Plastic Rotation Research Articles

Evaluasi Kinerja Seismik Rangka Beton Pemikul Momen Khusus dengan PERFORM-3D

Seismic performance of reinforced concrete frame Buildings which have been designed as Special Moment Resisting Frames in accordance to three Indonesian codes (SNI 1727-2013, SNI 1726-2012 and SNI 2847-2013) can be evaluated using nonlinear dynamic analysis. Criteria related to strength such as component plastic rotation capacity, lateral displacement as well as criteria related to damage of elements in the structures were used to evaluate the seismic performance of the buildings. Assessment to the moment and curvature capacities of the cross sections of beams and columns were done using XTRACT. The global seismic performance of the structures depends on the seismic performance of components in the structures. In nonlinear model of the structures, the degrading strength of the components were modeled to take into account the gradual reduction of the contributed components to the resistance of the structures. PERFORM-3D is one of the software that can be used to generate nonlinear model of structures. Seismic performance level of structures can be obtained from the results of the nonlinear dynamic analysis using PERFORM-3D. The Seismic performance level can be utilized for: (1) detecting any weaker part in the structures, and (2) evaluating the improved design of the structures for enhancing the seismic performance of structures.

Experimental Study on Energy Dissipation Performance and Failure Mode of Web-Connected Replaceable Energy Dissipation Link

In the current design method of the eccentrically braced frame structure, the energy dissipation link and the frame beam are both designed as a whole. It is difficult to accurately assess the degree of damage through this method, and it is also hard to repair or replace the energy dissipation link after strong seismic events. Meanwhile, the overall design approach will increase the project’s overall cost. In order to solve the above mentioned shortcomings, the energy dissipation link is designed as an independent component, which is separated from the frame beam. In this paper, the energy dissipation link is bolted to the web of the frame beam. Both finite element simulation and test study of eight groups of energy dissipation links have been completed to study their mechanical behaviors, and the energy dissipation links have been studied in the aspects of length, cross section, and stiffener spacing. The mechanical behaviors include the energy dissipation behavior, bearing capacity, stiffness, and plastic rotation angle. The results indicate clearly that the hysteretic loop of links in the test and finite element analysis is relatively full. By comparing the experimental and finite element simulation data, it can be found that the general shape and trend of hysteretic loop, skeleton curve, and stiffness degradation curve are basically the same. The experiment data explicitly shows that the energy dissipation link of web-connected displays good ductility and stable energy dissipation ability. In addition, the replaceable links possess good rotational capacity when the minimum rotation angle of each specimen in the test is 0.16 rad. The results of the experiment show that the energy dissipation capacity of the link is mainly related to the section size and the stiffening rib spacing of the link. The energy dissipation ability and deformation ability of the link is poorer as the section size becomes larger; meanwhile, these abilities are reduced with the decrease of the stiffening spacing. The experiment result shows that the damage and excessive inelastic deformations are concentrated in the link to avoid any issues for the rest of the surrounding elements, and the links can be easily and inexpensively replaced after strong seismic events. The results are thought provoking, as they provide a theoretical basis for the further study of the eccentrically braced frame structure with replaceable links of web-connected. In future work, the author aims to carry out his studies through optimized design methodology based on the yielding criterion.

A study on the accuracy of force analogy method in nonlinear static analysis

SummaryIn this paper, the accuracy of the force analogy method (FAM) for nonlinear static (pushover) analysis is investigated. Hence, after explanation of the concept of FAM by a new approach, 12 2D steel special moment resisting frames with different configurations were derived from two different 3D archetypes and modeled using four various methods of capturing nonlinearity including SAP2000 super elements, OpenSees force‐based and displacement‐based fiber method, and FAM. In addition, a MATLAB code was developed for modeling and analyzing the frames by FAM. The accuracy of FAM in predictions of pushover curves, base shear forces, and plastic rotation of the critical hinges was investigated. The results indicated that in general, the predictions obtained using the FAM had a good agreement and compatibility with those from other methods of analysis currently used in practice for seismic performance assessment of structures.

Alternative approach in distortion gradient plasticity theory

This study presents an alternative thermodynamically consistent distortion gradient plasticity theory for polycrystalline materials. The formulation employs the principle of virtual power, laws of thermodynamics, and codirectionality hypothesis for the constructions of macroscopic and microscopic balance laws governing the elastic and plastic responses of the materials. Expressing the plastic distortion tensor in terms of accumulated plastic strain and plastic rotation vector shows that the two quantities are governed by independent plastic flow equations. In addition, it is obtained that the flow equation which governs the accumulated plastic strain interacts with the elastic response of the materials, while the flow equation governing the plastic rotation vector is independent of the elastic response. Finally and among other things, it is shown that the present model is computationally less expensive in the sense that it requires lesser numbers of equations for the prediction of plastic behavior of the materials.

Assessment of Different Steel Material Characteristics on Shear Links Performance

The inelastic behavior of shear links depends on their material ductility. In order to investigate the effect of cyclic characteristics of steel on shear links behavior, five experimental links constructed of various steel grades are modeled by finite element approach. These models are verified using experimental shear links results. Moreover, cyclic stress-strain material curve is used for simulating links behavior and the models can simulate strength degradation of flange and web local buckling appropriately. The overstrength and plastic rotation of the links are modified due to the influence of test setup configuration once the buckling occurs. It can be concluded that the links material characteristics can affect the overstrength and plastic rotation. In this study, the various strain hardening of different grades of steel are evaluated and the amplitudes of strain which can simulate strain hardening of links are determined for five materials.

Simplified 3D model for the uplift analysis of liquid storage tanks

Vertical uplifting of the tank base is perhaps the most relevant characteristic of the seismic behaviour of unanchored cylindrical liquid storage tanks made of steel. When an unanchored tank is subjected to lateral loads due to the earthquake-induced hydrodynamic pressures, a portion of the base plate tends uplift locally. Analysis of the base plate uplifting of unanchored tanks implies many sources of nonlinear behaviour mechanisms such as the varying contact of the base plate with the foundation, large deflections, the material yielding and the plastic rotation of the base plate. This paper presents a comprehensive analysis of the partially uplifted base plate of two thin-walled cylindrical tanks (one slender and one broad). First, a nonlinear quasi-static cyclic analysis with a finite element model and a simplified model is carried out for each tank. Next, an efficient method for three-dimensional dynamic analysis is proposed and used in order to obtain the nonlinear time history response of each tank. The simplified non-linear model proposed in this paper was capable to provide a good estimation of both the rocking resistance of the liquid-loaded base plate and the stress distribution on the tank wall in contact with the foundation. A set of seven seismic ground motions was used for the time history analysis. Finally, the distribution of the tank wall stresses and the critical responses of the tanks are discussed. Both anchored and unanchored tanks may present a high compressive axial stress due to the seismic effect.

Effect of Shear Reinforcement on Flexural Strengths of Normal Weight and Palm-Kernel Shell Reinforced Concrete Beams

The focus of this research is to investigate the effect of shear reinforcement on flexural capacities of reinforced Normal Weight Concrete (NWC) and Palm Kernel Shell Concrete (PKSC) beams. Ten beams were cast: five from PKSC and five from NWC. The beams were with shear reinforcement spacing of 50 mm, 100 mm, 150 mm, 200 mm and without shear reinforcement respectively. The beams were loaded with a point load at beam centre, and the results showed that the flexural capacity of the beams decreases as the spacing of the shear reinforcements increases. The ultimate loads of PKSC beams were lesser than that of NWC beams by 9.0%, 7.1%, 14.5%, 21 and 26.8% for shear reinforcement spacing of 50 mm, 100 mm, 150 mm, 200 mm and for beam without shear reinforcements respectively. The deflections of the PKSC beams were greater than that of the NWC, hence the PKSC beams had more plastic rotation capacity than the NWC beams. The study shows that reinforced concrete beams produced from 20% partial replacement of crushed aggregate by PKS have the potential of being used for structural purposes in low cost buildings. Keywords: Palm Kernel Shell Concrete, Normal weight concrete, Palm kernel shell, Deflection, Shear reinforcement.

Seismic Fragility Assessment of Ordinary RC Shear Walls Designed with a Nonlinear Dynamic Analysis

Seismic performance of ordinary reinforced concrete shear wall systems commonly used in high-rise residential buildings is evaluated. Three types of shear walls exceeding 60m in height are designed by performance-based seismic design. Then, incremental dynamic analysis is performed collapse probability is assessed in accordance with the procedure of FEMA P695. As a result, story drift, plastic rotation, and compressive strain are observed to be major failure modes, but shear failure occur little. Collapse probability and collapse margin ratio of performance groups do not meet requirement of FEMA P695. It is observed that critical wall elements fail due to excessive compressive strain. Therefore, the compressive strain of concrete at the boundary area of the shear wall needs to be evaluated with more conservative acceptance criteria.

PARAMETRIC EVALUATION OF THE PLASTIC DEFORMATION CAPACITY OF FIBER REINFORCED POLYMERS CONFINED SQUARE AND RECTANGULAR COLUMNS

Confinement with fiber reinforced polymers of reinforced concrete columns is promising retrofit solution for improving ductility of existing structure. In the study, plastic deformation capacityof fiber reinforced polymers confined square and rectangular reinforced concrete columns were parametrically evaluated. Recently released seismic strengthening recommendations of American Concrete Institute were considered for calculating plastic rotation of specified columns. Fiber reinforced polymers confined concrete model provided by the design guideline was utilized for calculating moment curvature relationship of fiber reinforced polymers confined reinforced concrete columns. Numerous sectional analysis was performed with combination of various parameters (concrete strength, axial load ratio and number of fiber reinforced polymers plies). Plastic rotations of columns were determined with plastic part of the curvature and plastic hinge length for evaluating the effects of parameters on plastic deformation capacity.

Evaluation of the plastic hinge length of steel-concrete composite beams under hogging moment

Lumped plasticity is one of the most commonly used approaches for the nonlinear analysis of framed structures, but its effectiveness depends on the reliability of the plastic rotational capacity. In the case of RC or steel structures, this approach is based on well-known and reliable formulations, but no specific rules have been established for steel-concrete composite structures. This paper reports the results of a detailed analysis of the nonlinear behaviour of the section and entire element of a composite beam with the goal of determining its flexural ductility. In particular, the composite beam was examined under a hogging moment that results in its worst performance due to the concrete experiencing tension and the steel compression. An FE model is used to study the element; it was considered all the features of the materials and the geometry of the section to develop a parametric analysis that enabled to study the effect of different parameters on the rotational capacities of the composite beams. This formulation considers the local phenomenon of profile buckling and the global dimensions of the composite section. Finally, the obtained results allowed to define an equivalent plastic hinge length that provides the available plastic rotation when multiplied by the plastic curvature of the cross-section.

Influence of steel fibers on the flexural behavior of RC beams with low reinforcing ratios: Analytical and experimental investigation

In this work, the results of an experimental program intending to investigate the flexural characteristics of reinforced steel-fiber concrete beams (S/SFRC) are reported and discussed. Hooked end steel fibers with aspect ratios of 45 or 80 were used to produce matrices with fiber content ranging from 0 to 2%, in volume, and high compressive strength. A full mechanical characterization was carried, including the post-peak properties for concrete matrix in tension. Beams with reinforcing ratios of 0.28, 0.44 and 0.70% were analyzed using digital image correlation (DIC) to monitor displacement field and cracking distribution throughout the constant moment region during loading. Data reported included load-deflection and moment-curvature curves, evolution of compressive strains in concrete and neutral axis depth, spacing and openings of cracks and failure modes. Tests revealed gains of capacity ranging from 21 to 109% of R/SFRC with respect to plain RC beams and significant reductions in crack openings for a given rebar stress. R/SFRC beams exhibited sufficient plastic rotation capacity, but with a reduction in plastic hinge length as a consequence of the phenomenon of crack localization. Comparisons with current code provisions show that these are adequate for the design but residual stresses obtained from direct tensile tests are more appropriate.

Seismic design of the double-cell accordion-web reduced beam section connection

The Accordion-Web Reduced Beam Section (AW-RBS) connection consists of a corrugated web, replacing the flat web, within a limited area near the column face, which reduces the beam flexural strength and forces the plastic hinge to form in the corrugated zone. This paper presents a seismic design procedure in the framework of the U.S. design standards for a double-cell AW-RBS connection, which consists of two box sections oriented such that an accordion web is formed within a limited area in the beam. The analytical evaluation of the flexural strength of the beam with a corrugated web was first presented. Then, a step-by-step design method was proposed to size the connection. Quasi-static cyclic tests were conducted on two relatively identical specimens including double-cell AW-RBS connections. A detailed numerical model of a connection with deep beams and columns designed in accordance with the proposed design procedure was developed and a nonlinear analysis was performed to investigate the seismic response of the connection and verify the adequacy of the proposed design method for the beam sizes frequently used in steel moment-resisting frames. The results confirmed the satisfactory response of the double-cell AW-RBS connection under cyclic loading. The stable plastic hinge formed in the reduced area of beams as predicted in design and no yielding was observed in the beam-to-column groove weld. The findings of the numerical simulations confirmed that the AW-RBS connection with deep beams and columns could potentially exceed the plastic rotation limit for ductile moment connections without significant instability and strength degradation.

Review of experimental tests and numerical study on masonry vaults reinforced through fiber-reinforced mortar coating

The paper deals with the seismic vulnerability of masonry vaults: a review of the results of an experimental campaign recently performed by the authors and a numerical study are presented. In particular, the effectiveness of a strengthening technique based on the application, at the vault extrados or intrados, of a 30 mm thick mortar coating with glass fiber-reinforced polymer meshes embedded is discussed, referring to vaults carrying their self-weight and subjected to a lateral transversal load. The role of the connection of the vault with its abutments is particularly emphasised in this review of the experimental results, evidencing how slides and/or uplifts at the spring sections can reduce the strengthening effectiveness. The numerical study, based on non-linear static analysis, allowed to investigate in depth into the effects of an inadequate skewback configuration: it was found that a ductile connection, which allows plastic rotation at the spring section while maintaining the bending resistance and avoiding shear slip and uplift, is the optimal solution. Moreover, the results of a sensitivity study are also presented, as this permits to evaluate the incidence of the different mechanical and geometrical parameters on the behavior of the vaults and provides useful indications towards a proper design and optimization of the strengthening intervention.

Loading Definition and Design of Bridge Piers Impacted by Medium-Weight Trucks

Computational simulation was used to investigate the collision process between medium-weight, single-unit trucks and reinforced concrete bridge piers. The simulation results were used to formulate and calibrate a pulse model to describe, in a simplified manner, the dynamic force demands imposed on a bridge pier by a colliding truck. Key parameters in the force demand model were impact speed, truck weight, and pier dimensions. Accuracy of the proposed demand model was assessed by comparing the damage modes and displacement profiles of piers subjected to impact by the computational truck model and an equivalent, simplified pulse model. Extensive numerical simulations were carried out using the developed pulse model to identify prominent failure mechanisms. Damage levels were quantified through the use of macrolevel deformation parameters, such as plastic rotation and shear distortion. It was shown that shear damage can be substantially reduced by using capacity design theory to proportion the piers.

Evaluation of seismic behaviour of railway bridges considering track-bridge interaction

Railway bridges have historically performed well in the previous earthquakes. Although this performance has qualitatively been studied in some references such as AREMA code, no quantitative criteria has been proposed for it. Thus, this study aims to present quantitative criteria for railway bridge performance under seismic loads. In the paper, seismic behaviour of railway bridges, with and without track-bridge interaction (TBI), is calculated through finite element modeling. Pushover and incremental dynamic analyses, are utilized to assess the proposed method, considering fourteen records of the past earthquakes. The results clearly show superior performance of the proposed model with track system, in which the deck displacement, base shear, and plastic rotation decrease by 70%-90%, 20%-83%, and 85%-100%, respectively. Finally, two equations are proposed to calculate deck displacement and base shear of railway bridges without performing track-bridge interaction (TBI) by Peak Ground Acceleration (PGA) of the applied record approximately.

Progressive collapse resistance of a composite steel and concrete structural frame

During the past decade, numerous research studies have been conducted on building structures to resist progressive collapse. In the study reported in this paper, a new type of octagonal partially encased composite column was tested and analysed under compressive loads. A comprehensive finite-element analysis was then conducted to estimate the structural behaviour of composite steel and concrete frames under the loss of a column. Push-down and non-linear dynamic analyses were conducted to investigate the resistance of frames against progressive collapse, including collapse-resistance force, hinge-development mechanism, flexural stiffness and displacement ductility. The analysis showed that making use of partially encased composite columns can provide alternative paths for transferring loads originally only supported by the beams, thus improving the collapse-resistance capacity of the steel frame. The partially encased column, however, may reduce the ductility of the steel frame and may change the failure mode of the frame. Also, none of the beam–column connections can meet plastic rotation criteria.

Composite steel beam database for seismic design and performance assessment of composite-steel moment-resisting frame systems

This paper discusses the development of a publicly available database of composite steel beam-to-column connections under cyclic loading. The database is utilized to develop recommendations for the seismic design and nonlinear performance assessment of steel and composite-steel moment-resisting frames (MRFs). In particular, the sagging/hogging plastic flexural resistance as well as the effective slab width are assessed through a comparison of the European, American and Japanese design provisions. The database is also used to quantify the plastic rotation capacity of composite steel beams under sagging/hogging bending. It is found that the Eurocode 8-Part 3 provisions overestimate the plastic rotation capacities of composite beams by 50% regardless of their web slenderness ratio. Empirical relationships are developed to predict the plastic rotation capacity of composite steel beams as a function of their geometric and material properties. These relationships can facilitate the seismic performance assessment of new and existing steel and composite-steel MRFs through nonlinear static analysis. The collected data underscores that the beam-to-column web panel zone in composite steel beam-to-column connections experience higher shear demands than their non-composite counterparts. A relative panel zone-to-beam resistance ratio is proposed that allows for controlled panel zone inelastic deformation of up to 10 times the panel zone’s shear yield distortion angle. Notably, when this criterion was imposed, there was no fracture in all the examined beam-to-column connections.

Experimental analysis of load capacity in beams with steel fiber reinforcement on the compression face

Abstract The use of steel fibers in the concrete is mainly aimed at increasing the post-peak toughness, due to the adhesion of the fibers to the cementitious matrix. However, there are several typologies of steel fibers, and the main differences are in the form (relation between length and diameter), fiber geometry, and the characterization between macrofibers and microfibers, which generally serve to reduce macrocracking and microcracking, respectively. In this context, this work evaluated the use of microfibers (20 kg/m³ or volume equal to 0.26% (Vf) of concrete volume), macrofibers (20 kg/m³ or Vf = 0.26%) and hybridization (10 kg/m³) + macrofibers (10 kg/m³) inserted in a high strength concrete (fc = 80 MPa). Two types of steel fibers were used: macrofibers with a diameter of 0.75 mm and a length of 60 mm (a form factor of 80); and microfibers with a diameter of 200 μm and a length of 13 mm (a form factor of 65). The fibers were used in concrete to act as a reinforcement on the compression face of reinforced beams (12×20×160cm), and the mechanical characteristics of the concretes were analyzed: (i) flexural strength in prismatic specimens (10×10×35 cm), (ii) compressive strength in cylindrical specimens (20×Ø10 cm) and (iii) modulus of elasticity in cylindrical specimens (20×Ø10 cm). Analysis of the results showed that compressive strength increased by approximately 8% for all the compositions with fibers compared with concrete without fibers. Similar behavior was verified for the modulus of elasticity. In the prismatic specimens (10×10×35 cm) an increase in toughness was observed, with the macrofibers performing better. In beams measuring 12×20×160 cm, an increase in bearing capacity was verified regarding cracking time and plastic rotation, with the best result also obtained using macrofibers. Overall, it can be concluded that the application of reinforcement with steel fibers in the compression face of beams was efficient, even though it did not present a significant increase in compressive strength, a fact that could be correlated with the reduced volume of fibers used.

Simplified performance-based optimal seismic design of reinforced concrete frame buildings

This paper presents a simplified performance-based optimal seismic design approach for multi-story reinforced concrete moment frames. The proposed approach minimizes construction cost and takes member plastic rotation and optionally inter-story drift as optimization constraints. Other seismic design requirements reflecting successful design practice are also incorporated. Simplification is made by reducing design variables into two, one for overall system stiffness and the other for overall system strength. The optimization contains two stages, the determination of feasible region boundary in strength and stiffness domain and optimization in material consumption domain. Capacity spectrum method, which jointly considers nonlinear static analysis and inelastic design spectrum, is used to estimate the global and local deformation demands at peak dynamic response. The proposed optimization approach is applied to the design of a six-story reinforced concrete frame. The design results indicate that 30% of needed flexural strength and 26% of cross-sectional area can be reduced from the initial strength-based design. Nonlinear time-history analyses are conducted on the optimized structure using ten historical ground motions scaled to represent three levels of seismic hazard.

New Lateral Force Distribution for Seismic Design of Structures Based on Seismic Demand Ratio

The design of earthquake-resistant buildings starts with defining the maximum lateral earthquake forces or their resultant. The amount of these forces depends on various factors, including coefficient of system behavior which depends on over strength and its ductility. In this study, a method is proposed in order to design an earthquake-resistant system in which the distribution of lateral forces is adjusted based on equal distribution of the seismic demand ratio in structural elements for the optimum use of seismic capability of the structure. To this end, three types of 4-, 7-, and 10-story structures are Applied. Firstly, the above-mentioned structures are designed based on gravity loads and consequently analyzed based on linear and nonlinear dynamic analyses, applying the accelerograms of some major earthquakes. Pursuant to that, the average loading ratio to the allowed capacity of the elements of each story in linear analysis and the average ratios of plastic rotations to the allowed capacity of elements in nonlinear analysis are applied as the modified shear ratio in the Iranian National Seismic Code. On that account, the new lateral loading distribution is measured and identified. Based on this new distribution, the above-mentioned structures are designed and their seismic behaviors are identified, applying linear and nonlinear dynamic analyses of the same accelerograms. The findings indicate an ameliorated seismic behavior of the beams and the columns. Moreover, the distribution of the seismic demand ratios attains more uniformity along the height of the structures.