Alternative Load Research Articles

Simplified analytical method for the robustness assessment of precast reinforced concrete structural systems

The article presents the simplified implementation of alternative load path method based on the energy balance approach. This method should be used to check the global resistance of a damaged structural system after the occurrence of an accidental event. Basic assumptions of simplified analytical models for modelling resistance of horizontal ties in a damaged structural system, taking into account the membrane (chain) effects, were presented. An approach to modelling the dynamic resistance of a damaged structural system based on the energy balance method is described. Calculated dependencies for checking the robustness of a prefabricated multi-storey building with hollow-core slabs after the loss of the central column are proposed and considered using an example. On the considered example, a comparison of the required tie sections area with the dynamic resistance designed using the energy balance method (EBM) and according to the current standards, and a statistical assessment of the reliability of the load-bearing capacity models are carried out. In the end, a brief algorithm for the simplified calculation of the dynamic resistance of a damaged structural system is proposed.

Assessment on the Progressive Collapse Resistance of a Long-Span Curved Spatial Grid Structure with Main Trusses

The progressive collapse resistance of the terminal building of Zhongchuan Airport in Lanzhou, China was studied, which is a long-span curved spatial grid structure with main trusses. Firstly, the finite element model was built using MSC. Marc software adopting the fiber model based on material. Secondly, an improved method of zoned concept judgment and sensitivity analysis was proposed to determine the key components. Thirdly, the initial failure components were removed individually based on the alternate load path method (AP method). The responses of remaining structure were calculated using nonlinear dynamic analysis method. Lastly, the influences brought by the cross-sectional sizes of grid members were investigated through conducting parametric analysis. According to the results, the proposed selection method can avoid omitting the key components. The structural responses are significant when removing the concrete filled steel tubular (CFST) column SC14 directly supporting the front middle part of the roof, with a maximum vertical displacement of 10 m at cantilever end, which should be focused on for this kind of large-span spatial structure. In addition, the tensile strength and cross-sectional area of the upper and lower chords should be increased by 20% to enhance the progressive collapse resistance of the structure, and the changes of axial compression ratios of the columns supporting the roof have little effects.

How successful are maxillary implant-retained overdentures on two or four implants?

Design A randomised crossover clinical trial was designed to determine survival and success of four-implant overdentures in the edentulous maxilla, in participants with mandibular two-implant overdentures. Participants received four implants in the maxilla, two anteriorly and two posteriorly, then were randomly allocated into two treatment groups. The prosthetic phase included alternate loading of anterior and posterior implants for three months each, followed by loading of all four implants for another three months. Participants were then followed up in the recall phase for a mean period of 2.2 years.Case selection Four participants were taken from the authors' previous clinical study, meeting the inclusion criteria for a two-implant overdenture in the mandible. Another 21 participants were recruited from study calls after a widening of inclusion criteria. These patients were all pre-treated in accordance with the previous study protocol, so there was standardisation before maxillary implant placement.Data analysis A sample size calculation was performed and a Kaplan-Meier curve was used to demonstrate implant survival over time.Results Twenty-four patients were included in the study. Three implants were lost during the prosthetic phase and two during the recall phase; all were anterior implants. Implant survival after loading was 93.8% after a mean period of 3.1 years. There were 27 maxillary prosthetic complications overall. Denture success was 95.8% after a mean period of 2.2 years.Conclusions Implant survival of four asynchronously loaded implants in implant-supported overdentures in the edentulous maxilla was good and is a recommendable treatment option for patients with two-implant mandibular overdentures. Implant and prosthetic complications are common but mostly straightforward to manage. Two posterior implants are not superior to two anterior implants, but the majority of patients prefer the four-implant maxillary overdenture.

Total protein staining with Congo red as an alternative loading control for western blot analysis

ABSTRACT For western blot analysis, a housekeeping protein, such as β-actin or glyceraldehyde-3-phosphate dehydrogenase, is used as loading control with the assumption that these proteins are stable. In practice, these internal loading control proteins vary with different cell states and tissue types. These internal standards are not appropriate for use with serum, extracellular secretion, cerebrospinal fluid analysis or for protein purification. We investigated total protein measurement using Congo red staining and found it to be a superior alternative to routine loading controls. Advantages include lower cost, technical simplicity and improved linear regression. We propose using Congo red staining for total protein immunoblotting to evaluate protein loading in western blots.

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature

Gravity-Induced Progressive Collapse Response of Precast Corner-Supported Modular Buildings

Compared with conventional buildings, the design of interconnections in multistory modular buildings requires special attention, due to different load distribution mechanisms, level of redundancy, integration strategies, and the stability requirements, in particular under accidental load conditions. In this paper, the robustness of corner-supported modular steel buildings, subject to various sudden loss scenarios, is studied through investigating the collapse-resisting capacities and the probable gravity-induced progressive collapse mechanisms. The aim is to evaluate the minimum requirements and special considerations for the design of interconnections for robustness. To that end, archetypal precast room-sized volumetric modules with different heights are analyzed using the finite-element macromodelling method and the alternate load path approach. The load redistribution mechanisms are inspected, nonlinear dynamic responses are determined, and probable collapse mechanisms are identified for buildings with different heights and configurations. The dynamic increase factors are computed and compared with the values suggested by the design codes. Given that the individual modules are mainly made of inherently robust structures, the focus of this study is on the performance of interconnections and interactions between an assemblage of units. The results indicate that due to high redundancy in these systems, there is great reserve strength against gravity-induced progressive collapse scenarios, triggered by instantaneous removal of components.

Minimising carbon and financial costs of steam sterilisation and packaging of reusable surgical instruments.

The aim of this study was to estimate the carbon footprint and financial cost of decontaminating (steam sterilization) and packaging reusable surgical instruments, indicating how that burden might be reduced, enabling surgeons to drive action towards net-zero-carbon surgery. Carbon footprints were estimated using activity data and prospective machine-loading audit data at a typical UK in-hospital sterilization unit, with instruments wrapped individually in flexible pouches, or prepared as sets housed in single-use tray wraps or reusable rigid containers. Modelling was used to determine the impact of alternative machine loading, opening instruments during the operation, streamlining sets, use of alternative energy sources for decontamination, and alternative waste streams. The carbon footprint of decontaminating and packaging instruments was lowest when instruments were part of sets (66-77 g CO2e per instrument), with a two- to three-fold increase when instruments were wrapped individually (189 g CO2e per instrument). Where 10 or fewer instruments were required for the operation, obtaining individually wrapped items was preferable to opening another set. The carbon footprint was determined significantly by machine loading and the number of instruments per machine slot. Carbon and financial costs increased with streamlining sets. High-temperature incineration of waste increased the carbon footprint of single-use packaging by 33-55 per cent, whereas recycling reduced this by 6-10 per cent. The absolute carbon footprint was dependent on the energy source used, but this did not alter the optimal processes to minimize that footprint. Carbon and financial savings can be made by preparing instruments as part of sets, integrating individually wrapped instruments into sets rather than streamlining them, efficient machine loading, and using low-carbon energy sources alongside recycling.

High-rise structural stalling and drift effect owe to lateral loading

The challenge is to search out the economic structure system of high-rise buildings within the Indian scenario. This document covers numerous steel systems: moment-stabilizing frame system, composite frame system, luggage rack system with stabilizing belt, structural wall frame system, and frame tube system. Once coming up with multi-storey buildings, truss systems, cluster piping systems for high-rise buildings, lateral hundreds (wind or unstable loads) are principally chargeable for demolition, determining structural systems for high-rise buildings. To form the drift as slight as possible, the beams and columns should be more stiffed. In an exceedingly building with a bit of floor range, the lateral load seldom affects the rise within the building and, therefore, increases size. The part structure considers the aspect load and the doable arranging of the structure. In alternative side load resistance systems beneath study, the force frame’s side displacement is the highest. The lateral displacement of the double frame is the smallest, and the lateral displacement of the slippery wall system is slightly beyond that of the double system.

ROBUSTNESS ASSESSMENT OF PRECAST REINFORCED CONCRETE STRUCTURAL SYSTEMS IN AN ACCIDENTAL DESIGN SITUATION

The article presents the simplified implementation of the method of alternative load paths based on the energy balance approach. This methodshould be used to checking the global resistance of a damaged structural system after the occurrence of an accidental event. It is necessary to provide(reserve) enough ties with the required continuity and ductility in the original prefabricated structural system to ensure the integrity of the damaged system.We consider the system of ties as the “second line of defense” of the structural system after the exhaustion of the flexural resistance of its elements.The continuity and ductility of the tie elements provide a resistance of the damaged structural system under an accidental combination of actionsby mobilizing alternative load paths after the support or key element has been removed. Ductility is the ability of the tie to obtain significant plastic bondelongation before rupture. The ductility is important properties of the ties for redistributing internal forces and getting large deflections. It is necessary for the realization of the chain (membrane) effect, as well as a measure that provides energy absorption (damping) during the dynamic application of anaccidental action after the vertical support losing. The article presents analytical solutions and the working example for the design of horizontal ties in precast hollow-core slabs floor, which areobtained based on the energy approach.

Linear static progressive collapse analysis of RC structures

When there is a sudden loss of load carrying element in a structure, the structure will choose alternate load paths until equilibrium is reached. In this process, elements overloaded in the alternate load paths fails, leading to a large damage disproportionate to the initial event which is referred to as Progressive Collapse (PC). Fire, gas explosions, terrorist attacks, car crashes, and improper design and construction are all common causes of progressive collapse. As a result, it is important to research and examine the effects of this phenomena on structures, as well as to reconstruct the structure to be resistant to it. Government buildings, hotels, offices and residential buildings require different spacings and may require large spans. Though lot of research work has done on PC resistance of Reinforced Concrete (RC) structures to explore that research, in this study, RC buildings with 4 m, 6 m and 8 m clear span between columns have taken and linear static analysis (LSA) has done for different column removal conditions. PC resistance is measured in terms of vertical joint displacement (VJD), chord rotation (CR) and demand capacity ratio (DCR). The VJD and CR results are discussed and compared with each other. The calculated CR values and DCR values are compared with the limiting value as mentioned in GSA and DoD. The tendency to PC is more for 8 m span model is more than the other models with 6 m and 4 m.

Optimal Sizing and Assessment of a Renewable Rich Standalone Hybrid Microgrid Considering Conventional Dispatch Methodologies

This paper presents an evaluation of the optimized design of an off-grid hybrid microgrid for alternative load dispatch algorithms with the determination of the most optimal sizing of each equipment, analyzing the voltage and frequency outputs and various costs of the proposed microgrids. Kushighat and Rajendro Bazar, two geographical locations in Bangladesh have been taken as test sites. The proposed microgrids incorporating diesel generator, renewable resources, storage device, and 23.31 kW of demand have been optimized for five conventional load dispatch methodologies: HOMER predictive dispatch, Load Following, Generator Order, Cycle Charging, and Combined Dispatch to reduce the system’s net present cost, gas discharge and cost of energy. HOMER (Hybrid Optimization of Multiple Electric Renewables) software has been used for the analysis to determine the optimal sizes and costing and the voltage-frequency performances of the microgrids are analyzed using MATLAB/Simulink. From our analysis, load following is determined as the superior approach with a minimum operating cost of 3738 USD, net present cost of 152,023 USD, CO2 discharge of 3375 kg/year and cost of energy of 0.208 USD /kWh along with a steady voltage-frequency output. Combined dispatch is determined as the worst strategy for the proposed microgrids with the highest energy cost of 0.532 USD /kWh, the operational cost of 15,394 USD, net present cost of 415,030 USD, and high CO2 discharge. At the end of this work, a comparative analysis between the proposed design, another hybrid, and traditional generation plant is also presented. The findings of this work will be appropriate for any location with an identical demand profile and meteorological estate.

An investigation for battery energy storage system installation with renewable energy resources in distribution system by considering residential, commercial and industrial load models

Battery energy storage system technique work as alternative load during low demand situation by storing the excess generation and work as alternative power generation source by discharging the stored generation during peak demand. In this work, a comprehensive assessment is performed for battery energy storage system installation and their capacities selection by utilizing the Photovoltaics (PV) output in radial distribution network by considering commercial, residential and industrial time varying load models. The objective of proposed the work is to reduce annual energy losses, mitigate reverse power flow and overvoltage problem and provide peak power dispatch during peak demand in distribution network. A comparative investigation is performed by considering PV and PV-BESS case for each type of load model. Furthermore, the battery energy storage system (BESS) function developed that decide the time and capacity of charging and discharging in order to manage PV penetration and improve the voltage profile, minimize the daily energy losses and control the reverse power flow in the distribution system without deviating the operational limits. A voltage based sensitivity method is developed at initial step to find out the most prominent node in distribution network for BESS installation. The objective of the problem is resolved by genetic algorithm to find out the optimal solution and to assess the comparison of technical parameters between considered cases. The simulation results on IEEE 69 bus test system show that the proposed methodology for BESS placement decreases the annual energy losses, enhances the PV penetration and reduces the overvoltage and mitigate the reverse power flow. Results of this paper also shows that it is possible to dispatch peak power during the peak load hours for each type of load model.

Alternative Load Path Analysis for Determining the Geometric Agreement of a Cable-Stayed Bridge with Steel Truss Girders

The geometric agreement, commonly hailed as load-transferring paths within bridge structures, is significantly crucial to the bridge structural mechanical performance, such as capacity, deformation, and collapse behavior. This paper presents a methodology dependent on alternative load paths to investigate the collapse behavior of a double-pylon cable-stayed bridge with steel truss girders subjected to excess vehicle loading. The cable-stayed bridge with steel truss girders is simplified using a series-parallel load-bearing system. This research manifests that the enforced vehicle loading can be transferred to alternative paths of cable-stayed bridges in different load-structure scenarios. A 3-D finite element model is established utilizing computer software ANSYS to explore the collapse path of cable-stayed bridge with steel truss girders, taking into account chord failure, loss of cables together with corrosion in steel truss girders. The results show that chord failures in the mid-portion of the mainspan result in brittle damage in truss girders or even sudden bridge collapse. Further,the loss of long cables leads to ductile damage with significant displacement.The corrosion in steel truss girders has a highly slight influence on the collapse behavior of cable-stayed bridge. The proposed methodology can be reliably used to assess and determine the vulnerability of cable-stayed bridge with steel truss girders during their service lifetime, thus preventing structural collapses in this type of bridge.

Retrofit of existing steel structures against progressive collapse through roof-truss

The paper presents the results of a comprehensive study on the evaluation of the effectiveness of a retrofit strategy of existing steel buildings against progressive collapse. In this respect, it investigates the performance and the design of a retrofit solution to increase the robustness of steel Moment Resisting Frame buildings. A truss steel system added at the building's rooftop level (i.e., ‘roof-truss’), and intended to define an alternative load path, was investigated as a retrofit solution. The numerical model key components, including the plastic hinges and the beam-column connections, were validated against available experimental results. The validated models were then used to study the robustness of the structure under column loss scenarios by means of non-linear static and dynamic analyses performed in OpenSees. The simulations allowed for the identification of possible failure modes and alternative load paths together with the definition of the Dynamic Increase Factor (DIF). In this regard, it is shown that column buckling is critical for the selected case study. Moreover, the outcomes showed how the proposed retrofit solution allows the definition of effective alternative load paths when subjected to column loss scenarios and informs on the critical details that should be checked by employing this retrofit system.

Simplified Methods for Progressive Collapse Assessment of Frame Structures

AbstractThe Imperial College Robustness Assessment Framework is a methodology—based upon application of the alternate load path concept—for quantitatively comparing the performance of different str...

Power loss minimization load flow studies using Artificial Bee Colony swarm intelligence technique


 
 
 This paper presents the capability of an emerging swarm intelligence technique for power loss minimization known as the Artificial Bee Colony (ABC) used in the context of an Alternative Load Flow Analysis (LFA) technique (ABC-LFA) for the solution of a power systems network. Studies are performed considering the effect of an important parameter of the ABC, the “maxcycle” on the LFA process; experiments are conducted by applying the ABC-LFA to the Western System Coordinated Council (WSCC) 3-machine 9- bus power system and a section of the Nigerian 132-kV power transmission network Port-Harcourt Region (NPHC-132), and the results reported. The results indicate that increasing the value of the ABC “maxcycle” parameter has a pronounced effect on the results obtained by the ABC-LFA. The results also indicate the sensitivity of the ABC to low values of maxcycle parameter.
 
 

Experimental Study on Mechanical Properties and Seepage Laws of Raw Coal under Variable Loading and Unloading Rates

This manuscript studied the effects of variable axial pressure loading rate and variable confining pressure unloading rate on the deformation behavior and seepage characteristics of raw coal under alternate loading and unloading of axial pressure and confining pressure. It believed that as axial stress increases, axial strain ε 1 decreases, radial strain ε 3 increases, and permeability k decreases, and ε 1 ′ , ε 3 ′ , and k ′ increase when confining pressure is decreases. With the loading of axial stress and the unloading of confining pressure, the variation amplitudes of ε 1 ′ , ε 3 ′ , and k ′ values reduce gradually. During axial stress loading, the rise in the amplitude of ε 1 is larger than that of ε 3 and the reduction in the amplitude of k , indicating that ε 1 is more sensitive to axial stress than ε 3 and k . During unloading of confining pressure, the increase rate of ε 3 is larger than that of ε 1 and k ; also, ε 3 showed a high sensitivity to confining pressure. In the stage of axial stress loading and confining pressure unloading, the evolution law of deformation and permeability parameters is basically consistent with the change in loading and unloading rate.

Validation of simplified tying force method for robustness assessment of RC framed structures

The robustness of reinforced concrete (RC) structures is an important ongoing research topic in the civil engineering community. Especially in the last decades, the need for structural robustness assessment methods has become urgent, and several design methods have been proposed in codes and guidelines to mitigate the progressive collapse risk of reinforced concrete structures. The most used approaches are the Tying Force and Alternate Load Path methods. The first is typically applied as an indirect and prescriptive method where the building is considered mechanically tied together and able to enhance continuity and the resistance to progressive collapse. The second is a direct method, where the capacity of the structure to sustain the applied loads is evaluated after the loss of a load-bearing element, most effectively using advanced nonlinear structural analysis methods. In the context of the Tying Force method, the Eurocode is recognised to underestimate the tie force demands required by building structures subject to the loss of a load bearing member, which are better reflected in the USA UFC Guidelines. A new Tying Force method has been proposed by Izzuddin & Sio (2021) for the next generation of the Eurocodes, which addresses the shortcomings of the present Eurocode guidance, and provides a more comprehensive treatment than considered in the UFC code. The present paper is aimed specifically at the validation of the new Simplified Tying Force method (Izzuddin & Sio, 2021) for reinforced concrete structures, considering grillage and combined beam/slab floor systems, and considering the rotational ductility of such structures, which is explicitly considered in the new method.

Health monitoring of steel box girder bridges using non-contact sensors

This study investigates the behavior of simple and continuous span steel box girder bridges after various damage scenarios, including bracing failure and girder fracture, and develops a non-contact bridge health monitoring technique based on the bridge dynamic responses. A series of field tests were conducted to study the feasibility of using non-contact sensors to capture the bridge dynamic responses. Moreover, detailed finite element models of the bridges were developed and validated using the field test and available experimental test results and were used to investigate the bridge failure mechanisms, maximum load-carrying capacity, alternative load paths, and dynamic responses. The bridge dynamic analysis after damage showed that bridge frequencies are sufficiently sensitive for identifying partial or full-depth girder fracture in the simple span bridges. However, these significant damages may cause very small changes in the natural frequencies of continuous span bridges. The results show a significant change in the mode shapes after damage in both simple and continuous span bridges. The mode shapes are sensitive enough to detect damage at the inflicted locations, in most cases with better resolution when compared to the frequency changes. The comparison of the intact and damaged bridge mode shapes indicates that damage at different locations along the bridge has different amplitude changes in the mode shape that could be used to localize the damage. Moreover, the analyses show that either the individual modal sensitivities or combined sensitivities are indicative for most locations throughout the span. The results also indicate a clear pattern of changes in the frequency and mode shape for each damage scenario that can be used to detect the damage type, severity, and location along the bridge.

Thermal Resistance of Insulated Precast Concrete Sandwich Panels

Many nations are already working toward full implementation of energy efficiency in buildings known as Green Building. In line with this perspective, this paper aims to develop a thermally efficient precast concrete sandwich panels (PCSP) for structural applications. Therefore, an experimental investigation was carried out to determine the thermal resistance of the proposed PCSP using Hotbox method and the results were validated using finite element method (FEM) in COMSOL Multiphysics Software. The PCSP were designed with staggered shear connectors to avoid thermal bridges between the successive layers. The staggered connectors are spaced at 200 mm, 300 mm and 400 mm on each concrete layer, while the control panel is designed with 200 mm direct shear connection. In the experimental test, four (4) panels of 500 mm × 500 mm and 150 mm thick were subjected to Hotbox Test to determine the thermal resistance. The result shows that thermal resistance of the PCSP with staggered shear connection increases with increase in spacing. The PCSP with 400 mm staggered shear connectors indicates the best thermal efficiency with a thermal resistance (R value) of 2.48 m2K/W. The thermal performance was verified by FEA which shows less than 5% error coupled with a precise prediction of surface temperature gradient. This indicates that, with conventional materials, thermal path approach can be used to develop a precast concrete building with better thermal resistant properties. Hopefully, stakeholders in the green building industry would find this proposed PCSP as an alternative energy efficient load bearing panel towards sustainable and greener buildings.