Shear Lag Research Articles

Numerical modeling of the shear lag effect in GFRP as function of fiber content

Numerical modeling of the shear lag effect in GFRP as function of fiber content

Study on bending performance of prefabricated glulam-cross laminated timber composite floor

Abstract The glulam-cross laminated timber (CLT) composite floor is a type of prefabricated composite floor that integrates glulam beams and CLT slab into a unified structure using shear connectors. To investigate the bending performance of the glulam-CLT composite floor, the bending test was conducted on a full-scale composite floor under static load. The study comprehensively analyzed the failure mechanism, load–deflection behavior, interface slip and strain distribution of the glulam-CLT composite floor. The test results of the composite floor indicated that the failure mode was tensile fracture of the wood beam at the bottom. As the load increased, the deflection deformation of the mid-span beam exceeded that of the edge beam. When the load reached its ultimate limit, the deflection deformation of the mid-span beam increased by 14.4% compared to the edge beam. In the early loading phase, the strain distribution of the composite section satisfied the assumption of a plane section. However, the strain distribution deviated from this assumption with the increased load due to the relative slips between the glulam beam and CLT flange. To calculate the bending performance of the composite floor, the M-shaped section of the glulam-CLT composite floor was simplified as T-section composite beams. The linear-elastic method for determining the flexural rigidity and ultimate bearing capacity of the glulam-CLT composite floors was proved to be accurate and reliable. The findings provided valuable insights into the bending behavior of the CLT flange under load and emphasized the non-uniform stress distribution caused by shear lag effects.

Tensile properties of SiC/SiC obtained from epoxy‐encapsulated minicomposites

AbstractThe current study investigates the tensile behavior of SiC/SiC minicomposites, focusing on the efficacy of epoxy encapsulation in extracting the intrinsic fiber bundle response. Three minicomposite types were examined: two with Hi‐Nicalon Type‐S fibers and one with Tyranno ZMI fibers. Tensile tests were performed on minicomposites and fiber tows, both bare and epoxy‐encapsulated, whereas interface properties were measured via fiber push‐in tests. The results demonstrate that epoxy encapsulation partially mitigates non‐uniform loading in minicomposites with discontinuous matrices. Theoretical limits on fiber bundle strength, estimated using micromechanical models based on weakest‐link statistics and shear lag theory, are similar to measured encapsulated tow strengths when failure occurs within the elastic regime of the epoxy. In some cases, microstructural defects such as fiber–fiber contacts and debonded coatings play important roles in limiting composite strengths relative to theoretical values. Although encapsulation does not always directly improve properties, it provides useful context for evaluating composite performance and exposing microstructural limitations unaccounted for in idealized models.

Calculating shear lag in steel-concrete composite beams under combined compression and bending

Long and complex composite steel-concrete structures are becoming common, requiring a deep understanding of the effects induced by the simultaneous action of axial forces and bending. In fact, the axial force generated, for instance, by cable inclination in cable-supported structures can modify the stress distribution within the elements compared to bending scenarios, thereby necessitating a revision of the effective width to be utilized. Nonetheless, current design codes, including Eurocode specifications and others, lack provisions for addressing the combined effects of axial force and bending, as they are exclusively tailored for bending. This limitation can introduce design complexities, necessitating the implementation of intricate Finite Element (FE) models, which impose substantial computational loads and design efforts. The methodology proposed in this paper overcomes these challenges allowing to assess the stress distribution and resistance of composite deck at Serviceability Limit State (SLS) and Ultimate Limit States (ULS) by leveraging results obtained from standard beam models typically used by structural designers or practitioners. A comprehensive parametric analysis using nonlinear finite element models is performed to validate the developed methodology. A comparison with the Eurocode 4 formulations highlights that the proposed method provides superior accuracy in estimating peak stress in concrete slabs under combined compression and bending. Additionally, it facilitates straightforward verification at the ULS in compliance with Eurocode requirements.

Tough Monolayer Silver Nanowire-Reinforced Double-Layer Graphene.

Mixed-dimensional nanomaterials composed of one-dimensional (1D) and two-dimensional (2D) nanomaterials, such as graphene-silver nanowire (AgNW) composite sandwiched structures, are promising candidates as building blocks for multifunctional structures and materials. However, their mechanical behavior and failure mechanism have not yet been fully understood. In this work, we have performed integrated experimental, theoretical, and numerical studies to explore the performance and failure modes of graphene-AgNW composite under tensile and impact loading conditions. In situ tensile tests using a nanoindenter, implemented with a push-to-pull device and a laser-induced projectile impact test system, are used to shed light on load-bearing mechanisms in graphene-AgNW composites. Multiple failure modes have been observed in both experimental setups and analyzed with numerical and theoretical models. Results show that in the tensile loading the distribution of AgNW, as characterized by the effective free length, is the key parameter determining the failure mode. As for the impact failure scenarios, compared with failure modes observed in pure graphene cases, the mechanical reinforcing effect of AgNW will transform the failure mode from a scattered tensile fracture along radial directions to a shear failure that is constrained in a relatively local domain. Theoretical analysis using shear lag modeling, Timoshenko plate theory, molecular dynamics modeling, and finite element modeling approaches are adopted to further establish the failure modes.

Structural determinants of tendon multiscale mechanics and their sensitivity to mechanical stimulation during development in an embryonic chick model

There is an abrupt increase in the multiscale mechanical properties and load-bearing capabilities of tendon during development. While prior work has identified numerous changes that occur within the collagenous structure during this developmental period, the primary structural elements that give rise to this abrupt increase in mechanical functionality, and their mechanobiological sensitivity, remain unclear. To address this knowledge gap, we used a shear lag model along with ultrastructural imaging, biochemical/thermodynamic assays, and multiscale mechanical testing to investigate the dynamic structure-function relationships during late-stage embryonic chick development and to establish their sensitivity to mechanical stimulation. Mechanical testing and modeling suggested that the rapid increase in multiscale mechanics can be explained by increases in fibril length, intrafibrillar crosslinking, and fibril area fraction. To partially test this, we inhibited collagen crosslinking during development and observed a drastic reduction in multiscale mechanical behavior that was explained by a reduction in both fibril modulus and length. Using muscle paralysis to investigate mechanosensitivity, we observed a significantly impaired multiscale mechanical response despite minimal changes in fibril diameter and fibril area fraction. Additionally, the shear lag model found a trend toward lower fibril lengths with paralysis and experimental data found decreased crosslinking and fibril modulus values following flaccid paralysis. Together, these data suggest that both intrafibrillar crosslink formation and fibril elongation are critical to the formation of load-bearing capabilities in tenogenesis and are sensitive to mechanical loading. These findings provide critical insights into the biological and structural mechanisms that give rise to tensile load-bearing soft tissue. Statement of SignificanceDespite prior work investigating the structural and mechanical changes that occur during tendon development, there has not been a comprehensive analysis of how these simultaneous changes in structure and function are connected. In this study, we performed a comprehensive battery of mechanical and structural assessments of embryonic chick tendons and input these data into a shear lag model to estimate the individual importance of each structural change to the tendon mechanical properties. Additionally, we inhibited muscle activity in the embryos to evaluate the impact of mechanical stimulation on these evolving structure-function relationships during tendon development. These data provide insight into the primary structural elements that produce the tensile load-bearing capabilities of tendon, which will inform efforts to produce tissue engineered tendon replacements.

Shear Lag Effect on Box Steel Beams with Wide Curved Flanges

Shear Lag Effect on Box Steel Beams with Wide Curved Flanges

Investigating the mechanical properties related to the vertical bending of composite I‐beams with corrugated steel webs

AbstractThe maximum angular rotation attributable to the in‐plane shear deformation of flange slabs is used as generalised displacement in the conventional analysis method for I‐beams. However, the mechanical concepts are poorly understood due to the complex nature of this analysis method. Consequently, a novel strategy for analysing vertical bending in composite I‐beams is proposed in this study. This approach uses the additional deflection of composite I‐beams induced by the shear lag effect as the generalised displacement. Furthermore, this research comprehensively considers the accordion effect, shear lag and self‐equilibrium conditions for the shear lag warping stress and bending moment. Moreover, two longitudinal warping displacement difference functions are employed to accurately describe the variation of shear lag in composite I‐beams with varying flange slab widths. The differential equations of the I‐beams with corrugated steel webs in the elastic range are established based on the energy‐variation method. A complete mechanical system of a composite I‐beam is decomposed into two parts, namely, the shear lag mechanical system and the elementary beam mechanical system, which are independent of each other. The theory presented in this paper reflects the internal mechanical mechanism of composite I‐beams. The calculation accuracy is considerably improved in this study. Therefore, this method is more unambiguous and well‐defined. It enriches and advances the current analysis theory of composite structures, which can guide the design of composite I‐beams.

Investigations On the Effective Width of Wide Flange Steel Girders

AbstractEffective width, as presented in Eurocode 3 is analysed. Efforts have been made to distinguish between the behaviour of the various structural parts acting as wide flanges. Different mechanical models are adopted: for the bridge deck plate between girders, for the cantilever deck part, and for the bottom plate of box girders with the presumption to reflect more adequately their actual participation in the complex girder work at bending. Also, the interaction between girders in a superstructure at loading is simulated as far as possible in order to replace to some extent a sophisticated spatial analysis. The Eurocode 3 way of presenting the matter is preserved. The results obtained are compared with the corresponding Eurocode parts and an assessment on the reported differences is given. The goal is to supply the designers with extended understanding the effects arising from the shear lag phenomenon.

Uniaxial carbon nanotube fiber reinforced dielectric elastomer actuator with self-sensing

Compared to the isotropic dielectric elastomer (DE), uniaxial fiber reinforced DEs have larger deformation capabilities in specific directions, showing great application prospects. However, there are still significant challenges in achieving self-sensing without introducing additional sensing components. Inspired by the control method of biological muscles, in this article, we used carbon nanotube (CNT) fibers as reinforcing fibers that resistance changes are highly sensitive to tensile strain and exhibit a linear relationship within a small strain range. Based on the developed uniaxial reinforced strain behavior model of DEs, a shear lag model was adopted to introduce an interface transition layer between the DEs and CNT fiber to consider the strain difference caused by the difference in elastic modulus. The relationship between CNT fiber strain and DE strain was established, and the influence of CNT fiber mechanical properties on self-sensing performance was explored. The verification results under 0.05 Hz, 20 kV/mm signals show that the model has 4 % error, providing new ideas for the self-sensing function of uniaxial fiber reinforced DEs.

Research on spatial corrosion behavior and durability protection technology of concrete box girder bridge in cold regions

In order to study the corrosion behavior of concrete box girder in deicing salt environment, a series scaled model of concrete box girders were made to study the deterioration mode of concrete box girder under load, chloride corrosion, freeze-thaw cycle and their combined action. Combined with silane impregnation, the durability protection technology of concrete box girder bridges in cold regions was proposed. The experimental results show that under freezing-thawing action, the top plate of the box girder has the most serious deterioration, and the performance of the web is better. The surface erosion of the top plate is 65.38 % and 80.77 % different from that of the bottom plate and web plate, respectively. The freezing-thawing erosion of the concrete box girder has a significant spatial multi-dimension. The chloride ion erosion law of the top plate and bottom plate of concrete box girder is similar to the distribution law of shear lag effect under load. The inhibition effect of compressive stress on chloride ion is 9.67 %, and the overall inhibition effect is not large. The maximum difference of chloride ion concentration at each measuring point on the bottom plate is 30.14 %. Silane can be used as a protective coating for concrete bridges in cold areas, and the coating thickness of 2 mm can meet the requirements of anti-freezing. With the increase of freeze-thaw time, the silane protection ability began to decline. The maximum silane protection effect of 0–1 cm from the surface at 90d and 180d decreased by 40.8 % and 71.7 %, respectively. After the silane coating was applied, the chloride ion erosion rate of the bottom plate still showed a faster trend. When the freeze-thaw cycle exceeded 30 times, the silane protection ability decreased almost at a linear rate with the freeze-thaw time. Regardless of whether the silane coating protection technology is adopted, the chloride ion concentration of the bottom plate of concrete box girders is at least 10 % more than that of the top plate for freeze-thawing 90d and 180d, and the maximum can reach 32.1 %. The deterioration behavior of concrete box girders in cold regions has significant spatial multi-dimension. The existing single-parameter durability design methods, which mainly focus on solid section, are no longer suitable for box girder structures.

A NUMERICAL MODEL FOR ANALYZING CROSS LAMINATED TIMBER UNDER OUT OF PLANE LOADING

This paper targets the validity of a novel numerical model for analyzing CLT under out of plane loading. This numerical model was initially developed for determining the shear lag effect that appears in laminated thin walled composite beams. A parametric study was conducted in order to determine the influence of orientation of layers in CLT panels on bending strength and deflection. For confirming the accuracy of the proposed model, the results from the numerical model are compared with the external results of the computer software Ansys. The differences in bending stress vary from 0.27% to 1.69% depending on the orientation of layers and for deflection the differences are ranged from 2.25% to 7.42%. A numerical study was conducted and obtained data corresponds to results obtained from experimental study. It was concluded that the proposed numerical method can enough precisely predict the behavior of CLT under out of plane loading.

Ply curving termination for enhancing tensile strength of composite ply drop-off: static evaluation and failure mechanism

Composite structures are optimized in shape by terminating specific plies gradually. However, stress concentration at the ply drop-off can cause interlaminar delamination from the ply edge. In this study, Ply Curving Termination (PCT), which is introduced by locally curving fibers at 0° ply edges, is used to enhance tensile strength of the ply drop-off. To clarify the dependence of the PCT strength on the curved fiber angle (PCT angle), static tensile tests using ply drop-off specimens are conducted, followed by detailed damage observations using X-ray CT. The results indicates that the strength significantly increases with PCT but the fracture behavior differs depending on the PCT angle. Interestingly, specimens with large PCT angles fail from the position where the fibers curve, away from the ply edge. This PCT-specific failure mechanism is then elucidated using finite element analysis and the virtual crack closure technique, indicating that shear lag caused by the stiffness change due to fiber curving is important. Finally, using the revealed PCT failure mechanism, PCT angles that are the most effective in enhancing tensile strength is discussed.

Composite floor slab effect on seismic performance of steel-framed-tube structures with shear links

High-strength steel-framed-tube structures with low-yield-point shear links (SFT-RLYPSL) exhibit exceptional lateral and torsional stiffness, coupled with significant energy dissipation capacities. This study aims to investigate teh influence of composite floor slabs on the seismic performance of these structures. Expanding on previous research concerning SFT-RLYPSL, this paper presents a simplified numerical model for the SFT-RLYPSL, incorporating the influence of the composite floor slab. The developed model employs the steel4 constitutive relation to accurately depict the behavior of low-yield-point steel. Furthermore, the simplified numerical model utilizes two-node link elements to simulate shear links and integrates composite beams to represent the influence of the composite floor slab. Using this simplified model, elastic-plastic pushover analysis is performed on five distinct SFT-RLYPSL structural cases, and nonlinear time-history analysis is conducted on three structural configurations. The investigation explores various aspects of the seismic performance of SFT-RLYPSL, including modal behavior, pushover curves, progression of overturning failure, time-history roof displacements, inter-story drift angles, base reactions, inter-story shear, failure modes, residual inter-story drift angles, and the manifestation of shear lag phenomena. The findings suggest that incorporating the composite floor slab effect enhances initial stiffness and peak load capacity in pushover analysis, leading to distinct three-stage pushover curves. During nonlinear time-history analysis, the composite floor slab effect increases structural stiffness, decreases roof displacements and inter-story drift angles, while simultaneously increasing base reactions, worsening component damage, and raising collapse risk. Nevertheless, its influence on residual inter-story drift angles remains relatively minor, with a mitigating effect on the shear lag phenomenon. Importantly, the degree of this impact varies with alterations in floor slab thickness and seismic intensity, highlighting the critical importance of considering the composite floor slab effect in structural design deliberations.

Experimental and Analytical Study on Shear Lag Effect of T-Shaped Reinforced Concrete Shear Walls

Because of the flanges on T-shaped shear walls (TSSWs), the shear force acting on such walls results in a shear lag effect, making it impossible to forecast with accuracy the normal stresses of the flanges using the Bernoulli–Euler assumption. Shear lag (SL) in flanged walls has, however, received less attention from researchers, particularly in experimental studies. Understanding the SL in T-shaped reinforced concrete shear walls under shear and axial force is the main goal of this work. First, a SL model is suggested for TSSWs. In this model, the SL deflection is considered to be the generalized displacement and the SL warping deformation, and it is assumed to be a quadratic nonlinear function. Then, experimental and numerical simulation studies are, respectively, conducted to investigate SL effect of TSSWs, and also to evaluate the accuracy of the SL method. Finally, the parameter analysis is conducted to investigate the influence of axial load, shear force, and flange length on the SL effect of TSSWs. The results show that the SL of the TSSW is significant, the normal stress distribution (NSD) of the flange is uneven, and the normal stresses near the web are higher, according to the results of the analytical, simulated, and experimental results. The SL model can accurately predict the normal stresses of the flange of TSSWs, and the quadratic parabola assumption of the SL warp displacement of TSSWs is reasonable. Parameter analysis shows that axial force has little effect on the SL effect of TSSWs. The TSSWs under larger shear force have the more obvious SL effect. A more obvious SL effect occurs in the TSSWs with longer flanges.

Raman spectroscopic stress mapping of single high modulus carbon fibre composite fragmentation in compression

Fragmentation of high modulus carbon fibres is relevant to the failure mechanisms of advanced polymer matrix composites in compression. In situ spatially-resolved Raman spectroscopy during the fragmentation of model single fibre composites is used to map local stress distributions during failure events. The characteristic graphitic band (the G band) located around 1580 cm−1 is associated with the in-plane carbon-carbon bonds; this band shifts its position, and can be calibrated, with the local axial stress in the fibre. The analysis maps the evolution of local stresses with increasing overall composite compression strain, identifying a series of critical events, including fibre fracture, interfacial debonding, and the formation of inter-fragment ‘wedges’. Fitting shear lag models provides interfacial shear strength values. Multiple failure maps of two examples of high modulus PAN carbon fibres (M46J and M55J) demonstrate the possibility of local fragment bending due to fragment end contact. A timeline of potential fragmentation events is proposed for carbon fibres undergoing compression.

Shear Lag Effect and Its Additional Deflection Contribution of Composite Beam Bridges

The composite beam structure is widely used in the engineering field because it benefits from the advantages of two materials, presenting outstanding advantages for construction purposes. However, at present, there are issues with the analysis and solution of the composite beam structure, such as the difficulty in developing a suitable analytical theory and the low degree of refinement achieved by simulation analysis. To accurately grasp the mechanical behavior of the composite beam structure and achieve its refined analysis, this paper proposes a refined spatial grid element analysis method that can simultaneously obtain the internal forces, displacements, and stresses of various parts of a composite beam. Based on the above new method, the effects of geometrical structural factors such as wide-span ratio, high-span ratio, and web thickness with respect to the shear lag effect are analyzed. The distribution law of the shear lag coefficient and its additional deflection are analyzed. The results demonstrate that using this analysis method to calculate and analyze steel-concrete duplex type composite beams can directly obtain the internal forces and displacements of the joints of the composite beam roof, floor, and web. The spatial grid element analysis method provides both the theoretical and practical means to achieve both the overall and local refinement analysis of the composite beam structure.

Bond behavior and modeling of steel-FRP composite bars in engineered cementitious composites

The combination of the steel-FRP composite bar (SFCB) and engineered cementitious composite (ECC) holds favorable applications in terms of durable resilient structures. However, a clear understanding of the interfacial bond performance of this novel combination is currently lacking. Therefore, the bond behavior and mechanism of the SFCB-ECC interface were investigated through direct pullout tests. A total of 48 cube specimens were fabricated, with the test variables including bar type, bar diameter, embedment length, and matrix type. The experimental results indicated that the bond failure mode of SFCBs and FRP bars differed from that of deformed steel bars, attributed to the damage of resin-rich ribs in relatively high-strength ECC. The bond-slip curves revealed both the fundamental differences and similarities among steel bars, SFCBs, and FRP bars. The Poisson effect and shear lag effect increased with a decrease in bar stiffness and an increase in diameter. The combined impact of the interaction between the bar stiffness and diameter resulted in varying bond strengths for steel bars, SFCBs, and GFRP bars, despite their similar surface geometries. A theoretical model for the bond strength at the SFCB-ECC interface was derived using the thick-walled cylinder principle and subsequently validated with test data. Finally, a unified empirical model framework for predicting the bond strength of various bar-matrix combinations was proposed based on the theoretical model. The accuracy of this method was evaluated using a collected database.

Experimental Study on Shear Lag Effect of Long-Span Wide Prestressed Concrete Cable-Stayed Bridge Box Girder under Eccentric Load

Based on the engineering background of the wide-width single cable-stayed bridge, the shear lag effects of the cross-section of these bridge box girders under the action of the eccentric load were experimentally studied. The behavior of shear lag effects in the horizontal and longitudinal bridge directions under eccentric load in the operational stage of a single cable-stayed bridge was analyzed by a model testing method and a finite element (FE) analytical method. The results showed that the plane stress calculation under unidirectional live load was similar to the results from spatial FE analysis and structural calculations performed according to the effective flange width described in the design specification. At the position of the main beam near the cable force point of action, the positive stress at its upper wing edge was greatest. At a distance from the cable tension point, the maximum positive stress position trend showed that from the center of the top flange to the junction of the top flange and the middle web to the junction of the top flange and the middle web and the side web. Under eccentric load, the positive and negative shear lag effects on the end fulcrum existed at the same time, and the shear lag coefficient on the web plate was larger than the shear lag coefficient on the unforced side. Due to the influence of constraint at the middle fulcrum near the middle pivot point, positive and negative shear lag effects were significant, and the coefficient variation range was large, resulting in large tensile stress on the roof plate in this area. According to FE analytical results, stress and shear forces of a single box three-chamber box girder under eccentric load were theoretically analyzed, the bending load decomposed into the accumulation of bending moment and axial force, using the bar simulation method, and the overall shear lag effect coefficient λ was obtained and verified.

Assessment of hydraulic fracture height and distribution using timelapse crosswell shear-wave data

An in-depth study of the impact of hydraulic fracturing operations on the Marcellus shale formation and overburden is presented by analyzing a unique timelapse crosswell seismic survey suitable for four-component shear wave vector rotations in order to study fracture azimuth and intensity. The borehole source used for the survey generated both oriented compressional and shear wave energy, and the seismic acquisition included perpendicular source orientations at each shot level to allow isolation of fast and slow shear modes using the Alford rotation and linear transform technique. Estimates of fast shear azimuth and slow shear time delay before and after hydraulic fracturing indicate fracture creation throughout the overburden above the Marcellus shale and a possible vertical breach of the bounding Tully limestone formation. The magnitude of the timelapse change is consistent between travel-time and slow shear lag inversion, but the absolute change is small, suggesting that the increase in fracture intensity may not be significant. These results point to operational inefficiencies during hydraulic fracturing operations that could negatively impact production and pose risks to future development. The study demonstrates the value of crosswell seismic surveys for reservoir monitoring and highlights observations that might be missed by a monitoring program that does not include timelapse seismic data and analysis of shear wave changes due to hydraulic fracturing.