Initial Stiffness Research Articles

Finite element investigation of circular rubberized CFST beams under Four-Point loading

This paper presents the nonlinear finite element (FE) analysis of circular concrete-filled steel tubes (CFST) with rubberized infill concrete (RuC) under flexure. The FE models were first developed and validated against the existing experimental test results of the CFST beams with normal concrete (NC) and RuC (15% and 30% rubber replacement). Good agreement between the numerical and experimental results was obtained. The validated models were then used to perform parametric studies of forty-five specimens to examine the effect of parameters such as tube diameter, tube thickness, steel yield strength, loading distance, span length, and rubber replacement ratio on the CFST beams under four-point bending. Steel tube properties have a direct influence on the beam moment capacity, whereas loading distance and span length have negligible effects on the ultimate capacity. With 30%RuC, ductility improved significantly, but a lower capacity of up to 14% reduction was found compared to CFST beams with NC. A comparison of the initial flexural stiffness of the numerical results with four design codes showed that AIJ and BS5400 gave more accurate predictions compared to EC4 and AISC.

Experimental characterization of CFRP single lap joints under tension at various loading rates

The objective of this study is to experimentally characterize the performance of four different composite/composite single lap joint configurations at various loading rates. The four joint configurations are single bolted joint, simply bonded joint, single bolted hybrid joint (a single bolt is used along the lap length of a simply bonded joint) and multiple micro bolted hybrid joint (four micro-bolts are used along the lap length of a simply bonded joint). The lap joints are tested at various loading rates using tensile split-Hopkinson bar and fatigue testing machine. Experiments reveal that, for a given joint configuration, the peak load, initial stiffness, and energy absorbed generally increased with the loading rates, whereas the plateau load is relatively insensitive to the loading rates. Finite element analysis (FEA) using the commercial software Abaqus/Explicit solver for all the configurations is also performed to simulate experimental loading conditions. It has revealed that by accounting for rate dependency of adhesive one can qualitatively explain the experimental observations.

Experimental testing of post-tensioned steel-timber hybrid frames equipped with energy-dissipating braces

The weak properties of wood in perpendicular-to-grain direction have imposed significant design challenges for post-tensioned (PT) timber frame structures. To resolve the challenges, the authors of this study have introduced a novel solution, the steel-timber hybrid PT frame. To further enhance its lateral performance, additional damping and stiffness (ADAS) braces were integrated into the hybrid frame. In this study, the feasibility of the combination was experimentally examined at the system level. Cyclic tests were conducted to evaluate the performance of two 2/3 scaled frame specimens: a conventional PT timber frame and a PT steel-timber hybrid frame with ADAS braces. The combination of a hybrid frame with ADAS braces showed substantial enhancements in lateral strength, initial stiffness, system ductility, and energy dissipation compared to the conventional PT timber frame. The experimental results highlighted the significant role of ADAS braces in enhancing energy dissipation, while their contribution to stiffness was less dominant. Analytical analysis further revealed an inverse relationship between the increase in ADAS contribution to lateral stiffness and the self-centering competence of the frame. A design equation was proposed to assist practitioners in achieving an optimal balance between the self-centering capacity of the PT hybrid frame and the stiffness enhancement provided by ADAS braces.

Experimental study on seismic performance of frame with steel-hollow core partially encased composite spliced beam

This paper conducted design and experimental study on frame specimen equipped with steel-HPEC (Hollow-core partially encased composite) spliced beams (SHS beam in short). SHS beams are comprised of two bare steel beams and an HPEC beam with thinner flange plates, present similar deformation and bearing capacity to traditional I-shaped steel structure, in addition to the benefits of good lateral stiffness and steel saving. Lateral low-cyclic loading tests were conducted on a bare steel frame and a frame with SHS beams to investigate their failure modes, seismic performance, and evaluate the feasibility of implementing SHS beams in frame structures. The frame specimen with SHS beams exhibited similar failure modes as those observed in steel frame specimen. Due to the higher stiffness of SHS beams, which effectively limited out-of-plane deformation in frame, SHS beam frame presented higher initial lateral stiffness, ultimate bearing capacity and energy dissipation capacity when contrast with bare steel frame. For calculations, SHS beams could be construed as stepped beams with variable rigidity. Finally, the calculation methods and formulas for initial lateral stiffness and ultimate bearing capacity of both the frames with SHS beams and bare steel frames were proposed, and the calculated results agreed well with the experimental values.

Low-velocity impact performance of orthogonal grid reinforced CFRP-foam sandwich structure

Orthogonal grid structures, which are widely used in engineering, are incorporated into the foam to form the grid reinforced core. However, the impact resistance of this type of sandwich structure varies with position. In this paper, the low-velocity impact performance of orthogonal grid reinforced CFRP-foam sandwich structure at different positions was investigated. The drop hammer low-velocity impact tests were conducted at 30 J, 50 J and 80 J energy for the intersection, rib, and center positions, respectively, and the impact resistance of the three positions was further compared with the impact data. The test results showed that the intersection and rib exhibited fiber fracture and delamination of CFRP face and grid, as well as foam crushing and cracking. The center position showed face perforation and foam crushing. At the same impact energy, the intersection position had the strongest impact resistance, with an initial stiffness about 18 % higher than that of the rib, and their peak load per unit mass was higher than that of CFRP-foam sandwich panels, and the center was the weakest. In addition, numerical simulations were performed which were in good agreement with the tests, and the damage processes at different stages were discussed. The lightweight, high impact resistant sandwich structure proposed can provide a reference for structural design.

Research on mechanical property of glued timber truss connected by steel plates and bolts

In order to deeply understand the mechanical performance of glued-laminated timber trusses connected by steel-plates and bolts, two groups of truss specimens were designed and fabricated by changing the connection forms of the nodes, while maintaining the height and span of the trusses unchanged. Each group of truss specimens was subjected to the mid-span load. At the same time, finite element numerical analysis was conducted on the tested trusses. Based on the agreement between the experimental and numerical simulation results, the influence of the parameters of thickness-to-diameter ratio and height-to-span ratio on the mechanical performance of these trusses was explored. The research results show that both types of node connections in the glued-laminated timber trusses have good bearing capacity. The main failure modes are the splitting of the diagonal web members at the mid-span node and the crushing failure of the bolt holes. The HJ-C type truss, which has the upper and lower chord members connected, exhibits better ductility, greater stiffness, and better structural synergy in load-bearing capacity. As the thickness-to-diameter ratio increases, the form of the bolts at the truss failure gradually changes from being straight to yielding. The optimal thickness-to-diameter ratio is 8.3. As the height-to-span ratio decreases, the initial stiffness and ultimate load-bearing capacity of the truss show a decreasing trend. The truss exhibits better mechanical performance when the height-to-span ratio is 1/4.

New generation of superior single plating vs. low-profile dual minifragment plating in diaphyseal clavicle fractures: a biomechanical comparative study

Recently, a new generation of superior clavicle plates was developed featuring the variable angle locking technology for enhanced screw positioning and a less prominent and optimized plate-to-bone fit design. On the other hand, mini-fragment plates in dual plating mode have demonstrated promising clinical results. The aim of the current study was to compare the biomechanical competence of single superior plating using the new generation plate versus dual plating using low-profile mini-fragment plates. Sixteen paired human cadaveric clavicles were pairwise assigned to two groups for instrumentation with either a superior 2.7 mm Variable Angle Locking Compression Plate (Group 1), or with one 2.5 mm anterior combined with one 2.0 mm superior matrix mandible plate (Group 2). An unstable clavicle shaft fracture (AO/OTA 15.2C) was simulated by means of a 5mm osteotomy gap. Specimens were cyclically tested to failure under craniocaudal cantilever bending, superimposed with bidirectional torsion around the shaft axis and monitored via motion tracking. Initial construct stiffness was significantly higher in Group 2 (9.28 ± 4.40 N/mm) compared to Group 1 (3.68 ± 1.08 N/mm), p=0.003. The amplitudes of interfragmentary motions in terms of axial and shear displacement, fracture gap opening and torsion, over the course of 12,500 cycles were significantly higher in Group 1 compared to Group 2, p≤0.038. Cycles to 2mm shear displacement were significantly lower in Group 1 (22792 ± 4346) compared to Group 2 (27437 ± 1877), p=0.047. From a biomechanical perspective, low-profile 2.5/2.0 dual plates can be considered as a useful alternative for diaphyseal clavicle fracture fixation especially in less common unstable fracture configurations. 2.7 single superior variable angle locking plates and can therefore be considered as a useful alternative for diaphyseal clavicle fracture fixation especially in less common unstable fracture configurations.

Effect of tie column on the progressive collapse performance of infilled reinforced concrete frames

In practice, reinforced concrete (RC) infilled frames having longer span are provided with tie columns to improve structural integrity but previous work ignored tie columns in studying the effect of masonry infills on progressive collapse resistance of RC frames. Therefore, aim of this study is to explore the effect of tie columns on the progressive collapse resistance of RC infilled frames under column removal scenarios. The high-fidelity-based finite element model of RC infilled frames were first developed and validated with published experimental results. The validated model was then further evolved to an RC infilled frame having tie columns to evaluate the influence of tie columns on the load transfer mechanism and the resistance of the RC infilled frame against progressive collapse. Thereafter, the numerical model was further utilized to study the effects of the pertinent parameters, including the number of stories, the span length of the frame and the longitudinal reinforcement ratio of the tie columns. Finally, equivalent strut model was suggested for macro-modeling of RC infilled frames having tie columns in engineering practice. The results showed that incorporating tie columns makes truss mechanism more fully mobilized in masonry infill walls and the inclined angles of primary struts in each sub-panel of the infill wall are increased, improving the vertical components of diagonal compression in resisting the gravity load. Consequently, introducing tie columns at middle span of infill wall panels helped to increase the initial stiffness (about 19%), peak resistance (about 26%) and post-peak resistance of RC infilled frame under a middle column removal scenario. Such beneficial effect of tie columns becomes more significant for infilled frames with larger spans, and the longitudinal reinforcement ratio of tie columns should be ≤ 0.24%.

Mechanical and microstructural properties of iron mining tailings stabilized with alkali-activated binder produced from agro-industrial wastes

This study evaluated the stabilization of iron ore tailings (IOTs) with an alkali-activated binder (AAB) produced from sugar cane bagasse ash, hydrated eggshell lime, and sodium hydroxide solution. Unconfined compressive strength, split tensile strength, initial shear stiffness, mineralogy, chemical composition, and microstructure of IOTs-AAB were evaluated. Strength values up to 6.59 MPa were achieved after 28 days-curing at 40 °C. Reducing porosity and increasing the binder content improved the overall mechanical behavior. N-A-S-H like gels were identified in IOTs-AAB mixtures. Finally, longer curing times led to more compact structures.

Eccentric Compression Behaviors of Self-Compacting Concrete-Filled Thin-Walled Steel Tube Columns.

For the sake of solving sustainability issues and analyzing the complicated service force states, eccentric compression experiments on self-compacting concrete-filled thin-walled medium-length steel tube columns with a circular cross-section were carried out in the present study. Thereafter, the influence of the eccentric ratios and the wall thickness factors on the mechanical behavior and failure characteristics of both the eccentrically loaded and axially loaded columns was comprehensively analyzed. Finally, prediction formulas for the ultimate load of the columns under eccentric compression were proposed, and a comprehensive comparison of the ultimate loads between the predicted values and experimental values was also conducted. The results indicated that the typical failure characteristics of the eccentrically loaded columns presented lateral deflection together with buckling, while the axially compressed columns displayed expansion and rupture at local positions. Moreover, the ultimate loads of the eccentrically loaded columns decreased by 43.0% and 34.5% in comparison to the columns under axial compression, with the wall thickness factor decreasing from 116.7 to 46.7, respectively. Meanwhile, the ratios of the ultimate loads calculated using design codes to the tested values were in the range of 0.70~0.90, which demonstrated that the design codes could predict the ultimate loads conservatively. Additionally, the ratios of the ultimate loads calculated using the proposed formulas to the tested values were within the range of 0.99~1.08, implying that the proposed formulas were more accurate than the design codes. At the same time, the initial stiffness of the columns under eccentric compression was correspondingly lower than that of the columns undergoing axial compression. The lateral deflections along the height of the columns were almost symmetrical at different loading levels. This study could provide a meaningful approach for designing columns and facilitate their application in civil industry.

A Study on Mechanical Performance of an Innovative Modular Steel Building Connection with Cross-Shaped Plug-In Connector

Modular steel buildings show high assembly degree and fast installation speed. The inter-module connection (IMC) is one of the key technologies that restrict the robustness of modular steel buildings. An innovative IMC with a cross-shaped plug-in connector is proposed, and the connection consists of end plates of columns, the cross-shaped plug-in connector, bolts, cover plates, and one-side bolts. The proposed IMC is easily constructed, and the cross-shaped plug-in connector can improve the shear resistance of the core area. The mechanical model of the proposed IMC is presented, and the panel zone volume modified factor and initial rotational stiffness modified factor are proposed for calculating the shear capacity of the panel zone and the initial rotational stiffness. Numerical simulation was conducted considering the influences of axial compression ratios, sections of beams and columns, and the thickness of the tenon plate of the connector. The bearing capacity of the proposed IMC was analyzed, and the values of the two factors mentioned above were calculated, and their regression formulas are presented. The results show that the sections of beams and columns and the axial compression ratios show great influences on the bearing capacity of the proposed IMC, while the thickness of the tenon of the cross-shaped plug-in connector shows almost no effect. In addition, the sections of beams and columns show great influences on the shear capacity of the panel zone, as well as the initial rotational stiffness of the proposed IMC, while the thickness of the tenon of the cross-shaped plug-in connector and the axial compression ratios show little effect and almost no effect, respectively. Furthermore, the bending moment limit of the beam end of the proposed IMC is suggested to be 0.6 times the resistance bending moment, and the proposed IMC is considered to be a rigid connection or inclined to a rigid connection The proposed IMC has good mechanical performance, and design recommendations are presented.

Experimental and Numerical Study on the Seismic Performances of Reinforcement-Embedded RC Column-to-Precast Cap Beams with Socket Connections

Accelerated bridge construction (ABC) has attracted much attention in China as a new and efficient construction method. However, the seismic performance of the connections between precast piers and other structures limits the application of ABC in medium and high seismic zones. In this paper, a quasi-static test was conducted to investigate the seismic performance differences between a cap–column socket connection (PSC) specimen, which reinforced an embedded RC column-to-precast cap beam with a socket connection, and a cast-in-place (CIP) cap–column specimen. A fiber-based finite element model that considers bond slippage between the connection reinforcement and wet joint concrete is proposed. The numerical simulation results compared with the experimental results show an error of about 12% in peak bearing capacity and about 2% in initial stiffness. The experimental and numerical results show that the PSC specimen demonstrates comparable seismic performance to the CIP specimen. Experimental results verified that the finite element model in this paper is adequate to predict the seismic responses of a precast column with a reinforcement-embedded socket connection. A reinforcement-embedded RC column-to-precast cap beam with socket connection can be an effective solution for construction in medium and high seismic areas.

Resilient performance of steel connections with low yield point fuses considering the effect of RC floor slab

The beam-column connection of a steel frame equipped with replaceable low yield point steel cover plates (SF-LYCP) was proposed to address the significant repair challenge and financial losses caused by beam-column connection brittle failure after an earthquake. According to an experimental study, the SF-LYCP exhibited outstanding bearing capacity, ductility, energy dissipation, and post-earthquake rapid recovery performance. To explore the effect of the reinforced concrete (RC) floor slab on the mechanical behavior of SF-LYCP in a natural working environment, the finite element method of steel beam-column connection with low yield point (LYP) steel cover plates considering the effect of the RC floor slab (SF-LYCP-RCslab) was developed and analyzed by ABAQUS. The results demonstrated that the proposed finite method was able to accurately predict the behavior of SF-LYCP-RCslab. The load capacity, initial stiffness, and energy dissipation capacity of the SF-LYCP-RCslab were increased in comparison to the SF-LYCP. The LYP cover plates in the SF-LYCP-RCslab still played the desirable role of structural fuses. However, the concrete of the RC floor slab had severe damage and prevented the quick replacement of repairable LYP cover plates. Based on these findings, four improved strategies for the SF-LYCP-RCslab were proposed to reduce concrete damage and increase the replacement convenience of damaged elements. Comprehensively considering the bearing capacity, ductility, energy dissipation, structural fuse function, concrete damage, and post-earthquake rapid recovery performance, the improved strategy, which adopted a profiled steel–concrete composite floor slab with a gap, was recommended in steel frame beam-column connection design.

Ultimate strength behaviour of reinforced concrete beams strengthened by aluminium-alloy plates

This paper firstly proposed the new strengthening methods on reinforced concrete (RC) structures using the aluminium alloy (AA) plates. Then, the flexural behaviour of RC beams strengthened by externally bonded (EB) and mechanically fastened (MF) AA plates were studied through13 four-point bending tests. Four parameters were studied that included the strengthening method, thickness of AA plate, grade of AAs, and reinforcement ratio. Test results showed that the MF AA beams failed in flexure with concrete crushing, and the EB AA beam exhibited the bonding failure. Compared with EB AA beams, the MF AA beams exhibited larger load carrying capacity and ductility, but lower initial stiffness. Increasing the thickness of AA plate significantly improved the load carrying capacity, but slightly decreased the ductility of MF AA beams. The grade of AA plates exhibited weak influence on MF AA system since the strain of AA plate was significantly limited by the AA plate hole-anchor gap. The strengthening effect was more significant for RC beams with a relatively lower reinforcement ratio. Moreover, theoretical models were proposed to evaluate the ultimate carrying capacity of MF AA beams that considered the strengthening AA plate-concrete slips. Validations of the theoretical predictions against test results showed that they predicted reasonably on the ultimate load carrying capacity of strengthened RC beams by AA plate.

Axial compressive behavior of corroded double-steel-plate composite shear wall with binding bars

Steel structure is susceptible to corrosion, and corrosion will seriously affect its own load-bearing capacity and service life. In this paper, the axial compressive behavior of double-steel-plate composite shear wall (DSCW) with binding bars under different corrosion degrees is experimentally studied. The typical failure modes include the steel plate local buckling, binding bars fracture, concrete crushing, and steel plate weld tearing. The increase of corrosion rate has unfavorable influence on the axial compressive bearing capacity, initial stiffness, and ductility of DSCW. Finite element (FE) models are established to further investigate the axial compressive behavior of DSCW. It is concluded that the concrete and steel plate strength grade, the concrete section area, the steel plate thickness, and the binding bars diameter and spacing significantly affect the axial compressive bearing capacity of DSCW. A formula calculating the axial compressive bearing capacity of corroded DSCW with binding bars is proposed. The formula agrees well with the test results and can provide a reference for the engineering application.

Hysteretic and rotational performance study of outwardly extending shape-steelprefabricated beam-column joints

This paper proposes fully-bolted extending shape steel prefabricated beam-column joints to achieve rapid construction and reliable connection of the precast reinforced concrete frame. The prefabricated component uses steel tube-concrete composite structures with outwardly extended shape steel, which achieves efficient installation and internal force transfer. Horizontal hysteresis tests were conducted on four components to determine the joint mode of failure and seismic performance index. The results show that the joint exhibits a “double plastic” failure mode, with plastic deformation occurring at the end of the reinforced concrete beam and buckling deformation at the shaped steel. Compared to cast-in-place joints, the new joints have a 30% increase in yield load, a 51% increase in peak load, an approximately 50% increase in initial stiffness, a 33% increase in equivalent viscous damping coefficient, and a ductility coefficient greater than 4.0. Analysis of strain showed that the stiffness of the connection area was too high, which will have a significant extrusion effect on the concrete at the end. Reducing the thickness of the steel plate in the joint space and weakening the shape stee by opening holes can significantly improve the rotational deformation capacity of the joint - further developing the plastic zone of reinforced concrete beams to improve the mechanical performance of the joint. Finally, the finite element model of the joint is established, and the numerical calculation is in good agreement with the experimental results. The research in this paper can provide technical support for the engineering application of the prefabricated joint.

Experimental and numerical investigation of bolted steel endplate with bonded sleeve end connections for pultruded GFRP circular tubular hollow beams

The paper presents an experimental and numerical investigation of bolted steel endplates with bonded sleeve connections developed for connecting pultruded glass fibre-reinforced polymer (GFRP) circular tubular beams. The moment-rotational responses were investigated in detail in terms of initial rotational stiffness, moment capacity, and rotation capacity for all the connections. The effect of endplate thickness and bonded sleeve length was also investigated. Predominant failure modes include bending and yielding of thinner endplates, while thicker endplates with low bonded sleeve lengths exhibit splitting failure in the bonded GFRP beam region. Available design codes for steel joints were used to classify the developed connections in terms of rigidity and strength. The failure modes from the finite element models were well matched by the experimental observations, which include the deformation of the endplate and the cohesive failure within the bonded sleeve region with the GFRP beam.

Influence of Column Base Connections on the Cyclic Loading Performance of Double-Jointed Engineered Bamboo Columns

The cyclic loading performance of bamboo double-jointed components of different column base connection types was investigated through reversed cyclic loading tests and finite element analysis. Test results indicated that the types of column base connections played an important role in the failure modes of the engineered bamboo double-jointed columns: for an encased steel plate column base connection, the main failure mode was tensile fracture failure of the bamboo scrimber section at the bottom of the cladding plate; for a slotted-in steel plate column base connection, the main failure mode was splitting failure of the bamboo scrimber cross-grain at the bolt connection line at the bottom of the sheathing plate. The initial stiffness of the encased steel plate column base connection specimen was 41.8% higher than that of the slotted-in steel plate column base connection specimen, with the two specimens having similar average bearing capacities. The ductility ratio of the two specimens was below 3.0 due to the brittle failure nature of the engineered bamboo connections. The finite element model accurately predicted the ultimate bearing capacity of the double-jointed bamboo column members. The modeling error was within 12%, which was sufficient to satisfy the accuracy requirements for engineering purposes.

Seismic performance of corrugated steel plate shear walls under various constraint conditions

Corrugated steel plate shear walls (CSPSWs) support vertical or horizontal corrugated plates attached to boundary frames through two- or four-sided connections. While two-sided constraints offer better applicability and convenience, this study aims to investigate the seismic behavior of CSPSWs with both two- and four-sided constraints. The investigation considers the coupling effects of direction, aspect ratio, thickness, and axial compression ratio. The study analyzes hysteresis curves, capacity characteristics, stiffness, ductility, and energy consumption for various failure modes. The results indicate that two-sided-constrained specimens exhibit lower mechanical properties compared to four-sided-constrained specimens, especially the initial stiffness. However, both constraint types show X-shaped tension fields diagonally along the CSP under low-cycle reciprocating loading. The horizontal and vertical directions of the corrugated plates have no significant impact on the seismic performance of the four-sided-constrained system, whereas they directly affect the stiffness and lateral load of the two-sided-constrained system. Additionally, an increase in plate thickness results in greater design requirements, particularly for surrounding frame members. Furthermore, when the axial compression ratio does not exceed 0.4, the specimen exhibits good seismic performance and energy dissipation capacity.

Damage Assessment of Segmental Concrete Beams with Different Types of Joints and Prestressed External Tendons

Precast segmental beams with prestressed external tendons have become increasingly common in bridge constructions owing to the merits of high-quality control and fast onsite construction with minimum environmental impact. Due to the nonlinear characteristics of the dynamic behavior of these segmental beams associated to the joint opening, the traditional condition monitoring and damage assessment methods based on vibration parameters either in time or frequency domain using the linear theory are unsuitable. To overcome this challenge, this paper proposes a damage assessment method through analyzing nonlinear structural dynamic responses for monitoring the conditions of segmental beams with different joint types and prestressed external tendons. Two damage indices are proposed to identify the occurrence of damage and to qualitatively indicate the damage severity. In the proposed approach, the measured dynamic responses of the segmental concrete beams under hammer impact are first adaptively decomposed into a finite number of mono-components by using variational mode decomposition (VMD) technique. Then, the instantaneous frequencies of the decomposed mono-components from the dynamic responses are obtained by conducting the Hilbert transform. Two damage indicators are defined for the damage assessment and for the identification of the damage location, respectively. Three four-span segmental beams with different types of joints (i.e. dry joints or epoxy joints) and prestressing tendon types (i.e. steel and carbon fiber reinforced polymer tendons) were constructed and tested under five loading levels with different damage severities. The feasibility and accuracy of the proposed approach are verified by comparing the identification results with the secant and initial stiffness extracted from the load–deflection curves at different loading levels. The effectiveness of these two damage indicators is also validated with the structural conditions observed in the tests. The results show that the proposed approach can successfully identify damage in segmental concrete beams.