Instantaneous Removal Research Articles

Damage mitigation strategies for progressive collapse of modular steel buildings following sudden corner module removal

AbstractThis study evaluates gravity‐induced progressive collapse performance and damage mitigation strategies in modular steel buildings (MSBs) A typical three‐dimensional six‐story structure was modeled and analyzed using the finite element method, focusing on the instantaneous removal of a corner module. The study includes a parametric evaluation of the influence of beam moment capacity on progressive collapse and investigates the effect of using concrete as an infill for square hollow section columns. Additionally, the effectiveness of short K‐shaped braces in limiting gravity‐induced collapse was assessed. A response/damage index (DI) was proposed to quantify the overall structural response. The findings indicate that semirigid beam‐column connections outperform fully rigid connections. Both concrete‐filled columns and K‐shaped braces mitigate structural damage, with K‐shaped braces proving more effective in preventing collapse. Although increasing the beam moment‐resisting capacity reduced the DI, improvements were marginal beyond 50% of the fully rigid connection capacity. Higher beam moment capacities reduced local vertical displacement at the corner joint but led to undesirable lateral deformations. Reducing beam rigidity/capacity by 25% mitigated global structural deformations. The optimal beam moment capacity was identified as 75% of the total section capacity when using concrete‐filled columns. K‐shaped braces applied at the column midpoint entirely prevented progressive gravity‐induced collapse and no lateral deformations were observed in braced structures with fully rigid beam‐column connections, unlike unbraced structures. Concrete‐filled columns offer a cost‐effective solution for preliminary production of MSBs, while K‐shaped braces are suitable for retrofitting existing buildings. Further research is necessary to address other parameters influencing the mitigation of progressive collapse in MSBs.

Rapid removal of methyl orange from aqueous media by modified Mg–Al layered double hydroxides

The current work deals with the synthesis of polymer modified synthetic clay, composed of Mg–Al layered double hydroxides (LDHs) and using a non-toxic organic polymer polyethylene glycol-400 (PEG400). A series of polymer-composites of Mg–Al LDH (LDHP-400) are prepared by changing concentrations of PEG-400 from 4% to 20 %, to find out the maximum adsorption efficiency for the adsorption of an industrially important anionic azo dye, MO from aqueous. The results depicted that LDH-P400, with 16 % PEG-400 shown the removal efficiency of 99.49 % for 100 ppm solution of MO (20 min). Effect of different factors such as dose of adsorbate, temperature, contact time, and pH of the solution, etc. are systematically investigated using batch experiments and thermodynamics parameters as well as kinetic studies are also carried out for the quick and instantaneous removal of MO from aqueous media. Maximum adsorption capacity of 198 mg/g has been achieved at pH4.2 and at temperature 313K for 100 ppm (mg/l) of MO in aqueous media using 0.5 g/l of adsorbent dose. Desorption studies reveal that prepared LDHP-400 can be reused and recycle up to three successive cycles with achieving 88.23 % recovery of MO, which confirmed that prepared LDHP-400 can be reused effectively for laboratory or industrial wastewater which has MO concentrations up to 100 ppm.

Dynamics of magnetization growth and relaxation in ferrofluids.

The dynamics of the growth and relaxation of the magnetization in ferrofluids are determined using theory based on the Fokker-Planck-Brown equation, and Brownian-dynamics simulations. Magnetization growth starting from an equilibrium nonmagnetized state in zero field, and following an instantaneous application of a uniform field of arbitrary strength, is studied with and without interparticle interactions. Similarly, magnetization relaxation is studied starting from an equilibrium magnetized state in a field of arbitrary strength, and following instantaneous removal of the field. In all cases, the dynamics are studied in terms of the time-dependent magnetization m(t). The field strength is described by the Langevin parameter α, the strength of the interparticle interactions is described by the Langevin susceptibility χ_{L}, and the individual particles undergo Brownian rotation with time τ_{B}. For noninteracting particles, the average growth time decreases with increasing α due to the torque exerted by the field, while the average relaxation time stays constant at τ_{B}; with vanishingly weak fields, the timescales coincide. The same basic picture emerges for interacting particles, but the weak-field timescales are larger due to collective particle motions, and the average relaxation time exhibits a weak, nonmonotonic field dependence. A comparison between theoretical and simulation results is excellent for noninteracting particles. For interacting particles with χ_{L}=1 and 2, theory and simulations are in qualitative agreement, but there are quantitative deviations, particularly in the weak-field regime, for reasons that are connected with the description of interactions using effective fields.

A thermal infrared imaging observation system for the measurement of overland flow velocities under controlled laboratory conditions

Flow velocity is an important physical parameter in characterizing the hydraulics of water flow. The accurate measurement of overland flow velocities has great significance for understanding and modeling sediment transport and soil erosion. In this study, a Thermal Infrared Imaging Observation System (TIIOS) based on thermal infrared imaging techniques and computer vision recognition technology was established to measure overland flow velocities under controlled laboratory conditions. TIIOS has three subsystems including thermal tracer control, image acquisition and transmission, and image storage and processing. It can be used to dynamically monitor changes in shallow flow velocity by means of automatic control of thermal tracer, instantaneous image acquisition, image correction, noise removal and centroid determination. The observation precision was high with a standard deviation of 0.004 m·s−1 for flow velocity, a temporal resolution of 1/9th s, and a spatial resolution of 2 mm. The new system achieved higher accuracy compared to the traditional dye tracing and salt tracing techniques in observing the dynamic transport process of thermal tracer movement. The relative errors of the centroid velocity measured by the TIIOS ranged from −9.83 % to 6.40 %; whereas the relative errors of centroid velocity measured by salt tracer ranged from −21.36 % to 17.22 %. Measurements by the established TIIOS under different hydraulic conditions demonstrate that the relative errors of the centroid velocity are all smaller than those of the leading-edge velocity. This observational system provided a reliable way to measure shallow flow velocity for better understanding the mechanisms of water erosion processes and showed its potential to be used in field experiments under natural conditions.

Progressive Collapse and Post Impact Damage Assessment in a Regular Beam-Slab Building & Flat-Slab Building on the Intermediate Floor

Progressive collapse, where a localized member failure causes widespread structural collapse, has become a critical concern nowadays, due to its potential to cause significant financial losses and loss of human life. Triggers include natural disasters like earthquakes and floods, as well as accidents, attacks and explosions. Reinforced concrete flat slab structures, which are eminent for their architectural flexibility and have larger spans, are particularly susceptible to disproportionate collapse, due to the lack of floor beams, which can redistribute loads after a column failure, unlike moment frame buildings. This research examines how multi-story reinforced concrete flat slab buildings behave, under prescribed gravity load combinations, compared to conventional framed buildings. The effects of removing columns at specified locations from an intermediate floor of the multistorey building are also examined. However, this investigation covers both the column removal approaches to check a possibility of disproportionate collapse which are; static removal and dynamic instantaneous removal. Furthermore, the research also assesses the efficacy of perimeter beams, in minimising the risk of gradual collapse in flat slab structures, by scrutinising their ability to reduce joint displacement, chord rotation, and demand capacity ratio. ETABS v18 was used to analyze all the 18 models. The findings revealed that buildings are more prone to progressive collapse when corner columns are removed, as opposed to edge and interior columns, due to higher Demand-Capacity Ratios (DCR) and joint displacement. In comparison to dynamic analysis, the static evaluation exhibited greater DCR values and vertical joint displacement. Furthermore, since they have a more efficient load redistribution mechanism, traditional framed structures performed better than flat slab models. The simulations additionally indicated that, adding edge perimeter beams, substantially lowered the possibility of progressive collapse in flat slab structures. Moreover, the tested flat slab building models, with and without perimeter beams showed no indications of progressive collapse, when specified columns were removed from the intermediate floors, since the DCR values of the crucial columns stayed within the permissible range of 2.0. In conclusion, structures built in compliance with IS 1893:2016 code and designed to withstand seismic loads demonstrate stronger resistance against significant damage, brought about by column failures.

Robustness assessment of precast concrete connections using component-based modelling

Employing highly optimised precast concrete product-based building solutions increases on-site productivity through elimination of formwork and reduction in propping as well as reducing waste, accidents and embodied carbon. The construction related benefits of precast concrete product-based building solutions are maximised by eliminating structural topping and designing connections between members for ease of assembly. A key challenge in the design of precast concrete buildings is the achievement of robustness under accidental loading. In this paper, sudden column removal is used to assess the robustness of a precast-concrete building system without structural topping. In this case, the development of an alternative load path under sudden column removal relies on the joint response. Joint behaviour is replicated using a component-based design procedure which captures localised failure modes. Robustness is evaluated using a ductility-centred approach and quantified in terms of the pseudo-static resistance. Two types of connection are considered for the provision of continuity at a critical half-lapped joint. The first is a plated connection which was designed initially to meet the tying requirements outlined in Eurocode 2. Under sudden column removal the plated connection’s deformational capacity is limited, which in turn reduces the pseudo-static resistance. An alternative bracketed coupler connection is proposed in which the ductility supply is controlled through debonding of reinforcement. The design concept for the bracketed connection is validated with test results from two full scale sub-assemblies. The experimental results are used to validate a component-based numerical model which is subsequently used to investigate the influence of boundary conditions, and debonding length on the pseudo-static resistance following sudden column loss. The paper shows that the pseudo-static resistance can be significantly enhanced by flexure and compressive membrane action. Consequently, the authors suggest that connection design in precast concrete structures without topping should be based on a realistic assessment of the ability of the structure to develop alternative load paths following instantaneous column removal rather than simplified tying rules.

Instantaneous and efficient removal of glyphosate with low concentration by amine-functionalized SBA-15 chelated with Fe(III)

Glyphosate has drawn great attention due to its potentially detrimental effect to ecosystems, but the selective removal of low-concentration glyphosate from surface water remains challenging. Herein, a novel adsorbent (Fe(III)/NN-SBA-15) for the adsorption of low-concentration glyphosate from aqueous solution was prepared by using ethylenediamine (EDA) chelating with Fe(III) to modify SBA-15. Adsorption study showed that the Fe(III)/NN-SBA-15 has excellent adsorption capacity for glyphosate (71.4 mg/g). Most importantly, the Fe(III)/NN-SBA-15 exhibited fast adsorption kinetics for glyphosate, 99% of glyphosate could be quickly removed within 1 min when the glyphosate concentration from 5 mg/L to 21 mg/L, which was outperforms many other adsorbents previous reported. In addition, the results of the effect of competing ions on the adsorption process showed that Fe(III)/NN-SBA-15 had good selectivity for glyphosate removal from water. According to the FTIR and 31P solid-state NMR spectra, the direct Fe(III)-phosphate complexation played the dominant role in glyphosate removal on Fe(III)/NN-SBA-15. In summary, the high adsorption capacity, fast adsorption kinetics, and good selectivity make Fe(III)/NN-SBA-15 a promising sorbent for high-efficient removal of glyphosate from aqueous solutions with low initial concentration.

Analysis and Evaluation of the Progressive Collapse of Cable Dome Structures Induced by Joint Damage

The current literature lacks an effective progressive collapse analysis of a cable dome structure induced by joint damage. In this study, a dynamic analysis was performed using actual construction cases, an ANSYS LS-DYNA analysis platform, and a fully dynamic equivalent load instantaneous removal method. First, the structure’s dynamic responses and collapse modes induced by different joints with different types of damage were explored. Subsequently, joint importance coefficients were proposed depending on the structure’s displacement before and after joint removal, and the relationships between the joint importance coefficients and the joint properties and collapse modes, respectively, were then identified. Finally, the relationship between the joint damage and the connected component damage was explored. The results revealed that different joints and identical joints with different types induced a variety of dynamic responses. However, the dynamic response induced by the discontinuous joint damage was more apparent than that induced by the continuous joint damage. When a continuous joint model was used, the damage on all joints did not result in the progressive or local progressive collapse of the structure. Thus, all these joints were considered as common joints. However, when a discontinuous joint model was used, the failure of the joints resulted in three distinct collapse modes, namely a progressive collapse, a local progressive collapse, and a nonprogressive collapse, corresponding to the key joints, the important joints, and the common joints, respectively. These three types of joints corresponded to different importance coefficients. When damage occurred in the discontinuous joints separately linked to the key components, the important components, and the common components, the joints resulted in the progressive collapse, local progressive collapse, and nonprogressive collapse, respectively, of the structure.

Fast Procedure for Removing Silver Species in Waters Using a Simple Magnetic Nanomaterial

The increase in the production and use of disinfectants containing silver atoms (in both its ionic and nanomeric forms) in their formulation, due to the global pandemic situation caused by COVID-19, has increased the presence of silver species in wastewater. Moreover, silver atoms are now considered as emerging pollutants in water. In this work, we propose a novel method for the instantaneous and simultaneous removal of ionic and nanomeric silver in water samples, using a previously unpublished methodology consisting of the in situ formation of magnetic nanoparticles in the aqueous samples to be treated. While the nanoparticle precursors react to form them, the silver atoms present in the sample are adsorbed onto them due to a strong electrostatic interaction. As the final nanoparticles are magnetic, they can be easily removed from the aqueous medium using a magnet, leaving the samples free of silver species. The innovative feature of the method is that the adsorbent is synthesized in situ, within the sample to be treated, making the approach a low-cost, easy-to-perform solution. Temperature, contact time, dose of Fe3O4, and concentration of nanomeric and ionic silver were investigated. The results showed that at 50 °C, 100% of both silver species were removed from the water samples simultaneously. The surface of Fe3O4 was characterized before and after the application of the removal process using energy-dispersive X-ray spectroscopy and Field Emission scanning electron microscopy. Adsorption kinetics and equilibrium isotherms studied reveal a Langmuir-type physicochemical process. The procedure has been applied to different water samples (river and drinking water) with excellent results, making the method a new standard for the removal of ionic and nanomeric silver. In addition, the nanoparticles formed could be recycled and reused for other analytical and decontamination purposes.

Adsorption Studies of Pb(II) and Cd(II) Heavy Metal Ions from Aqueous Solutions Using a Magnetic Biochar Composite Material

Heavy metal toxicity in water is a serious problem that may have harmful effects on human health and the ecosystem. Lead [Pb(II)] and cadmium [Cd(II)] are two such heavy metal ions, present in water, whose severity is well-known and well-studied. In the current research, magnetic biochar composite (MBC) is studied as an adsorbent material for the effective removal of lead and cadmium ions from water solutions. Magnetite (Fe3O4) nanoparticles and pine-needle-derived ultrasonicated magnetic biochar were used in different weight ratios to prepare APTES (3-aminopropyl triethoxysilane)-functionalized MBC (FMBC). An average crystalline size of ~10 nm for magnetite NPs was obtained via XRD analysis. The adsorption characteristics of both Pb(II) and Cd(II) ions were investigated in a batch experiment. The FTIR spectra of raw biochar, MBC, FMBC, and metal-loaded FMBC were obtained at different stages. The decrease in the intensity of the –NH2 functional group in the FTIR spectra of the residue confirmed the successful adsorption of heavy metal ions. The SEM-EDX spectra of the residue showed the uniform adsorption of Pb(II) and Cd(II) heavy metal ions onto the surface of the adsorbent. Magnetic biochar composite (MBC) was found to be a very effective adsorbent at basic pH, as a maximum of 97% instantaneous heavy metal removal was observed for both ions in synthetic water solutions. The Langmuir isotherm model predicted the monolayer adsorption and good affinity between the metal ions and adsorbent. The prepared MBC is low-cost, environmentally friendly, and it has shown good adsorption performance. Therefore, our study suggests that the magnetic biochar composite under study is an effective adsorbent for lead and cadmium metal ion removal from aqueous solutions at normal room temperature. Only a few hundred milligrams of the adsorbent dose is sufficient to remove higher concentrations (~100 ppm) of lead and cadmium at basic pH conditions of aqueous solutions.

A novel integrated multiphase crystal system of Kavlite for the effective and instantaneous removal of cationic and anionic dyes

Textile dye effluent pollution is one of the major threats to the environment in this generation. Various techniques have emerged to remove the textile dye effluent, but adsorption is the best process for effective removal. Aluminosilicate is one of the universal adsorbents to remove textile effluents from wastewater because of its large surface area and large availability of active/acid sites. But it shows a higher affinity for the cationic dyes alone. This limits the usage for the removal of both cationic and anionic dyes. Moreover, it takes a longer time to attain equilibrium. Herein, we invented an integrated multiphase crystal system of Kavlite (NiO@AS) is nothing but multiphase nickel aluminosilicate. This is prepared by one-pot sol-gel method at room temperature and atmospheric pressure for the effective removal of Victoria Blue (VB) and Metanil Yellow (MY) within a short span of time. It is characterized by XRD, FTIR and HRTEM. Integration of nickel oxide into the aluminosilicate framework creates more active/acid sites in the framework, as evidenced by XRD analysis. Furthermore, XRD results revealed the formation of 6 different phases with 3 different crystal systems in the framework. This could also additionally induce the adsorption performance. This resulted in a faster adsorption rate of VB and MY within 10 and 35 min respectively, with 83% removal. The adsorption capacity of VB is higher than that of MY (Experimental Qe = 113.32 mg/g for VB and 20.92 mg/g for MY). This is because of the large availability of possible interaction sites in VB. This work provides a deep insight into understanding the interaction possibilities between the adsorbent and adsorbate interface based on the XRD, adsorption kinetics, isotherms and thermodynamic study.

Investigation on surface quality in micro milling of additive manufactured Ti6Al4V titanium alloy

The additive manufactured technology is widely applied to produce titanium alloy parts with complex structures. The subsequent machining operations are necessary for additive manufactured parts to achieve the required machining quality. In this paper, the theoretical surface roughness model in micro milling was established. The model indicated the theoretical milled roughness mainly depends on the feed per tooth, tool nose radius and bottom edge inclination angle. Then, micro milling experiments are conducted on additive manufactured titanium alloy using PCD micro end mill. The surface roughness on milled surface was measured and investigated. At the middle position of micro milled surface, the distribution curves of surface roughness Ra and Sa show the same variation trend under different milling parameters. Moreover, the measured surface roughness results on different transverse positions of milled surface showed that the difference value between the actual and theoretical surface roughness of milled surface is mostly induced by the unstable cutting behaviors, which is also mainly responsible for the surface roughness size effect. The transverse distribution of surface roughness on milled surface exhibited a W shape because of the variation of the instantaneous undeformed chip thickness and material removal mode at different transverse positions.

Method for Early Diagnosis of Real-Time Traffic Loss with Timeout Monitoring in Software-Configurable Networks

The purpose of the research is to develop the method for early diagnosis of real-time traffic loss with time-out control in software defined networks (SDN).Methods. An overview and description of the transfer of heterogeneous traffic in an Ethernet switch with support for quality of service and Time-Triggered Ethernet technology is given. The functioning of the timeout control blocks for instantaneous removal of a frame from the hard timeout control system and depending on the length of the frame when the idle timeout receiving side is reached is described in detail. These control units are included in the hardware guard of control time-outs for real-time traffic. The work of the switch OpenFlow is described using guard of control time-outs. The formation of time windows of timeouts during frame transmission is described and developed.Results. With the help of the proposed method of early diagnosis of real-time traffic losses with control of timeouts in SDN, a modeling of SDN based on Petri nets and using the CPN Tools modeling package was carried out. The obtained model and experimental results are consistent with the theoretical calculations and the proposed method of transmitting real-time traffic, taking into account its losses in SDN.Conclusion. Using the model, the functional and temporal behavior of the model was investigated; the method was verified using Petri nets. The results were obtained in the form of time diagrams reflecting the work on traffic types in accordance with the proposed method.

Effects of operational parameters on the performance of unialgal Oedogonium sp. filamentous algae nutrient scrubbers under controlled environmental conditions

Filamentous algae nutrient scrubber (FANS) operating parameters can strongly influence algal biomass productivity and nutrient removal. However, few studies to date have investigated the effects of FANS operating parameters such as initial standing crop, harvesting frequency and influent flow rate on biomass productivity and nutrient removal performance, especially for FANS that cultivate a single species of algae. Therefore, the overall aim of this study was to investigate how operating parameters affect the biomass productivity and nutrient removal performance of Oedogonium sp. - a promising species for unialgal FANS. The initial standing crop had a significant effect on biomass productivity, with productivities being highest (8.6 ± 0.5 g DW biomass m−2day−1) when the initial standing crop was 60–70 g DW m−2. However, the daily nutrient removal rate was highest (0.47 ± 0.06 g N m−2 day−1and 1.24 ± 0.13 g P m−2 day−1) at the highest initial standing crop (100–110 DW m−2). Biomass productivity was highest with a three-day growth period, regardless of size of the initial standing crop. Therefore, a four-day harvesting interval was selected as the optimal harvesting regime to promote exponential growth and high biomass production. Influent flow rate had a significant effect on biomass productivity, which was highest (9.3 ± 1.7 g DW m−2 day−1) for the 1 L min−1 flow rate. This flow rate also gave the highest instantaneous nutrient removal rate (0.05 ± 0.02 g N m−3 and 0.14 ± 0.05 g P m−3). Current results suggest that an optimum initial standing crop of 70–80 g DW m−2, harvesting frequency of four days and influent flow rate of 1 L min−1 (16.7 L min−1 m−1 width) were optimal for Oedogonium sp. cultivated on FANS to maximize their biomass production and nutrient removal under controlled laboratory conditions. These results contribute to understanding the impacts of operating parameters on optimizing unialgal Oedogonium sp. FANS biomass production and nutrient removal performance.

Performance Evaluation of Calcined Meretrix lusoria Beads Fixed Bed Column for Instantaneous Removal of Phosphate and Nitrate from Domestic Wastewater

Performance Evaluation of Calcined Meretrix lusoria Beads Fixed Bed Column for Instantaneous Removal of Phosphate and Nitrate from Domestic Wastewater

Dynamic response and collapse resistance of RC flat plate structures subjected to instantaneous removal of an interior column

Through quasi-static loading regimes, notable research efforts have been made in recent years towards understanding the structural behaviour and resistance mechanism of reinforced concrete (RC) flat plate structures against progressive collapse events. Nevertheless, dynamic responses, being an inherent nature of any progressive collapse, were unable to be adequately studied in these quasi-static studies. Moreover, fewer studies were performed on flat plate structures under dynamic loading conditions, especially their behaviours under large deformations, i.e., the post-punching stages. To fill this research gap, this paper presents three sequential dynamic tests performed on a 1/3-scaled 2 × 2-bay RC flat plate substructure specimen by instantaneously removing the interior column under three levels of additional gravity loads. In these tests, the substructure specimen was able to withstand the gravity loads up to 2.08 times the load capacities recommended by the DoD and GSA guidelines for nonlinear dynamic analyses. The dynamic responses of the specimen in the flexural, punching and post-punching stages were examined in detail. In addition, a high-fidelity finite element model was developed and validated by the experimental test results. The validated numerical model was subsequently used to quantify the dynamic load redistribution patterns, and the influences of two loading considerations (i.e., loading on the slab overhangs and load release time) on the dynamic responses were also investigated. Finally, the dynamic load increase effects were evaluated based on the analysis model results. The obtained load-based dynamic increase factors (DIFs) of the specimen under different gravity loads were between 1.11 and 1.46 in the pre-punching (flexural) stage, whereas they were no more than 1.06 in the post-punching stage.

Conversion of waste bottle PET to magnetic microparticles adsorbent for dye-simulated wastewater treatment

Mass production and consequent accumulation of plastic wastes in the environment urges the development of technologies for the efficient plastic wastes utilization and valorization to materials and products to support circular economy. Here, we report a novel conversion of PET plastic to a magnetic microparticles adsorbent prepared by co-precipitation of Fe3O4 nanoparticles with oligomeric products of PET aminolysis. The obtained adsorbent represents highly water-dispersible oligo(terephthalamide) particles of several tens μm size embedding magnetic nanoparticles randomly distributed in the organic matrix. The PET-derived magnetic adsorbent was used for the rapid and facile magnetic separation of an anionic dye (Congo Red, CR) from dye simulated water samples. The adsorbent containing plenty of amine groups showed superb adsorption capacity for CR of ca. 780 mg/g which is pH dependent and optimal at pH 6.5. Furthermore, the microparticular, non-aggregative state of the adsorbent coupled with its magnetic functionality provided rapid saturation of the adsorbent with dye by ca. 70% of the equilibrium adsorption capacity within 5 min and possibility of instantaneous removal from solution by a magnet. The proposed here material design addresses simultaneously the problem of plastic wastes utilization and preparation of cost-effective and efficient adsorbents for environmental cleaning purposes.

Digital modeling of progressive collapse for high-rise building

Objective. The article substantiates the need for digital simulation of emergency impact in the study of the stability of a building to progressive collapse by creating a simulator of local destruction.Method. To ensure the unique architectural appearance of the projected multifunctional high-rise complex, a complex shape has been developed with recesses in which elevator shafts are located. The principle of control of the structure due to the influx of external energy is observed. Energy conversion and the necessary protection is provided by the presence in the spatial frame of the building of balancing connections near architectural recesses, which allow stabilizing the state of a complex system. The spatial rigidity of the structural scheme of a high-rise building is ensured by the use of symmetrically located diaphragms and stiffening cores, rigid nodes for interfacing with the supporting structures of outrigger systems.Result. The calculation algorithm for progressive collapse includes the calculation of the stress-strain state of the building frame elements during normal operation. An analogue of the emergency action is created by excluding from the design model the bearing element, the instantaneous removal of which is modeled by a force with the opposite sign, determined by the results of the calculation in the normal operation stage.Conclusion. The stress-strain state of the frame, which occurs during local destruction, is a criterion for resistance to progressive collapse. The question of the need and the established form of outrigger floors in relation to a specific building has been investigated. The dependence of the dynamic characteristics when changing the structural solutions of the frame of a unique building is given.

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.

Dynamic response of RC beam-slab substructures following instantaneous removal of columns

High fidelity solid-element-based numerical modeling is employed in this paper to study the dynamic response of reinforced concrete (RC) beam-slab substructures following instantaneous removal of columns. After validation of the numerical model against experimental results, incremental dynamic analysis is conducted to obtain the dynamic structural resistance to progressive collapse. The numerical results for development of internal forces and distribution of stress and strain are used to illustrate the load redistribution and load transfer mechanisms of RC beam-slab substructures subjected to sudden loss of columns. The numerical model is further employed to explore parameters affecting the dynamic response and structural resistance of beam-slab substructures under sudden column removal scenario. The parameters studied include damping ratio, slab thickness, location of removed columns, multi-column removal sequence and interval. The numerical result shows that the dynamic progressive collapse resistance of the beam-slab substructure is much smaller than the quasi-static test result due to a dynamic increase factor (DIF) of 1.14. Moreover, a minimum slab thickness of 1/45 of span length is found vital for the improvement of progressive collapse resistance of RC beam-slab substructures through developing compressive membrane action (CMA) and tensile membrane action (TMA) as well as enhancing the development of compressive arch action (CAA) and tensile centenary action (TCA) of beams. When the damping ratio is smaller than 5%, the increase of damping ratio can significantly benefit the structural resistance against progressive collapse by producing smaller deflection and milder vibration. The additional loss of the corner column besides the penultimate perimeter column is found to form the most hazardous situation among the double-column removal scenarios. In contrast to the location of removed columns, the column removal sequence and interval tend to little affect the maximum deflection developed and consequently the progressive collapse resistance of substructures.