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During past decades, substantial studies on the external bonding of fiber reinforced polymer (FRP) strips to deficient reinforced concrete (RC) beams have been carried out for the well-known superior properties of the FRP. Several shear prediction models have been established by using the effective strain of the FRP or introducing an ultimate stress discount coefficient. And the latest design concept is the use of stress distribution factor. In this paper, an equivalent effective strain model of the FRP is presented, which contains the concepts of maximum strain, stress distribution factor and critical shear crack angle influences. To develop a simple and accurate approach for such equivalent effective strain, major influenced factors are investigated and analyzed by the statistical independent hypothetic tests on a database of 128 RC beams wrapped by the FRP. Finally, a simple and rational shear design proposal is given, which is more accurate than the existing models using the above database.

The effects of doping with different Mo contents on the microstructure and properties of Fe36Ni Invar alloys were investigated. The results show that when 0.9 wt.% Mo and 1.8 wt.% Mo were added to Fe36Ni, the tensile strengths of the hot rolled alloys were 46 and 61 MPa higher than that of the 0 wt.% Mo sample, respectively. With an increase in Mo content from 0.9 to 1.8 wt.%, the solution temperature of the highest hardness after heat treatment increased from 800${}^{\circ }$C to 850${}^{\circ }$C, respectively. The addition of 0.9 wt.% Mo refined the average grain size from 37 to 15 $\mu$m, and an excessive amount of Mo (1.8 wt.%) did not refine the grains further. After Mo was added, the precipitates on the original grain boundaries changed into nanoprecipitates dispersed in the grain boundaries and inside the grains. Mo was present in the alloy in the form of a carbide and in solid solution, which affected the magnetic lattice effect and increased the thermal expansion coefficient of the alloy. However, upon comparing the samples doped with 0 wt.% Mo, 0.9 wt.% Mo and 1.8 wt.% Mo, it was found that the addition of 0.9 wt.% Mo not only refined the grain size and improved the mechanical properties of the alloy but also led to a low coefficient of thermal expansion (CTE) over the range from 20${}^{\circ }$C to 300${}^{\circ }$C.

The confinement of concrete columns using fiber-reinforced polymer (FRP) jackets or wraps is a popular structural retrofitting technique. More recently, the benefits of FRP confinement of concrete-filled steel tubes have also been explored by researchers. Failure of such FRP-confined concrete-filled steel tubes is usually governed by the rupture of the FRP jacket in the hoop direction. However, the observed FRP hoop strain at failure (i.e. the hoop rupture strain) is typically lower than the ultimate tensile strain from a flat coupon test. Many factors may contribute to this phenomenon, one of which is the geometrical discontinuities at both the starting and finishing ends of the wrapping process commonly used to form an FRP jacket. This paper examines the effect of these geometrical discontinuities on the hoop rupture strain of FRP jackets in FRP-confined concrete-filled circular steel tubes. Detailed finite element (FE) analyses conducted using both linear elastic and elastic-perfectly plastic adhesive constitutive models are presented. Comparison between the FE predictions and available test results shows that the hoop rupture strains of FRP jackets predicted by FE analysis using an elastic-perfectly plastic adhesive model are in reasonable agreement with the test results. The influence of parameters such as the FRP thickness, FRP orthotropy, FRP elastic modulus, adhesive yield strength, adhesive thickness, and column size are examined.

This paper reports an experimental study on the use of carbon fiber-reinforced polymer (CFRP) sheets to strengthen non-load-carrying cruciform welded joints subjected to fatigue loading. Failure modes and corresponding fatigue lives were recorded during tests. Scatter of test results was observed. Thereafter, a series of numerical analyses were performed to study the effects of weld toe radius, the number of CFRP layers and Young's modulus of reinforced materials on local stress concentration at a weld toe. It was found that fatigue life of such welded connections can be enhanced because of the reduction of stress concentration caused by CFRP strengthening. Parametric study indicates that the weld toe radius and the amount of CFRP are the key parameters influencing the stress concentration factors and stress ranges of the joint. Enhancement of modulus for adhesive and CFRP sheets can also be beneficial to the fatigue performance to some extent.

Results from finite element modeling (FEM) of large-scale steel-concrete composite beams strengthened in flexure with prestressed carbon fiber-reinforced polymer (CFRP) plate were validated with experimental results and presented in this paper. The effect of varying the level of prestressing as percentage of the ultimate tensile strength of the CFRP plate was investigated. Comparison was carried out in terms of overall load-deflection behavior, strain profile along the length of the CFRP plate, and strain distribution across the depth of the beam at mid-span section. Very good agreement was observed between the finite element (FE) and the experimental results. The validated FE models were used to perform a comprehensive parametric study to investigate the changes in the behavior through wider range of prestressing levels and then, determine the optimum prestressing level that maintain the unstrengthened beams' original ductility (or energy absorption). An iterative analytical model was also developed, validated with both the FE model and the experimental results, and showed good agreement. A parametric study was carried out to investigate the effect of changing the yield strength of the steel and the concrete compressive strength on the moment of resistance of the section and the strain in the CFRP plate at ultimate.

Advanced carbon fiber reinforced polymer (CFRP) demonstrates promise for the fatigue strengthening of steel structures. By decreasing the stress field at the crack tip, the stress intensity factors (SIFs) can be effectively reduced by CFRP reinforcement. In this paper, the mode I SIF of CFRP-reinforced center-cracked tensile (CCT) steel plate is proposed based on a series of fatigue tests. The selected fatigue tests include experiments conducted by the authors as well as fatigue tests reported in the literature, covering different CFRP systems (low/high modulus, CFRP sheeting/plate) with various CFRP strengthening dimensions. The classical mode I SIF of CCT steel plate without CFRP strengthening is selected as the basis of the proposed solution. Then two reduction factors, similar to the correction factors given in the Japanese Society of Steel Construction (JSSC) standard, are introduced to study the effects of the mechanical properties of CFRP composites and the geometries of the CFRP reinforcement, respectively. Modified SIFs for both single-side CFRP-reinforced and double-side CFRP-reinforced CCT steel plates are proposed. It is found that the experimental SIFs of CFRP-reinforced CCT steel plates can be reasonably captured by the proposed mode I SIF formula. Finally, parametric studies for investigating the sensitivity of SIF to various mechanical and geometric factors are presented.

The end bearing capacity of a rectangular hollow section (RHS) steel tube can be substantially increased through local strengthening using bonded carbon fiber reinforced polymer (CFRP) plates. This paper presents a combined experimental and numerical study into the behavior of such CFRP-strengthened RHS steel tubes with particular attention to debonding failure in such tubes. The results of an experimental study are first presented, which showed that debonding failure occurred in all the CFRP-strengthened steel tubes and the effectiveness of strengthening depended significantly on the slenderness of the webs. A finite element approach for modeling the behavior of such CFRP-strengthened steel tubes is next presented, in which a coupled cohesive zone model is employed to depict the response of FRP-to-steel bonded interfaces with a linear or a nonlinear adhesive. The finite element approach, which is shown to provide close predictions for CFRP-strengthened RHS steel tubes under an end bearing load, offers a valuable tool for understanding the behavior of these CFRP-strengthened steel tubes.

Basalt fiber-reinforced polymer (BFRP) has been applied for strengthening concrete structures. However, studies on reinforced concrete (RC) slabs strengthened by BFRP strips under impact loads are limited in open literature. This study investigates the efficiency of using BFRP strips with various strengthening layouts and anchoring schemes on the impact resistance of RC slabs. A total of 11 two-way square slabs were prepared and tested, including one reference specimen without strengthening and ten slabs strengthened with BFRP strips and/or anchors. The RC slabs were impacted by a drop weight with increasing height until slab failure. The observed failure modes include punching shear failure, BFRP sheet debonding and reinforcement fracture. The failure modes and the effects of using various strengthening schemes on the impact resistant capacity of RC slabs were examined. The quantitative measurements, such as impact velocity, indentation depth and diameter, were compared and discussed. In addition, numerical studies were carried out by using LS-DYNA to simulate the impact tests of RC slabs with and without BFRP strengthening. With the calibrated numerical model, the impact behavior of slabs with various dimensions and strengthening layouts under different impact intensities can be predicted with good accuracy.

Non-ductile response of structural elements, particularly columns, has been the cause of numerous documented failures during earthquakes. The objective of this experimental study was to evaluate the non-linear behaviour of non-ductile reinforced concrete short columns under lateral cyclic deformations and to evaluate rehabilitation schemes. Three reinforced concrete short columns were tested under cyclic lateral loads and constant axial load. The behaviour and effectiveness of different rehabilitation systems using carbon fibre reinforced polymers (CFRP) were investigated. Two different techniques to improve concrete confinement were used in the two rehabilitated specimens. It was found that it is possible to eliminate the non-ductile modes of failure of short column using anchored CFRP wraps. In addition, an analytical model to predict the confining effect and the total shear resistance of rectangular reinforced concrete columns with anchored fibre wraps was introduced. The confinement model is an extension to an available model for concrete confined by steel reinforcement. The model was used to predict the shear capacity of the tested specimens and has shown good results.

The research work presented in this paper deals with the seismic assessment of hollow bridge piers strengthened with fibre-reinforced polymer (FRP). The scope of the strengthening is to overcome some common deficiencies derived from the use of non-seismic design rules, which can often lead to inadequate response when operating in cyclic loading. The strengthening design was studied by means of a parametric analysis considering different fibres and geometrical parameters applied to typical case studies. Quasi-static cyclic tests were performed on five 1:4 scaled piers designed according to old non-seismic Italian codes and strengthened according to the previous analytical study. Efficiency of FRP strengthening was evaluated by comparing the experimental results with those obtained in a previous experimental research performed on similar non-strengthened specimens. Base shear versus lateral deflection curves, dissipated energy and collapse mechanisms comparison shows the achievable effectiveness once the debonding risk has been overcome.

An experimental study on half-scale brick-masonry models with different strengthening and retrofitting measures has been studied under cyclic loading in a quasi-static test facility. The strengthening measures undertaken for the studies are the horizontal bond beam at the lintel and sill level with a combination of vertical reinforcement at corners and openings. The retrofitting measures studied are grouting with epoxy-sand-mortar and cement-grout-injection with welded wire mesh in the cracked region. The tests reveal that the horizontal bond beam at lintel level with vertical reinforcement is effective in reducing the cracking above the lintel level. The insertion of an additional sill-band significantly reduces the cracking in walls. The epoxy-sand-mortar techniques for retrofitting of cracked regions prove to be effective enough to restore the initial strength, stiffness and deformation capacity. Although specimen retrofitted with cement-grout-injection with welded wire mesh is effective to regain the ultimate strength yet the brittle failure is observed as the specimen is stressed beyond the elastic limit.

Experimental and analytical investigations were performed to verify an original methodology that was developed for the repair and seismic strengthening of Byzantine churches. This work was part of the long-term research project entitled Study for Seismic Strengthening, Conservation and Restoration of Churches Dating from the Byzantine Period (9th–14th century) in the Republic of Macedonia. The project was realised jointly by the Institute of Earthquake Engineering and Engineering Seismology (IZIIS) — Skopje, the Republic Institute for Protection of Cultural Monuments (RZZSK) — Skopje, and the Getty Conservation Institute (GCI) — Los Angeles, California.

A model of St. Nikita church was constructed to a scale of 1:2.75 and tested on a seismic shaking table simulating the existing and the strengthened state to investigate the linear behaviour, non linear behaviour, and behaviour in the heavily damaged state (close to failure). To investigate the non-linear dynamic response of the structure, an original trilinear model of stiffness degradation and pinching of the hysteretic loop was developed on the basis of the experimental results obtained for the original and the strengthened model as well as from the results of the quasi static testing of wall elements. This model allows successful modelling and description of the behaviour of the church structures in all phases of behaviour: elastic range, non-linear range (occurrence of cracks), sliding range, and the heavily damaged range that resulted in failure.

To strengthen reinforced concrete (RC) structures against possible future earthquakes, several techniques are used in practice such as adding new RC shear walls, column jacketing using steel or RC or carbon fibers, adding steel bracing, and using seismic isolation and dampers. To apply these techniques, the whole building or part of it should be evacuated for several months and if this building is a school or a factory it means that the building will lose its function for several months during the strengthening construction. In this paper, parallel braced steel frame strengthening technique is proposed to strengthen the low or middle raise RC structures in which all the construction works are applied from outside of the building and do not affect the building function. The main features of this technique are ensuring the view, ventilation, and sunlight from windows after the retrofitting work is done. Furthermore, using the construction steel members lead to shortening the construction term, improve in quality, and reduce costs. The idea of this technique is to reduce the earthquake displacement demand on the nonductile existing RC structures by attaching steel frames to the building floors. These frames are parallel to the structural system of the building and their foundations are connected to the existing building's foundation. In doing so, it is expected that during an earthquake the building's interstory drifts will reduce in half and prevent building collapse. The parallel steel frames can be designed to the desired limit states using performance-based design method in FEMA or Turkish earthquake code. A study case of a factory building in Turkey is presented. The seismic performance of the building before and after the strengthening was evaluated according to the Turkish earthquake code TERDC-2007. Analysis results indicate the effectiveness of the proposed technique.

This paper presents a study on strengthening infill walls using composite materials to enhance shear capacity. The cementitious matrix-grid (CMG) material was employed for this purpose. Various configurations of the CMG, including single or double layers, applied to one or both sides of the wall, with or without anchorage, were tested. The study consisted of two stages. Initially, the mechanical properties of the bricks, mortar, and CMG mortar were determined using twenty-seven specimens. In the second stage, ten specimens, divided into five groups with one group left unstrengthened, underwent shear tests. Shear strength and shear strain relationships were determined for each specimen. Comparative analysis between strengthened and unstrengthened specimens revealed the effectiveness of the strengthening technique. The strengthened specimens exhibited superior structural performance compared to the control specimens. Specifically, the average maximum shear strength of all strengthened specimens surpassed that of the controls. Moreover, double-layer strengthening notably improved ductility. The findings suggest that applying a double layer of CMG to both sides of the wall with anchorage is the most effective method for strengthening. CMG composites significantly enhance the shear strength of infill walls and promote ductile failure. The comparisons of different strengthening combinations can contribute significantly to the existing literature and the construction sector by offering retrofitting options that can be tailored to address various economic and temporal, as well as target strengthening considerations.

In the present work, experimental investigation and the numerical analysis are carried out for strength analysis of A356 alloy matrix composites reinforced with alumina, fly ash and hybrid particle composites. The combined strengthening effect of load bearing, Hall–Petch, Orowan, coefficient of thermal expansion mismatch and elastic modulus mismatch is studied for predicting accurate uniaxial stress–strain behavior of A356 based alloy matrix composite. The unit cell micromechanical approach and nine noded isoparametric finite element analysis (FEA) is used to investigate the yield failure load by considering material defect of porosity as fabrication errors in particulate composite. The Ramberg–Osgood approach is considered for the linear and nonlinear relationship between stress and strain of A356 based metal matrix composites containing different amounts of fly ash and alumina reinforcing particles. A numerical analysis of material porosity on the stress strain behavior of the composite is performed. The literature and experimental results exhibit the validity of this model and confirm the importance of the fly ash as the cheapest and low density reinforcement obtained as a waste by product in thermal power plants.

Aesthetic revolution in restorative dentistry spins around the development of suitable ceramic materials. Though feldspathic porcelain holds promise as one of the best options due to its aesthetic, durability and biocompacibilty, its application is limited since the strength is relatively low. Dispersion strengthening controlled crystallisation and surface heat treatment have been reported in literature to improve the strength. In the present investigation, feldspathisc dental porcelain (Vivodent PE, Ivoclar, licherstein) with potash to soda ratio 2:1 was used as the starting material. Discs prepared by uniaxial pressing and sintered at 960°C in vacuum were strengthened by, i. Exchanging sodium ion with potassium ion at temperature above and below glass transition temperature, ii. Annealing and iii. Dispersion of PSZ. The results showed that the annealed samples showed significant strengthening followed by ion-exchanged samples. The results are analysed with different strengthening mechanisms.

In the modern Chinese teaching process, the expressive skills of students are the comprehensive reflection of their knowledge of the language theory and their ability to communicate effectively. Improving the expressive skills of college students is currently one of the most urgent problems in the teaching of modern Chinese. In this paper, the connotation of the college students’ expressive skills is briefly introduced. We conducted analysis of the factors that affect the expressive skills of college students is conducted and proposed several methods to strengthen their expressive abilities.

During past decades, substantial studies on the external bonding of fiber reinforced polymer (FRP) strips to deficient reinforced concrete (RC) beams have been carried out for the well-known superior properties of the FRP. Several shear prediction models have been established by using the effective strain of the FRP or introducing an ultimate stress discount coefficient. And the latest design concept is the use of stress distribution factor. In this paper, an equivalent effective strain model of the FRP is presented, which contains the concepts of maximum strain, stress distribution factor and critical shear crack angle influences. To develop a simple and accurate approach for such equivalent effective strain, major influenced factors are investigated and analyzed by the statistical independent hypothetic tests on a database of 128 RC beams wrapped by the FRP. Finally, a simple and rational shear design proposal is given, which is more accurate than the existing models using the above database.

In order to investigate the strengthening problem of reinforced concrete pipeline sufferring from the seismic damage, the computational formula for the crack of reinforced concrete pipeline retrofitted with the Fiber Reinforced Polymer (FRP) was deduced. For simulating the damage of the medium or small earthquake, four pre-damage reinforced concrete pipelines under the internal pressure were loaded to damage, and then strengthened with the different FRP. Compared with the experiments of three undamaged reinforced concrete pipelines and one strengthened reinforced concrete pipeline without being damaged, the results show that the strengthening method with FRP can improve mechanical properties of pipeline, and delay the developing speed of crack. The serviceability ultimate load of the seismic damage pipelines not only could fully satisfy the application requirements before the damage, but also was improved. The theoretical and experimental data agree well. And it indicates that the computational model has the good applicability and may supply the reference for engineering applications.