Strength Formula Research Articles

A Study on the Ultimate Strength and Failure Mode of Stiffened Panels

Different buckling failure modes of stiffened panels will result in differences in ultimate strengths. In this study, the benchmark model of the bottom of bulk carrier with appropriate initial imperfections, boundary conditions and mesh size are selected for a series of non-linear FE analyses. A failure mode discrimination method considering the change rule of ultimate strength and the stress and strain distribution of stiffened plates in ultimate limit state is proposed, and then the boundary function of the failure modes composed of four key parameters, λ, β, hw/tw, λe, is established. Based on this boundary function, the rapid identification of failure modes and the classification of ultimate strength under different failure modes can be realized. Furthermore, the ultimate strength formulas of stiffened panels for different failure modes are obtained by data analysis from many nonlinear finite element analyses.

Dynamic characteristics of coral silt with consideration of static-cyclic loading coupling

Coral silt, a type of coral soil with more than 50% silt content, is formed during the process of land reclamation. Given the frequent action of waves, wind, earthquakes and other dynamic loads, the cyclic dynamic shear characteristics of coral silt are important for determining the seismic safety of reef infrastructures. A series of symmetrical and asymmetrical cyclic simple shear tests were performed to characterize the cyclic behavior of coral silt with particular consideration given to the static-cyclic shear stress coupling. Two empirical formulas for the undrained peak shear strength and critical state strength in monotonic simple shear tests are proposed. For both symmetrical and asymmetrical-loading cyclic simple shear tests, a CSR threshold value lying between 0.05 and 0.075 controls the final failure. The cyclic shear stress significantly influences the cyclic deformation, cyclic pore water pressure, cyclic strength, and cyclic shear modulus of coral silt.

鋼繊維補強コンクリートにおける引張靭性の評価に関する実験的研究

The quantitative evaluation of tensile ductility of steel fiber reinforced concrete (design strength 30-60 MPa) containing 0.5-1.0% steel fiber with hooks at the ends was investigated. The maximum value of tensile stress after cracking in the tensile softening curve could be roughly evaluated by the linear formula of compressive strength. The influence of aggregate type, coarse aggregate content and air content on the formula was relatively small. Similarly, the average value of tensile stress up to 1 mm crack width in the tensile softening curve could be roughly evaluated by the linear formula of compressive strength.

A STUDY ON BUCKLING STRENGTH OF TIMBER MATERIALS (PART 2): DISCUSSION FOR APPLICATION OF YOUNG’S MODULUS ON ELASTIC BUCKLING STRESS EVALUATION

Continuing from the previous report, we discuss the buckling strength of wooden materials. The 50th %ile lower limit and the 5th %ile lower limit of the Young's modulus were obtained by two type of the non-destructive test and bending tests. Applying these values to Euler's buckling strength formula, we compared the calculation results and the experimental results. The calculated values with 5th %ile lower limit were to be close to the lower limit of buckling strength test results. The calculated values with 50th %ile lower limit weren’t useful for estimating the average of buckling strength in this study.

Experimental Study on Lap-Spliced Performance of High-Strength Stainless Steel Wire Mesh in Engineering Cementitious Composites.

To investigate the mechanical properties of high-strength stainless steel wire mesh (HSSSWM) in Engineering Cementitious Composites (ECCs) and determine a reasonable lap length, a total of 39 specimens in 13 sets were designed and fabricated by considering the diameter of the steel strand, spacing of the transverse steel strand, and lap length. The lap-spliced performance of the specimens was tested through a pull-out test. The results revealed two failure modes in the lap connection of steel wire mesh in ECCs: pull-out failure and rupture failure. The spacing of the transverse steel strand had little effect on the ultimate pull-out force, but it restricted the slip of the longitudinal steel strand. A positive correlation was found between the spacing of the transverse steel strand and the slip amount of the longitudinal steel strand. With an increase in lap length, the slip amount and 'lap stiffness' to peak load increased, while the ultimate bond strength decreased. Based on the experimental analysis, a calculation formula for lap strength considering the correction coefficient β was established.

Review of Bond-Slip Behavior between Rebar and UHPC: Analysis of the Proposed Models

With superior mechanical properties and workability, ultra-high-performance concrete (UHPC) has been utilized extensively in engineering projects. To gain a comprehensive understanding of the bond behavior of UHPC or ultra-high-performance fiber-reinforced concrete (UHPFRC), researchers studied the factors influencing the bond-slip between rebar and UHPC or UHPFRC over the past few years. The literature-proposed ultimate bond strength formulas and the bond-slip constitutive model between rebar and UHPFRC are analyzed and compared. Based on the bond test database of UHPFRC, the results indicate that UHPFRC strength, relative concrete cover thickness, relative bond length, and steel fiber volume content are the primary parameters influencing the ultimate bond strength between rebar and UHPFRC. In the bond-slip constitutive model, the nonlinear ascending and linear descending model is more accurate than other models. This paper concludes by discussing the shortcomings in UHPC or UHPFRC bond research and predicting the future research trend.

A mix design methodology of blast furnace slag and fly ash-based alkali-activated concrete

Although the application of blast furnace slag and fly ash-based alkali-activated concrete (BFS/FA-AAC) has both economic and environmental benefits, it is limited by the lack of a straightforward mix design method. In this paper, an experiment was conducted to investigate the effect of control factors, including the Na2O/binder ratio, the SiO2/Na2O ratio, the BFS/binder ratio, the water/binder ratio, and the water content on the workability (slump and rheology) of BFS/FA-AAC, and the effect of control factors include the Na2O/binder ratio, the SiO2/Na2O ratio, the BFS/binder ratio, the water/binder ratio, and the curing time on the compressive strength of BFS/FA-AAC. As a result, the influence degree and mechanism of each control factor on the performance of BFS/FA-AAC were quantitively explored and the accuracy of an empirical compressive strength formula was validated. Based on that, a practical mix design method of BFS/FA-AAC was eventually established. It is found that the mixture composition and content of paste can significantly influence the workability of BFS/FA-AAC. The compressive strength of BFS/FA-AAC is determined by control factors when the water content is within 160–195 kg/m3. The mechanical predictive method of BFS/FA-AAC is proven of high accuracy. The mixture designed by this methodology exhibits satisfied fresh and hardened performance as well as high environmental benefits.

Experimental investigation on the flexural performance and damage process of steel fiber reinforced recycled coarse aggregate concrete

The application of recycled concrete requires the reliable information on its flexural performance especially after cracking. In this study, the three-point bending tests were carried out on 40 notched beam specimens to investigate the flexural performance and damage process of steel fiber reinforced recycled coarse aggregate concrete (SFRCAC). The effects of water-cement ratio, recycled coarse aggregate replacement ratio and steel fiber volume fraction on the residual flexural tensile strength and flexural toughness of SFRCAC were analyzed. Moreover, the flexural damage process of the SFRCAC notched beam was explored and analyzed by Acoustic Emission (AE) technology. The results show that the residual flexural tensile strength and flexural toughness of SFRCAC decrease with increased water-cement ratio and recycled coarse aggregate replacement ratio, respectively. Adding steel fibers can effectively improve the residual flexural tensile strength and flexural toughness of SFRCAC. The post-cracking behavior of SFRCAC changes from strain-softening to strain-hardening when steel fiber volume fraction increases from 0.5% to 2%. Finally, the empirical formula of residual flexural tensile strength for SFRCAC has been put forward by analyzing and fitting the test results in this study and related literature.

Study on Temperature-Dependent Uniaxial Tensile Tests and Constitutive Relationship of Modified Polyurethane Concrete.

Modified polyurethane concrete (MPUC) is a new material for steel deck pavements. In service, the pavement is often cracked due to excessive tensile stress caused by temperature changes. In order to study the tensile properties of MPUC in the diurnal temperature range of steel decks, uniaxial tensile tests of MPUC were carried out at five temperatures. Three kinds of specimens and a novel fixture were designed and fabricated to compare the results of four different tensile test methods. The deformation of the specimen was collected synchronously by two methods: pasting strain gauge and digital image correlation (DIC) technique. Based on the experiment, the tensile mechanical properties, failure modes, and constitutive relations of MPUC were studied under the effect of temperature. The research results show that the novel fixture can avoid stress concentration. By observing the fracture surface of the specimens, the bonding performance is great between the binder and the aggregate at different temperatures. The tensile strength and elastic modulus of MPUC decrease with increasing temperatures, while the fracture strain, and fracture energy increase with increasing temperatures. The formulas of temperature-dependent tensile strength, fracture strain, and elastic modulus of MPUC were established, and the constitutive relationship of MPUC is further constructed in the rising stage under uniaxial tension. The calculation results show good agreement with experimental ones.

Research on the improvement of rainfall infiltration behavior of expansive soil slope by the protection of polymer waterproof coating

The repetitive expansion and contraction cracks, as well as the strength attenuation induced by the precipitation-evaporation cycles, are important factors influencing the instability of expansive soil slopes. In this study, a polymer waterproof coating was proposed to protect the expansive soil slope against slope instability caused by precipitation penetration. The bonding performance of expansive soil blocks (with different soil densities) and polymer waterproof coatings (with different coating thicknesses) were analyzed by performing a laboratory pull-out test. The impacts of different protection methods and protection layer coverage on rainwater infiltration behavior were studied using three groups of slope model tests and numerical simulation approaches. The results showed that the bond strength between the expansive soil test block and the coating increased with the increase in soil compaction density, and the test block strength was an important factor affecting the bond performance. The influence of density of test block on bond strength was greater than that of coating thickness. The calculation formula of bond strength was obtained by fitting the test results. Compared to the unprotected slope, the fluctuation of soil moisture content and rainwater infiltration rate in the slope protected by polymer coating was found to be the least. Protective layer of polymer coating proved to have the most significant role in blocking rainwater infiltration, followed by polymer coating + three-dimensional vegetation net protective layer. When the coverage rate of the protective layer exceeds more than 90%, the effect of blocking rainwater infiltration was remarkable. Simultaneously, the variation range of slope water content, rainwater infiltration depth, and infiltration rate decreased significantly. This research result provides a new solution for expansive soil slope protection and rainwater infiltration control.

Bond performance between recycled concrete and steel bar after high temperature

Abstract To investigate the influence of high temperatures on the bond performance of recycled concrete and steel bar, this article considers the influence of different concrete types (ordinary concrete and recycled concrete) and different temperatures (20, 100, 150, 200, 250, and 300°C) on the concrete compressive strength and the bond performance of concrete and steel bar. On this basis, the calculation formula of bond strength and bond slip between concrete and steel bar after the high temperature is established. The test results show that the concrete compressive strength presents a downward trend with the increase in temperature; the compressive strength loss of recycled concrete is higher than that of ordinary concrete; when the temperature reached 300°C, the compressive strength loss of ordinary concrete is 24.4%, while that of recycled concrete is 41.6%. The bond strength of pull-out specimens decreases with the increase of temperature, while the bond slip increases with the increase of temperature; the bond strength between recycled concrete and steel bar is lower than that between ordinary concrete and steel bar, while the bond slip between recycled concrete and steel bar is higher than that between ordinary concrete and steel bar. This article can provide a theoretical basis for the application of recycled concrete in high-temperature environment.

Experimental investigations on the load-bearing properties of dowel connection joints of bamboo scrimber

The joints in bamboo structures are critical, and dowel connections are the most convenient form of joint. Research on dowel-bearing behaviour is important to develop the theory of joints for bamboo structures. One hundred fifteen half-hole dowel-compression specimens were tested in this study to explore the effects of specimen length, dowel diameter and fibre direction on the dowel-bearing behaviour of bamboo scrimber. Results showed that length had little effect on the stiffness and dowel-bearing strength of bamboo scrimber. When the dowel diameter increased from 8 to 20 mm, the stiffnesses of parallel to grain and perpendicular to grain specimens both increased by more than 43%, while the dowel-bearing strength of parallel to grain specimens decreased linearly from 177.11 MPa to 126.74 MPa, and the variation law of the perpendicular to grain specimens conformed to the trend of the quadratic function. When the angle between the direction of the bamboo fibre and the horizontal direction changed from 90° to 0°, the stiffness decreased from 63.55 kN/mm to 32.62 kN/mm, and the dowel-bearing strength decreased from 167.22 MPa to 138.43 MPa and exhibited different downwards trends with 45° as a boundary. Based on the calculation concept in Code for the design of timber structures in China, the calculation formula of dowel-bearing strength of bamboo scrimber was proposed by considering the influence of dowel diameter and fibre direction. The predicted results are in good agreement with the test results, which have good applicability to bamboo scrimber and can effectively provide a design method for dowel connection joints of bamboo structures.

Experimental study on the mechanical properties of the hot-cast anchor of steel cables at elevated temperatures

Although commonly used as critical joints in prestressed space structures, hot-cast anchors tend to be weak in the fire. Currently, there is a lack of research on the mechanical properties of the hot-cast anchor at high temperatures. In this study, pull-out tests were performed on hot-cast anchors of Galfan-coated steel cables and locked coil wire ropes at elevated temperatures to determine failure mode, failure mechanism, and mechanical properties at high temperatures. The following conclusions were obtained: (1) The ultimate tensile strength of the hot-cast anchor decreased at an accelerated rate with increased temperature. When the temperature reached 200 °C, it decreased to about 80% of that at room temperature. (2) The peak point displacement of the hot-cast anchor of the locked coil wire rope increased significantly with increased temperature, while the Galfan-coated steel cable did not. (3) The stiffness of the hot-cast anchor decreased with increased temperature. When the temperature reached 200 °C, it decreased to about 75% of that at room temperature. (4) Additionally, this study proposed a prediction formula for the ultimate tensile strength of a hot-cast anchor at different temperatures, thus providing a theoretical basis for the fire resistance design of hot-cast anchors.

Experimental research on the performance of a Novel Geo-filament anchor for an Earthen architectural site

At present, most studies of anchorage techniques for earthen architecture ruins are conducted so as to improve the anchor force, however, the damage caused to the ruins by anchor reinforcement has not been fully considered in practice and no special anchor technique has been applied to reinforce the small sliding mass. This paper summarizes the application and R&D of anchor rod techniques as applied to the protection of the Gaochang Ruins, Turpan, in China. Based on the reinforcement of the small sliding mass of the earthen historical ramparts, a new type of Geotechnical Filament Anchor (GFA) is designed. By changing six parameters, including anchorage length (L), GF thickness (H), bore diameter (D), slurry strength (S), GFA surface state (R) and inclination Angle (A), the tensile strength, failure mode, load displacement (P-S) relationship and strain (ζ-L) distribution characteristics are studied, and corresponding analysis is performed on the test data and phenomena. (1) A formula for the design value of the anchorage force N is presented. (2) Combining the data on the strain distribution at the GF-slurry interface under the action of N, the shear stress distribution model of the anchorage system is obtained. (3) Taking into account the soil mechanical properties of the above-mentioned ruins, the shear stress diffusion coefficient (α) is conceptualized, the formula for the shear strength of the grouting material is obtained, and the allowable ranges of L, D, H, R, and S determined. A new design is proposed for the application of anchorage techniques to earthen ruins in the context of protection of cultural relics, which promotes the design and calculation method described in this paper.

Lateral behavior and PFI model of sinusoidal corrugated steel plate shear walls

This study focused on the lateral behavior of sinusoidal corrugated steel plate shear walls (CoSPSWs), which consist of a steel boundary frame and sinusoidal corrugated infill wall plates. Firstly, eigenvalue buckling analyses were conducted on sinusoidal corrugated wall plates under pure shear, and local as well as global shear buckling stress formulas were proposed. Nonlinear pushover analyses were then conducted on sinusoidal corrugated steel plate shear walls with different corrugation configuration, corrugation direction as well as influences from gravity loads. The results show that the lateral behavior of sinusoidal corrugated wall plates is obviously affected by the corrugation configuration and gravity load effects, but not much by the corrugation direction. Based on the shear slenderness ratio, sinusoidal corrugated wall plates could be classified into stocky, moderate and slender walls, with lateral load-resisting mechanism corresponding to shear yielding, inelastic shear buckling, and elastic shear buckling followed by incomplete tension field action, respectively. CoSPSWs with stocky wall plates tend to have both good lateral capacity and ductility, CoSPSWs with moderate wall plates would still have good lateral capacity but lower ductility, and CoSPSWs with slender wall plates would have good ductility but lower lateral capacity. Shear strength formulas were proposed for horizontal corrugated wall plates, not affected by gravity loads due to accordion effects, as well as vertical corrugated wall plates considering the gravity load effects. Plate-frame interaction (PFI) models were also proposed for horizontal and vertical CoSPSWs considering the gravity load effects.

A Beam Test Study on the Bond Performance between Epoxy-Coated Reinforcement and Geopolymer Concrete

An epoxy-coated reinforcement geopolymer concrete structure with good durability and energy-saving properties can be formed by combining epoxy-coated reinforcement and geopolymer concrete. The bond strength is the precondition for the two to work together. In this paper, 13 beam specimens (11 epoxy-coated reinforcements and 2 ordinary deformed reinforcements) were designed to investigate the influence of the strength of geopolymer concrete, diameter of the reinforcement, bonding length and type of reinforcement on the bond performance between reinforcement and geopolymer concrete. The test results show that the ultimate bond strength of the epoxy-coated reinforcement (ECR) and geopolymer concrete decreased by 7.32% and 14.76%, respectively, when the rebar diameter increased from 14 mm to 16 mm and then to 20 mm. The ultimate bond strength between ordinary threaded reinforcement and geopolymer concrete was slightly higher than that between ECR and geopolymer concrete. When the length of the bond section is small or the concrete strength is low, the beam specimen is prone to the failure of the reinforcement pullout. The specimen with the larger reinforcement diameter is prone to concrete splitting failure. However, the specimens with medium bond length and small reinforcement diameter suffered from pull-out failure after concrete splitting. In this paper, based on the test data, the bond-slip constitutive model of ECR and geopolymer concrete was established, and the bond-slip curve obtained by this model was in good agreement with the measured curve. In addition, the calculation formula of the ultimate bond strength between ECR and geopolymer concrete was also proposed in this paper, which can provide theoretical reference for the engineering application of geopolymer concrete.

Strength model of a cemented body based on self-compacting characteristics of tailings

To examine the strength and mechanical characteristics of self-compacting tailings, a direct shear test was conducted under various consolidation states and moisture contents to determine the cohesion and internal friction angle of the tailings. The degree of cohesion and the internal friction angle of unsaturated tailings increased initially before declining as the moisture content rose. The maximum cohesion and internal friction angle were reached when the moisture content was around 14%. When combined with the Coulomb shear strength formula and the tailings self-weight compaction model, the expressions for the active pressure and passive pressure of tailings at any height on the lateral restraint were obtained. An improvement in cohesion and the internal friction angle of unsaturated tailings was seen with increased consolidation stress, which became stable when the consolidation stress was greater than 1 MPa. The limited equilibrium method was used to establish the three-dimensional mechanical equilibrium of the cemented body. A strength model of cementation at the open stoping stage with subsequent filling was developed after the three-dimensional strength analytical model of cementation in step 1 was modified. The difference between the design value and the measured value was 0.2 MPa. The strength of the one-step cemented backfill design, as well as the design and erection of the backfill retaining wall, was supported technically and theoretically by this study.

A method for calculating permanent displacement of seismic-induced bedding rock landslide considering the deterioration of the structural plane

The mechanism of seismic-induced bedding rock landslide is distinct from that of slope instability/landslide in normal gravity conditions; their failure modes are mainly characterized by vibration deterioration effect of rock mass structural plane due to a seismic loading, which has a significant effect on the stability of the bedding rock landslide. Several advanced methods have been proposed to assess earthquake-induced bedding rock landslide. However, the quantitative evaluation of the vibration deterioration effect of structural plane, along with its application in the dynamic stability analysis of bedding rock slopes, remains a challenging topic that requires further study. In this study, on the basic of the analysis of the cyclic shear condition and the cyclic shear test of the structural plane, the expressions to calculate the dilatancy angle and basic friction angle of structural plane under cyclic shear loading are studied. A deterioration formula for structural plane shear strength is proposed, which fully considers the deterioration effect during cyclic shear. Furthermore, a new calculating method of the seismic-induced permanent displacement of the bedding rock landslide, which introduces the deterioration effect of the structural plane, is developed. A case study was used to compare the permanent displacement calculated with the proposed method with those obtained using the Newmark and Qi methods, which demonstrates the effectiveness and applicability of the proposed method.

Theoretical and Experimental Investigation on the Flexural Behaviour of Prestressed NC-UHPC Composite Beams.

To investigate the normal section strength and cracking bending moment of normal concrete-ultra-high-performance concrete (NC-UHPC) composite beams, calculation formulas were established considering the tensile strength of UHPC based on the current railway bridge design code. Using the railway T-beam as a template, prestressed NC-UHPC composite beams with different NC layer heights were built. A static bending test was performed, the pressure of the steel strand and the deflection and strain of the beam were measured, and the evolution of cracks in each beam was observed. The calculation formulas of the normal section strength and cracking bending moment of NC-UHPC composite beam were verified by the test. The results showed that the type of strain was similar to load-deflection curves with increasing load; the bending failure process of the NC-UHPC composite beam showed four obvious stages: elasticity, uniform cracking, crack development, and yield. Cracks in the beam started to appear at stage II, developed rapidly at stage III, and stopped emerging at stage IV. The calculation formulas for the normal section strength and the cracking bending moment of the NC-UHPC composite beam were in good agreement with the test values. Normal concrete with a compressive strength of 80 MPa can replace UHPC for the design of NC-UHPC composite beams.

The performance optimization of concrete bricks using a sagu fiber

Sagu (sinonggi/kapurung) is a typical food of the Tolaki ethnic group. Sagu (Metroxylon sagu rottb) is an endemic plant in Southeast Sulawesi Province. So far, sagu waste in the form of fibers (sagu fiber) has not been optimally utilized. Sagu fiber waste is only left to mount; some are dumped into the river, so it is feared that it could pollute the environment. Through innovation in reducing waste in the principles of sustainable construction, sagu fiber will be used as an added material to manufacture concrete brick wall pairs. This study aimed to test the compressive strength and water absorption capacity of sagu fiber concrete bricks with variations of 0%, 50%, 60%, and 70% sagu fiber under the sand. This study uses an experimental method with stages such as preparing work tools and work materials, making test objects, and testing. Data were analyzed using mathematical formulas for the compressive strength of concrete bricks and water absorption capacity, compared with SNI 3-0349-1989 for solid concrete bricks, and analyzed comparatively. Based on the test results in this research laboratory, it is concluded that a balanced composition to get good quality is found in 70% sagu fiber and 30% sand.