Structural Reinforcement Research Articles

Numerical Integration Study of Penetration and Blasting Damage for Composite Underground Protective Structure with Reinforcement Layers

In response to the increasing threat of powerful earth-penetrating weapons, underground protective structures typically employ composite structural systems with reinforced steel layers. However, current numerical studies often simplify the entire structural system to plain concrete when assessing damage effects, and penetration and blasting processes are treated separately using a restart method. In this paper, we adopt an integrated simulation approach to analyze the resistance performance of composite protective structures with reinforcement layers. The results reveal significant differences in failure modes between plain concrete and reinforced concrete protective structures. The diameter of the steel bars and the spacing between mesh layers notably impact the penetration and blasting damage. Based on the results of a parameter analysis, we propose a method for optimizing the design of reinforcements in composite underground protective structures. The results of the study show the following: (1) The penetration and blast damage patterns of EPWs on plain concrete and composite protective structures with reinforcing mesh are significantly different. Compared to the plain concrete layer, the composite protection structure can effectively resist the damage of EPWs. (2) With the increase in reinforcement diameter, the decrease in reinforcement mesh spacing, and the increase in reinforcement dosage, the penetration depth gradually decreases; the amount and range of the blast damage also decrease accordingly. (3) Under the condition of the same reinforcement ratio, reducing the number of layers of reinforcement mesh, increasing the diameter of reinforcement, and configuring the reinforcement on the top of the protective structure as much as possible can improve the performance of the protective layer against penetration. At the same time, the reasonable arrangement of the reinforcement mesh can also enhance the ability of the protective structure to resist blasting damage.

Experimental study on the composite reinforcement method for single-column piers in existing bridges

Steel–concrete composite reinforcement technology has developed rapidly in recent years. This method has emerged as one of the best reinforcement alternatives in bustling sections because it saves time and space. In this paper, a combination reinforcement plan for single-column piers in curved bridges is proposed, with its interface performance being comprehensively investigated. Nine sets of comparative experiments were conducted to analyze the key issue of shear resistance at the interface between new and old concrete in the combination reinforcement scheme. It was found that under the proposed circumferential reinforcement structure, the stress changed from interface shear to overall compression; therefore, both ductility and the failure bearing capacity were improved owing to the Poisson effect in the later stage of the interface treatment component. Meanwhile, using the calculation formulas in existing reinforcement specifications, we introduce the shear strength parameters under a new "serrated groove" situation, which has higher bearing capacity than the commonly used chiseling and groove modes. The methodology and findings of this study supplement the single-column pier combination reinforcement for existing bridges in urban sections and lays the foundation for future research.

Optimal design of seismic reinforcement for structures with asymmetric rigidity plans using genetic algorithm

Optimal design of seismic reinforcement for structures with asymmetric rigidity plans using genetic algorithm

A Comprehensive Overview of Recycled Glass as Mineral Admixture for Circular UHPC Solutions

This review article analyzes the influence of recycled glass (as sand and powder) beyond the durability, rheology and compressive strength of plain UHPC, even exploring flexural and direct tensile performance in fiber-reinforced UHPC. Interactions with other mineral admixtures like limestone powder, rice husk ash, fly ash, FC3R, metakaolin and slags, among others, are analyzed. Synergy with limestone powder improves rheology, reducing superplasticizer usage. Research highlights waste glass–UHPC mixtures with reduced silica fume and cement content by over 50% and nearly 30%, respectively, with compressive strengths exceeding 150 MPa, cutting costs and carbon footprints. Furthermore, with the proper fiber dosage, waste glass–UHPC reported values for strain and energy absorption capacity, albeit lower than those of traditional UHPC formulations with high cement, silica fume and quartz powder content, surpassing requirements for demanding applications such as seismic reinforcement of structures. Moreover, durability remains comparable to that of traditional UHPC. In addition, the reported life cycle analysis found that the utilization of glass powder in UHPC allows a greater reduction of embedded CO2 than other mineral additions in UHPC without jeopardizing its properties. In general, the review study presented herein underscores recycled glass’s potential in UHPC, offering economic and performance advantages in sustainable construction.

Loop technique for anterior cruciate ligament reconstruction combined with anterolateral structure reinforcement: technical description and clinical results

PurposeWe describe a surgical technique for ACL reconstruction combined with anterolateral structure reinforcement and report early clinical follow-up results.MethodsThe semitendinosus and gracilis tendons are braided into 5 strands and the ACL femoral tunnel and tibial tunnel are created. The graft is passed through the tunnel with the use of a traction suture and the tibial end is fixed with absorbable interference screws at 30° of knee flexion. The ACL graft traction suture is used as an anterolateral reconstruction structure to pass through the proximal exit of the ACL femoral tunnel and then through the depth of the iliotibial bundle to the anterior to Gerdy’s tubercle, a bony tunnel is created from the anterior to Gerdy’s tubercle to the goose foot, and the traction suture is passed through this bony tunnel to form a Loop structure at 20° of knee flexion. Between March 2021 and May 2022 IKDC score, Lysholm score, and Tegner score were performed preoperatively and 6–12 months postoperatively in 24 consecutive patients who met the indications for this procedure and underwent surgery. The patient’s maximum flexion angle, the circumference of the thigh, and the stress X-ray between the operated and healthy knee were measured.ResultsPatients showed significant improvement in IKDC score, Lysholm score and Tegner score at a mean follow-up of 7 months postoperatively compared to preoperatively. No significant increase in anterior tibial displacement was found between the patient’s operated side and the healthy side.ConclusionThe Loop technique ACLR combined with ALSA can be used in patients with an ACL tear combined with a high degree of positive pivot shift. The patient’s subjective perception was significantly improved from the preoperative period and knee stability was restored.Level of evidenceIV, therapeutic study.

The flexural strength of high-ductile concrete in saline-alkali area

Sulfate corrosion is an important cause of accelerated structural failure in concrete structures in coastal and saline alkali areas. High ductility concrete has good tensile and durability properties, and is therefore widely used for the repair and reinforcement of damaged structures. To investigate the flexural performance of high ductility concrete on ordinary concrete structures in saline alkali environments, experimental methods were used to test it. The experimental data validated that the bearing capacity of the 10 mm specimen reinforced with high ductility concrete before and after corrosion is 125 kN and 117 k, respectively. After reinforcement and corrosion, the bearing capacities of the specimens were 115 kN, 129 kN, and 139 kN, respectively. In addition, sodium sulfate reduced the deformation capacity of the original specimen by 13.9 %, but after reinforcement, the deformation capacity of the specimen increased by at least 97.1 %. Compared to reinforced specimens in non saline alkali environments, the deformation capacity of reinforced specimens in saline alkali environments decreases by no more than 23 %. Compared to unreinforced specimens, the strain capacity of reinforced concrete and longitudinal bars in sulfate environments increased by at least 28.1 % and 34.5 %, respectively. However, compared to reinforced specimens in conventional environments, the strain capacity of reinforced specimens in sulfate environments decreased by no more than 19 %. The above results indicate that high ductility concrete can effectively improve the bending resistance of specimens, while also slowing down the corrosion of sulfates on specimens and effectively extending the service life of concrete structures.

3D FRP Reinforcement Systems for Concrete Beams: Innovation towards High Performance Concrete Structures.

Despite the advantages of using lightweight and non-corrosive carbon fiber reinforced polymer (CFRP) reinforcements in concrete structures, their widespread adoption has been limited due to concerns regarding the brittle failure of CFRP rupture and its relatively softer load-deflection stiffness. This work offers logical solutions to these two crucial problems: using aggregate coating to strengthen the CFRP-concrete bond and ultimately the load-deflection stiffness, and using CFRP-concrete debonding propagation to create pseudo-ductile behavior. Subsequently, the concrete cracking behavior, the apparent CFRP modulus with aggregates, and the post-peak capacity and deflection of three-dimensional (3D) CFRP-reinforced concrete are all described by equations derived from experiments. These formulas will be helpful in the future design of non-prismatic concrete components for low-impact building projects. The potential of this innovative design scheme in terms of increased capacity and deflections with less concrete material is demonstrated through comparisons between non-prismatic CFRP-reinforced concrete and measured steel reinforced equivalency.

Improving the performance of CFRP-reinforced concrete cylinders in sulfate-laden environment through nanoclay modification of epoxy resin

The durability of epoxy-concrete interface is a crucial factor for practical application of externally bonded fiber-reinforced polymer (FRP) retrofit systems, particularly when the strengthened structure is subjected to severe environmental conditions. Given the demonstrated potential of nanoclays in enhancing engineering performance of polymers, this work assesses the beneficial effect of organic montmorillonite (OMMT) nano-modification of epoxy resin on the axial compressive properties of FRP-reinforced concrete under a 10 wt% sodium sulfate wet/dry (W/D) cycling environment. Three types of concrete samples were fabricated and tested: plain concrete cylinders, CFRP-reinforced concrete cylinders using unmodified vs. OMMT-modified epoxy resin as the adhesive, respectively. The optimal dosage of OMMT was determined to be 2 wt% through tensile and lap shear tests, as well as microscopic characterization of the fractured cross-section of the molded resin samples. This optimal dosage of OMMT allows the epoxy adhesive to achieve the highest values in the tensile strength (90.4 MPa), lap shear strength (80.0 MPa), Tg (280.5°C) and water contact angle (115.1°). In the fracture section of epoxy resin with a 2 wt% OMMT, multiple microcracks developed and the OMMT nanoplatelets were well dispersed in the epoxy matrix. The laboratory testing program explored various W/D cycle periods. The experimental results indicate that the OMMT-modified epoxy resin significantly improved the mechanical properties and deformation resistance, altered the failure mode, and effectively delayed the strength degradation of the protected concrete. After 150 W/D cycling days, the OMMT-modified CFRP-confined concrete samples maintained their ductility coefficient and axial compressive strength at 3.58 and 123.5 MPa, respectively, 12.6 % and 9.1 % better than the common CFRP-confined samples. Combining these results with the residual axial compressive strength ratio, we propose an improved design model for calculating the axial compressive strength of CFRP-retrofitted concrete structures in sulfate-laden environments. This study demonstrates the beneficial role of OMMT in enhancing the epoxy adhesive and provides insights into the reinforcement of concrete structures by externally bonded CFRP in sulfate-rich environments.

FDI and industrial development in a mega-city region: a modelling study on the Pearl River Delta

ABSTRACT Foreign direct investment (FDI) and regional development are mutually interwoven phenomena. This paper introduces an analytical framework to investigate the interaction mechanism between FDI and regional industrial structure. This framework posits first that FDI generally has a significant influence on the industrial structure in the region concerned, specifically through intervening mechanisms such as capital supply, active selection, passive competition, product linkage, imitation and demonstration and employee flows. Secondly, the industrial structure, in turn, also affects FDI flows through mechanisms including market demand, factor supply and policy or institutional factors. Finally, there are bi-directional interactions; using a spatial interaction framework, the present study applies and tests a simultaneous equation model and a spatial Durbin model to analyse empirical data from 15 urban regions in the Pearl River Delta mega-city region (PRD) in China spanning the period 2005–2018. The key findings from this multi-scalar analysis are: (i) there are substantial interactive effects between FDI and industrial structure, with the rationalisation and upgrading of the industrial structure significantly promoting FDI inflows into the PRD; (ii) FDI inflows, in turn, contribute to the reinforcement and upgrading of the industrial structure in the PRD; and (iii) the interactions between FDI and industrial structure exhibit significant spatial-economic growth effects. We also find that moderator factors, including independent R&D level, market size, marketisation level, labour cost, infrastructure and government expenditure, have discernible impacts on FDI inflows and the rationalisation and upscaling of the industrial-economic structure in the area concerned. Finally, we note that, in our study, significant spatial dependence effects among urban areas inside the PRD area are observed and modelled. The discussion of the empirical findings leads to the identification of several important policy implications and lessons for regional development strategies from an FDI perspective.

USE OF GPR TECHNOLOGIES IN THE ROAD CONSTRUCTION INDUSTRY

The article continues the study on determining the possibility of applying ground penetrating radar (GPR) technologies in the road construction industry. The authors conduct research using an antenna unit that registers the cross-polarisation component of the reflected signal. In this case, processing the obtained radar images comes down to subtracting two mutually orthogonal components of the signal, which allows the determination of areas of the environment with anisotropic properties. Identifying and positioning extraneous inclusions, finding communications, and determining the location of reinforcement in roadway and bridge structures are relevant tasks. Their solution lies in studying the phenomenon of wave diffraction on extraneous inclusions of the investigated environment. Metal inclusions of different diameters are distinctly visible on radar images obtained during laboratory research. The laboratory studies conducted by the authors showed that the shape and nature of the hyperbola of the diffracted wave significantly depend on the object’s depth, diameter, and material. Therefore, further research in this direction should aim at studying the shape of the diffracted wave, which ultimately allows for judging the depth of occurrence and the diameter of a local extraneous inclusion. When finding and identifying reinforcement in structural layers of road surfaces and elements of bridges, difficulties arise due to the spacing of the reinforcing mesh. With a small reinforcing mesh spacing, when the wavelength is longer than the spacing, the reflections from the adjacent reinforcement bars merge into a common continuous boundary and make the lower layers of the structure almost indistinguishable. Solving the mentioned difficulties is possible by improving the equipment base and the algorithms for processing and interpreting the received radar images. Completed theoretical studies and computational experiments allow us to state that the development of road surface thickness measurement and defect detection techniques will become the basis of the road surface monitoring system using the subsurface geolocation method. Keywords: ground penetrating radar, radar image, road surface, dielectric constant, defect detection, thickness measurement, local inclusions.

Feasibility of Repairing Concrete with Ultra-High Molecular Weight Polyethylene Fiber Cloth: A Comprehensive Literature Review

This review explores the use of Ultra-High Molecular Weight Polyethylene (UHMWPE) fiber cloth as an innovative solution for the repair and reinforcement of concrete structures. UHMWPE is a polymer formed from a very large number of repeated ethylene (C2H4) units with higher molecular weight and long-chain crystallization than normal high-density polyethylene. With its superior tensile strength, elongation, and energy absorption capabilities, UHMWPE emerges as a promising alternative to traditional reinforcement materials like glass and carbon fibers. The paper reviews existing literature on fiber-reinforced polymer (FRP) applications in concrete repair in general, highlighting the unique benefits and potential of UHMWPE fiber cloth compared to other commonly used methods of strengthening concrete structures, such as enlarging concrete sections, near-surface embedded reinforcement, and externally bonded steel plate or other FRPs. Despite the scarcity of experimental data on UHMWPE for concrete repair, this review underscores its feasibility and calls for further research to fully harness its capabilities in civil engineering applications.

Structural Analysis of Deck Reinforcement on Composite Yacht for Crane Installation

The crane installation on the deck of a yacht redistributes the stress field and affects the local structural integrity and performance. The safe operation of the yacht is associated with the optimal placement of the crane on the deck and the proper local structural reinforcement. Here, the structural analysis of the bow part of a yacht made of composite materials is studied, considering the retrofit installation of a crane, in three different cases of reinforcing the deck: (a) without any reinforcement, (b) with a T-type reinforcement, and finally, (c) with a longitudinal beam. The T-type connects the longitudinal bulkhead and the deck, reinforced locally with overlamination skin and adhesive-filler. The longitudinal beam works as a local longitudinal stiffener attached to the deck and connects the second, third, and fourth transverse frames. The structural analysis is performed using the finite element method following the classification societies’ rules. The local reinforcements are made from the same composite materials as the unreinforced deck. The maximum deformations, the principal stresses, and the safety factors following Tsai-Wu and Hashin criteria are calculated and compared for the three different cases. The T-type and longitudinal reinforcements reduce deck stresses by 33%, with longitudinal reinforcement reducing deck deformation by 17%. Composite failure analysis shows the structure was near failure, and the reinforcements enhance safety; T-type is better for multiaxial loads (Tsai-Wu), and longitudinal is superior for micromechanical failure (Hashin). By considering the structural performance and safety aspects, designers and engineers can make optimal decisions regarding yacht crane installation and proper reinforcement, leading to safer and more efficient structures.

ANALISA PENGUATAN STRUKTUR PENAMBAHAN LANTAI BANGUNAN GEDUNG (STUDI KASUS DI DPMPTSP KAB. KUDUS)

The research was conducted in the Kudus Regency Public Services building which originally had a floor area of 1172 m2. In 2022 there will be development, so a new floor will need to be added. Where the land area cannot be used to build horizontally, add vertical floors to a 2-story building to become 3 floors. The research was carried out by testing the quality of concrete using the Hammer Test, obtaining a result of 20.75 MPa, then modeling analysis was carried out using SAP 2000 v14 software and manual calculations based on SNI 03-2847-2002, SNI 031726-2012, and SNI 1729-2015. This analysis was carried out in 3 stages, the first was an analysis of the initial conditions of the existing building, the second was an analysis of the existing structure with the additional load of the new floor, and the third analysis was with the additional load and structural strengthening. The results of the structural analysis stages 1 and 2 stated that the beam structural elements experienced overstrength (O/S) or could not withstand the additional load of the 3rd floor. With this data, structural reinforcement calculations were carried out using the concrete jacketing method with a number of longitudinal reinforcement 7D16 stirrups Ø10-100 for beams and the amount of longitudinal reinforcement 8D19 stirrups Ø10-100 and the method of strengthening with steel profile IWF 200.200.8.12.

Non-Destructive Inspection Method Using Elastic Waves for Quality Management in the Bending Process Region of BFRTP

In order to establish a sustainable infrastructure, structures must maintain their minimum required performance for an extended period. Typically, existing concrete structures are reinforced with steel, but the susceptibility of steel reinforcements to corrosion, attributed to factors such as carbonation and chlorides, can lead to performance degradation, rendering the specified requirements unmet. As a remedy, there has been a growing interest in using lightweight and corrosion-resistant fiber-reinforced polymer (FRP) bars as an alternative to traditional steel reinforcement in concrete structures. Particularly noteworthy is the use of FRP bars manufactured with thermoplastic resins (FRTP) due to their ease of processing and convenient applicability on construction sites. This study delves into the mechanical behavior evaluation by examining the propagation characteristics of elastic waves in the curved section of basalt FRTP (BFRTP). Multiple BFRTP bars underwent a 180-degree bending process, subject to various conditions, including heat and twist variations. Subsequent measurements focused on the propagation characteristics of elastic waves in the curved sections, emphasizing wave attenuation, frequency features, and propagation velocity. Additionally, bending tensile tests were conducted on the curved bars, and a comparative analysis was performed between the tensile strength and the aforementioned elastic wave propagation characteristics. The results affirm a consistent correlation between the propagation characteristics of elastic waves (amplitude ratio, centroid frequency, velocity) during the traversal of the curved BFRTP section and its tensile strength. Notably, both centroid frequency and velocity exhibited correlation coefficients exceeding 0.7, suggesting their potential efficacy as reliable indicators for estimating tensile strength.

An Outstanding Engineer, Scientist, Teacher — Alexander Matveevich Ivanov. To the 110th Anniversary of His Birth

The scientific works of an outstanding scientist, A.M. Ivanov, devoted to the development of new methods for calculating wooden elements taking into account the time – creep factor have so far aroused great interest among modern researchers. The Voronezh Scientific School of Polymer Concrete A.M. Ivanov has substantiated and created universal models called “structural diagrams”, which lay the probabilistic foundations for evaluating the properties of materials, as well as polymer concrete and other composites. The article describes the life path, the formation of scientific activity and teaching of an outstanding scientist, Dr. of Technical Sciences, Professor A.M. Ivanov, a participant in the Great Patriotic War. Grateful students and followers showed that the issues of reinforcement of steel-polymer concrete structures, anchoring of reinforcement in polymer concrete and calculation of joints of prefabricated steel-polymer concrete structures of solid and annular cross-section with various types of reinforcement; the development of a whole range of polymer materials reinforced with fiberglass reinforcement and wood chips is the result of mentoring activities of an outstanding teacher and scientist.

Durability of Fe-SMA/steel single-lap joints exposed to hygrothermal environments

Due to the adverse impact of hygrothermal environments and fatigue load, the performance degradation of existing steel structures necessitates repairs to extend their service life. Structures retrofitted by bonding iron-based shape memory alloy (Fe-SMA) have been demonstrated as an active non-destructive repair method. Nevertheless, the deterioration of the adhesives triggered by hygrothermal environments is a crucial challenge in its practical reinforcement applications. In this study, 54 Fe-SMA/steel single-lap joints (SLJs) are aged in 55°C and 98 % relative humidity environments for 30, 60 and 110 days, and tested under shear loads. The long-term performance, failure patterns, load-displacement responses and shear-resistance capacity of the SLJs are investigated, considering the essential parameters of aging time, overlap length and adhesive types. The experimental results exhibit that the failure patterns of aged Fe-SMA/steel SLJs depend highly on the adhesive types. The shear-resistance capacity of Fe-SMA/steel SLJs decreases dramatically with the prolongation of aging time. After 110 days of aging, the shear-resistance capacity of type-C, type-S and type-P SLJs decreases by about 14 %, 39 % and 49 %, respectively. When the overlap length increases from 50 mm to 150 mm, the shear-resistance capacity of type-C, type-S and type-P Fe-SMA/steel SLJs improves by 21 %, 39 % and 22 %, respectively, increasing the overlap length can safeguard the optimal functionality and long-term performance of the retrofitted steel structures. While the environments are relatively aggressive, it is recommended to use type-C adhesive to obtain the satisfactory serviceability of the retrofitted steel structures. The experimental achievements are significant for repairing deteriorated steel infrastructures by bonding Fe-SMA, guaranteeing the long-term performance and normal-use safety of structural reinforcement design, and reducing carbon emissions due to the avoidance of reconstruction.

Studi Komparasi Bangunan Tahan Gempa Berdasarkan SNI 1726-2012 dan SNI 1726-2019

Indonesia is an archipelago that is flanked by oceanic plates and land plates that cause the two plates to often collide. This causes Indonesia to be an earthquake-prone area and has many volcanoes. Research related to earthquakes in Indonesia continues to develop. This has resulted in several points such as new earthquake hazard maps and the latest regulations related to earthquake-resistant building planning, resulting in the building planning process having to follow the latest applicable regulations. The purpose of this study is to analyze changes in SNI, structural dimension requirements, reinforcement requirements, and structural behavior and internal forces due to the application of SNI 1726:2012 and SNI 1726:2019 in a building. The research method used was to conduct a literature study on the changes from SNI 1726:2012 to SNI 1726:2019 using the SNI 2847:2019 planning which will be used in the structural analysis. The results obtained from this study show that there are differences in the earthquake maps used in SNI 1726:2012 and SNI 1726:2019, there are differences in parameters in SNI 1726:2012 and SNI 1726:2019 which result in an increase in the forces acting on the structure which affects the need for reinforcement. Structural planning is carried out by following SNI 1726:2019 and SNI 2847:2019, for existing buildings that have been built based on SNI 1726:2012, it is necessary to carry out a re-examination or assessment to determine the condition of the existing building in relation to earthquake in Indonesia.

Comparative study on fracture evolution in steel fibre and bar reinforced concrete beams using acoustic emission and digital image correlation techniques

In recent decades, the demand for sustainable construction practices has increased, but raw materials such as reinforcing steel remain scarce. Therefore, steel fibres have emerged as a popular and sustainable choice in the construction industry, offering a cost-effective alternative to traditional steel bar reinforcement for both flatwork and elevated structures. The purpose of this study is therefore to compare the performance of fracture behaviour between steel fibre-reinforced concrete (SFRC) and steel bar-reinforced concrete (SBRC) beams subjected to three-point bending. The fracture process was monitored by using two non-invasive techniques: acoustic emission (AE) and digital image correlation (DIC). The damage level was identified by characterizing the parameter-based AE data such as hit rate, energy release, count, rise time, amplitude, and signal strength. DIC images were employed to visualise the crack propagation in parallel with the AE data. To further understand the fracture characteristics, the integration of 2D source localization of AE events (based on local AE fracture energies) with DIC results was investigated. The parameter-based AE results showed that SBRC beam experienced a high density of AE hits with large peak amplitude events that were accelerated during the pre-peak loading phase. The Ib-value analysis revealed that SBRC beam exhibited a higher degree of fracture magnitude during the primary crack development process than SFRC beam. Following the main cracking stage, SFRC beam demonstrated an improved post-cracking softening behavior and superior ability to arrest crack propagation compared to SBRC beam. The integration of local AE fracture energy and DIC results provided a novel approach for a better understanding of the fracture behaviour in both SFRC and SBRC beams. This study’s findings contribute to more precise monitoring of fracture evolution in SFRC and SBRC beams, ultimately improving the selection process for primary reinforcement in flatwork and elevated structures.

Applicability Evaluation of Modified Epoxy Resin in the Repair and Reinforcement of Ancient Building Timber Members

To investigate the potential of modified epoxy resin for repairing and strengthening historical wooden structures, this study utilized polyurethane and silicone-modified epoxy resin as the base, alongside a polyamine curing agent. The resin mixture was cured at ambient temperature, resulting in the creation of ten unique epoxy resin systems. Investigation into the chemical structure and alterations to the glass transition temperature were conducted. The study conducted tests and characterization of viscosity, curing rate, mechanical properties, stress failure mode, hygrothermal aging resistance, and bonding properties. The results reveal that the curing degree of the two modified epoxy resins is high after being cured at room temperature, and the chemical structure and curing rate show insignificant changes. The range of the glass transition temperature for the modified epoxy resin is between 61.31 °C and 70.51 °C. The incorporation of polyurethane and silicone molecular chains into the epoxy resin cross-linking curing system enhances the toughness of the epoxy resin. The modified resin achieves a maximum elongation at break that is 5.18 times greater than that of the unmodified resin, along with a maximum tensile strength and a compressive strength that are 7.94 and 1.74 times, respectively, higher than those in the Chinese technical specifications for the maintenance and reinforcement of ancient wooden structures. The increase in toughness changes the failure mode of the cured epoxy resin. The modified epoxy resin exhibits great bonding ability to aged wood, with a shear strength of up to 9.6 MPa along the grain. As a result, the modified epoxy resin meets the requirements for the reinforcement and repair of the timber members of ancient buildings.

Experimental investigation into corrosion effect on buckling and low-cycle fatigue performance of high-strength steel bars

The reinforcement in marine RC structures will inevitably be corroded under long-time erosion of chloride ions, which will weaken steel mechanical properties and then structural seismic resistance. The new metallurgical technology is adopted for manufacturing high-strength steel bars (HSSB), but that may affect the corrosion resistance of steel bars at the same time. This paper experimentally investigates the effects of corrosion on monotonic and low-cycle fatigue properties of HSSB HTRB600 and normal strength steel bars (NSB) HRB400E. The HRB400E and HTRB600 steel bars were corroded to different corrosion rates by electrochemical accelerated corrosion technique. The monotonic tensile and compressive, as well as low-cycle fatigue tests of corroded steel bars were conducted to investigate the effects of corrosion on steel mechanical properties, of which corrosion levels (0–20% target corrosion mass loss), slenderness ratios (L/D=6, 8, 10, 12) and strain amplitudes (2%, 4%) are considered. Test results show that, the corrosion morphology of steel bars under electrochemical accelerated corrosion is basically consistent with that observed under natural corrosion. Compared with uncorroded HRB400E and HTRB600 steel bars, 20% corrosion mass loss leads to 38% and 35% decrease in tensile strength, as well as 33% and 28% reduction in buckling stress, respectively. The HTRB600 steel bars present slightly superior monotonic tensile and compressive corrosion resistance than HRB400E steel bars. Corrosion obviously decreases the low-cycle fatigue (LCF) life of steel bars, resulting in reductions of 44% and 36% in LCF life at 20% corrosion mass loss for HTRB600 and HRB400E steel with a L/D of 6, respectively. Moreover, the HTRB600 steel bars present more significant corrosion degradation in total hysteretic dissipated energy, compared with HRB400E steel bars. The combined effect of corrosion and inelastic buckling further exacerbates the deterioration of LCF performance of steel bars. The corresponding deterioration models are proposed to determine the LCF life and energy dissipation capacity of corroded steel bars.