Channel Section Research Articles

Influence of Non-Newtonian Viscosity on Flow Structures and Wall Deformation in Compliant Serpentine Microchannels: A Numerical Study.

The viscosity of fluid plays a major role in the flow dynamics of microchannels. Viscous drag and shear forces are the primary tractions for microfluidic fluid flow. Capillary blood vessels with a few microns diameter are impacted by the rheology of blood flowing through their conduits. Hence, regenerated capillaries should be able to withstand such impacts. Consequently, there is a need to understand the flow physics of culture media through the lumen of the substrate as it is one of the vital promoting factors for vasculogenesis under optimal shear conditions at the endothelial lining of the regenerated vessel. Simultaneously, considering the diffusive role of capillaries for ion exchange with the surrounding tissue, capillaries have been found to reorient themselves in serpentine form for modulating the flow conditions while developing sustainable shear stress. In the current study, S-shaped (S1) and delta-shaped (S2) serpentine models of capillaries were considered to evaluate the shear stress distribution and the oscillatory shear index (OSI) and relative residual time (RRT) of the derivatives throughout the channel (due to the phenomena of near-wall stress fluctuation), along with the influence of culture media rheology on wall stress parameters. The non-Newtonian power-law formulation was implemented for defining rheological viscosity of the culture media. The flow actuation of the media was considered to be sinusoidal and physiological, realizing the pulsatile blood flow behavior in the circulatory network. A distinct difference in shear stress distributions was observed in both the serpentine models. The S1 model showed higher change in shear stress in comparison to the S2 model. Furthermore, the non-Newtonian viscosity formulation was found to produce more sustainable shear stress near the serpentine walls compared to the Newtonian formulation fluid, emphasizing the influence of rheology on stress generation. Further, cell viability improved in the bending regions of serpentine channels compared to the long run section of the same channel.

Improving the crashworthiness of carbon fiber-reinforced composite channel section structure through controllable failure mechanisms

To improve the crashworthiness of the composite channel section structure (CCSS), three external triggers including ditch plug trigger (DPT), trapezoidal groove trigger (TGT), and v-groove trigger (VGT) are proposed. A progressive damage model for CCSS is developed considering the damage initiation and evolution of intra- and inter-ply. Based on the model, the effects of the size of the external trigger and the friction coefficient between the external trigger and the structure on the axial energy absorption characteristics and failure modes of CCSS are investigated. The results show that the external trigger has a large influence on the failure process. The increase in ditch height of DPT is beneficial to improve the load-bearing capacity of the structure in the middle stage of crushing. Compared to DPT and TGT, VGT is more effective in decreasing the initial peak load and increasing the crushing load efficiency. The failure mechanisms of CCSS induced by the external trigger are revealed. The proposed external trigger can induce specific failure modes, and the structure tends to slide toward the middle after contact with TGT and VGT. The increase of the friction coefficient between CCSS and TGT or VGT can improve energy absorption. The results of the study can provide a reference for the design of external triggers for CCSS.

Elastic critical local buckling stress in cold-formed lipped channel and hat sections under uniform compression

The classical design approach for the elastic critical local buckling load of the cold-formed open section (CFOS) neglects the plate element interaction at the cross-section, which compromises the benefits of CFOSs designed for high performance. To derive a novel formula for the local buckling coefficient, taking into account the plate element interaction at the cross-section, a series of displacement functions for expressing the buckling deformations of the web, flanges, and lips caused by local buckling in CFOSs is proposed in this paper. The effect of cross-sectional geometry on the buckling coefficient was investigated using the proposed formula derived from Timoshenko’s plate buckling theory. Further, simplified formulae were proposed for the buckling coefficient and half wavelength of the elastic critical local buckling for practical use. The reliabilities of the proposed formulae were verified by comparing the results obtained from the proposed formulae with the analysis results based on the finite element method and finite strip method.

Web crippling behaviour of cold-formed steel channel sections having elongated edge-stiffened web holes under interior-two-flange loading condition

In the past decade, cold-formed steel (CFS) channel sections having circular edge-stiffened 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 holes, while still allowing full service integration. In the case of web crippling, previous research has found that use of edge-stiffened holes almost results in the same strength of an equivalent channel-section having a plain web. Such circular edge-stiffened web holes can now be extended to elongated edge-stiffened web holes. However, for such elongated holes, no experimental tests have been reported in the literature. In this paper, a numerical investigation was carried out, and non-linear finite element (FE) analyses were used to investigate the web crippling behaviour of CFS channel sections having edge-stiffened web holes under the interior-two-flange (ITF) loading condition. The cases of both flange fastened and flange unfastened were considered. The FE models were validated against test results of sections having circular edge-stiffened web holes; good agreement in terms of the load–displacement curves and deformed shapes was shown. Using the validated FE models, a parametric study was carried out on CFS channel sections having elongated un-stiffened and edge-stiffened web holes, comprising 1,227 finite element analyses (FEA) results. Compared to sections having a plain web, for the case of an elongated opening, without any edge-stiffener, having an aspect ratio of two and three, the average reduction in web crippling strength was 39% and 49%, respectively. However, for an edge-stiffened hole, the reduction in the web crippling strength was reduced to only 2% and 16%, respectively. Finally, the design equations in the form of the web crippling reduction factor (Rp) and the equations based on the direct strength method (DSM) for CFS sections with elongated web holes were proposed.

Web bearing design of cold-formed austenitic stainless steel un-lipped channels under localised interior loading

The high corrosion resistance, recyclability, ductility, and durability of stainless steels make them appealing for use in the construction industry. However, when used as structural channel sections, they are subject to localised failure in the web. This study aims to evaluate the structural behaviour of cold-formed austenitic stainless steel unlipped channels under localised interior loading. The results of conducting a novel testing programme with 21 new tests on such channels with different cross-section sizes and thicknesses are presented. Then a non-linear quasi-static Finite Element (FE) model is developed. The FE model is validated against experimental test results and found to demonstrate a good agreement in terms of bearing capacity and failure modes. It is found that no cold-formed stainless steel standard provides web bearing capacity equations for the localised interior loading (IL) that apply when simulating a floor joist on a solid foundation. The web bearing capacities are compared with capacities determined from the literature (including DSM). It is found that for the case of unlipped channels (unstiffened flanges), the current equations are unreliable and unconservative by up to 36%. The experimental investigation shows that, the American specification (SEI/ASCE 8:2002) is unconservative as much as 41%. Using both experimental and numerical results from this study, a new design equation is proposed for austenitic stainless steel unlipped channels under localised interior loading.

Stainless steel built-up section stub columns: Testing, numerical modelling and design

This paper presents experimental and numerical investigations into the cross-sectional compressive behaviour and resistances of stainless steel built-up section stub columns. An experimental programme was firstly conducted on six built-up (open) I-sections and seven built-up (closed) tubular sections, with each composed of two identical press-braked stainless steel channel sections assembled by self-tapping screws, and included tensile coupon tests, initial local geometric imperfection measurements and twenty stub column tests. The experimental programme was followed by a numerical modelling programme, where finite element models were developed and validated against test results and then used to conduct parametric studies, aiming at investigating the effect of screw spacings and generating further numerical data over a wide range of cross-section dimensions. For the design of a stainless steel built-up section stub column, the current European code and American specification treat it as two individual channel section members and adopt effective width methods for calculating the cross-section compression resistance of each channel section member. Both design codes were found to result in many unsafe failure load predictions for stainless steel built-up I-section stub columns but conservative failure load predictions for stainless steel built-up tubular section stub columns. Finally, revised codified design rules were proposed by treating each built-up section as a whole and using an equivalent thickness of the overlapped plate elements, and shown to provide accurate, consistent and safe cross-section compression predictions for stainless steel built-up section stub columns.

Topology Optimization of Aircraft Wing

The objective of this paper is to obtain an optimal concept design of aircraft wing. Topology optimization is used to yield an optimized shape and material distribution for a set of loads and constraints within a given design space. Initially a solid wing was considered as design space and meshed using hexahedral elements to derive the optimal location of spars and ribs such that the structure has minimum compliance. Load data includes flight, fuel and engine loads. The wing was constrained in all degrees of freedom at the root. It was shown that the results can be used to derive an appropriate configuration similar to the existing design practices. A new geometry with spars, ribs, hinge locations and lug attachments was next considered. The skin was meshed with shell elements. Hinge loads were also included. The optimization gave a box section for front spar, channel section for rear spar, truss pattern for ribs and V shaped member for hinges. Using this global material distribution a component level topology optimization was performed. The concept design is realized in to CAD and then a composite free-size optimization is performed to determine material distribution and ply drop regions etc. Finally a composite size and shape optimization is done.

Experimental study and prediction of two-phase flow pattern distribution diagrams in multi-channel cylinder dryer

The multi-channel cylinder dryer (MCD) is designed to improve heat transfer. Although there are numerous research studies on the pressure drop, heat transfer characteristics, and flow pattern in static state of MCD, there is little research on the flow pattern in the rotating state. In this paper, the distribution of flow pattern in MCD under different rotating speeds and steam mass flow rates is studied. Furthermore, the logistic regression method (LR) is used to predict the flow pattern diagrams. The results show that in the front section of the flow channel, the flow pattern is basically annular flow, which is not affected by mass flow rate and rotating speed. On the other hand, wavy flow, vortex flow, slug flow, and bubble flow can be observed when the fluid enters the middle and the end section. The higher the rotating speed and the steam mass flow rate, the more the flow pattern tends to be an annular and wavy flow. At the end of the passage, the flow pattern is mainly slug flow. The predicted flow pattern diagrams are in good agreement with the experimental result, and to obtain an effective flow pattern in the middle and the end section of the flow channel, the influence of increasing rotating speed is greater than that of increasing steam mass flow rate. However, the specific rotating speed, steam mass flow rate, and other parameters should still be set by combining with the actual situation. This work can provide some references for the further study of MCD flow characteristics.

TerraSAR-X and GNSS Data for Deformation Detection and Mechanism Analysis of a Deep Excavation Channel Section of the China South–North Water-Diversion Project

Due to expansive soils and high slopes, the deep excavated channel section of the China South–North Water-Diversion Middle-Route Project has a certain risk of landslide disaster. Therefore, examining the deformation law and mechanism of the channel slope in the middle-route section of the project is an extreme necessity for safe operation. However, the outdated monitoring method limits research on the surface deformation law and mechanism of the entire deep excavation channel section. For these reasons, we introduced a novel approach that combines SBAS-InSAR and GNSS, enabling the surface domain monitoring of the study area at a regional scale as well as real-time monitoring of specific target regions. By using SBAS-InSAR technology and leveraging 11-view high-resolution TerraSAR-X data, we revealed the spatiotemporal evolution law of surface deformations in the channel slopes within the study area. The results demonstrate that the predominant deformation in the study area was uplifted, with limited evidence of subsidence deformation. Moreover, there is a distinct region of significant uplift deformation, with the highest annual uplift rate reaching 19 mm/y. Incorporating GNSS and soil-moisture-monitoring timeseries data, we conducted a study on the correlation between soil moisture and the three-dimensional deformation of the ground surface, revealing a positive correlation between the soil moisture content and vertical displacement of the channel slope. Furthermore, combining field investigations on surface uplift deformation characteristics, we identified that the main cause of surface deformation in the study area was attributed to the expansion of the soil due to water absorption in expansive soils. The research results not only revealed the spatiotemporal evolution law and mechanism of the channel slope deformation in the studied section of the deep excavation channel but also provide successful guidance for the prevention and control of channel slope-deformation disasters in the study area. Furthermore, they offer effective technical means for the safe monitoring of the entire South–North Water-Diversion Middle-Route Project and similar long-distance water-conveyance canal projects.

Analisis Volume Sedimen Terhadap Pendangkalan Di Dalam Saluran Primer Jaringan Irigasi (Studi Kasus: D.I. Cipicung Subang)

Research conducted in the primary canal of D.I Cipicung, Subang Regency, experienced damage to the irrigation network. Damage to the D.I Cipicung irrigation canal network in the primary canal, so that research is needed to find out how much silting volume is caused by sediment deposition in the irrigation canal. The method in this study uses a mathematical method to determine the volume of sediment deposition in the channel. The results show that the volume of sediment in the primary canal in the Cipicung D.I irrigation network is Vq Primary = 16.24 m3 (difference in depth 0.64 m) or 0.16% of the length per section 50.5 m of the total length of the primary canal 300 m and the change in the cross section of the primary channel is A = 1.25 m2 or 27.11%. So that the results of these calculations, it is necessary to resolve by repairing the right side of the canal lining with construction, the entrance channel from the river to the primary canal needs to be built a gate, dredging of sediment is required in the primary canal, and maintenance is required so that the canal is routinely once a week or once a month so that the strong channel is not quickly damaged.
 Keywords: Sediment Siltation, Primary Canal, Irrigation Network Damage.

Web crippling tests on cold-formed high strength steel channel sections having different stiffened flanges and stiffened web

This paper reports 59 tests on cold-formed high strength steel channel sections with different stiffened flanges and stiffened web. The test specimens were brake-pressed from high strength zinc-coated grades G450, G500 and G550 structural steel sheets. The test program consisted of 6 series of channel sections having different stiffened flanges, web slenderness, material strengths and loading conditions. The loading conditions were End-Two-Flange (ETF), and Interior-Two-Flange (ITF) loadings as specified in the North American Specification for cold-formed steel structures. The web crippling test strengths and load–displacement relationships of the channel section specimens were obtained from the tests. The channel sections having stiffened flanges as well as the channel sections having stiffened web enhanced the web crippling strengths of the specimens, especially for those specimens loaded under ETF loading condition. The web crippling test strengths were also compared with the design strengths calculated using the current North American Specification and European Code for cold-formed steel structures. In addition, reliability analysis was performed to assess the reliability of the design rules. Generally, it is found that the predictions obtained from the North American Specification are unconservative and unreliable for the cold-formed high strength steel channel section specimens, except for the specimens with unstiffened flanges under ITF loading condition, while the European Code was unreliable but conservative in predicting the web crippling strengths, except for the specimens with unstiffened flanges under ETF loading condition.

Large-scale shaking table tests of a six-story floor-by-floor assembled CFS frame-framing shear wall structure

To study the seismic performance of a proposed multi-story floor-by-floor assembled structure using cold-formed steel (CFS) frame with square columns and double-channel beams connected by novel joints, and CFS framing walls as shear walls, shake table tests were conducted on a 2:3 scaled six-story CFS frame-framing shear wall structure (CFSF-FSWS) using bidirectional seismic inputs. A prefabricated concrete floor slab was proposed utilizing the channel section beams as the molds during prefabricating processes. The CFS framing shear walls were designed with various configurations researched before: framed or trussed skeleton, single or double side sheathing, flat or corrugated steel sheathing sheet. The observed damages, dynamic properties, seismic responses and failure mechanisms of the CFSF-FSWS under different peak ground accelerations (PGAs) were analyzed. The CFS frame carried gravity load, and the horizontal earthquakes were mainly resisted by CFS framing shear walls. The results indicated a good deformation capacity and seismic performance of the CFSF-FSWS building. The damping ratio of the test model gradually increased with the accumulation of damage, varying between 3.30%∼6.95%. After all seismic loading, the CFS frame remained intact and the damages were concentrated on the CFS framing shear walls, achieving the design objective of “separated gravity and lateral resisting systems”.

Design of aluminum alloy channel sections bent about the minor axis

Aluminum alloy extruded channel sections are often used as rafters for light roofs, columns in framed buildings and chords of roof trusses. In this paper, a numerical study is carried out on the response of aluminum alloy channel sections under minor axis bending. Numerical models were developed and validated based on the experimental data of aluminum alloy channel sections under minor-axis bending. Subsequently, parametric studies covering various cross-sectional geometries were performed to expand the numerical data. The results were used to assess the applicability of Eurocode 9 slenderness limits, revealing that the Class 2 and Class 3 limits for outstand flanges under stress gradient with peak compression at tip are too conservative. Moreover, Eurocode 9 underestimates the predicted bending strengths of slender cross-sections due to the lack of consideration of the effect of stress gradient. The equivalent stress gradient factor applied in the effective thickness approach was proposed based on the buckling coefficient of BS 5950. For channel sections bent about minor-axis with the web in compression, flanges exhibit pronounced inelastic behavior even when the web locally buckles. An alternative design method based on the ultimate shape factor of a rectangular plate is proposed for semi-compact and slender channel sections in minor-axis bending (producing compression in the web), which leads to more favorable and less scattered capacity predictions.

Structural performance of stainless steel sections fabricated by laser-welding, hot-rolling and extrusion

This paper presents an experimental investigation on the structural performance of austenitic stainless steel columns with open sections fabricated by laser-welding, hot-rolling and extrusion. The aim of the experimental programme was to quantify and compare the effect that different fabrication techniques have on the structural behaviour of the columns. The investigated cross-sections were extruded and laser-welded I-sections with the American designation S5x10, and hot-rolled and laser-welded channel sections with the European designation UAP 120x60x6. All sections were fabricated from austenitic stainless steel grade 1.4307/1.4301 (dual certified). The experimental programme consisted of stub and long column tests, as well as measurements of all the parameters that were considered to have an impact on the structural behaviour of the sections, including: material properties, cross-sectional geometry, residual stresses and global geometric imperfections. The tests showed that although the residual stresses and geometric imperfections of the austenitic stainless steel laser-welded columns are similar to those of the extruded/hot-rolled columns, their structural performance was noticeably better than that of the extruded sections, and equivalent to that of the hot-rolled sections. The experimental data was also used to assess the adequacy of the European column curves for laser-welded and hot-rolled open sections susceptible to flexural buckling about the minor axis. It was found that while for laser-welded I-sections it may be possible to justify a higher buckling curve, more research is needed for channels.

Web Crippling Behaviour of High-Strength Aluminium Alloy Channel Sections under Concentrated Loading: Numerical Modelling and Proposed Design Rules

Two types of high-strength aluminium alloy (HA)—namely, AA-6086 and 7075-T6—have been developed and extensively used in recent years. These high-strength aluminium alloys offer advantages such as lower prices and higher yield strength than traditional alloys. The webs of aluminium channel members under concentrated loads are susceptible to web buckling failure, which restricts their applications. However, no research work has been reported that has evaluated the web buckling performance of high-strength aluminium alloy channel sections subjected to end-two-flange (ETF) loading, and the material characteristics of these high-strength aluminium alloys differ significantly from those of conventional aluminium alloys. This work addresses this gap by conducting a detailed numerical investigation. A parametric investigation consisting of 1024 models was performed using the finite element (FE) models previously developed for traditional aluminium alloys. A wide range of high-strength aluminium alloy sections covering varying web slenderness ratios, internal corner radii, bearing lengths, and aluminium alloy grades were considered in this investigation. It was shown that the latest design recommendations in the Australian and New Zealand Standards (AS/NZ S4600) and (AS/NZS 1664.1) were over-conservative when estimating the web buckling strength of such channel sections. Finally, new web buckling design equations for high-strength aluminium alloy channel sections were proposed through reliability analysis in this investigation.

Experimental study on suppressing pressure feedback and combustion product backflow of the rotating detonation engine

To further improve the feedback suppression effect of rotating detonation engines (RDEs), an optimized Tesla valve inlet structure (TVI-II) was designed on the basis of the previous research of our research group. Taking kerosene and 29% oxygen-enriched air as the reactants, the operation characteristics, the feedback suppression effect, and the feedback suppression mechanism were obtained through a series of experiments. It is found that due to the existence of bypass channel, TVI-RDE can effectively suppress the occurrence of longitudinal pulsed detonation and broaden the working boundary of the engine. The working range of the TVI-I-RDE was broadened by 183.3%, and that of the TVI-II-RDE was broadened by 700%. The TVI-II-RDE is more effective in suppressing pressure feedback and combustion product backflow. When the pressure feedback phenomenon occurs, the rotating detonation wave mainly decoupled and attenuated in the converging section of bypass channel. The minimum pressure feedback percentage (PFdw) of TVI-II-RDE was 11.4%, as compared to about 40% for the TVI-I-RDE. The change law of the air plenum pressure fluctuation percentage (PFap) was similar to that of PFdw, and the minimum PFap of the TVI-II-RDE was about 7.7%. Narrower bypass channel width would lead to longer residence time of combustion products. The effective inlet area ratio (EA) of the TVI-II-RDE was at least 95.7%, which is at least 6.1% higher than that of the CDI structure. The results show that the TVI-II-RDE has great potential in suppressing feedback, which promotes the engineering application of RDE.

Simulations of Flows via CFD in Microchannels for Characterizing Entrance Region and Developing New Correlations for Hydrodynamic Entrance Length.

Devices with microchannels are relatively new, and many correlations are not yet developed to design them efficiently. In microchannels, the flow regime is primarily laminar, where entrance length may occupy a significant section of the flow channel. Therefore, several computational fluid dynamic simulations were performed in this research to characterize the developing flow regime. The new correlations of entrance length were developed from a vast number of numerical results obtained from these simulations. A three-dimensional laminar flow for 37 Reynolds numbers (0.1, 0.2, …, 1, 2, …, 10, 20, …, 100, 200, …, 1000), primarily in low regime with water flow through six rectangular microchannels (aspect ratio: 1, 0.75, 0.5, 0.25, 0.2, 0.125), has been modeled, conducting 222 simulations to characterize flow developments and ascertain progressive velocity profile shapes. Examination of the fully developed flow condition was considered using traditional criteria such as velocity and incremental pressure drop number. Additionally, a new criterion was presented based on fRe. Numerical results from the present simulations were validated by comparing the fully developed velocity profile, friction factor, and hydrodynamic entrance length for Re > 100 in rectangular channels, for which accurate data are available in the literature. There is a need for hydrodynamic entrance length correlations in a low Reynolds number regime (Re < 100). So, the model was run numerous times to generate a vast amount of numerical data that yielded two new correlations based on the velocity and fRe criteria.

Analysis of Vortex Evolution in the Runner Area of Water Pump Turbine under Runaway Conditions

In order to study the evolution principle of the coherent structure in the low flow rate runaway condition, the pump turbine of a certain pumped storage power plant was employed. The transient dynamic stress of the runner was numerically simulated and examined in this study in order to analyze the coherent structure of the vortex and the stability of the grid connection during the transition process. Based on the realizable k-ε turbulent model, the unsteady flow of the whole pump turbine channels was calculated. The results show that the flow in the runner channels presents with a turbulence state, and with many different scales vortices. These vortex structures are mainly distributed in the inlet region of the blade, the area of the blade trailing edge and the middle section of the runner channels. These vortex structures affect the distribution of the blade pressure load. Moreover, the vortex structure at the inlet of the runner depends on the change in the attack angle. In the flow region formed at the outlet of the blade near the suction surface and the runner cone, the blade has a limited effect on the fluid; thus, the vortex structure depends on the Coriolis force and the centrifugal force joint action. The evolution of these vortex structures will have a greater impact on the grid connection of the power station. During the operation of the power station, it is necessary to reduce the time of transitional conditions so that the power station can operate efficiently.

Structural behaviour and design of press-braked S690 high strength steel channel sections under combined compression and minor-axis bending

This paper presents experimental and numerical investigations into the cross-sectional behaviour and resistances of press-braked S690 high strength steel channel sections under combined compression and minor-axis bending. An experimental programme was firstly conducted and included initial local geometric imperfection measurements and ten minor-axis eccentric compression tests. The experimental programme was accompanied by a numerical modelling programme, where finite element models were developed and validated against the test results and then employed to perform parametric studies to expand the test data pool over a wider range of cross-section dimensions and loading combinations. The obtained test and numerical data were then used to assess the relevant codified design interaction curves, as provided in the European code, North American specification and Australian/New Zealand standard. The assessment results revealed that all the codified design interaction curves led to excessively conservative and scattered resistance predictions for press-braked S690 high strength steel channel sections under combined compression and minor-axis bending, mainly owing to the conservative linear shapes and inaccurate end points. Finally, a new design interaction curve, with more accurate end points and nonlinear shape, was proposed and shown to offer more accurate and consistent resistance predictions than the codified design interaction curves.

Flexural Behavior of Built-Up Cold-formed Steel Channel Section Strengthened with Oriented Strand Board

The objective of the study is to determine the flexural behavior of the built-up cold-formed steel (CFS) channel section strengthened with an oriented strand board (OSB) in the three-point bending experiment. CFS with a variety of shapes and grades is classified as a steel-based material and exposed to buckling failure when subjected to compression or flexural load. Thus, the CFS channel section with 100 mm of the web, 50 mm of the flange, 12 mm of the lip, and 1.55 mm of thickness has been selected. Then, the built-up CFS channel section is designed by filling with an OSB between the gap of each section. Channel, face-to-face built-up, and back-to-back built-up CFS sections are three types of tested specimens. From the result and discussion, the specimen with back-to-back built-up CFS section is recognized to sustain the ultimate load with the highest value when compared with other specimens.