Concentrated Load Research Articles

Basic static behaviours of an arch-cable composite bridge

To improve the material utilisation efficiency, a new type of arch-cable composite bridge was proposed based on the tied-arch bridge and beam string structure. Then, the stress mechanism of this system, as well as its deformation and stress under vertical loading, were analysed. Arch-cable composite bridges use arch ribs and main cables as their main load-bearing components. The main cable anchors are fixed to the arch springing in place of the tie rods employed in tied-arch bridges. The main cable is not only used to balance the thrust of arch springing but also directly bears dead and live loads. Theoretical analyses show that, in arch-cable composite systems, when the bending moment of the vault is zero, the ratio of dead load carried by the arch and the cable equals the ratio of the rise of the arch to the cable sag. In light of this situation, a simplified mechanical model of the arch-cable composite bridge was established to derive the analytical equations for the vertical deformation of the structure, as well as the bending moment of the arch rib and the horizontal force of the main cable under the impact of concentrated load and full-span uniform load. Subsequently, a finite element model (FEM) of the arch-cable composite bridge was established to verify the theoretical equations. The finite element simulation results are consistent with the theoretical values. Furthermore, a tied-arch model with the same span was established to compare and analyse the stress differences between its main members and those of the arch-cable composite bridge model. Results show that, compared with the tied-arch bridge, the arch-cable composite bridge bears fewer stresses on the arch rib, main cable and hangers, showing greater structural stiffness and excellent structural performance.

A Simplified Method to Analyze Dynamic Response of VLFS Based on the Kane Method

Abstract A two-dimensional (2D) simplified model of the very large floating structure (VLFS) is formulated based on Huston's interpretation of the Kane methodology. In this proposed model, the VLFS is considered as a series of discrete floating bodies connected by elastic hinges. The rotation stiffness of elastic hinges has a great influence on the dynamic responses of VLFS and its value is determined based on the vertical displacements equivalent between the simply supported beam model and the elastically hinged multiple bodies model with the same boundary conditions on a concentrated load. Reduced Kane equations are used in the actual dynamic analysis, once initial conditions and mechanical analysis of the system have been formulated. Validation of the Kane-based method and the reliability of the corresponding program developed are established by several comparative studies on a continuous structure and a hinged structure with three parts. The predictions based on the proposed method are essentially identical to the model test data and calculation results provided by related literature.

Machine learning (ML) based models for predicting the ultimate strength of rectangular concrete-filled steel tube (CFST) columns under eccentric loading

Concrete-filled steel tubes (CFSTs) are popularly used in structural applications. The accurate prediction of their ultimate strength is a key for the safety of the structure. Extensive studies have been conducted on the strength prediction of CFSTs under concentric loading. However, in real situation CFSTs are usually subjected to eccentric loading. The combined compression and bending will result in more complex failure mechanisms at the ultimate strength. The accuracy of methods in design codes is usually limited due to their simplicity. In this study, three machine learning (ML) methods, namely, Support Vector Regression (SVR), Random Forest Regression (RFR), and Neural Networks (NN), are adopted to develop models to predict the ultimate strength of CFSTs under eccentric loading. A database consisting of information of 403 experimental tests from literature is created and statistically analyzed. The database was then split to a training set which was used to optimize and train the ML models, and a test set which was used to evaluate performance of trained ML models. Compared with the methods in two typical design codes, the ML models achieved notable improvement in prediction accuracy. The parametric study revealed that the trained ML models could generally capture the effect of each primary input feature, which was verified by the relevant experimental test results.

Calculations of additional axial force and coupling ratio for coupled shear walls

The additional axial forces (AAFs) in walls and coupling ratio (CR) of coupled shear wall (CSW) systems have significant effects on the local behaviors of the individual walls and the overall structural performance, respectively. A new analytical approach to obtaining AAF and CR for three different types of lateral loads has been proposed to avoid complex numerical simulations or time-consuming analyses. Firstly, a differential equation with respect to AAF was established using a concise expression of the external moment; AAF calculation method considering triangular, uniform, and top concentrated lateral loads was developed. Secondly, CR calculation formulas for three different types of lateral loads were derived based on the formulas of AAF and applied to simplify the formulas of calculating top lateral deflection of CSWs. Thirdly, the calculation method of AAF, CR and the simplified formulas of top lateral deflection were validated by conducting numerical simulations using ABAQUS and OpenSees. Finally, the advantages of the proposed methods as well as the impact of lateral load types and nonlinearities, etc. were discussed. It was found that AAF and CR could be efficiently calculated by the proposed approach for CSWs including asymmetric ones subjected to three typical lateral loads, and the relative errors compared with numerical simulation are less than 10%. Besides, different types of lateral loads affect the distributions of AAFs and the values of CR.

Performance evaluation of normal- and high-strength concrete column specimens reinforced longitudinally with different ratios of GFRP bars

Glass fibre-reinforced polymer (GFRP) bars, as reinforcement in concrete structures, have several desirable properties over conventional steel bars, such as high tensile strength, low density and resistance to corrosion. However, there are still some concerns about using GFRP bars as longitudinal reinforcement in concrete columns primarily due to their low compressive strength and low modulus of elasticity. It is evident that the compressive behaviour of GFRP bars as longitudinal reinforcement in normal strength concrete (NSC) and high strength concrete (HSC) columns has not been extensively investigated to formulate adequate design guidelines. In this study, 12 reinforced concrete column specimens were tested under concentric compression loading. All the tested column specimens were 600 mm in height and 154 mm in diameter. The column specimens were divided into two groups as per the compressive strength of the concrete used in casting the column specimens, which were 45 MPa and 90 MPa. Each group consisted of six column specimens, one plain concrete column specimen and five column specimens reinforced transversely with 6 mm steel helices spaced at 40 mm pitch (transverse reinforcement ratio ρt = 2.2 %). Out of those five column specimens, one had no longitudinal reinforcement (ρ = 0), one was reinforced longitudinally with steel bars (ρ = 2.4) and the rest were reinforced longitudinally with GFRP bars (ρ = 2.7, 3.2, and 4.3 %). From testing results, it was observed that steel and GFRP bar reinforced NSC column specimens exhibited two peak axial loads, with a higher second peak axial load than the first peak axial load, whereas steel and GFRP bar reinforced HSC column specimens exhibited one peak axial load only. It was also observed that the contribution of the longitudinal steel bars was about two times the contribution of GFRP bars in both NSC and HSC column specimens. Finally, the ductility of GFRP bar reinforced NSC column specimens was greater than the steel bar reinforced NSC counterpart, whereas this trend was the opposite in the column specimens cast with HSC.

Numerical investigation and design of cold-formed lean duplex stainless steel Z-sections undergoing web crippling

This paper presents a numerical investigation on web crippling of cold-formed lean duplex stainless steel Z-sections under concentrated bearing loads. The two concentrated loading conditions are End-Two-Flange (ETF) and Interior-Two-Flange (ITF) as specified in North American Specification. The numerical models were firstly validated against the test results obtained from the literature. After successful verification, the models were used to perform a comprehensive parametric study. The critical parameters that affect the web crippling strength were considered and investigated, including web flat height-to-web thickness ratio, bearing length-to-web thickness ratio, inside bent radius-to-web thickness ratio, and bearing length-to-web flat height ratio. The numerical results were used to assess the current codified design rules from American Specification, Eurocode and North American Specification. It was found that these design specifications could not predict well the web crippling strengths of cold-formed lean duplex stainless steel Z-sections under the two loading conditions. Therefore, two design equations were proposed, including the modified unified equation and the Direct Strength Method (DSM). It is shown that the two proposed design equations generally provide more accurate and reliable strength predictions than the current codified design equations. Hence, the two proposed equations are recommended for the web crippling design of cold-formed lean duplex stainless steel Z-sections subjected to ETF and ITF loading conditions.

Modelling of Web-Crippling Behavior of Pultruded GFRP I Sections at Elevated Temperatures.

The concentrated transverse load may lead to the web crippling of pultruded GFRP sections due to the lower transverse mechanical properties. Several investigations have been conducted on the web-crippling behavior of the GFRP sections under room temperature. However, the web-crippling behavior is not yet understood when subjected to elevated temperatures. To address this issue, a finite element model considering the temperature-dependent material properties, Hashin failure criterion and the damage evolution law are successfully developed to simulate the web-crippling behavior of the GFRP I sections under elevated temperatures. The numerical model was validated by the web-crippling experiments at room temperature with the end-two-flange (ETF) and end bearing with ground support (EG) loading configurations. The developed model can accurately predict the ultimate loads and failure modes. Moreover, it was found that the initial damage was triggered by exceeding the shear strength at the web-flange junction near the corner of the bearing plate and independent of the elevated temperatures and loading configurations. The ultimate load and stiffness decreased obviously with the increasing temperature. At 220 °C, the ultimate load of specimens under ETF and EG loading configurations significantly decreased by 57% and 62%, respectively, whereas the elastic stiffness obviously reduced by 87% and 88%, respectively.

Experimental investigation on anti-falling protection systems for reinforced concrete-brick composite floors

Reinforced concrete and brick composite floors are typical features of Italian buildings. In these floors, falling debris caused by the detachment of non-structural parts - such as portions of brick, plaster, or concrete joist cover - is quite frequent. To prevent injuries to people and economic losses due to property damage, nowadays public authorities and companies invest considerable resources to install fall protection systems on existing floors.In this context, the present work is addressed to the experimental investigation of the performance and failure mechanism of anti-falling protection systems composed of galvanised electro-welded steel wire meshes attached to the intrados of the slab. Tests are performed under quasi-static concentrated loads up to failure. Two configurations of the protection system are analysed: with and without the presence of plaster. Experimental findings show that: (i) the electro-welded steel wire mesh can withstand considerable load up to failure (ii) the application of plaster layer modifies the failure mode and considerably increases the load-bearing capacity and the stiffness of the system. Based on the experimental investigation, the study: (i) experimentally confirms the effectiveness of this method as an anti-fall system, and (ii) provides information about the behaviour of the system that is essential for its modelling.

Punching Shear Characterization of Steel Fiber-Reinforced Concrete Flat Slabs

Punching shear failure in thin slabs under concentrated loads can cause shear stresses near columns. The use of steel fiber is a practical way to improve a slab-column connection's punching strength and deformation capacity. In this study, the capacity and behavior of steel fiber-reinforced concrete flat slabs are examined under punching shear force. Ten small-scale flat slabs were tested, eight of which had steel fiber and two without. Two parameters are studied in this paper, which are the fiber volume ratio (from 0% to 2%) and the stub column load shape (circle and square). The test results include the concrete compressive strength, crack patterns, punching shear, and load-defection behavior of the slabs. Based on the experimental results, it was found that the punching shear capacity of slabs with steel fiber (S5) increased by 21.8% compared to slabs without steel fiber (S1), and the slabs with steel fiber had more ductility compared to the slabs without fiber. Doi: 10.28991/HIJ-2022-03-04-08 Full Text: PDF

Study on mechanism and influential factors of progressive collapse resistance of base-isolated structure

The progressive collapse of the structure caused by the partial failure of the structure will cause severe consequences and massive losses, and structural progressive collapse resistance has always been a hot topic of current research. In order to study the progressive collapse mechanism of base-isolated structures, the test study and numerical simulation of the base-isolated structures were carried out based on the vertical Pushover method and analysis of the variation rule of the capacity of the remaining structure and influence mechanism. The isolation bearing failure position, the size of the beam of the seismic isolation layer, the type of the isolation bearing, and the horizontal stiffness of the seismic isolation layer on the capacity of the remaining structure were compared and analyzed. The results show that the non-uniformity of the beams and the concentrated loading at the nodes were easy to form a linear catenary mechanism, resulting in more severe beam end damage than mid-span damage. In the case of side isolation bearing failure, due to the lack of sufficient lateral restraint, the capacity was significantly lower than other conditions, which were more likely to cause partly collapse. Therefore, setting more transfer paths to improve the structure’s resistance to progressive collapses was necessary. Increasing the size of the beam of the seismic isolation layer could improve the capacity of the remaining structure of the alternate load path in the base-isolated structure. The changes in the horizontal stiffness of the seismic isolation layer and the type of the isolation bearing have little effect on the progressive collapse resistance capacity of the remaining structure.

DYNAMIC AND STABILITY ANALYSIS OF AN INCLINED BEAM SUBJECTED TO MOVING CONCENTRATED LOAD

— The aim of this paper is to develop the dynamical and stability analysis of an inclined beam subjected to a moving concentrated load. The problem is solved for using the method of Laplace transformation for an initial-boundary-value problem, such that an integro-differential solution is obtained and used to simply deal with the condition of singularity by the load functional. The stability of general motion of the elastic system is determined by a direct variational approach. The result derived showed good agreement with that reported in literature.

Predictive models of behavior and capacity of FRP reinforced concrete columns

This paper proposes a new model for predicting the axial capacity and behavior of Fiber Reinforced Polymerreinforced concrete (FRP-RC) columns using a promising variant of Genetic Expression Programming (GEP). Current design codes, such as the ACI 440.1R-15 and the Canadian Code CSA S806, disregard the compressive contribution of FRP bars when used in compression members. The behavior of concentrically short FRP-RC columns has been widely investigated in the past few years; however, limited research has been dedicated to investigating the effect of load eccentricity and the slenderness ratio of FRP-RC columns. In addition, the methodologies adopted for including the effect of column slenderness remain a subject of debate, as no solid conclusions are withdrawn in this regard. In this paper, the experimental results of FRP-RC columns are gathered from the literature and used to formulate two GEP models to predict the axial capacity based on load eccentricity. The experimental data includes columns reinforced with different FRP types and subjected to concentric and eccentric axial compressive loads. In addition, the database comprises short and slender columns. The proposed GEP models are functions of concrete compressive strength, longitudinal reinforcing bars ratio, FRP bars elastic modulus, eccentricity level, and column dimensions. For the aim of comparison, a preliminary evaluation of previously suggested empirical equations/models for estimating the axial capacity of FRP-RC columns was carried out over the collected database. The proposed models showed superior accuracy in axial capacity prediction with coefficients of determination R2 equals to 0.978 and R2 equal to 0.992 for eccentric and concentric axial load, respectively. The proposed models were found to give reliable estimates of the axial capacity of columns reinforced with FRP longitudinal bars. Finally, a parametric study to evaluate the effect of each variable on the proposed models was conducted.

Asymmetric response of inelastic circular plates to blast loading

The dynamic behaviour of clamped circular plates subjected to the concentrated blast loading is studied. The load is applied at a non-central point of the plate, non-axisymmetric deflections are taken into account. An approximate theoretical procedure developed earlier is applied for the evaluation of residual maximal deflections. The solution technique is based on the idea of equality of the power of the internal and external work, respectively. As it was shown earlier this concept leads to results which are close to exact ones in the case of axisymmetric loading of circular plates, also in the case of circular cylindrical shells.

The Study of the Influence of Temperature and Low Frequency on the Performance of the Laminated MFC Piezoelectric Energy Harvester

MFC (Microfiber composite) piezoelectric transducers are one of the smart composite materials used among others in alternative energy sources and autonomous wireless sensors which exploit vibrational energy. This work presents the theoretical and experimental investigations of the integration of MFC piezoelectric transducers on epoxy glass fiber composite material and explores the capacity of power generation based on a variety of ambient temperatures and frequencies. The study examined the use of ambient vibrational energy to power small electronic devices of wireless sensor networks which eliminates the need for external power, periodic battery replacement costs, and chemical waste from conventional batteries. The test was conducted using a laboratory stand equipped with a thermal chamber and an Instron ElectroPulse waveform generator which induces a concentric cyclic load to the laminated beam. Laminated MFC was loaded with a low–frequency range, controlled displacement under different moderate temperatures. The test was conducted at temperatures ranging from 25 to 60 degrees Celsius and at frequencies ranging from 5 to 25 Hz. The results show that the voltage generated by the transducer is highly affected by both temperature and frequency of excitation.

Behavior of large-scale hybrid FRP-concrete-steel double-skin tubular columns subjected to eccentric compression

Hybrid FRP-concrete-steel double-skin tubular columns (DSTCs), consisting of an outer FRP tube, an inner steel tube and a concrete infill between the two tubes, are a novel form of hybrid columns which possess excellent mechanical performance and durability. Extensive studies have been conducted on such columns under concentric axial compression. However, limited research has been focused on the behavior of hybrid DSTCs subjected to eccentric compression which is a common loading case in practice. Therefore, an experimental program on nine large-scale hybrid DSTCs subjected to concentric or eccentric compression was conducted in the present study. The load eccentricity and the thickness of the filament wound FRP tube were the main test variables. The test results demonstrated that the hybrid DSTCs exhibited a highly ductile behavior under eccentric compression. A theoretical column model was then adapted by incorporating three stress–strain models for FRP-confined concrete for predicting the behavior of test DSTCs under eccentric compression. It was found that all the three stress–strain models provided reasonably accurate predictions for the axial load-carrying capacities of the test columns. However, the concentric loading stress–strain model led to significant underestimation in the deformation capacities of the test columns due to the neglect of the effect of eccentric compression.

Evaluation of the Structural Health Monitoring Results of the Applied Fiber Optics in the Pile-Raft Foundations of a High-Rise Building

Fiber optics are increasingly being used in structural health monitoring applications. In addition to the well-known advantages, they most reliably transmit the stress–strain condition of the structure in the long term. This article presents the results of structural health monitoring on the embedding of fiber optics in the upper layer of the raft over the entire area of a high-rise building in Astana city (Kazakhstan), including the 75-storey 320 m block R. Temperature and strain data were collected constantly via a distributed fiber optic strain sensing system (DFOSS). The analysis of strains in fiber optic chainage indicated that the compression strains were observed over the entire area of the building, with values from −20 to −40 µε and with progression of the compression loaded up to −80 µε along the core wall closer to the eastern facade of the building. Tension strains were concentrated along the extreme axes of the building, with a predominance in the southern part of the R block, as well as in the immediate vicinity of the columns, in a range of −20 to −40 µε, with separate spots from −40 to −60 µε. Individual patches of tension strains near the columns have been explained by the increased deflection of the raft under the application of a concentrated load (columns). Fiber optic monitoring results at the time of testing did not exceed the permitted values for high-rise building operation; however, they characterized the general picture of the strain in the raft plane and made it possible to determine the initiation of cracks in concrete at an early stage.

Numerical modeling of iron-based SMA confined concrete columns under axial compressive loading

This paper presents the results of a Finite Element (FE) model developed to simulate the behavior of confined concrete columns with iron-based shape memory alloys (Fe-SMA) under compressive loading. The performed simulations aimed to accurately demonstrate the combined effect of external shape memory alloy (SMA) reinforcement and internal transverse steel reinforcement under different loading conditions and presented a simplified approach to model external confinement as discrete elements near the surface of the concrete element.The primary objective of this study was to develop a FE model that can be used to predict and replicate the response of actively confined columns using Fe-SMA. The FE model was developed using the results of an experimental study conducted on circular Fe-SMA confined columns under concentric loading. The experimental study evaluated the influence of: 1) the presence of internal reinforcement, and 2) the ratio of external SMA confinement used. The simplifications and approximations considered in the numerical approach to predict the capacity and deformation responses showed to be adequate, and the results obtained were in good agreement with the compressive behavior of the actively SMA confined columns obtained from the experimental work.In addition to the concentric case, eccentric loading simulations are presented in this study to evaluate the combined confinement mechanism in terms of the structural element response to a different loading configuration. The predictions obtained in terms of load-carrying capacity and deformations can be used to expand the research work done using the SMA as a form of active confinement.

Investigations on the influence of load width on web compression buckling strength of wide-flange steel members

A comprehensive study on web-compression buckling strength of wide-flange steel members subjected to concentric transverse loads spread over lengths longer than member section depth is presented in this paper. Calculation methodologies previously developed for web-compression-buckling strength of wide-flange steel members were established for use in beam-to-column moment connections, where the load width is relatively very narrow compared to the depth of the section, therefore does not include load width as a parameter in strength equations. More recently developed calculation procedures that account for load widths are typically limited to member section depth and are merely based on numerical models, and lack experimental evidence that validates these models. This study presents experimental research on steel wide-flange members subjected to transverse compression loading by having the load length as the primary variable. Experiments were conducted on specimens with measured imperfection levels and provided results on the buckling strength, displacement, and strain variation of the web portion during testing. The experimental program also investigated the potential of creep under sustained loading on web compression buckling strength of wide flange members at load levels near buckling strength. Benchmark numerical models using the finite element method were developed using the test results to obtain insights into the observed behavior and were employed in conducting numerical parametric studies to investigate the sensitivity of results due to load width and the angle of the applied load for various cross sections. The results obtained from the experimental and numerical studies were compared with the calculation methods provided in the North American and European design codes to evaluate their accuracy. The parametric study results were also used to develop an analytical calculation procedure for estimating the web-compression-buckling strength of steel wide-flange shapes subjected to vertical and inclined loading.

Experimental investigation of GFRP‐reinforced concrete columns made with waste aggregates under concentric and eccentric loads

AbstractNowadays, reducing the waste and recycled material resources in nature and environmental protection, as well as reducing the use of natural resources, has gained the attention of engineers and researchers. One of the ways to reach this goal is to use waste and recycled materials in new concrete members' construction. Additionally, using glass fiber‐reinforced polymer (GFRP) rebars has gained high consideration owing to their advantages such as high tensile strength and corrosion resistance. Therefore, this study aims to measure the influence of recycled coarse aggregates (RCA) on the structural performance of reinforced concrete (RC) columns reinforced by GFRP rebars under concentric and eccentric loading conditions. A total of 24 RC columns were cast and subjected to concentric and eccentric loads with different eccentricity ratios (e/h):0 (no eccentricity), 0.25 (moderate eccentricity), and e/h = 0.5 (high eccentricity). A total of 18 columns were strengthened with longitudinal GFRP rebars, and six specimens were considered control samples reinforced by steel rebars. RCA was used at two contents of 0% and 100% in terms of weight as a substitute for natural coarse aggregates (NCA). In addition, to measure the influence of transverse reinforcement, three different spacings were considered: 60, 120, and 180 mm. Evaluation of axial behavior, the strain of rebars and concrete, and the ductility were the main aims of this study. Moreover, a comparison between the experimental results and existing standards was carried out. Findings revealed the adequate axial resistance of specimens when RCA was used. Therefore, RCA incorporation improved the axial resistance of GFRP‐RC columns by about 25% and 35% when the stirrup spacing declined by 60 and 120 mm, respectively in comparison with the same specimens made with NCA. However, the influence of RCA on the RC columns' axial behavior was declined by raising the eccentricity distance.

Nonlinear analysis of flat slab‐column connections to optimize the use of HPFRC under monotonic vertical loading

AbstractNumerous studies have shown that incorporating fibers in concrete can improve its mechanical properties, including tensile strength and toughness. Due to these outstanding properties, the use of fiber‐reinforced concrete (FRC) composites has been investigated for applications in structural members subjected to shear, in which brittle failure mode may occur. An example of this type of application is the use of high/ultrahigh‐performance fiber‐reinforced concrete (HPFRC/UHPFRC) in flat slab‐column connections as an alternative to shear reinforcement. The experimental results revealed that the use of advanced concrete materials led to an increase in the punching shear and deformation capacities. Despite these advantages, the use of HPFRC/UHPFRC in practical design is somehow limited by the lack of guidelines in codes for this type of new material. Furthermore, the study of constitutive models for nonlinear finite element analysis is also necessary. In this regard, this article addresses the simulation of two‐way slabs with HPFRC, subjected to concentrated monotonic vertical loading, tested in a previous experimental study, where the HPFRC was used only in a limited slab region around the column, and the rest of the slab was cast with normal strength concrete. The numerical models were developed in the commercial finite element software DIANA. The concrete nonlinear behavior was modeled by a total strain‐based constitutive model, in which the HPFRC softening is represented by a tensile stress‐crack width (σ − w) relationship. The validity of the numerical model is checked by the comparison with the experimental results and a punching shear mechanical model, leading to the formulation of a closed‐form equation. Finally, a parametric study was conducted to extrapolate the results obtained in the experimental campaign and to optimize the use of HPFRC to obtain a more economical and sustainable solution.