Channel Section Research Articles

Вторичные течения Прандтля 2-го рода в пространственно-неравновесном турбулентном течении

In this work, a numerical study of turbulent flow and heat transfer in a plane channel was carried out. The features of secondary flows of Prandtl's 2nd kind, which arise in the vicinity of longitudinal ribs on the channel walls, are studied under conditions of spatial inhomogeneity of the flow. Simulations of four turbulent flows were carried out: flows in a smooth channel uniform in length, a uniform ribbed channel, as well as flows in a smooth and ribbed channel with an average velocity varying along the length. It is found that the presence of a rib in a homogeneous channel in the considered case significantly changes the distribution of turbulent flow characteristics over the channel section. These changes are due to the action of the emerging secondary flow with a maximum velocity of 5.2% of the average flow rate. In this case, changes in the velocity and thermal characteristics are similar. Both friction and heat transfer increase by about 10% due to the increased wetted surface area. The inhomogeneity of the flow, which is provided by the organization of blowing and suction through the upper wall of the channel, leads to more noticeable changes. In areas where the flow slows down, the fluid moves under conditions of an unfavorable pressure gradient. The intensity of turbulent pulsations in these places increases noticeably. In the presence of ribs, this leads to a significant increase in secondary flows. Both in the smooth and in the ribbed channel, an increase in the Reynolds analogy coefficient to a value of 1.07 was recorded, which is 6% higher than the uniform flow index. In general, based on the results of this work, we can conclude that the longitudinal ribbing is hardly capable of significantly changing the thermal-hydraulic properties of a flat surface in a turbulent flow, at least without taking special optimization measures. The spatial inhomogeneity of the flow, on the contrary, due to the different effects on the velocity and temperature profiles, has a certain potential for designing heat exchange devices with more suitable thermal-hydraulic properties.

Effects of functionally graded graphene reinforcements on nonlinear post-local buckling and axial stiffness of laminated channel section struts

The role of local buckling on the behavior of slender members under compression has received considerable attention in structural engineering. For thin-walled sections, in particular, there is a noticeable decrease in the axial compressive stiffness, resulting in a substantial reduction in their load-bearing capacity due to the occurrence of local buckling. The principal purpose of this article is to explore the potential improvements in the postbuckling characteristics of polymeric composite channel section struts subjected to a progressive end-shortening by employing multi-layer graphene sheets reinforcements. The solution methodology incorporates the von Karman geometrical nonlinearity and is based on the layerwise third-order shear deformation theory (LW-TSDT). To verify the accuracy of the results obtained based on LW-TSDT and to evaluate its computational efficiency, a three-dimensional (3D) finite element model is also developed using ABAQUS for the comparative analysis. A thorough examination of nonlinear instability is conducted on composite laminated channel section struts, featuring distinctive graphene distribution patterns through the thickness directions of the flanges and webs to identify the most effective material distribution with the objective of a significant increase in critical end-shortening and axial compressive stiffness. The influence of the geometrical parameters on the critical end-shortening, postbuckling equilibrium paths, and load-bearing capacity of functionally graded graphene reinforced composite (FG-GRC) laminated channel section struts are elicited. The conducted parametric analyses emphasize that altering the distribution patterns of graphene reinforcement across the flanges and web can enhance the critical end-shortening and load-bearing capacity by 80% and 25%, respectively.

In0.53Ga0.47As/In0.52Al0.48As Quantum Well Step Gate LDMOS to Improve the Device Performance

In this work, a new laterally double diffused metal oxide semiconductor (LDMOS) using In0.53Ga0.47As/In0.52Al0.48As Quantum well (QW) layer with a p-well step gate has been proposed. In the proposed device structure, the gate region splits into three steps in which the oxide thickness increases from the source to the drain end. As the gate insulator width varies from source to drain end, it results in better control of the gate over the channel and also a reduction in the gate-to-drain capacitance (CGD). These features offer higher transconductance with reduced switching delays, which makes the device appropriate for RF applications. Again, the concentration of current in the channel section is enhanced due to the presence of the Quantum well region and the InP spacer layer, which drastically reduces the On-resistance. But, the device achieves lesser gate-to-drain capacitance which results in decrease in the switching speed. On the other hand the proposed device offers less gate charge with the low value of CGD gives minimised switching loss. Based on 2D TCAD simulation, the proposed QW LDMOS exhibits 70% improvement in On-resistance, 45% in breakdown voltage, 84% improvement in peak transconductance, 26% improvement in switching delay, and 19% improvement in gate charge density as compared to conventional In0.53Ga0.47As devices.

Numerical and experimental study on the synergistic effect of vortex and contact surface of fluid in the inlet section of micromixer

The promoting effect of vortex on the mixing performance of micromixer is difficult to be quantitatively evaluated. In this study, the concept of flux across line (FAL) is proposed for the first time to quantitatively analyze the influence of synergistic effect between the vortex and the contact surface of fluid on the mixing. The FAL value of T-shaped and cross-shaped micromixers is obtained by integrating the velocity component after decomposing the velocity vector on the cross section of the straight channel. The intensity distribution and development of vortex in the inlet section are quantitatively revealed by numerical simulation at Re = 50. According to the FAL analysis, a two-layer feed T-shaped micromixer (TLFT-shaped) is designed to verify the effective synergy between vortex and contact surface of fluid. The FAL value of TLFT-shaped is 40–50 % higher than that of cross-shaped, the promoting effect of vortex on mixing is reflected in the mixing index, which experiences a notable 56 % increase. The concentration distributions of visualization experiments and simulations are consistent, which proves the accuracy of simulation results. The FAL analysis can quantitatively evaluate the promotion effect of vortex on mixing, which provides valuable guidance for the design of microfluidic devices.

Numerical investigation of cold-formed steel channels with edge-stiffened and unstiffened elongated web holes under shear

Over the past decade, cold-formed steel (CFS) channel sections having edge-stiffened circular web holes have been developed in New Zealand. Such edge-stiffened holes increase the strength of the CFS channel sections, compared to an equivalent section having unstiffened web holes, while still allowing full building service integration. In the case of shear, previous research has found that the use of edge-stiffened web holes significantly improves the shear strength of such channel sections. However, no studies are available in the literature investigating the shear strength of CFS channel sections with edge-stiffened elongated web holes. The issue is addressed herein. Non-linear finite element (FE) analyses are used to investigate the shear strength of CFS channel sections with a shear span aspect ratio of 2.0. The FE models were validated against the experimental test results of sections having unstiffened elongated web holes and edge-stiffened circular web holes; good agreement in terms of the load-displacement curves and failure behaviour was shown. Using the validated FE models, a parametric study was conducted, comprising 2124 finite element analyses (FEA) results. The parametric results were then compared to the design predictions of the American Iron and Steel Institute (AISI 2016), and Australia/New Zealand Standards (AS/NZS 2018) and Wanniarchchi et al. (2017) for unstiffened elongated web holes, showing that the design predictions are unconservative in comparison results. Moreover, the direct strength method (DSM) approach of Pham et al. (2020a and 2023) provides conservative results for channels with unstiffened elongated web holes. It was also found that the design equations proposed by Chen et al. (2022) for edge-stiffened circular web holes were unconservative in predicting the shear strength of channels having edge-stiffened elongated web holes. Therefore, design equations in the form of a shear reduction factor and a modified DSM approach for CFS channel sections having unstiffened and edge-stiffened elongated web holes were proposed. Finally, a reliability analysis was carried out to ensure that the proposed equations are reliable to predict the shear strength of CFS channel sections with edge-stiffened and unstiffened web holes.

Quantifying Intermittent Flow Regimes in Ungauged Basins: Optimization of Remote Sensing Techniques for Ephemeral Channels Using a Flexible Statistical Classification

Intermittent and ephemeral channels are a critical component of the global hydrologic network. The dominant feature in dryland environments, ephemeral channel transmission loss facilitates aquifer recharge. Characterizing flow intermittency improves groundwater storage estimates; however, limited gauging of intermittent systems impedes this understanding. This research develops an improved classification for surface flow, optimized for ephemeral systems using linear discriminant function analysis and remotely sensed imagery. It further applies this methodology to assess temporal and spatial flow patterns across the Souss channel, an ungauged, ephemeral system in central Morocco. Linear discriminant function analysis demonstrates high predictive accuracy for Landsat imagery, with significantly improved classification success as compared to the Modified Normalized Difference Water Index. Application to the Souss channel from 1984 to 2022 points to a decreasing trend in flow frequency. Despite this change, flow events remain concentrated within the wet season, critical for regional aquifer recharge. Spatial flow characteristics further support sustained infiltration, with the majority of events focused within the upstream channel section during both dry and wet seasons. Decreased occurrence moving downstream highlights the likely impact of additional factors such as transmission loss, evapotranspiration, and agricultural abstraction contributing to channel intermittency.

Simulation of High-Viscosity Generalized Newtonian Fluid Flows in the Mixing Section of a Screw Extruder Using the Lattice Boltzmann Model.

The mixing quality of polymer melts in the mixing section of a single-screw extruder and an injection molding machine has considerable effects on the properties of the molded products. Therefore, the study of the flow field of polymer melts in the mixing section is of great importance. The lattice Boltzmann method (LBM) exhibits unique advantages in simulating non-Newtonian fluids. Many researchers have used LBM to study the flow of medium- and low-viscosity fluids. In their studies, the Reynolds number of fluid flows is generally moderate. However, polymer melts are typical high-viscosity fluids, and their flow Reynolds number is generally very small. The single-relaxation-time lattice Boltzmann method (SRT-LBM) has been used previously to study the flow field of power law fluids in the mixing section. Herein, the flow field of high-viscosity generalized Newtonian fluids in the mixing section of a single-screw extruder is studied using SRT-LBM, the two-relaxation-time lattice Boltzmann method (TRT-LBM), and the multiple-relaxation-time lattice Boltzmann method (MRT-LBM). Through comparison, TRT-LBM has been found to exhibit obvious advantages regarding stability, calculation accuracy, calculation efficiency, and selection of simulation parameters. The TRT-LBM is more suitable for studying high-viscosity generalized Newtonian fluids than SRT-LBM and MRT-LBM. SRT-LBM has low computational efficiency when simulating high-viscosity generalized Newtonian fluids, and instability is easily caused when the fluid has a yield stress. For MRT-LBM, only by studying the relaxation parameters can its advantages be fully utilized. However, optimizing the accuracy and stability of the MRT-LBM via parameter research and linear stability analysis is difficult. For non-Newtonian fluids, it is difficult to optimize the relaxation parameters to make the MRT-LBM more stable and accurate than the TRT-LBM. It is difficult for the MRT-LBM to realize its potential when simulating high-viscosity generalized Newtonian fluids. In addition, we studied the flow pattern in the cross section of the screw channel and compared it to the results reported in previous studies.

Design and Performance Analysis of Massive MIMO Modeling with Reflected Intelligent Surface to Enhance the Capacity of 6G Networks

Reflected Intelligent Surface (RIS) can establish a virtual line-of-sight link to enhance system performance while consuming less power in non-line-of-sight. RIS technique is utilized to minimize the spreading of electromagnetic signals by modifying the surface's electric and magnetic field characteristics. RIS can be adopted with the existing environment to effectively increase efficiency by modifying the radio channel characteristics. The signals are steered to the receiver using an RIS thus improving the link quality. The radio channel is viewed in traditional wireless systems as an uncontrollable entity that typically tampers with transmitted signals. This paper suggests an alternate theoretical model after examining the prevalent models and potential issues. Security of the wireless communication physical layer can be improved with an RIS by just changing the phase of the reflective unit. In this work, the massive Multiple Input Multiple Outputs (MIMO)-based iterative modeling technique is used to build the transmitter, channel, and receiver section. This will simultaneously optimize the RIS passive beamforming pre-coding matrix and thus avoid multi-user interference. At the base station cyclic programming is adopted, it iteratively calculates the active and passive beam-forming RIS matrices. The simulation results demonstrate that the combined pre-coding technique used in this work improves the weighted sum rate, efficiency, and coverage ratio. The results show that MIMO with continuous phase shift RIS achieves a higher Weighted Sum Ratio (WSR) and minimum Channel State Information (CSI) error in comparison with the random phase shift RIS. The performance metrics sum rate, signal-to-interference plus noise ratio (SINR), energy efficiency, and transmit power are analyzed and compared.

Flood Estimation and Control in a Micro-Watershed Using GIS-Based Integrated Approach

Flood analyses when using a GIS-based integrated approach have been successfully applied around the world in large-sized watersheds. This study employed hydrological-hydraulic modeling to analyze flash floods by integrating HEC-HMS, HEC-RAS, and ArcGIS software for flood evaluation and control in a micro-watershed in the Samaru River, Nigeria. The watershed boundaries, its characteristics (soil and land use), the topographical survey, and the intensity duration frequency curve (IDF) of the study area were produced using data-driven techniques. The HEC-HMS model was used to derive the peak discharges for 2-, 5-, 10-, 25-, 50-, 100-, and 200-year return periods with the frequency storm method. Afterward, the water surface profiles for the respective return periods were estimated using the HEC-RAS hydrodynamic model. The simulated design flood for the 2-, 5-, 10-, 25-, 50-, 100-, and 200-year return periods at the reference location (the NUGA gate culvert) were 3.5, 6.8, 9.1, 12.1, 14.3, 16.6, and 19.0 m3/s, respectively, while those at the watershed outlet for the respective return periods were 7.5, 14.9, 20.3, 27.3, 32.6, 38.0, and 43.5 m3/s, respectively (with a water height of 0.9 m, 1.1 m, 1.3 m, 1.33 m, 1.38 m, 1.5 3m, and 1.8 m, respectively), at the NUGA gate culvert cross-section. The maximum water depths of about 0.9 m and 1.0 m were recorded in the right and left overbanks, which were similar to the simulated water depth for the 2- and 5-year return periods. Hence, for the smart control of floods passing through the river and major hydraulic structures, a minimum design height of 1.50 m is recommended. For the most economic trapezoidal channel section, a normal depth of 1.50 m, a bottom width of 1.73 m, a top width of 3.50 m, and a free board of 0.30 m is proposed to curb the overtopping of floods along the channel sub-sections. The findings of this study could help hydraulic engineers minimize flooding in streams and rivers overbanks in a micro-watershed.

ИССЛЕДОВАНИЕ ОСНОВНЫХ ПАРАМЕТРОВ ГИДРОМЕХАНИЧЕСКОГО ДЕМПФЕРА ТРАНСПОРТНЫХ СРЕДСТВ, ИСПОЛЬЗУЕМЫХ В АГРОПРОМЫШЛЕННОМ КОМПЛЕКСЕ

The article presents materials related to the development of a promising design of a hydraulic damper in-stalled in the suspension of vehicles used in the agro-industrial complex. A special feature of the hydraulic damper design is the transition from vertical channels to horizontal channels in the piston and stem of the vi-bration damper. In this case, the vertical sections of the rod channels are mated with the horizontal sections of the piston channels. The presence of such calibrated holes in the piston and rod, as well as due to the ab-sence of bypass valves, can significantly reduce sudden pressure changes in the vibration damper during high-speed movements of both the rod and the piston. This significantly increases the smoothness of the ride, and, consequently, the comfort and safety of the vehicle and, thus, improves the working conditions of the personnel operating it. Analytical studies have been carried out, as well as hydrodynamic and strength calcu-lations of such determining parameters as the pressure of the working fluid and its flow rate. Recommenda-tions are given on the choice of rod and piston material for a promising design of a hydraulic damper for ve-hicles. A method of engineering calculations for determining the parameters of the throttling system is pro-posed, which allows to establish the criteria for the operability of the developed technical solution with a view to its possible application in industrial conditions.

CHANNEL COMPONENT OF SEDIMENT YIELD: SPECIFIC FEATURES FOR THE LARGE RIVERS OF RUSSIA

Bank and riverbed erosion produce a significant part of the sediment flux, i.e. its channel component. The article deals with the quantitative assessment of the channel sediment input for more than 14 000 km of the lower reaches of the Ob, Yenisei, Lena, Kamchatka and the Selenga River net. The absolute volumes of sediments supplied by bank erosion are maximum for the lower and middle Lena River (up to 38,7 million tons per year per 100 km of the channel). They are significantly lower for the lower and middle Ob River (down to 19,9 million tons per year per 100 km of the channel), and an order of magnitude smaller (about 2 million tons per year) for the Yenisei River because of the limited conditions for the development of channel processes, and for the Selenga and Kamchatka rivers because of the smaller size of rivers. The volume of sediments of channel origin is two times smaller, than the sediment runoff, for the Yenisei River and exceeds the sediment runoff up to 9 times for other rivers. The maximum rates of bank erosion are common for meandering and branched channels with wide floodplains. Most of the bank erosion within the braided sections of channels is the deformation of islands.

МОДЕЛИРОВАНИЕ ТЕЧЕНИЯ ПОЛИМЕРОВ В СЕЧЕНИЯХ МАЛЫХ КАНАЛОВ

The problems of modeling the flow of polymers in channels with a small section in the overall production of about 2-3 cm3 are considered. The influence of channel dimensions on the thermosetting plastic movement in such channels is described. The arguments are given to prove necessity of careful control of the flow sections of small channels in the production of polymer products. A simulation of pressing a small product with the thermosetting plastic in a mold with a built-in filling element is carried out. The location of the filling element will allow to assess the nature of the flow front movement in the mold cavity most closely to reality. An attempt is made to analyze the influence of pressing conditions on obtaining a high-quality product and the behavior of the filling element in the mold cavity.

Influence of elevated temperature on buckling capacity of mild steel-based cold-formed steel column sections– experimental investigation and finite element modelling

PurposeThe capability of steel columns to support their design loads is highly affected by the time of exposure and temperature magnitude, which causes deterioration of mechanical properties of steel under fire conditions. It is known that structural steel loses strength and stiffness as temperature increases, particularly above 400 °C. The duration of time in which steel is exposed to high temperatures also has an impact on how much strength it loses. The time-dependent response of steel is critical when estimating load carrying capacity of steel columns exposed to fire. Thus, investigating the structural response of cold-formed steel (CFS) columns is gaining more interest due to the nature of such structural elements.Design/methodology/approachIn this study, experiments were conducted on two CFS configurations: back-to-back (B-B) channel and toe-to-toe (T-T) channel sections. All CFS column specimens were exposed to different temperatures following the standard fire curve and cooled by air or water. A total of 14 tests were conducted to evaluate the capacity of the CFS sections. The axial resistance and yield deformation were noted for both section types at elevated temperatures. The CFS column sections were modelled to simulate the section's behaviour under various temperature exposures using the general-purpose finite element (FE) program ABAQUS. The results from FE modelling agreed well with the experimental results. Ultimate load of experiment and finite element model (FEM) are compared with each other. The difference in percentage and ratio between both are presented.FindingsThe results showed that B-B configuration showed better performance for all the investigated parameters than T-T sections. A noticeable loss in the ultimate strength of 34.5 and 65.6% was observed at 90 min (986℃) for B-B specimens cooled using air and water, respectively. However, the reduction was 29.9 and 46% in the T-T configuration, respectively.Originality/valueThis research paper focusses on assessing the buckling strength of heated CFS sections to analyse the mode of failure of CFS sections with B-B and T-T design configurations under the effect of elevated temperature.

Experimental and numerical investigation of corroded cold-formed steel channel section columns subjected to in-plane compression and bending

This paper investigates the effect of corrosion on bearing capacity of corroded cold-formed steel (CFS) channel section columns subjected to in-plane compression and bending. Herein, 14 CFS columns with different column lengths and corrosion degrees were investigated. The mass loss rate, surface morphology, and initial geometric imperfections of corroded CFS columns were measured. The eccentric compression test of corroded CFS columns that were accelerated corrosion by the outdoor periodic spray test were carried out. The relationships among the failure mode, load–strain curves and load–axial displacement curves, and mass loss rate were analyzed, and then the deterioration laws of bearing performance of corroded CFS channel section columns were discussed. The non-linear finite element model for corroded CFS columns considering surface morphology was then developed by using Geomagic Studio and ABAQUS. The results indicated that the local and overall initial geometric imperfections of corroded specimens were greater than those of non-corroded specimens. With increasing mass loss rate, the distortional buckling deformation of corroded CFS columns occurred in advance and the failure locations were diversified. Corrosion exhibited a greater impact on the buckling critical load than on the ultimate load and post-buckling strength. The failure positions of corroded CFS channel section columns subjected to in-plane compression and bending were found to be mainly related to the areas with severe corrosion of the flange.

Algorithms for Clarification of the Operating Modes of Channel Sections in the Management of Water Resources in Channel Irrigation Systems

The optimal operating modes are determined for channel sections based on the condition that all lateral water intakes are guaranteed to receive the planned flow rates of water resources with minimal filtration and evaporation water losses. Lateral outlets are guaranteed to receive water flows if they have appropriate heads of water in front of the facility. These necessary heads determine the values of water levels in the channel sections, which are determined in the process of water distribution. In the process of operational management of water resources in mechanical water-lifting systems, established water distribution limits are implemented, taking into account the current actual situation with the availability of water resources and the technical characteristics of pumping stations and hydrotechnical structures of the irrigation system, as well as the technical characteristics of hydrotechnical structures and canal sections of the entire irrigation system. Currently, optimal management of water resources is carried out with the help of a dispatch service, and the operating modes of canal sections are determined by dispatchers. Therefore, significant deviations of actual regimes from planned values, unevenness and instability of water supply to consumers are constantly observed. Based on the above, the article developed mathematical models of the unsteady flow of water resources in the section of the main canal and seasonal reservoir based on the nonlinear differential equations of Saint-Venant. An algorithmic sequence for determining the operating modes of a hydraulic structure is also given, with the help of which it is possible to manage the water resources of the main canal, which will satisfy the needs of water users with minimal losses of water and energy resources. Определены оптимальные режимы работы участков канала осуществляется из условия, что все боковые водозаборы гарантированно получают плановые расходы водных ресурсов при минимальных потерях воды на фильтрацию и испарение. Боковые отводы гарантированно получают расходы воды в том случае, если у них имеются соответствующие напоры воды перед сооружением. Эти необходимые напоры определяют значения уровней воды на участках канала, которые определяются в процессе водораспределения. В процессе оперативного управления водными ресурсами в механических водоподъемных системах реализуются установленные лимиты водораспределения с учетом сложившейся фактической ситуации с обеспеченностью водными ресурсами и технических характеристик насосных станциях и гидротехнических сооружений оросительной системы, а также технических характеристик гидротехнических сооружений и участков каналов целое оросительной системы. В настоящее время оптимальное управление водных ресурсов осуществляется с помощью диспетчерской службы, а режимы работы участков канала определяются диспетчеров. Поэтому постоянно наблюдаются значительные отклонения фактических режимов от плановых значений, неравномерность и нестабильность подачи воды потребителям. Исходя из выше сказанного, в статье разработаны математические модели неустановившегося течения водны ресурсов участке магистральном канале и водохранилище сезонного регулирования на основе в нелинейных дифференциальных уравнений Сен-Венана. Также приведена алгоритмическая последовательность определения режимов работы гидротехнического сооружения, с помощью которой можно управлять водными ресурсами магистрального канала, что позволит удовлетворить потребности водопользователей с минимальными потерями водных и энергетических ресурсов.

Investigation of Parameters Affecting Rotational Behavior of Cold-Formed Steel Connection

This study aims to understand the behavior of connection, which holds an important key to efficient designs of the cold-formed steel structure. The focus is on examining parameters that affect the rotational stiffness and behavior of the cold-formed steel connection made of single-lipped channel sections with a bolt and gusset plate system. The numerical study has been conducted using component-based finite element analysis, with the studied parameters including bolt diameters, number of bolts in the group, size of the bolt group, thickness of the cold-formed steel cross-section, and thickness of the connecting plate. The effect of the variables is evaluated and explained by comparison. The result of the study reveals that the rotational behavior of the connection depends on the details of the assembly. For the given base connection, the parameters that give the greatest effect on the rotation stiffness and the moment capacity are the number of bolts and the bolt diameters, whereas the parameter that provides the least effect is the bolt spacing. On the other hand, the bolt group size is the most influential parameter for the member connection. For both types of connections, the thickness of the cold-formed steel section and the thickness of the gusset plate have shown limited effect on stiffness and strength. Using different variables in assembling the connection can also lead to different failure types, either bolt failure or excessive bolt hole deformation, which leads to plate failure. Doi: 10.28991/CEJ-2023-09-11-08 Full Text: PDF

Axial compressive behavior of cold-formed steel built-up box-shape columns with longitudinal stiffeners

This paper presents a study on the behavior of cold-formed steel built-up box-shape columns with longitudinal stiffeners (CFS-BCL) under axial compression. The specimens are fabricated using a pair of channel sections and lipped channel sections with longitudinal stiffeners, which are expected to enhance the local buckling resistance of the web. Sixteen specimens were prepared for compression tests, with varying lengths and screw arrangements. Prior to the tests, initial geometric imperfections of the specimens, material properties, and shearing-resistance behavior of the screw fasteners were measured. The results indicate that screw arrangements have a significant effect on simply supported specimens; reducing the screw spacing from 300 mm to 100 mm can increase load-bearing capacity by up to 11%. Finite element models were developed using ABAQUS and validated against test results. The parametric analysis revealed that screw arrangements had minimal impact on the local buckling capacity of specimens, with an increase in capacity of <8%. However, global buckling behavior was significantly affected by screw arrangements, resulting in an increase in capacity of up to 20% for slender columns. The test and analytical results were compared with the Direct Strength Method (DSM), and indicate that the DSM is conservative when the non-dimensional slenderness ratio λg and λl is higher than 1.2 and 1.4, respectively. The coefficients of the DSM were modified based on the test and simulation results, and its predictive accuracy was found to be highly increased.

Cost-effective methods for flexural strengthening of one-way RC precast flat slab bridges in South Carolina

In South Carolina, there are one-way precast RC flat slab bridges that were constructed in the 1950 s for H-10 and H-15 design trucks (lower than the current design standards) and have deteriorated over time. To ensure public safety and continued usage, strengthening the bridges is imperative. Various methods exist for flexural strengthening, including application of UHPC from above and strengthening from below with FRP, steel plates, and external prestressing. However, these methods may compromise the ductile behavior of the slabs and they are also challenging, labor-intensive, and expensive to apply. The innovation of this paper lies in investigating the methods for strengthening from above that have the potential to improve both the flexural strength and ductility of slabs, while offering advantages in terms of ease of implementation and cost-effectiveness compared to existing methods. Five slabs obtained from decommissioned bridges in South Carolina were tested under monotonic loading to failure: one reference slab; one slab strengthened with steel channel sections from above; one slab strengthened with steel plate sections from above, and two slabs connected at the joint by near surface mounted steel rebars for strengthening. Strengthening the slabs with steel channel sections from above effectively improved the flexural strength and ductility of the slabs while being more economical and easier to implement than other methods of strengthening. Following strengthening, some slabs may require overlays to cover the steel sections and ensure that bridge traffic may go on them. Even after accounting for reduction in strength gain due to the deadload of the overlay, a positive net strength gain in measured peak moment was observed in the strengthened slabs. The moment capacities of the slabs, as determined through design calculations following the ACI 318–19 code, exhibit a good agreement with the measured peak moment observed in experimental tests, thus validating their reliability as a dependable alternative to solely relying on experimental tests.

Building a bimodal landscape: bedrock lithology and bed thickness controls on the morphology of Last Chance Canyon, New Mexico, USA

Abstract. We explore how rock properties and channel morphology vary with rock type in Last Chance Canyon, Guadalupe Mountains, New Mexico, USA. The rocks here are composed of horizontally to near-horizontally interbedded carbonate and sandstone. This study focuses on first- and second-order channel sections, where the streams have a lower channel steepness index (ksn) upstream and transition to higher ksn values downstream. We hypothesize that differences in bed thickness and rock strength influence ksn values, both locally by influencing bulk bedrock strength and also nonlocally through the production of coarse sediment. We collected discontinuity intensity data (the length of bedding planes and fractures per unit area), Schmidt hammer rebound measurements, and measured the largest boulder at every 12.2 m elevation contour to test this hypothesis. Bedrock and boulder mineralogy were determined using a lab-based carbonate dissolution method. High-resolution orthomosaics and digital surface models (DSMs) were generated from drone and ground-based photogrammetry. The orthomosaics were used to map channel sections with exposed bedrock. The United States Geological Survey (USGS) 10 m digital elevation models (DEMs) were used to measure channel slope and hillslope relief. We find that discontinuity intensity is negatively correlated with Schmidt hammer rebound values in sandstone bedrock. Channel steepness tends to be higher where reaches are primarily incising through more thickly bedded carbonate bedrock and lower where more thinly bedded sandstone is exposed. Bedrock properties also influence channel morphology indirectly, through coarse sediment input from adjacent hillslopes. Thickly bedded rock layers on hillslopes erode to contribute larger colluvial sediment to adjacent channels, and these reaches have higher ksn values. Larger and more competent carbonate sediment armors both the carbonate and the more erodible sandstone and reduces steepness contrasts across rock types. We interpret that in the relatively steep, high-level ksn downstream channel sections, the slope is primarily controlled by the coarse alluvial cover. We further posit that the upstream low-level ksn reaches have a base level that is fixed by the steep downstream reaches, resulting in a stable configuration, where channel slopes have adjusted to lithologic differences and/or sediment armor.

Design recommendation of cold-formed steel built-up sections under concentric and eccentric compression

A parametric investigation and design proposal for the back-to-back built-up cold-formed steel (CFS) channel sections with V-stiffeners and Σ-stiffeners under concentric and eccentric loading are presented in this paper. A nonlinear finite element model considering the initial geometric imperfection was developed and validated against experimental results. A total of 594 simulations were conducted involving a variety of slenderness ratios, eccentric axis directions, eccentricity, screw spacing and number of longitudinal holes. Simulation results including the load-carrying capacity, failure modes, ultimate bearing capacity versus eccentricity relationships, and load versus lateral displacement relationships were discussed. The influence of several member parameters on the load-carrying capacity and buckling modes was analyzed. Additionally, the applicability of the design strengths calculated from Chinese standard GB50018–2002 and North American specifications AISI S100–16 was evaluated based on the preliminary experimental results and simulation results. It was shown that both methods are conservative. Finally, a proposed DSM-based interaction equation considering the relationship between P/Pnd and M/Mnd was proposed and evaluated.