Strength Grade Research Articles

Early age bond-slip behavior of reinforcing steel bars in concrete subjected to uniaxial lateral pressure: An experimental study

The bond between reinforcing bars and concrete is a crucial factor concerning the serviceability of reinforced concrete structures, particularly for those during construction in some developing areas where plain bars were still used as reinforcements. Despite numerous studies on early age bond behavior between steel bars and concrete, little research has been conducted to quantify the effect of uniaxial lateral pressures on this bond. This study involved testing a total of 378 pullout specimens to evaluate the early age bond-slip behavior of plain bars in concrete under uniaxial lateral pressure. The main test parameters included the concrete ages (1, 3, 7, 14 and 28 days), lateral pressures (0, 0.1, 0.2, 0.4 and 0.6 times the compressive strengths of concrete), concrete strength grades (C20, C35 and C45), and bar diameters (12, 16 and 20 mm). Based on the experimental results, a series of analytical expressions were developed for bond strength, maximum bond slip and residual bond stress predictions considering the effects of early age and lateral pressure. The results demonstrate that degradation of bond strength at early ages can be effectively mitigated by uniaxial lateral pressures. As the age decreases from 28 to 1 days, the bond strength exhibits a significant decrease of up to 51.59 %, while this adverse effect can be reduced by around 10 % in the presence of lateral pressures. Increasing the pressure level from 0 to 0.4 results in a significant increased early age bond strength by 112.6 % to 199.0 % for different bar diameters. However, the residual-to-maximum bond stress ratio remains nearly constant at 0.49 regardless of age and lateral pressure, as the pressure primarily contributes to frictional forces at the bar-concrete interface. An age-dependent bond-slip constitutive model considering the effect of uniaxial lateral pressures was finally proposed and verified with the test results. The paper concludes that given the concrete compressive strength at 28 days, the proposed bond strength and bond stress-slip models can predict the early age bond responses of plain bars in concrete under uniaxial lateral pressures with reasonable accuracy.

<i></i>Ring width distribution as a valuable anatomical trait for predicting bending strength and rigidity in European oak wood beams

Ring width variability affects the elasticity and strength of wood members. This study was conducted to determine which dispersion statistics of annual ring width distributions measured in cross section in European oak (Quercus robur L.) wood beams are useful as covariates in models for predicting modulus of elasticity (MOE) and modulus of rupture (MOR). For this purpose, 21 European oak trees growing in north-western Spain were felled, logged and sawn. The planks obtained were air-dried and surfaced into beams (50×100×2,000 mm), which were visually graded according to the UNE 56544:2022 standard. MOE, MOR, moisture content and density (determined according to EN 408:2010 standard) and abundance of sapwood and ring widths were determined in 30 beams apt for structural purposes. MOE was significantly related to standard deviation, variance and interquartile range of the ring width distribution in the beam. MOE was also related to mean ring width (r =-0.52, p<0.01) and maximum ring width per beam (r =-0.54, p<0.01), an easy to measure variable. MOR was also related to ring width distribution parameters, although yielding lower r values. The influence of ring width evenness and maximum ring width can be considered to improve visual strength grading standards for European oak timber.

Dynamic shear strength of precast connection with UHPC-based and traditional grouted sleeves: Test, simulation, and analytical formulas

Dynamic shear strength is critical for ensuring the integrity of prefabricated structures with grouted sleeve connections under dynamic loads such as impacts and earthquakes. However, studies have yet to be conducted to clarify the dynamic shear strength of grouted sleeve connections for designs. To this end, this study systematically investigated the dynamic shear behavior of precast connection with grouted sleeves through physical experiments, numerical simulations, and theoretical analysis. Drop hammer impact tests were performed on nine precast connection specimens that differ in amounts of impact energy, axial loads, rebar ratios, and grouting materials. Experimental data indicated that the dynamic shear performance of the ultra-high-performance concrete (UHPC)-based connections is superior to that of traditional grouted sleeve connections. The impact-induced displacement of a grouted sleeve connection is very sensitive to the amount of impact energy. Detailed finite element (FE) models were further developed to examine the dynamic shear strength of precast connections. Good agreements are observed between the numerical results and experimental data, demonstrating the rationality of the developed FE modeling method. It was found that the dynamic shear strengths of grouted sleeve connections are more sensitive to axial load levels and concrete strength grades than rebar ratios. Based on extensive simulation results obtained from the validated modeling method, the analytical formulas were proposed to predict the dynamic increase factor (DIF) and shear strength of precast connections. The analytical results predicted by the proposed formulas agree well with the FE results, demonstrating the applicability of the proposed formulas.

Comparative study on the performance of fresh concrete comprising manufactured sand vs. river sand during full-scale long-distance pumping

The shift from river sand (RS) to manufactured sand (MS) as a fine aggregate in concrete is driven by environmental sustainability concerns. However, negative impacts of MS on concrete workability have raised doubts about its suitability for long-distance pumping in construction projects. This study evaluates the performance of MS concrete compared to RS concrete of the same strength grade during long-distance pumping. A full-scale coiled pipeline with measured length of 348 m was built, twelve batches of C30 and C60 concrete were prepared, and pumping tests were conducted at discharge rates of 2.5–18.9 liter per second (L/s). The workability and rheological parameters were assessed before and after pumping. The measured and predicted pumping pressure were analyzed and calculated based on rheological parameters and lubricating layer (LL) parameters. Results indicate that MS increased the yield stress and decreased the LL thickness index of C30 concrete, while it decreased the viscosity coefficient of C60 concrete. Post-pumping, the change in yield stress was similar for both MS and RS concrete, but MS reduced the plastic viscosity change in C60 concrete. MS did not significantly affect the pumping pressure loss, but influenced the pumping pressure prediction deviation by influencing the thixotropy. The classic pumping pressure prediction model developed by Kapan obviously overestimated the pumping pressure during long-distance pumping, and the deviation was more prominent in high-strength concrete pumping. MS increased the thixotropy of C30 concrete and reduced the prediction deviation of pumping pressure, but had the opposite effect on C60 concrete.

Mesoscopic analysis on the coral aggregate reinforced concrete column under axial and eccentric compression

Coral aggregate concrete (CAC) has been identified as a promising building material for reef engineering construction, yet its practical application remains challenging due to incomplete research on the mechanical behaviors of the CAC beam and column components. In this study, a 3D mesoscale modeling approach considering the heterogeneity of CAC was utilized to investigate the mechanical performance of coral aggregate reinforced concrete columns (CARCCs) under axial and eccentric compression. Through numerical delineation of failure processes and damage mechanisms at the mesoscale, comprehensive parametric analysis integrating both numerical simulations and experimental validations were executed to assess the load-bearing capacity of CARCC. Results indicate that the mesoscale model has significant reliability in simulating the deformation and cracking failure behaviors and analyzing the load-displacement relationships of CARCC under axial and eccentric compression loads. When under axial loads, macroscopic cracks in CARCC primarily develop in an oblique manner, precipitating significant concrete spalling and extensive cracking failure along the longitudinal axis. Under eccentric loads, failure advances from crack initiation at load points to abrupt vertical fractures in stressed zones, manifesting a decrement in the load-bearing capacity with escalating eccentricity. Furthermore, the strength grade and reinforcement ratio exert a profound influence on the load-bearing capacity, with disparate impacts under varied loading conditions. It is concluded that reinforcement strategies tailored to specific loading conditions have significant implications for the design and safety of reinforced concrete structures in reef engineering projects.

Developing ultra-high performance concrete with different strength grade based on mix proportion sensitivity factor analysis

Abstract Owing to the excellent strength and durability, ultra-high-performance concrete (UHPC) has been used for fabricating large-scale and important infrastructures. However, mix proportion of UHPC is still the core factor influencing its workability, strength, cost and energy resource consumption. Based on this, the amount of cementitious materials, water-binder ratio, and the content of steel fibers were matched to obtain UHPC with required workability and strength according to three-factor five-level orthogonal range analysis considering the interaction of these three parameters. Experimental results show that the water-binder ratio and steel fiber content is the primary factor to guarantee the fluidity/compressive and flexural strength of UHPC, respectively. For developing UHPC with compressive strength grade of 150 MPa and flexural strength higher than 50 MPa, the amount of cementitious materials (including cement, silica fume, cenosphere, and fly ash) and the content of steel fibers should be higher than 1000 kg m−3 and 2.5 vol.%, and the corresponding water-binder ratio is equal to 0.16. When the aim is to fabricate UHPC with compressive strength grade of 120 MPa and flexural strength higher than 40 MPa, the water-binder ratio can be increased but should be lower than 0.20 with the increasing amount of cementitious material, and the volume fraction of steel fibers should be higher than 1.5 vol.%. High steel fiber content and water-binder ratio all easily coarsens the microstructure and pore structure of UHPC, and this phenomenon cannot be compensated by using high amount of cementitious materials. It should be adjusting the matching degree of amount of cementitious materials and water-binder ratio to obtain a slurry with appropriate fluidity and cohesiveness, and then content of steel fibers can be selected to perform without adverse effects.

The axial compression mechanical performance of CFRP-confined fully replaced nonnatural coal gangue aggregate columns after freeze[sbnd]thaw cycles

With the continuous mining of coal worldwide, the accumulation of coal gangue, a byproduct of coal production, has increasingly posed severe environmental challenges. To mitigate the environmental pollution caused by coal gangue, this paper proposes the use of processed coal gangue as a replacement for coarse aggregates in concrete. Additionally, carbon fiber-reinforced polymers (CFRP) are employed to confine these square concrete columns, with the aim of expanding the application of nonnatural coal gangue concrete in freezethaw environments. Taking the number of CFRP layers, number of freezethaw cycles, and concrete strength grade as variables, a total of 54 samples were designed. Experimental and theoretical analyses were conducted to investigate the mechanical behavior of CFRP-confined fully replaced nonnatural coal gangue aggregate (FNCGA) columns. The specific conclusions are as follows: (1) Under a freezethaw environment, the stressstrain behavior of the CFRP-confined FNCGA columns undergoes three stages: an elastic ascending stage, a plastic descending stage, and a plastic ascending stage. (2) When the number of freezethaw cycles increases from 100 to 300, the Poisson's ratio of the elastic stage of the sample exhibiting an upward trend. (3) For the three-layer CFRP confined sample, the volumetric strain is positive (in compression), and the bearing capacity of the sample exceeds that of the unconfined concrete by approximately 10%. (4) Compared with existing models and experimental results, the bearing capacity and stressstrain model proposed in this study have greater accuracy, enabling better simulation of the mechanical performance of CFRP-confined FNCGA columns.

Cross-sectional analysis of timber boards using convolutional long short-term memory neural networks

This paper proposes a one-dimensional convolutional long short-term memory (1D-CNN-LSTM) model for estimating the pith position and average ring width in Norway spruce timber boards. The model predicts these cross-sectional parameters by processing sequences of light-intensity signals derived from optical scans of the board’s four surfaces. The dataset used for training the model consists of synthetic boards sawn from simulated 3D logs. The model was evaluated on a dataset consisting of 552 end cross-sections from actual Norway spruce boards. Comparisons between the automatic and manual pith and ring width estimations demonstrated a very good accuracy. The computational speed of the model was more than twice as fast as the quickest method available in the literature. A large set of boards was then used to determine the advantages of incorporating the automatically determined average ring width in formulating indicating properties for machine strength grading. This evaluation revealed that the average ring width could, in certain situations, compensate for unknown variables such as density or resonance frequency in predicting the tensile and bending strength of Norway spruce boards.

Revisiting the Concept of Property Optimization of Low Temperature Phase Transformed Microstructures of GIGASTEEL Welds

Although the need for automobile lightening continues to increase in preparation for the era of electrical vehicles, the application of steel, which has strengths in price and recycling in the automotive industry, is expected to continue along with the developments of various driving energy sources. Recently, when lightening and stiffness reinforcement are required for the electric vehicles or medium and large SUVs, newly-designed parts using GIGASTEEL with a tensile strength of 980MPa or higher are being developed. However, it is difficult to secure sufficient weld strength and fatigue performances when applying welding consumables that have been applied normally and ultra-high strength welding materials that have been commercialized so far. It has also limitations that are not easy to apply due to excessive manufacturing costs in the automotive industry. In this study, the application of commercial welding consumables by strength grade to GIGASTEEL was reviewed and the properties of the weldments were compared to address all of the above issues. Here, we consider the effects of C, Mn, Si, Cr, Ni, Mo and microalloying to implement interlocked nature with dense and complex microstructures of lath-like bainitic and acicular ferrite that can effectively improve both strength and toughness of GIGASTEEL welds in a more economical way.

A model for predicting flexural capacity of PVC‐CFRP tube confined reinforced concrete beams

AbstractThis paper presents an experimental study on 18 specimens, including 15 polyvinyl chloride (PVC)‐carbon fiber‐reinforced polymer (CFRP) tube confined reinforced concrete beams with longitudinal CFRP sheets (PCT‐RCBs‐LCS) and 3 PVC‐CFRP tube confined reinforced concrete beams (PCT‐RCBs). The effects of five studied parameters, such as longitudinal reinforcement rate (), concrete strength grade (), width () and number () of longitudinal CFRP sheet, and specimen dimensions (), on the failure mode and flexural capacity are investigated. The PCT‐RCBs‐LCS with lower and fail by the breakage of the PVC tube and the fracture of longitudinal CFRP sheets. Conversely, the cracking of PVC tube dominates the damage of the PCT‐RCBs‐LCS with higher and , while the longitudinal CFRP sheets are not broken. The introduction of longitudinal CFRP sheets can significantly improve the flexural capacity. The ultimate flexural capacity of the PCT‐RCBs‐LCS increases as the , , , or increases. In addition. considering the influence of RC beam section shape, a model for predicting the ultimate flexural capacity of the PCT‐RCBs‐LCS is proposed based on the limit equilibrium theory and cross‐sectional strain relationship. The predicted results of the proposed model agree well with test data.

Thermal activation of multi-recycled concrete powder as supplementary cementitious material for repeated and waste-free recycling

Utilizing powder generated during concrete recycling process is considered crucial for achieving complete recycling of concrete waste. However, integrating recycled concrete powder (RCP) often reduces cementitious mixture performance. This study aims to enhance RCP characteristics through thermal activation, facilitating its recycling as cement replacement over multiple recycling cycles. RCPs from three cycles of concrete recycling were heat-treated at 200 °C, 400 °C, 600 °C, and 800 °C for 2 h, and their chemical composition was analyzed before and after treatment. Subsequently, the RCPs replaced cement in mortar by 10 %, 20 %, and 30 %. Various properties of the mortars, such as flow, mechanical strength, water absorption, and drying shrinkage, were tested. The results showed a general decline in mortar properties with increasing RCP replacement ratios and recycling cycles. However, RCPs activated at 600 °C and 800 °C enhanced compressive and flexural strengths by up to 19 % and 16 %, respectively, and enhanced shrinkage resistance by 19 %. Particularly, the three-times RCP activated at 800 °C achieved mechanical performance comparable to standard mortar at 10 % replacement, meeting strength grading requirements per industry standards. This study demonstrates a viable pathway for the repeatable and waste-free recycling of concrete, contributing to more sustainable construction practices.

Research on bridge safety early warning method based on strain energy theory and health monitoring data

Bridges are technology-intensive and heavily invested permanent infrastructure. After completion and opening to traffic, bridge structures are easy to be affected by factors such as traffic load and atmospheric environment. Therefore, it is necessary to do safety warning and evaluation of bridges, especially the abnormal behavior in the early stages of bridge operation. In this research paper, a large-span continuous rigid frame bridge installed with the health monitoring system (HMS), of which a large amount of health monitoring data are collected by the HMS, is used as an example, and then a bridge safety early warning method is proposed when the bridge is during early operating period. First of all, the research finding that the internal stress of the prototype bridge obeys normal distribution through statistical analysis is used; next, we deduce that the strain energy inside the prototype bridge is subject to the Non-central Chi-square distribution combined with the strain energy and statistical theories; in the end, the key probability density distribution function of strain energy and its parameters are derived by using the key stress distribution function of the high performance concrete C50 strength grade used in the prototype bridge. The method recommended in this paper is conducive to the formulation of bridge preventive maintenance strategies.

New four-point bending test protocol for the strength grading of timber: relationship between local and global modulus of elasticity (MOE) of maritime pine

ABSTRACT This study focuses on the characterisation of maritime pine according to standards EN408 and EN384 required for timber grading. A comparison of the EN408 bending test setup is performed with a new four-point bending protocol, reducing as much as possible, the effects of the shear force in the span where the deflection is measured. The study highlights difficulties to estimate accurately, the elasticity modulus of wood by using EN408 bending test setup. This is probably due to inaccuracies in the measurements of small curvatures and due to the local heterogeneities of wood. An original four-point bending test is proposed with 75% of the span of the wood beams in pure bending. This configuration clearly exhibits the convergence of measurements, in comparison to EN408 setup. The deformations generated by this new loading protocol allow a better evaluation of the bending modulus E 0. Moreover, the study reveals that the proposed setup supplies an increase of elasticity modulus close to 20%. In addition, dynamic tests are also performed to characterise the Young’s modulus. The experimental results reveal a better agreement between static test, using the new four-point bending configuration and dynamic method, than considering EN408 as a reference.

Experimental study on mechanical properties and toughness of recycled steel fiber rubber concrete

Adding rubber particles to concrete can improve its brittleness, but it also significantly reduces its compressive strength. In order to maintain the compressive strength of concrete unchanged and enhance its tensile strength and toughness, waste steel fibers are added to rubber concrete (RC). This not only achieves the reuse of solid waste materials, but also achieves the goal of high-performance concrete. By adding different amounts of scrap steel fibers to three different strength grades of rubber concrete, scrap steel fiber rubber concrete (SSFRC) is formed. Compression strength, tensile strength, and flexural strength tests were conducted on SSFRC with different mix ratios. The toughness of SSFRC was evaluated by introducing the tensile compression ratio, flexural compression ratio, and toughness index. The microscopic characteristics of SSFRC were observed using scanning electron microscopy (SEM), and the strengthening and toughening mechanism of waste steel fibers on RC was analyzed. The results show that: adding rubber decreases the mechanical properties of concrete with various matrix strengths; adding steel fiber admixture causes a trend in the mechanical strengths of SSFRC with various matrix strengths to increase and then decrease; getting the greatest compressive strength at 1 % and the peak tensile and flexural strengths at 1.5 %; Steel fibers and rubber particles can cooperate at a specific admixture amount to increase the toughness of RC. The local hydration of the scrap steel fibers may have taken place, according to the microscopic morphology of the Transition zone at the interface between the matrix and the scrap steel fiber. In conclusion, the best mechanical strength enhancement effect and the best toughness of SSFRC are achieved at 10 % of rubber and 1.5 % of scrap steel fiber.

Effect of steam curing on strength, durability and microstructure of concretes with and without mineral admixtures

This research explores the effect of steam curing on the strength, durability and microstructure of concretes with and without mineral admixtures of fly ash (FA) and ground granulated blast-furnace slag powder (SL). Two types of C55 strength grade concretes (one was pure cement concrete, the other was a concrete made by replacing part of the cement with 12% FA and 18% SL) were prepared and their compressive strength, chloride diffusion coefficient and carbonation depth under standard and steam-curing conditions were measured and compared. The phase composition and microstructure of the concretes under the two curing conditions were tested by X-ray diffraction, scanning electron microscopy and mercury intrusion porosimetry. The results showed that, on the one hand, compared with standard curing, steam curing is beneficial to the early strength, but not conducive to the later strength development and chloride permeability resistance of both types of concretes. Furthermore, for the steam-cured concrete, the 28 days carbonation depth of the forming surface is higher than that of the bottom surface. In addition, steam curing can reduce the carbonisation resistance of pure cement concrete and improve the carbonisation resistance of concrete mixed with FA and SL. On the other hand, composite mineral admixtures of FA and SL reduce the early strength and the carbonisation resistance of concrete cured by standard curing, but improve the later strength, the carbonisation resistance and chloride permeability resistance of concrete cured by steam curing. FA and SL are thermally activated under steam curing and can react with the calcium hydroxide formed by cement hydration in the early stage, which produces a larger amount of secondary hydration products to improve the pore structure and interfacial microstructure of the concrete with FA and SL. In this way, the adverse effects of steam curing on later strength and durability of concrete are significantly restrained by composite mineral admixtures of FA and SL.

The study on bond‐slip constitutive model of recycled concrete under different loading rates

AbstractIf recycled concrete is to be widely, reasonably, and safely applied in practical engineering, the study of bond‐slip performance between steel bars and concrete is crucial. In this paper, the central pull‐out test of recycled concrete under different loading rates was conducted. The characteristics of failure mode and crack directions of the specimens were observed and analyzed. The ultimate bond strength and slip displacement between rebar and concrete were analyzed. The effects of three parameters, namely concrete strength grades, replacement percentage of recycled coarse aggregate, and loading rates on the failure modes and bond‐slip mechanical properties of recycled concrete, were analyzed and summarized. The experimental results showed that there were significant differences in the influence trend and amplitude of the above three parameters on the ultimate bonding strength, slip amount, and slip curve. Based on the above experimental and theoretical analysis, a reasonable bond‐slip constitutive model was established in this paper and was in good agreement with the experimental results.

Preparation Method and Benefit Analysis for Unburned Brick Using Construction Solid Waste from Residue Soil

Highly efficient resource utilization of construction solid waste has significant environmental and socioeconomic benefits. In this study, a fabrication method and process optimization of unburned brick from construction residue soil were investigated based on experiments. The effects of cementing the material content, the raw material treatment process, the brick moisture content, and the molding method on the compressive strength of unburned brick were studied and discussed. The experimental results show that 5–20% of ordinary cement can produce a strength grade of 5 MPa–20 MPa for unburned brick, and the utilization rate of the residue soil is greater than 80%. In the case of well-dispersed residual particles, complete drying and rolling are not necessary, and soil particle size within 5 mm is beneficial for obtaining proper sand grading and low mud content, which will improve the strength of unburned brick. The pressure for the press forming of unburned brick should be 10 MPa, and the optimal moisture content of the residue-soil mixture is about 13%. The proposed residue-soil unburned brick has remarkable environmental and economic benefits with low carbon emissions, low cost, and high profit. The methods proposed and optimized in this study can provide important technical support for realizing the large-scale production of residue-soil unburned brick.

Experimental and simulation study on seismic performance of seawater sea-sand PVA cementitious composite columns with GFRP bars

The seismic properties of seven seawater sea-sand (SWSS) PVA cementitious composite columns with Glass Fiber Reinforced Polymer (GFRP) bars were studied. The effects of four parameters, namely polyvinyl alcohol (PVA) fiber content, axial compression ratio, cementitious composite strength and stirrup spacing, on the seismic performance of composite columns were analyzed. The failure of the specimen was observed, and the hysteresis curve, skeleton curve, stiffness degradation, energy dissipation capacity, ductility and strain of the specimen were analyzed. The test results show that the large chip-based spalling will occur when the specimen without fiber incorporation is damaged, and the incorporation of PVA fiber, the reduction of stirrup spacing and the reduction of axial compression ratio will delay the rate of crack formation and development. In addition, through cross-section analysis and considering the reinforcement effect of PVA fibers, a proposed formula for calculating the horizontal bearing capacity of composite columns is proposed. Finally, the finite element model of SWSS PVA cementitious composite columns with GFRP bars is established, and it is found that increasing the strength grade of cementitious materials can greatly improve the seismic performance of composite columns. The conclusions could be references for the engineering application. In the context of the global emphasis on green development and environmental protection, seawater and sea-sand cementitious composites and components with fiber reinforcement will have a wide range of application prospects in the construction of coastal areas.

An innovative strategy for improving ductility of seawater sea-sand engineered cementitious composites beam reinforced with GFRP bar

Seawater sea-sand engineered cementitious composites (SS-ECC) members with glass fiber reinforced polymer (GFRP) bars have inferior ductility due to the brittle nature of GFRP bars. In the current research, an enlarged head anchorage system (EHAS) was recommended to improve the ductility of GFRP bars reinforced SS-ECC beams. To explore the bond characteristics between SS-ECC and GFRP bars with EHAS, a total of 39 specimens were tested by pull-out loading. The influences of enlarged head shape, stirrup spacing and SS-ECC’s strength grade on the bond characteristics were experimentally investigated. GFRP longitudinal bars in specimens with EHAS presented rupture failure rather than anchorage failure. EHAS could effectively realize the slip hardening of GFRP bars in low strength SS-ECC, and ensure the reliable bond of GFRP bars in high strength SS-ECC. Additionally, the failure mechanism of specimens under pull-out loading was explored by finite element analysis (FEA). The pull-out resistance was mainly provided by EHAS in force transition stage and slip hardening stage. The influences of fiber reinforced polymer (FRP) bar type on the bond performance were investigated by FEA. EHAS could realize the slip-hardening behaviors of aramid, basalt and carbon FRP bars in normal strength SS-ECC. More importantly, to verify the effectiveness of the proposed ductility enhancement strategy, SS-ECC beams reinforced with GFRP bars were tested by four-point bending. These beams with different enlarged head shapes possessed excellent ductility and strong ultimate deformation capacity. It was recommended that low strength SS-ECC and GFRP bars with EHAS were jointly utilized to enhance the ductile performance of the beams.

Maximizing growth without compromising wood density: Selecting superior Norway spruce clones

The study examined a free-growing (initial stand density 400 trees ha–1), 50-year-old grafted clonal Norway spruce plantation in Eastern Latvia to assess the genetic control and variability of growth traits and wood density. The latter was used as a proxy for structural timber strength. Results showed moderately high heritability in growth traits and moderate variability in wood density among clones, with an estimated genetic coefficient of variation CVg, of 8.6%. Even when grown at a very low density on nutrient-rich soil, 85% of the trees met the density requirements for construction timber (C18 in accordance with EN 338). The negative correlation between growth traits and wood density was weak at both individual tree and clonal levels (–0.08 < rP < –0.06; –0.16 < rG < –0.09), making it feasible to select fast-growing clones with wood density required for structural timber. The observed variation underscores the importance of selective breeding to ensure optimal timber quality, with implications for enhancing sawn wood strength grades and promoting climate-resilient forestry practices. Keywords: tree breeding; structural timber; clonal forestry; wood properties; plantation forestry; climate-smart forestry