Ductile Response Research Articles

Rotational capacity of exposed base plate connections with various configurations of anchor rod sleeves

This paper presents a new approach that can enhance the rotational capacity of exposed base plate connections without degrading the initial stiffness or strength of the standard configuration. By inserting a steel sleeve with a designated geometry between the base plate and the anchor rod washer, the load path between the end plate and the rod can be interrupted, promoting a more ductile response. Exposed base plate connections with various sleeve geometries are numerically investigated using a validated FE model to demonstrate the concept of the proposed method. It was concluded that the proposed sleeve system substantially enhances the rotational capacity of the exposed column bases. An elastic response consistent with standard base plate connections is maintained indicating that the proposed system is compatible with existing codified elastic design approaches without modification.

Enhancement of RC T‐beams toughness using laced stirrups reinforcement for blast response predictions

AbstractThe dynamic behavior of laced reinforced concrete (LRC) T‐beams could give high‐energy absorption capabilities without significantly affecting the cost, which was offered through a combination of high strength and ductile response. In this paper, LRC T‐beams, composed of inclined continuous reinforcement on each side of the beam, were investigated to maintain high deformations as predicted in blast resistance. The beams were tested under four‐point loading to create pure bending zones and obtain the ultimate flexural capacities. Transverse reinforcement using lacing reinforcement and conventional vertical stirrups were compared in terms of deformation, strain, and toughness changes of the tested beams. The inclination angles of the used lacing reinforcement with respect to the longitudinal reinforcement were 45° and 60°. The lacing reinforcement was efficient and participated actively in resisting the bending moments and shear forces at the same time. For the same diameter of lacing reinforcement, the 60° inclination angle imposed more ductility before failure than beams with lacing reinforcement of a 45° inclination angle. Moreover, the lacing bar diameter was more effective in improving the load‐carrying capacities when using the inclination angle of 45°. A finite element (FE) model was developed and validated using the experimental results based on the measured deformations and strains to conduct a parametric study. The investigated parameters included the effect of the arrangements of the applied loads, laced rebar diameter, inclination angle, tension reinforcement ratio, and concrete strength.

Modeling the behavior of shear‐dominated walls retrofitted with ultra high‐performance fiber‐reinforced concrete jackets

AbstractLarge‐scale tests of shear‐dominated walls with ultra high‐performance fiber‐reinforced concrete (UHPFRC) jackets have shown the high effectiveness of this retrofitting solution. The jackets can suppress brittle shear failures and result in a ductile response governed by yielding of the flexural reinforcement. In addition, due to the low porosity of UHPFRC and the crack control provided by the fibers, the jackets can also provide an effective corrosion protection. However, while this retrofitting solution is very promising, there is a lack of mechanical models that can predict the effect of UHPFRC jackets. This paper proposes such a model based on a three‐parameter kinematic theory (3PKT) for reinforced concrete walls. The 3PKT is extended by modeling three important effects associated with the UHPFRC jackets: tension in the fibers across the critical diagonal cracks, increased compression resistance of the critical loading zones, and enhanced crack control. The results show that the proposed approach can be used to design the properties of UHPFRC jackets in order to achieve a desired structural response in terms of strength, ductility, and crack control.

Gradient damage model for ductile fracture introducing degradation of damage hardening modulus: implementation and experimental investigations

This study presents a gradient damage model for ductile fracture, in which the damage hardening modulus is degraded by the accumulation of plastic deformation and the volume expansion caused by negative hydrostatic pressure. The proposed model fulfills the thermodynamic requirements, and the governing equations are derived from energy minimization principles. Two parameter studies are carried out to confirm the basic performance of the proposed model, in which some typical ductile fracture responses are demonstrated by changing parameters for degrading the damage hardening modulus. Also, a series of numerical experiments are presented to reveal the ability of the proposed model to successfully simulate the fracture tests of advanced high strength steel sheets with different tensile strengths. It is indeed confirmed by the close agreement with experimental results that the proposed model is capable of realizing the breaking elongation, the transitional behavior from unstable to stable crack propagations, and the corresponding load–displacement curves. Also, the model successfully reproduces and predicts the crack initiation positions in notched specimens with different notch radii.

Cyclic performance of moment connections with reduced beam sections using different cut-flange profiles

Abstract Reduced beam section (RBS) behaviours with various cut-flange configurations were investigated numerically in this study. A three-dimensional finite element model material non-linearity was built and validated experimentally, and the impacts of the cut--flange profile on the moment-rotation behaviour and ductility response of moment-resisting connections were investigated in a parametric form. Five-moment connections with various forms of decreasing beam flange were thus modelled using ABAQUS software and compared in terms of cyclic behaviour. RBS with circular, rectangular, trapezoidal, triangular, and drilled holes cut-flange configurations were adopted, and the finite element analysis results showed that radius cut RBS have uniform stress contours, while a re-entrant corner in rectangular, trapezoidal, or triangular cut-flange profiles’ connections may result in stress concentration, resulting in a fracture of the flange. In addition, the numerical testing showed that the RBS connection with a circular cut-flange profile offers a lower rupture index than other connections. Thus, the RBS created using circular cut-flange profiles dissipates more energy than other connections.

Behavior and design method of double skin composite wall under axial compression

This paper presents an experimental and analytical study on the behavior of DSCW loaded in axial compression. Two full-scale tests of DSCW were conducted under the axial compressive load. The effect of the height of DSCW was taken into consideration. Moreover, the failure mode, axial load versus displacement relationship, displacement ductility, and strain response of DSCW were studied comprehensively. The results showed that all DSCW specimens underwent a similar damage process and exhibited the global buckling failure mode. DSCW can provide high axial load-carrying capacity and satisfied displacement ductility. The nonlinear FE model, which could capture the material and geometric nonlinearity of DSCW was proposed and validated against test results. Parametric analysis was conducted to study the influence of various parameters (yield strength of steel, thickness of steel plate, width-to-thickness ratio, and compressive strength of infilled concrete.) on the axial behavior of DSCW. The formulae for calculating the cross-sectional axial load-carrying capacity of DSCW were proposed. The predicted results agreed well with the FEA results. The theoretical formulae for predicting the axial load-carrying capacity of DSCW were present and validated by the test results. The proposed design method could provide a reliable reference for designing DSCW under axial load.

Experimental and numerical investigation of 3D-printed mortar walls under uniform axial compression

This study aims to investigate and trace the behavior of 3D-printed load-bearing walls under uniform axial compression load. The manufacturing procedure of 3D-printed structures is unique as they are printed layer by layer where the interface between layers is usually a weak plane for 3D-printed structures. This weak plane also causes the printed mortar to behave as an orthotropic material. To analyze and trace the behavior of 3D-printed structures, the basic mechanical properties of the 3D-printed mortar as well as the interface strength between printed layers are investigated in this study. In addition, a series of load tests on 3D-printed load-bearing walls were performed to investigate the behavior of this kind of printed structure under uniform axial compression load. There are three different printing wall patterns tested in this study, plain, diamond, and carp walls. Both diamond and carp walls failed by buckling of the printed mortar. However, with a better load transfer path of the diamond wall, the diamond wall showed a more ductile response compared to the carp wall. The diamond wall requires less printing time and less mortar consumption, but it shows a higher load at first crack, higher load-carrying capacity, and more ductile response compared to the other two walls, depicting its better overall performance as a load-bearing wall. This research also proposes an FE model which considers the interface strength of the 3D-printed layers. The proposed model can be used to predict the load–displacement, stress–strain distribution, load transfer path as well as failure pattern of the tested 3D-printed walls with satisfactory accuracy. The model can also capture well a complex geometrical non-linearity of the printed wall observed through buckling of the tested walls.

In-plane cyclic response of unreinforced masonry walls retrofitted with ferrocement

Unreinforced masonries are weak against seismic loads which necessitates their retrofitting. Ferrocement is widely used as it is cheaper than alternative methods of retrofitting. Some crucial parameters can significantly affect the performance of such retrofitted structures under cyclic loading conditions, such as: aspect ratio, difference of wire mesh arrangements & pattern of retrofitting. To quantify the impact of these parameters, this study has implemented two variations of each parameter. This study conducts experimental investigations of the ferrocement retrofitted unreinforced masonry walls (URM) and evaluation of their properties such as energy dissipation, stiffness degradation, hysteretic damping, ductility, and load deformation responses. Results show notable increase in strength after ferrocement retrofitting of URM walls. Retrofitting of URM walls with inexpensive material such as ferrocement is gaining popularity, our research is guided towards finding the in-plane cyclic load characteristics of such method of retrofitting. Sample walls were prepared in two categories: (1) Long walls (aspect ratio 0.57) and (2) Short walls (aspect ratio 1). A total of ten clay masonry walls (five for each category) were constructed with reinforced concrete base slab. The first variable parameter for the tests was ferrocement coating difference. Some sample walls were retrofitted completely even the base slab & wall panel connection point while on some walls the ferrocement lamination was only applied on the wall panels. Steel wire mesh’s opening size is another crucial variable test parameter. Two different wire mesh opening sizes: (1) 3.2 × 3.6 mm and (2) 8.5 × 8.5 mm were used on the walls. One control specimen with no retrofitting for both short and long walls were prepared for test comparison purpose. Laterally reversed cyclic loads and vertical loads both were applied to the sample walls during tests. Improvements in hysteretic damping, stiffness, energy dissipation and ductility were scrutinized in particular. Finally, a comparison was drawn between the test findings and allowable load provisions prescribed in the Bangladesh National Building Code (BNBC) 1993.

Seismic retrofitting design method for steel CBFs based on the energy-ductility model

A simplified seismic retrofitting method uses only one parameter (equivalent energy) instead of multiple parameters (strength and stiffness) was presented. Reserve parameters, including reserve strength and reserve stiffness, of BRBFs were developed. The relationship between the equivalent energy (E) and the reserve parameters was established. The ductility responses (μ) of the BRBF and CBF structures under a series of ground motions were calculated and compared. All acceptable parametric combinations of the BRBF for CBF retrofitting were obtained by taking the ductility response of the BRBF less than that of the CBF as the criterion. Then, the equivalent energy and ductility response were combined, and the results were fitted as the E-μ model, which is an easy-to-use equation. The seismic reinforcement design method of CBFs retrofitted with BRBs based on the E-μ model was proposed, which is a direct method without any nonlinear time-history analysis. Finally, the method was applied to a 6-story retrofitted braced frame structure project, and the results showed that the method proposed in this paper is accurate and applicable in seismic retrofitting design.

Shear Response of Lime/GGBS-Stabilised High-Sulphate-Bearing Clay under Consolidated-Undrained Conditions

This study investigated the consolidated undrained shear behaviour of a stabilised high-sulphate soil system. Lime was used to stabilise the soil with the inclusion of ground granulated blast furnace slag (GGBS) as an ettringite suppressor. Both volumetric changes and shear strength responses of the stabilised soil containing various proportions (10%, 20%, and 30%) of sulphates were examined with corresponding pore pressure developments and stress path changes using a modern computer-controlled stress-path triaxial system. Results indicated greater volume change for the non-stabilised soils containing lower amounts of sulphates. This shows that calcium sulphate, which is a soluble salt with relatively less alkalinity, is capable of binding particles of soils together. The amount of volume change increased with the quantity of sulphates in the stabilised soil even though the quantity of GGBS utilised as an ettringite suppressor was twice more than that of the lime. This was attributed to the unreacted gypsum (calcium sulphate) used, which resulted in a decrease in the overall specific weight, thus affecting the texture of the stabilised mix and causing an increment in pore sizes. Generally, the stabilised sulphate soils showed some initial ductile responses with the yielding followed by an almost perfectly plastic behaviour up to about 6–8% of the strain before finally undergoing small amounts of strain-softening. Lastly, higher levels of plastic failure were achieved and at higher constant effective stress for the stabilised soils containing lower percentages of sulphates.

Flexural–Shear Performance of Lightweight Concrete Panels with High Insulation Capacity

With the increased interest in the inherent fire resistance of organic insulators, various precast concrete insulation panels have been developed. However, precast concrete insulation panels still have structural and fire resistance problems resulting from a low composite action and unclosed cross-sectional details. To improve composite action and fire resistance, this study proposes the closed cross-sectional details of insulator panels with lightweight aggregate concrete, insulation material, and wire mesh. The objective of this study is to examine the flexural–shear performance of precast lightweight concrete panels with closed cross-sectional details developed for exterior cladding with high insulation capacity. Six full-sized insulation panels were tested under two-point top loadings. The main investigated test parameters to vary the moment–shear ratio of the insulation panels were the amount of the shear reinforcement and shear span–effective depth ratio. Test results indicate that the insulation panels with moment–shear ratios of 2.60 or higher were governed by shear, indicating that the longitudinal bars remained in an elastic state until the peak load of the insulation panels was reached. Thus, an increase in the moment–shear ratio of the insulation panels led to more brittle failure characteristics. Meanwhile, the insulation panels governed by flexure exhibited plastic flow performance in the applied load–deflection curve and well-distributed cracks. In particular, the maximal flexural moments of insulation panels with moment–shear ratios of 0.75 or less were higher than those calculated from the equations specified in ACI 318-19, indicating that the composite action was fully exerted. Overall, the developed insulation panels with cross-sectional details must be designed to a have moment–shear ratio of 0.75 or less to fulfil the ductile response under extreme lateral loads and exert full composite action.

Ductile–brittle failure of amorphous glassy polymers: A phase-field approach

Optimal use and design of amorphous glassy polymers in goods have become a significant task in the key industrial sectors ranging from micro-electronics to aerospace and medical industry. Depending on the microstructure, temperature level and the external loading rate to which these polymers are subjected, the fracture response may change from ductile to brittle or vice versa. While the ductile response is manifested by diffuse shear zones exhibiting volume-preserving inelastic deformations, the brittle response is revealed by very small crack-like defects containing a sequence of fibrillar bridges and elongated micro-voids, thereby resembling the void formation consisting of nucleation and growth stages. Their formation is driven by tensile straining followed by volumetric inelastic deformations. The present study is concerned with the description of shear yielding and crazing in terms of their respective evolution equations. Besides, an extension towards the modeling of the fracture is employed via the crack phase-field approach, accounting for ductile and brittle failure concomitantly. This is granted by the novel failure criterion that features a critical amount of plastic strain and void volume fraction. Such a modality simultaneously models the macroscopic crack initiation and growth leading to ductile or brittle fracture, as such purports to be more physically grounded compared to extant models in the literature. The predictive performance of the proposed model has been demonstrated by fitting of various extant experimental data of homogeneous and inhomogeneous tests in relation to initial boundary value problems.

Axial behavior of circular CFST encased seawater sea-sand concrete filled PVC/GFRP tube columns

In order to directly apply seawater and sea sand in construction without desalination, a new type of circular concrete-filled steel tube (CFST) encased prefabricated seawater sea-sand concrete filled Polyvinyl Chloride (PVC)/Glass Fiber Reinforced Polymer (GFRP) tube column was proposed. 24 short columns were tested under uniaxial loads and the test parameters included types of inner tubes, seawater sea-sand concrete replacement ratios, concrete strength, the wrapping area of Carbon Fiber Reinforced Polymer (CFRP) strips and the thickness of inner tube. Moreover, the effects of the parameters on bearing capacity, ductility, stiffness, and strain responses were discussed. The results indicate that the bearing capacity and the strength index of specimens with PVC tube wrapped with CFRP strips and GFRP tube as the inner tube was significantly improved, and the improvement level increased as the wrapping area of CFRP strips or the thickness of GFRP tube increased. The increase in the concrete strength can also improve the bearing capacity and stiffness. In addition, an analytical model was proposed for the composite column with PVC tube wrapped with CFRP strips or GFRP tube as the inner tube.

Amending foamed lightweight soil with tailings sand for embankment applications: Physical properties, durability, and microstructure

Making lightweight soil with bubbles from raw soil and cement, i.e., foamed lightweight soil (FLS), is an environmentally sustainable way to utilize tailings sand (TS) as a replacement of cement in embankment applications, enlightened by its excess strength. However, a comprehensive evaluation of its engineering performance is needed. Thus, this study develops a foamed lightweight soil amended with tailings sand (TS-FLS) and explores its physical and mechanical properties, durability, and microscopic properties. The results reveal that the fluidity, volumetric water absorption, and compressive strength of TS-FLS mixtures are within 164–182 mm, 13.3–16.0 %, and 0.76–1.74 MPa, which could satisfy the requirement of the embankment applications. After dry-wet cycles, freeze–thaw cycles, sulfate erosion, and long-term outdoor exposure, most compressive strength is applicable in the application of embankment (>0.3 MPa). Note that the strength and durability show a decreasing trend with the TS content, and the critical content is less than 50 %. Besides, the increasing TS content shifts the failure mode from brittle to ductile (33 % and 40 %), which is favorable for engineering applications, while overused content (50 %) decreases the ductile response. The microstructure observation indicates that the TS increases the pore diameter size and worsens its uniformity, making the walls more vulnerable to compression rupture by stress concentration, thereby increasing water absorption. Moreover, a large number of crystals (i.e., secondary gypsum and ettringite) are generated under sulfate solution, making mechanical properties either improved by void-filling or damaged by microstructure-destroying. Therefore, TS-FLS is promising for embankment applications when an appropriate TS content is chosen.

Numerical Study Regarding the Seismic Response of a Moment-Resisting (MR) Reinforced Concrete (RC) Frame Structure with Reduced Cross-Sections of the RC Slabs

In the first part of the current study, the effectiveness of the transversal cross-section reduction method for RC beams in marginal areas (by means of mechanical drilling) was validated. The said method “encourages” the formation of plastic hinges at the beam ends and, at the same time, allows for taking into account the bending stiffness of RC slabs, which is exerted upon the RC beams. In these conditions, the second part of the current research study (i.e., the current manuscript) highlights the real mode of reducing the lateral stiffness of the slabs upon the RC beams. These elements form a common body, together with the beam–column frame node. The same method as in the first part of the study—“weakening” the plates in the corner area through vertical drilling, without affecting the integrity of the reinforcing elements—was used. The analytical MR RC frame model, studied by means of the comparative method, highlights the efficiency of the transversal cross-section reduction method for RC slabs. Basically, the directing of the plastic deformations from the weakened slab areas towards the marginal areas of the reinforced concrete beams takes place. The beams rotate as far as the weakened slab areas allow its plastic deformation, thus being possible to observe the partial conservation effect of the beam–column frame joint. Furthermore, for the analytical model with the maximum number of vertical holes in the corner areas of the concrete plate, minimal plastic deformations are recorded for the marginal areas of the concrete columns. A partial conservation of the formation mechanism of the “beam-slab-frame node” common rigid block is also noted. Consequently, the dissipation of the seismic energy is made in a partially controlled and directed manner, in the “desired” areas, according to the “Strong Columns—Weak Beams” (SCWB) ductile mechanism of the lateral behavior to seismic actions for reinforced concrete frame structures. The mechanism is specified in current design norms for RC frame systems. The effectiveness of the method for reducing the transversal section of the RC plates in the corner areas by means of transversal drilling is highlighted and validated from the perspective of the local and global ductile seismic response of reinforced concrete frame structures. A significant reduction in the bending stiffness of the slabs upon the beams and a real development of the plastic hinges in the marginal areas of the beams (together with partial implications and plastic deformations) were observed.

Flexural strengthening of RC columns with EB-CFRP sheets and NSM-CFRP rods and ropes

Externally bonded (EB) and near-surface-mounted (NSM) systems have been investigated in the literature to be used in flexural strengthening of reinforced concrete (RC) columns. Research has shown that NSM-FRP systems are preferred in most cases over the use of EB-FRP systems especially in flexural strengthening RC columns against lateral loads. However, limited studies have been conducted to accurately compare the behavior of columns strengthened with EB-FRP or NSM-FRP systems. In this study, six specimens were fabricated and tested. To add to the novelty of this investigation, CFRP ropes were used for the first time in flexural strengthening of RC columns against cyclic lateral loads. Two of the columns were strengthened with NSM-CFRP ropes, one with NSM-CFRP rods, one with EB-CFRP sheet, and one with CFRP lateral confinement only. The results showed that both EB-CFRP and NSM-CFRP techniques can improve the flexural resistance of RC columns. The percentage of enhancement in lateral resistance ranged from 35% to 60%. Limited slippage of NSM-CFRP rods was an advantage and led to a more ductile response. Finally, theoretical analyses were performed to predict the lateral response of strengthened RC columns. The predicted load–displacement relationships had good agreement with the experimental results.

Performance of reversible timber connections in Australian light timber framed panelised construction

This paper provides a novel insight into using reversible mass timber connectors in light-timber framed (LTF) construction to create dismountable, panelised LTF construction systems that enable adaptable building design and panel reuse in the context of a circular economy. The study presented in this paper focused on Australian LTF panelised construction:. A total of 10 IdeFix 304 connectors by SIHGA GmbH, and 20 M20 connectors by SHERPA Connection Systems GmbH were installed in Australian machine graded pine and subjected to monotonic tensile and shear loads to assess their feasibility in the given application. Two strength prediction models were evaluated in comparison to experimental results: Formulae given in the manufacturers’ European Technical Assessments (ETAs) and a prediction model adapted from literature. On average, the latter was more accurate in the given configuration. Considering the set goal of repeated assembly and disassembly, the connectors with a tight fit faced tolerance issues due to moisture fluctuations. Furthermore, rupture of the connector was observed in some instances, owed to higher screw withdrawal capacity in Australian timber. A reduction of the number of screws or their length is suggested to achieve a more ductile response with screw withdrawal. Finally, following comparative analysis of experimental tests and prediction models, recommendations were made for future design of novel LTF panel connectors in the context of disassembly and reuse.

Overview of the cyclic response of reinforced concrete members subjected to artificial chloride‐induced corrosion

AbstractReinforced concrete (RC) elements suffer continuous deterioration across their lifetime from in situ aggressive environmental factors. Chloride‐induced deterioration of the steel reinforcement presents significant repercussions on the mechanical and seismic behavior of affected RC members. This paper introduces and summarizes experimental work carried out at the University of Canterbury, investigating the long‐term implications of chloride‐induced deterioration on various mechanical properties. The impact of chloride corrosion on bond‐slip behavior, the cyclic flexural response of large‐scale RC piers, and the shear resistance of short RC columns, with particular focus on the latter, is reported. Results indicate that corrosion damage presents more severe consequences to the displacement ductility of RC columns than the load‐bearing capacity. Transverse reinforcement presents a much greater risk and vulnerability to deterioration, leading to a transition in failure mechanism from a ductile response to a brittle shear/shear‐bond failure. Reduced confinement negatively impacts the stress–strain response of the confined concrete and bond‐slip behavior in cracked members, where friction is relied upon as the primary load‐transfer mechanism once mechanical interlock is lost through the generation of rust by‐products and concrete splitting.

Connection behaviour of through reinforced concrete beam to concrete-filled steel tube column after exposed to heating

The experimental study presented in this paper investigate the post-fire performance of through reinforced concrete (RC) beam to concrete-filled steel tube (CFST) column connection. A total of twelve connection specimens were tested under hogging moment. The connection specimens are grouped into two groups; group A-connections, without fire exposure and group F-connections that are exposed to fire. Two classical connection types were used in this study (type A and B) and one new connection type were proposed herein (type C) by associating additional steel plates to the connection zone. In addition, different beam reinforcement ratios were used. These parameters were considered to evaluate the strength, stiffness, joint classification, ductility, failure modes and strain response of the composite joints. Three failure modes of the connections were found. The connection specimens without fire exposure were found to be a rigid connection. The fire exposure significantly influenced the connection performance, and that influence is varied based on the connection type and beam reinforcement ratio. The proposed connection type is found to have the highest residual capacity among the other connection types. However, a comprehensive analysis of the post-fire behaviour of each connection type is illustrated.

Influence of the longitudinal steel ration in RC beams and steel reinforcement ration in RC slabs on the seismic energy dissipation mechanisms for a MR RC frame structure

The MR RC frame structures present a special engineering interest regarding the practical mode of ductile seismic response, through plastic hinges formation in specially designed RC beams end areas and inferior zones of the RC columns from the ground floor. Thus, it was proposed to verify the capacity design concept for this structural system type through seismic response observation of the optimal MR RC frame model. Until this objective is achieved, it was proposed to perform a complex analytical study, which has as finality the current research paper. Thus, in the previous analytical studies the influence of the concrete strength class, the influence of the longitudinal steel reinforcement ratio in RC columns and influence of the RC beams cross sections on the local and global seismic response for a group of RC frame models were analysed. In these conditions, the present paper contains the results obtained in previous research papers and concludes the current analytical study through the observation of the effectiveness of the inferior longitudinal steel reinforcement ratio in the RC beams on the cracking mode, in potentially plastic areas. Finally, it was specified that the K_7 RC frame model represents the optimal structural system for the experimental test.