Nominal Ultimate Strength Research Articles

Corrosion characteristics and evaluation of galvanized high-strength steel wire for bridge cables based on 3D laser scanning and image recognition

The study investigates the corrosion behavior of galvanized high-strength steel wire, which significantly affects the bearing capacity and residual fatigue life of cables in cable-supported bridges. Through standardized salt spray accelerated corrosion tests, steel wires with varying corrosion degrees are obtained. Three-dimensional laser scanning technology reconstructs the corroded wire surface, while image recognition techniques extract geometric characteristics of corrosion pits. Fitting expressions are established to correlate the minimum cross-sectional area, maximum pit depth and dip angle, and mass loss ratio of the wire. Statistical analysis reveals log-normal distributions for the lengths of major and minor axes of corrosion pits over time. Fitting curves for elongation after fracture, nominal yield strength, and nominal ultimate strength, along with elastic modulus distribution, are derived for different mass loss ratios. Comparing corrosion grading criteria, the study quantitatively describes corrosion characteristic parameters for distinct corrosion grades. These insights enhance understanding of corrosion behavior and mechanical property degradation in high-strength steel wires, offering a quantitative framework for assessing and classifying corrosion extent based on measurable parameters.

Tensile-Mechanical Degradation-Properties and J-C Constitutive Model of Studs after Strong-Acid Corrosion

This paper presents an investigation on strong-acid relations between corrosion rate and corrosion time in 30 studs, dipped into 36% industrial hydrochloric acid through 0.5 h, 1 h, 2 h, 4 h, 8 h, 12 h, 24 h, 48 h, and 72 h, respectively. These corroded studs are performed tensile tests to study failure mode and stress-strain curves in studs with different corrosion time. Thereafter, a 3-D finite element is established through computer program to validate test results, and then analyze mechanical properties along with failure mode of studs exposed to strong-acid corrosion. The analysis results show that the failure mode gradually changes from ductile-damage state to brittle-damage state. The corrosion rates present a non-linear elevation with an increase of strong-acid-corrosion time. The nominal yield strength, the nominal ultimate strength, and the elongation in the corroded studs exhibit a fast-downward trend when increasing corrosion time. However, the degradation of elastic modulus turn into a slow step and the yield strength ratio in studs tends to be steady. The J-C model (Johnson-Cook Constitutive) with updated coefficients can be applied to reflect the constitutive relations in studs after strong-acid corrosion under quasi-static tension conditions. Further, this model can simulate stress flows within studs after strong-acid corrosion. This research results can provide a guide for long-lifetime construction and safe maintenance in steel structural bridge.

Time-Dependent Reliability Analysis of Corroded Steel Beam

The time-dependent reliability of corroded steel beam was investigated. Nine groups of specimens were subjected to accelerate corrosion by the outdoor periodic spray test and monotonic tensile test. The surface profile of corroded steel plates and the 3D data of corrosion depth were measured by the three-dimensional non-contact surface topography instrument (PS50 3D). The probability distribution of corrosion depth and nominal yield strength of corroded steel plates were studied. Finally, a probabilistic limit state equation for corroded steel beams was established and the time-dependent failure probability and reliability index of corroded steel beams was calculated by Monte Carlo simulation method (MCS). The results of study show that the corrosion depth on steel plate surface and nominal yield strength of corroded steel plate conformed to the normal distribution. With the increase of corrosion time, the average, the standard deviation of the corrosion depth and relative yield strength increased while the mean of relative yield strength, nominal yield strength, nominal ultimate strength, the elongation decreased. The reliability index decreased rapidly with corrosion time, which shows that the reliability of steel structures under the aggressive environmental should be caused attention.

Load-Carrying Performance and Hydrostatic Tests of Encapsulated Anchor Systems for Unbonded Post-Tensioning Single-Strands

ACI 318-14 and 423.7-14 require the use of encapsulation system for an unbonded single-strand tendon for the purpose of corrosion protection and enhanced durability. In this study, load-carrying performance and hydrostatic tests were conducted for a newly developed, unbonded post-tensioning (PT) anchor with encapsulation, following the guidelines put forth in KCI-PS101 and ACI 423.7-14. The static load and fatigue tests as part of this study were used to evaluate the anchorage system behavior under static and cyclic loads, respectively. The hydrostatic test was used to demonstrate that the encapsulation system withstood at least 9.3 kPa of water pressure in a 24 h period according to ACI 423.7-14, and thus has been proven to promote the durability of unbonded PT single-strand tendons. Additionally, the push-in and jacking tests were used to assess the compressive and tensile strengths of the anchor as used in the field. Although these tests were not performed to failure for safety reasons, the anchor endured at least 1.18 and 1.02 times the nominal ultimate strength of a strand in each test, respectively. The authors’ previous load transfer tests were also reported in this paper, showing that test specimens with only two horizontal backup bars were capable of resisting at least 1.7 times the nominal ultimate strength of a strand. Based on the favorable results from the load-carrying performance and hydrostatic tests, the developed encapsulated anchor systems are being applied in actual practice as an economically feasible option in Korean PT industry and are expected to improve the corrosion resistance and durability of post-tensioned structures.

Analysis on the Mechanical Properties of Corroded Reinforced Concrete

The paper reviews the current research status of corroded reinforced concrete. The mechanical properties of corroded steel bars and the overall mechanical properties of the components were compared and analyzed. Analysis showed that with the growth of corrosion rates, the elongation of corroded steel bars decreased faster than nominal yield strength and nominal ultimate strength; element bearing capacity of large diameter decreased faster than the diameter of the small. Compared with the electrifying corrosion and practical engineering components, the mechanical properties of the actual engineering under the same corrosion rate are founded to decrease more seriously.

Experimental studies on mechanical properties of corroded steel bars after elevated temperature

Abstract The mechanical properties of steel bar deteriorates after erosion and elevated temperature. In the study 16 mm diameter bars were corroded by an electrochemical accelerated corrosion technique, and then heated at temperatures 300, 500 and 700℃. The bars were cooled naturally in furnace to ambient temperature and were tested in tension. The nominal yield strength, nominal ultimate strength and elongation were observed. The observations showed that nominal yield strength, nominal ultimate strength and elongation was changed significantly on the coupling effects of corrosion and temperature.

The Time-Dependent Effect of Corrosion of Steel Strands on Prestressed Concrete Beam Bridges

Based on the concrete carbonization theory, we analyze the time when prestressed steel strands begin to corrode, and put forward the degradation time-dependent model for cross-sectional area of a corroding steel strand; with the comparison of existing research results, we propose the degradation time-dependent model for mechanical properties of corroded steel strands, including the nominal ultimate strength and nominal elastic modulus. We deduce a time-dependent model for the prestressing loss due to steel strand corrosion. Taking a prestressed concrete hollow slab bridge as an example, we analyze the time-dependent effect of the corroded strands on the concrete stress at serviceability limit state and flexural bearing capacity at ultimate limit state. Research shows that the bottom edge stress and flexural bearing capacity at mid-span of the beams will reduce sharply if the prestressed strands corrode, even corrosion can damage the safety of bridge in just a few years. These results can be for information of further experiments and researches.

The Impact of Corrosion on the Mechanical Properties of Smooth Steel Rebar HPB235

The Impact of Corrosion on the Mechanical Properties of Smooth Steel Rebar HPB235 The impact of corrosion on the mechanical properties of steel rebar was examined. An experimental investigation was carried out in order to gain better insight of the effect of corrosion on the mass loss, strength, of smooth Steel Rebar HPB235 10 mm diameter steel bars that were artificially corroded for different corrosion levels. Corrosion is a negative contributor on the structural integrity of concrete structures and leads to degradation of the mechanical properties of steel rebar. In order to evaluate the influence of corrosion on the mechanical properties of steel rebar, an experimental investigation was conducted on smooth steel rebar of 10 mm diameters, and which were artificially corroded for 1, 3, 5 and 7 months. The laboratory tests suggest that corrosion duration had a significant impact on the strength degradation of the specimens. The mechanical properties of tensile test before and after corrosion indicated progressive variation and drastic drop in their values. The corrosion enhanced the damage and created pits and notches, resulting in stress concentration points and progressive reduction of strength. It gets the express formula nominal ultimate strength and nominal yield strength.

Size Dependence of Strength and Fracture Properties of Brick Masonry Walls

The problem of size dependence of the fracture properties in brick masonry structures is addressed. The constitutive heterogeneity of the material seems to be responsible for this effect, which provides multiscale cooperation as fracture develops. Three-point bending tests have been carried out on notched masonry walls with five different sizes, and the nominal ultimate strength and fracture energies have been computed according to conventional theories. It is shown that the multifractal hypothesis for the composite mesostructure of the masonry allows for the proper determination of the scaling regimes of these physical quantities. By means of two multifractal scaling laws, for strength and toughness, respectively, the asymptotic values of these quantities, valid for real-sized structures, and the threshold scale between the disordered regime and the homogeneous one can be determined.

A Modification of the Coulomb-Mohr Theory of Fracture

The inability of the Coulomb-Mohr theory of fracture to explain the main features of compression, tension, and torsion tests on brittle materials is pointed out. It is shown that the introduction of suitably chosen tension cut-offs and “friction angles” removes this deficiency and leads to a satisfactory explanation of the fracture stresses and angles of fracture for these three simple tests. The modified Coulomb-Mohr theory is a three-parameter theory, but all three parameters in principle can be obtained from only two simple tests. It is shown that in the case of cast iron there is an extremely close relationship between cohesive resistance in shear and nominal ultimate strength in single or double shear. The modified theory fits the data of Coffin, Cornet, and Grassi on biaxial fracture of cast iron very well. The three-dimensional fracture surface is described and used to explain some apparently anomalous points in the experimental data. Finally, a hypothesis is advanced which explains the appearance of concavities in the yield locus for certain classes of materials.