International Journal of Concrete Structures and Materials最新文献

The contribution of shear resisted by flanges of T-beams is usually ignored in the shear design models even though it was proven by many experimental studies that the shear strength of T-beams is higher than that of equivalent rectangular cross-sections. Ignoring such a contribution result in a very conservative and uneconomical design. Therefore, the aim of this research is to investigate the capability of machine learning (ML) techniques to predict the shear capacity of reinforced concrete T-beams (RCTBs) by incorporating the contribution of the flange. Five machine learning (ML) techniques, which are the Decision Tree (DT), Random Forest (RF), Gradient Boosting Regression Tree (GBRT), Light Gradient Boosting Machine (LightGBM), and Extreme Gradient Boosting (XGBoost), are trained and tested using 360 sets of data collected from experimental studies. Among the various machine learning models evaluated, the XGBoost model demonstrated exceptional reliability and precision, achieving an R-squared value of 99.10%. The SHapley Additive exPlanations (SHAP) approach is utilized to identify the most influential input features affecting the predicted shear capacity of RCTBs. The SHAP results indicate that the shear span-to-depth ratio (a/d) has the most significant effect on the shear capacity of RCTBs, followed by the ratio of shear reinforcement multiplied by the yield strength of shear reinforcement (({rho }_{{text{v}}}{f}_{{text{yv}}})), flange thickness (({h}_{{text{f}}})), and flange width (({b}_{{text{f}}})). The accuracy of the XGBoost model in predicting the shear capacity of RCTBs is compared with established codes of practice (ACI 318-19, BS 8110-1:1997, EN 1992-1-2, CSA23.3-04) and existing formulas from researchers. This comparison reinforces the superior reliability and accuracy of the machine learning approach compared to traditional methods. Furthermore, a user-friendly interface platform is developed, effectively simplifying the implementation of the proposed machine-learning model. The reliability analysis is performed to determine the value of the resistance reduction factor (ϕ) that will achieve a target reliability index (({beta }_{T})= 3.5).

Among infrastructure, concrete bridges are the most exposed to various environmental effects. Structural degradation occurs due to natural and artificial influences shortening the lifespan of the structure. Therefore, bridges need to be reinforced over time. The structures used in this study are re-formed using aged bridge floor decks that have been used for 50 years, approximately. The fiber-reinforced polymer (FRP) adhesion method, using sheets and plate forms, was selected among various reinforcement methods to investigate the performance of reinforced structures. We have tested various reinforcement scenarios including one and two layers FRP sheets and FRP plates. The mechanical properties of the reinforced structures were evaluated experimentally through tensile strength and flexural test experiments. In contrast to most available literature focused on model-based studies, our present work represents an experimental test validation of structural reinforcement on an actual bridge. Our results indicate that fiber-based reinforcement in sheet form exhibits higher performances of the reinforced structure compared to reinforcement using the plate form. This study is intended to provide sufficient data for reinforcing bridge floors that could be used for reference at future construction sites.

Ultra-high performance engineered cementitious composite (UHP-ECC), which is known for its exceptional compressive strength, tensile strength, and ductility, has been emerged as a promising option for repairing and strengthening reinforced concrete (RC) structures. The bond between UHP-ECC and normal concrete is the key issue for the material to be successfully implemented. This paper presents an experimental investigation focused on understanding the tensile and shear behavior of the bonding interface between UHP-ECC and concrete. A total of 78 specimens were prepared and tensile splitting tests and push-out tests were carried out. The study examined key parameters including the strength of the concrete substrate, the roughness of the interface, and the moisture condition at the interface. Various failure modes are observed in the specimens under tensile splitting force and direct shear force, and it is found that the influence of the key parameters varied depending on the type of failure mode. In specimens experiencing full interface debonding or interface failure combined with substrate cracks, the roughness of the interface and the moisture degree have a significant impact on the tensile and shear strength. Conversely, in specimens with full substrate disruption, the strength of the substrates plays a more significant role. Additionally, the study reveals that the grooving treatment is highly effective in improving the shear strength of the interface, but its impact on enhancing the tensile strength is comparatively less pronounced. Prediction models for the tensile and shear strength of the interface are established and verified against the test results. The proposed models provide valuable insights into the behavior of the UHP-ECC to concrete interface and can aid in predicting its performance in practical applications.

Non-sintered cement (NSC) mortar was developed using only industrial by-products, such as ground granulated blast furnace slag, classes C and F fly ashes, and slaked lime. The characteristics of different NSC mortar formulations were investigated, as well as their applicability for use in forming precast concrete products. X-ray diffraction and scanning electron microscope analyses were performed to examine the internal structure of the different formulations. Overall, the developed NSC mortar satisfied the existing quality standards in terms of strength performance and absorption rate. Therefore, it is expected to be highly applicable as a raw material for production of the desired cement products.

In this paper, the shear behavior of ferro-cement hollow beams is investigated experimentally and analytically. Ten reinforced concrete beams with cross-sectional dimensions of 100 × 200 × 1300 mm and a clear span of 1000 mm were cast and tested until failure under a two-point loading system. Ferrocement beams in this research contained either an autoclaved aerated lightweight brick core (AAC) or an extruded foam core (EFC) and were reinforced with either expanded metal mesh (EMM) or welded wire mesh (WWM). The structural behavior of the studied beams, including first crack, deflection, ultimate load, crack pattern, failure mode, and ductility index, was investigated. The experimental data were used to validate finite element models created with the ABAQUS finite element program. It can be concluded that the optimum performance of ferrocement beams can be achieved using beams with a second layer of expanded steel mesh as additional reinforcement, which led to an increase in the ultimate load and maximum deflection by 12.9% and 22.8%, respectively. Furthermore, the Numerical results agreed with the experimental results, where the ratio between the NLFE ultimate loads and the experimental ultimate loads varies between 1.02 and 1.07, with an average ratio of 1.04.

An experimental study on reinforced concrete one-way slabs strengthened by various methods and materials is introduced in this paper. Innovative anchorage procedures are presented and evaluated to prevent the strengthening elements with FRP system from de-bonding at the initial stages. Externally bonded embedded in concrete cover (EBECC) strengthening technology was proposed to save the fiber strips from being subjected to heat, degradation, and sabotage. Nine RC one-way slabs, including a control slab and eight strengthened slabs, were cast. One RC slab was strengthened using externally bonded embedded in concrete cover (EBECC), whereas the other tested RC slabs were strengthened using either externally bonded (EB) or near-surface mounted (NSM) procedures. The following test variables are used in this study: the proposed anchors, the area of steel, the kind of material utilized in NSM rods (carbon fiber reinforced polymer (CFRP), glass fiber reinforced polymer (GFRP), and steel), and the strengthening scheme. The ultimate and initial cracking loads, load–deformation response, cracking patterns, and failure behavior were recorded and discussed. Additionally, a comparison of the stiffness, ductility, and energy absorption of the examined slabs was reported. The strengthened slabs by various techniques showed a boost in flexural strength that varied from 67 to 107% compared to the control slab. In addition, RC slabs strengthened by NSM-CFRP bars showed a maximum flexural capacity when compared with slabs strengthened by GFRP and steel bars. Also, the results supported the superiority of a novel end anchorage. The ABAQUS program was employed to conduct a finite element analysis (FEA) employing 3-D geometries to compare and assess the numerical performance of the identical slabs under similar test settings. The results showed good agreement between the experimental and numerical findings.

Recently, studies on blast-proof panels, which were attached to structures to protect facilities from local damage caused by explosions, have been actively performed. However, blast-proof panels are impractical yet due to the high installation cost and difficulty in construction, and protection performance for explosions inside a structure is not evaluated. In this study, a blast-proof panel consisting of concrete material was devised to ensure economic feasibility and constructability. Then, the protection performance of the concrete blast-proof panel for internal explosions was analyzed by numerical simulations and field experiments. First, field experiments on concrete explosion-proof panels were conducted for two cases, where panels without and with energy-absorbing foam were installed. As a result, the concrete blast-proof panel reduced the displacement of structures by up to 22% and the acceleration of structures by up to 86%. However, the reliability of the field experiment data was insufficient due to the shear failure of the test structure during experiments. Therefore, additional analysis was conducted by developing a numerical model. A series of numerical simulations was conducted according to the various densities of the energy-absorbing foam that was inserted between the panel and structure. Consequently, the optimum density of the impact-absorbing material differed depending on the type of structure damage to reduce (i.e., the displacement or acceleration of the structure).

A new ultra-high strength concrete, in which oxidized graphene nanoplatelet (GO) and hollow glass powder (HGP) are added, has been developed by authors. This paper presents the material properties of the concrete such as workability, compressive and tensile strengths, internal micro structure (SEM and MIP) as well as air-tightness which was tested using an equipment developed in this study. Test results show that workability and tensile strength significantly increase by a small addition of HGP, and that cGO (GO product of company c) and HGP are well dispersed without agglomeration effect, resulting in more than 20% of reduction in porosity. It is also observed that air-tightness increases by 40% compared with conventional ultra-high strength concrete due to reduction in porosity; thus, new ultra-high strength concrete is anticipated to be effectively used for structures that requires air-tightness such as hyperloop tube. Consequently, it was observed that the workability and mechanical properties of UHSC were increased when cGO and HGP were used instead of silica fume (SF), and authors believe that utilization of new material would contribute to the change in manufacturing method and increase in mechanical properties of concrete.

The current code provisions in ACI 440.11 are based on the flexural theory that applies to slender members and may not represent the actual structural behavior when the shear span-to-reinforcement depth ratio is less than 2.5 (i.e., deep members). The Strut-and-tie method (STM) can be a better approach to design deep members; however, this chapter is not included in the code. Research has shown that STM models used for steel-reinforced concrete (RC) give satisfactory results when applied to glass fiber-reinforced polymer-reinforced (GFRP)-RC members with a/d less than 2.5. Therefore, this study is carried out to provide insights into the use of STM for GFRP-RC deep members based on the available literature and to highlight the necessity for the inclusion of a new chapter addressing the use of STM in the ACI 440.11 Code. It includes a design example to show the implications of ACI 440.11 code provisions when applied to GFRP-RC deep members (i.e., isolated footings) and compares it when designed as per STM provided in ACI 318-19. It was observed that current code provisions in ACI 440.11 required more concrete thickness (i.e., h = 1.12 m) leading to implementation challenges. However, the required dimensions decreased (i.e., h = 0.91 m) when the design was carried out as per STM. Due to the novelty of GFRP reinforcement, current code provisions may limit its extensive use in RC buildings, particularly in footings given the water table issues and excavation costs. Therefore, it is necessary to adopt innovative methods such as STM to design GFRP-RC deep members if allowed by the code.