Load-displacement Characteristics Research Articles

Python-based numerical study on bolted joints between Fe-SMA and steel plates for structural reinforcements

In order to rehabilitate the performance of deteriorated steel structures, the active prestressed reinforcement employing new intelligent material, Iron-based shape memory alloy (Fe-SMA), has received extensive attentions. To reveal the mechanical properties of bolted joints between Fe-SMA and steel plates, a parametric method to establish finite element model via secondary development of ABAQUS based on Python scripts was proposed. It greatly reduces modelling costs and improves modeling efficiency. Besides, the proposed numerical models were verified against the experimental results by failure mode, final deformation, load-displacement characteristics, ultimate load-bearing capacity and initial stiffness. It is demonstrated that the numerical simulation results are in good agreement with the experimental results. What is more, a parametric study on thickness and geometry of steel plates, as well as the end distance, edge distance and thickness of Fe-SMA plate was conducted to verify the applicability of current leading specifications for steel structures. It is evident from the results that the thickness of Fe-SMA should be controlled to prevent failure of parent steel structures. Furthermore, similar to steel plates, the thickness of Fe-SMA plate can be considered linear and the failure of bolt can be avoided, as described in Chinese code GB 50017–2017 and Eurocode 3 Part 1–8. However, the minimum allowable edge distance in Chinese code GB 50017–2017 and the ultimate load-bearing capacity calculated by Eurocode 3 Part 1–8 is conservative for bolted joints between Fe-SMA and steel plates. Hence, it is urgent to formulate design specifications for this kind of bolted joints for the scientific and economical application of Fe-SMA in structural active reinforcements.

Load-Displacement Characteristics for Out-of-Plane of Unreinforced Masonry Walls

Load-Displacement Characteristics for Out-of-Plane of Unreinforced Masonry Walls

Modeling and strength validation of a building partition in frame construction

The article presents experimental research and numerical analysis of a building partition in frame construction. The subject of the analysis were sections of the building partition consisting of cold-bent steel profiles and plasterboard cladding. The experiment was carried out using a four-point bending test and recording a continuous load-displacement curve until failure. Next, a computational model based on the finite element method was developed to simulate the experiment. The results from the experimental tests were then compared with that obtained from the numerical analysis. The validation of the numerical model demonstrated a high level of agreement in terms of load-displacement characteristics. The use of numerical analyses provides an alternative to time-consuming experimental tests for estimating displacements of building partitions in frame construction

Load Bearing Capacity and Failure Analysis of Fibrous Plaster Wads

ABSTRACT Fibrous plaster is a culturally significant material used in high-status buildings from the late nineteenth century. Fibrous plaster ceilings are typically suspended using load-bearing fibrous plaster wads, which are attached to roof structure components. Understanding the behaviour of wads is highly significant, with important safety implications emphasised by the partial collapse of the Apollo Theatre ceiling in 2013. This study demonstrates an original, innovative test method for fibrous plaster wads that enables quantification of load capacities, with manufactured specimens representative of historic in situ wads. The methodology is rigorously evaluated for traditional and alternative wad designs, reinforced with hessian scrim or continuous fibre glass (CFG) mat, with and without steel wires in looped (untwisted) or looped-twisted configurations. Tensile tests generated load-displacement characteristics and determined failure modes including cracking of plaster, deformation and tearing of fibrous reinforcement, and if present, plastic failure of a wire. Results demonstrate that hessian performs better than CFG in axial tension and inclusion of a wire increases tensile load capacity and ductility. An industry standard repair wad with hessian and looped-twisted wire can typically support 3 kN. Looped wire performed better in isolation than looped-twisted wire, with higher peak loads and greater ductility, while looped-twisted wire carried a greater load as part of a fibrous plaster composite wad. The test methodology and findings have revealed new insights into the mechanical behaviour of wads which will inform commercial practice and conservation of historic buildings, preserving important heritage and promoting safe longevity.

Experimental study on the evolutive shear fracture behaviour and properties of cemented paste backfill

Shear stress prevalence in in-situ cemented paste backfill (CPB) makes understanding mode-II fracture behaviour and properties vital for the mechanical stability of the backfill structure. This study delves into the effect of cement content on CPB's shear fracture behaviour and properties. Results reveal that higher cement content leads to notable changes in load-displacement characteristics under mode-II loading, including steeper pre-peak slopes, higher peak loads, smaller peak-load displacements, and minimal post-peak resistance. However, increased cement content does not linearly enhance fracture properties. Furthermore, this study proposed predictive models to capture the influence of cement content on the evolutive fracture properties.

Comparison of frustum confining vessel (FCV) and full-scale testing for helical and expanded piles geotechnical performance

This study focuses on investigating the compression and pullout load-displacement characteristics of various pile types using a frustum confining vessel at Amirkabir University of Technology (FCV-AUT) and full-scale tests. The FCV-AUT provides a versatile platform for physically modeling reduced-scale deep foundations in a laboratory setting, accounting for flexible geometric and stress factors, and the full-scale load tests took place at two research sites situated along the southern coastline of the Caspian Sea. A comprehensive dataset comprising 40 model-scale and 15 full-scale load tests on different pile configurations (including conventional, helical, and expanded piles) installed in sands has been compiled to facilitate a geotechnical performance evaluation. Conventional piles, encompassing cast-in-place drilled shafts, H piles, pipe piles, and box piles, were considered in the analysis. Helical piles with one to three helixes and various expanded piles, including self-expanded, bubble, and wing piles, were also examined. Notably, among the tested piles, those installed through jacking and expanded piles displayed the highest resistance to compression. Conversely, helical piles and expanded piles demonstrated superior pullout performance when compared to conventional piles. Comparisons between physical model-scale tests and full-scale tests validate the suitability of FCV-AUT for assessing the geotechnical performance of diverse pile types in sand under realistic stress conditions.

Adoption of hooped-battens in cold-formed steel built-up columns for superior axial performance

Previous research on cold-formed steel (CFS) battened columns has identified the critical factors influencing their performance and accordingly, their limiting values for improved performance have been recommended. However, these studies involved connecting battens to the chords (channels) via their flanges, leaving the slenderest component disconnected from the web. This study introduces a novel hooped-batten (tubular-element) that links both webs and flanges of the chords together, thereby improving the structural integrity of the built-up system and curtailing the half-wave buckling length in the webs. As a result, axial strength and stability in these built-up columns may improve adequately. Firstly, a numerical model of a conventional CFS battened column was developed in ABAQUS and verified against test results on the same reported in literature. Afterward, the validated model was used to simulate the behaviour of CFS built-up columns with hooped-battens. Two key parameters i.e., unbraced chord slenderness and overall column slenderness were varied to explore their influence on the axial behaviour of built-up columns in terms of peak strengths, failure modes and load-displacement characteristics. The performance of the hooped-battened columns was compared with the identical conventional battened columns, which reflects that the former exhibits superior strength and stability characteristics over the latter.

Finite element modelling of reinforced concrete beam strengthening using ultra-high performance fiber-reinforced shotcrete combined with reinforcing bars

Ultra-high performance fiber-reinforced shotcrete (UHPFRS) is advanced concrete material for strengthening and repairing concrete structures, especially in narrow and difficult-to-access places. However, there has been little quantitative analysis of its strengthening capacity for concrete structures. Therefore, this paper develops a Finite Element (FE) model to simulate the structural behavior of reinforced concrete (RC) beams strengthened by a UHPFRS layer. The traction-separation model combined with the concrete damaged plasticity (CDP) model can accurately simulate the structural behavior of the NSC-UHPFRS composite beam by calibrating and validating with experimental results. Based on this FE model, a parametric study is conducted to asset the effect of the height, reinforcement ratio, and fiber orientation of the UHPFRS layer on the strengthening capacity of UHPFRS for the RC beam. The findings show that those parameters significantly impact the composite beam's load-displacement characteristics. It also contributes to a better understanding of applying UHPFRS in strengthening RC beams as well as structures to extend the service life effectively.

Seismic Performance Evaluation of Reinforced Concrete Buildings Retrofitted with a New Concrete Filled Tube Composite Strengthening System

This study proposes a concrete-filled tube composite strengthening system (CCSS), which is a new concept that can improve and supplement the vulnerability of existing CFT seismic strengthening methods. The CCSS seismic reinforcement method is easy to construct and integrates with the existing frame and reinforcement. It is one of the seismic strengthening methods that allows the simple calculation of the required amount of seismic reinforcement and can efficiently increase the strength when applied to existing reinforced concrete (R/C) buildings with non-seismic details dominated by shear failure. To examine the seismic safety of the proposed CCSS, two framework specimens were prepared based on an existing R/C building with non-seismic details. A pseudo-dynamic test was conducted on the unreinforced framework specimen and the framework specimen reinforced with CCSS to verify the seismic strengthening effect of applying CCSS to the existing R/C framework, i.e., in terms of the load–displacement characteristics and seismic response control capability. Based on the pseudo-dynamic test results, restoration of the force characteristics was proposed for the nonlinear dynamic analysis of the building reinforced with CCSS. Nonlinear dynamic analysis was conducted based on the proposed restoration of the force characteristics, and the results were compared with the pseudo-dynamic test results. Finally, for the commercialization of CCSS, nonlinear dynamic analysis was conducted on the existing whole R/C building with non-seismic details that was reinforced with CCSS. The seismic strengthening effect was then verified by examining the seismic response load, displacement characteristics, and the degree of seismic damage to the members based on the ductility ratio before and after seismic strengthening. The study results show that under a design basis earthquake with a magnitude of 200 cm/s2, the unreinforced R/C building exhibits shear failure, and light seismic damage is expected on the CCSS-reinforced building.

Analysis of Group Pile Bearing Modes of Permeable Pile Dam with Different Incoming Flow Angles

Based on ABAQUS finite element analysis software, the group piles and single piles under different incoming flow angles are compared and calculated, the horizontal bearing characteristics of the group piles of permeable pile dam under different incoming flow angles are analyzed, the pile-soil force is solved, and the change rules of the load-displacement characteristics, the displacement distribution of the pile body, and the distribution of the pile body bending moment are analyzed in detail. The study shows that: for the group piles with flow angles of 0° and 45°, the stresses from the upstream piles to the downstream piles tend to increase along the flow direction, and a stress concentration occurs at the downstream pile; for the group piles with flow angles of 90°, the stresses gradually increase from the central pile to the piles on both sides, and the stress concentration area is distributed at the outermost pile. With the increase of the incoming flow angle, the horizontal bearing capacity of the whole group of piles shows an increasing trend, but due to the effect of the group piles, the bearing capacity of the unit piles is smaller than that of the single piles; The displacements of the group piles at different incoming flow angles were greater than those of the single piles, and the turning points were all at about 12 m below the mud surface; With the increase of incoming flow angle, the group pile starts to change from rigid deformation to flexible deformation, the maximum bending moment of the pile body decreases, and the maximum value of the bending moment of the pile body occurs at the burial depth of 5 m. The maximum value of the bending moment of the pile body decreases with the increase of incoming flow angle.

Investigation of Load–Displacement Characteristics and Crack Behavior of RC Beam Based on Nonlinear Finite Element Analysis Using Concrete Damage Plasticity

Crack patterns provide critical information about the structural integrity and safety of concrete structures. However, until now, there has been a lack of sufficient studies on using the Finite Element (FE) method to investigate the characteristics of the crack patterns of reinforced concrete (RC) beams. Therefore, this study aims to develop an FE model to analyze the load–displacement and crack characteristics of a beam under a four-point bending test using the concrete damaged plasticity (CDP) model that accounts for the influence of mesh size. The simulation results were validated against experimental results, including mesh convergence analysis, energy balance, load characteristics, and crack patterns. A parametric study was then conducted using this model to investigate the influence of the rebar’s diameter, number, and spacing on the RC beam’s load–displacement characteristics and crack behavior. The findings demonstrate that the FE model accurately simulates the working behavior of the RC beam, with a maximum deviation at a cracking load of 8.7% and crack patterns with a maximum deviation in the mean crack height of 12.1%. In addition, the results of the parametric study suggest that the rebar configuration significantly affects the RC beam’s loading carrying capacity. This study provides deeper insights into the use of FE modeling for analyzing the behavior of RC beams, which can be useful for designing and optimizing structures in civil engineering.

Performance of Prefabricated Hollow Concrete-Filled Steel Tube Bracings on Transverse Bending: Experimental and Numerical Analyses

Due to the complex hydrogeological conditions in coastal regions, the use of internal bracing systems is necessary for supporting coastal foundation pits. This paper introduces a novel prefabricated foundation pit bracing system based on Hollow Concrete-Filled Steel Tube (H-CFST) structures that can be reused, offering significant economic and societal benefits. However, there is a severe lack of research on the application of H-CFST bracing systems. Through model tests and finite element simulations, the load-displacement characteristics and failure modes of prefabricated H-CFST bracing under transverse bending were investigated. The study revealed that when a wall thickness of 1.5 d was chosen, the self-designed hoop effectively mitigated strength and stiffness reduction at the bracing connection point. When the load reached 150 kN, the outer steel tube of the H-CFST components experienced localized yielding, and when the load was increased to 300 kN, the end supports exhibited cracking. Finite element analysis provided a more accurate prediction of bracing failure at 147.18 kN, and it offered valuable insights for optimizing the bracing design. Based on the above research, theoretical methods for calculating the bearing capacity of each bracing component under transverse bending conditions have been proposed and validated against experimental results.

Modeling of disc springs based on energy method considering asymmetric frictional boundary

Disc springs have excellent ability to absorb and dissipate energy, and are widely used as basic vibration isolation units in the design of vibration isolators for naval power systems. Focusing on the effect of friction on disc springs, a mechanical model of disc springs considering asymmetric frictional boundary is developed. The additional load to overcome the Coulomb friction damping is derived analytically by the energy method. Finite element analysis of disc springs is carried out and the results for large and small frictional conditions are compared with the theoretical results. Quasi-static experiments on disc springs are carried out and the proposed method is further validated. The results show that the analytical model based on energy method can describe the load–displacement characteristics of disc springs and their combinations under symmetric and asymmetric frictional boundaries accurately. Based on the analytical solution, the influence of the structural parameters of the disc springs on the damping effect is investigated. The stiffness and damping of disc springs are linearly related to the friction coefficient. In addition, the magnitude of the effect of asymmetry of the boundary friction on the mechanical properties of the disc springs varies with the structural parameters.

Load-Displacement and Stiffness Characteristics of Carbon-Fiber Reinforced Polymer (CFRP) Strengthened Reinforced Concrete Beams

In the current study, the efficiency of the carbon-fiber reinforced polymer (CFRP) strengthening technique is experimentally applied to reinforced concrete (RC) beams. In total, four types of test beam specimens are fabricated and tested, labeled as B-1, B-2, B-3, and B-4 for controlled specimens; the beams strengthened at high-level bending-moment regions, beams strengthened at bending-moment regions with enhanced development length, and U-wrapped shear plus flexural strengthened beams, respectively. The control specimens were fabricated under-reinforced in order to exhibit ductile failure according to ACI 318-08. The variation in the CFRP external configuration included a change in the bond length and use of U-shaped strips to limit the CFRP debonding. For strengthening the beams, Sika group CFRP was used in this study. The test specimens were subjected to three-point loading following seven days of strengthening. The test result includes failure modes, load displacement curves, and stiffness degradation. The proposed CFRP strengthening configuration of the RC beams (B-2, B-3, and B-4) demonstrated improved behavior of their load response as compared to that of control beam (B-1). The CFRP configuration used of RC beam B-4 exhibited almost double flexural strength to that of control beam B-1. Moreover, the deformability of the CFRP strengthened RC beams was also increased.

Experimental investigation on translaminar fracture behavior of cross-laminated bamboo

Cross-laminated bamboo (CLB) is a bamboo-based construction product with bamboo's advantages, which are green, environmentally protective, and sustainable. However, bamboo is easy to crack. Structural elements in bamboo constructions are assembled onsite, making splitting cracks easily form at joints and bolt connections. Therefore, it is essential to assess cracked structure safety with fracture mechanics. However, rare studies are addressed on fracture properties of bidirectional laminated bamboo, especially the translaminar fracture resistance, which represents the ability to arrest a catastrophic crack in structures. This paper studies the translaminar fracture properties of CLB composite using three-point bending beam tests. Load-displacement and load-CMOD curve characteristics, fracture process, and the failure modes of bidirectional laminated bamboo are analyzed. The R-curve expressed by the energy release rate is calculated by three methods. Results demonstrate that the R-curves obtained by the three different methods show similar results. The methods to determine R-curves employed in this study are simple and can describe the translaminar fracture toughness of laminated bamboo. The methods are validated by comparing the traction-separation relations calculated from the R-curves to those measured by double-edge notched tests (DENT). A comparison of the bidirectional laminated bamboo's energy release rate to the matrix-dominated energy release rate of unidirectional laminated bamboo reveals that bidirectional fiber arrangement has a remarkable improvement on the toughening of laminated bamboo at and after crack initiation. Moreover, the lay-up effects of CLB are analyzed by relating the energy release rate results to the failure pattern of fractured specimens. It is found that fiber pullout/bridging caused by 90°direction crack propagation around fiber bundles is the dominant toughening mechanism of CLB. The lay-up sequence of 0° and 90° plies also has an effect on 90°direction crack propagation; therefore, it will influence the toughness of CLB.

Load-displacement characteristics of self-compacting steel fiber reinforced concrete beams

Measurements of ductility in steel-fiber (SF)-reinforced self-compacting concrete (SCC) are rarely studied, despite the fact that many studies have concentrated on enhancing our understanding of the ductility index of the reinforced concrete element. The objective of this analysis is to evaluate the resilience of SCC beams strengthened with SF in the face of impact loads. All together, twelve reinforced SCC beams (six beams per set) were subjected to flexural tests (with and without steel fibers). In this investigation, the use of three different concrete strengths (designated as M30, M60, and M90) and two different steel ratios (qmin and qmax.) were carried out. The ductility Energy index (μE). of the experimented SCC beams is calculated from the load–displacement curves (P). The results demonstrate that beam deformation and the resulting restricted cracking can be avoided thanks to the increased flexural toughness of the fibrous self-compacting concrete beam samples. Fibrous material growth to SCC is also shown to be highly efficient. Its flexural strength, ductility index, and energy dissipation rate are all ductility energy index (μE.). Steel fibre content, steel reinforcement to concrete, and concrete compressive strength all contribute to the material's flexural strength.

Investigation on Behavior of Stone Columns in Soils under Predominant Settlement

Abstract: Recent advances have made stone columns more efficient and effective for addressing soil instability and improving the load-bearing capacity of weak soils. The present study aims to show that the behavior of stone columns can support most of the load transferred to the soil. The use of innovative materials, such as recycled glass, plastic, or tire shreds, as a replacement for traditional stone fill, has been investigated in recent years and has shown promising results in cost and sustainability. The development of advanced numerical modeling techniques, such as finite element analysis, has enabled engineers to understand the behavior of stone columns better and optimize their design for specific soil conditions. The load-displacement characteristics are considered governing parameters for understanding the capacity of stone columns. The study reveals that, stone column method significantly increases strength with the use of concrete waste lo demolished waste rather than stone aggregate, which can overcome this soil behavior. Additionally, stone columns are helpful for soil stabilization in areas with high water tables when other stabilization techniques are ineffective

Numerical study on upgrading beam-column connections in steel framed buildings for progressive collapse mitigation

This research used intensive numerical analysis to identify weak points and structural issues important to limiting the spread of collapse. As a consequence, four specimens of strengthened and unstrengthened steel beam-column joint assemblies were examined using scaled models. The data were used to validate numerical models. The control specimen was a simple shear joint from one of the four experimental assemblies. The second specimen was a bolted steel beam column joint used as a reference specimen to represent the ideal beam-column joint often used in intermediate moment-resisting frames in seismic zones across the globe. The third specimen, like the control, but it had two side plates welded together to strengthen the joint site, while the fourth specimen had high-strength, hot-rolled steel bars pretensioned inside the joint zone. ABAQUS software was used to create numerical finite element models to evaluate the behavior of steel frame assemblies before and after upgrading. The FEM matrix included 22 specimens with various characteristics, including plate thickness, steel grade, a contact between beam flange-strengthening plates, and a column that was either welded or not welded in the first scheme, number and diameter of hot-rolled steel bars were for the second scheme. The effectiveness of the strengthening techniques was established by comparing the mode of failure and load–displacement characteristics of the investigated specimens.

黄銅を用いた免震ダンパーとダンパー形状及び材料特性がその変形性能に及ぼす影響

The authors focus on the performance prediction of yielding dampers for seismic isolation structure. The performance of these devices is mainly evaluated by two characteristics. The one is load-displacement characteristics, and the other is the durability in the cyclic loading test. The research consists of two phases. First, proposing yielding damper with C4641 Naval brass and the modeling of non-linear mechanical properties which is used in the FEM analysis based on tensile test and load-displacement characteristic test for specific damper prototype. Second, the optimization was performed by applying concept of Quality Engineering with the L12 orthogonal array and FEM analysis and the effects of each design factors of prototypes on the performance of the damper were clarified. The authors conclude that the effect of optimization has been confirmed.

Numerical Investigation on Progressive Collapse Mitigation of Steel Beam-Column Joint Using Steel Plates.

This research employed extensive numerical analyses to locate the weak areas and determine the structural issues critical to preventing the spread of collapse. As a result, three specimens were tested using scaled models of strengthened and unstrengthened steel beam-column joint assemblies. The data were utilized to verify numerical models. One simple shear joint from the three experimental assemblies was used as the control specimen (unstrengthened joint). The second was a bolted steel beam-column joint utilized as a reference specimen to reflect the ideal beam-column joint generally employed in intermediate moment-resisting frames in seismic zones worldwide. Similar to the control, the third specimen (strengthened joint) had two side plates welded together to strengthen the connection site. Numerical finite element models were developed using ABAQUS (2020) software to extensively investigate the behavior of steel frame assemblies before and after upgrading. The FEM matrix comprised 17 specimens with varying parameters, including plate thickness, steel grade, a joint between the beam flange-strengthening plates, and a column that was either welded or not welded. The effectiveness of the strengthening techniques was established by comparing the mode of failure and load-displacement characteristics of the investigated specimens. The results indicate that the average increase in peak load due to a change in plate thickness for grades A36 and A572 is approximately 22% and 8%, respectively. Plates made of A572 steel increase peak load by 30%. All strengthened specimens attained catenary action, mitigating the possibility of progressive collapse.