Properties Of Column Research Articles

A modal-based method for blast-induced damage assessment of reinforced concrete columns: Numerical and experimental validation

Reinforced concrete (RC) columns play a crucial role in the overall performance of modern RC frame buildings under blast loading. The RC columns under blast loads might experience various irreversible consequences such as concrete cracks, crushing and spalling, changing the status of both modal properties and load-carrying capacity. In this paper, the blast-induced damage assessment of the RC columns involving the measurement of modal parameters was introduced and validated. Firstly, a modal-based method for blast-induced damage assessment of RC columns was proposed, in which the damage is characterized as the reduction of axial bearing capacity and further expressed as the explicit function of the vibration frequencies and the mass-normalized displacement mode shapes. Then, the finite-element analysis program LS-DYNA was employed to establish the numerical model of RC columns under axial compression loads and lateral blast loads. The residual load-bearing capacities and modal properties of the RC columns were illustrated. By using the numerical results collected in the present study, the validity of the proposed damage assessment method was discussed and proved numerically. Further, field explosion tests and experimental modal tests were conducted, and the results showed that the modal-based damage assessment method exhibited remarkable agreement with the blast damage determined by residual bearing capacities. Based on the numerical and experimental results, the proposed modal-based damage assessment method is applicable for the non-destructive evaluation of blast-induced damage of RC columns.

Increased coral biomineralization due to enhanced symbiotic activity upon volcanic ash exposure

Coral reefs, which are among the most productive ecosystems on earth, are in global decline due to rapid climate change. Volcanic activity also results in extreme environmental changes at local to global scales, and may have significant impacts on coral reefs compared to other natural disturbances. During explosive eruptions, large amounts of volcanic ash are generated, significantly disrupting ecosystems close to a volcano, and depositing ash over distal areas (10s - 1000s of km depending on i.a. eruption size and wind direction). Once volcanic ash interacts with seawater, the dissolution of metals leads to a rapid change in the geochemical properties of the seawater column. Here, we report the first known effects of volcanic ash on the physiology and elemental cycling of a symbiotic scleractinian coral under laboratory conditions. Nubbins of the branching coral Stylophora pistillata were reared in aquaria under controlled conditions (insolation, temperature, and pH), while environmental parameters, effective quantum yield, and skeletal growth rate were monitored. Half the aquaria were exposed to volcanic ash every other day for 6 weeks (250 mg L−1 week−1), which induced significant changes in the fluorescence-derived photochemical parameters (ΦPSII, Fv/Fm, NPQ, rETR), directly enhanced the efficiency of symbiont photosynthesis (Pg, Pn), and lead to increased biomineralization rates. Enhancement of symbiont photosynthesis is induced by the supply of essential metals (Fe and Mn), derived from volcanic ash leaching in ambient seawater or within the organism following ingestion. The beneficial role of volcanic ash as an important micronutrient source is supported by the fact that neither photophysiological stress nor signs of lipid peroxidation were detected. Subaerial volcanism affects micronutrient cycling in the coral ecosystem, but the implication for coral ecophysiology on a reef scale remains to be tested. Nevertheless, exposure to volcanic ash can improve coral health and thus influence resilience to external stressors.

Cyclic behavior of self-centering RCFST column to beam joints with prefabricated connectors

This paper presents the cyclic behavior of reinforced concrete-filled steel tube (RCFST) column to beam joint with prefabricated connectors. The cyclic performance of four specimens was investigated to focus on the hysteretic behavior, reinforcement tension, residual deformation, and strain distribution of joints. The equivalent viscous damping coefficients (ξeq) corresponding to the four specimens range from 0.049 to 0.087 at the yield point. And the final residual drift ratio of the specimens ranged from 3.6% to 12.9%. The tested column-beam joint specimens had good hysteretic behavior, energy dissipation, and self-centering ability. The PT steel bars without hollow channel or weakened treatment enhanced the self-centering ability and workability of joints. The finite element models were developed to verify the main mechanical properties of the self-centering RCFST column to beam joint. The average of KE/ KFEA, Mc,y/ My,FEA and Mc,p/ Mp,FEA were 0.89, 0.98, and 1.03, respectively. The FEA models could predict mechanical properties of the joints with high accuracy.

Life-cycle assessment and prediction on ultimate capacity of corroded Q690 steel columns with H-section under bi-directional cyclic loading

The structures or structural members made of high-strength steel may have time-varying mechanical properties in whole life-cycle due to the ageing effects. In particular, the corroded steel structures in high-seismicity regions could have unexpected failure modes when subjected multi-directional excitations. Therefore, in this study, the mechanical properties of Q690 steel H-section columns during the life-cycle under bi-directional cyclic loads are investigated. Firstly, a refined finite element (FE) model is built, which takes the time-varying of corrosion characteristics into consideration. Then, the degradations of mechanical property and failure mechanisms of steel columns with different design parameters at whole life-cycle are analysed by the FE models. Finally, a quantitative calculation method of ultimate resistance and damage index of steel columns considering ageing effects is proposed. The findings demonstrate that several factors affect the ultimate strength of steel columns during the life-cycle stage, with the axial compression ratio and flange width-thickness ratio having the greatest impacts on the ultimate capacity. The ageing effect decreases the plastic flow capacity of steel columns, increases the stress concentration, and induces the failure mode transition from plastic flow to buckling failure. The ageing effect may be accurately estimated by the suggested calculation method for the ultimate capacity and damage index of steel columns at the life-cycle stage. The findings of this study highlight the significance of taking into account the ageing effects of steel columns in the seismic design.

A method to establish marine bio-regions in the pelagic ecosystem based on phytoplanktonic communities. Aplication to the southern Spanish coast

Bioregions in the pelagic ecosystem are frequently established on the basis of remotely sensed properties of the sea surface, such as sea surface temperature or sea surface chlorophyll concentration. Those works dealing with the regionalization of the marine ecosystem by means of the use of properties of the water column are less frequent, and even less those that obtain the data from periodic in situ monitoring programs, which are scarce. In this work we use time series of micro, nano and pico-phytoplanktonic abundances in the upper 100 m of the continental shelves of the Gulf of Cadiz and the Alboran Sea from the projects STOCA and RADMED (southern coast of Spain, Western Mediterranean). The use of times series allows us to estimate the median phytoplanktonic abundances of several phytoplanktonic groups along the water column. These statistics differ substantially from those abundances obtained for one particular campaign, reflecting the large seasonal and inter-annual variability of phytoplanktonic communities. These median profiles, estimated for the four seasons of the year and for several phytoplanktonic groups characterize each of the locations sampled in the aforementioned monitoring programs and are used for establishing the similarity between them. Then, these locations are grouped using a cluster analysis. Using some simulations from numerical experiments we determine which metrics and methods of analysis are the more suitable ones for the regionalization of the area of study. A bootstrap method is also used to determine which differences among bioregions can be considered as statistically significant. Despite the existence of a fast current that connects the Gulf of Cadiz and the Alboran Sea, our results show that the outer part of the Gulf of Cadiz shelf, and that of the Alboran Sea, can be considered as two differentiated bioregions. The latter region shows a higher productivity with a higher abundance of large cells such as diatoms, and the dominance of Synechococcus bacteria over Prochlorococcus ones.

Semi-analytical model for deep-water hyperspectral imaging.

We propose a semi-analytical (SA) model for relating seafloor reflectance to measured radiance in deep-water hyperspectral imaging in artificially illuminated scenes. Using accurate sensor-seafloor geometry from photogrammetry and the principle of two-viewpoint observation, we estimate the inherent optical properties (IOPs) of the water column. We demonstrate the SA model and estimation of IOPs for hyperspectral imaging of a deep-water coral reef from a remotely operated vehicle. For the calibrated SA model, evaluation of across-viewpoint similarity demonstrates the model's ability to compensate for water column and light source effects.

Universal boosting ML approaches to predict the ultimate load capacity of CFST columns

SummaryEstablishing a universal machine learning (ML) model in structural engineering is vital for understanding how various parameters, like geometry and material properties, influence a structure's behavior. This study aims to create a comprehensive ML model that considers the impact of different cross‐sectional parameters on the ultimate load capacity (ULC) of concrete‐filled steel tube (CFST) columns. This model assists engineers in making informed design decisions. The study employs a large dataset of 3094 data points with diverse geometric and material properties of CFST columns. After adjusting input features, robust boosting ML models (Catboost, LightGBM, and XGB) are meticulously fine‐tuned using grid search and fivefold cross‐validation. Monte Carlo simulation is used for further assessment. The results demonstrate that the most accurate XGB model delivers impressive accuracy, comparable to or better than existing literature models that focused on a single CFST column cross‐section. The chosen XGB model is then utilized for feature importance analysis, local performance assessment, and sensitivity analysis through 1‐D and 2‐D partial dependence plots. These analyses help assess the input's contribution and effect on ULC prediction for CFST columns.

Strength prediction and stochastic analysis of ultra-high performance concrete columns under the explosive blast load

The performance research based on numerical and experimental studies on ultra-high performance concrete (UHPC) generally considers it as an isotropic material, which is obviously different from what it really is in practical engineering. A database of UHPC compressive strength was investigated, having the same UHPC mix proportion as the field blast experiment, to show how the strength of UHPC varies in compression. It is found that Weibull distribution is the best fit of its probability model. A combination of Monte-Carlo and Finite Element method is used, adopting the available UHPC compressive strength, to reproduce the field blast test on UHPC columns. Both the non-spatial and spatial variability of material properties of the UHPC columns are under consideration to conduct the UHPC column strength prediction under blast loads. The residual loading capacity, damage index and failure mode of UHPC columns with different sizes damaged by different explosion severities are obtained by non-spatial simulation and spatial simulation respectively. It can be concluded that compared with the non-spatial model, the numerical simulation results of the spatial model are closer to the experimental situation. Therefore, inclusion of spatial variability is recommended for reliability-based blast-resistant design for UHPC column.

Mechanical properties of CFST column with bolt-welded joints under eccentric compression

With the increase of arch bridge span and difficulty in welding construction, the traditional connection method of arch rib steel tube cannot satisfy the requirements of construction safety and economy. In this paper, a new bolt-welded connection method for arch rib of long-span Concrete Filled Steel Tubular (CFST) arch bridge is proposed, which can avoid the stress redistribution of joints of arch rib caused by cutting the joint flange in the traditional connection method. In order to study the mechanical properties of the bolt-welded joint of CFST, the eccentric compression scale tests were carried out, and the finite element model is validated based on the experiment. The parameter analysis was performed and the calculation formula of eccentric bearing capacity of bolt-welded joint of CFST is proposed. The results show that the bolt-welded joint can significantly improve the stiffness, stability and effectively avoid buckling at the joint. With the increase of steel tube strength, core concrete strength and steel ratio, the bearing capacity of bolt-welded joints of CFST significantly improved, and the bearing capacity of bolt-welded joints under small eccentric is better than welded joints. The bolt-welded area ratio is recommended not to exceed 0.3. The calculation results of the proposed formula are consistent with the experimental and simulated results.

Axial stress strain behavior of FRP-confined rectangular rubber concrete columns with different aspect ratio

At present, the mechanical properties of FRP-confined rectangular rubber concrete columns have not been studied. To fill this gap, thirty-six concrete columns were prepared and tested under axial compression in this study. The effects of the aspect ratio (1, 1.25 and 1.5), rubber volume replacement ratios of fine aggregates (0 %, 40 % and 60 %) and FRP layer number (2 and 3) on the failure state and stress–strain relationship were investigated. The test results showed that with increasing section aspect ratio and rubber volume replacement ratio, the damage zone of the specimen increased, and the compressive strength decreased. As the number of FRP layers increasing, the damage zone and compressive strength of the specimens both showed an upward trend. Based on the test results, the stress–strain model, compressive strength model and ultimate strain model of FRP-confined rubber concrete columns were proposed. The proposed models can accurately predict the stress–strain relationship, compressive strength and ultimate strain of FRP-confined rectangular rubber concrete.

Uptake of barium, molybdenum, and lithium and incorporation into scallop shells: Refining proxies for primary production dynamics

AbstractBa/Cashell, Mo/Cashell, and Li/Cashell chronologies of Pecten maximus can provide information on past phytoplankton dynamics. Distinct Ba, Mo, and Li peaks in the shells are associated with algal blooms. This study evaluated the underlying hypothesis that respective element profiles reliably record variations in phytoplankton dynamics occurring within the water column. Therefore, the chemical content of scallops from the Bay of Brest, France, that lived on the sediment surface was compared to conspecific specimens living in a cage above the seafloor and compared with the phytoplankton abundance and the physicochemical properties of the water column. As demonstrated, Ba/Cashell and Mo/Cashell peaks occurred contemporaneously in specimens within the cage and on the sediment, but were higher in the latter. Furthermore, element/Ca peaks agreed with the timing of particulate Ba and Mo enrichments in the seawater. These data support the assumption of a dietary uptake of both elements. Differences in peak heights between shells living in a cage and on the seafloor were controlled by rates of filtration and biomineralization. While the timing and magnitude of Ba/Cashell peaks were linked to Ba‐containing diatoms, Mo/Cashell peaks were related to blooms of Mo‐enriched dinoflagellate and diatom aggregation events. Two episodes of slight Li enrichment occurred synchronously in cage and sediment shells. Although the exact mechanism causing such Li increases remains unresolved, the findings suggest a link to large diatom blooms or the presence of a specific diatom taxon. This study refines previously hypothesized relationships between trace element enrichments in scallop shells and phytoplankton dynamics.

Confinement properties of circular concrete columns wrapped with prefabricated textile-reinforced fine concrete shells

Confinement properties of circular concrete columns wrapped with prefabricated textile-reinforced fine concrete shells

Evaluating fire resistance of timber columns using explainable machine learning models

The global attention to using timber products as sustainable construction material urges careful assessment of their performance against different hazards, particularly fire. However, the current methods prescribed by design codes for evaluating the fire resistance of timber components tend to underpredict the outcomes of standard fire resistance tests, and lack interpretability due to the use of semi-empirical equations. This study develops explainable data-driven models to predict fire resistance of timber columns using geometry- and material-related properties based on a comprehensive experimental database. Nine different single and ensemble-based machine learning algorithms were trained, and their performance was optimized through rigorous hyperparameter tuning and feature selection. The best models were then interpreted using partial dependence and Shapley plots to infer the underlying relationship between fire resistance and column properties. Lastly, the models’ predictive capabilities were compared to available prescriptive equations. The results show that a random forest-based model provides the best performance with an average ratio of predicted to observed fire resistance of 1.03 on the test set. The random forest prediction is mainly governed by column capacity at ambient temperature, and to a lesser degree, columns’ cross-section dimension. In addition, the partial dependence plots indicate that the effect of density, modulus of elasticity, length, and compressive strength on fire resistance was not notable. Finally, while the considered prescriptive equations consistently underpredict fire resistance, the random forest model provides a consistently accurate and balanced prediction.

Mechanical properties of CFST short columns with different void ratios

Mechanical properties of CFST short columns with different void ratios

Monitoring of 137Cs, 239+240Pu, and 90Sr in the marine environment of South Korea and their impact on marine biota: 10 years after the Fukushima accident

This study conducted an analysis of the behavior of radionuclides and assessment their radioactive risk based on seawater and seabed sediment samples gathered from the East, South, and Yellow Seas of South Korea over the period from 2011 to 2020. The distribution for each radionuclides in seawater obtained from the East, South, and Yellow Seas were similar. However, the concentrations of 137Cs and 239+240Pu in sediments from the East Sea were observed to be higher compared to those from the South and Yellow Seas. This variation can be attributed to differences in the ocean inflow, water column properties, and seabed characteristics among the seas around South Korea. There were no statistically significant differences between the radioactive concentrations of seawater and seabed samples collected before and after the Fukushima accident, and no areas with unusually high radiation levels were detected. Using the distribution coefficient (Kds) and the concentration ratio (CR) calculated from the 2011-to-2020 data, we evaluated the radiological impact on fish. The ERICA tool was utilized to assess these data, and indicated a negligible radiological risk from radioactivity in the seawater, seabed sediments, and marine biota in the South Korean Ocean.

Experimental research on axial mechanical properties of circular CFSST columns after exposure to temperature and sliding

This paper presents experimental investigations on axial mechanical properties of circular concrete-filled stainless steel tube (CFSST) columns after exposure to temperature and sliding. A total of 117 CFSST specimens were tested under axial compression loading with four factors (i.e., tube thickness, temperature, duration, and concrete compressive strength) considered. Test results indicated that the initial stiffness of circular CFSST short columns was degenerated due to high-temperature sliding. Circular CFSST specimens exhibited a 50.9% lowest residual strength at 1000 ℃. The influence of high-temperature duration on the residual strength of circular CFSST short columns was limited. The residual strength of specimens was positively correlated with the thickness and concrete compressive strength. All circular CFSST columns after exposure to temperature and sliding experienced an outward local buckling under axial compression. In addition, the parameters formulae of residual strength for circular CFSST columns after exposure to temperature and sliding are proposed, which achieve sufficient accuracy. The research could offer valuable references for strengthening circular CFSST columns after fire.

High-resolution insights of physical properties of water columns of lakes at the Larsemann Hills, East Antarctica

During the Austral summer of 2022, a study was conducted to investigate the physical properties of six lakes in the Larsemann Hills, East Antarctica. The lake water column's key properties, viz. temperature, salinity, density, fluorescence, and depth, were examined using a CTD profiler to establish a high-resolution description of their variations and identify the factors influencing intra and inter-lake variations. The results indicated that the shallow lakes LH14, LH04, and Discussion were well mixed. Lakes LH04 and LH14 on Stornes were affected by salinity, likely sea spray. In contrast, the deeper lakes, namely Nella, Cameron and Progress, were primarily driven by temperature and density dynamics. The hydrological characteristics of Cameron and Progress were notably impacted by their proximity to the ice sheet, while Nella was influenced by the presence of a partial lake ice cover. The lake depth, geographical location and presence of ice cover in the catchment significantly influenced temperature and salinity variations within the lakes. Deep lakes may be more sensitive to changes in temperature and density as compared to shallow lakes and could potentially affect other physical lake parameters. This baseline information is a valuable reference for future investigations on these lakes and similar environments.

Effect of molybdenum tailings aggregate on mechanical properties of engineered cementitious composites and stirrup-confined ECC stub columns

Abstract Engineered cementitious composites (ECC) exhibit behaviors of multiple cracking and strain-hardening compared to ordinary concrete. However, the use of ultrafine silica sand (S) to produce ECC results in increased cost and environmental overload. This study was to develop an eco-friendly and cheaper ECC by incorporating different replacement ratios of industrial byproduct molybdenum tailings (MT). The mechanical properties of ECC with MT were evaluated. Based on industrial computer technology, nuclear magnetic resonance, and scanning electron microscope techniques, the three-dimensional spatial distribution and fluid distribution of pores and the microstructure of the ECC were investigated, respectively. The mechanical properties of stirrup-confined ECC stub columns were also investigated. Results indicated that the ECC incorporating 25% MT exhibited the best mechanical properties, in which the tensile strength (f t) increased by 32.16% and exhibited well strain-hardening behaviors. Under a 25% MT replacement ratio, ECC had the lowest porosity and good interfacial transition zone, and bonding interface between polyvinyl alcohol (PVA) fiber (PF) and matrix. Moreover, the stirrup-confined ECC stub column with 25% MT can ensure better both the peak stress (f cc) and peak strain (ε cc). The assessment of environmental impact and cost further indicated that the incorporation of MT to prepare ECC is a promising method.

Tailored compressive properties of origami thin-walled column with multi-corner elements

To improve the load stability and energy absorption of the energy absorber, a novel design strategy of the cruciform origami column with multi-corner elements (COC) is proposed. The axial compressive test shows that the COC can effectively tailor the deformation mode based on the creases. The comparisons of compressive properties indicate that the COC has lower initial stiffness and higher load stability than the conventional straight column (CSC) and overcomes the disadvantage of the low energy absorption of typical origami columns. In addition, the mechanical advantages of COC with rib reinforcement are more significant. Specifically, the specific energy absorption of COC with cruciform rib reinforcement (COC-C) can increase by 22.98% compared to the COC without rib reinforcement (COC-W), which both have high load stability. Furthermore, the origami module, dihedral angle and thickness have significant effect on tailored deformation characteristics and compressive indicators of the COC, in which the module and dihedral angle can determine the deformation and the trigger effect, respectively. This study finds that the multi-corner elements origami design can improve the compressive properties of thin-walled structures, providing a new design concept for energy absorbers with controlled deformation and load stability.

Axial compressive property of square and rectangular UHPC-filled duplex stainless steel tube stub columns

This study presents experimental and numerical investigations of the axial compression performance of square and rectangular ultrahigh performance concrete (UHPC)-filled duplex stainless steel tube (UFSST) stub columns. A total of twelve UFSST stub columns, six ordinary concrete filled duplex stainless steel tube (CFSST) stub columns, and six hollow duplex stainless steel tube (HSST) stub columns were tested under axial compression. The test parameters include the section type, three kinds of concrete strength grades, and three kinds of duplex stainless steel tube thicknesses. The test results showed that UFSST stub columns behaved with high bearing capacity and favourable ductility. In the UFSST stub columns with ξ ≥ 1.87, the square and rectangular duplex stainless steel tubes could well confine the shear failure of UHPC. The developed finite element model could effectively reflect the compressive behavior of the HSST, CFSST and UFSST stub columns. The available experimental database was employed to evaluate the feasibility of current design codes and existing calculation models in the literature to design UFSST stub columns. Finally, a modified computational model was proposed that takes into account the nonuniform confinement effect induced by square and rectangular section tubes on concrete and showed a higher prediction accuracy.