Ductility Factor Research Articles

Prefabricated bolted PEC beam-to-CFST column joints: Development and its seismic behavior

This paper developed a novel bolted connection of prefabricated partially encased composite (PEC) beam to concrete-filled steel tubular (CFST) column by end-plates or π-connectors, and two joints with varying design details were tested subjected to cyclic loading. The seismic performance of the developed connections was investigated by experimental and finite element (FE) analysis. It was observed that both the two type connections exhibited concrete crushing within the PEC beam, accompanied by localized buckling and eventual fracture of the flanges in the main steel component of the beam. At the same time, other components were essentially in the elastic phase, such as end-plates, π-connectors, high-strength bolts, and column steel tubes. The bolted end-plate connections demonstrated excellent hysteretic performance, exhibiting high ductility factors. The stiffness, ductility, and energy dissipation capacity of the bolted π-connector connections were significantly diminished due to the influence of relative slippage between the π-connectors and the beams, in stark contrast to the bolted end-plate connection. According to Eurocode 3, the suggested connection configurations exhibited semi-rigid behavior and full-strength characteristics for non-sway frames.

Numerical Study of Shear Behavior of Geopolymer Concrete Beam Without Stirrups

Abstract The need to develop the concrete industry has increased with the increase in environmental damage resulting from building and construction operations. In the present research, the Numerical study of shear behavior of geopolymer concrete beams without stirrups by using the ANSYS program. It also includes concrete modelling to study the behavior of geopolymer concrete (GPC). The longitudinal reinforcements of beams (without stirrups) were "basalt fiber reinforced polymer bars". In order to enhance the shear behavior of the specimens, various types of fibers were added to geopolymer concrete (GPC): "steel fibers (SF), synthetic polypropylene fibers (PF), polyvinyl alcohol fibers (PVF), and carbon fibers (CF)". A numerical analysis was performed by the ANSYS version 15 program to study many parameters affecting the shear behavior of geopolymer concrete, such as longitudinal reinforcements,, and the inclusion of the opening. The results indicated that using steel fibers (SF) in geopolymer concrete increased the load failure of the tested specimens. On the other hand, using carbon fibers (CF) in the geopolymer concrete enhanced the ductility factor of these beams. The load capacity of the geopolymer concrete specimen is enhanced with longitudinal reinforcement by the CFRP bar compared to those reinforcements by BFRP bars. While the use of GFRP bars was less efficient than BFRP bars. Using FRP bars, and steel bars in strengthening geopolymer concrete beams with openings enhanced the failure load of these specimens.

Experimental study on seismic performance of squat RC shear walls reinforced with hybrid steel and GFRP rebars

This laboratory study investigates the effect of using steel and glass fiber reinforced polymer (GFRP) rebars in shear walls with aspect ratios less than two. The study evaluates six full-scale shear walls subjected to constant axial load and cyclic lateral loading, with aspect ratios of 1.08 and 1.75. The aim is to analyze how the use of steel and GFRP rebars affects crack patterns, fracture, seismic performance, dissipated energy, and ductility of shear walls. The six specimens consist of two reference ones (SRC1 and SRC2) reinforced with steel rebars, two specimens (GRC1 and GRC2) reinforced with GFRP rebars, and two specimens (S-GRC1 and S-GRC2) reinforced with a hybrid of steel and GFRP rebars. The conclusions drawn suggest that employing a hybrid combination of steel and GFRP rebars resulted in a notable alteration of crack propagation behavior and failure mode, transitioning from flexural compression to flexural tension. Additionally, compared to the specimens reinforced solely with GFRP rebars, there was an observed expansion of the hysteresis curve. Additionally, parameters such as cumulative dissipated energy, ductility, and load modification factor based on ductility increased in the S-GRC1 and S-GRC2 specimens compared to the GRC1 and GRC2.

The damage-based inelastic displacement ratio for performance-based design of fully self-centering systems under pulse-like near-fault earthquake ground motions

In this investigation, the damage-based inelastic displacement ratio (IDR) for fully self-centering (SC) systems with flag-shaped hysteresis behavior is determined under pulse-like earthquake ground motions to use in performance-based design theory. Pulsive earthquakes are known as dangerous natural phenomena due to the location of structures in the vicinity of the fault with forward-directivity and high-velocity amplitude features, which expose the system to high risk. Before this, the IDRs were obtained based on constant-ductility and strength reduction factor intensities for designing new and evaluating existing structures with SC behavior. However, the issue could be extended to an energy-based theory using the Park-Ang damage model as a popular index among researchers, with the ability to consider record amplitude, frequency content, and duration. Therefore, the damage-based IDR was determined under 252 pulse-like records with 126 pairs at four damage levels, 30 periods of vibration, four ultimate ductility factors (µu), four stiffness hardening ratios (α), and three dissipative energy factors (βn) by conducting comprehensive nonlinear dynamic analysis. Then, the influence of the mentioned parameters on obtained IDRs is evaluated to propose a robust equation for estimating target displacement in these systems. Statistical results illustrate that the approximate equation based on normalizing the structural period to the predominated period can predict the target displacement compared to achieved ones from direct time-history analysis, where the difference between estimated and mean target displacements is below 15%.

Seismic response modification factors of single-layer diamatic dome structures

In this research, the seismic behavior of single-layer diamatic dome (SLDD) structures was analyzed under earthquake loads, and then the seismic response modification factors (SRMFs) of these structures were extracted. For this purpose, 16 models with different span lengths (SLs) and rise-to-span ratios (RSRs) were designed, and the effects of SL and RSR on the SRMFs of these structures were evaluated. Also, the effect of member density on the SRMFs was studied. The models were first designed under the applied loads based on relevant design codes. Then, by performing the nonlinear time history analyses using the three translational components of ground motion records, the control point and target displacement in the horizontal and vertical directions were obtained to implement the pushover analyses. Thereafter, the pushover analyses were implemented by using the target displacements derived from the nonlinear time history analyses, and the SRMFs of SLDD structures in both horizontal and vertical directions were obtained. The results indicate that models with RSRs of 1/7 to 1/3 remained in the elastic range in the horizontal direction. For the models with an RSR greater than 1/3, if the RSR increases, the ductility and behavior factor increases in the horizontal direction. However, there is a downward trend in the vertical direction due to the increase in the vertical stiffness. The horizontal and vertical behavior factor was obtained in the range of 1.155–2.459 and 1.155–2.893, respectively. Finally, by using the results obtained and through the nonlinear regression analysis, equations were proposed for the period, target displacement, displacement amplification factor, and behavior factor for SLDD structures in terms of the SL and RSR in the horizontal and vertical directions.

Cyclic response of innovative modular joints for modular buildings under bidirectional loading

Based on their dual functions of loading-bearing and energy-dissipating, modular loading-bearing and energy-dissipating joints (MVJ) was used to vertically connect modules, particularly high-rise modular building applications. Fully bolted MVJs can be assembly and disassembly rapidly, and the modules can be recycled after disassembly. Quasi-static tests were conducted on two full-scale space specimens to evaluate seismic resistance properties of the MVJs. Owing to the critical function of MVJs in the buildings, the constant axial loading on the modular column and the vertical displacement on both double beams were implemented simultaneously to simulate the worst loading condition. Owing to the characteristics of double beams under vertical forces, and the requirements of simulation of boundary conditions, a double-beam hinged loading device was proposed. The experimental results demonstrate that the proposed MVJs exhibited great moment capacity. Accordingly, the ratios of the tested average ultimate moment capacity Mu to the designed ultimate moment capacity of double beams MP,beam were 0.828 for S1 and 0.995 for S2. Diagonal cracks occurred on the ends of MVC web for both S1 and S2, indicating that the proposed MVJs were crucial in both loading-bearing and energy-dissipating; the MVC web was used to dissipate energy. Because of the insufficient weld strength between the column and the ceiling beam, as well as the bidirectional cyclic displacement observed at both ends of double beams, the error in the average ultimate moment capacity between the tested and the predicted result is 17.08 %. Analysis conducted on the ductility factor and inter-storey drift ratio demonstrated the feasibility of implementing MVJs in seismic regions.

Experimental study on seismic performance of stainless steel full-scale frames: Global response

This paper presents an experimental study of the seismic performance of austenitic stainless steel full-scale frames using the pseudo-static test method. The bottom single-span, two-storey substructure of the designed prototype frame was chosen as the test frame. Two full-scale frames were tested, one with a bolt-welded joint and the other with an extended end-plate joint. This paper is the first of two accompanying papers to this experimental study and focuses on the specimen design, testing details and global response of the stainless steel frame under cyclic loading. The test results were utilized to analyse the global response of the frames, encompassing failure mode, bearing capacity, deformation capacity, energy dissipation capacity, the overstrength factor, ductility factor and seismic response modification factor. The experimental findings suggest that the stainless steel frames with two joint types demonstrate consistent ability to dissipate energy during cyclic loading. The structure also performs well in terms of deformation, with uniform inter-storey deformation and no soft-storey detected. The maximum storey drift ratio of the frame is 7%. Prior to reaching a storey drift ratio of 2%, the frames with both joint types exhibit similar cumulative plastic deformation, stiffness degradation, and cumulative energy dissipation.

Modification of response reduction factors of overhead water tanks based on ductility factor

In the earthquake-resistant design of overhead tanks, this research dealt with the determination of the response reduction factor applicable to overhead water tanks performing beyond the elastic limit. Eight existing water tanks were selected for the investigation and 127 ground accelerations due to 10 Indian earthquakes were selected. The magnitude of the earthquakes selected ranges from 4.5 to 7.2. Initially, 10.16 million nonlinear dynamic data of response reduction factor had been produced using Newmark’s β method by varying parameters. From the results obtained, multi-linear regression analysis was made to arrive at the empirical formula relating the parameters and it was found that ductility factor was the most significant factor among others such as damping ratio, pre-post stiffness ratio, natural period, and soil types, in influencing response reduction factor. Eventually, It is concluded that the values of the response reduction factor to be adopted in the dynamic analysis of Overhead water tanks should be based on the desired value of the ductility factor.

Effect of nano-SiO2 modification on the seismic performance of recycled aggregate concrete shear walls

Nano-silicon dioxide (nano-SiO2) can strengthen recycled aggregates and interface transition zones (ITZs), thereby improving the properties of recycled concrete structures. This study adopted nano-SiO2 modifications to improve the seismic behavior of recycled concrete shear walls. Quasi-static tests of one natural aggregate concrete shear wall and four concrete shear walls with different replacement ratios (30%, 50%, 70%, and 100%) of nano-SiO2 modified recycled aggregate (NSMRA) were conducted. The ductility factor, energy dissipation, lateral displacement components, stiffness, and strength degradation of NSMRA concrete (NSMRAC) shear walls were evaluated. The replacement ratio effects of NSMRA on the seismic behavior of shear walls were analyzed. It was determined that the NSMRAC shear walls exhibited higher ductility factor compared to recycled aggregate concrete (RAC) shear walls with similar conditions. The seismic behavior of the shear walls degraded as the replacement ratio of NSMRA increased. Based on the comprehensive evaluation of failure patterns and seismic performance indexes, the replacement ratio of NSMRA is suggested to be taken as 50% in the concrete shear walls. Finally, based on the summary of experiments and studies on the seismic behavior of RAC shear walls with shear failure, the applicability of existing formulae was evaluated by calculating the shear capacity of RAC shear walls, and the effect of nano-SiO2 modifications on the shear capacity of recycled concrete shear walls was analyzed.

Cyclic shear test and finite element analysis of TRC-reinforced damaged confined masonry walls

Due to the low level of seismic fortification during construction, masonry walls are highly vulnerable to earthquakes, but some walls remain in service after repair. To investigate the strengthening effect of textile-reinforced concrete (TRC) on the seismic performance of seismically damaged confined masonry (CM) walls, tests were conducted on four masonry walls, and a finite element model was established for parametric analysis. A TRC facing improves the overall performance of the wall and increases the ductility of the wall. TRC reinforcement technology increases the peak load of CM walls by 19.9%-21.7%, the ductility factor by 42.1%-52.8%, and the cumulative energy dissipation by 95%-118%. The more severe the damage to the wall is, the less effective the strengthening effect of the TRC reinforcement. As the number of layers of textile increases, the load-bearing capacity, deformation capacity and energy dissipation capacity of the walls increase. When the vertical compressive stress increases, the increase in the shear bearing capacity and energy dissipation of walls due to the TRC facings first decreases and then increases. Moreover, TRC facings have limited effectiveness in reinforcing walls with high aspect ratios and high mortar strengths.

Phản ứng động đất của các hệ nhị tuyến tính đàn - dẻo và tự tâm định dưới tác dụng của các chuyển động nền do động đất xa và gần

This study presents seismic response of single degree of freedom (SDOF) elasto-plastic and self-centering systems under far and near-fault ground motions. These parameters was conducted to determine the influence on SDOF structure response in term of ductility, absolute acceleration, absorbed energy, strength ratio and strength reduction factor. It was found that maximum ductility for bilinear elasto-plastic systems was qualitatively similar to self-centering hysteretic systems, by adjusting the value of α and β, a self-centering hysteretic systems could be made qualitatively better than bilinear elasto-plastic systems in term of ductility. With respect to the absorbed energy, the self-centering hysteretic systems always less than comparable bilinear elasto-plastic systems. A three 3-story steel frame Self-Centering Brace Frame (SCBF) was designed according AISC seismic provison to validate of response of single degree of freedom self centering systems. 20 far field earthquake groundmotion are used for analysing of three 3-story steel frame SCBF under DBE (Design Based Earthquake) and MCE (Maximum Considerded Earthquake) level by using computer program PISA3D. The maxmimun value of interstory drift are under 1% and 2%, while residual drift are small.

Simulation and design model for reinforced concrete slabs with lacing systems

Lacing reinforcement plays a critical role in the design and performance of reinforced concrete (RC) slabs by distributing the applied loads more evenly across the slab, ensuring that no specific area of the slab is overloaded. In this study, nine slabs, divided into three groups according to the investigated parameters, were meticulously designed and evaluated to study the interplay between the lacing reinforcement and other key parameters. Each slab was crafted for simple support and was subjected to both static and repeated two-point load tests. The lacing reinforcement had an angle of 45° with various tension and lacing steel. The repeated-tested specimens with lacing reinforcement experienced smaller ductility than those of similar static-tested specimens, where the reduction in ductility factor ranged between 8.4% and 22.3% for all specimens. Additionally, the tested slabs were analyzed numerically using the ABAQUS software package. The validated FE test program was used to study the effect of varying the lacing reinforcement ratio, the compressive strength of concrete, and the material types of the tension and lacing reinforcements. The lacing reinforcement becomes more effective in increasing the slab capacity when using the higher compressive strength of concrete.

Effect of Beam-Column Connection Types on the Response Modification Factors of Steel Frames

A key component of steel structural design is the careful selection of structural modeling joints in steel structures, as the behavior of the joints affects the structure's strength and displacement characteristics. According to the capacity for transferring moment, connections in the analysis of frames are categorized as rigid, semi-rigid, or pinned. Also, the response modification factor (R-factor) is an effective parameter used in the seismic design of structures. However, the influence of the beam-column connection's stiffness factor on the response modification factor did not seem to have been considered in seismic design codes. Consequently, the R-factor under static pushover and dynamic loading is being studied for moment-resisting steel frames (MRSFs) with 3-, 6-, and 12-story using three different forms of beam-column connections depending on the connections' stiffness (m). The rigidities of the connections are taken 20, 10, and 5 for rigid, stiff semi-rigid, and flexible semi-rigid connections, respectively. The MRSFs are subjected to ten records with varying frequency contents and ground motion durations. The ductility reduction factor (Rμ), the over-strength reduction factor (Ro), and the R-factor were determined. The results indicated that the beam-column connection rigidity factors affected the R0, Rμ, and R-factors. Also, the R-factors were more affected by the rigidity factors for the beam-column connections and the number of story frames.

Experimental and numerical study of stirrup‐confined concrete‐filled L‐shaped steel tube stub column under axial compression

AbstractIn this paper, three concrete‐filled L‐shaped steel tube (CFLST) stub columns subjected to axial compression were tested, with one normal CFLST stub column and two stirrup‐confined specimens. The investigation focused on the effect of the equivalent stirrup ratio on ultimate bearing capacity, axial compression stiffness, ductility factor, and strain ratio of the columns. 3D finite element (FE) models of the specimens were constructed and verified against the tests results and data from literature Parametric analysis was carried out to analyze the influence of different section length–width ratios, steel ratios, material strength grades, and equivalent stirrup ratios on the ultimate bearing capacity. Additionally, the confinement effect of stirrups on the core concrete was analyzed. By generalizing the stress nephogram of the core concrete at the ultimate state and considering the equilibrium of forces, a formula was proposed for calculating the ultimate bearing capacity of the stirrup‐confined CFLST stub column under axial compression using the superposition method. The accuracy of the proposed formula was demonstrated by comparing its results with experimental results, FE model results, and those proposed by other scholars.

Post-Fire Behavior of Modified SIFCON One-Way Plates with Waste Tire Rubber under Flexural Load: Experimental and Numerical Study

In this research, an experimental and numerical investigation was conducted to study the flexural behavior of modified slurry-infiltrated fiber concrete slurry-infiltrated fibrous concrete (SIFCON) one-way plates after being subjected to a high temperature. The first part is an experimental work to ensure that the model developed is adequate, while the second part is a 3D finite element modeling of the SIFCON plates with the program ABAQUS using a sequentially coupled thermal displacement analysis. The experimental program included testing eight modified SIFCON plates containing waste powder rubber as a partial substitute for natural sand (0%, 5%, 10%, and 15%). All adopted specimens had identical dimensions (1,000 mm length, 300 mm width, and 50 mm thickness). Four specimens were exposed to fire for 2 hr at a constant temperature of 600°C, after which they were rapidly cooled by spraying them with water. Test results showed that increasing the powder rubber content of burned and unburned modified SIFCON specimens decreased the failure load and increased the specimens’ ductility factor, as well as the ultimate and service deflections. During the test, the failure of SIFCON was observed to be gradual, and the plates remained in contact even after the ultimate load was attained, whereas the failure of the reference mix (without wasted rubber) was observed to be more rapid than that of other SIFCON mixtures. For the flexural test, it gives desirable strength and good fire resistance. This study provides guidance for the study of SIFCON with waste rubber. Overall, the percentage of error between the experimental and numerical results for the load capacity and midspan displacement was about 5.05% and 8.65%, respectively.

A Physics‐Informed Neural Network for the Nonlinear Damage Identification in a Reinforced Concrete Bridge Pier Using Seismic Responses

The condition assessment of reinforced concrete (RC) bridge piers after an earthquake using measured responses is important for ensuring the safety of road and railway users. The problem is nonlinear, and the locations and extents of damages are various. However, previous research works focused on linear structural identification or model updating assuming a limited number of nonlinear materials for reasonable estimates. Leveraging the ability of deep learning (DL) for robustly estimating a large number of unknown parameters, this study proposes an ALL nonlinear spring multi‐degree‐of‐freedom (MDOF) damage identification algorithm based on a physics‐informed neural network (PINN). The algorithm is applied to a stacked bilinear rotational spring and damper model of a pier. The number of unknown parameters reaches about 50. The errors of estimated elastic stiffnesses, damping coefficients, and ductility factors (DFs) using simulated responses added with noises are 0.4%, 0.6%, and 3.1%, respectively. Using full‐scale RC bridge pier shaking table experiments, the algorithm revealed the distributions of elastic stiffnesses and DFs along the pier height and their deteriorations. The effects of different types of local damages are quantitatively evaluated and visualized on the distributions.

Rehabilitation of Fire-damaged Reinforced-concrete Slabs Using Ferro-cement

his study was conducted to investigate the effect of strengthening with ferro-cement on the flexural behavior of two-way RC slabs after exposure to direct fire. Twelve reinforced-concrete slabs were exposed to direct fire for one hour and cooled with air and water. They were then rehabilitated with a layer of ferro-cement using different bonding patterns (surface roughening, SBR material and screws). The effect of these variables was studied on the load-deflection relationship, ultimate load capacity, stiffness, energy absorption, ductility factor and strains of the compressed zone. The results showed a significant improvement in all the investigated parameters, demonstrating the efficiency of ferro-cement strengthening in improving the behavior of the slabs. It contributed to increasing the ultimate load capacity and initial stiffness of the slabs and to preventing and arresting crack propagation after cracking and even after reaching collapse. The effectiveness of SBR material in ensuring the bonding between the surface of the damaged slabs and the reinforcement layer was also revealed. KEYWORDS: Solid slab, Direct fire flame, Ferro-cement, Rehabilitation, SBR (styrene-butadiene rubber), Roughing.

Earthquake response prediction of seismically isolated buildings based on response spectrum method considering changes in characteristics of lead rubber bearings due to repeated deformations, part 2: Improvement of prediction accuracy by equivalent damping factor calculation method using effective ductility factor

AbstractThe response spectrum method (RSM), specified by the Ministry of Construction notification Vol. 2009, is not part of the countermeasure to address the Nankai trough long‐period and long‐duration ground motions (LPGMs) announced in 2016. Consequently, in this study, an approach was proposed to assess the effect of changes in characteristics due to repeated deformations using the RSM for LPGMs and seismically isolated buildings using lead rubber bearings (LRBs). However, this study identified potential areas for improvement in the calculation of effective damping using the RSM. An effective damping calculation method of the RSM using an effective ductility factor is introduced to enhance the accuracy of the proposed method. The proposed RSM‐based method was verified against the methods based on nonlinear time history analysis. The earthquake response prediction results using the proposed method were compared with those of not only the simplified method but also the precise and the quasi‐precise methods. The accuracy of earthquake response prediction using the proposed approach is increased by 30%–50% when the effective ductility factor is used to compute the effective damping. Therefore, earthquake response can be predicted using the proposed method, and the accuracy achieved is similar to the nonlinear time history analysis.

Fire Performance of Reinforced Concrete Slabs: Direct Flame Effects

The behaviour of two-way reinforced-concrete slabs exposed to direct fire was investigated in this study. The slabs were exposed to fire for one hour in a gas furnace and the flame-spread area was varied by increasing the number of fire sources from three to six. The slabs were cooled in two different ways: gradual cooling and sudden cooling. The results showed that the flame-spread area had a significant effect on the load-carrying capacity and deflection of the slabs. The load-carrying capacity decreased by 20.68% with gradual cooling and by 33.78% with sudden cooling when the flame-spread area was increased. The deflection at failure increased by 26.3% with gradual cooling and by 33.78% with sudden cooling when the flame-spread area was increased. The ductility factor showed an increase of 12.6% to 50.3 % for gradually-cooled slabs and of 50.3% to 59.6% for suddenly-cooled slabs with an increasing flame-spread area, compared to reference slabs. KEYWORDS: Reinforced solid concrete slabs, Direct fire flame, Thermal flame, Cooling method.

Investigation on damage evaluation index with ductility factor based on simulation analysis for loading test of piping support structure

Investigation on damage evaluation index with ductility factor based on simulation analysis for loading test of piping support structure