Embedding Strength Research Articles

Experimental study on the embedment strength of smooth dowels inserted in cross-laminated timber narrow side

The embedment properties of the dowel-type fasteners is a fundamental parameter that can determine the shear resisting performance of the connections utilized in cross-laminated timber (CLT) structures. To investigate the embedment strength of the smooth dowels inserted in CLT narrow side, totally 504 CLT embedment specimens were tested to evaluate the effects of the influencing factors on the embedment strength, which included the loading angle, the embedment angle, the embedment position, the diameter of the dowels, and the gaps between the lumbers. The existing predictive equations of the embedment strength were validated based on the experimental results, and modified empirical equations were proposed for a more accurate prediction on the average embedment strength. It is found that when the loading direction with a loading angle of 90 degree is parallel to the adhesive layer, for the dowels embedded in the core layer and for those embedded between layers, the average embedment strength decreases by 27.89% and by 33.61% with an increase of the diameter from 8 to 24 mm, respectively. When the loading direction is perpendicular to the adhesive layer, the average embedment strength of the smooth dowels with an embedment angle of 90 degree is 85.25–218.96% higher than that of the dowels with an embedment angle of 0 degree. Furthermore, almost no drop can be identified for the embedment strength of the dowels with an embedment angle of 0 degree when the gap exists in their embedment position. A more accurate prediction on the average embedment strength can be achieved based on the modified empirical equations.

Embedment Strength of Low- and Medium-Density Hardwood Species from Spain

The embedment strength is a key parameter in the design of timber connections with metal fasteners. This property can be determined by the equations given by design codes such as the Eurocode 5, which are based on the European Yield Model proposed by Johansen, and it depends on the value of timber density among other parameters. These equations provided by design codes are based on experimental tests performed mainly in softwood species; thus, the objective of this work is to evaluate the embedment strength of two low- and medium-density hardwood species from Spain (poplar—Populus x euroamericana; beech—Fagus sylvatica) in the parallel and perpendicular to grain directions. Four different experimental test configurations were carried out according to EN 383 for each species using two different fasteners: (i) a 9 mm-diameter screw and (ii) a 12 mm-diameter bolt. Results of embedment strength were evaluated according to three different determination methods, and later compared with the current equations provided by Eurocode 5 (EC5) and new ones proposed in the draft of the new Eurocode 5 (prEC5). Results showed that current equations overestimated perpendicular to grain embedment strength for the cases studied, while the equation proposed in prEC5 for screws fitted best perpendicular to grain embedment strength. However, it underestimated the parallel to grain one because it does not consider any difference due to load-to-grain angle (α). Finally, ratios between experimental parallel and perpendicular to grain embedment strength were studied (k90), showing 30% and 44% higher values than the theoretical values resulting from k90 equations of EC5 and prEC5 for beech with screws and bolts, respectively, and 4% and 49% higher than the theoretical values for poplar with screws and bolts, respectively.

Video adaptive watermark embedding and detection algorithm based on phase function equation

Abstract In order to improve the video watermark embedding strength and balance the transparency of the watermark system, this paper proposes a combination of all phase Biorthogonal Transform and watermark embedding to complete the experiment. Firstly, the all phase biorthogonal transform is described. Referring to the construction process of APBT, combined with APDF and DST, a new all phase biorthogonal transform, all phase discrete sinusoidal biorthogonal transform (APDSBT), is proposed. This paper makes full use of MPEG-2 compression format to embed watermark directly in DCT domain. The low-frequency coefficients in the DCT block of the brightness space of I frame are selected as the watermark embedding space. The brightness component of each image block is transformed by two-dimensional DCT in the unit of 8×8 image blocks. By introducing the idea of energy receiver into the detection of digital watermark, the following correlation detector can be obtained. Implemented with MATIAB and VC + +. In the experiment, the foreman video test sequence is used as the watermark carrier, and the copyright logo image designed by ourselves is used as the watermark image to test the video watermarking system. The results show that when the coding rate is 3Mvps, the accuracy of each plane is 100%, 98.48%, 98.12% and 96.27% respectively. When the coding rate is 2.6Mvps, the accuracy of each plane is 100%, 96.38%, 94.87% and 95.21% respectively. This algorithm selects the frame of video to embed watermark. On the premise of ensuring video quality, this algorithm is robust to common video watermark attacks (MPEG compression, frame loss, frame clipping and frame rearrangement).

Optimal blind colour image watermarking based on adaptive chaotic grasshopper optimization algorithm

ABSTRACT This paper proposes an effective optimal blind colour image watermarking based on Triangular Vertex Transform (TVT), Lifting Wavelet Transform (LWT) and Schur decomposition. Firstly, the RGB channels of the colour host image are processed with TVT to attain , and coefficients. The image quality is preserved by applying LWT on the coefficients. As the middle frequency (HL and LH) components of the LWT wavelet domain achieve much robustness, these two components are split into nonoverlapping blocks further it is processed with Schur decomposition for improving perceptual transparency. The optimal solution attained by an Adaptive Chaotic Grasshopper Optimization Algorithm (ACGOA) is used as the embedding factor to ensure the embedding strength of the watermark. The confidentiality of the watermark is improved by 2D Logistic-Modulated-Sine-Coupling-Logistic Chaotic Map (LSMCL). Subsequently, each bit of encrypted watermark image is inserted in the highest eigenvalue of upper triangular matrix of Schur decomposition using the embedding factor β obtained by ACGOA to accomplish the watermarked image. The watermark recovery is performed using the embedding factor β and the decryption process is done using LSMCL. The efficiency of the ACGOA based scheme is estimated and the highest Peak signal-to-noise ratio (PSNR) value achieved is 54.2987 dB. The Normalized Cross-Correlation (NCC) results show better reliability for different attacks including geometric attacks and the NCC value obtained is close to 1.

Half hole and full hole dowel embedment Strength: A review of international developments and recommendations for Australian softwoods

Embedment strength is an essential system property of the European Yield Model which is commonly used to predict the ductile capacity of timber joints using dowel-type fasteners. This paper presents a comprehensive review of international embedment test methods and prediction formulae in design codes and literature, as well as an experimental study to evaluate the impact of different test methods parallel to the grain. A total of 224 full hole (FH) tension and half hole (HH) compression tests were conducted according to AS/NZS ISO 10984.2 on Australian sawn softwoods (Radiata Pine and Southern Pine) to compare embedment strength resulting from FH specimens sized to EN 383 and HH specimens sized to ASTM D5764, respectively. The results were compared to dowel embedment strength formulae from literature, those contained in Eurocode 5, the National Design Specification (NDS) for Wood Construction, and the respective joint group strength values contained in AS 1720.1, which are based on empirical test data. It was found that all strength prediction models were non-conservative except for a formula proposed by Smith et al. in 2004, which was based on FH tension tests in Australian Radiata Pine and Slash Pine. Furthermore, a strong correlation between timber density and embedment strength was found for both test methods, however, only FH tests displayed a correlation between dowel diameter and embedment strength, which is consistent with the embedment strengths formulae currently contained in Eurocode 5 and the NDS.

Embedment strength of smooth nails in timber construction – Characteristic and mean values

Studies have been conducted on the embedment strength of timber. However, those dealing with small diameter dowel type fasteners, particularly the transition from mean to characteristic values are lacking. This study is an investigation into the embedment strength of small diameter dowel type fasteners; with a focus on discussing the procedure of going from mean to characteristic values. Questions about the derivation of the existing embedment strength equations were discussed and some dark areas were clarified. Using two independent statistical methods and 14 test series, the inter-connection between the mean and characteristic embedment strength values was investigated. The investigations showed that the characteristic embedment strength values obtained by replacing the mean density with the characteristic density values in established equations, yield values which are higher than the actual characteristic values by an average of 14% and 19% for the non-predrilled and predrilled cases respectively. Detailed explanations to these findings were given and proposals with reference to the existing equations were presented and discussed.

MantaRayWmark: An image adaptive multiple embedding strength optimization based watermarking using Manta Ray Foraging and bi-directional ELM

Digital watermarking schemes based on a single value of embedding strength do not take into account the local characteristics of the host signal for watermark embedding. Consequently, striking a balance between imperceptibility and the robustness of the watermarking scheme becomes a challenging task. The use of multiple values of the embedding strength provides a solution to this problem. Multiple embedding strength-based watermarking schemes often deploy meta-heuristic techniques to look for locally optimal values of the embedding strength. However, meta-heuristic techniques being inherently slow, such watermarking schemes cannot be applied in real-time applications. This paper proposes MantaRayWmark—a novel image adaptive watermarking scheme that uses Manta Ray Foraging Optimization (MRFO) to optimize the locally relevant multiple embedding strengths (MES) for balancing the imperceptibility and robustness. However, the time-intensive MRFO-based optimization is carried out only once to train a bi-directional ELM (B-ELM) for a set of images. Each training image is subjected to 4-level DTCWT to produce approximation coefficients. For B-ELM training, the approximation coefficients act as the input features and the corresponding MES values (obtained by way of MRFO using imperceptibility and robustness as the optimization criteria) act as the target outputs. Subsequently, given a new image, the trained B-ELM is used to predict the optimized multiple embedding strengths. For watermark embedding, an image is transformed using 4-level DTCWT and the resulting approximation sub-band matrix is decomposed using SVD to get the principal component (PC) matrix. To avoid the false-positive problem, a binary watermark is inserted into the PC matrix using the MES. To ensure the robustness of the proposed scheme against geometric attacks, we have deployed a novel convolution neural network (ConvNet) based geometric correction procedure. Further, image authentication is achieved by applying SVD-based hashing on the watermarked image. To ensure the security of watermark, the watermark is scrambled using transposition cipher. Experimental results reveal that MantaRayWmark achieves a high degree of watermark recoverability from the signed image in the presence of a number of common geometric and image processing attacks, thus proving its robustness. The results also demonstrate the superiority of the proposed MantaRayWmark when compared to the existing state-of-the-art schemes in terms of robustness and imperceptibility. The proposed scheme being time-efficient may find use its in various multimedia applications.

All-round improvement in DCT-based blind image watermarking with visual enhancement via denoising autoencoder

Discrete cosine transform (DCT)-based watermarking has received great success in the copyright protection of digital images. This study exploited the orthonormal expansion properties of DCT to achieve superior performance in computational efficiency and watermarking efficacy. In particular, we reformulated the relative modulation to allow the modification of paired DCT coefficients as if operable in the spatial domain. To account for human visual characteristics, we also adjusted the embedding strength adaptively according to image entropy. The use of a range regulation mechanism enabled perfect watermark retrieval. The pursuit of an ideal balance between robustness and imperceptibility could be benefited from the grey wolf optimizer. Using the above-discussed techniques, the proposed watermarking scheme demonstrates superior robustness in terms of bit error rate and normalized correlation coefficient with the peak signal-to-noise ratio tuned at around 38 dB. Compared to the regular DCT approach, the computational acceleration is on the scale of N2/(log2N)2, where N signifies the side length of the image block under processing. Furthermore, for the type of character-style watermark, we explored the feasibility of using a denoising autoencoder (DAE) to enhance the retrieved watermark comprehensibility. The proposed DAE was found to be capable of contributing a 60% reduction of the bit error rate, thus making the recovered watermark visually more recognizable.

Analysis and Tests of Lateral Resistance of Bolted and Screwed Connections of CLT

The lateral resistance of dowel-type connections with CLT is related to its lay-up, species of the laminations and even the manufacture method. Treating the CLT as homogeneous material, current methods develop new equations through test results or make use of the existing equations for the embedment strength already used in design codes; thus, the lateral resistance of dowel-type connections of CLT can be calculated. This kind of approach does not take the embedment stress distribution into account, which may lead to inaccuracy in predicting the lateral resistance and yield mode of the dowel-type connections in CLT. In this study, tests of the bolted connections and the screwed connections of CLT were conducted by considering the effects of the orientation of the laminations, the thickness of the connected members, the fastener diameter and strength of the materials. The material properties including yield strength of the fasteners and embedment strength of the CLT laminations were also tested. Using analysis of the dowel-type connections of CLT by introducing the equivalent embedment stress distribution, equations for the lateral resistance of the connections based on the European Yield Model were developed. The predicted lateral resistance and yield modes were in good agreement with the test results; the correctness and the feasibility of the equations were thus validated.

Hybrid Timber Concrete Composite Slab for Analysis of Lag Screw Embedment Connections

Push‐out‐shear tests were used in this study to analyze lag screw connections in timber‐concrete composite (TCC) slabs based on the embedment depth. The goal of this research is to look into the relationship between shear capacity and embedment depth in TCC, as well as to investigate the embedment strength of the wood. Experiments were carried out at different embedment depths (5.08 cm, 7.0 cm, and 8.9 cm). The prepared samples were examined in order to determine the failure modes and provide an accurate assessment of the influence of embedment depth on TCC slabs. The investigation on the embedment strength of the wood was performed then for the analysis of the crushing of wood fibers, lag screw yielding strength, and maximum load applied at embedment depths of 6.6 cm and 7.0 cm. The results indicate that between 5.08 cm and 7.0 cm, there was an apparent improvement in the relationship between embedment depth (ED) and shear capacity of TCC slabs in terms of the shear strength, while a significant difference was observed between 7.0 cm and 8.9 cm. The study suggests that the ED of the TCC slab should be maintained at around 7.33 times the diameter of the lag screw.

Robust Watermarking of Screen-Photography Based on JND

With the popularity of smartphones, it is often easy to maliciously leak important information by taking pictures of the phone. Robust watermarking that can resist screen photography can achieve the protection of information. Since the screen photo process can cause some irreversible distortion, the currently available screen photo watermarks do not consider the image content well and the visual quality is not very high. Therefore, this paper proposes a new screen-photography robust watermark. In terms of embedding region selection, the intensity-based Scale-invariant feature transform (SIFT) algorithm used for the construction of feature regions based on the density of feature points, which can make it more focused on the key content of the image; in terms of embedding strength, the Just noticeable difference (JND) model is applied to limit the intensity of the watermark embedding according to the luminance and texture of the picture to balance robustness and invisibility; after embedding watermark, the coefficients in the neighborhood are again adjusted with optimal constraints to improve the accuracy of watermark extraction. After experiments, it is shown that the method we proposed can improve the correct rate of watermark extraction, the quality of the visual aspect of the watermarked picture is also improved.

Half Hole and Full Hole Dowel Embedment Strength: A Review of International Developments and Recommendations for Australian Softwoods

Half Hole and Full Hole Dowel Embedment Strength: A Review of International Developments and Recommendations for Australian Softwoods

Influences of rock microstructure on acid dissolution at a dolomite surface

Acid etching in a naturally fractured carbonate formation is one of the most significant mechanisms to enhance the fluid conductivity in fractures. In this paper, an acid dissolution experiment has been employed to understand the influence of rock microstructure on the acid etching involving reaction rate, the morphology of acid corrosion, and the embedding strength of a fracture surface. Three typical dolomite samples with almost the same mineral composition but distinct microstructures were selected from the Wumishan Geothermal carbonate formation that is composed of dolomudstone, algal dolomudstone, and silt-to-fine crystalline dolostone. A couple of measurement approaches including the thin section, SEM, 3D laser scanning, and nano indentation tests were used to observe and quantify the microstructures, reaction rate, and embedding strength of the fracture surface. Microstructure characterization indicates that the dolomudstone contains much finer crystal particles and a loose microstructure compared to other two samples. On the contrary, the silt-to-fine crystalline dolostone reserves coarse crystal particles and a tight microstructure. The structure of algal dolomudstone falls in between those two mentioned cases. Results of acid dissolving reveal that rock microstructures offer control over the acid-rock reaction of dolomite. Specifically, the loose microstructure of dolomite depicts a fast acid reaction, a rough surface, but weak embedding strength, while the compact microstructure behaves as a slow acid reaction, a uniform etching, and with a strong embedding strength. The knowledge obtained from this study is valuable to optimize the acid dissolution strategy from the view of the microstructure analysis.

Ownership protection for light-field 3D images: HDCT watermarking

Watermarking plays an important role in ownership protection. The embedding strength of the watermark determines the robustness of the watermark and affects the imperceptibility of the watermark. Setting appropriate embedding parameters can balance the robustness and imperceptibility of the watermark. Considering the high-dimensional characteristics of the light-field 3D image, we decide to extract more features from the light-field image to control the embedding parameters accurately to improve the visual quality of the watermark. Therefore, in this paper, we present a method of ownership protection for the light-field image based on high-dimensional color transform (HDCT) watermarking. Our paper introduces an HDCT space to unify multiple different color spaces, rather than selecting a specific color space for processing. By mapping low-dimensional RGB colors into high-dimensional color space, in which the feature vectors can separate the salient region from the background linearly, and extract the embedding parameters accurately. The experimental results show the superiority of the proposed algorithm compared with the existing light-field watermarking algorithm, from the two aspects of imperceptibility and robustness.

Embedment properties of thermally modified spruce timber with dowel-type fasteners

This study investigates the effect of thermal modification, ThermoWood Thermo-D treatment versus no treatment, on the embedment properties of Norway spruce timber (Picea abies [L.] Karst.) with dowel-type fasteners. The test specimens were reinforced to prevent splitting of the wood. The influence of density, load direction, test specimen configuration (full hole versus half hole), moisture content, gauge points and calculation method were also evaluated. Thermal modification primarily affected the embedment strength parallel to the grain, which was ∼ 25% higher after thermal modification, mainly due to the change in physical properties because of the treatment, i.e. the lower equilibrium moisture content. The influence of the investigated parameters on embedment properties of thermally modified spruce followed similar trends as for unmodified spruce. It was for example seen that the density–embedment strength relationships still hold after the treatment despite the decrease in density and the increase in embedment strength parallel to the grain. However, after thermal modification, the influence of load direction on embedment strength was ∼30% larger and the influence of calculation method (yield versus ultimate strength) on embedment strength perpendicular to the grain was ∼10% smaller.

Geotechnical capacities of large-diameter cylindric foundations in clay under general loadings

The large-diameter cylindric (LDC) foundation is the recently-emerging solution to support the bridge, wharf and storm surge barrier etc. used in the waterway, port and coastal engineering. Although it can be thought as a shallow foundation similar to bucket foundation without top lid, geotechnical capacities could be significantly different. It is because the absence of top lid potentially results in the change in mechanism of force transfer, thereby the change in failure mechanism. Therefore, this paper reports a comparative study of capacities for LDC and conventional circular skirted foundations in clay under general loadings. Both ultimate uniaxial and combined loadings capacities underlying the corresponding failure mechanisms are systematically investigated, with the effects of foundation embedment, foundation-soil interface and soil strength heterogeneity explicitly considered. Based on these, a suit of closed-form expressions is proposed to estimate the bearing performance of LDC foundations in clay under general loadings. Differences of LDC and conventional circular skirted foundations in bearing performances are compared, with the influence of absence of top lid on capacities discussed.

Investigation on surface strength of acid fracture from scratch test

Acid fracture surface strength plays an important role in acid fracture conductivity. Previous experimental studies have proven mechanical deterioration of carbonate after acid etching. However, such conclusion drawn from cylindrical samples could not be applied into conductivity evaluation as such samples represent the rock mechanical properties of the carbonate mass rather than the fracture surface. As another representative of fracture surface strength, embedment strength has not met an agreement on the evolution pattern during acid etching. So the absence of fracture surface strength measurement data during acid etching causes a challenge to conductivity evaluation and acid fracturing optimization. In an effort to overcome this challenge, scratch test was adopted for the measurement of the fracture surface strength before and after acid etching, as scratch test could acquire the uniaxial compressive strength of asperities on the fracture surface. In an aim to study the influence of mineral composition, acid contact time and acid injection rate, acid etching experiments under different etching conditions were carried out. The scratch test results uncovered the strong heterogeneity on the limestone samples, and strength of limestone fracture surface would experience both rising and declining trend during acid etching process. Dolomite in limestone samples was responsible for the strength increase while Calcite contributed to the decrease of strength according to the X-ray diffraction experimental results. What is more, the rising Dolomite strength and the decreasing Calcite strength affected the average strength of acidized fracture inherently. As acid contact time increased, the firstly strengthened then weakened Dolomite strength and constantly decreasing Calcite strength gave rise to an average surface strength change tendency that rises in the beginning and later declines. The change tendency of surface strength clearly indicated an optimal acid contact time in acid fracturing operation. Calcite strength showed the decreasing trend and Dolomite exhibited both the rising and decreasing trend as injection rate increased, resulting in an indefinite evolution trend of average strength of acid fracture surface.

Knowledge-based learning of nonlinear dynamics and chaos.

Extracting predictive models from nonlinear systems is a central task in scientific machine learning. One key problem is the reconciliation between modern data-driven approaches and first principles. Despite rapid advances in machine learning techniques, embedding domain knowledge into data-driven models remains a challenge. In this work, we present a universal learning framework for extracting predictive models from nonlinear systems based on observations. Our framework can readily incorporate first principle knowledge because it naturally models nonlinear systems as continuous-time systems. This both improves the extracted models' extrapolation power and reduces the amount of data needed for training. In addition, our framework has the advantages of robustness to observational noise and applicability to irregularly sampled data. We demonstrate the effectiveness of our scheme by learning predictive models for a wide variety of systems including a stiff Van der Pol oscillator, the Lorenz system, and the Kuramoto-Sivashinsky equation. For the Lorenz system, different types of domain knowledge are incorporated to demonstrate the strength of knowledge embedding in data-driven system identification.

Discrete wavelet transform processing system based on digital watermarking algorithm

This paper introduces the concept of multimedia digital watermarking and summarizes the current technology status. This paper summarizes the research status and basic principle of digital watermarking. The advantages of digital watermarking algorithm based on wavelet transform are analyzed. The proposed algorithm combines Arnold scrambling method and DWT transform multi-resolution characteristics, and adopts linear and different embedding strength methods. Effectively improve the security of the watermark. According to the classification results, different intensity watermarking components are embedded into the DCT low frequency coefficients of different image blocks. Experimental results show that this algorithm has strong masking and robustness, and the watermarking realized by using the proposed algorithm has good robustness against common image processing and noise interference.

The European Yield Model (EYM) for laterally loaded timber connections with smooth nails

ABSTRACT The European Yield Model (EYM) is a commonly accepted procedure to calculate the capacity of laterally loaded connections with dowel type fasteners. The standard procedure is specified in EC5 (EN 1995-1-1 2004) and uses characteristic values as input parameters for the calculation of characteristic values of the resistance of the connection. These characteristic values are the basis for an engineering design of structures. Nevertheless, there are situations, e.g. the design of a test set-up or a pushover analysis in earthquake engineering, when mean values of the resistance of a timber connection are needed. In this context, analytical equations and mechanical models were assessed on two levels by comparing theoretical values to experimental results. The first part of the research considered all the input parameters. The mechanical definition of the plastic moment proved to be more appropriate than the definition of a modified plastic moment according to EC5 for the determination of the yield moment of nails. On the other hand, it was confirmed that the embedment strength of Norway spruce softwood can be predicted reliably and slightly conservatively according to code regulations given by EC5. The definition for the withdrawal strength according to EC5 also seems to define a conservative lower boundary. The situation is not so clear for the embedment strength of oriented strand board (OSB). Test results are very scarce and do not account for the inhomogeneity regarding the thickness of the boards with higher density at the surfaces, which is the section where contact forces are transferred. In the second part, over 110 specimens considering eight different types of nailed connections were tested to assess different calculation procedures. The study focused on nailed connections with OSB and solid timber. This combination together with smooth nails as fasteners is very common in Europe for light-frame structures, especially in areas of low and medium seismicity because they exhibit large deformation capacity without losing strength. On the level of mean values, relationships are found between 1.00 and 1.47 for experimental results over calculated resistance, and it was found that the EYM is more conservative when the thickness of the sheathing is 10 mm instead of 18 mm, which means, that the expected failure mechanism changes from one to two plastic hinges. The findings are approximately the same if the relationship is studied on the level of characteristic values. Here, the relationship of values from experimental investigations over analytical calculation lays between 1.27 and 1.58 for a mechanism with one plastic hinge and between 0.90 and 1.12 for a mechanism with two plastic hinges. Based on these results, the question arises, if the EYM is the appropriate tool to predict the capacity of laterally loaded connections if comparatively large deformations occur between the connected parts. This question should be studied more detailed in the future.