Load Carrying Capacity Of Structure Research Articles

Retrofitting Techniques: A Comprehensive Review

The need of improving the structural performance of old constructed structures has grown significantly as a result to increasing concerns over deteriorating infrastructure, changing building codes and natural calamities. Retrofitting is one of the best processes to make an existing building safe against future coming earthquakes or other environmental forces. Retrofitting is the process of adding new features to older buildings, bridges and many other structures. It aims to strengthen the structure, to satisfy the load carrying capacity of structure and seismic design. This paper includes study of research papers published in past years related to various methods of retrofitting such as seismic retrofitting, retrofitting by glass fibers, retrofitting by chemicals such as epoxy resin and many other methods. Structures lose their strength in some years, some structures are important in view of public, social or any historical. Retrofitting helps to increase the strength, resistivity and lifespan of structure. Key Words: Retrofitting, Strength, Safety.

Mechanical Characteristics of Cracked Lining Reinforced with Steel Plate–UHPC Subjected to Vertical Load

The steel plate reinforcement method is widely used for strengthening damaged linings. Nevertheless, low durability is one of the disadvantages of the steel plate reinforcement method, which uses epoxy resin as the interface binder. To enhance the load-bearing performance and strengthening effect of steel-plate-reinforced structures, this study introduced ultra-high performance concrete (UHPC) as the reinforcing bonding layer and proposed a novel method for steel plate–UHPC reinforcement of cracked linings. A mechanical performance model test was conducted on a 1/5 scale lining model using a loading test device to evaluate the load-bearing performance and stress deformation of both conventional steel plate and steel plate–UHPC reinforced cracked linings. The characteristics, mechanisms of failure, and impacts of strengthening of the steel plate reinforcement method and steel plate–UHPC reinforcement method for cracked linings were compared. A numerical simulation model was developed to investigate the reinforcement effect of cracked linings using steel plate–UHPC reinforcement. The analysis included examining the influence of steel plate thickness, UHPC bonding layer thickness, and reinforcement timing. Model test results show that the overall damage mode of the steel plate–UHPC-reinforced structure had good elastic–plastic behaviour, and the deformation and damage process under the vertical concentrated load can be divided into four typical phases. Compared with the traditional steel plate reinforcement, the ultimate load-carrying capacity and ductility of the steel plate–UHPC-reinforced structure were increased by 53% and 366%, respectively, showing significantly better load-carrying capacity and deformation performance. Numerical simulation results show that the reinforced structure’s load-carrying capacity and stiffness enhancement rate increased non-linearly with the increase in UHPC layer thickness and steel plate thickness. However, reasonable reinforcement timing exists for steel plate-UHPC reinforcement, and too late reinforcement timing leads to a decrease in structural load-carrying capacity and stiffness enhancement rate.

Multiscale analysis of the flexural performance of FRP reinforced concrete structures

Based on existing experimental data and analysis, seven different fiber-reinforced polymer (FRP) bar models including carbon fiber-reinforced polymer (CFRP), basalt fiber-reinforced polymer (BFRP), aramid fiber-reinforced polymer (AFRP), glass fiber-reinforced polymer (GFRP), GFRP and CFRP combined (G–C), GFRP and AFRP combined (G–A), BFRP and CFRP combined (B–C), and BFRP and AFRP combined (B–A) were established. Finite element simulation analysis was conducted on seven different FRP bar combinations under static load bending tests. The flexural behavior of the specimens reinforced with different FRP bar combinations and their influencing factors were analyzed. The results showed that using AFRP as the reinforcement material for FRP composite bars in FRP reinforced concrete beams cannot effectively enhance the overall load-carrying capacity of the composite bars. The combination of CFRP with GFRP and BFRP bars significantly increases the stiffness of the FRP bar structure and improves the structural load-carrying capacity of the concrete beams.

Mechanistic Study of Failure in CFRP Hybrid Bonded-Bolted Interference Connection Structures under Tensile Loading.

Hybrid bonded-bolted composite material interference connections significantly enhance the collaborative load-bearing capabilities of the adhesive layer and bolts, thus improving structural load-carrying capacity and fatigue life. So, these connections offer significant developmental potential and application prospects in aircraft structural assembly. However, interference causes damage to the adhesive layer and composite laminate around the holes, leading to issues with interface damage. In this study, we employed experimental and finite element methods. Initially, different interference-fit sizes were selected for bolt insertion to analyze the damage mechanism of the adhesive layer during interference-fit bolt installation. Subsequently, a finite element tensile model considering damage to the adhesive layer and composite laminate around the holes post-insertion was established. This study aimed to investigate damage in composite bonded-bolted hybrid joints, explore load-carrying rules and failure modes, and reveal the mechanisms of interference effects on structural damage and failure. The research results indicate that the finite element prediction model considering initial damage around the holes is more effective. As the interference-fit size increases, damage to the adhesive layer transitions from surface debonding to local cracking, while damage to the composite matrix shifts from slight compression failure to severe delamination and fiber-bending fracturing. The structural strength shows a trend of initially increasing and then decreasing, with the maximum strength observed at an interference-fit size of 1.1%.

Study of Mechanical Properties of Three-Dimensional Framed Plate Protective Structures with Negative Poisson’s Ratio

In this paper, the negative Poisson’s ratio and rigidity of a protective structure are improved to allow the structure to exert a negative Poisson’s ratio effect in multiple directions and to enhance the structural load-carrying capacity. Therefore, a 3D framed plate honeycomb is designed on the basis of a traditional 2D negative Poisson’s ratio honeycomb. The Poisson’s ratio and modulus of elasticity are derived, and the equivalent mechanics model (EMM) of a 3D framed plate protective structure is established by combining bending deformation, shear deformation, and compression deformation. To verify the validity of the equivalent mechanics model (EMM), a compression test and numerical simulation study are carried out by combining 3D printing technology and numerical simulation methods. In addition, the effects of structural parameters on the modulus of elasticity, negative Poisson’s ratio, and other mechanical properties are discussed. The results show that, under vertical loading, the equivalent Poisson’s ratio and the modulus of elasticity of the cell elements decrease with the increase in the ratios of the lengths of the cell element walls in the upper and lower planes to the length of the diagonal cell element in the concave direction. In addition, it is shown that the elastic modulus increases with increasing concave angle and thickness. Moreover, under lateral loading, the equivalent Poisson’s ratio of the cell elements increases with the ratios of the lengths of the upper and lower planar cell element walls to the length of the diagonal cell element walls, with the angle of concavity and with the thickness of the plate frame, while the modulus of elasticity of the cell elements exhibits the opposite trend and decreases with the thickness of the framed plate structure.

Corrosion-resistant L12-strengthened high-entropy alloy with high strength and large ductility

Corrosion-resistant alloys with high strength and large ductility are desirable for applications in harsh environments where high structural load-carrying capacity is required. In this work, we designed an L12-strengthened high-entropy alloy (HEA) of composition (NiCo)77Cr13Al5Nb5 (at.%) that combines excellent mechanical properties and good corrosion resistance. The formation of a thin passive film of non-stoichiometric compounds with an amorphous structure, characterized by an enrichment of Cr2O3 and Nb2O5, contributes to the superior localized corrosion resistance. The precipitation strengthening brought about by coherent L12 particles and the multi-stage plastic deformation dominated by stacking faults (SFs) provides ultrahigh strength and appreciable ductility, respectively.

Study on progressive collapse demolition method of double-layer space truss

This paper conducted a demolition test of a double-layer space truss (DLST) to investigate more efficient, safe and environmentally friendly demolition methods of truss systems. The high-speed 3D displacements of representative joints and the global dynamic strain response of the structure were well collected. The internal force redistribution and load-carrying mechanisms of DLST structures during demolition were explored. The results indicate that new equilibrium states were sought in the DLST through local and global internal force redistribution. When the main force transmission members were removed, the load-carrying mechanism of the DLST underwent sudden changed, which resulted in a snap-through in the structural load-carrying capacity. The test DLST exhibited three load-carrying mechanisms in time sequence during the proposed demolition: arch action, catenary action, and beam action. The theoretical vertical load-carrying capacity provided by each load-carrying mechanism was investigated separately. Finally, a progressive collapse demolition method was presented for the engineering DLST structures subjected to certain demolition external loads.

Data-driven ensemble learning approach for optimal design of cantilever soldier pile retaining walls

Cantilever soldier pile retaining walls are used to ensure the stability of excavations. This paper deploys ensemble machine learning algorithms towards achieving optimum design of these structures. A large dataset was developed consisting of 40,569 combinations of pile geometry, external loading, soil properties, and concrete unit cost, with two different values of soil reaction coefficient. Optimum pile diameter that minimizes the total cost of the retaining wall was computed considering the structural load-carrying capacity as the optimization constraint. The dataset was split into training and testing sets at 70% to 30% ratio. The predictive accuracy of the ensemble machine learning models was appraised on the testing dataset using various statistical metrics. Model performance was also evaluated for its ability in predicting the optimum pile diameter. The developed models demonstrated excellent predictive accuracy. Furthermore, the effect of different input variables on the model predictions was explained using the SHapely Additive exPlanations (SHAP) approach. Through the SHAP algorithm, the pile length was identified as the design variable having the most significant effect on the optimum pile diameter. The study demonstrates ensemble learning techniques as a viable alternative to the traditional techniques in the optimum design of cantilever soldier pile retaining walls.

Mechanical performance of hybrid high-strength steel composite cellular beam under low cyclic loading

This study aimed to compensate for the impairments in structural load-carrying capacity and stiffness caused by conventional reduced web section beams, and to meet the strength design requirements for engineering. A new hybrid high-strength steel composite cellular beam (HHS-CCB) using high-strength steel in the beam flange and ordinary steel in the web was proposed. A composite cellular beam between the rigid joint and inflection point in the frame structure was selected as the research object, and low cyclic loading tests were conducted on one homogeneous ordinary steel composite cellular beam (HOS-CCB) and four HHS-CCB specimens. The effects of the hybrid use of high-strength steel and ordinary steel on the failure modes, load-carrying capacities, strength and stiffness degradation, ductility, and energy-dissipation capacities of the composite cellular beams were investigated. The test results show that with reasonable values for the diameter of the web opening and for the distance from the first opening at the beam end to the column surface (abbreviated as the hole edge distance), the HHS-CCB specimens exhibit local plastic damage at the first opening at the end of the beam but maintain a good ductility, stiffness degradation, strength degradation, and energy dissipation capacity, while significantly improving the structural load-carrying capacity loss owing to the web opening. Compared with HHS-CCB specimens using HHS in both the upper and lower flanges, the HHS-CCB specimens using HHS only in the lower flange show superior mechanical properties. Considering the poor plastic deformation capacity of HSS, the steel plate strength of the flange should not be much higher than that of the web to ensure the full development of plasticity in the cross-section, and Q460 steel or Q550 steel is generally recommended. A nonlinear finite element (FE) model was developed using ABAQUS software to predict the hysteresis behavior of specimens. Numerical simulation shows that the simplified FE model can be used to simulate the hysteresis performance of HOS-CCB and HHS-CCB.

A low computational cost optimization procedure for axial load carrying capacity of the multi-beam structure

The paper presents an improved algorithm to compute an axial load carrying capacity of the specific multi-beam structure in order to failure avoidance. The former approach based on the finite element method is reduced to determine a relation between the axial load and axial displacement for a single beam, while the time-consuming FE procedure applied on several beams is replaced with a numerical optimization process. The developed approach provides faster and simpler computation of the minimum axial load carrying capacity of the structure considering the beam length tolerances, where the results are in a good agreement with the complex FE analysis. Supporting theoretical and experimental analyses were performed to confirm the correctness of the mentioned method where the load carrying capacity of the multi-beam structure made up of six steel circular beams was analyzed.

Postbuckling responses of porous FGM spherical caps and circular plates including edge constraints and nonlinear three-parameter elastic foundations

An analytical investigation on nonlinear stability of porous functionally graded spherical caps and circular plates under uniform external pressure and elevated temperature, respectively, is presented in this article. Porosities are evenly and unevenly distributed within the structures and the effective properties of functionally graded material (FGM) are determined according to a modified rule of mixture. Governing equations are established within the framework of classical theory taking into account geometrically nonlinear terms, initial geometric imperfection, and interactive pressure from nonlinear three-parameter elastic foundation. Both temperature dependence of material properties and tangential elasticity of edge constraint are included. Approximate analytical solutions are assumed to satisfy clamped condition of boundary edge and Galerkin method is applied to derive load-deflection relations from which buckling loads and postbuckling paths are determined. Numerical results indicate that porosities have deteriorative and beneficial influences on load-carrying capacity of structures under external pressure and elevated temperature, respectively. Furthermore, the snap-through buckling response of pressurized FGM spherical cap can be alleviated and even eliminated by virtue of elastic foundations with suitable stiffness parameters.

Experimental Study on the Mechanics Characteristics of CFRP Strengthening of Highway Tunnels at Different Damage States

Cracks and other diseases may occur in the long-term operation of highway tunnels and reduce the structural load-carrying capacity. Strengthening using carbon fiber reinforced polymer (CFRP) sheets and other materials could extend the service time of the tunnels. However, the process of strengthening tunnels is remarkably different from the process of strengthening aboveground structures because of the secondary load. In order to understand the development of stress and deformation of strengthened tunnels under secondary load, a 1 : 10 scaled model was tested to simulate the tunnel strengthened with CFRP under different damage states. The test results show that CFRP strengthening improved the stiffness of the structure and inhibited the propagation of the existing cracks. The peeling of the CFRP sheets made the strengthened structure quickly lose its load-carrying capacity, causing the instability of the structure. The failure loads of the structures strengthened at different damage states were essentially the same, with an average value of 184% of the original failure load. Nevertheless, the early strengthening helped control the structural deformation. The test results also demonstrate that the bonding strength between the CFRP and the lining is essential for strengthening effectiveness. This study provides a theoretical basis for similar engineering reinforcement designs.

Tensile behavior of bio-inspired hierarchical suture joint with uniform fractal interlocking design

Hierarchical interlocking leads to optimal mechanical properties for sutures in nature. Inspired by this, a design method for describing a hierarchal triangular suture joint based on Koch fractal interlocking is developed. The effect of geometrical interlocking was examined by the analysis of the load transmission between joined parts. Samples of hierarchal suture joints were fabricated by using a high-resolution 3D printer and tensile tests were conducted to examine the mechanical behavior of these joints. The surface displacement and strain fields were obtained using the Digital Image Correlation (DIC) technology where the images were taken by a high-resolution microscope camera. Finite element models of the hierarchal suture joints were generated to simulate the tensile responses and to predict the stress distributions and failure modes. The numerical results show good agreement with the experimental data. The results of this study show that the second order suture joint with a sinusoidal center line exhibits not only high strength but also high ductility. Moreover, by increasing the hierarchical order from two to three, the stiffness and strength do not improve while the fracture toughness actually decreases, suggesting that increasing the fractal complexity does not always lead to the improvement of the structure's load-carrying capacity, even with low iterations for the fractal complexity. The results obtained in this study can serve as a guideline to the engineering design of suture joints with fractal interlocks.

Progressive collapse behavior of joints in steel moment frames involving reduced beam section

In this study, nine laboratory tests were conducted to estimate the performance of earthquake-resistant structures, i.e., reduced beam section (RBS) connection, under a scenario in which the middle column is removed. Four types of joints were tested, namely, welded unreinforced flange – bolted web connection without RBS (WUF-B-NRBS), welded unreinforced flange – bolted web connection with RBS (WUF-B-RBS), welded unreinforced flange – welded web connection without RBS (WUF-W-NRBS), and welded unreinforced flange – welded web connection with RBS (WUF-B-RBS), to investigate the effect of RBS and different beam web connection methods. The experimental results involving the responses of general behavior, resistance mechanisms, failure modes, deformation shapes, and limit displacements are presented in detail. A performance comparison of different connection types indicated that the RBS connection exhibits the optimum performance against progressive collapse, and its practical rotational capacity is >1.9 and 2.7 times larger than that provided by Federal Emergency Management Agency (FEMA) 350 and Department of Defense (DOD) guidelines, respectively. Additionally, in the design of the RBS connection, the welded web connection joint exhibited good load-carrying capacity, whereas the bolted web connection joint performed poorly owing to early fracture near the bolt holes. Furthermore, the research parameters were extrapolated within and beyond the limits using ABAQUS. This demonstrated that by increasing the values of horizontal distance from the column flange to the beginning of the beam flange reduction, a, or the length of the beam flange reduction, b, is beneficial to structural load-carrying capacity and ductility. However increasing the value of depth of the beam flange reduction, c, has the opposite effect. Based on the comparison, the recommended design details of RBS connections are presented.

A comparison of structural collapse of fully clamped and simply supported hybrid composite sandwich beams with geometrically asymmetric face sheets

This paper focuses on structural collapse of fully clamped and simply supported hybrid sandwich beams of geometrically asymmetric carbon fiber-reinforced composite face sheets and an aluminum foam core under three-point bending. Both bending behavior and collapse mechanism have been explored and identified through the collapse mechanism map. Limit analyses have been conducted and these predictions are validated by experimental results. Experimental results show two active failure modes: face fracture and core shear. Effect of fully clamped boundary condition is to make bending deformation mechanism towards stretching of face sheets and core and strengthen the structural load-carrying capacity. Geometric parameters have significant influence on the initial failure load of hybrid sandwich beams under different boundary conditions. The initial failure modes are significantly affected by the mass distributions of face sheets with the same core thickness. The fully clamped sandwich beams with thick front face sheet have better fracture-resistance. For the similar failure modes, the load-carrying capacity of the simply supported sandwich beam with thick front face sheet is higher than that with thin front face sheet. The initial failure load of face fracture increases with increasing the front face sheet thickness and the initial failure load of core shear increases with increasing the core thickness.

The collapse response of web-core sandwich panels partially filled with metallic foams under drop-weight impact

Thin-walled web-core sandwich structures are widely applied due to their weight specific mechanical performance. When subjected to a transverse load, the sandwich structures are apt to undergo local deformation which would considerably decrease the cross-sectional height and their global load resistance, especially under a concentrated load. In the paper, a novel method is proposed only to fill the upper compressive region of the web-core sandwich panels other than the whole cross section with metallic foams, which would effectively restrain the local deformation at the cost of slight increase of the structural total mass. The collapse response of web-core sandwich panels with four different reinforcing configurations under drop-weight impact is investigated using ABAQUS code. The numerical results show that the two empty panels without foam filler have a close valley force and the foam filler significantly improves the structural load-carrying capacity after the initial elastic peak force. Moreover, it is noticeable that the partially filled panel suggested here demonstrates the similar load resistance to the fully filled one and much more weigh specific energy-absorbing performance than the other three sandwich panels.

Structural reliability of RC elements with electric arc furnace slag as recycled aggregates

Sustainable development issues have become very important in the recent years, and the increased sensibility on sustainability of civil engineering structures are inducing to set the attention in recycling operations, also in the context of building materials. Concrete is the most used construction material in the world and its production requires a considerable demand of energy and raw materials, inducing significant gases emissions and huge quantity of natural materials and non-renewable resources exploitation. Electric Arc Furnace Concrete (EAF concrete) is a kind of recycled concrete in which its aggregates are the by-product of steel and iron producing processes, the so called Electric Arc Furnace (EAF) slag: while its environmental positive effect is easily understandable and intuitive, its effective usefulness and reliability in the building field is more difficult to accept. From the literature data, it seems that EAF concrete presents higher values of compressive and tensile strengths and modulus of elasticity than the natural concrete ones, and this might induces one to think that a higher structural reliability could be expected. However, it is worth recalling that this material is characterized by also a higher self-weight, thus, increasing the dead-load values. Hence, in this study, a reliability-based analysis of the structural load-carrying capacity of EAF reinforced concrete (RC) elements is carried out, through a fully probabilistic approach based on Monte Carlo simulations improved by Latin Hypercube method (LHS). The analysed RC elements are designed according to the Italian current construction code, and then, considering all the uncertainties included in the random variables definition, failure probability and relative reliability index are estimated and compared to the reliability of the same RC elements with natural concrete. Results indicate that, for the analysed cases, when EAF slag is used as coarse recycled aggregate, it is possible to guarantee the same reliability level than in RC elements realised with natural concrete.

Fire tests of steel tension rod systems with intumescent coating

Purpose The purpose of this paper is to investigate the performance of intumescent coating on tension rod systems and their components. Steel tension rod systems consist of tension rods, fork end connectors and associated intersection or gusset plates. In case of fire, beside the tension rods themselves, the connection parts require appropriate fire protection. Intumescent fire protection coatings prevent a rapid heating of the steel and help secure the structural load-carrying capacity. Because the connection components of tension rod systems feature surface curvature and a complex geometry, high demand is placed on the intumescence and thermal protection performance of the coatings. Design/methodology/approach In this paper, experimental studies were carried out for steel tension rod systems with intumescent coating. The examined aspects include the foaming and cracking behaviour, the influence of different dry film thicknesses, the heating rate of the steel connecting parts in comparison to the tension rods, and the mounting orientation of the tension rods together with their fork end connectors. Findings The results show that a decrease in surface curvature and/or an increase in mass concentration of the steel components leads to a lower heating rate of the steel. Moreover, the performance of the intumescent coating on tension rod systems is influenced by the mounting orientation of the steel components. Originality/value The findings based on fire tests contribute to a better understanding of the intumescent coating performance on connection components of tension rod systems. This subject has not been extensively studied yet.

Saturated analysis of pulse-loaded beams based on Membrane Factor Method

Under intense transverse loading, beams or thin plates will experience large elastic-plastic deflection. The membrane force induced by large deflection will enhance the structure's load-carrying capacity. Since 1950s, various analytical tools have been developed to account for the effect of membrane force and predict the final deflection of beams and plates under quasi-static or dynamic loading. Among those tools, Membrane Factor Method (MFM) has been proved to be a powerful one. On the other hand, it has been revealed that beams and plates under pulse loading exhibit a kind of saturation phenomena, i.e. there exist saturated impulse and saturated deflection due to the membrane enhancement of the beams and plates. The present paper will, for the first time, show that a combination of MFM and SA (Saturation Analysis) can provide an advanced theoretical tool for the study of large plastic deflection of beams under pulse loading. Then the complete solutions obtained by this MFM+SA approach are compared with modal solutions and FE simulations. Finally, a set of simple formulae are proposed for predicting the saturated duration and saturated deflection of beams to facilitate engineering applications.

Partial safety factors for the anchorage capacity of corroded reinforcement bars in concrete

Many reinforced concrete bridges in Europe and around the world are damaged by reinforcement corrosion and the annual maintenance costs are enormous. It is therefore important to develop reliable methods to assess the structural capacity of corroded reinforced concrete structures and avoid unnecessary maintenance costs. Although there are advanced models for determining the load carrying capacity of structures, it is not obvious how they should be used to verify the performance of existing structures. To confidently assess the bond of corroded reinforcement in concrete, for example, the calculation model must give a sufficient safety margin. When designing new structures, semi-probabilistic approaches (such as the partial safety factor method) are adopted to achieve the target reliabilities specified in structural design codes. This paper uses probabilistic methods to develop partial factors for application in an existing bond model, to assess the safety of corroded reinforced concrete structures. The response of the bond model was studied using Monte Carlo (MC) simulations for several design cases, with probability distributions fitted to the results. Partial factors were then derived, based on these distributions. Furthermore, an MC-based simulation technique called “importance sampling” was used to study the reliability of several deterministic bond assessments conducted using these partial factors. The results show that deterministic assessments which use the proposed partial factors lead to a safety level at least equal to the target value. The results presented in this paper will support the assessment of reinforced concrete structures with anchorage problems and give a reasonable approximation of the anchorage capacity with sufficient safety margin. When generalised to cover other failure modes and structural configurations, this will enable better utilisation of damaged structures and lead to major environmental and economical savings for society.