Reduction In Ultimate Strength Research Articles

Performance of reinforced concrete non-prismatic beams having multiple openings configurations

Abstract This experimental study demonstrates the gable-reinforced concrete beams’ behavior with several number of openings (six and eight) and posts’ inclination, aimed to find the strength reduction in this type of beam. The major results found are: for the openings extending over similar beam length it is better to increase the number of posts (openings), i.e., increasing opening number led to decrease in opening area, which allows us to transmit stresses and act as lever arms between the upper and the lower chords. Also, findings revealed that the inclined posts have larger loading at the mid-point relative to vertical ones. For gables with vertical posts having six and eight openings, the ultimate strength reduction was 31.5 and 25.6%, whereas it was 29 and 17.3% for those with inclined posts, respectively.

Computationally aware estimation of ultimate strength reduction of stiffened panels caused by welding residual stress: From finite element to data-driven methods

Ultimate limit state (ULS) assessment examines the maximum load-carrying capacity of structures considering inelastic buckling failure. Contrary to the traditional allowable stress principle which is mainly based on experiences, the ULS assessment focuses on explicitly evaluating the structural safety margin and thus enables a consistent level of safety/risk between conventional and novel structural designs. Modern structures are usually designed as a network of plates and stiffeners (e.g., ship structures, offshore and onshore wind turbine, and land-based bridge) joined by welding which induces a residual stress field. Hence, predicting the ultimate strength reduction of stiffened panels caused by welding residual stress is a crucial problem addressed by many scholars with different approaches, among which the Nonlinear Finite Element Method (NLFEM) is the prevailing approach within the community of structural engineering. Unfortunately, the NLFEM has a high computational requirement which prevents its use in the design, appraisal, and optimisation phases of stiffened panels. To well approximate the nonlinear finite element method, a data-driven method is proposed in this paper, with a functional which is computationally expensive to build but computationally inexpensive to use allowing its application at design stage. Results obtained in different (i.e., interpolation and extrapolation) scenarios using data generated by a state-of-the-art NLFEM on a series of stiffened panels will support the proposed method.

Ultimate strength assessment of cracked stiffened box girders subjected to extreme cyclic bending moments

This paper aims at obtaining insight on the ultimate strength characteristic of stiffened box girder under extreme cyclic bending. Nonlinear finite element analysis is performed to investigate the ultimate bending moment of cracked stiffened box girder. It is presumed that the preset crack is a through-thickness and transverse crack on the deck, the corresponding five types of cracked models are analyzed. The effects of crack type, crack length and crack location under cyclic loads are examined. Two load patterns are considered in this study, and crack propagation under bi-directional cyclic bending is simulated by applying the element erosion approach. The individual and coupling effects of fatigue crack damage and accumulated plastic damage on the ultimate bending moment of stiffened box girders are discussed. The mechanism of ultimate strength reduction under extreme cyclic bending is analyzed, it could be concluded that ultimate strength reduction is attributed to the coupling effect of these two damages and its applicability is verified by other stiffened box girders.

Effect of composition and microstructure on the rusting of MS rebars and ultimately their impact on mechanical behavior

Rebar steel is used for reinforcement to aid concrete because concrete does not sustain tension. Thermomechanical treatment is an advanced manufacturing technique for rebar production, but rusting problems emerged in the local steel industry. Raw material sampling included ingot casting (IC) and continuous casting (CC). IC samples corroded more frequently than CC samples. Spectroscopy indicated a small amount of chromium and an improper ratio of manganese to sulfur in IC samples. The improper ratio of manganese to sulfur in IC samples promoted hot cracking at grain boundaries, which resulted in intergranular corrosion. The microstructural results of G40 (air cooled) and G60 (water cooled) showed ferrite and martensite in different proportions. The deformed ferrite in G60 indicated inclination to corrosion, and no proper stable layer of martensite was found. The percentage of martensite was not enough to retaliate against intergranular corrosion. Highly pressurized water initiated pitting corrosion due to the formation of small pits on the surface. Tensile testing revealed 10% reduction in ultimate strength, 8% reduction in yield strength, and 30% reduction in percentage of elongation of corroded samples. Environmental study revealed that the humidity level in the industry was greater than in the laboratory space. High values of SOxand NOxemission revealed the involvement of the environment in the deterioration of the product surface.

A fully coupled chemo-mechanical cohesive zone model for oxygen embrittlement of nickel-based superalloys

For nickel-based superalloys subjected to high temperatures and oxygen-rich environments, mechanical loading in combination with oxygen diffusion along grain boundaries leads to an acceleration of crack propagation. To account for these phenomena, a fully coupled thermodynamically consistent chemo-mechanical modeling framework for stress-assisted oxygen embrittlement of grain boundaries in polycrystals is proposed. We formulate an extended cohesive zone model where the grain boundary strength is reduced by the presence of oxygen and the oxygen diffusion is enhanced by tensile mechanical loading. We show that the model can qualitatively predict experimental results such as: reduction of ultimate tensile strength and accelerated crack growth due to dwell time combined with mechanical loading and saturation of crack growth rates for increasing environmental oxygen pressure levels. In addition, numerical simulation results of intergranular crack growth are shown for a 2D polycrystalline structure. An emphasis is put on the difference in cracking behavior after dwelling with or without mechanical loading.

Mechanical properties of bridge-steel weldments at elevated temperatures

The fire-resistance design of welded steel bridges depends on the temperature-dependent mechanical properties at elevated temperatures. This study investigates experimentally the temperature-induced degradation of the mechanical properties of a bridge-steel weldment. A butt-welded joint, containing the base metal (BM) Q345qD steel and weld metal (WM), was welded via submerged arc welding. Monotonic tension tests of BM and WM cylindrical specimens were carried out under various temperatures in the range of 20–700 °C, and their stress-strain relationships, failure modes, yield strength, elastic modulus, and ultimate strength at elevated temperatures were obtained and analyzed. The reduction factors of yield strength, elastic modulus and ultimate strength are compared with those recommended in current design codes. It is shown that elevated temperatures can decrease significantly the material performance of the Q345qD weldment, and the degradation of the mechanical properties of the BM and WM differs with increasing temperature. The test data indicate that the reductions in yield strength, elastic modulus, and ultimate strength at 700 °C from those at 20 °C are 78%, 55%, and 84%, respectively, for the BM and 75%, 53%, and 79%, respectively, for WM. The predictive equations for characterizing the material properties and stress-strain relationships of the BM and WM at elevated temperatures are proposed, thereby providing essential data for evaluating the fire response of steel bridges.

Behavior of reinforced concrete tapered beams

Long span framed buildings and simply supported bridges produce high bending moment and deflection at mid-span. For these structures, using conventional prismatic beams with high depth shall be uneconomic. In such instances; using tapered beams may be considered a viable alternative to overcome this issue. There is lack of experimental and analytical studies on the behavior of reinforced concrete tapered beams (RCTBs) having mid-span depth enlargement.This research introduces experimental and finite elements method (FEM) study on the behavior of RCTBs with mid-span depth enlargement and different tapering angles and reinforcement configurations. Accordingly, six RCTBs and one prismatic beam were cast and tested up to failure. The test RCTBs were divided into two groups (three tapered beams for each group) depending on the tapering angle. Consequently, tapering angles of about 20° and 36° were adopted for beams of Group I and Group II, respectively. For each group, three different reinforcement configurations were adopted. It is observed from test results that RCTBs reinforced with bottom bent rebars have developed higher ultimate strength, stiffness and toughness compared with those beams having other reinforcement configurations. However, for RCTB with tapering angle of about 20° and reinforced with bottom bent rebars, a somewhat small reduction in ultimate strength of about 16% with gain in weight of about 27% was recorded compared to the prismatic beam. FEM using ABAQUS software was used to simulate the test beams. Good agreement was obtained between the experimental and FEM results in terms of load-deflection response and crack pattern. Moreover, the FEM study was extended to cover a reasonable range of tapering angles (17° to 45°) and bottom bent reinforcement ratios (0.0031 to 0.0086). It is observed from numerical results that decreasing of the tapering angle from 45° to 17° resulted in a significant increase in the ultimate load, initial stiffness and toughness and decreasing the mid-span deflection within entire range of loading. In addition, normalized charts were presented in this study to easily estimate the ultimate strength, initial stiffness, and toughness of a RCTB having a certain tapering angle and bottom bent reinforcement ratio.

EFFECTS OF WEB OPENINGS ON SHEAR BEHAVIOUR OF NORMAL AND INTERNALLY STRENGTHENED CONCRETE BEAMS

Web openings in reinforced concrete (RC) beams are provided to pass utility pipes and ducts through them. This causes high stresses (with local cracking) around the transverse web openings, which may lead to reduction in ultimate strength and stiffness of RC beams. Internal strengthening with shear reinforcement can increase ultimate strength of the beam with web openings. This paper presents an experimental study which was conducted to investigate load carrying capacity, mid-span deflection and failure modes of beams with web openings. A total of eighteen RC beams were included in the testing programme, which were tested under two-point loading. The beams contained both pre-planned and post-planned web openings. Experimental results showed that ultimate load of the beams decreased from forty-two to sixty-seven percent due to the presence of web openings in the shear zones. Shear strength of the beams with pre-planned web openings increased by thirty-six percent and one-hundred two percent as compared to the reference beam due to the increase of shear reinforcement by one-hundred twenty-two percent and three-hundred three percent, respectively. Similarly, increase in shear capacity up to six percent and fourteen percent was found for the beams with post-planned web openings due to the aforementioned increase in the area of shear reinforcement, respectively. The ultimate load carrying capacity was also compared with the theoretical models. Internal strengthening and pre planned opening were found effective for providing web openings in the beams.

Ultimate strength assessment of hull structural plates with general corrosion based on fractal theory

It is difficult to accurately evaluate the ultimate strength of hull plates due to the nonuniformity of general corrosion. The present study aims to introduce fractal theory to explore the influence of the nonuniformity of general corrosion on the ultimate strength reduction of hull plates. The monofractal characteristics and multifractal characteristics of the corroded plates constructed by fractional Brownian motion (FBM) are extracted. The fractal analysis of the corroded hull plate confirms the applicability of fractal theory in the evaluation of the irregularity of corrosion morphology. Finally, a series of nonlinear finite element analyses (FEAs) are carried out to establish the ultimate strength assessment formula with fractal parameters and the corroded volume loss.

Residual post fire strength of non-prismatic perforated beams

The main aim of this study is to assess the performance and residual strength of post-fire non-prismatic reinforced concrete beams (NPRC) with and without openings. To do this, nine beams were cast and divided into three major groupings. These groups were classified based on the degrees of heating exposure temperature chosen (ambient, 400, and 700°C), with each group containing three non-prismatic beams (solid, 8 trapezoidal openings, and 8 circular openings). Experimentally, given the same beam geometry, increasing burning temperature caused degradation in NPRC beams, which was reflected in increased mid-span deflection throughout the fire exposure period and also residual deflection after cooling. But on the other hand, the issue with existing openings was exacerbated. The burned NPRC beams were then gradually cooled down by leaving them at ambient temperature in the laboratory, and the beams were loaded until failure to examine the effect of burning temperature degree on the residual ultimate load-carrying capacity of each beam by comparing them to unburned reference beams. It was found, increasing the exposure temperature leads to a reduction in ultimate strength about (5.7 and 10.84%) for solid NPRC beams exposed to 400 and 700°C, respectively related to unburned one, (21.13 -32.8) % for NPRC beams with eight trapezoidal openings, and (10.5 - 12.8) % for those having 8 circular openings. At higher loading stage the longitudinal compressive strain of Group ambient in mid-span of solid beams reach 2700 με, while the others with openings exhibit divergent strain higher than that, it’s about 3300 με meanwhile, the lower chord main reinforcements have been pass beyond yielding stress. Exposure to high temperatures reduces rafters’ stiffness causing a reduction in load carrying capacity, companion with premature failure consequently reduce the strain at the ultimate stage.

Effect of nylon fabric reinforcement on the mechanical performance of adhesive joints made between glass and GFRP

The use of reinforcements in adhesive joints makes the stress distribution more uniform, improving their mechanical performance and adhesion. The present paper aims to verify the effectiveness and efficiency of the insertion of nylon 6 fabric in the adhesive layer, to study their applicability and functionality in building components. The increase in stiffness achieved by applying nylon 6 fabric in the adhesive layer between glass and GFRP pultruded profiles and steel laminates applied to GFRP beams is investigated. Three different epoxy adhesives and one epoxy resin are used and compared. Three different types of tests are carried out in order to study the different properties of the reinforcement system: tensile tests on GFRP/GFRP single-lap adhesive joints, with and without nylon fabric reinforcement; tensile tests on double-lap adhesive joints between float glass and pultruded GFRP profiles reinforced with nylon fabric according to four configurations (in the middle plane of the adhesive layer, on the glass surfaces, on the GFRP surfaces, on both GFRP and glass configurations) to verify the influence of its position; three-point bending tests on long GFRP tubular profiles reinforced with steel plates and nylon fabric in different configurations, to study resistance to bending loads. The results from the experimental campaign show the effectiveness of the reinforcement system using nylon fabric 6. In general, both a reduction in ultimate strength and an increase in joint stiffness compared to unreinforced configurations are observed.

Effect of grain size on deformation behavior of pure rhenium

A comprehensive study of grain size effect on twins, slips and work hardening of rhenium during tension was conducted using EBSD and SEM analysis. Slip/twinning trace and Schmid factor (SF) were analyzed to elucidate the activities of deformation modes. The deformation behavior was found to be sensitive to grain size. Non-basal slips and {112¯1} <1¯1¯26> extension twins were found to be the dominated deformation modes in the samples with large grain size. Large KAM values are located in twin GBs and severely deformed grains. Basal slip with low SFs was also activated to adapt strain-compatibility. With the decrease of grain size, non-basal slip was suppressed and an obvious transition from non-basal to basal slip-dominated flow occurred. The pure Re with coarse grain size (d = 67 μm) had a high elongation (27.6%) and ultimate strength (1168 MPa). In contrast, intergranular compatibility became difficult with decreasing grain size due to the progressively lower activation ability of deformation mechanisms, resulting in a reduction of ductility and ultimate strength. The exceptionally high work hardening rate of rhenium was mainly attribute to twin formation and basal slip activity during the initial straining. With the increase of grain size, high density cross-slip and twins provide additional work hardening, leading to extrapolated work hardening limit.

Effect of Cu Ion Concentration on Microstructures and Mechanical Properties of Nanotwinned Cu Foils Fabricated by Rotary Electroplating.

Rotary electroplating was employed to fabricate high-strength nanotwinned copper (nt-Cu) foils serving as a current collector for high energy-density lithium ion batteries (LIBs). The effect of Cu ion concentration on the microstructural and mechanical properties of the nt-Cu foils was then investigated. Formation of nano-scaled grains was found at the bottom. Its size gradually increases toward the top surface to form a microstructural mixture of gradient nano-scaled and columnar grains in the upper region. Experimental results show that the grains and elongation of the nt-Cu foils increase with increasing concentration of Cu ions. However, a trade-off between tensile strength and elongation is present. The elongation of nt-Cu foils has been enhanced by 22% (from 3.1% to 3.8%) while 8.3% and 3.9% reductions in ultimate tensile strength (UTS) and yield stress (YS) are seen. The current study shows a promising method to tune and optimize the microstructure and mechanical properties of such nt-Cu foils for various applications.

The Application of the Strength Reduction Shortest Path Method to the Stability Analysis of Shallow Buried Tunnel

To improve the theoretical analysis of surrounding rock stability of shallow buried tunnels. The strength reduction shortest path theory is applied to the stability analysis of shallow buried tunnel surrounding rock, combined with the ultimate equilibrium strength reduction theory. We discussed the influence of the depth and span ratio of tunnel, cohesion, and internal friction angle on the shortest path of the strength reduction, and studied the effects of various factors on shallow buried tunnel safety relationship by using strength reduction factor of safety and the shortest path of the shallow buried tunnel surrounding rock and the grey relational analysis theory. The results show that: in the analysis of shallow buried tunnel in strength reduction, the approximate distribution obeys parabolic between reduction path length and the reduction ratio. When the strength reduction of cohesion is the shortest path the reduction rate is greater than the internal friction angle. The internal friction angle and cohesive force have a great influence on the stability of shallow tunnels under the method of shortest path of strength reduction. Finally, the comprehensive safety factor of shallow buried tunnels calculated by the finite element strength reduction shortest path method is greater than that calculated by the limit equilibrium method.

Process Parameters Optimization for Maximizing Tensile Strength in Friction Stir-Welded Carbon Steel

The present study focuses on improving the ultimate tensile strength of friction stir welded carbon steel (AISI 1018). The effect of the process parameters (welding speed, tool RPM, and shoulder diameter) on the response parameters (ultimate tensile strength, percentage elongation and percentage reduction in area) were studied. Response surface methodology was used to develop the mathematical model for response parameters, and the adequacy of the model was checked using analysis of variance (ANOVA). The welding speed and tool RPM were found to affect the ultimate tensile strength significantly. The percentage elongation was affected only by welding speed. The percentage reduction in the area was affected by welding speed and shoulder diameter. The microstructure and microhardness of the weld have been studied and reported in the study.

A study on the residual ultimate strength of continuous stiffened panels with a crack under the combined lateral pressure and in-panel compression

In this study, the effects of the crack on the residual ultimate strength of a continuous stiffened panel with a crack under the combined lateral pressure and in-panel compression are investigated numerically. Based on the fact that the extent of model should be sufficient to analyze the surrounding structure, a two-span (1/2 + 1+1/2) model is modeled. Periodic and symmetric boundary conditions are used to calculate the ultimate strength of stiffened panels with a crack, a Plug-in that can be executed in ABAQUS has been developed using Python language. The accuracy of the advanced model is verified, and the influences of various parameters on the ultimate strength reduction rate of a continuous stiffened panel with a crack are comprehensively investigated. The results of the investigation showed that crack location was very important in the evaluation of the residual ultimate strength of a stiffened panel with a crack, and in particular, the cracks under the stiffener have a great influence on the ultimate strength reduction rate of the stiffened panel. Finally, a prediction equation capable of predicting the ultimate strength reduction rate of continuous stiffened panels with a crack is proposed and verified for its accuracy.

Tensile stress strain model of polyvinyl chloride/calcium carbonate (PVC/CaCO3) nanocomposite plank

This paper presents the tensile stress strain model of a recyclable polyvinyl chloride/calcium carbonate (PVC/CaCO3) thermo-formable, fire/water proof resistant, and durable composite mineral plank. The paper presents experimentally obtained material stress-strain properties in direct tension as a function of its parameters including thickness, surface texture and grain alignment. With an increase in thickness from 1 mm (0.039 in.) to 12 mm (0.47 in.) for rough surface texture and parallel grain alignment, tensile and rupture strengths decreased from 27.4 MPa (4.11 ksi) to 14 MPa (2.1 ksi) and from 14 MPa (2.1 ksi) to 6 MPa (0.9 ksi) respectively. Strains at rupture increased from 0.01 to 0.02 while the modulus of elasticity decreased from 23078 MPa (3462 ksi) to 2139 MPa (320.85 ksi). Smoothness of surface texture increased the ultimate and rupture stresses by 16% while rupture strains increased by 45% leading to a more ductile material. Grain orientation perpendicular to the load direction resulted in an 18% reduction in ultimate strength. The paper proposes models for predicting the stress strain relationship including modulus of elasticity, toughness, stress and strain in the proportional, ultimate and rupture states in terms of the material parameters. The developed models are essential for establishing code requirements and design criteria for structural members retrofitted with this type of composite.

The influence of residual stress on the ultimate strength of longitudinally compressed stiffened panels

Welding-induced residual stress is known to reduce the ultimate compressive strength of moderately slender stiffened panels under longitudinal compression. This paper contributes a quantified measure of this strength reduction and draws some qualitative observations linking the significance of the residual stress influence to the collapse mode of the panel. A series of nonlinear finite element analyses are completed which covers a range of plate slenderness ratios (β=1.0−4.0) and column slenderness ratios (λ=0.2−1.2) typical for application to ship structures. Two residual stress scenarios are compared to a baseline stress-free condition. The first scenario includes residual stress in the plate only and the second scenario includes residual stress applied in the plate and the stiffener web. A modified edge function approach, which can be used in combination with a rule-based approach to account for the effects of residual stress, is examined with reference to the numerical results. A significant ultimate strength reduction due to residual stress is found in most test cases. It is found that residual stress in the plate causes a reduction of the ultimate compressive strength of stiffened panels regardless of failure modes. However, the residual stress in the stiffener web dominates the strength reduction of stiffened panels where collapse is triggered by beam-column buckling. Conversely it has little influence on the stiffened panels which collapse in a plate buckling mode. In addition, the modified edge function approach is demonstrated as conservative compared to the present numerical results, with its applicability confined to stocky panels.

Residual Ultimate Strength of Steel Plates with Longitudinal Crack and Pitting Corrosion under Axial compression: Nonlinear Finite Element Method Investigations

The main aim of present study was to determine the ultimate strength of cracked and corroded plates under uniform in-plane compression. Corrosion is considered as pitting-type corrosion at one side of the plate with a central longitudinal crack. Nonlinear finite element analysis using commercial computer code, ANSYS, is used to determine the ultimate strength of deteriorated plates. Different geometrical parameters, including the aspect ratio (AR) and thickness of the plate, number of pits, pit depth-to-thickness ratio, and crack length, are considered. It is found that the AR of plates have great influence on the ultimate strength of cracked-pitted plates. Because of the position and orientation of the crack, the length of central longitudinal crack has no influence on ultimate strength reduction of cracked and cracked-pitted plates. The results show that regardless of the number of pits and crack length, in thin plates where buckling controls failure modes at ultimate strength, the number of pits has less influence on reduction of the ultimate strength than thick plates where yielding controls failure mode. Also it is concluded that in rectangular plates, arrangements of pits has more effect on reduction of the ultimate strength of cracked-pitted plates than the number of pits.

Effects of process interruptions on microstructure and mechanical properties of three face centered cubic alloys processed by laser powder bed fusion

Many factors can influence the thermal history during laser powder bed fusion (L-PBF) that contribute to the microstructure and mechanical performance of produced components. These factors can include process parameters, geometry, feedstock characteristics, and more. In this work, we report on the effect that process interruptions have on the thermal history during L-PBF fabrication of simple geometries made out of three alloys of interest: AlSi10Mg, Inconel 718 and Inconel 625. Systematic experiments were carried out with programmed process interruptions lasting one hour and simulating a stop to refill the system with powder, or an unexpected power outage. Specimens produced through these experiments enabled studying microstructural differences using microscopy techniques, and the evaluation of tensile and hardness properties when compared to uninterrupted controls. The findings from this study indicate that there were no distinguishable microstructural differences from interrupted specimens and uninterrupted controls for all three materials. Also, although Inconel 718 interrupted specimens showed a slight reduction in ultimate tensile strength and elongation, these properties remained essentially unchanged for AlSi10Mg and Inconel 625. Although a more comprehensive study is still required that accounts for the effect of thermal post-processing and other factors, the results described here provide several observations of the potential effects of process interruptions, and the implications towards process validation and quality assurance of L-PBF.