Yield Load Research Articles

Experimental Investigations of Seismic Performance of Girder–Integral Abutment–Reinforced-Concrete Pile–Soil Systems

Integral abutment bridges (IABs) have been widely applied in bridge engineering because of their excellent seismic performance, long service life, and low maintenance cost. The superstructure and substructure of an IAB are integrally connected to reduce the possibility of collapse or girders falling during an earthquake. The soil behind the abutment can provide a damping effect to reduce the deformation of the structure under a seismic load. Girders have not been considered in some of the existing published experimental tests on integral abutment–reinforced-concrete (RC) pile (IAP)–soil systems, which may not accurately represent real conditions. A pseudo-static low-cycle test on a girder–integral abutment–RC pile (GIAP)–soil system was conducted for an IAB in China. The experiment’s results for the GIAP specimen were compared with those of the IAP specimen, including the failure mode, hysteretic curve, energy dissipation capacity, skeleton curve, stiffness degradation, and displacement ductility. The test results indicate that the failure modes of both specimens were different. For the IAP specimen, the pile cracked at a displacement of +2 mm, while the abutment did not crack during the test. For the GIAP specimen, the pile cracked at a displacement of −8 mm, and the abutment cracked at a displacement of 50 mm. The failure mode of the specimen changed from severe damage to the pile top under a small displacement to damage to both the abutment and pile top under a large displacement. Compared with the IAP specimen, the initial stiffness under positive horizontal displacement (39.2%), residual force accumulation (22.6%), residual deformation (12.6%), range of the elastoplastic stage in the skeleton curve, and stiffness degradation of the GIAP specimen were smaller; however, the initial stiffness under negative horizontal displacement (112.6%), displacement ductility coefficient (67.2%), average equivalent viscous damping ratio (30.8%), yield load (20.4%), ultimate load (7.8%), and range of the elastic stage in the skeleton curve of the GIAP specimen were larger. In summary, the seismic performance of the GIAP–soil system was better than that of the IAP–soil system. Therefore, to accurately reflect the seismic performance of GIAP–soil systems in IABs, it is suggested to consider the influence of the girder.

Design theory of self-centering column foot joint with dog bone weakened flange cover plate

Basing on the concept of post-earthquake repairability, plastic damage control, and self-centering, this study introduces a novel self-centering column foot joint with dog bone weakened flange cover plate (FCP) for prefabricated steel structure. The method and design theory for the target yield load and initial stiffness of the new joint were established. Parametric research was conducted using finite element simulation to assess the influence of the dog bone weakened FCP thickness, initial cable force, and axial compression ratio on the bearing performance of the new joint, thereby verifying the above method and theory. The results reveal the accuracy of the proposed method for determining the target yield load and initial stiffness, and provide practical design guidance for the new joint. The design theory values of the new joint and the simulation values demonstrate an error within 10%, which satisfies the engineering accuracy requirements. The corresponding procedures and suggestions for the design theory of this new joint were finally provided. Based on design theory, the overall plastic damage concentrates on the dog bone weakened FCP, successfully controlled by the new joint design, ensuring minimal damage to the main structure and demonstrating good bearing capacity and self-centering performance.

Research on Coordinated Relationship Between Deformation and Force in Shaft Foundation Pit Support Structures

In order to investigate the coordinated relationship between lateral deformation of the diaphragm wall and axial force of the internal strut, this paper first carried out a scaled model test on the mechanical features of a foundation pit support system based on a novel axial force servo device. Then, a finite element model was established to simulate the scaled model test, and the correctness of the finite element modeling approach was validated by comparing test results. After that, the same finite element modeling method was used to analyze the coordinated relationship between axial force and lateral deformation in the prototype foundation pit support structure. The results show that the axial force of the inner strut is negatively correlated with the lateral deformation in the diaphragm wall. The initial maximum lateral deformation in the diaphragm wall of the shaft foundation pit occurs at the bottom of the foundation pit, so changing the length of bottom strut simultaneously is the most effective way to adjust the mechanical behavior of the support structure. Under various support conditions, the maximum lateral deformation of the diaphragm wall in the prototype project is 0.59~0.66‰ of the total excavation depth of the foundation pit, and the maximum axial force of internal support is 11~30% of the yield load of a single steel strut.

Experimental Study on the Mechanical Properties of Squat RC Shear Walls with Corrosion Along the Base

In corrosive environments containing chloride and sulfate, the corrosion of steel bars is common along the base of squat RC shear walls (SRCSW) due to problems such as construction quality, concrete stress concentration, local defects, and accumulation of water and corrosive media. In this paper, three SRCSWs are designed and constructed and their mechanical properties assessed. One side of each SRCSW was exposed to a corrosive environment for 70 days, while the other side was subject to the same conditions over different corrosion times (i.e., 0 day, 42 days, and 70 days). Then, the corrosion-induced cracking process, the mechanical properties of SRCSWs corroded along the base, the relationship between the mass loss of total steel bars (MLTSB) in the corroded area and the wall mechanical properties, and the relationship between the average width of corrosion-induced cracks (CICs) and the wall mechanical properties were studied through an accelerated corrosion test and a loading failure test. The results indicate that the area of corrosion-induced cracking on SRCSWs increased with the corrosion time, and the cracking area on the different SRCSWs was approximately identical when the SRCSWs were exposed to the same corrosion time. When the degree of corrosion was different, the loading failure characteristics of the SRCSWs were obviously different, but the failure mode always corresponded to shear failure. The load–displacement curves of the SRCSWs with different degrees of corrosion along the base basically coincided and were linear when the loading was in the elastic stage. Compared to SW-1, the peak load of SW-2 decreased by 4.0%, but that of SW-3 increased by 2.7%. Compared to SW-1, the yield loads of SW-2 and SW-3 decreased by 22.4% and 11.8%, respectively. When the MLTSB increased from 13.05% to 16.71%, the crack, yield, and peak loads of the SRCSWs corroded along the base decreased by 8.8%, 22.4%, and 6.8%, respectively. The cracking, yield, and peak loads of the SRCSWs corroded along the base decreased linearly with the increase in MLTSB and the average width of the CICs, and the corresponding fitting relations were established. The results of this study can serve as a reference for the durability design of SRCSWs in corrosive environments.

Parameters Affecting Seismic Performance of Longitudinally Connected Track Lateral Blocks on Bridges Under Low-Cycle Reciprocating Loads

In the current seismic analysis of high-speed railway track–bridge structures, the constitutive parameters of track lateral blocks (TLBs) are not uniform. A finite element model of the TLB’s main beam is established, which considers concrete plastic damage, interface bond between old and new concrete, and bond slip between anchorage steel bars (ASBs) and concrete. Quasi-static tests of nine TLBs with different numbers and ASB diameters at a 1:2 scale was carried out to verify the accuracy of the TLB finite element model in terms of the failure pattern, interface damage, hysteretic properties, and skeleton model. Based on the verified TLB finite element model, the influence of different TLB design parameters on its seismic performance parameters was studied. The results show that the established TLB finite element model is in good agreement with the test data in terms of failure pattern, interface damage, hysteretic properties, and skeleton model, which verifies the accuracy of the TLB finite element model. ASB number has the greatest influence on the TLB yield load, followed by ASB diameter, concrete strength, ASB strength, and ASB spacing. ASB diameter has the greatest influence on the TLB peak load, followed by ASB number, ASB strength, concrete strength, and ASB spacing. ASB diameter has the greatest influence on the TLB energy dissipation capacity, followed by ASB number, concrete strength, ASB strength, and ASB spacing. With the increase in concrete strength and ASB strength, TLB ductility decreases. When the ASB number is higher than eight or the diameter is higher than 12 mm and the corresponding interfacial steel bar ratio reaches 0.82%, the TLB ductility will decrease.

Waste rubber recycling in concrete-filled steel tube members: Mechanical performance, reliability and life cycle assessment

This paper focuses on the axial compression mechanical performance, reliability analysis and environmental impact of rubber concrete-filled circular steel tube (RuCFST) columns. Initially, the research of the axial compression performance reveals that enhancing the wall-thickness or yield strength of steel tubes variably increases the yield, peak, and ultimate loads of RuCFST columns. The degree of enhancement of each characteristic point by growing the wall thickness of the steel tube is 5 %–44 %, 6 %–44 %, and 9 %–44 %, respectively; while the degree of enforcement is 5 %–55 %, 23 %–53 %, and 24 %–61 %, respectively, upon yield strength increase. Reliability analysis indicates that higher concrete grades decrease the probability of axial compression failure in RuCFST columns. Raising the yield strength and wall-thickness of steel tubes leads to a reduction in the reliability index. Both larger and smaller live-to-dead load effect ratios adversely impact the reliability index. In addition, the life cycle assessment method was used to evaluate the environmental impact of RuCFST columns, and the analysis was made after considering the superposition effect of waste rubber incineration and recycling into rubber aggregates.

Global buckling bearing capacity of corroded H-section steel beams

To understand the effect of seawater corrosion on the stability of steel beams, a global buckling bearing capacity test is conducted on steel beams corroded via an electrochemical method while considering the initial geometric imperfections. The equivalent remaining thickness of the corroded steel beam is calculated based on the yield load obtained from material property tests. Subsequently, this novel approach for calculating the corrosion thickness is utilized to establish a numerical model to simulate the global buckling bearing capacity of the steel beam. Employing this method enables a parameter analysis to be conducted. Furthermore, a new formula for the global buckling of the ultimate bearing capacity of steel beams is proposed based on the differential equilibrium equation of the microdeformation of steel members subjected to bending and torsion. The virtual work principle is employed to develop this formula, which not only simplifies the calculation process, but also assigns clear physical significance to each term.

Crack characteristic and fractal analysis of SFRC shear wall with CFST columns under repeated low cycle load

In this study, we conducted a comprehensive analysis of the crack characteristics and fractal behavior in steel fiber reinforced concrete shear walls (SFRCSW) reinforced with concrete-filled steel tube columns (CFSTCs) under repeated low-cycle loading conditions after failure. Notably, the incorporation of steel fibers and CFSTCs did not alter the fundamental shear failure mode but effectively constrained crack widths to 2.0 mm and 1.6 mm, respectively, from an initial width of 2.4 mm. The use of steel fibers or CFSTCs led to significant improvements in the surface crack fractal dimension (SCFD) of shear walls, with increase ratios of 9.7 % and 7.88 %, respectively. Conversely, an increase in SCFD was associated with improvements in yield load, peak load, failure load, and cumulative hysteretic energy consumption in SFRCSWs. SCFD is suitable for comparative evaluation of the bearing capacity and energy dissipation capacity of different shear walls, but it is not suitable for comparative evaluation of displacement and ductility. For shear walls, it seems more reasonable to evaluate the damage degree in loading process by displacement - fractal dimension relation, rather than load - fractal dimension relation, with the critical values of fractal dimension are about 1.12 and 1.17.

The Learning Curves of Adelaide- and Gan-Modified Lim-Tsai Flexor Tendon Repair Techniques

Surgical performance that improves with experience is often depicted as representing a "learning curve." Although numerous studies examine the tensile properties of various flexor tendon repairs, few compare the associated learning curves. This study aims to address this gap by comparing the learning curves of Adelaide- and Gan-modified Lim-Tsai repairs. Emphasizing the difference in learning curves is crucial because it highlights the tension between achieving biomechanically superior repairs, which may be challenging to many surgeons, and opting for possibly incrementally less strong but more feasible techniques. We organized a workshop attended by 20 medical students whose experience in surgery was limited to a few suturing exercises. Each participant repaired five porcine tendons in situ either with Adelaide- or Gan-modified Lim-Tsai, followed by a peripheral suture. We tested all tendons with linear static testing to measure ultimate and yield loads. In addition, repair times were recorded for each repair. We used a linear mixed model to compare learning between the techniques. Ultimate loads increased with experience and were higher in Adelaide technique during the first two repairs, compared with Gan-modified Lim-Tsai (80 N vs 63 N and 79 N vs 66 N, respectively). Yield loads also increased with experience but did not differ between the repair techniques at any time point. Mean repair times decreased from 44 to 28 minutes and from 46 to 25 minutes with Adelaide- and Gan-modified Lim-Tsai repairs, respectively. The Adelaide core suture had a higher initial ultimate load capacity despite fewer suture strands, possibly indicating better tension consistency. The ultimate load of the Gan-modified Lim-Tsai repair increased between the first and fifth repair, and repeats were needed to achieve comparable results with the Adelaide repair. The results of this study suggest that both repair methods are suitable for novice surgeons, but Adelaide tends to result in higher strength from the first repair. Generalizability to other repairs should be made with caution.

Biomechanical comparison of ultra-high molecular weight polyethylene sutures of different thicknesses of the tensile strength for pullout repair of medial meniscal posterior root tear.

Medial meniscus posterior root tears (MMPRT) are a risk factor for knee osteoarthritis. The predominant treatment for MMPRT is transtibial pullout repair, and loop suture remains the gold standard procedure. This study aimed to investigate the structural properties of the meniscus-suture-tibia (MST) complex after loop stitch using ultra-high molecular weight polyethylene (UHMWPE) suture tape of different thicknesses. This study used 20 fresh porcine MMPRT model knees. All specimens were randomised into two treatment groups: (1) pullout repair using 1.3 mm suture tape (thin group, n = 10; 1.3 mm PERMATAPE, Mitek Sports Medicine) fixation and (2) pullout repair using 2.5 mm suture tape (thick group, n = 10; 2.5 mm PERMATAPE, Mitek Sports Medicine) fixation. The single-loop stitch MS technique was utilised. The MST complex specimens were placed on a tensile tester. The structural properties of the MST complex (yield load, maximum load, liner stiffness, and elongation at failure) were identified. No significant differences were found between the thin and thick groups in terms of maximum load (108.8 ± 49.6 vs. 90.1 ± 33.6 N; p = 0.34), yield load (43.8 ± 15.2 vs. 39.4 ± 15.5 N; p = 0.53), liner stiffness (12.6 ± 8.4 vs. 11.2 ± 5.5 N/mm; p = 0.45), and elongation at failure (27.1 ± 19.4 vs. 19.9 ± 10.0 mm; p = 0.32). The structural properties of the thickness of the different UHMWPE were comparable in MMPRT repair. Additionally, 1.3 mm PERMATAPE may demonstrate similar repair potential as 2.5 mm PERMATAPE. Level Ⅳ.

Effects of Temperature and Water Pressure on Mild Steel Strength: A Comparative Study

This study delves into the dynamic realm of mild steel strength variations under the influence of temperature fluctuations and alterations in water pressure during the rolling process. With a focus on elucidating the nuanced relationship between these factors and steel durability, the research employs a systematic investigation approach. The experimental design involves controlled temperature adjustments and varying water pressure scenarios to assess their impact on the structural integrity and tensile strength of mild steel. Through meticulous analysis and measurement, the study aims to uncover the intricate interplay between temperature, water pressure, and steel strength, providing valuable insights for optimizing rolling processes in industrial settings. The experimental works have been conducted at 870°C, 890°C, 910°C, 930°C, 950°C of temperature and 5.800 Kg, 6.000 Kg, 6.200 Kg, 6.400 Kg, 6.600 Kg of water pressure. At 870°C, 890°C, 910°C, 930°C, 950°C of temperature, the yield point values are 548 Mpa, 541 Mpa, 533 Mpa, 525 Mpa and 520 Mpa respectively. At 5.800 Kg, 6.000 Kg, 6.200 Kg, 6.400 Kg, 6.600 Kg of water pressure, the yield point values are 521 Mpa, 527 Mpa, 534 Mpa, 538 Mpa, 544 Mpa. The Yield Load, Yield Strength, Maximum Force, Tensile Strength, TS/YS Ratio, and Elongation after Fracture were carried out in the Metrocem and Mohammadi Steel Works Ltd (MSW) laboratory. However, the results of two laboratories are almost similar. The findings aspire to contribute to enhanced manufacturing techniques and the development of more resilient steel products, thereby advancing the understanding of material behavior in mechanical applications.

Machine learning based multi-objective optimization on shear behavior of the inter-module connection

Prefabricated prefinished volumetric construction (PPVC) has become a research hotspot in recent years. Inter-module connections have a crucial influence on the mechanical behavior of PPVC. However, current studies on shear behavior and optimization design method of the inter-module connection are insufficient. This paper investigated shear behavior and machine learning based optimization method of an innovative fully bolted liftable connection (FBLC) for PPVC. The failure mode, force transferring mechanism, and ultimate load bearing capacity of the FBLC under shear force were revealed by the shear behavior tests. Four specimens were tested and the design parameters included the strength and number of the long stay bolts. Subsequently, a refined finite element model (FEM) of the FBLC was established and validated with the ratios of the shear bearing capacity between the FEA and test results ranging from 0.99 to 1.10. Then, six mainstream machine learning algorithms were utilized to predict shear behavior of the FBLC. The Genetic Algorithm Optimized Neural Network (GANN) provided better prediction accuracy on the shear bearing capacity, with an improvement on R2 by 0.1% to 3% compared with other algorithms. Similarly, the Support Vector Regression (SVR) showed higher prediction accuracy on the ultimate displacement, improving R2 by 0.4% to 12.9% compared with other algorithms. A stacking algorithm combing the GANN and SVR was developed as the proxy model between the input variables and optimization metrics. In addition, the NSGA-II algorithm was linked to establish a multi-objective optimization method on shear behavior of the FBLC. The yield load, ultimate load and steel consumption were selected as the optimization objectives and the stacking algorithm was used as the proxy model. The Pareto optimal solution sets on the optimization objectives were explored by the NSGA-II algorithm and the optimization design method of the FBLC was established. Compared with the unoptimized specimen, the yield and ultimate shear bearing capacity of the optimized specimen were increased by 113.5% and 123.6%, respectively, with the steel consumption reduced by 26.3%. Finally, a four-story PPVC was established, and the static analysis was carried out under vertical load and wind load. The shear behavior of the FBLC and inter-story drift ratio of the PPVC before and after optimization were compared to verify the reliability of the optimization method.

Study on seismic performance of a novel connection for exterior wall panels

In order to avoid the damage of the external wall panel and connecting joints caused by the incompatibility between the steel structure and the external wall panel under earthquake loads, as well as to control the interaction between the structure and wall panel to ensure favorable impacts on the main structure, a new connection for external wall panel is proposed. This connection combines the features of the sliding connection and the energy dissipating connection. To investigate the deformation behavior, failure modes, and energy dissipation capacity of the connection, a total of ten specimens with different parameters were designed for cyclic loading. The results indicate that the new connection dissipates energy through bending plastic deformation and pull-bending plastic deformation of the side plate, demonstrating excellent deformation and energy dissipation capacity with noticeable post-yield strengthening effect. Additionally, the effects of different geometric parameters on the initial stiffness, yield load, bearing capacity and hysteretic properties of the connections are also analyzed. Finally, based on the theoretical model of the space rigid frame, the calculation formula of the characteristic parameters at elastic stage of the joint is proposed by the assumptions of ignoring torsion, axial and shear deformation, which is validated by the test results and finite element simulation.

보 단부에 철판을 매립한 PC 콘크리트 보의 실험연구

In this study, an experiment was conducted to evaluate the flexural performance of steel plate embedded beams, in which the steel plate was embedded at the end of the PC beam. From the factory manufacturing stage of the PC beam, the design process of each step in which the construction and finishing loads were applied at completion was reviewed to produce a 12 m span beam. A stud bolt was installed on the embedded steel plate at the end of the beam to ensure adhesion, and the experiment was performed using two specimens with embedded depths of 250 and 450 mm. When the load was removed owing to the pre-stressing effect of the strand, the displacement recovery rate averaged 87.0%, and the stiffness gradually increased even after yielding, exhibiting trilinear behavior that was approximately 1.8 times higher than that of the yield load when the load reached perfect plasticity. Even after the 250-mm test, which was the minimum depth of the steel plate embedment in the beam end, the joint remained in excellent condition, indicating that the bonded steel plate had a minimum depth of 250 mm.

Mechanical Performances of Concrete-Filled Steel Pipe Composite Segments in Complex Geological Conditions

When shield tunnels are under complex geological conditions, tunnel damage, decreased structural performance, and shield tunnel deformation and destruction may occur. Therefore, a new type of composite segment and combined splicing joint were suggested and experimentally investigated in this study. According to the test results, the new composite segment effectively enhanced the load capacity of the segment, and the yield and ultimate loads of the segment were increased. Compared with the reference specimen, the ultimate load capacities of the proposed segments with different numbers were 23.8%, 50.0%, and 64.3% greater. Moreover, the combined splicing joint enhanced the initial bending stiffness and load capacity of the segment joint, reduced the opening displacement, and improved the rotational stiffness of the segment joint. The addition of a plug-in joint at the segment joint increased its load capacity by approximately 25%. A parametric study showed that the number and posit ion of the plug-in joint clearly affected the load capacity of the segment joint. In addition to the above test results, reasonable theoretical formulas for the new composite segment and combined splicing joint are given in this paper.

Behavior of CFRP-strengthened short spiral welded tubes under axial load

Spiral welded tubes (SWTs) are formed by rolling steel plates at a certain angle and welding the resulting abutting edges. They are extensively utilized because of their large diameter ranges, high production efficiency, and low production cost. Thin-walled spiral welded tubes with large diameter-to-thickness ratios are susceptible to local buckling under compressive load, and their performance can be affected by corrosive environments. Therefore, this paper proposed the use of carbon fiber-reinforced polymer (CFRP) to strengthen tubes by external bonding. There are limited studies on the axial compression behavior of CFRP strengthened spiral welded tubes, particularly studies that consider the initial imperfections and residual stresses in spiral welded tubes. To bridge this gap, this paper first investigated the distributions of initial imperfections and residual stresses in spiral welded tubes, finding that both are significantly influenced by distinct forming and welding manufacturing processes. Subsequently, axial compression tests were carried out on four unstrengthened specimens and twelve CFRP-reinforced specimens to investigate the compressive behavior by considering the diameter-to-thickness ratio, the length of the steel tubes, and CFRP layer orientation. The experimental results indicate that CFRP strengthening delays local buckling, and significantly enhances the yield load, ultimate load, and initial stiffness of spiral welded tubes, achieving a maximum increase of the yield load up to 69.11 % and the ultimate load up to 61.99 %, while its impact on the ductility index remains uncertain and is influenced by variables such as the diameter-to-thickness ratio of the tubes and the CFRP layer orientation. Finally, a comparison of the ultimate loads of the specimens by tests and design codes was conducted.

Test and Analysis of Concrete Beams Reinforced by Polyurethane Concrete–Prestressed Steel Wires (PUC–PSWs)

In order to solve the problems of low tensile strength of composite mortar prone to cracking when reinforced concrete beams are strengthened by traditional methods, this paper proposes a new polyurethane concrete–prestressing wire (PUC–PSW) reinforcement method using polyurethane concrete (PUC) as the wire embedding material. Twelve reinforced concrete T-beams were tested for PUC–PSW flexural reinforcement. These consisted of one unreinforced beam, four PSW-reinforced beams and seven PUC–PSW-reinforced beams. The wire embedding material, wire anchorage form, PUC material depth, amount of wire and loading type were used as variables. The test results show that PUC–PSW reinforcement can significantly increase the yield load and ultimate load of the reinforced beams by 24.1% and 44.6%, respectively, compared with PSW reinforcement. When the load reached 90 kN, the crack widths of PSW-reinforced beam A2 and PUC–PSW-reinforced beam A8 were 0.17 mm and 0.1 mm, respectively. The ability of PUC–PSW reinforcement to limit crack development is better than that of PSW reinforcement, especially after the main beam steel yield. The strength, stiffness and crack-limiting ability of the reinforced beam increase with the PUC thickness of the reinforced layer.

Experimental and numerical investigation of the load-bearing capacity of bolt-fastened wedge active joints for prestressed internal bracing in subway excavations

The present study develops a novel type of active joint node-bolt fasten wedge (BFW) active joints, aiming to investigate the load-bearing capacity of a BFW joint in a quantitative way and put forward precise formulas for its yield load and compression rigidity. To achieve this, indoor axial loading tests were conducted on two BFW joints, accompanied by a set of numerical simulations with the finite element approach (FEA) implemented in ABAQUS. Parametric research was then conducted to assess the impact of various factors on the yield load and initial compression rigidity of BFW joints, leading to the derivation of precise calculation formulas for accurate prediction of these parameters. The key findings indicate that enhancing the bolt strength from 10.9 to 12.9 significantly improves mechanical performance. Under axial compression, the final bearing force, yield load, and initial compression rigidity increase by 0.86, 1.06, and 0.15 times, respectively. Numerical models accurately predict joint behavior under axial force, confirming their reliability. Parameter studies reveal that increasing web and eaves thickness, bolt strength, and diameter improves bearing capacity, while splint thickness has little effect. The fitting formulas introduced can precisely estimate yield load and rigidity, providing practical value for engineering applications.

Flexural behavior of reinforced concrete beams externally strengthened with ECC and FRP grid reinforcement

To prevent premature delamination of FRP sheets in strengthened concrete structures, this study explores a novel method of laying a composite layer of fiber reinforced polymer (FRP) grid reinforced with engineering cementitious composite (ECC), designated as FGRE, and applied at the soffit of reinforced concrete (RC) beams to improve its flexural performance. Experimental studies were conducted on RC beams with different strengthening configurations to validate the effectiveness of the proposed strengthening method. In addition, analysis on the working mechanism and a parametric analysis were performed for the composite strengthened beam using nonlinear finite element modeling. The experimental results showed that FGRE composite layers can significantly improve the bearing capacity of RC beams. Compared with the control RC beam, the FGRE composite strengthening technique significantly increased the cracking load, yield load, and ultimate load of the beam specimens up to 28, 11, and 12 %, respectively. The ECC grout layer maintained a good bonding performance with the concrete substrate until beam failure. The flexural capacity of RC beams with the proposed FGRE strengthening systems is determined by the thickness of the ECC layer. In addition, the effect of strengthening on the flexural capacity was more significant when the yield and tensile strength of the steel reinforcement were lower. Moreover, the prediction deviation from the experimental data of the FE models and analytical models for the ultimate load-bearing capacity were less than 2 and 7 %, respectively. It can be concluded that the proposed FGRE system is a viable solution to enhance the flexural capacity of RC beams.

Alteration of growth performance, glycolipid metabolism, and bone characteristics of broiler chickens in response to different inclusion levels of dietary wheat.

The aim of this study was to evaluate the effects of different levels of wheat inclusion on growth performance, glycolipid metabolism, and tibial properties of broiler chickens. A total of 480 1-d-old male broiler chickens were initially fed identical starter diets until d 10. Subsequently, they were divided into 3 treatments consisting of 8 replicates with 20 birds per replicate, i.e., 1) low-level wheat addition group, with wheat ratios of 15% and 25% during the grower and finisher periods, respectively; 2) medium-level wheat inclusion group, incorporating 30% and 40% wheat in the grower and finisher diets, respectively; and 3) high-level wheat addition group, containing 55.8% and 62.4% wheat in the grower and finisher diets, until d 39. When compared to the low- and medium-level wheat diet, the high-level wheat inclusion in the diet increased feed intake and reduced the feed conversion ratio (both p<0.01), which was accompanied by a longer jejunum (p=0.031). Meanwhile, the high-level addition of wheat displayed a decreased abundance of Ruminococcin, Bacteroidetes, and Lactobacillus than the low-wheat group. With the increase of the proportion of wheat treatment, the contents of cholesterol, triglyceride, and high-density lipoprotein cholesterol were elevated in serum, whereas the concentration of serum C-terminal cross-linked telopeptide of type I collagen, a bone resorption marker, was decreased. In addition, the diet with medium and high levels of wheat improved the yield load of tibia, along with comparable bone dimension and weight. The medium- and high-level wheat additions increased serum glycolipid deposition and enhanced tibial mechanical properties, whereas the high-level wheat diet compromised the growth performance of broiler chickens, which might be associated with the alteration of gut microbiota.