Strength Design Research Articles

Carbon-footprint based concrete proportion design using LSTM and MOPSO algorithms

Artificial intelligence can design more sustainable concrete mixtures to reduce costs and CO2 emissions. In this paper, a concrete mix ratio design method based on deep learning algorithm and meta-heuristic algorithm is proposed. The main parameters that control and affect the strength of the concrete were selected as input variables, including Cement, Fly ash, Blast furnace slag, Water, Superplasticizer, Coarse aggregate, and Fine aggregate of concrete per unit volume. The compressive strength of concrete as output variables, a long short-term memory network model was developed to predict and explain the compressive strength characteristics of concrete. Sensitivity analysis showed that cementitious material and concrete age are the most important factors affecting the compressive strength of concrete. This is in good agreement with the relevant theoretical research. Taking the trained prediction model as the objective function of compressive strength of concrete mix ratio design, combined with the concrete material cost and carbon emission from cradle to gate, the multi-objective particle swarm optimization algorithm is used to optimize the proportion of each component of concrete to find the optimal mix ratio under specific conditions. The results show that the long short-term memory network can predict the compressive strength of concrete with high accuracy, and replace the traditional explicit mathematical expression to simulate the complex nonlinear relationship of multiple parameters. The established algorithm can calculate the Pareto optimal solution set according to the objective function, and obtain the optimal mix ratio with the least material cost and carbon footprint while meeting the compressive strength required by the project. The results of this work provide an intelligent and efficient design method for determining concrete mix ratio design, which can provide a reference for practical engineering applications to a certain extent.

ASD and LRFD: Reliability comparison for designs subjected to wind loads

Current design practice in the United States allows engineers to use either Allowable Strength Design (ASD) or Load and Resistance Factor Design (LRFD) method, under the assumption that both methods provide similar levels of economy (available design strengths) and safety (probabilities of failure and reliability indices) regardless of the design conditions. Recent studies have demonstrated that significant differences in economy can arise between ASD- and LRFD-based designs subjected to combinations of gravity and wind loads, suggesting inconsistencies between the safety levels. This study investigates the safety levels provided by the ASD and LRFD methods for such design cases. The safety levels were estimated using a formal reliability analysis with consideration of geometrically non-linear second-order effects. The reliability analysis was performed using Monte Carlo simulations with appropriate probability distributions for the random variables associated with both resistance and loads. The findings of this study indicate that generally accepted uniformity of reliabilities achieved by the ASD and LRFD methods does not hold for design cases governed by wind loads. The safety levels achieved by using the ASD method are less consistent than those achieved by using the LRFD method. The use of the ASD method generally entails the acceptance of failure risks many times greater than for those of the LRFD method, and target safety levels lower than those stipulated by the ASCE 7 Standard. These results highlight the need for a reevaluation of the current design practices to ensure that the required target levels of structural safety are consistently met.

Elastic buckling analysis and optimization of thin-walled bamboo-like pipe beam subjected to pure bending

In this paper, a stiffening design imitating the bamboo node is proposed for weight reduction of the long composite pipe beam subjected to bending load. The distribution of bamboo nodes can efficiently suppress the ovalization of the section, thus significantly improving the bending resistance of the bamboo. Based on this principle, ring stiffeners are proposed to be fixed to the pipe beam, making the long beam equivalent to the combination of a series of short pipes that suffered less section ovalization. A database of the optimal laminate orientations for different normalized lengths is obtained through optimizations, where the discreteness of the ply count is considered. Based on this database, weight optimizations are conducted, and the optimal designs of beams with and without stiffeners are obtained and compared. The comparison results show that the proposed bamboo-like stiffened beam not only regains a near-linear load–displacement relationship, but also reduces the weight by up to 16% under the same buckling load. In addition, it is found that for the pipe beams with radius-to-thickness ratios of more than 18, increasing the radius leads to a decrease in elastic buckling resistance when the weight remains a constant, which is opposite to the design for strength and stiffness. The model and database developed in this paper can provide a reference for weight reduction design and weight estimation for composite pipe beams.

Strength-based life cycle CO2 of fly ash concrete: Variation with common mix parameters

The addition of fly ash (FA) to concrete will not only reduce the CO2 content of concrete but also affect the compressive strength of concrete. However, most studies on carbon emissions have underestimated the complexity of the relationship of emissions with the concrete mix design and compressive strength. In this study, a database of mix designs was established by considering 1062 datasets related to the laboratory concrete mix designs and compressive strength values, and by using an artificial neural network model, a multiple nonlinear regression model, random forest model and support vector machines to simulate and predict the compressive strength of concrete. Moreover, the differences in the life-cycle CO2 corresponding to FA concrete among three different allocation types-no, mass, and economic value allocations-based on two functional units (FU)-per unit volume and per unit volume and strength were investigated. Finally, sustainable mix design method of FA concrete was established to find the optimal FAC mixtures and the correlation between CO2 emission and concrete mix parameters was analyzed by the maximal information correlation (MIC). The results indicate that the neural network model has a better regression effect than the multiple nonlinear regression model and other machine learning models on the prediction of compressive strength and CO2 emissions. For different functional units, the CO2 emissions under FU1 increases with the strength of concrete regardless of different allocation types; the CO2 emissions under FU2 varies considerably with changes in the amount of added FA under no allocation and economic value allocation. The CO2 emission under FU1 has a stronger correlation with various mix parameters than that under FU2.

Characteristics of multi-span transmission lines following ice-shedding

Numerical simulation method for dynamic responses of multi-span transmission lines with evenly and unevenly distributed ice following ice-shedding from full and partial span in the cases without and with wind loads, is presented and verified by reduced-scale modeling tests. Jump envelop, dynamic swing parameters, maximum reactions on tower and tensions in conductors are defined to depict the dynamic response characteristics of transmission lines following ice-shedding. The characteristics of multi-span lines with various parameters following ice-shedding are numerically studied, meanwhile a dataset is built. Using the dataset and the back-propagation (BP) neural network algorithm, prediction models for the dynamic response characteristics providing instructions for the design of electric insulation clearance and strength of transmission lines in ice zones are established and the software is developed.. The suitability of the prediction model and existing methods are discussed.

A New Insight into the Design Compressive Strength of Ultra-High Performance Concrete

Compressive strength is one of the most critical mechanical properties of various types of concrete and is the main input variable for structural concrete design. Recently, with the advances in concrete technology, applications of fiber-reinforced concrete (FRC), including ultra-high performance concrete (UHPC), have grown rapidly. These new types of concrete are well known to exhibit superior mechanical characteristics such as compressive strength, fracture toughness, and durability compared to conventional concrete and thus are popularly used in urgent repair jobs where compressive strength is an important parameter to determine the required curing time until open to the public. Considering the importance of compressive strength in practice, this study aims to evaluate the effect of age and maturity on the compressive strength characteristics of three different types of concrete, namely UHPC with micro and macro steel fibers, FRC, and plain concrete, and to propose a new design strength criterion for UHPC. To this end, 180 concrete cube specimens were tested at 12 different ages between 3 and 126 days. The results indicated that irrespective of the type and presence of fibers, UHPC gained more than 90% of their ultimate compressive strength after only 21 days, while FRC and plain concrete specimens required a longer time (i.e., 28 days) to achieve 90% of their ultimate strength. Therefore, UHPC may adopt a 21-day compressive strength as a design input instead of a 28-day compressive strength commonly required for structural concrete specified by many codes of practice. Moreover, the obtained experimental results were compared with existing compressive strength predictive models in the codes of practice.

Experimental study on the seismic performance of concrete shear walls partially replaced by MRPC

Shear wall structures are widely used in high-rise buildings, due to their satisfactory integrity and force transmission, thus superior seismic performance. However, due to insufficient material strength, non-standard construction, and the fact that some buildings have reached their design service life, many shear wall structures can no longer resist natural disasters such as earthquakes, nor can they meet the functional requirements. Therefore, it is of practical significance to reinforce shear wall structures and study their seismic performance. This paper uses the partial replacement method to reinforce and renovate concrete shear walls, using modified reactive powder concrete (MRPC) with excellent durability and toughness as the replacement material. The effects of different materials and different replacement positions on the seismic performance of shear walls were studied. A total of 5 shear wall specimens were designed and manufactured, including Specimen SW1 that did not reach the designed concrete strength, Specimen SW2 that met the original design strength, SW3 with the middle part of the wall was replaced by MRPC, and another two specimens that used ordinary concrete (SW4) or MRPC (SW5) to replace the two ends of the wall. Pseudo-static tests were carried out on the specimens and their seismic performance indicators such as bearing capacity, stiffness degradation, displacement ductility, and energy dissipation capacity were analyzed. Finally, finite element simulation analysis was also performed for the specimens. The results show that compared with the original design strength specimen SW2, the specimens SW4 and SW5, which used C45 concrete and MRPC to replace the two ends of the walls, effectively improved the bearing capacity, energy dissipation, and ductility of the shear wall. By comparing the mechanical properties of SW3 and SW5, it can be found that replacing the two ends of the shear wall can obtain better results.

Sectional strength design of a double-skin truss-reinforced composite shear wall

The double-skin truss-reinforced composite shear wall is an innovative element which comprises two steel plates, core concrete, concrete-filled steel tubes (CFSTs), which act as boundary members, and steel truss connectors. Truss connectors decrease the out-of-plane deformation that affects the steel plates, and due to the resultant connection and constraint effects, the truss connectors enhance the bearing capacity of the wall. This paper briefly introduces the quasi-static test of five full-scale rectangular double-skin truss-reinforced composite shear wall specimens. The specimen exhibited shear compression failure with an aspect ratio of 2.0, and flexure shear failure occurred when the aspect ratio exceeded 2.0. Based on the analysis of actual stress state of the steel web and actual working performance of the infilled concrete, the shear strength and flexure strength design formulas of double-skin truss-reinforced composite shear wall were established. Comparison results with 26 specimens demonstrate that the design formulas exhibit remarkable accuracy, as most errors are within 20 % and 25 %, respectively. Which provide a preliminary sectional strength design proposal for the double-skin truss-reinforced composite shear wall.

Optimized design of wind turbine airfoil aerodynamic performance and structural strength based on surrogate model

Though offshore wind turbines have great potential for applications in ocean energy harvesting, their subject to complex unsteady aerodynamic loads. To obtain wind turbine airfoils with both aerodynamic performance and structural strength, an airfoil optimization method was proposed by adding the torsion constant to the objective function under the premise of improving the lift-to-drag ratio. The optimization method characterizes the airfoil geometric profile by using Class/Shape function transformation (CST) parameterization. The airfoil aerodynamics and the structural properties were solved by the computational fluid dynamics (CFD) method and Matlab program, respectively. To reduce the number of CFD calculations, a Kriging surrogate model was established. The combination of an optimized Latin hypercube sampling method and expected improvement (EI) points infill criteria is to improve surrogate modeling efficiency. The NREL 5 MW wind turbine blade was used as the research object. The NACA64618 with 18% relative thickness, the DU91-W2-250 with 25% and the DU97-W-350 with 35% were optimized by assigning different weights to aerodynamic and structural objectives based on airfoil position in the blade. The results showed that the aerodynamic performance of the optimized airfoils was improved. Subsequently, the three optimized airfoils were replaced in the same positions of the blade for lay-up design. The blade structural properties were calculated by finite element method (FEM) and it found that the blade torsion angle was reduced, which indicated that adding structural objectives in the airfoil optimization could enhance the blade structural performance.

Club coefficients in the UEFA Champions League: Time for shift to an Elo-based formula

ABSTRACT One of the most popular club football tournaments, the UEFA Champions League, will see a fundamental reform from the 2024/25 season: the traditional group stage will be replaced by one league where each of the 36 teams plays eight matches. To guarantee that the opponents of the clubs are of the same strength in the new design, it is crucial to forecast the performance of the teams before the tournament as well as possible. This paper investigates whether the currently used rating of the teams, the UEFA club coefficient, can be improved by taking the games played in the national leagues into account. According to our logistic regression models, a variant of the Elo method provides a higher accuracy in terms of explanatory power in the Champions League matches. The Union of European Football Associations (UEFA) is encouraged to follow the example of the FIFA World Ranking and reform the calculation of the club coefficients in order to avoid unbalanced schedules in the novel tournament format of the Champions League.

Performance of eco-friendly concrete made from recycled waste tire fine aggregate as a replacement for river sand

Tires are non-biodegradable and can last long, providing an environmental risk. This material could substitute natural aggregate in concrete, reducing aggregate consumption, promoting sustainable development, and protecting the environment. This study examines the mechanical strength, shrinkage, durability, and structural performance of concrete prepared with varied content of waste tire fine aggregate (WTFA) up to 75 % as a substitute for sand at two water-to-cement ratios of 0.30 and 0.55. Results indicate that slump, dry density, and mechanical strength all decrease as WTFA content increases. At both w/c ratios, the compressive and splitting tensile strength decreases by up to 71–77 % and 59–62 %, respectively, when the WTFA content is 75 %. Young's modulus dropped by about 71–77 % when the WTFA content was 75. In contrast, the flexural load-carrying capacity declined by about 63–69 % for the beam with 75 % WTFA. The 100-day shrinkage test reveals no apparent shrinkage up to 20 % WFTA. However, the control specimens show the lowest shrinkage. Further, increased WTFA content increased the apparent porosity, water absorption, and chloride ion penetration. Nevertheless, the statistical analysis (ANOVA) revealed no significant effects on mechanical and durability properties due to incorporating WTFA in concrete. The outcome demonstrates that 20 % WTFA can be used as a replacement for river sand in many structural concrete whose design strength is not significantly high (fcat28days ≈ 20 MPa).

Influence of Temperature–Humidity Sensor Housing Depth on Concrete and Mortar Compressive Strength

Recent advancements in sensor technology have led to an increase in embedding sensors into construction materials for monitoring purposes in the construction industry. However, systematic research on the resulting changes to the material properties is still lacking. A previous study confirmed that the copper–nickel-plated housing of SHT-31 sensors affects the compressive strength of mortar. Moreover, it is necessary to conduct further research to determine if this analogous occurrence takes place in concrete. This study embedded temperature–humidity sensor housings in concrete at 10 mm, 20 mm, and 30 mm, before performing compression tests and a finite element analysis (FEA). The empirical findings indicate that the compressive strengths of concrete at 10 mm, 20 mm, and 30 mm depths were 26.1 MPa, 28.4 MPa, and 29.4 MPa, respectively. In contrast, the control concrete that did not have a sensor housing had a compressive strength of 31.9 MPa. In the case of mortar, a design strength of 28 MPa was achieved at a depth greater than 30 mm, while concrete reached this design strength at 20 mm. Based on these findings, embedding temperature–humidity sensor housings in concrete is recommended at depths greater than 20 mm from the surface. These results serve as important reference data for determining the optimal embedding depth of sensor housings in structures using cement-based materials.

Strength design optimization of sandwich composite structures under heavy dynamic loads

Recent researches have witnessed an increased interest in the Rapid Runway Repair (RRR) methods to rehabilitate damages that may be caused by different incidents, such as: natural disasters of earthquakes, floods or man-made vandalism in civil wars. RRR is a strategic process for airport operations for civil and peace-making missions. The current RRR techniques like precast concrete slabs, metal mats, and fiberglass mats have different pros and cons. The current study numerically investigates CFRP sandwich composite structure for RRR usage, where its strength is maximized by design optimization to reach the possible carrying aircraft wheel capacity and safety factors. The proposed composite structure is advantageous of no corrosion, low erection time, high capacity-to-weight ratio, same finish of runway surface and repaired area, and can be applied over spots of unlevelled or inadequate bearing capacity of 60 cm diameter. The strength of the basic design of composite sandwich structure is first assessed to its maximum allowed carrying aircraft wheel capacity by FE modelling. Secondly, The Genetic Algorithm (GA) optimization technique is applied for maximizing the strength of the composite structure webs satisfying the minimum safety factor of five failure criteria of Tsai-Wu, Tsai-hill, Hoffman, Hashin and maximum stress. Finally, the achieved results promoted the usage of the composite structure to operate at the taxiways, runways, and theoretically, landing and take-off areas.

Equivalent Design Strengths for Spatially Variable Cement-Treated Soil Slope

Equivalent Design Strengths for Spatially Variable Cement-Treated Soil Slope

The Characteristics of Refractory Steel and Its Development and Application in Petroleum and Other Fields

Because the strength of structural steel decreases sharply at high temperature, it must be sprayed with fire-resistant coating or fire-resistant materials for composite use. The strength of refractory steel can be reduced by no more than 1/3 of the room temperature at high temperature, and maintain good high temperature strength. This article mainly summarizes the development history of refracto-ry steel in China and other countries, analyzes the material selection basis and strengthening mecha-nism of refractory steel, and finds that by combining Mo element solid solution strengthening, phase transformation strengthening, and Nb, the strength guarantee of refractory steel at high temper-atures and V element precipitation strengthening are obtained. Designers can calculate the service temperature of steel structure through the initial stress and design strength of components to select refractory steel. Finally, the application status of refractory steel and its application prospect in the field of oil rescue are summarized and prospected.

Quantification of process-induced effects on fatigue life of short-glass-fiber-filled adhesive used in wind turbine rotor blades

Cracks in the adhesive joints of wind turbine blades can often cause severe structural blade damage. Effects induced by the manufacturing process can have a significant impact on the cycle number toward crack initiation in the bonding material. This research compared two experimental series of neat adhesive, dog-bone-shaped specimens with different degrees of cure, fiber orientation, and porosity content, which were subjected to static and cyclic tension-tension loading. To enhance the comparability of the two coupon series, the experimental data was normalized. Normalization factors were introduced to compensate for the different properties of the two series. These factors were derived from correction models. After normalization, the S-N values of the two data series were in good agreement in the high-cycle fatigue regime. In the very-low-cycle fatigue regime, however, there was still a lack of agreement in some cases, including the static strength. Moreover, the failure mechanisms were investigated by analyzing images from the fracture surfaces and dedicated samples using X-ray microscopy. The correction models presented can be applied to estimate the design strength of adhesives. This knowledge can then be used to make rotor blade structures more resistant to crack initiation.

Static strength design of local thickened plate joints between multi-cell concrete-filled steel tubular column and steel beam

A new-type local thickened plate joint (LTPJ) between multi-cell concrete-filled steel tubular columns (CSTC) and steel beams is adopted in residential building structures. However, no available strength design method for such beam-column joints is reported. This paper presents the mechanical behavior and static strength design of such joints. The local thickened plates are adopted to replace the normal thickness plates of the CSTCs within the LTPJ region. The rectangular section and L-shaped section of the multi-cell CSTC are involved in the joint study, respectively. Firstly, a finite element model (FEM) of the LTPJ between CSTCs and steel beams is established, which is then adopted to investigate the mechanical behaviour and static load-bearing capacity of the LTPJ. Codirectional and inverse bending moments are applied on the beams on two opposite sides of the LTPJ to simulate lateral loads (arise from wind or earthquake) and dead gravity loads, respectively. It is revealed that the LTPJ experiences shear failure when subjected to lateral loads, whereas it succumbs to bending failure when under dead gravity loads. The shear-bearing capacity of the LTPJ results from the three-part contribution of the steel tube web, the steel tube flange, and the core concrete. The bending-bearing capacity of the LTPJ is determined by the plate normal tension-bearing capacity of the steel tubes, which is predicted by adopting the theory of yielding line and numerical fitting. Finally, the load-bearing capacities of LTPJ under bidirectional bending moment are investigated numerically, and accordingly, some strength design recommendations are proposed in practical application. To conclude, these results provide a method for accurately predicting the load-bearing capacity of the LTPJ subjected to lateral loads and gravity loads, which holds the potential to expand and enhance the application of LTPJs and CSTCs in the design of high-rise residential buildings.

MSD applied to the construction of the British Library basement: a multi-stage excavation in London Clay

This note presents the application of the mobilisable strength design (MSD) method to the monitoring results of the multi-propped excavation in the south area of the British Library Euston, constructed in a highly overconsolidated stiff clay deposit. The MSD method is an energy-based approach (a nonlinear finite-element method for a single-degree-of-freedom soil-wall system) introduced to develop a simplified design methodology that satisfies both ultimate and serviceability limit states. Wall displacement predictions based on the MSD method are compared with considerable field monitoring data. The sensitivity of the method to reasonable variations in input parameters is considered. A spreadsheet and python code demonstrating the MSD analysis from this paper are provided in the online supplement alongside details of the mathematical formulation.

A Method Based on Fracture Mechanics to Investigate the Deformation of Reinforced Concrete Columns

In the use of non-linear structural performance models, including models that consider the critical over-performance at the failure stage, is very important when performing seismic calculations of reinforced concrete buildings and structures.The use of such models is especially important if the structures have primary damage caused by fire or corrosion, as well as mechanical damage caused by force factors. The purpose of this study is to develop an analytical model of the deformation of eccentrically compressed reinforced concrete columns by considering the failure stage, which includes processes such as peeling of the protective layer, reduction of the stability of the compressed reinforcement and softening of the encased concrete after reaching the design strength. , the existing models that describe the residual behavior of reinforced concrete structures under low cycle loading have been investigated. The models are analyzed considering monotonic curves, which are cyclic deformation boundaries. The model proposed in the research is constructed by analyzing the stages of the stress-strain state of a reinforced concrete column. At each stage, formulas are found for determining moment and curvature by solving equations of equilibrium of internal forces. Calculations based on the obtained model for a particular reinforced concrete column are carried out, monotonous diagrams are obtained, and a conclusion about the significant influence of the level of axial load on the character of deformation is made. On the basis of the obtained model, the construction of hysteresis diagrams under low-cycle loading is expected in the future.

Research on Strength Model of Cemented Tailings Deposit Body in Underground Tailings Reservoir

Due to the lack of clarity in the strength design of underground tailings reservoirs, it is imperative to investigate the interaction between the tailings deposit body (TDB) and surrounding rock. Taking the TDB as the subject of analysis, a differential equation for vertical stress on the TDB is proposed, considering the stresses from the hanging wall of the surrounding rock and physical and structural parameters of the TDB. Considering the similarity between the underground tailings reservoir and one-step subsequent filling, in situ data of the one-step subsequent filling body from a mine was utilized to compare calculated values of the theoretical model. The resulting theoretical prediction error was less than 10%, thus verifying the reliability of the proposed model. According to the theoretical model analysis, the height of the TDB exerts the most significant influence on vertical stress, while the width and length of the TDB have a negligible impact. Moreover, internal friction angle has a more pronounced effect on vertical stress than cohesion force. A case study for a lead–zinc mine in China is presented in this work. Through uniaxial compressive strength and triaxial shear experiments, the key mechanical parameters of TDB at different ratios of cement to tailings are obtained. According to the theoretical model proposed herein, the distribution law of vertical stress in the height direction of TDB is determined for various ratios of cement to tailings. The original technical scheme of the mine has been optimized by using uniaxial compressive strength greater than vertical stress as the evaluation index, achieving both storage safety and cost reduction goals.