Search Results (185)

Current research on the stress mechanisms of composite connectors within steel–concrete structures of bridge towers is sparse, and there is a lack of established experimental methods and finite element modeling techniques for studying these mechanisms. This study focuses on a specific type of composite shear connector within the steel–concrete section of the Shunde Bridge tower. By employing proposed experimental methods and finite element model analysis, this research examines the load–slip curves and stress distribution of these shear connectors. It aims to elucidate the stress mechanisms and mechanical relationships between the composite connectors and the individual perforated plate connectors and shear stud connectors that comprise them. The results demonstrate that the proposed experimental methods and finite element modeling approaches effectively analyze the stress mechanisms of composite connectors, revealing that the ultimate load-bearing capacity and elastic stiffness of the composite connectors are approximately the sum of those of the individual connectors configured in parallel; The mechanical performance of the composite connectors in the steel–concrete section of the bridge tower is approximately the additive sum of the mechanical performances of the individual connectors comprising them. By comparing the experimentally measured load–slip curves with those calculated from the finite element models, it validates the modeling approach of the finite element model, and the material parameters established through material characteristic tests and literature review are reasonable. Full article

To address the challenges of slow construction and high self-weight in steel–concrete composite floors for rural light steel frame structures in China, a new prefabricated floor system was developed. This system features prefabricated slabs made from recycled concrete, connected via reinforced shear pocket joints. In seismic environments, assembly floor joints often become vulnerable points, making their shear resistance particularly crucial. This study investigated the shear performance of this new type of floor joint, examining the effects of various parameters such as joint configuration, stud diameter, recycled concrete strength, and grout strength. A refined finite element model was established for an in-depth parameter analysis. The research revealed stud–shear failure as the mode of floor joint failure under different design parameters. The detailed design of the new joint structure ensures safety in the floor joint area. Increasing stud diameter, recycled concrete strength, and grout strength all contributed to enhancing the joint’s shear capacity and stiffness, with stud diameter having the most significant impact. Higher recycled concrete strength improved shear capacity, although its influence decreased beyond a certain threshold. Optimal reserved hole diameter proved beneficial for enhancing joint shear performance, with a diameter of 40 mm showing superior performance. Full article

Background: There are very few studies in literature concerning the bonding between 3D-printed resin posts and the core build-up material. This study aimed to evaluate and compare the adhesion of 3D-printed and milled resin posts to composite resin core build-up material following different surface treatments. Methods: Three types of resin posts were utilized in this study: ready-made glass-reinforced fiber post (3M ESPE, Germany), milled PEEK POST (Bredent, Germany), and 3D-printed resin post (CROWNTEC, Saremco Dental AG, Switzerland). Each type of post was categorized into three groups based on surface treatments: C: untreated surfaces; SB: Air abrasion with 50 μm aluminum oxide particles was applied to the posts’ surfaces.; HO: the posts’ surfaces were immersed in 30% H₂O₂ for 5 min. A dual-cured composite resin (Grandio DC; VOCO) was utilized for core build-up in each group to evaluate adhesion through the push-out bond strength test. The modes of failure were analyzed, and the surface morphology of the post was characterized using SEM. Data were analyzed using a two-way analysis of variance (ANOVA) along with Tukey’s test. Results: The two-way ANOVA indicated a significant effect for surface treatment (F = 583.54, p < 001), post type (F = 79.96, p < 0.001), and their interactions (F = 265.74, p < 0.001). Regarding 3D-printed resin post, 30% H₂O₂ for 5 min recorded the highest statistically significant bond strength value (13.11 ± 1.61) compared to other groups. Regarding the milled PEEK post, the air particle abrasion recorded the highest statistically significant value (23.88 ± 1.66) compared to other groups. Adhesive failure was the predominant failure type, with an occurrence rate of 70.35%. Mixed failure was noted in 24.07% of the cases, with a significant prevalence in the PEEK post within the air particle abrasion group (58.3%). Cohesive failure was noted in 5.54% of cases, with a significant prevalence in the air particle abrasion group, occurring at rates of 16.6% in the resin fiber post group and 33.3% in PEEK posts. Conclusions: Air particle abrasion significantly improved the push-out bond strength of milled PEEK posts, but it did not have a similar effect on the 3D-printed resin posts. The application of 30% H₂O₂ for 5 min to 3D-printed resin post enhanced the adhesion to core build-up material. The manufacturing method of posts, the surface treatments utilized, and their interactions affect the interfacial bond strength between posts and the composite resin core build-up material. Full article

This study evaluated the effects of mechanical agitation of Aloe vera Barbadensis Miller solution at different concentrations using passive ultrasonic irrigation (PUI), XP Endo Finisher (XPF), XP Clean (XPC), and Easy Clean (ECL), compared to conventional endodontic irrigation (CIE), on bond strength and adhesive failure patterns in the cervical, middle, and apical thirds of the root canal. Aloe vera solutions at 1%, 3%, and 5% were tested to reverse collagen fiber collapse induced by hypochlorous acid, a free radical released by 2.5% sodium hypochlorite, which impairs dentin hybridization and the light curing of resin cement. Fiberglass posts were cemented using an etch-and-rinse adhesive system (Ambar; FGM) and conventional dual resin cement (Allcem Core) in root dentin across all thirds. Human teeth underwent chemical–mechanical preparation, and the Aloe vera solution was agitated using the CIE, PUI, XPF, XPC, or ECL protocols. Slices from each root third were evaluated under a stereomicroscope at 10× magnification and subjected to the push-out test. Cytotoxicity was assessed by applying various Aloe vera concentrations to stem cells from the apical papilla (SCAPs) for 24 h, followed by analysis of cell metabolism (Alamar Blue), viability (Live/Dead), and proliferation (F-actin). Aloe vera demonstrated significant biological activity and enhanced bond strength, particularly at 3% and 5%, irrespective of the agitation method or root third. Thus, it can be concluded that using Aloe vera solution is an alternative for pre-treatment before the cementation of fiberglass posts with conventional dual-cure resin cement in endodontically treated dentin. Full article

Achieving the appropriate primary stability for immediate or early loading in areas with low-density bone, such as the posterior maxilla, is challenging. A three-dimensional (3D) stabilization implant design featuring a tapered body with continuous cutting flutes along the length of the external thread form, with a combination of curved and linear geometric surfaces on the thread’s crest, has the capacity to enhance early biomechanical and osseointegration outcomes compared to implants with traditional buttressed thread profiles. Commercially available implants with a buttress thread design (TP), and an experimental implant that incorporated the 3D stabilization trimmed-thread design (TP 3DS) were used in this study. Six osteotomies were surgically created in the ilium of adult sheep (N = 14). Osteotomy sites were randomized to receive either the TP or TP 3DS implant to reduce site bias. Subjects were allowed to heal for either 3 or 12 weeks (N = 7 sheep/time point), after which samples were collected en bloc (including the implants and surrounding bone) and implants were either subjected to bench-top biomechanical testing (e.g., lateral loading), histological/histomorphometric analysis, or nanoindentation testing. Both implant designs yielded high insertion torque (ITV ≥ 30 N⋅cm) and implant stability quotient (ISQ ≥ 70) values, indicative of high primary stability. Qualitative histomorphological analysis revealed that the TP 3DS group exhibited a continuous bone–implant interface along the threaded region, in contrast to the TP group at the early, 3-week, healing time point. Furthermore, TP 3DS’s cutting flutes along the entire length of the implant permitted the distribution of autologous bone chips within the healing chambers. Histological evaluation at 12 weeks revealed an increase in woven bone containing a greater presence of lacunae within the healing chambers in both groups, consistent with an intramembranous-like healing pattern and absence of bone dieback. The TP 3DS macrogeometry yielded a ~66% increase in average lateral load during pushout testing at baseline (T = 0 weeks, p = 0.036) and significantly higher bone-to-implant contact (BIC) values at 3 weeks post-implantation (p = 0.006), relative to the traditional TP implant. In a low-density (Type IV) bone model, the TP 3DS implant demonstrated improved performance compared to the conventional TP, as evidenced by an increase in baseline lateral loading capacity and increased BIC during the early stages of osseointegration. These findings indicate that the modified implant configuration of the TP 3DS facilitates more favorable biomechanical integration and may promote more rapid and stable bone anchorage under compromised bone quality conditions. Therefore, such improvements could have important clinical implications for the success and longevity of dental implants placed in regions with low bone density. Full article

Concrete-filled steel columns are increasingly recognised for their enhanced structural performance. This study investigates an innovative shear connector design with screw connectors as an alternative to conventional connection types. From push-out testing, the shear capacity of screw connectors in composite columns comprising cold-formed steel sigma sections and concrete infill was evaluated. Experimental push-out testing demonstrated the effectiveness of theoretical equations in estimating the shear strength of screw connections. The comparison indicates that established design methods provide reasonable predictions, supporting their applicability in practical scenarios. Theoretical equations in the literature for estimating shear strength were tested for suitability and gave comparable results. Disassembling of tested specimens showed that a concrete failure was the prominent mode of ultimate condition. Shear screws offer a novel design alternative to conventional shear connection methods. They demonstrate significant potential for structural applications when integrated with advanced composite column sections, such as the four-sigma built-up CFS sections. The study highlights screw connectors as a cost-effective, sustainable, and practical solution for innovative composite column designs, offering significant potential for construction and maintenance efficiency. Full article

Purpose: The aim of this in vitro study was to investigate the adhesive bond strength of glass fiber posts when cemented with universal resin cement in two different adhesion modes: adhesive and self-adhesive. Methods: A total of 20 extracted single-root teeth were endodontically treated, decoronated and prepared to receive glass fiber posts (GFPs) with a diameter of 1.6 mm (RelyX fiber post 3D). Specimens were randomly divided into two groups: (G1) GFPs were cemented using RelyX Universal cement in self-adhesive mode, and (G2) GFPs were cemented using Scotch Bond Universal Plus and RelyX Universal cement (adhesive mode). Afterwards, the specimens were sliced at three root levels: coronal, middle and apical. Bond strength was measured using a push-out test. Data were analyzed with a two-way analysis of variance (ANOVA) test and independent sample T-test. Results: Bond strength was significantly influenced by the adhesive strategy (p < 0.025) and the position of the root third (p < 0.007). Microscopic analysis of failure mode revealed a higher prevalence of adhesive failures (cement–dentine). Conclusions: Glass fiber posts cemented with universal resin cement applied in adhesive mode showed significantly higher push-out bond strength than when applied in self-adhesive mode. In both study groups, the apical root regions exhibited the highest retention values, followed by the middle and coronal regions. Full article

To reduce the cast in place work of concrete and realize the industrial production of a bamboo–concrete composite (BCC), innovative connection systems composed of an assembled bamboo–lightweight concrete composite (ABLCC) structure featuring perforated steel plate connectors are presented for use in engineering structures. This study examined the shear performance of connection systems composed of an assembled BCC structure featuring perforated steel plate connectors based on the design and fabrication of three groups of shear connectors with nine different parameters using bamboo scrimber, lightweight concrete, perforated steel plates, and grout. Push-out tests were conducted on these shear connectors. A linear variable differential transformer (LVDT) and digital image correlation (DIC) were utilized for measurements. The test parameters comprised fabrication techniques (assembled and cast-in-place/CIP) and connector size (steel plate thickness). This study investigated mechanical performance indicators, including the failure mode, load–slip relationship, shear stiffness, and shear capacity of the shear connectors. The experimental results showed that the shear connector failure modes involved concrete spalling near the connectors and deformation of the perforated steel plates. The load–slip curves generally included three stages: high slope linear increase, low slope nonlinear increase, and rapid decrease. The shear capacity and stiffness of the assembled shear connectors were 0.84 times and 2.46 times those of the CIP connectors, respectively. The stiffness of the 4 mm steel plate connectors increased by 42% compared to the 2 mm steel plate connectors. Analysis showed that the shear capacity of the BBC primarily consisted of four aspects: the end bearing force of the steel plate, contact friction, and forces due to the influence of tenon columns and the reinforcing impact of through-rebars. This study proposes a simple and suitable formula for obtaining the shear capacity of perforated steel plate connectors in the BCC structure, with the analytical values being in good agreement with the test results. Full article

Additional steel supporting joists (ASSJs) can effectively enhance the anti-overturning capacity of the existing solo-column concrete pier (SCP) bridges. Although the interface consists of bolt connections between steel and concrete is the crucial load-transmitting portion, the design of the interface between the ASSJ and SCP still mainly relies on practical experiences. In an actual bridge rehabilitation project with ASSJs in China, a novel connection comprising large-diameter bolts and an epoxy resin layer was adopted to overcome the shortcomings of the initial design. In this study, connections composited with large-diameter bolts and different interfacial treatments were investigated. Four push-out tests on the interfacial shear performance of steel–concrete connections were carried out. The experimental parameters encompassed the interface treatment method (barely roughened surface, smearing epoxy resin, and filling epoxy mortar) and the number of bolts (single row and double rows). The failure modes were unveiled. According to the experimental results, the interfacial treatment method with filling epoxy mortar could uniformly transfer stress between concrete and steel and improve the shear stiffness and shear resistance of the steel–concrete connections. Compared with specimens with barely roughened interfaces, epoxy mortar and epoxy resin employed at the steel–concrete interface can increase the shear-bearing capacity of connections by approximately 47.71% and 43.46%, respectively. However, the interfacial treatment method with smearing epoxy resin resulted in excessive stiffness of the shear members and brittle failure mode. As the number of the bolts increased from a single row to a double row, the shear-bearing capacity of a single bolt in the specimen exhibited approximately an 8% reduction. In addition, by comparing several theoretical formulae with experimental results, the accurate formula for predicting the shear-bearing capacity of bolts was recommended. Furthermore, the load-bearing capacity of an ASSJ in the actual engineering rehabilitation was verified by the recommended formula GB50017-2017, which was found to accurately predict the shear-bearing capacity of large-diameter bolt connectors with an epoxy mortar layer. Full article

A steel–concrete composite beam with a straddle monorail is a lightweight and easily installable structure. The mechanical performance of group stud connectors and their arrangement are key design parameters that govern the beam’s overall performance. This study investigates the behavior of group stud connectors by conducting push-out tests on four specimens, comprising three full-scale models and one 1:3 scaled model. Variables such as the number of connectors, arrangement, and specimen size were explored. The results indicated that all the specimens exhibited ductile failure due to stud shearing. The strain distribution analysis revealed higher strain at the edges and lower in the middle, persisting as the load increased. The group stud effect resulted in a 23.4% to 27.2% reduction in shear capacity for the full-scale specimens and 16.5% for the scaled specimen. The reduction was proportional to the density of the studs, but the size effects were less significant. This study provides valuable insights into the mechanical behavior of group stud connectors and offers design recommendations for practical applications. Full article

The calcium silicate-based sealers currently available on the market have different compositions and formulations, which is why their physical and chemical properties may vary. (1) The aim of the study was to measure the physico-chemical properties of calcium silicate-based sealers and their push-out bond strength to root dentine, comparing two push-out testing protocols. (2) Standardized specimens of EndoSequence BC, BioRoot RCS, MTA Fillapex, and AH Plus (control) were subjected to pH measurements over 28 days. Radiopacity was measured using a CCD sensor, and flexural strength was assessed using a three-point bending setup. Push-out bond strength was measured in coronal, middle, and apical sections of 40 single-root teeth (conventional method), and cylindrical cavities were prepared for all sealers on the same root dentine disks in 11 third molars (disk method). (3) EndoSequence BC exhibited a higher pH than MTA Fillapex and the highest radiopacity (p < 0.05). The highest flexural and push-out bond strengths were found for AH Plus. The push-out bond strength of EndoSequence BC and BioRoot RCS was higher than MTA Fillapex (p < 0.05). The conventional and disk methods exhibited similar push-out bond strength results, but the data were more homogeneously distributed in the disk method. (4) All calcium silicate-based sealers exhibited a higher pH than AH Plus. MTA Fillapex did not meet the ISO standard. Calcium silicate-based sealers showed weaker performance in terms of physical properties compared to AH Plus. Full article

Background/Objectives: The primary purpose of the study is to investigate the bond strength of apical fillings following retreatment in teeth with failed apical resection. Methods: After the preparation and obturation of the 120 human upper central and canine teeth, apical 3 mm was resected and separated into two main groups to prepare retrograde cavities using tungsten carbide burs or ultrasonic retro-tips. Each main group was separated into three subgroups according to retrograde filling material (Glass ionomer cement, MTA and Biodentine), and each subgroup was divided according to placement technique: manual condensation and indirect ultrasonic vibration. After the retrograde filling, retreatment procedures were performed, and 2 mm sections were removed from the apical filling and analyzed for push-out test. A Kolmogorov–Smirnov test was used to check the normal distribution of the data while Levene’s test was used to check the homogenity of group variances. The data were analyzed using three-way ANOVA. Results: The analysis of variance demonstrated a significant difference between cavities prepared with tungsten carbide and ultrasonic retro tips in push-out bond strength. Conclusions: There was no effect on the bond strength of the retrograde filling material and the placement technique of the material. Full article

The number of resin cements marketed for fiber post cementation has increased significantly. This study compared the push-out bond strength (PBS) of self-adhesive and universal resin cements used to lute fiber posts at 24 h and after 6 months of aging in artificial saliva. Fiber posts were luted to eighty human roots endodontically treated with four self-adhesive/one-step resin cements, with one of them also used in combination with its appropriate tooth primer; one universal resin cement, applied as one-step or together with its corresponding universal adhesive (multi-step); and one adhesive/multi-step resin cement, as a control. After storage (24 h or 6 months), the interfaces were subjected to PBS tests and the data were analyzed by two-way ANOVA and Tukey and Student’s t-tests (p < 0.05 defined as statistical significance). The results showed that Scotchbond Universal Plus + RelyX Universal attained statistically higher values at 24 h and 6 months. At 24 h, all resin cements yielded similar PBS to root dentin, while at 6 months, NormoCem obtained the lowest PBS. Storage for 6 months significantly decreased PBS for NormoCem and Multilink Automix. Root section did not influence PBS regardless of storage time. It was concluded that PBS is resin cement dependent. The universal resin cement, RelyX Universal, applied in combination with Scotchbond Universal Plus adhesive, obtained a higher and more stable PBS than the other resin cements tested. Full article

Recent research indicates that high-strength bolts could be more effectively and efficiently used to connect steel girders and fabricated decks or retrofit existing composite girders than headed studs. To reduce the number of bolt shear connectors and, thus, further accelerate the construction of composite girders, high-strength large bolts could be an excellent alternative, resulting in greater concrete stress below the bolt. Also, hybrid fiber-reinforced concrete (HFRC) has better tensile ductility and strength than that of ordinary concrete (OC). Therefore, this study tried to design eighteen push-out test specimens, including different configurations of bolt shear connectors, to investigate the static properties of post-installed, high-strength, large-bolt shear connectors with fabricated HFRC/OC slabs. The experimental results indicated that the capacity and initial stiffness of a high-strength large through-bolt shear connector was the smallest. The fiber might enhance the capacity and initial stiffness of bolt shear connectors. Increasing the bolt diameter can significantly enhance the initial stiffness and load-bearing capacity, while the clearance of the bolt hole had a great influence on the capacity, initial stiffness, and slippage of the post-installed high-strength large-bolt shear connector. Finally, the capacity equation and slip behavior of post-installed, high-strength, large-bolt shear connector with fabricated HFRC deck were obtained using the regression method, which could provide the reference for their design. Full article

Background: The optimum bond strength of glass fiber posts can be compromised; it has not yet been established which final irrigant, when used in combination with luting cement, can improve this bond strength. Objectives: This study assessed the effectiveness of 2% chitosan as a final irrigant in combination with different types of luting cement used to improve the bond strength of glass fiber posts bonded to root canal-treated teeth. Methods: Thirty single-rooted anterior teeth were collected and sectioned 2 mm above the most incisal point of the cementoenamel junction. After root canal filling, post spaces were prepared and irrigated in Group I using 17% EDTA for 3 min and in Group II using 2% chitosan for 3 min. Each group was divided into three subgroups: Fiber posts were cemented in subgroup A with Fuji II Cement (resin-reinforced glass ionomer cement), in subgroup B with RelyX Unicem (self-adhesive resin cement), and in subgroup C with Metacem Refill (total-etch resin cement). Push-out bond strength (N) for each sample was measured using a universal testing machine, and the failure mode was assessed with a stereomicroscope at 30× magnification. The fiber post’s morphological structure was analyzed through scanning electron microscopy. Statistical analysis included one-way ANOVA followed by Tukey’s post hoc test in the case of significant differences between the groups. p-Values less than 0.05 were considered statistically significant. Results: This study found no statistically significant difference between using 17% EDTA and 2% chitosan as the final irrigant before post placement (p > 0.05). RelyX Unicem cement showed significant bonding strength when used with 2% chitosan in the coronal, middle, and apical thirds (p = 0.009, p = 0.02, p = 0.01, respectively). Conclusions: Chitosan at 2% can be considered a good alternative to 17% EDTA when used as a final irrigant for the post space. Full article