Capacity Of Joints Research Articles

Experimental investigation of the post-fire response of single-shear bolted lap joints

PurposeThis study aims at investigating experimentally the behavior of single-shear bolted lap joints with N-bolts and X-bolts (XB) after exposure to fire temperatures.Design/methodology/approachSixteen single-bolted lap joints with M20 Grade 8.8 bolt are heated to various targeted temperatures ranging from 400 °C to 900 °C and subsequently cooled back to ambient temperature. Following the heating and cooling stages, the specimens are subjected to direct tension tests to determine the reduction in shear capacity and slip resistance of the lap joints. Post-fire reduction factors are estimated from the axial load–displacement curves to determine the residual strength of N-bolted and X-bolted lap joints after exposure to fire temperatures. These reduction factors are incorporated into Equation J3-1 of ANSI/AISC 360 (2022) for the design of simple bolted connections acting in shear after fire exposure.FindingsThe results show that X-bolted lap joints exhibit a larger reduction in bolt shear capacities compared to those with N-bolts. The shear strength of lap joints with N-bolts begins to degrade after exposure to 500 °C, reaching a maximum reduction in shear strength of 40% at 900 °C. Conversely, the strength of lap joints with XB starts to degrade after exposure to temperatures beyond 400 °C, reaching a maximum reduction in shear strength of 42% at 750 °C. The post-fire reduction factors computed in this study showed that XB reduction factors are more conservative than the N-bolts and those available in the literature.Practical implicationsThis study provides preliminary data for the development of design guidelines of bolted connections with N-bolts and XB after fire exposure.Originality/valueThis study provides preliminary data for the development of design guidelines of bolted connections with N-bolts and XB after fire exposure.

Shear mechanism and bearing capacity calculation of steel fiber reinforced concrete beam-column joints

Based on the strut-and-tie model, the shear mechanism of steel fiber reinforced concrete (SFRC) beam-column joints is analyzed. In addition, based on the stress characteristics of SFRC beam-column joints, the influence of randomly distributed steel fibers at the cracks is equated to the effective bond stress of the steel fibers. Consequently, a formula for calculating the shear capacity of SFRC beam-column joints is proposed. Furthermore, a database of 132 SFRC beam-column joints is compiled. Based on the database, the proposed calculation method is optimized using statistical analysis method. Furthermore, the contributions of concrete, stirrups, and steel fibers to the shear bearing capacity are discussed. Finally, the proposed calculation method is compared with the existing calculation methods to validate the accuracy of the model. The results indicate that the shear bearing capacity provided by concrete can reach 90% of the total shear bearing capacity. The maximum shear bearing capacity provided by stirrups and steel fibers is 27% and 26% of the total shear bearing capacity respectively. When the stirrup ratio exceeds 1%, the enhancement of shear bearing capacity by the stirrups becomes more pronounced. Compared to straight steel fibers, hooked-end steel fibers can better enhance shear capacity. The proposed calculation method demonstrates higher accuracy compared to existing calculation methods, which can be used to predict the shear bearing capacity of SFRC beam-column joints.

Design model for shear keys used as thermal break systems in balcony-slab joints under combined shear and bending loads

Balcony-slab joints (BSs) are common in residential buildings. Integrating thermal break systems (TBSs) can reduce the energy loss resulting from thermal bridging. However, the mechanical performance of BSs equipped with TBSs against shear and bending remains hardly explored in design and experimentation. The aim of this study is to evaluate the mechanical behavior of BS joints under combined shear and bending actions, taking into account the presence of TBSs. Seven large-scale balcony-slab specimens were fabricated and tested under vertical loading with different moment-shear ratios (M/V). The BSs are equipped with TBSs comprising steel bars and shear profiles. A simplified finite element (FE) model was then developed using the ABAQUS software. The FE model employs spring-like elements to simulate the bond and contact behavior between concrete and steel, reproducing both the resistance and stiffness of the tested specimens. On the basis of the experimental and FE results, a resistance model consistent with the Eurocode design guidelines was drawn. Finally, moment-shear (M-V) interaction curves for balcony-slab joints were generated at the ultimate (ULS) and serviceability (SLS) levels, considering the impact of horizontal loading to achieve comprehensive design insights. The tests and FE results showed that the moment-shear ratio (M/V) significantly influences the shear capacity of the BS joints. The steel profiles effectively acted as shear keys connecting the balcony and the slab. A strength reduction coefficient of 0.701 was introduced for the design.

Eccentric load bearing performance of high bolt screw (HBS) active joints for prestressed internal supports in the subway excavation

This study introduces a novel High Bolt-Screw (HBS) active joint for enhancing the load-bearing performance of steel support systems used in subway foundation pits. The HBS joint addresses the limitations of traditional steel wedge joints, particularly in handling eccentric loads and tensile forces. Experimental and numerical analyses were conducted on specimens with different screw diameters to evaluate the mechanical behavior of the HBS joint under eccentric compression. Load-strain curves, load-displacement curves, and failure modes were documented to compare the performance of the HBS joint with an equal length steel support (ELSS) and a traditional wedge joint. The data and results obtained from numerical simulations exhibited a high degree of concordance with those derived from laboratory tests. Finite Element Analysis (FEA) was employed to perform parametric studies, examining the effects of key design factors such as screw diameter and eccentricity. The results indicate that the HBS joint provides superior preloaded axial force retention. Additionally, the HBS joint exhibited a yield load 1.35 times greater than that of traditional wedge joints, with an initial compressive stiffness 3.5 times higher, enhancing its resistance to deformation under eccentric loads. Parametric analysis indicated that the yield load is influenced by the eccentric distance but unaffected by the eccentric angle, with screw diameter, barrel nut height, and extension length identified as key factors. A yield load formula was derived through rigorous theoretical analysis and validated against experimental data, showing a relative error of less than 10 %. These findings emphasize the exceptional eccentric load-bearing capacity and stiffness of HBS joints, providing valuable insights for designing and implementing advanced support systems in subway foundation pit construction.

Full-scale testing of the bending behaviour of UHPC gravity–grouted sleeve–prestressed anchor joints in assembled frame tunnels

Joints are weak parts of a prefabricated tunnel frame structure, and the joint bending resistance is a crucial factor controlling the deformation and bearing capacity of the tunnel structure. This study proposes a joint with dual anchoring of ultrahigh-performance concrete (UHPC) gravity-grouted sleeves and prestressed steel reinforcement. The material strain, opening amount, deflection, stiffness, rotation angle, and ductility of the grouted sleeve-prestressed anchor joint and grouted sleeve joint types were tested through full-scale bending tests, and with the help of noncontact measurement technology, the dynamic process of joint bending failure was captured. In addition, the finite element method was used to evaluate the influences of the prestressing magnitude and the position of the prestressing steel bars on the bending performance of the joints. The results indicate that the damage to the concrete joint is concentrated at the top of the joint and that the damage to the top surface of the joint concrete is distributed in an "m" shape, indicating that the damage to the concrete in the area between the sleeves is relatively extensive. Owing to the turning points of grouting material fracture and joint yielding, the joint bending process clearly shows a three-stage change. The grouted sleeve-prestressed anchor joint exhibits greater bending stiffness than the grouted sleeve joint does, and the slip of the grouting material in the sleeve is smaller. Prestressing plays a key role in enhancing the bearing capacity and deformation resistance of joints. Considering that excessive prestress may increase the brittleness of the structure, the prestress of the grouted sleeve-prestressed anchor joint is recommended to be 200 kN. This study provides theoretical support for the joint design and construction of prefabricated tunnel frame structures.

Effect of high-strength SCC with and without steel fibres on the shear behaviour of dry joints in PCSBs

The structural behaviour of precast concrete segmental bridges (PCSBs) heavily relies on the strength of the joints between segments. Multi-keyed dry joints are currently the most commonly used solution in these discontinuity zones. Employing high-strength concrete is becoming increasingly common in civil engineering given its higher strength and improved durability. It specifically allows higher prestressing levels in PCSBs. Using self-compacting concrete enhances workability and adding steel fibres improves mechanical properties. The existing scientific literature includes experimental tests to analyse the shear behaviour of castellated dry joints in different concrete types. However, no experimental tests appear specifically for the castellated dry joints made with high-strength self-compacting concrete (HS-SCC) with and without steel fibres. Therefore, this experimental study conducted 31 push-off-type tests to analyse the behaviour and shear capacity of dry joints made of HS-SCC by investigating the influence of adding steel fibres to the concrete mix. The study examined crack patterns, load-displacement behaviour, failure modes and different (cracking, ultimate and residual) loads. The addition of steel fibres improved joints’ shear capacity. However, brittle behaviour was observed after reaching ultimate load when using HS-SCC, even when steel fibres were added to the concrete mix. Finally, the adequacy of existing formulations was analysed. Standard AASHTO proved to be on the unsafe side for the castellated dry joints specimens made of HS-SCC without steel fibres, and provided a good approximation for the specimens with steel fibres.

Compression-shear capacity of circumferential joint with dowel in shield tunnel: From experiments to analytical solution

Dislocations of circumferential joints are commonly prevalent in shield tunnels. Generally, the displacement space of bolt in rigid segment joint is very small. When the dislocation of the circumferential joint is large, plastic deformation of the bolts or concrete crushing is inevitable, which will affect the service life of the shield tunnel. The flexibility of the joint can be achieved by embedding in a dowel, which can reduce the damage of the segment joint during the misalignment of the circumferential joint. However, the addition of the dowel changes the structure of the circumferential joint. At present, the shear bearing capacity of the circumferential joint, affecting the design, safety verification, and service performance evaluation, cannot be accurately calculated through the existing mechanical models. Therefore, the envelope curves of the shear bearing capacity of the circumferential joint with dowel were investigated in this paper. Firstly, a series of shear resistance experiments were conducted to clarify the failure characteristics of the circumferential joint with the dowel. Subsequently, based on the experimental results, several shear mechanical calculation models for the circumferential joint were proposed. And the analytical method for the envelope curves between axial force (N) and shear force (Q) was derived. Finally, the accuracy of the analytical method was verified, and corresponding optimization methods to improve the bearing performance of the circumferential joint were proposed. The research results indicate that the circumferential joint with dowel has both concrete shear stage and steel rebars shear stage. The N-Q envelope curves is determined by the combination of concrete, connectors (including the dowel and the bolt), and steel rebars, and the leading factor can be clarified by the proposed method. A constructive conclusion has been found that the optimization design of the circumferential joint must consider the axial force in order to effectively improve its shear bearing performance. The research results can serve the joint optimization, load-bearing verification during design process, and the physical model in big data analysis during the operation and maintenance of the shield tunnel.

Study on the tensile failure mechanisms of CFRP‐Al flat‐joggle‐flat bonded joints

AbstractThis paper focuses on CFRP‐Al bonded joints, experimentally investigating the effects of joint geometries, different types of adhesives, and overlap lengths on the mechanical properties of bonded joints. Digital Image Correlation (DIC) technology was used to monitor the entire tensile processes, and the deformations and fracture processes of the bonded joints were captured. The strain evolution processes of the joints were obtained through analysis, and quantitative analyses of the joint fracture surfaces were conducted. The results indicate that the special geometric shape of the Flat‐Joggle‐Flat (FJF) bonded joint reduce secondary bending effects. Additionally, the joggle section participates in load transfer, significantly enhancing the joint's mechanical performance and altering its failure mode. Joints using ductile adhesives exhibit higher tensile mechanical properties compared to those using brittle adhesives. Compared to the bearing capacity of single‐lap bonded joints with the same overlap length and adhesive, the mechanical performance improvement of FJF bonded joints using ductile adhesives is less pronounced than that of FJF bonded joints using brittle adhesives. Increasing the overlap length enhances the mechanical properties of bonded joints. This study is expected to provide a reference for the engineering application of FJF bonded joints.Highlights FJF joints have higher bearing capacities compared to single lap joints. Ductile adhesives can effectively increase the bearing capacities of joints. Increasing the overlap length can improve the bearing capacities of joints. The end and middle of the FJF joints jointly bear the load effect. The failure modes of FJF joints are different from that of single lap joints.

Theoretical and experimental investigations on the mechanical performance of friction-enhanced steel fixtures for column underpinning

To improve construction efficiency of underpinning columns in building translation or rectification projects, a new Friction-enhanced Steel Fixtures (FSF) for column underpinning is created by using the effect of bottle corks. Two screw-linked trapezoidal box girders (TBG) are applied as surrounding constraints, and two ribbed V-shaped inserters (VI) are involved to realize transformation from pressure to friction. In this thesis, mechanical analysis is first carried out to determine viable geometrical parameters for each composed component of FSFs. Thereafter, a static experiment is conducted to verify the load-carrying performance of FSF-underpinned joints, and numerical evaluation is then developed to analyze their stress as well as deformation of typical composed components. It is concluded from the theoretical analysis that the suitable dip angle of the TBG is related to two friction coefficients. One friction coefficient is that between TBG and VI, and the other one is that between VI and columns. The bearing capacity of the FSF-underpinned joints, which has been experimentally certified as no less than 2000 kN, depends on the interfacial resistance between columns and VIs which is relative to the strength of concrete. In addition, the experiment-updated numerical model can accurately profile load-displacement relation between FSFs and underpinned columns, by which the components of FSFs can be optimized and improved.

Reinforcement learning for dynamic pricing and capacity allocation in monetized customer wait-skipping services

ABSTRACT We consider how to facilitate a dynamically-priced premium service option that enables customer parties to shorten their wait in a queue. Offering such a service requires that some of a business’s capacity be reserved continuously and kept ready for premium customers. In tandem with capacity reservation, pricing must be coordinated. Hence, a joint dynamic pricing and capacity allocation problem lies at the heart of this service. We propose a conceptual solution architecture and employ Proximal Policy Optimization (PPO) for dynamic pricing and capacity allocation to maximize total revenue. Simulation experiments over multiple scenarios compared PPO against a human-engineered policy and a baseline policy having no premium option. The human-engineered policy led to significantly greater revenues than the baseline policy in each scenario, illustrating the potential increase in revenues afforded by this concept. The PPO agent substantially improved upon the human-engineered policy advantage, with improvements ranging from 28% to 161%.

Prediction of Strength and Failure Modes in Reinforced Concrete Beam–Column Joints using Ensemble Machine Learning Techniques

The beam-column joint is one of the important structural elements that control the structural behaviour during seismic excitation. Moreover, failure of any of these components may lead to the partial or overall collapse of the entire structure. In view of the safety concern, there is a need to evaluate the response properties, such as failure modes and ultimate shear capacity of the beam-column joints. Conventional methods to evaluate the shear capacity of beam-column joints are usually time-consuming. Therefore, in this study, an attempt has been made to evaluate the joint shear capacity and mode of failure of an exterior beam-column joint using ensembled machine learning (ML) approaches like Decision Tree, Random Forest, AdaBoost, CatBoost, and LightGBM. The present study highlights the potential use of the CatBoost model as a useful tool that can assist in predicting the shear strength and failure mode. The results of the study reveal that this model has performed well in predicting the load-carrying capacity and shear strength with high correlation coefficients of 0.9836 and 0.9978, respectively. Moreover, it has been observed that the prediction model provided by the CatBoost algorithm exhibits the highest accuracy for classification in the failure mode of beam-column joints.

The Influences of Selected Factors on Bending Moment Capacity of Case Furniture Joints

This study experimentally investigated the effects of selected factors on the bending moment capacity (BMC) of case furniture joints. The main aim was to explore mixed applications of wood-based materials and fasteners in manufacturing case furniture to reduce material costs. The study examined the effects of the face member material—particle board (PB), plywood (PL), and block board (BB)—edge member material (PB, PL, and BB), and joint shape (T-shape and L-shape) on BMC. Additionally, the study evaluated the effects of joint type (two eccentrics (TE), two dowels (TD), and one eccentric and one dowel (ED)), and material type (PB, PL, and BB) on BMC for L-shaped joints. The results showed that joint shape and face member material significantly affected the BMC of case furniture joint. The BMCs of T-shaped joints were significantly greater than those of L-shaped joints, regardless of the material of the face and edge members, except when the face member was made of PL. For L-shaped joints with PL face members, the BMCs were significantly higher compared to others. Joints constructed with TE exhibited significantly higher BMC compared to ED and TD for the same material type. For PB, TE joints exhibited an increase of approximately 3.0 Nm and 2.0 Nm compared to TD and ED, respectively. For PL, TE showed an increase of 9.1 Nm and 4.1 Nm compared to ED and TD, respectively. For BB, the increases were 7.0 Nm and 6.6 Nm compared to ED and TD. The BMC of joints made with PL and constructed with TE and ED was significantly greater than those of BB, followed by PB. However, for joints assembled with TD, there was no significant difference among the three materials. The ratios of BMC for joints constructed with ED compared to the half-sum of TE and TD were 0.73, 1.04, and 0.79 for PB, PL, and BB, respectively. These results suggest that the face member material predominantly influences the BMC of case furniture joints, indicating the potential to reduce costs by combining different materials and joint types.

7.G. Round table: Primary prevention and management of NCDs – the added value of joint actions across Europe

Abstract Two ambitious European joint action projects, funded through the EU4Health programme, are ongoing to reduce the burden of non-communicable diseases (NCDs) and related risk factors in Europe, targeting both individual and societal levels. Together, these projects aim to scale up effective prevention and management strategies, strengthen public health policies and promote equitable and sustainable healthcare systems across Europe. The Joint Action on CARdiovascular Diseases and DIabetes (JACARDI), with 21 participating countries and a total budget of over €66 million, is focusing on enhancing the implementation of evidence-based innovative pilot projects across the entire patient journey. This includes efforts to improve prevention, early diagnosis, and proactive management of NCDs. The Joint Action Prevent Non-Communicable Diseases (JA PreventNCD), with 25 participating countries and a total budget of over €95 million, particularly aims to enhance joint capacities of countries for implementing, scaling up and evaluating prevention policies and actions at various levels. These projects represent complementary responses to calls for action in Europe’s Beating Cancer Plan and the Healthier Together - EU NCD Initiative, with JA PreventNCD emphasizing primary prevention and policy while JACARDI focuses on secondary prevention and health systems strengthening. Both projects will generate new policy-relevant evidence based on implementation, monitoring and scaling-up of best and innovative practices and policies across Europe. The projects share a focus on equity, diversity, scalability and sustainability, while avoiding fragmentation and duplication of actions. Under the EU4Health programme, launched to strengthen European health collaboration in the wake of the COVID-19 pandemic, the EU has recently invested over €200 million in public health initiatives, with additional investments from national authorities participating in the joint actions. With this new wave of funding, real population impact should be anticipated, but what can we realistically expect to be the outcomes and what are the criteria for success? In this round table discussion 1) these two joint action projects will be presented, highlighting their innovative aspects; 2) views on the added value and potential in cross-national collaborations for prevention and management of NCDs will be debated, and 3) how synergies will be leveraged for maximum impact will be explored. Panelists will share their perspectives on the projects’ potential to change the public health landscape in Europe. Workshop participants will subsequently be encouraged to engage in the discussion with the objective that views and experiences are exchanged, opportunities for collaboration and engagement are shared and energy is mobilized to harness the benefits of such large-scale policy-relevant collaborations. Key messages • Synergies and collaboration to drive policy development and foster increased capacity are the pillars to build a healthier Europe. • Two large-scale Joint Actions drive impact by highlighting innovative NCD prevention strategies and fostering collaborative engagement.

Performance of SRC unequal-depth beam-column irregular joint in NPP under progressive collapse

The prototype structure of this study is taken from the main shield building of nuclear power plant (NPP) conventional island facilities. Emphasis is on steel reinforced concrete (SRC) unequal-depth beam-column irregular joints, studying their resistance to progressive collapse via analysis of two 1/5 scale irregular joints. Vertical monotonic loading tests were conducted on the joints, followed by numerical simulations to analyze their mechanical properties, failure modes, and progressive collapse resistance. Experimental analyses focused on irregular joint failure modes, central column load changes with displacement, beam deformations, strain variations in critical sections, and resistance mechanism development. Finite element (FE) software modeled these behaviors and was validated against experimental data. Then, according to the various beam section depths of the connected beams, this research applied the validated numerical models to examine the load-bearing capacity of the irregular joints. The results indicate that the damage of the unequal-depth beam-column irregular joint exhibits significant asymmetric characteristics. In terms of load performance, the performance of the irregular joint depends on the component performance of the shallow beam section. Within a certain range, the greater the height difference between the various beams, the greater the joint bearing capacity, but the stability of the bearing performance deteriorates. The fracture yield of H-shaped steel significantly reduces the bearing capacity, and it is recommended to reinforce shallow beams. Providing data reference for the design of the irregular joints has important practical significance.

Experimental and numerical investigations on flexural behavior of apex joints in aluminum alloy portal frames

Aluminum alloy portal frames (AAPFs) find extensive applications in lightweight and temporary structures owing to their light weight, excellent corrosion resistance, and ease of installation and disassembly. Existing design equations for cold-formed steel portal frame (CFSPF) apex joints are not applicable to AAPF apex joints due to significant differences in structural configuration. Therefore, dedicated research is needed to develop design guidelines for AAPF apex joints. Consequently, this paper conducts experimental and numerical investigations on flexural behavior of AAPF apex joints. Initially, bending tests are conducted on three AAPF apex joints, revealing failure modes including clamping plate buckling and beam failure. The flexural behavior of apex joints throughout the entire process is analyzed based on moment-rotation curves and moment-strain curves. Subsequently, finite element (FE) models are established and validated by comparing the FE results with the experimental results. Following this validation, parameter analysis is conducted considering the influence of beam cross-sectional dimensions, clamping plate dimensions, bolt dimensions, and layout. Finally, based on theoretical and numerical investigation, the calculation equation for the flexural capacity of AAPF joints is derived, offering valuable reference for engineering design.

Seismic performance of mortise-tenon joint in prefabricated platform canopy

To optimize the prefabricated canopy joints, improve the construction efficiency, and enhance the seismic performance of assembly joints, a novel mortise-tenon joint (MTJ) was proposed. To evaluate the seismic performance along the vertical and track directions, two 1:1.5 scaled specimens were tested under low-cycle reciprocated loading. The test results find the hysteretic curves in both directions exhibit the “pinch” effect especially in the vertical direction, indicating the feature of shear slippage. The displacement ductility coefficients were all above 5.0, and the ultimate drift ratios were 4.54 % and 5.88 % respectively, showing excellent deformation ability and ductility. The parameters, such as the sectional strength ratio, the stirrup ratio of the prefabricated beam, the reinforcement ratio and the cross-sectional area of the enlarged section, were analyzed by the validated finite element (FE) models. The analysis shows as the section strength ratio decreases and the stirrup ratio increased, the seismic bearing capacity improved, while the plastic hinge located on the prefabricated column varied to the prefabricated beam ends. Based on the results, it is recommended the number of longitudinal rebars through the prefabricated beam is 4, the stirrup diameter in the prefabricated beam is 10 mm and the the column cap is no less than 400 mm. Finally, based on the truss-diagonal strut model, a method for calculating the shear strength capacity of the novel joint was proposed. Compared with the test and FE results, the theoretical equations exhibit good computational accuracy.

Parametric study on the load-carrying capacity of plain-woven composites hybrid bonded-bolted joints

This work presents procedures and results from quasi-static uniaxial tensile experiments carried out on hybrid bolted bonded (HBB) joints using carbon fibre reinforced plastic (CFRP) adherends. The impact of various dimensional parameters, including lap length (L), lap width (W), number of bolts ( N), bolt diameter (D), and bolt arrangement, on its ultimate load and failure modes of the HBB joint is investigated. The failure mechanism of the HBB joint is examined and summarized, offering theoretical insights for the engineering application of this structural configuration. The findings of the study indicate that the ultimate load capacity of the hybrid joint is notably enhanced by increasing both the lap length and lap width, and is further influenced by the effective dimensions at the edges and end distances. The transverse configuration of multiple bolts within the adhesive-bolt hybrid joint demonstrates superior maximum load capacity and average stiffness in comparison to a longitudinal arrangement. During tensile testing, the primary mode of failure observed in the Hybrid Bolted-Bonded (HBB) joint is adhesive failure, often accompanied by delamination. Cleavage failure is predominantly observed in configurations with longitudinally aligned multiple bolts arranged in a singular row. On the other hand, shear tear-out and bearing failures are commonly encountered in single-bolt joints characterized by a substantial width-to-diameter (W/D) ratio. Specifically, shear tear-out failure tends to manifest in cases with a small length-to-diameter (L/D) ratio, whereas bearing failure is more prevalent in instances with a large L/D ratio.

Additive technologies for improving the strength and deformation characteristics of plastic washer joints of wooden structures

Introduction. Modern wooden structures are mostly connected by mechanical working joints. To increase the reliability of nodal joints, various kinds of washers can be pressed, inserted, or glued into the wood of the elements, thus ensuring the transmission of forces from one element to another. Joints on glued washers can transfer significant forces on a relatively small area of mutual contact, which is due to their high loadbearing capacity. Thus, the gluing of steel washers in places of increased stress concentration during force transfer ensures a significant redistribution of buckling/cracking stresses over a larger area of the connected parts. However, steel washers are highly corrosive, so additional measures are required to protect metal parts from corrosion or to replace the material with the composites. The results of full-scale tests of the samples with glued-in plastic washers are used to consider the ways of increasing the strength and deformation characteristics of the plastic washer material by applying additive technologies.Aim. To increase the load-bearing capacity of the wooden structure joints by increasing the strength and deformation characteristics of the glued washer material.Materials and methods. A method for full-scale tests of wooden specimens with glued fiberglass washers is presented. The wooden elements are made of second grade pine, while the washers are of REC Formax and REC Friction plastics. The test was performed in compression along the fibers, with control of vertical shear deformations. The methods of increasing the strength and deformation characteristics of plastic washers by using additive technologies are considered.Results. Using the data of full-scale tests the diagrams of sample deformations on glued plastic washers are drawn, the obtained results are analyzed. The sufficiently high plasticity of washer materials is established. The ways for increasing the strength and deformation characteristics of plastic washers, particularly by reinforcing the plastic washers is suggested.Conclusions. In order to increase the load-bearing capacity of the joints on the glued fiberglass washers, the reinforcement of plastic using additive CFC printing technologies and the use of different reinforcing fiber materials is adopted.

Optimization of Shear Resistance in Horizontal Joints of Prefabricated Shear Walls through Post-Cast Epoxy Resin Concrete Applications

The horizontal joint is a critical component of the prefabricated shear wall structure, responsible for supporting both horizontal shear forces and vertical loads along with the wall, thereby influencing the overall structural performance. This study employs direct shear testing and finite element analysis to investigate the horizontal joint in walls with ring reinforcement. It examines the impact of various factors on joint shear performance, including the type of joint material, joint configuration, buckling length of ring reinforcement, strength of precast concrete, reinforcement ratio of ring reinforcement and dowel bars, and the effect of horizontal binding force. The findings indicate that the shear bearing capacity and stiffness of joints incorporating post-cast epoxy resin concrete and keyways are comparable or superior to those of integrally cast specimens. A larger buckling length in ring reinforcement may reduce shear strength, suggesting an optimal buckling length at approximately one-third of the joint width. As the strength of precast concrete increases, ductility decreases while bearing capacity increases, initially at an increasing rate that subsequently declines. Optimal results are achieved when the strength of precast concrete closely matches that of the post-cast epoxy concrete. Enhancing the reinforcement ratio of ring reinforcement improves shear capacity, but excessively high ratios significantly reduce ductility. It is recommended that the diameter of ring reinforcement be maintained between 10 mm and 12 mm, with a reinforcement ratio between 0.79% and 1.13%. Increasing horizontal restraint enhances stiffness and shear capacity but reduces ductility; thus, the axial compression ratio should not exceed 0.5.

Research on flexural behavior and design method of formwork free UHPC wet joint in prefabricated small box girder bridges

This study aims to enhance the bearing capacity of wet joints in prefabricated small box girder bridges while simplifying the on-site construction process. Experimental tests were conducted on formwork-free ultra-high-performance concrete (UHPC) wet joints, focusing on failure modes, ultimate flexural capacities, and cracking and strain behaviors. These were compared to the behaviors observed in rectangular and funnel-shaped wet joints. The results demonstrate that the width of the joint significantly influences flexural performance, with the horizontal strip playing a crucial role in resisting cracks. It is recommended that for formwork-free UHPC wet joints, the strip height h2 should be no less than 0.1 times the thickness of the bridge deck, and the joint width W should be at least eight times the diameter of the transverse steel reinforcement. Considering the contribution of UHPC in the tensile zone, formulas were developed to calculate the flexural capacity of UHPC-normal concrete (NC) composite section beams. Based on these flexural test results and numerical analysis, a design method for formwork-free UHPC wet joints is proposed.