Quasi-static Cyclic Loading Research Articles

Modelado de paredes de mampostería confinada: revisión de métodos y aplicación utilizando macroelemento discreto

One of the main challenges assessing masonry structures is numerical simulation. An overview and classification of the current developments and available techniques for nonlinear analysis of confined masonry structures is presented. As an exploratory study, an application of a numerical model using a Discrete Macro Element Method was carried out. It consisted on the calibration of mechanical parameters for representing the capacity curve and damage progression of a confined masonry wall tested under quasi static cyclic load. Then a sensitivity analysis was carried out. It has been found that global behavior is well captured by the model regarding strength and deformation. However, failure mode at confining elements was not consistent with the observed damage. Calibration has been made only for one experimental test; thus, conclusions are only valid for this set of experimental results. It is considered that the Discrete Macro Element Method is suitable not only to reproduce the global behavior of complete buildings, which is its original purpose, but also it may be used to study element behavior with appropriate modifications. ILIA: Investigaciones Latinoamericanas en Ingeniería y Arquitectura, No. 01, 2024: 108-114.

Fragility functions for structural-architectural shear walls with interlocking modules

ABSTRACT Tessellated structural-architectural (TeSA) shear walls, consisting of interlocking tiles, enable repairability because of modularization, and can satisfy both structural and architectural demands. This paper characterizes the behavior of TeSA walls made of 1-D interlocking reinforced concrete tiles using fragility functions. Two TeSA walls with varying tile patterns are analyzed under lateral loading. The modeling approach is validated using test results under quasi-static cyclic lateral loading. Damage states at tile and wall levels are defined, and a framework for generating fragility functions for TeSA walls is proposed considering uncertainties in the applied axial loading, tile-interface properties, modeling approach, and material properties of concrete. The results show that TeSA wall fragility functions are sensitive to tile shapes and patterns, particularly for the severe damage state. The onset of moderate and severe damage for TeSA walls is at 1% and beyond 2% drift ratios, respectively, showing high resistance of TeSA walls to damage.

Modeling of residual stiffness phenomenon in modified Iwan model of bolted joints and its application

Bolted joints have been widely used in various mechanical structures. Due to the presence of contact interfaces, the joints exhibit complex nonlinear behavior under dynamic loading. Effective prediction of the dynamic response of bolted structures requires the construction of appropriate dynamic models. This paper proposes a modified Iwan model which gives a more comprehensive description of joints than the previous Iwan models, especially for the phenomenon of residual stiffness in macro slip. The equations of the model's backbone curve, hysteresis curve, and energy dissipation are derived. The parameter identification procedure is also provided. Subsequently, connection elements based on the modified Iwan model are integrated into a single bolted joint and a thin-walled cylinder containing multiple bolted joints, the responses under quasi-static unidirectional loading, quasi-static cyclic loading and constant-frequency excitation are investigated. The physical interpretation of the parameters in the model is discussed, thus explaining the relationship between the bolted joint's physical parameters and some important variables. The results indicate that the model can effectively characterize the nonlinear mechanical behavior of the bolted joint for both micro and macro slip regime, with significant improvement in computational efficiency.

Enhanced seismic performance: A novel cable brace with bending energy dissipation for semi-rigid steel frames

Ordinary braces upon experiencing compressive buckling, reach a fully plastic state, rendering them ineffective against further seismic action. Moreover, their post-earthquake repair and reinforcement pose significant challenges. Addressing these issues, this research introduces an innovative lateral force-resisting element: the bending energy dissipation-cable brace. This novel design utilizes steel cables in a unique tension-only arrangement, effectively dissipating seismic energy by inducing bending in a steel plate. A semi-rigid steel frame was constructed, incorporating two variations of the cable brace, differentiated by the thickness of their energy-dissipating frames. These were subjected to quasi-static cyclic loading tests to evaluate their hysteretic behavior, deformation pattern, load-bearing capacity decay, and energy dissipation capacity. The experimental results reveal the superior seismic performance of the bending energy dissipation-cable brace, evidenced by a 22 % enhancement in energy dissipation and a 38 % increase in stiffness when the thickness of the energy-dissipating frame is doubled. These results offer a promising solution to the current limitations in energy dissipation and difficulty of application of the combined brace of steel cable and bending yielding energy dissipation devices.

Experimental study on seismic performance of replaceable shear links with low-yield-point steel

Based on the design concept of controllable seismic damage during earthquakes and rapid functional recovery after earthquakes, a replaceable shear link with low-yield-point steel was proposed. Quasi-static cyclic loading tests and numerical analysis were conducted on six specimens. The failure mode, seismic performance, energy dissipation behavior, and shear distribution of each specimen were carefully considered to investigate the effects of web steel, web stiffening configuration and stiffener-plate stiffness ratio. The results showed that the stiffened specimens showed full-sectional shear yielding behavior, while the non-stiffened specimens exhibited coupling behavior of web yielding and buckling. Specimens with reasonable design parameters had excellent ductility and energy dissipation capacity, with the plastic shear angle exceeding 0.157 rad and the maximum equivalent viscous damping coefficients greater than 0.51 (80% of the theoretical maximum value). Owing to the cyclic strengthening of the low-yield-point steel web and the contributions of stiffeners and flanges, the specimens showed obvious overstrength behavior, with the overstrength factor ranging from 1.99 to 2.39. The cross-stiffening configuration was conducive to enhancing the seismic performance of shear links. Smaller web width-to-thickness ratios were recommended to match with smaller stiffener-plate stiffness ratios. Extended cross stiffeners and diagonal stiffeners resulted in earlier cracking of the web welds, which adversely affected the ductility of the specimens.

Study on seismic failure mechanism and damage model of unconstrained adobe block walls

Through the quasi-static cyclic in-plane loading test of three kinds of unconstrained adobe block walls, namely plain adobe wall, modified mud adobe wall and modified adobe wall, the failure mode and seismic performance of each specimen were clarified. Using residual deformation and cumulative energy dissipation as failure parameters, a two-parameter seismic damage model of unconstrained adobe block walls was established. and a calculation method for the adjustment coefficients of energy consumption items was provided. The results showed that the failure mode of the typical unconstrained adobe block wall under earthquake action was not affected by the modification of adobe materials, and the final failure mode was shear failure along the mud crack and the inclined crack extending through the block. Furthermore, the proposed seismic damage model can well reflect the evolution law of earthquake damage of adobe block walls, and the recommended damage index boundary values for five performance levels were given, providing a reference for performance-based seismic design and damage assessment of adobe block walls.

Quasi-static cyclic tests of FRP-confined steel-reinforced HPFRCC circular columns

This study presents a novel composite component comprising of steel-reinforced high-performance fiber reinforced cementitious composites (HPFRCC) circular columns confined by fiber-reinforced polymer (FRP), with the goal of improving the mechanical behavior of conventional reinforced concrete (RC) columns. Quasi-static cyclic loading tests were conducted to investigate various aspects of the column specimens, including failure phenomena, load-displacement response, sectional compression-bending performance, plastic hinge length, and lateral strain distributions in the FRP jacket, etc. A self-designed frictional force measurement device was employed to accurately measure the actual force borne by the specimen. The experiment results revealed that FRP confinement effectively improved the load-bearing capacity and deformation capacity of the specimens and delayed the deterioration of the sectional compression-bending performance. The superior tensile ductility of HPFRCC led to increased yielding displacement and peak load compared to FRP-confined concrete specimen, although this enhancement was limited. Furthermore, the peak load of the FRP-confined HPFRCC specimen increased with axial load, while the sectional compression-bending performance after the peak load remained relatively stable until approaching the collapse prevention (CP) limit state.

Behavior of circular ultra-high-strength concrete-filled steel tube columns subjected to combined high-axial and cyclic lateral loads

The present study examined the seismic performance of circular concrete-filled steel tube (CFST) columns infilled with ultra-high-strength concrete (UHSC >100 MPa) as well as the beneficial effect of embedded spiral confining (SC) reinforcement at high axial load ratios (0.53–0.70) in order to enhance the safety and structural integrity of high-rise buildings. Seven specimens, including four CFST columns and three SC-CFST columns, were investigated under combined high axial and quasi-static cyclic lateral loads. The test parameters included axial load ratio (0.53–0.70), concrete compressive strength (64–111 MPa), embedded spiral confining reinforcement (pitch of 30 mm and 60 mm), and concrete vibration state. The test results demonstrated that adding spiral reinforcement improved the deformation capacity of CFST columns, which was reduced by the increased concrete strength. By embedding spiral confining reinforcement (volumetric ratio 3.3 %), the SC-CFST columns attained a deformation capacity comparable to that of CFST columns with normal concrete (64 MPa) for an axial load ratio of 0.53. The higher axial load ratio and concrete strength of composite columns led to a significant P-Delta moment effect, resulting in a substantial drop in columns' lateral load capacity. Composite columns with UHSC showed a larger contribution from the column base rotation to the specimen's lateral deformation when compared to composite columns with normal-strength concrete because the rigidity offered by UHSC made the column more rigid and reduced its flexural deformation. The unvibrated core concrete of the CFST column did not influence the initial stiffness and energy dissipation capacity. However, during the later stages of loading, the damage in core concrete rapidly accumulated, resulting in instant degradation of the load capacity and stiffness, considerable axial shortening, and poor deformation capacity. The experimental investigation offered a reliable reference on the performance of CFST columns constructed under high-axial load ratios (0.53–0.7) using ultra-high-strength concrete (>100 MPa) and spiral confining reinforcement so as to promote their application in practical engineering.

Nonlinear modeling and time-history analysis of dry-assembled precast concrete frames with buckling-restrained braces

A combination of dry-assembled precast concrete frames and buckling-restrained braces (BRB) is a viable choice for achieving the full potential of building industrialization and promoting the popularization of precast structures in earthquake-prone zones. A recent study has tested the seismic performances of a dry-assembled precast concrete frame with BRBs (BRB-DPCFs) under cyclic quasi-static loading. To study the comparative seismic behaviors of BRB-DPCFs and the monolithic concrete frames with BRBs (BRB-MCFs) under ground motion records, buildings between 3 and 12 stories in height were designed based on GB50010-2016, Chinese code for design of concrete structures, and investigated numerically. This investigation includes two-dimensional nonlinear time-history analyses of BRB-MCFs and BRB-DPCFs under two seismic hazard levels. BRB-DPCF demonstrated a larger maximum story drift compared to BRB-MCF, while the maximum residual story drift of the former is negligible in comparison to the latter at a higher building height or under a higher seismic intensity. The two systems show similar drift concentration factors, which was observed irrespective of the hazard level and the specific height of the building.

Local scour effects on seismic behavior of pile-group foundations in cohesionless soils: Insights from quasi-static tests

Local scour has been reported as a common phenomenon for pile-group foundations in marine, coastal, and riverine sites, while its effects on the seismic behavior of pile-group foundations are yet to be well documented. This paper reported a pair of quasi-static cyclic loading tests on 2 × 3 scoured pile-group foundation specimens, one in global scour and the other in local scour, to understand the influence of local scour on the seismic behavior, particularly in terms of soil-pile interaction features and failure mechanisms. Test results indicate a flexural failure mode for both specimens. Local scour does not change the order of limit states but postpones the occurrence of concrete cover cracking and rebar yielding due to the reduced lateral stiffness of the locally scoured piles. Moreover, local scour rarely changes the aboveground damage regions at the top of outer piles (one time the side length of squared pile section, D), but significantly aggravates and deepens the underground damage regions at outer piles (from 4 ∼ 5D for global scour to 3.7 ∼ 6D for local scour). Besides, local scour reduces the displacement ductility factor from 2.50 to 1.25 for the Easy-to-Repair limit state, resulting in adverse impacts on pile-group foundations in general.

Effect of corrugated plate arrangements on the performance of steel shear wall frames

Nowadays, the use of corrugated steel shear walls with sinusoidal, triangular, and trapezoidal profiles, which are stiffened steel walls without stiffener, is recommended for delaying the premature occurrence of buckling in the plate. The arrangement of corrugated plates in the structural frame alters seismic parameters; therefore, this research focuses on various arrangements of inclined corrugated plates. For this purpose, experimental specimens are first validated under cyclic quasi-static loading using ABAQUS finite element software. Subsequently, the design of four different arrangements of inclined corrugated plates with three profiles of trapezoidal, sinusoidal, and triangular is conducted and compared with vertical and horizontal arrangements. Based on the results, the triangular waveform demonstrated better energy absorption, initial stiffness, and ultimate strength. Investigation of different plate thicknesses for triangularly corrugated shear walls, including 0.75, 1.25, and 1.75 mm, showed that increasing the wall thickness improved the seismic behavior. Additionally, Arrangement No. 1 (inclined arrangement) provided the highest energy absorption and ultimate strength; however, its behavior in the hysteresis curve was asymmetric. This issue has been addressed by implementing a double arrangement of plates.

The mechanical responses of SiC-coated carbon-bonded carbon fiber composites under quasi-static cyclic compressive loading

SiC-coated carbon-bonded carbon fiber composites (CBCFs), serving as novel thermal protection materials for hypersonic vehicles, are manufactured to investigate their mechanical properties concerning reusability. Comprehensive analyses are performed on their microstructures, including the fiber arrangement and the morphology of individual fibers and interconnecting bonds. The results demonstrate that SiC-coated CBCFs exhibit higher elastic moduli and strengths in both typical directions compared to bare CBCFs. To evaluate their durability in repeated use scenarios, a series of quasi-static uniaxial cyclic compressive experiments are conducted with emphasis on the variations of deformation recovery, load bearing and energy dissipation. The results indicate that SiC-coated CBCFs exhibit stable deformation recovery ability in the OP direction after the 25th cycle, with a decelerating decline in their load-bearing capacity observed over subsequent cycles. The energy loss coefficient initially decreases with increasing cycle number, and higher compression loads enlarge the amount of energy that is dissipated in the first cycle. These insights elucidate critical correlations between the mechanical properties of SiC-coated CBCFs and the number of compressive cycles, contributing to the optimization of their practical utilization in reusable scenarios.

Hysteretic performance of novel grouted steel beam-column corner-connections for modular integrated construction

In this study, three types of socket steel beam-column corner-connections with grouting for modular integrated construction are proposed and experimentally investigated. Six grouted and two ungrouted specimens were fabricated and divided into two groups: one group underwent monotonic loading and the other was subjected to quasi-static cyclic loading. A comprehensive comparison was conducted across all these specimens. The test results show that grouted bolted socket corner-connection with diagonal stiffeners can enhance its lateral stiffness, bearing capacity, structural integrity, and energy dissipation capacity. Conversely, the absence of diagonal stiffeners and bolts connecting the flanges of the floor and the ceiling channel beams led to a significant decrease to the bearing capacity, lateral stiffness, and energy dissipation capacity of the grouted bolted socket corner-connection. This underscores the critical role of diagonal stiffeners and bolts in these connections. Notably, weld cracking or tearing was a common failure, especially at the welds connecting the beam to the column and those linking the diagonal stiffeners. This failure highlights the importance of ensuring weld quality in practical engineering applications. According to Eurocode 3, all the specimens tested could be classified as semi-rigid connection, however, only the grouted bolted socket corner-connection with diagonal stiffeners met the criteria for full-strength connections.

A comparative investigation on experimental lateral behaviour of bare RC frame, non-strengthened and ferrocement strengthened masonry infilled RC frame

Although concrete framed structures are widely used with masonry infills, the contribution of masonry infills in structural design is limited to their dead loads only. Therefore, the full-fledged stiffness characteristics of masonry infill are not often considered. However, recent earthquakes showed the impact of masonry infill on the lateral behavior of surrounding RC frames. Moreover, sometimes existing masonry infills are strengthened using Ferrocement (FC), Textile Reinforced Mortar (TRM), Carbon Fiber Reinforced Polymer (CFRP), etc., which might also have a similar impact on surrounding RC frames. The impact includes enhanced shear demand, damage, etc. However, the effect of the enhanced shear demand on RC columns is a relatively less investigated issue. In this context, an experimental program was designed to compare the effect of non-strengthened and FC strengthened masonry infill on the behavior of the surrounding RC frame in terms of lateral strength, hinge formation, shear demand enhancement, and damage to columns. The test specimens, including a bare RC frame, a masonry infilled RC frame, and a FC strengthened masonry infilled RC frame, were subjected to a quasi-static cyclic lateral loads. The experimental result showed that the masonry infill and FC strengthened masonry infill increased lateral strength, on average, by 81% and 244%, respectively, when compared to that of the bare RC frame. Meanwhile, FC strengthening of masonry infill improved the lateral strength, on average, by 90% when compared with the masonry infilled RC frame’s lateral strength. In this study, low-strength masonry infill caused the formation of a short column on the tension column of the RC frame. The application of ferrocement to low-strength masonry altered the position of the plastic hinge formed on the tension column of the RC frame when compared to that of the masonry infilled RC frame. Therefore, ferrocement strengthening of masonry eliminated the short column phenomenon in this particular study. Nevertheless, the shear demand (in terms of strain on the column tie) enhancement of the tension column was not substantial due to the ferrocement strengthening of the masonry infill when compared to that of the masonry infilled RC frame. Moreover, the damage concentration on RC columns (i.e., residual crack width) after insertion of masonry infill and ferrocement strengthened masonry infill changed to a smaller extent when compared to the bare RC frame damages, where the residual crack widths were within 1.0 ~ 2.0 mm.

Experimental and analytical investigation of opening effects on the in-plane capacity of unreinforced masonry wall

A test programme consisting of four half-scale URM walls was conducted under quasi-static cyclic loading to evaluate the negative influence of openings. Test results showed that the masonry adjacent to the opening experienced significant damage, and the specimens with a door opening was found to have complete detachment of the masonry pier, resulting in a reduction in the capacity of more than 25%. Furthermore, a detailed parametric nonlinear finite element analysis was performed to assess the influence of parameters affecting the in-plane load capacity of the URM wall. Numerical results showed that depending upon the size and location of openings and the material and geometric properties of walls, the in-plane load capacity was reduced by 6–82%. Considering the results of available experimental studies and present numerical analyses, a simplified equation was proposed to estimate the reduction in the in-plane load capacity of the specimen with different types of openings. The analytical study demonstrated that the proposed equation effectively provided reliable and consistent predictions of the strength reduction factor for walls with different types of openings.

Cyclic behaviour of welded stainless steel beam-to-column connections: Experimental and numerical study

This paper presents an experimental and numerical programme on six welded stainless steel beam-to-column connections subjected to cyclic loading. The test specimens were designed in accordance with Eurocodes and comprised an I-section beam made from 316 L stainless steel welded to an I-section column made from 304 L stainless steel. Each specimen was subjected to a quasi-static cyclic loading protocol and the load-displacement curves are monitored and reported. The results are analysed in terms of failure characteristics, skeleton curve, strain distribution and energy dissipation. Typical failure modes are combined global flexural and torsional buckling and localised web and flange buckling of the beams. The slope of skeleton curve in the hardening region and the energy dissipation capacity appeared to reduce with the section size. Numerical models capable of successfully replicating the experimentally observed response were developed. The load-displacement behaviour and the failure pattern were compared to the experimental ones, showing a good validation. Overall, it has been demonstrated that good hysteretic performance has been achieved for the welded stainless steel beam-to-column connections.

Seismic performance assessment of RC bridge piers with variable hysteresis performance dampers

A novel variable hysteresis performance damper (VHD)—multi-stage slip friction damper is developed and applied to implement multi-level seismic resistance of structures. Different from the conventional slip friction dampers, which feature only a single type of slip friction surface, this innovative damper incorporates two types: a flat slip surface and a wedge slip surface. The quasi-static cyclic loading tests of the VHD were carried out to investigate its variable hysteresis performance. The test results revealed that the developed damper presented excellent adaptive performance, and its hysteresis behavior changed from a complete rectangle with efficient energy dissipation to a flag-shaped curve with exceptional self-centering capacity as deformation increases. Subsequently, the developed VHD with unique adaptive performance was applied in RC bridge piers (BP) to improve the seismic performance. Nonlinear time history and fragility analysis methods were employed to assess the seismic performance of the RC bridge piers with VHDs (BP-VHD) in deterministic and probabilistic manners, considering maximum and residual deformations as performance indicators. For comparison, seismic responses of RC bridge piers with traditional buckling restrained braces (BRBs) and self-centering energy dissipation braces (SCEBs) were also presented. The analysis and comparison results demonstrate that the developed VHD is as effective as BRB in reducing maximum deformation at small PGAs, meanwhile, it can effectively reduce the residual deformation of the structure to allowable values when the PGA is large. Furthermore, the failure probability of BP-VHDs is lower compared to piers with BRBs and SCEBs, particularly concerning maximum and residual drift ratios as performance indicators. The application of the VHD can effectively achieve the goal of multi-level seismic resistance for RC bridge piers.

The action of heated RC joints strengthened with a novel strategy combined CFRP and SSEMSM under a quasi-static cyclic load

The current work presents the application of a novel strategy for strengthening heated beam column (B-C) joints under a quasi-static cyclic load. This technique involves utilizing a layer of carbon fiber-reinforced polymers (CFRP) sheets with a layer of stainless-steel expanded metal sheet mesh (SSEMSM). These two layers are installed on the steel reinforcement cage inside the joint before concrete casting. Then the reinforced concrete B-C joints, after being cast and cured, were subjected to heat (i.e., 400 °C and 600 °C). The joints were divided into three groups: three joints were kept as is (i.e., reference joints; no strengthening was applied), whereas three joints were strengthened with the previously mentioned strategy. With a view to investigating the seismic behavior of RC joints, a quasi-static cyclic load was applied to the joints to simulate a seismic load. Results showed that the average maximum load capacity for upgraded joints (strengthened) increased by 30%, 19%, and 1% at ambient (i.e., 23 °C), 400 °C, and 600 °C temperatures, respectively, with respect to the reference joint (JCTA). More importantly, the experimental results reveal a significant increase in the cyclic response of strengthened joints (i.e., higher load capacity, greater displacement, higher dissipated energy, higher ductility, and slower degradation in the secant stiffness).

Investigation on laminated steel slit shear walls with low yield steel

To improve the energy dissipation capacity of steel slit shear walls made of thin plates and mitigate the adverse effects from the large out-of-plane deformation and potential local buckling failure, a novel laminated steel slit (LSS) shear wall assembled from two single-layer steel slit (SSS) shear walls is proposed in this study. First, the theoretical analysis method for predicting the shear strength and stiffness of the LSS shear walls is proposed. To validate the theoretical method as well as investigate the hysteretic performance of the LSS shear walls, two specimens made from different materials, common carbon steel and low yield steel, are designed and tested experimentally under quasi-static cyclic loading. Refined finite element models are developed to simulate the hysteretic behaviors of the LSS shear walls, which show good agreement with the test results. Further, the performance differences between the LSS shear walls and SSS shear walls are analyzed using the validated numerical simulation approach. The strength and stiffness of the LSS shear walls are greater than the summation of the individual SSS shear walls, attributed to the interaction between the different layers in the LSS shear walls. The energy dissipation efficiency of the LSS shear walls is improved and the stiffness degradation is effectively delayed, thanks to the incorporation of the low yield steel material. Finally, to evaluate the effects of the contributing factors on the seismic performance of the LSS shear walls, a series of parametric analyses are performed. Parametric analysis results show that the use of the low yield steel helps to improve the ductility and energy dissipation capacity of the LSS shear walls and delay the stiffness degradation. A large link width ratio, small link length ratio and large link thickness ratio can all contribute to a large strength, stiffness and absolute energy dissipation of the LSS shear walls, but the former two at the same time deteriorate the stiffness degradation.

Investigation on the influence of previous in-plane loading on the out-of-plane behavior of the innovative damped masonry infill wall

The damped masonry infill wall (DMIW) is an innovative masonry infill wall (MIW), wherein multiple horizontal subpanels, also called masonry units, are subdivided by inserting the horizontal damping layer joints (DLJs). While existing research on DMIW primarily focuses on its pure in-plane (IP) and pure out-of-plane (OOP) behavior, it is crucial to account for the interaction effect between IP and OOP behaviors to accurately assess OOP performance, Failure to consider this interaction may lead to an overestimation of OOP capacity, a concern previously highlighted in traditional MIW studies. Addressing this gap, this study conducts a sequential experiment involving IP cyclic quasi-static loading followed by OOP monotonic quasi-static loading. The aim is to examine the influence of previous IP cyclic loading on OOP behavior, considering factors such as OOP damage evolution, performance parameters, deformation patterns, and resistance mechanisms. The results show that, in DMIW, the effect of previous IP cyclic loading on the reduction of OOP performance is significantly lower compared to traditional MIW. Furthermore, the fundamental OOP resistance mechanism of DMIW remains unchanged under IP-OOP sequential loading. However, the OOP deformation pattern is altered due to the previous horizontal cracks developed in the masonry units under IP cyclic loading. Finally, a simple bi-linear equation is derived to quantify the effect of the previous IP cyclic loading on the primary OOP performance parameters of the DMIW.