modes and operation strategies to construct a universal coupling matching diagram, and the impact of the coupling matching parameters (operational energy efficiency, load matching degree, etc) on system integration and operation in different energy use scenarios was quantitative analyzed to illustrate the inherent mechanism of energy saving characteristics. In addition, the coupling mechanism between the systems and the users from a global perspective was reconstructed, and a coupling method of capacity design factor and dual source regulation was proposed to realize the collaborative integration of centralized energy supply systems, combined cooling, heating, and power systems and load demands, as well as the active regulation of the internal cascade utilization of the systems, so as to improve the energy saving potential of the systems under all operating conditions. Finally, a case analysis and method verification were conducted using typical summer days at Kunming hotel as an example. The results show that the coupling matching relationship is the internal mechanism that affects the energy saving of the systems, and the average energy saving rate of the whole day can be increased by 7.45% through collaborative integration and active regulation.

Study on the dynamic characteristics of the head cover-bolts-stay ring of a variable-speed pump-turbine

Abstract The design and operation of variable-speed pump-turbine units is more difficult than that of conventional units due to their adjustable speed, frequent start stop, and forward and reverse operation. Due to the development of variable-speed pump-turbines towards variable-speed, high head, and large capacity, the vibration instability caused by frequent switching between turbine and pump operating conditions is more prominent. The study on the dynamic characteristics of the head cover-bolts-stay ring system is an important guarantee for the long-term safe and stable operation of the units. This article uses the finite element method to conduct modal analysis on the head cover-bolts-stay ring system of a variable-speed pump-turbine. The natural frequency and mode shape are analyzed, and resonance analysis is carried out in combination with the dynamic and static interference characteristics of the variable-speed unit. The research results show that the dynamic and static interference frequency of the unit during the variable-speed process may be close to the natural frequency of the head cover-bolts-stay ring system, which needs to be paid attention to during operation. The results and findings in this article provide theory and practical basis for the research and design of high head, large capacity, and variable-speed pump-turbine units.

Shear capacity prediction of carbon-fibre-reinforced polymer mesh fabric (CFRP-MF) stirrups reinforced concrete beams

Fibre-reinforced polymer mesh fabric (FRP-MF) is an effective substitute for normal steel stirrups in concrete to prevent steel corrosion in reinforced concrete (RC) structures. Nevertheless, methods for calculating the shear resistance of RC members rehabilitated in shear with FRP-MF configurations are lacking. Moreover, the methods for quantitative analysis of the shear contribution caused by the cracking control effect produced by CFRP-MF longitudinal FRP strips are unclear. In this paper, a mechanics-based segmental model is presented based on partial interaction analysis considering both transverse FRP strips and longitudinal reinforcements. By incorporating the carbon-fibre-reinforced polymer mesh fabric (CFRP-MF) stirrups into this model, a shear strength model was proposed and extended for design purposes in a closed form. In addition, the modified compression field theory (MCFT) model considering the shear strength of concrete in compression and the shear friction model (SFM) in the literature were appropriately modified and used for comparison with the segmental model. It should be noted that if the tensile strength of the longitudinal strips was added into the corresponding calculation formulas, it would cause the difference between the proposed novel models with the previous models. Finally, the shear strength of 14 CFRP-MF reinforced concrete beams were evaluated using these three models. The average ratios of the experimental values of the CFRP-MF RC beams to the shear capacity predicted by the modified segmental model, MCFT with the shear contribution of compressed concrete and SFM were 1.30, 1.19 and 1.19, respectively. It turns out that the modified mechanics-based segmental model yields the minimum discreteness based on the experiment results. This study can provide shear capacity calculation and design reference of RC beams with longitudinal FRP strip reinforcements for researchers and engineers.

Cotton Ginners Handbook – Packaging Lint Cotton

Bale packaging is the final step in processing cotton at the gin. Bale packaging is critical to protecting and preserving the quality of the ginned lint during shipping and storage before consumption at the textile mill. Smooth operation of the bale press and associated systems is required for the efficient operation of the ginning plant. Properly shaped bales are important to the safe and efficient handling and storage of bales. The bale press, condenser, and hydraulic systems must be sized to match the design capacity of the ginning plant in order to maximize capacity. Bale presses may be designed to produce Universal Density bales or High Density bales, although only Universal Density bales are currently approved by USDA. Proper maintenance of the bale press and related systems translates into reduced downtime for the ginning plant. All bale packaging, including the bale covering and strapping or ties, must be approved by the Joint Cotton Industry Bale Packaging Committee in order for the bales to be eligible for collateral in the Commodity Credit Corporation loan program. This manuscript discusses the individual components of a cotton gin bale packaging system and settings to ensure the consistent production of uniform bales of cotton lint.

Moment capacity of cold-formed steel channel beams with edge-stiffened and unstiffened elongated web holes

Cold-formed steel channel beams (CFSCB) often incorporate web holes to accommodate building services, but this reduces their moment capacity due to decreased web area. Recent studies have shown that a new type of edge-stiffened web holes can enhance moment capacity, especially for circular ones, and can now be extended to elongated web holes. However, there hasn't been research on the moment capacity of such CFSCB with elongated web holes. This paper uses finite element analysis (FEA) to examine the moment capacity and flexural behaviour of such beams with both elongated edge-stiffened web holes (EEH) and elongated unstiffened web holes (EUH). After validating the FEA models against experimental results available in the literature, a comprehensive parametric study involving 2160 FEA models was conducted. Results showed that CFSCB with EEH exhibited, on average, a 9% increase in moment capacity compared to those with EUH. Additionally, the parametric results were compared with the design capacities calculated from existing standards for CFSCB with unstiffened web holes. It was found that the current design equations for CFSCB with EUH were overly conservative by 9% and 66%, on average, for distortional or local buckling failure and lateral-torsional buckling failure, respectively. Consequently, modified Direct Strength Method (DSM) design equations were proposed to calculate the moment capacity of CFSCB with both EEH and EUH. Finally, a reliability analysis was conducted to assess the accuracy of the proposed design equations.

Capacity Design of Cascaded Diode Rectifier-MMC Based HVDC for Offshore Wind Farm Integration

Capacity Design of Cascaded Diode Rectifier-MMC Based HVDC for Offshore Wind Farm Integration

THERMAL TECHNOLOGICAL CONDITION OF IVG.1M RESEARCH REACTOR CORE UNDER VARIOUS OPERATING MODES

The relevance of the study is related to the determination of the thermal characteristics of the IVG.1M research reactor core with the low enriched uranium fuel under the nominal and design operating modes. The thermal technological condition of the IVG.1M research reactor during the start-up are determined by the readings of the temperature, pressure and coolant flow sensors of the information and measuring system. The indirect methods including the computer simulating ones are used to determine the temperature of the core structural materials and the distribution of the coolant temperature by the height of the fuel assembly. The research has been carried out using the method of the finite element analysis using the ANSYS Fluent software package. The study goal was to verify the adequacy of the calculation methodology and obtain the calculated data on the temperature distribution in the fuel assembly in the reactor power range from the nominal to design one. The article presents a description of the IVG.1M reactor, the research methodology, computer model, simulation results and the comparison of the calculated data with the experimental ones. The study scientific novelty consists in determining the temperature conditions of the fuel rods during the reactor operation at various levels of the design capacity with a conservative approach to the cooling conditions. The significance of the research results lies in the fact that a computer model can be used to determine the characteristics of the IVG.1M reactor core under the reactor various operating modes and to analyze the thermohydraulic processes in the fuel assembly.

Performance and reinforcement of air-cooled embankments traversing degrading permafrost of the Qinghai-Tibet Plateau

The reliable operation of railway embankments traversing degrading permafrost regions is challenged by climate warming. This study examines performances of four main types of railway embankments on the Qinghai-Tibet Plateau in thermally stabilizing permafrost foundation over warm permafrost using numerical modelling and 10-year monitoring data. Then, a reinforcement measure that combines a thermal conductivity variable system (TCVS) was designed to improve the cooling capacity of the crushed-rock sloped embankment (CRSE) by countering the heat absorption of slopes during summers. A coupled thermal-fluid-solid model was built to simulate and assess the cooling performance and reinforcing capacity of the new design. Results show that the crushed-rock embankments can produce convection cooling on the permafrost subgrade but the performances vary with different structures. The CRSE has insufficient cooling capacity to withstand the underlying permafrost degradation in warm permafrost regions. The optimized CRSE that combines the TCVS can effectively cool the underlying warm permafrost and decrease the shady-sunny slope effect under a warming climate, and can be used as an effective reinforcement measure. This study confirms the application of air-cooled embankments in protecting permafrost subgrade and provides guidance for structural design of embankment traversing degrading permafrost.

Design and water-saving capacity of planting roof with compound irrigation and stab-resistant function

With the continuous development of urban construction, the contradiction between human settlement and the natural environment is becoming increasingly prominent. Increasing the green area and improving the local environment and microclimate through roof planting can effectively alleviate this contradiction. On the basis of the research on the current situation and challenging problems of planting roofs, a comprehensive study of construction, stab-resistance, waterproofing, irrigation and plant landscape is combined with a designed roof case. Research results show that the planting roof is simple in construction, has high resistance to plant root thorns, can take into account the function and aesthetics of plant landscape design, and saves irrigation water by more than 60%, which will help the popularization and promotion of urban planting roofs.

Theoretical model of ultimate shear capacity and flexural capacity design method of boundary elements for reinforced concrete frames with steel plate shear walls

AbstractThe steel plate shear walls (SPSWs) have been proven effective in reinforced concrete frames (RCFs) as a lateral force‐resistant structure. Despite of advancements, accurately predicting the ultimate shear capacity of RCFs with SPSWs remains challenging using current simplified models. Additionally, the flexural capacity design procedure for the boundary elements (beams and columns) in previous studies of RCF‐SPSWs involved intricate iterative procedures, hindering its widespread implementation. To address the two issues, this paper investigates the pushover responses and the plate‐frame interaction (PFI) of an RCF‐SPSWs system using theoretical and numerical methods. There are three main contributions. First, a theoretical model of ultimate shear capacity for RCF‐SPSWs is proposed, which can also be used to predict shear contributions of boundary frames in RCF‐SPSWs. Calculation errors for ultimate shear capacity of RCF‐SPSWs and shear contribution from the boundary frame are only 3.7% and 6.7% respectively, which are reduced dramatically compared with the traditional model. A simplified schematic diagram for the global collapse mechanism (uniform distribution of plastic hinges within a structure) of RCF‐SPSWs is developed to facilitate the calculation of internal work and reaction forces. Secondly, a flexural capacity design method for the boundary elements to avoid in‐span plastic hinges is proposed. The proposed method enables the achievement of direct estimation of the flexural demands that could trigger a global collapse mechanism, all without intricate iterative procedures. The applicability of current assumptions for the design of steel boundary frame in RCF‐SPSWs system is discussed, and engineering suggestions are provided to ensure safer and more economic designs. Comparison results confirmed the applicability of the proposed design method, which can be adopted to achieve the global collapse mechanism for RCF‐SPSW system. Thirdly, impacts of yielding panel actions on the flexural capacity of boundary elements of RCF‐SPSWs are clarified. Comparison results demonstrated that adding SPSWs to an RCF alters the axial force on boundary elements and significantly impacts the flexural capacity. A design suggestion is made to emphasize the importance of avoiding the balanced failure of boundary elements. The proposed theoretical model can be used to economize the cross‐section of boundary elements in RCF‐SPSWs system under seismic loads due to accurate prediction of their shear contribution; the proposed flexural capacity design method can achieve a global collapse mechanism, and thus the structural safety and energy dissipation capacity are improved; moreover, the building design efficiency is also improved due to avoidance of intricate iterative procedures.

Code-based brittle capacity models for seismic assessment of pre-code RC buildings: comparison and consequences on retrofit

The existing Reinforced Concrete (RC) buildings stock is often characterized by a significant seismic vulnerability, due to the absence of capacity design principles, even in regions with high seismic hazard, such as Italy. Approximately 67% of existing RC buildings in Italy have been designed without considering seismic actions (GLD), resulting in very low transverse reinforcement amount in beams and, particularly, in columns. Additionally, beam-column joints typically totally lack stirrups. Consequently, shear failures under seismic actions are very likely for this pre-code building typology, often limiting their seismic capacity. However, the assessment of shear failures in beams/columns or joints varies significantly from code to code worldwide. The main goal of this work is to quantify the impact of different code-based brittle capacity models on the seismic capacity assessment and retrofit, focusing on GLD Italian pre-1970 RC buildings. This comparative analysis is carried out by first considering three current codes, emphasizing their, even significant, differences: European (EN 1998-3-1. 2005), Italian (D.M. 2018), and American (ASCE SEI/41 2017) standards. Then, shear capacity models prescribed by the current drafts of the next generation of Eurocodes are implemented and compared to the current models. The assessment includes: (i) a parametric comparison among models; (ii) the evaluation of case-study buildings capacity in their as-built condition and after shear strengthening interventions. The latter is performed on 3D “bare” models, due to the lack of practical guidance in most codes on modelling masonry infills.

A district-level building electricity use profile simulation model based on probability distribution inferences

District-level building energy systems play a significant role in urban energy networks in the future. Understanding the key distributive features of district electricity use profiles is essential for the optimal planning and design of energy networks. Due to the diversity of building electricity use characteristics, the district-level electricity use profile exhibits a prominent “peak staggering effect.” Current physics-based and statistical models cannot fully represent realistic distributions and the uncertainties of district profiles. Thus, it is critical to quantitatively investigate the changing patterns and distributive features of electricity use profiles at various district levels. This paper proposes a novel approach for district building electricity use profile simulation. Probability distribution inference methods integrating Gaussian Mixture Model (GMM)/lognorm distribution fitting, singular value decomposition (SVD)-based feature transformation, and distribution addition theorems have been proposed to generate the feature parameters of electricity use profiles at various district scales, thus generating simulated district electricity use profiles. The performance of the proposed model was validated using engineering-informed metrics, including peak demands, load duration curves, and standard deviations of the load parameters. The results of the case study suggest that the average relative error of the 99 % peak demand is reduced from 17.60 % in the baseline model to 3.48 % in the proposed model, the average relative error of the duration of 2Qm reduced from 40.82 % in the baseline model to 0.99 % in the proposed model, and the average relative error of the standard deviation of load parameters was reduced from >100 % in the baseline model to <35 % in the proposed model. The results indicate a better quantification of district electricity use distributions and uncertainties, providing practical tools to support the capacity design and optimization of integrated district energy systems.