Intermediate Ductility Research Articles

Seismic-Resistant Design Regulations for Structures, Earthquake and Experimental Results Lessons

The Mexico City earthquakes of September 19, 1985, and September 19, 2017, showed that the seismic requirements for these earthquakes exceeded those specified in the Mexico City building code. This study illustrates limitations in current procedures for the seismic analysis of structures. The Uncertainties in the assessment of seismic design requirements and limitations in the seismic analysis of structural systems indicate that the lateral strength specified in building codes is not sufficient and that structures must have lateral deformation capacity. It follows that structural systems with low or intermediate ductility, such as those allowed in the Mexico City Building Code (MCBC, 2017), would not be desirable for resisting strong earthquakes. The last part of this work shows computed story drifts in buildings with different structural systems, either based on frames or using structural walls. This study compares story drifts in these structural systems for both using the seismic demands specified by MCBC 2017 and for the seismic demands corresponding to the September 19, 2017, earthquake in Mexico City. The results for these story drifts show the importance of rigid structural systems for reducing story drift demands, not only for avoiding collapse in strong earthquakes but also for significantly reducing building damage.

Evaluation of strength and stiffness degradation of RC shear walls: An integrated image processing and deep learning approach

AbstractIn the aftermath of an earthquake, damage detection and performance evaluation of structural components are imperative for assessing the residual seismic capacity of a building. In this study, an integrated image processing and deep learning approach was developed to evaluate the degradation in strength and stiffness (i.e., strength reduction and stiffness reduction) of reinforced concrete (RC) shear walls. The approach comprised two main tasks: detecting and localizing visible seismic damage from photographs and evaluating strength and stiffness degradation based on this information. The semantic segmentation network, Damage‐Net, was used for damage detection and localization. A novel crack morphological processing layer and a patch feature extraction layer were developed for damage feature extraction and compression. A lightweight deep convolutional neural network named DegradeEval‐Net_v2, featuring the upgraded dilated and separable convolution block and multi‐layer perception, was developed to link the damage feature with strength and stiffness degradation. A database comprising test data and photographs of 14 RC shear wall specimens with a flexural‐dominated behavior mode and high to intermediate ductility was constructed to train and test the DegradeEval‐Net_v2 network. The results indicate that DegradeEval‐Net_v2 substantially improved the performance assessment accuracy of damaged RC shear walls, with a 35% smaller root mean square error (RMSE) for stiffness degradation evaluation and 75% smaller RMSE for strength degradation evaluation, compared with the provisions specified in JBDPA and FEMA guidelines. Moreover, evaluation results on test sets demonstrate that introducing the damage feature extraction and compression layers effectively preserved local crack information and improved the accuracy with which stiffness reduction was evaluated. In addition, DegradeEval‐Net_v2 outperformed ResNet18 and MobileNet V3 in terms of balanced efficiency and accuracy. Interpretability analysis demonstrates that the model learned the distinct contribution patterns of various visible damage indexes to stiffness and strength degradation across different loading levels.

Probabilistic investigation of the pounding effect in steel moment resisting frames with equal and unequal heights

In this research, the influence of the pounding phenomenon of two adjacent steel moment resisting frames (SMRFs) with 2 and 5-story with an intermediate ductility is investigated by considering equal and unequal heights under seismic excitations. In this way, two scenarios are applied. The first and second scenarios are related to the pounding of two SMRFs with an equal height (both frames with 2-story) and an unequal height (2-story and 5-story frames), respectively. In the following, at first, sensitivity analysis is conducted by the Monte Carlo simulation (MCS) method. Then, the collapse performance of the studied SMRFs is evaluated by incremental dynamic analysis (IDA), and fragility curves under 14 far-fault records and also, the failure probability is predicted by the Kriging meta-model. The results of sensitivity analysis indicate that the yield strength of cross-sections and dead load were the greatest effect on failure probability computation. Also, in the statistical level of 50%, the collapse probability of SMRFs with an equal height is 17% compared to the SMRFs with an unequal height. Also, the results of the Kriging meta-model show that the failure probability is increased by 65% in an unequal height versus an equal height.

I‐beam to RHS‐column joints with welded studs under cyclic loading

AbstractThe design of removable beam‐column joints between open structural steel beams and rectangular hollow section (RHS) columns is not easy because of the inaccessibility to the tube interior from outside. I‐beam to RHS‐column joints with threaded welded studs are of great interest due to their low‐cost assembling technique and easy on‐site execution. This study examines the cyclic performance of these joints with welded studs. A quasi‐static experimental study on the cyclic response of eight joint specimens is described. The strength of the joint and the failure modes were revealed. The ductility of the joints was also evaluated according to the rotation capacity after yielding, classifying all of them as having intermediate ductility and, therefore, implying some capacity to withstand limited plastic deformations when subjected to seismic forces. Some equations were also used to classify the joints according to the components that mainly govern the deformation of the full joint. In addition, the energy dissipation rate was assessed for all the specimens, finding the highest energy dissipation rates in the most rigid joints.

Considering the Yielding Displacement Uncertainty in Reliability of Mid-Rise R.C. Structures

In structural analysis and design, there are always uncertainties in determining loads and capacities. Structural reliability quantitatively considered uncertainties in analysis and design procedure. One of the well-known criteria to assess structural reliability is the Total Reliability Index (TRI) of structures. Yielding Displacement (YD) is an important component for calculations of TRI. Due to the changes in the analysis method, input type, normalization procedure, and the definition of target displacement, there are uncertainties in YD calculation. In structural reliability studies, both loads and resistance parameters are modeled as random variables. Therefore, the YD can be considered as a random variable. This study utilizes incremental dynamic analysis (IDA) to calculate TRI in mid-rise reinforced concrete moment resistant frames with intermediate ductility. The effect of uncertainty caused by YD is calculated based on pushover dynamic analysis. The reliability indices for the six structures of 3, 5, and 8 stories and three and five-span reinforced concrete moment frames show that the uncertainty caused by the YD reduces the TRI, but does not affect the seismic performance of the structure, significantly.

Tying Devices to Mitigate Pounding of Adjacent Building Blocks

Adjacent building blocks separated by thermal expansion joints are vulnerable to pounding during earthquakes. The specified Saudi building code minimum separation may be very large and does not necessarily eliminate pounding forces. This research discusses the feasibility of tying the adjacent building blocks with simple devices to mitigate structural pounding when separated by thermal joints. Six and twelve-story moment resistance frames of intermediate ductility were designed for seismic loads of moderate risk. The seismic response was studied for frames with variable separation distances in three cases related to thermal joint, code minimum separation, required separation to eliminate pounding force, and in a fourth case in which the tying device was used along with thermal separation. A linear elastic model was used to model the assigned gap links between the adjacent building blocks. The tying device was modeled with a tension-only hook element. Four normalized earthquake records were used with inelastic-time history analysis to assess the seismic response of the adjacent building blocks. The proposed tying devices reduced successfully the pounding forces by 40% to 60% for adjacent building blocks with installed thermal separations. Building damage as observed from damage index and the hysteretic response was not influenced by the pounding force, indicating that the tying may be used on existing buildings with thermal separation as a partial mitigation technique to reduce the pounding hazard in such cases. Further improvement on the tying device will increase the mitigation of the pounding hazard.

A study on influencing factors for simplified seismic collapse risk assessment of steel moment-resisting frames with intermediate ductility

Purpose Mid-rise steel moment-resisting frames (MRFs) with intermediate ductility are a major part of conventional residential buildings in Iran. According to Iranian seismic design codes, in this resisting system, considering the strong-column/weak-beam (SCWB) criterion is not mandatory. Where a metal deck ceiling system is used, the composite action of a concrete slab and steel beams could change the collapse mechanism of the structure, especially in the MRFs with intermediate ductility. The purpose of this paper is to investigate the influence of the composite action in the seismic collapse risk of this type of structures. Seismic collapse risk assessment can be carried out by using simplified pushover-based methods. In these methods, the cyclic deterioration of an equivalent single degree of freedom (ESDoF) system must be considered when the modified Ibarra–Medina–Krawinkler is used for nonlinear modeling of MRFs. Accordingly, a modified method is developed to use in simplified collapse risk assessment process. For these purposes, two mid-rise MRFs with intermediate ductility located in Tehran have been selected as case studies. The results confirm that the composite action is very effective in collapse risk value in the steel MRFs in which their SCWB ratio is less than 1. Moreover, the proposed approach of considering the cyclic deterioration of ESDoF systems increases the accuracy of the simplified collapse assessment approaches. Design/methodology/approach Identifying seismically vulnerable buildings to collapse requires using robust methods. These methods can be simplified based on pushover analysis methods. An attempt was made to apply one of these approaches for steel MRFs with intermediate ductility. In these frames, the composite action of a concrete slab and steel beams could change the collapse mechanism. Here, two MRFs were investigated in order to assess this effect on collapse risk value. This process was done by modifying the SPO2IDA method as a simplified collapse capacity evaluation approach by developing a relationship to consider the cyclic deterioration effects for the ESDoF systems. Findings The results showed that it is necessary to consider the slab effects in the analytical model in the collapse assessment process of MRFs with intermediate ductility, especially in the condition in which the SCWB ratios of the frame are less than 1. Furthermore, by utilizing the proposed method of considering the ESDoF cyclic deterioration, the error values of the SPO2IDA program were reduced significantly. Moreover, estimating the collapse risk parameters shows that the utilized simplified method presents suitable accuracy and could be an acceptable approach to collapse risk assessment of mid-rise steel MRFs. Originality/value The influence of the composite action in seismic collapse risk of MRFs with intermediate ductility is investigated. Also, a modified relationship is developed to consider the deterioration effects on the ESDoF parameters used in simplified collapse risk assessment process. Also, a framework is presented for utilized methodology.

Controlled annealing of sandwich-structured aluminum AA1050 for optimized combinations of strength and ductility

A heavily rolled AA1050 sample with a microstructurally continuous sandwich structure, characterized by distinct microstructural evolution in the center and subsurface layers, has been annealed at different temperatures for 2 h with the objective of establishing optimized combinations of strength and ductility. It is observed that a large reduction in the fraction of high angle boundaries taking place during recovery in the subsurface layers results in delayed onset of recrystallization compared to that in the center layer, where the change in the fraction of high angle boundaries during recovery is small. The different recrystallization rates in this sandwich structure facilitate control of the overall recrystallized fraction, and can therefore be advantageous in obtaining a desired combination of both strength and ductility. A good combination of moderate strength and intermediate ductility is obtained in the material annealed at 250 °C and 270 °C, where the area fractions of recrystallized microstructure in the center are 7% and 36%, respectively. By analyzing the dependence of mechanical properties on the microstructure it is found that the mechanical strength can be described by a simple composite model using a rule of mixtures.

Comparison between the ENF and 4ENF fracture characterization tests to evaluate GIIC of bonded aluminium joints

ABSTRACTAdhesively bonded joints have been increasingly used in structural applications over mechanical joints. Cohesive Zone Modelling (CZM) is the most widespread technique to predict the strength of these joints, and it uses the tensile fracture toughness (GIC) and the shear fracture toughness (GIIC). Different fracture characterization methods are available for shear loadings, among which the End-Notched Flexure (ENF) is undoubtedly the most popular. The 4-Point End-Notched Flexure (4ENF) is also available. This work consists of a detailed comparison between the ENF and 4ENF tests for the experimental estimation of GIIC of bonded aluminium joints. Three adhesives were used: a strong and brittle (Araldite® AV138), a less strong but with intermediate ductility (Araldite® 2015) and a highly ductile (SikaForce®7752). Different data reduction methods were tested, and the comparison included the load-displacement (P-δ) curves, resistance curves (R-curves) and measured GIIC. It was found that the ENF test presents a simpler setup and has a higher availability of reliable data reduction methods, one of these not requiring measuring the crack length (a) during its growth. For the 4ENF test, only one test method proved to be accurate, and the test geometry revealed to be highly affected by friction effects.

A Parametric Study on the Progressive Collapse Potential of Steel Buildings under Truck Collision

In this paper, the initiation and propagation of structural damage in a building due to the truck collision to one of its corner columns were investigated. For this purpose, a three-dimensional 4-story moment resisting steel frame with intermediate ductility was considered. The structure was designed using ETABS software under standard dead, live, and earthquake loads, and then impact loading was applied on the structure using ABAQUS software. The effect of truck collision with different weights and speeds was simulated conducting three-dimensional nonlinear dynamic analyses. The internal stresses and forces created in the directly impacted column, as well as other parts of the structure, were obtained. Using appropriate plasticity models, the shear failure of a steel material was considered. A parametric study was performed in order to investigate the effect of different parameters on the possibility of progressive collapse. To validate the procedure of impact modeling, some available experimental vehicle to column collision tests were simulated. The results revealed that the mass and speed of the impactor had a significant effect on the response of the structure. So that, for high-momentum impactors, the traditional column removal method may yield a good approximation of the behavior of the structure. However, for low-momentum impactors, a time-history analysis without removing the hit column is needed.

Intermediate temperature embrittlement of one new Ni-26W-6Cr based superalloy for molten salt reactors

Ni-26W-6Cr based superalloy is considered a potential structure material for the molten salt reactors due to its high strength and good compatibility with the fluoride salt. In the present work, the temperature dependence of the tensile behavior of the alloy was studied by tensile tests in the temperature range of 25–850°C. This alloy exhibited a good ductility at RT and 450°C, a ductility minimum from 650 to 750°C and an intermediate ductility at 850°C. TEM and EBSD characterization was performed on specimens tested at three typical temperature points (RT, 650°C and 850°C) to determine the deformation and fracture mechanisms accounting for the intermediate temperature embrittlement. At RT, the grain boundaries can accommodate enough dislocations to provide compatibility of the sliding between adjacent grains, then M6C carbides act as crack origins and cause the fracture. In case of 650°C, the grain boundaries cannot withstand the local stress even if only a small number of dislocation pile-ups exist. The premature cracks at grain boundaries impede the development of plastic deformation from single slips to multiple ones and cause the low ductility. If tested at 850°C, the fracture process is retarded by the dynamic recovery and local dynamic recrystallization at crack tips.

Determining the optimal topology for intermediate steel moment resisting frames with eccentric braces in a hybrid system

Steel structures with intermediate ductility level are one of the systems widely employed all over the world. Given the significance of construction costs and its association with the selected structural system, number of the floors, length of spans, location of columns, and the soil type, this paper investigates the optimum values of these parameters. The present article aims at discovering the optimal topology with respect to architectural and applicability considerations. To this end, models of steel moment resisting frames with eccentric bracing with 5, 10, and 14 floors were selected. The selected models were assumed with equal area and two different soil types are considered. In order to provide parking space based on the urban development regulations, models were considered with span length of 5.6, 7.5, and 11.2 metres for two, three, and four car parks, respectively. Having analysed the models and designed the structural members and foundations, amount and cost of the building material were estimated based on the available rates and the results were compared using figures.

Collapse response assessment of low-rise buildings with irregularities in plan

The present paper aims at evaluating damage and collapse behavior of low-rise buildings with unidirectional mass irregularities in plan (torsional buildings). In previous earthquake events, such buildings have been exposed to extensive damages and even total collapse in some cases. To investigate the performance and collapse behavior of such buildings from probabilistic points of view, three-dimensional three and six-story reinforced concrete models with unidirectional mass eccentricities ranging from 0% to 30% and designed with modern seismic design code provisions specific to intermediate ductility class were subjected to nonlinear static as well as extensive nonlinear incremental dynamic analysis (IDA) under a set of far-field real ground motions containing 21 two-component records. Performance of each model was then examined by means of calculating conventional seismic design parameters including the response reduction (R), structural overstrength (<TEX>${\Omega}$</TEX>) and structural ductility (<TEX>${\mu}$</TEX>) factors, calculation of probability distribution of maximum inter-story drift responses in two orthogonal directions and calculation collapse margin ratio (CMR) as an indicator of performance. Results demonstrate that substantial differences exist between the behavior of regular and irregular buildings in terms of lateral load capacity and collapse margin ratio. Also, results indicate that current seismic design parameters could be non-conservative for buildings with high levels of plan eccentricity and such structures do not meet the target "life safety" performance level based on safety margin against collapse. The adverse effects of plan irregularity on collapse safety of structures are more pronounced as the number of stories increases.

Evaluation of seismic behavior improvement in RC MRFs retrofitted by controlled rocking wall systems

SUMMARYUsing rocking wall systems is a recent technique to improve seismic behavior in reinforced concrete structures. This paper compares three 10‐story and three 20‐story reinforced concrete frames (moment‐resisting frames) with intermediate ductility, reinforced concrete frames with shear wall, and reinforced concrete frames with controlled rocking wall (RCRW) by the use of pushover analysis. At the end of the research, the wall in a 20‐story RCRW system is post‐tensioned then analyzed, and its results were compared with RCRW results. Simulation and numerical analysis were performed with OpenSees software. The results show that plastic hinge formation and inter‐story drifts are well distributed in the structure with rocking wall system in comparison with the other systems. Meanwhile, energy dissipation and displacement ductility are increased in RCRW frames. With post‐tensioning wall in RCRW, the drift ratios are more uniformed. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Effect of the microstructure on the notched tensile strength of as-cast and austempered ductile cast irons

In this study, the effect of microstructure on the mechanical properties of four types of ductile cast irons with different morphologies was investigated using circumferentially notched cylindrical specimens with different notch root radii. These cast irons were also austempered using the same austempering heat treatment to make a comparison with the as-cast samples. Characterization of the specimens has been carried out by means of microstructure, hardness, tensile properties, notch tensile strength, notch sensitivity, fracture toughness, and fractography. A mixture of ferrite and pearlite in the microstructure of cast irons gives rise to a material of the highest tensile strength, notch tensile strength, and fracture toughness properties with the intermediate ductility and notch sensitivity. A higher pearlite in the matrix of cast irons gives very important mechanical properties such as hardness and strength, but brittleness of the matrix andnotch sensitivity are greatly increased. Austempering significantly increased the mechanical properties and also reduced the difference between the mechanical properties of the cast irons. Austempered ferritic ductile irons exhibited the highest notch tensile strength and fracture toughness, and the high tensile strength and the intermediate ductility properties with the lowest notch sensitivity, whereas austempered pearlitic ductile irons had the lowest tensile strength, ductility, notch tensile strength, fracture toughness, and the intermediate notch sensitivity properties. The mechanical properties of the as-cast and austempered ductile irons have increased almost linearly with increase in the notch root radius.

Scaling of maximum strength with grain size in nanotwinned fcc metals

Engineers usually face the difficulty of making careful choices between one good and another in terms of strength, ductility, and electrical conductance in nanostructured metals. The emergence of polycrystalline Cu with ultrafine grains and the included nanotwins supplies an ideal solution because such materials owe high strength, high electrical conductance, and intermediate ductility. We answer in this Brief Report where the strength of such materials maximizes and how it depends on grain size. Based on the competitive plastic deformation mechanisms-the strengthening mechanism by inclined dislocations (with respect to twin planes) and detwinning-induced softening-we find that the critical twin thickness where the strength maximizes is proportional to d(1/2) and the maximum strength is proportional to d(-1/2).

Seismic Performance Evaluation of Steel Moment-Resisting Frames Using Iranian, European and Japanese Seismic Codes

There have been changes in concepts of different countries seismic design codes. Therefore it seems useful to compare some of these seismic codes. In this study, four two-dimensional steel moment resisting frame buildings with 3, 6, 9 and 12 storey with intermediate ductility levels are designed using Iranian (Standard No. 2800), European (EC8) and Japanese (BCJ) seismic codes under identical circumstances, and performance of these structures are evaluated with FEMA-356 and ATC-40 provisions. Also, case studies are implemented according to the corresponding codes. At the end, advantages and disadvantages of these codes are discussed. Results of nonlinear static analysis indicate that yield displacement for the designed structures using three codes are close enough in different period ranges (short, moderate, long). Assessment of performance levels shows that BCJ code generally satisfies life safety performance level based on ATC-40. Standard No. 2800 doesn’t satisfy life safety performance level in general. EC8 code satisfies life safety based on both FEMA-356 and ATC-40. In addition, most of plastic hinges are within IO-LS performance range. From strength point of view, overall strength of short and middle period structures among these three codes are almost identical but differ for high rise structures with relatively long periods.

Experimental Assessment of Reinforced Concrete Columns with Deficient Seismic Details under Cyclic Load

To assess seismic vulnerability of existing reinforced concrete buildings in Iran, cyclic and monotonic load tests on seven columns have been carried out. Four specimens represent existing buildings with deficient seismic details. Three others represent well proportioned constructions in accordance with provisions of intermediate ductility, ACI318–99, which is a common reference in Iran. Both types of columns are in similar positions in the reference building and are subject to similar seismic demand. Based on test results, hysteresis curves, backbone curves, and idealized curves are established. The deficient specimens show 35% reduction in both strength and initial stiffness and 37% loss of energy dissipation capacity in comparison to the well proportioned specimens. The length of plastic hinge of most tested columns is almost equal to full depth of the section. The maximum measured shear force is at least 20% greater than the shear force derived from expected nominal flexural strength.

Fracture toughness of polycrystalline YCu, DyCu, and YAg

Room temperature fracture toughness was measured for YCu, DyCu, and YAg. Standard tensile tests indicated that YCu was the least ductile of these three intermetallics (11% elongation at failure); DyCu had an intermediate ductility (16% elongation at failure); while YAg was the most ductile (20% elongation at failure). The K IC value was determined directly for YCu using ASTM test method E 399-90; J IC values were measured using ASTM test method E 813-89 for DyCu and YAg, and these J IC values were converted to K IC values. The K IC values were found to be 12.0 MPa m for YCu, 25.5 MPa m for DyCu, and 19.1 MPa m for YAg. These values are relatively high for polycrystalline, fully ordered, stoichiometric intermetallic compounds tested in room air of normal humidity. Factors that may contribute to the high fracture toughness of these materials are discussed.

Tectonic origin of fractures for fissure vein emplacement in the Boulder Batholith and adjacent rocks, Montana

In the Boulder batholith and adjacent rocks, the dominant and most productive metalliferous fissure veins trend approximately east and dip steeply. Other steep veins, generally narrower, trend northwest, northeast, and rarely north. Fissure veins also occur locally in thrust faults in volcanic rocks along the west side of the batholith. Fractures along which these veins were emplaced were probably initiated by a regional compressional stress field during Laramide (Late Cretaceous-early Tertiary) time. The batholith was emplaced during the Late Cretaceous and is synorogenic with respect to the surrounding Laramide thrust and fold belt, which is characterized by east-west compression. Postorogenic rocks (Eocene and younger) do not host major fissure vein deposits.Fractures utilized by east-trending metalliferous veins are parallel to the axis of maximum compressional stress and thus appear to be extensional; this may be the reason these veins are widest and longest. Northeast- and northwest-trending veins were probably emplaced along conjugate shears; these veins are narrower than east-trending veins. Veins that trend north are less common and probably formed along release fractures perpendicular to the principal axis of compressional stress. These veins are narrower than many of those that trend east.Mechanical behavior of various rock units during deformation had an important effect on ore deposition. The longest, widest, and most productive fissure veins occur in competent, brittle rocks (Precambrian crystalline basement, batholith intrusions, and Elkhorn Mountains Volcanics). Ductile rocks (Mesozoic shales and Belt Supergroup argillites) do not commonly contain major fissure veins, except where these rocks have been contact metamorphosed and have become more brittle. Paleozoic strata, mainly carbonates, are of intermediate ductility and are hosts to fissure veins in only a few districts adjacent to the batholith.