Search Results (25)

Wood, steel, and concrete constitute the three predominant structural materials employed in contemporary commercial and residential construction. In composite applications, bond interfaces between these materials represent critical structural junctures that frequently exhibit a reduced load-bearing capacity, rendering them susceptible to the initiation of cracks. To elucidate the fracture propagation mechanisms at composite material interfaces, this study implements the cohesive zone method (CZM) to numerically simulate interfacial cracking behavior in two material systems: glued laminated timber (GLT) and reinforced concrete (RC). The adopted CZM framework utilizes a progressive delamination approach through cohesive elements governed by a bilinear traction–separation constitutive law. This methodology enables the simulation of interfacial failure through three distinct fracture modes: mode I (pure normal separation), mode II (pure in-plane shear), and mixed-mode (mode m) failure. Numerical models were developed for GLT beams, RC beams, and RC slab structures to investigate the propagation of interfacial cracks under monotonic loading conditions. The simulation results demonstrate strong agreement with experimental cracking observations in GLT structures, validating the CZM’s efficacy in characterizing both mechanical behavior and crack displacement fields. The model successfully captures transverse tensile failure (mode I) parallel to wood grain, longitudinal shear failure (mode II), and mixed-mode failure (mode m) in GLT specimens. Subsequent application of the CZM to RC structural components revealed a comparable predictive accuracy in simulating the interfacial mechanical response and crack displacement patterns at concrete composite interfaces. These findings collectively substantiate the robustness of the proposed CZM framework in modeling complex fracture phenomena across diverse construction material systems. Full article

In the case of load increases and the refurbishment of existing buildings, it is often necessary to carry out strengthening measures on existing timber beams. When timber concrete composite (TCC) ceilings cannot be used, it is possible to reinforce the undersides of the beams with structural steel or fiber composites (aramid or carbon-fiber-reinforced polymer). This work investigates how significant effects on the load-bearing and deformation behavior can be achieved with these materials in terms of construction practice. The article is intended to show structural engineers which reinforcement measures lead to which forces, deformations, etc., and how these are utilized. This should form the basis for the planning of reinforcement measures, as it is not clear from the beginning whether AFRP, CFRP, or steel is the most suitable material. For this purpose, a comparative parameter study was carried out under practical conditions and with a variable degree of reinforcement using the corresponding formulas. The internal forces in the timber and reinforcement cross-sections, the deflection behavior, and the failure loads at the strength and design levels were calculated. It was demonstrated that, particularly for steel and carbon-fiber-reinforced polymer (CFRP) reinforcements, significant increases in the ultimate load can be achieved and the often-important deformation behavior can be significantly improved. Especially the steel variant leads to high improvements in deflection and breaking load behavior, with the base material (wood) also being utilized more economically as a result. A comparative ecological study in the form of the global warming potential showed that reinforcement methods are also advantageous from the point of view of sustainability compared to renovations with timber concrete composite slabs or new concrete slabs. Full article

The building and construction sector accounts for nearly 40% of global greenhouse gas emissions, with steel-framed buildings being a significant contributor due to high CO₂ emissions during production. To mitigate this issue, integrating Cross-Laminated Timber (CLT) into structural systems has emerged as a sustainable alternative. CLT, known for its carbon sequestration properties, offers an environmentally friendly replacement for reinforced-concrete slabs, particularly when paired with steel structures to enhance material reuse and reduce lifecycle impacts. This study focuses on hybrid systems combining H-shaped steel beams and CLT floor panels connected using high-strength friction bolts. A four-point bending test, simulating a secondary beam, was conducted, demonstrating that the composite effect significantly enhances flexural stiffness and strength. Additionally, a simplified method for evaluating the flexural stiffness and yielding strength of these composite beams, based on material and joint properties, was shown to successfully evaluate the test results. Full article

This study presents a comprehensive three-dimensional finite element modeling and parametric analysis of composite beam-to-column joints in steel–timber composite structures. The investigation encompassed a variety of shear connector configurations, end plate designs, and bolt dimensions, aiming to elucidate their respective influences on the structural performance and behavior of these joints. Through meticulous numerical simulation, this research sought to enhance the understanding of the interactions and load transfer mechanisms within composite connections, thereby contributing to the optimization of design practices in the field of structural engineering. The load–displacement relationship for timber–steel composite joints subjected to monotonic loading was investigated using ABAQUS 6.14 software. This study systematically analyzed the effects of various parameters, including different configurations of shear connectors, end plate thicknesses, and bolt dimensions, on the overall performance of the joints. Through this comprehensive numerical analysis, the research aimed to provide deeper insights into the mechanical behavior and structural integrity of these composite connections under the applied loading conditions. A non-linear finite element model of timber was developed and verified with the results of the experiment in this study. The findings are discussed in detail, highlighting the intricate relationships between the selected parameters and their respective effects on the performance and overall stability of the composite connections. This thorough evaluation aimed to enhance the understanding of how these variables interact within the context of composite joint design and behavior. Finally, design recommendations for composite structures, such as the dimensions of the bolt, end plate thickness, and different sizes of shear connectors are provided. Full article

A cold-formed, thin-walled steel/fast-growing timber composite system has recently been presented for low-rise buildings. It aims to increase the use of fast-growing wood as a green building material in structures, thus contributing to the transformation of traditional buildings. This study proposed a composite I-beam combined with fast-growing radiata pine and cold-formed thin-walled U-shaped steel. A four-point bending test was used to measure the bending properties of steel–timber composite I-beams under various connection methods. Based on experimental results, this study examined the specimen’s failure mechanism, mechanical properties, and strain development. In addition, a method for calculating flexural bearing capacity based on the superposition principle and transformed section method was suggested. It is evident from the results that fast-growing timber and cold-formed thin-walled steel can have significant composite effects. Different connecting methods significantly impact beams’ failure mode, stiffness, and bearing capacity. Furthermore, the theoretical method for calculating the flexural bearing capacity of composite beams differs from the test value by less than 10%. This paper’s research encourages the applications of fast-growing wood as light residential components, and it serves as a reference for the development, production, and engineering of steel–timber composite structural systems. Full article

Steel–timber composite beams are a relatively new type of composite structure. They have many important advantages, owing to which they may be considered a sustainable solution. Their connectors may be demountable, which makes it possible to separate steel girders from LVL panels at the end of their service life. After disassembly, the structural elements can be recycled. One of their advantages is that they are lighter than steel–concrete composite beams. However, this may result in the poor performance of floors with steel–timber composite elements subjected to dynamic loadings. For this reason, the dynamic characteristics of floors should be investigated to verify the serviceability limit state of human-induced vibrations. In this study, the dynamic response of the three steel–timber composite beams with varying screw spacing was captured and used to validate their numerical models. The frequencies obtained from the numerical analyses correspond to the experimental results. A very high agreement between the vibration mode shapes was obtained because the MAC index values were close to 1. The validated numerical model of a single steel–timber beam may be used in future studies to create a complex numerical model of a steel–timber composite floor. Full article

The use of composite precast or steel bars as reinforcements for timber beams is an important technique that can improve effectiveness or allow cross sections to be reduced. This paper presents experimental, theoretical, and numerical studies of full-size timber beams measuring 82 × 162 × 3650 mm³ using prestressed steel bars and 10 mm diameter basalt and glass bars with a prestress of 10 MPa. In addition, parametric studies were carried out using FEM numerical simulations. In the experimental tests, an increase in load-bearing capacity and stiffness of up to 58% and 10.7% for steel bars, 32% and 10.1% for basalt bars, and 27% and 7.8% for glass bars, respectively, was obtained compared to unreinforced beams. The different levels of improvement in reinforcement efficiency was also related to the different elastic modulus of the reinforcement itself. Unreinforced beams showed a linear elastic range. In contrast, on beams reinforced with steel bars, the curve had a slightly steeper line than the control beam, and the slope of the curve then decreased when a certain load was reached. All beams failed when the lower wood fibers reached maximum tensile strain. The allowable compressive strain then decreased by 36.6% for basalt bars, 32.9% for glass bars, and 30.4% for steel bars. The use of prestressing further exploited the strength of the reinforcement beyond the yield point. All unreinforced beams primarily failed in the tension zone due to fracture of the timber fibers. Prestressed and reinforced beams were already failing due to bending and shear. The experimental and numerical analysis was also compared, and the results showed a good agreement and a maximum difference of approximately 5.7%. Full article

This paper proposes a new type of composite box beam combined with cold-formed thin-walled steel and glued laminated timber to develop green building structures while improving the load-carrying capacity of a single steel girder and glued timber girder. Two composite beams composed of laminated timber and Q235 cold-formed thin-walled steel were designed and fabricated. Then, the shear performance test with quadratic loading was carried out to analyze the load carrying capacity, damage modes, and deformation characteristics of the test beams, as well as their influencing factors. Subsequently, a finite element model of the composite beam was established, and the loading mode was the same as that of the test to further study the parameters affecting the shear performance of the composite beam. The results of the study indicate that steel and glued timber in composite beams connected by adhesive bonding can work and deform together under load and each give full play to its material properties, especially the composite beams, which exhibit higher shear strength than a steel or timber beam. The effects of parameters such as steel cross-sectional area, shear span ratio, steel skeleton form, and steel cross-sectional strength on the shear capacity of the composite beams were observed, among which the shear span ratio had the greatest effect on the shear capacity of the composite beams. The shear capacity decreased by 14.3% and 19.5% when the shear span ratio was increased from 1.5 to 2.0 and 2.5, respectively. The shear capacity of the combined composite beams increased by 10.6%, 6.3%, and 5.8% when the thickness was increased from 1.5 mm to 2.0 mm, 2.5 mm, and 3.0 mm, respectively. When the combination of the steel cross-section was a box beam, the overall shear-bearing capacity could be increased by 12% compared with the “I” type composite beam, although its shear stiffness was close to that of the “I” section composite beam. Full article

Floor vibration, although not a safety concern, is a prevalent performance complaint in multi-story structures. With the increasing use of mass timber construction, various types of long-span timber floors (LSTFs), including plain cross-laminated timber (CLT), CLT with secondary beams (ribbed-deck), and hybrid systems such as timber–concrete composite (TCC) and CLT on-steel-support beams, are gaining popularity. However, due to limited knowledge regarding their vibration characteristics and acceptance criteria, these construction types are often overlooked during the design stage by architects, engineers, and builders. Existing standards and guidelines primarily calibrated for steel and concrete floors lack a validated and calibrated method for evaluating the vibration performance of LSTFs. Nonetheless, it is essential for structural engineers to address vibration concerns during the design stage and potentially investigate excessive vibration in existing buildings, providing mitigation solutions. This article provides a comprehensive overview, discussion, and analysis of the measurement, analysis, design, perception, and acceptability of vibration of timber floors as outlined in international standards and commonly used guidelines. Experimental and theoretical case studies, including vibration measurements of a CLT floor and a comparison of vibration acceptability in lightweight timber floors using different methods, are reported. The results highlight discrepancies between simplified equation calculations and modal analysis observations, underscoring the limitations of relying solely on simplified equations. Furthermore, it is observed that current modal superposition methods tend to be conservative in predicting floor acceleration and velocity responses. Recommendations are provided for future research in the field to enhance floor vibration assessment techniques, aiming for improved design optimization and occupant comfort. Full article

These elements are innovative and of interest to many researchers for the reinforcement of wooden elements. For the reinforced beam elements, the effect of the reinforcement factor, FRP and steel elastic modulus or FRP and steel arrangement of the reinforcement on the performance of the flexural elements was determined, followed by reading the load-displacement diagram of the reinforced beam elements. The finite element model was then developed and verified with the experimental results, which was mainly related to the fact that the general theory took into account the typical tensile failure mode, which can be used to predict the flexural strength of reinforced timber beams. From the tests, it was determined that reinforced timber beam elements had relatively ductile flexural strengths up to brittle tension for unreinforced elements. As for the reinforcements of FRP, the highest increase in load-bearing capacity was for carbon mats at 52.47%, with a reinforcement grade of 0.43%, while the lowest was for glass mats at 16.62% with a reinforcement grade of 0.22%. Basalt bars achieved the highest stiffness, followed by glass mats. Taking into account all the reinforcements used, the highest stiffness was demonstrated by the tests of the effectiveness of the reinforcement using 3 mm thick steel plates. For this configuration with a reinforcement percentage of 10%, this increase in load capacity was 79.48% and stiffness was 31.08%. The difference between the experimental and numerical results was within 3.62–27.36%, respectively. Full article

In this paper, the short-term behaviour of innovative aluminium–timber composite beams was investigated. Laminated veneer lumber panels were attached to aluminium beams with screws. Recently conducted theoretical, experimental, and numerical investigations have focused on aluminium–timber composite beams with almost full shear connections. However, no experiments on aluminium–timber composite beams with partial shear connections have yet been conducted. For this reason, composite action in composite beams with different screw spacing was studied in this paper. Four-point bending tests were performed on aluminium–timber composite beams with different screw spacing to study their structural behaviour (ultimate load, mode of failure, load versus deflection response, load versus slip response, and short-term stiffness). The method used for steel–concrete composite beams with partial shear connection was adopted to estimate the load bearing capacity of the investigated aluminium–timber composite beams. The resistance to sagging bending of the aluminium–timber composite beams with partial shear connections from the theoretical analyses differed by 6–16% from the resistance in the laboratory tests. In addition, four 2D numerical models of the composite beams were developed. One model reflected the behaviour of the composite beam with full shear connection. The remaining models represented the composite beams with partial shear connections and were verified against the laboratory test results. Laminated veneer lumber was modelled as an orthotropic material and its failure was captured using the Hashin damage model. The resistance to sagging bending of the aluminium–timber composite beams with partial shear connections from the numerical analyses were only 3–6% lower than the one from the experiments. Full article

The present paper investigates the impact of bolt distance, bolt diameter, and the number of bolt rows on the bending performance of timber–steel composite (TSC) beams. This study aims to facilitate the application of bolt connections in assembled TSC structures. Composite steel I-beams were designed with timber boards connected in the upper section with bolts. Three-point static bending tests were conducted on nine timber–steel composite beams divided into four groups (L1, L2, L3, and L4) with varying bolt arrangements. The destruction mode, ultimate bearing capacity, ductility coefficient, load–midspan deflection curve, and load–midspan strain curve of each specimen were obtained. In addition, the destruction mechanism, the quantitative relationship between the bolt area ratio and interfacial slip, and the ideal bolt area ratio were identified. It was found that when the midspan deflection of the timber–steel composite beam approached the prescribed limit, the main failure mode can be explained as follows: The top surface of the boards of all the specimens had longitudinal local splitting, except L1, which had fewer bolts and no obvious damage. Moreover, due to compression and because the stress at the lower edge of the I-beam entered the flow amplitude stage, some of the specimens were crushed but were not pulled off. The composite beams had high flexural load capacity and ductility coefficient, and the maximum relative slips of the timber–steel interfaces were in the range of 2–6 mm. It was also found that the maximum slip of the interface and the ductility coefficient decreased steadily as the bolt area ratio increased, while the specimen’s flexural bearing capacity increased. The optimal bolt area ratio was determined to be 8 × 10⁻³. Using the total bolt area, we designed the arrangement of the bolts on the board. For convenience, multiple bolt variables were converted into one bolt variable. The longitudinal distance of the bolts had a greater impact on the slip, and the bolt diameter had a smaller impact. The theoretical values of total relative slip were found to be in good agreement with the experimental results, which were based on the superposition of the relative slip equations with varying bolt distances. The effective bolt area ratio and the formula of the relative slip of each segment can provide instructions for the arrangement of bolts and the control of the relative slip of intersections in engineering practices. Full article

To promote the development of timber–steel composite (TSC) structures, this paper proposes a TSC I-beam with an I-beam as the webs, covered with a timber board on its upper and lower surfaces and bolted together; the effect of varying the ratio of the timber board thickness to I-beam on the bending performance of the TSC I-beam was investigated. Considering the same total height of the beam cross-section and the variation of timber board thickness and I-beam height, three groups of six TSC beam specimens were designed and fabricated to carry out bending load failure tests, and the effects of the variation of timber board thickness with respect to I-beam height on the failure mode, flexural load capacity, ductility, and composite degree of TSC beams were analyzed. In addition, a model for predicting the elastic ultimate bending capacity and mid-span deflection of TSC I-beams was proposed on the basis of the composite coefficient method, which avoids the need to test the joints, and the theoretical calculation results were in good agreement with the test results, which can provide a reference for the design of TSC I-beams. Full article

Steel–timber composite (STC) systems are considered as an environmentally friendly alternative to steel–concrete composite (SCC) structures due to its advantages including high strength-to-weight ratio, lower carbon footprint, and fully dry construction. Bolts and screws are the most commonly used connectors in STC system; however, they probably make great demands on the accuracy of construction because of the predrilling in both the timber slabs and steel girder fangles. To address this issue, the STC connections with grouted stud connectors (GSC) were proposed in this paper. In addition, stud connectors can also provide outstanding stiffness and load-bearing capacity. The mechanical characteristic of the GSC connections was exploratorily investigated by finite element (FE) modeling. The designed parameters for the FE models include stud diameter, stud strength, angle of outer layer of cross-laminated timber (CLT) panel, tapered groove configurations, and thickness of CLT panel. The numerical results indicated that the shear capacity and stiffness of the GSC connections were mainly influenced by stud diameter, stud strength, angle of outer layer of CLT panel, and the angle of the tapered grooves. Moreover, the FE simulated shear capacity of the GSC connections were compared with the results predicted by the available calculation formulas in design codes and literatures. Finally, the group effect of the GSC connections with multiple rows of studs was discussed based on the numerical results and parametric analyses. An effective row number of studs was proposed to characterize the group effect of the GSC connections. Full article