Pre-damage Levels Research Articles

Synergistically-enhanced ion track formation in pre-damaged strontium titanate by energetic heavy ions

Latent ion tracks created by energetic heavy ions (12 MeV Ti to 946 MeV Au) in single crystal SrTiO3 are investigated using Rutherford backscattering spectrometry and scanning transmission electron microscopy. The results demonstrate that pre-existing irradiation damage, introduced via elastic collision processes, interacts synergistically with the electronic energy deposition from energetic heavy ions to enhance formation of latent ion tracks. The average amorphous cross-section increases with the level of pre-damage and is linearly proportional to the electronic energy loss of the ions, with a slope dependent on the pre-damage level. For the highest energy ions (629 MeV Xe and 946 MeV Au), the tracks are continuous over the pre-damaged depth, but become discontinuous beyond the pre-damaged region. This work provides new understanding and insights on ion-solid interactions that significantly impact the interpretation of latent track formation processes, models of amorphization, and the fabrication of electro-ceramic devices.

Testing and analysis of basalt FRP-confined damaged concrete cylinders under axial compression loading

Fiber-reinforced polymer (FRP) composites has been widely used in the retrofitting of earthquake-damaged concrete structures. In literature, the studies on FRP-confined intact concrete columns have been well documented. However, research on FRP-confined damaged concrete columns is relatively rare. Aiming to solve this problem, the confinement performance of basalt FRP (BFRP) on pre-damaged concrete columns was investigated in the present study. In total, twenty-six concrete cylinders were constructed and tested under axial compression. The effects of pre-damage levels and number of BFRP wrapping layers on the compressive performance of the concrete cylinders were investigated. Eighteen plain concrete cylinders were preloaded at three different stress levels (i.e., up to f′co, 0.9f′co and 0.8f′co on the descending branch of the axial compressive stress-strain curve of plain concrete, f′co was compressive strength of plain concrete and was 37.7 MPa here) to represent the moderate, moderately-severe, and severe damage levels, respectively. The thin surface layer of the damaged plain concrete specimens was removed and the damaged concrete specimens were repaired using early strength cement mortar. Then, the cylinders were wrapped with BFRP sheets and retested under axial compression. The experimental results showed that compared with the plain concrete, the ultimate compression strength and axial strain capacities of the pre-damaged concrete were improved by 10–104% and 186–590% respectively after the BFRP confinement. The ultimate compressive strength and the initial elastic modulus of the BFRP-confined concrete tended to reduce with an increase in pre-damage level. Based on the test results, a modified strength expression and a strain expression were developed to predict the compressive behavior of the BFRP-confined concrete (undamaged). Based on the modified strength and strain expressions, a modified stress-strain expression was further proposed for BFRP-confined damaged concrete. This research concludes that BFRP is an effective external confining material for damaged concrete column members after earthquakes.

Effects of predamage on the compression performance of CFRP-confined rectangular steel reinforced concrete columns

This study investigates the axial compressive behavior of predamaged steel reinforced concrete (SRC) rectangular short columns confined by carbon fiber reinforced polymer (CFRP) laminates. The authors tested 13 large-scale CFRP confined SRC columns. The primary variables were the predamage level and number of CFRP's layers. All confined columns failed in the mode of CFRP laminates rupture after peak load. Both the working strain of CFRP and the peak load of columns decreased with predamage level. This paper also presents a new finite element numerical model for the nonlinear analysis of confined columns. This model was verified against experimental results, which led to the adoption of concrete damaged plasticity model (CDP). Simulation confirmed that the confinement effects of concrete provided by CFRP laminates is mainly restricted in the corner zones and the core area surrounded by the steel in column sections. Both the circumferential CFRP strains and confined concrete compressive stress significantly decreased with the increasing predamage level under peak load states.

Outcomes of a major research on full scale testing of RC frames in post earthquake fire

Post-earthquake fire (PEF) can cause a rapid collapse of structures that have been already damaged as a consequence of prior earthquake. It is a matter of concern for all the stake holders that almost all the standards and codes for the design of structures ignore the risk of PEF and thus the designs developed using these codes could be ineffective during the PEF events. This paper represents the results of a major research carried on four full scale RC frames. A novel test setup for fire following earthquake has been developed and tested in the current exercise. A number of sensors were used to monitor the kinematic and thermal fields during the test. The results (in terms of strains, displacements and temperatures) provide valuable information about earthquake-damaged RC structures in fire in fully developed and decay stages. The study investigated the effect of the pre-damage level, the reinforcement detailing and the infill on the performance of RC frames subjected to post earthquake fire. The results show significant variation in structural temperatures within a compartment, demonstrating that the assumption of uniform temperature, which is implicit in many design fires, is incorrect. The RC frames designed with ductile detailing of reinforcement displayed better lateral load carrying capacities before and after fire. The pre-damage level affects the rise in temperatures in the structural elements and also affects the spalling of the members. This paper describes the experimental investigation and serves as a vehicle for dissemination of the key findings and all the important test data to the engineering community which could be used for validating numerical simulations for further advancing the knowledge and understanding in this relatively poorly researched area.

Artificial neural network models for FRP-repaired concrete subjected to pre-damaged effects

Confining damaged concrete columns using fibre-reinforced concrete (FRP) has proven to be effective in restoring strength and ductility. However, extensive experimental tests are generally required to fully understand the behaviour of such columns. This paper proposes the artificial neural networks (ANNs) models to simulate the FRP-repaired concrete subjected to pre-damaged loading. The models were developed based on two databases which contained the experimental results of 102 and 68 specimens for restored strength and strain, respectively. The proposed models agreed well with testing data with a general correlation factor of more than 97%. Subsequently, simplified equations in designing the restored strength and strain of FRP-repaired columns were proposed based on the trained ANN models. The proposed equations are simple but reasonably accurate and could be used directly in the design of such columns. The accuracy of the proposed equations is due to the incorporation of most affecting factors such as pre-damaged level, concrete compressive strength, confining pressure and ultimate confined concrete strength.

Post-earthquake fire performance of flange-welded/web-bolted steel I-beam to hollow column tubular connections

Natural extreme events such as earthquake and fire are destructive for building structures. Earthquake is not only a destructive extreme event but also can trigger other extreme events such as fire. The possible post-earthquake fire (PEF) can be a more destructive scenario for building structures. For safety reasons, it is necessary to capture the behaviour of structural components under PEF scenario. This study aims to investigate the behaviour of flange-welded/web-bolted steel I-beam to box column connections subjected to PEF scenario. Experimental tests were carried out on two groups of steel connections under ISO fire. In each group, four connections were fabricated with the same specifications in which one connection was tested under fire only while the other three connections were tested under cyclic loading and subsequent fire. During the fire stage, the connections were subjected to constant static load equivalent to 30% of their ultimate monotonic loading strength. The furnace temperature, temperature distribution of connection and the beam deflection of connection were measured during the fire tests. It was found that the load-carrying capacity of the flange-welded/web-bolted connections decreases significantly with the increase of pre-damage level induced by cyclic loading. Additionally, in order to study the temperature distribution of the connections under fire, preliminary finite element modelling was carried out for a heat transfer analysis on the basis of uniform fire exposure.

BEHAVIOR OF HIGH-STRENGTH CONCRETE CYLINDERS REPAIRED WITH CFRP SHEETS

This study aims to investigate the behavior of damaged high-strength concrete cylinders repaired using carbon fiber reinforced polymer (CFRP) sheet. The experimental work on CFRP-wrapped concrete cylinders with various predamage levels indicated that CFRP can precisely resist the axial aggravated deformation of cylinders caused by damaging under uniaxial loading. The findings also revealed that the energy absorption of the damaged specimens confined with CFRP was restored approximately three times more than that of the undamaged specimens without confinement. Therefore, an empirical relationship exists between the pre-damage levels and the uniaxial compressive strength reduction of the concrete cylinders.

Post-earthquake fire behavior of welded steel I-beam to hollow column connections: An experimental investigation

Extreme events such as earthquake and fire can cause severe damage to building structures. The possible coupling of various extremes such as earthquake followed by fire is more destructive. It is necessary to capture the behavior of building structures subjected to the post-earthquake fire (PEF) for safety reasons. This study aims to investigate the behavior of unstiffened welded steel connections subjected to the PEF scenario. Experimental tests were carried out on two groups of steel I-beam to hollow column connections with different column wall thicknesses under ISO fire including 4 connections with the same specifications within each group in which 3 connections were tested under the coupling of cyclic loading and subsequent fire while 1 connection was only subjected to fire. All undamaged and pre-damaged connections were tested in a gas furnace under the given constant static load which was about 30% of the ultimate monotonic loading strength of the connections. The furnace temperature, temperature distribution and the deflection of the beam were measured during the fire tests. It was found that the load-carrying capacity of the welded connections decreases significantly with the increase of the pre-damage level. Preliminary finite element modeling was carried out for a heat transfer analysis on the basis of uniform fire exposure as well, which showed nonuniform temperature distribution of the connections.

Experimental Study of the Seismic Behavior of Predamaged Reinforced-Concrete Columns Retrofitted with Basalt Fiber–Reinforced Polymer

AbstractReinforced concrete (RC) frame structures are widely used in earthquake regions, and damage to these structures has been reported after many earthquakes. Small parts of seriously damaged RC frames should be demolished and reconstructed, and a large number of earthquake-damaged RC frames can be retrofitted and used again. In this paper, the seismic behavior of predamaged reinforced concrete columns repaired using early-strength cement mortar and basalt fiber–reinforced polymer (BFRP) has been investigated through lateral reversed cyclic tests on seven large-sized RC columns. Two predamage levels [(1) moderate damage, and (2) severe damage] were assigned to the RC columns through cyclic loading. The axial load and residual displacement were kept constant during the retrofitting process, and the retrofitted columns were retested after 6 days of mortar and epoxy curing at room temperature. The ductility and energy dissipation capacities of the fiber-reinforced polymer (FRP)-retrofitted predamaged RC c...

Experimental investigation on HCF strength affected by predamage from LCF of a near alpha titanium alloy

Abstract

Effect of self-healing on water permeability and mechanical property of Medium-Early-Strength Engineered Cementitious Composites

The demand for repair and retrofit of aging concrete infrastructures increase over time. Normal concrete repair materials are brittle and tend to crack, resulting in a lack of durability due to cycles of repair and retrofit. In order to combat this problem, a Medium-Early-Strength Engineered Cementitious Composites (MES-ECC) was introduced and its self-healing behavior was investigated in this paper. Autogenous healing of MES-ECC with different pre-damage levels and different pre-damage times was investigated after exposure to different conditioning regimes: water/room air cycle, submersion in water, 90%RH/room air cycle and room air curing. Rapid penetration test and four point bending test were used to assess the influence of self-healing on water permeability and mechanical properties of MES-ECC. The self-healing process and chemical characteristic of self-healing products were examined by environment scanning electron microscope (ESEM) and energy dispersive X-ray spectroscopy (EDS). The MES-ECC develops a compressive strength of 24MPa at the age of three days and has high tensile ductility with crack width of below 50μm. Furthermore, the self-healing test results show that relative water permeability decrease to 0 after 10 healing cycles. Additionally, the mechanical properties such as flexural stiffness, flexural strength and deformation show certain recovery after 10 healing cycles. The self-healing process was largely occurred in the initial 3 cycles, and the self-healing product is a mixed Ca(OH)2/CaCO3 system with the CaCO3 as the main ingredient.

NONLINEAR FINITE ELEMENT ANALYSIS OF DAMAGED AND STRENGTHENED REINFORCED CONCRETE BEAMS

Bending test of seven reinforced concrete beams are modeled in finite element program to validate the modeling strategies by comparing the structural response of the beams. Three beams in the set are pre-damaged and strengthened with fiber reinforced composites before the bending tests. Cracks are implemented into the model by inserting geometrical discontinuities to represent the pre-damaged beams. Parametric variables such as crack width, length and interval are chosen to simulate different pre-damage levels. Once the proposed modeling strategies are validated by real experimental tests then 196 finite element models are created to study the effects of pre-damage levels on the moment capacity of reinforced concrete beams repaired with CFRP. Results indicate that inclusion of pre-damage levels by means of cracks into the cross sections have significant effect on beams moment capacity.

Effect of temperature on mechanical properties of pre-damaged steel reinforcing bars

The effect of simulated earthquake-induced damage on the residual mechanical properties of steel bars exposed to elevated temperatures are reported towards understanding the behaviour of such bars in a fire-following-earthquake scenario. Earthquake damage was simulated by inducing two levels of tensile strains in the rebars corresponding to the desired levels of pre-damage. Subsequently, the pre-damaged rebars were tested for residual strength in tension after exposure to a single cycle of heating and cooling for different target temperatures ranging from room temperature to 800°C. The other variables in the investigation were: yield strength, rebar diameter and the rebar manufacturing process (cold-worked or thermo-mechanically treated). It was observed across all the rebars of this study that the selected pre-damage levels had practically no influence on residual mechanical properties and the effect of heating the rebars was significant only for temperatures greater than or equal to 400°C. The findings of this investigation have implications for prediction of residual capacity of reinforced concrete structures exposed to fire-following-earthquake scenarios.

Repair Effects and Acoustic Emission Technique–Based Fracture Evaluation for Predamaged Concrete Columns Confined with Fiber-Reinforced Polymers

During the last two decades, the use of fiber-reinforced polymer (FRP) in the retrofitting of concrete structures has been widely studied. However, there is limited research on the effect of initial concrete damage on the retrofitting effect of FRP on concrete columns, especially when the initial damage is severe. For FRP-confined concrete columns, the fracture process inside the concrete is covered by FRP and is not visible to inspectors during the service period. This paper investigates these problems through an experimental study of 28 100×100×300 mm concrete columns using axial compression tests and acoustic emission (AE) fracture monitoring. Prior to FRP wrapping, three different damage levels were assigned to the concrete columns. The stress-strain results showed that the predamage levels had a small effect on the ultimate strength of the FRP-confined predamaged concrete columns, even when the predamage was severe, whereas the axial/lateral strains were more affected by the predamage levels. AE parameter analysis showed that at the early loading stage, AE signals generated from FRP-confined predamaged concrete columns contained less energy than those from the FRP-confined intact concrete columns. The fracture processes of unconfined and FRP-confined concrete columns were also studied through concrete failure modes, b-value and improved b-value (Ib-value) analyses, and fractal analysis. The following conclusions were drawn from the analyses: (1) during compression of the FRP-confined concrete columns, the concrete failure modes shifted from cracking type to cracking-crushing mixed type; (2) the fracture process of the confined concrete columns could be divided into three stages, which are different from those for unconfined concrete columns and reinforced concrete beams; (3) the fractal dimension of the crack network had a relationship with the b-value and decreased from a value between 3 and 2 to a final value of 2 during the fracture process for unconfined and FRP-confined concrete columns.

Experimental investigations of partially-damaged RC beams and columns

This paper summarises experimental investigations of undamaged and partially damaged reinforced-concrete beams and columns. The aim of the work was to establish and carry out experimental methods for determining the load–deformation behaviour and strength of these simple structural elements under varying levels of localised pre-damage (such as weakening or partial loss of concrete material). In particular, the effect of such partial/local damage on the overall behaviour and, crucially, its contribution to structural collapse, were also studied. There is little experimental evidence to validate predictions obtained from analysis or numerical modelling of partially damaged concrete members. Often, the ultimate capacity is the primary output of interest and it is usually determined using specimens that have no prior local damage. The present study produced data that led to a comparative study between the structural behaviour of both damaged and undamaged structural elements in order to help understand the ef...

Altered hepatic expression of selenoprotein S1 in septic mouse induced by LPS attack

To investigate the change of selenoprotein S1 (SEPS1) hepatic expression in septic mouse induced by LPS attack. The septic murine model induced by LPS attack was established. Ten mice were randomly selected as control group from 84 BALB/c mice and others as septic group. The mice were sacrificed after anesthesia in control group and 10 mg/kg LPS was injected intraperitoneally into septic group mice. Liver and blood samples were taken at 6, 12, 24, 48, 72 and 96 h after LPS injection. Ten mice were randomly selected at each time point. The levels of blood ALT, AST, LDH and liver IL-6, TNF-α were detected. And the SEPS1 expression was simultaneously detected by Western blot. There was liver damage in septic group compared with normal control group. The levels of ALT, AST and LDH markedly increased. And all peaked at 24 h. The levels were (99 ± 11), (299 ± 48) and (1523 ± 131) U/L respectively (versus level at zero hour, P < 0.05). Then there was a gradual decrease and the pre-damage levels were restored during 24-72 h. The levels of IL-6 and TNF-α also markedly increased. The damage deteriorated rapidly and peaked at 48 h. The levels were (30,325 ± 17,901) and (36,509 ± 20,794) ng/L respectively [versus level at zero hour (23,802 ± 11,150), (29,799 ± 8239) ng/L, P < 0.05]. Western blot showed that SEPS1 protein expression markedly increased simultaneously in liver of septic mouse. And the peak value was reached at 24 h post-injury. Then there was a gradual decrease and normal level returned at 72 h. Immunohistochemical results showed that SEPS1 protein expression in liver of septic mouse also markedly increased. And the peak value was reached at 24 h post-injury. Pathologic results showed that liver lesion was apparent in septic mouse and it was the worst during 6-12 h. Liver damage to different extents may be induced by LPS attack in septic mouse. The levels of IL-6 and TNF-α markedly increase. The SEPS1 protein expression in liver of septic mouse is also markedly elevated. And it peaks at 24 h post-injury and returns to normal at 72 h.

Fatigue Behavior of RC Slab Retrofitted with Carbon Fiber Mesh after Different Levels of Pre-Damage

Three RC slab specimens were designed and manufactured to investigate the fatigue behavior of RC slab retrofitted with carbon fiber mesh (CFM) and mortar. Among three slab specimens, two slabs were pre-loaded to introduce damage prior to the fatigue loading tests. Fatigue loading was applied to the top of slab maintaining 40% of the ultimate strength of specimen at 2Hz loading speed. The fatigue test was terminated when the loading cycle exceeded 1,000,000 cycles. From the test results, the effectiveness of the retrofitting using CFM was evaluated. Test result showed that the specimens retrofitted after either severe or light damages had very similar strength and stiffness to those of the specimens retrofitted without damage. It was found that the strength was even slightly improved in the specimen retrofitted with CFM.

Characterization of a BAHD acyltransferase responsible for producing the green leaf volatile (Z)‐3‐hexen‐1‐yl acetate in Arabidopsis thaliana

Green-leaf volatiles are commonly emitted from mechanically and herbivore-damaged plants. Derived from the lipoxygenase pathway, these compounds may serve as attractants to predators and parasitoids of herbivores, prevent the spread of bacteria and fungi, and induce several important plant defense pathways. In Arabidopsis thaliana, the major volatile released upon mechanical wounding of the leaves is the GLV ester, (Z)-3-hexen-1-yl acetate. We have characterized a member of the BAHD acyltransferase gene family At3g03480 which catalyzes the formation of (Z)-3-hexen-1-yl acetate from acetyl-CoA and (Z)-3-hexen-1-ol. The encoded acetyl CoA:(Z)-3-hexen-1-ol acetyltransferase (CHAT) has the ability to accept several medium-chain-length aliphatic and benzyl-derived alcohols, but has highest catalytic efficiency with (Z)-3-hexen-1-ol. The highest expression of CHAT occurs in the leaves and stems. Upon mechanical damage, the (Z)-3-hexen-1-yl acetate emission peaked after 5 min and declined to pre-damage levels after 90 min. However, CHAT gene transcript levels increased much more slowly with the highest levels detected between 3 and 6 h after wounding. An increase in CHAT enzyme activity in vitro followed the transcript increase, with levels peaking between 10 and 12 h after wounding. Plants expressing either an RNAi cassette for the CHAT gene or plants harboring a T-DNA insertion in the CHAT coding region had greatly reduced (Z)-3-hexen-1-yl acetate emission, showing that the CHAT enzyme is responsible for the in planta production of this ester.

Ionisation stimulated defect annealing in GaAs and InP

GaAs and InP samples were pre-damaged by 600 keV Ge ions at 77 K to obtain different damage levels and then post-irradiated at room temperature with different fluences of 390 MeV Xe ions. The samples were analysed by means of RBS and TEM. In GaAs the large electronic energy deposition causes pronounced annealing within the pre-damaged layers. The relative annealed fraction is nearly constant in a wide range of the pre-damage, it decreases remarkably for very high pre-damage levels, and increases with the Xe fluence. The Xe irradiation results in a local crystallisation of amorphous regions. In InP a slight damage annealing occurs at low Xe fluences, while with increasing dose additional damage is produced. This result is in accordance with previously found ionisation-stimulated damage production in virgin InP.

Effects of bone cement volume and distribution on vertebral stiffness after vertebroplasty.

The biomechanical behavior of a single lumbar vertebral body after various surgical treatments with acrylic vertebroplasty was parametrically studied using finite-element analysis. To provide a theoretical framework for understanding and optimizing the biomechanics of vertebroplasty. Specifically, to investigate the effects of volume and distribution of bone cement on stiffness recovery of the vertebral body. Vertebroplasty is a treatment that stabilizes a fractured vertebra by addition of bone cement. However, there is currently no information available on the optimal volume and distribution of the filler material in terms of stiffness recovery of the damaged vertebral body. An experimentally calibrated, anatomically accurate finite-element model of an elderly L1 vertebral body was developed. Damage was simulated in each element based on empirical measurements in response to a uniform compressive load. After virtual vertebroplasty (bone cement filling range of 1-7 cm3) on the damaged model, the resulting compressive stiffness of the vertebral body was computed for various spatial distributions of the filling material and different loading conditions. Vertebral stiffness recovery after vertebroplasty was strongly influenced by the volume fraction of the implanted cement. Only a small amount of bone cement (14% fill or 3.5 cm3) was necessary to restore stiffness of the damaged vertebral body to the predamaged value. Use of a 30% fill increased stiffness by more than 50% compared with the predamaged value. Whereas the unipedicular distributions exhibited a comparative stiffness to the bipedicular or posterolateral cases, it showed a medial-lateral bending motion ("toggle") toward the untreated side when a uniform compressive pressure load was applied. Only a small amount of bone cement ( approximately 15% volume fraction) is needed to restore stiffness to predamage levels, and greater filling can result in substantial increase in stiffness well beyond the intact level. Such overfilling also renders the system more sensitive to the placement of the cement because asymmetric distributions with large fills can promote single-sided load transfer and thus toggle. These results suggest that large fill volumes may not be the most biomechanically optimal configuration, and an improvement might be achieved by use of lower cement volume with symmetric placement.