Source Of Energy Dissipation Research Articles

Seismic response and energy dissipation in partially restrained and fully restrained steel frames: An analytical study

The damage suffered by steel structures during the Northridge (1994) and Kobe (1995) earthquakesrnindicates that the fully restrained (FR) connections in steel frames did not behave as expected. Consequently,rnresearchers began studying other possibilities, including making the connections more flexible, to reduce thernrisk of damage from seismic loading. Recent experimental and analytical investigations pointed out that thernseismic response of steel frames with partially restrained (PR) connections might be superior to that of similarrnframes with FR connections since the energy dissipation at PR connections could be significant. Thisrnbeneficial effect has not yet been fully quantified analytically. Thus, the dissipation of energy at PRrnconnections needs to be considered in analytical evaluations, in addition to the dissipation of energy due tornviscous damping and at plastic hinges (if they form). An algorithm is developed and verified by the authors tornestimate the nonlinear time-domain dynamic response of steel frames with PR connections. The verifiedrnalgorithm is then used to quantify the major sources of energy dissipation and their effect on the overallrnstructural response in terms of the maximum base shear and the maximum top displacement. The resultsrnindicate that the dissipation of energy at PR connections is comparable to that dissipated by viscous dampingrnand at plastic hinges. In general, the maximum total base shear significantly increases with an increase in thernconnection stiffness. On the other hand, the maximum top lateral displacement Umax does not always increasernas the connection stiffness decreases. Energy dissipation is considerably influenced by the stiffness of arnconnection, defined in terms of the T ratio, i.e., the ratio of the moment the connection would have to carryrnaccording to beam line theory (Disque 1964) and the fixed end moment of the girder. A connection with a Trnratio of at least 0.9 is considered to be fully restrained. The energy dissipation behavior may be quite differentrnfor a frame with FR connections with a T ratio of 1.0 compared to when the T ratio is 0.9. Thus, for nonlinearrnseismic analysis, a T ratio of at least 0.9 should not be considered to be an FR connection. The studyrnquantitatively confirms the general observations made in experimental results for frames with PR connections.rnProper consideration of the PR connection stiffness and other dynamic properties are essential to predictrndynamic behavior, no matter how difficult the analysis procedure becomes. Any simplified approach mayrnneed to be calibrated using this type of detailed analytical study.

Seismic risk analysis of frames with uncertain support and PR connection conditions

A hybrid reliability evaluation procedure is proposed to estimate the risk of steel frames considering the rigidity of connections and supports as accurately as possible. Nonlinearities due to geometry, material, partially restrained (PR) connections, and flexible supports are considered in the proposed algorithm. The four-parameter Richard model is used to represent the flexibility of connections and supports. All major sources of uncertainty in the loading and resistance-related parameters and the parameters in the Richard model are incorporated in the algorithm. The unique feature of the algorithm is that the earth-quake loading can be applied in the time domain, providing an alternative to the random vibration approach. The proposed algorithm intelligently integrates the concepts of the finite element method, the response surface method, the first order reliability method, and the iterative linear interpolation scheme. The algorithm is verified using Monte Carlo simulation. With the help of an example, it is shown that the proposed algorithm can be used to estimate risk for both the serviceability and strength limit states. The presence of PR connections and/or flexible supports alters the dynamic properties (stiffness and damping) of the structure and adds a new and major source of energy dissipation. The serviceability limit state may become the controlling limit state, particularly for seismic loading. Thus, the common practice of considering all connections and supports to be rigid and designing the frame for the strength limit state may not be appropriate. The flexibility of connections and supports and the uncertainty in modeling them have a considerable influence on the overall behavior of frames, particularly under seismic loading. An efficient, robust, and accurate method is proposed to evaluate the reliability of such frames.

TEACHING NOTES

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Energy Dissipation at PR Frames under Seismic Loading

The major sources of energy dissipation, lateral deformation, and base shear in steel frames with partially restrained (PR) connections subjected to seismic loading are analytically studied. The analytical study confirms, in general, the behavior observed during experimental investigation: PR connections reduce the overall stiffness of frames, but add a major source of energy dissipation. It is observed, in general, that the maximum total base shear may significantly increase as the connection stiffness increases. The maximum top lateral displacement does not always increase with a decrease in the connection stiffness. The response under earthquake loading largely depends on the dynamic characteristics of both the structure and the earthquake excitation. Proper consideration of the stiffness of the PR connections and other dynamic properties is essential to predict the dynamic behavior, no matter how difficult the analysis procedure becomes.

Energy Dissipation in Soil-Structure Interaction

Energy dissipation as a means of reducing the seismic response of structures has become a popular topic among researchers and structural engineers who have developed and implemented devices, such as friction dampers, fluid dampers, and isolators, in the design or retrofit of structures. However, a natural source of energy dissipation is the interaction between a structure, its foundation, and the supporting soil medium. To account for this frequency-dependent energy dissipation in dynamic analysis based on modal superposition, relatively simple and practical systems-identification methods are presented to estimate the composite modal damping ratios for the significant modes of vibration. SSI experiments and analysis of simple theoretical models using this method have yielded relatively large modal damping ratios in certain situations for structures such as short to mid-rise buildings, short-span bridges, flat bottom fuel storage tanks, offshore concrete gravity platforms, nuclear power plant containments, and nuclear waste processing plants.

Impact behavior of a short glass fiber reinforced thermoplastic polyurethane

AbstractThe temperature dependence of critical strain energy release rate (Gc′) and standardized Charpy notched impact strength (CNIS) were measured for a thermoplastic polyurethane (TPUR) reinforced with 30 wt% of short glass fibers (SGF) over a temperature interval ranging from −150°C 23°C (RT) at two strain rates, 70 and 150 s−1, respectively. Fractographic observation of fracture planes was used to qualitatively assess the fracture modes and mechanisms. Adhesion between the reinforcement and the matrix was excellent and the integrity of the fiber‐matrix interfacial contact was relatively insensitive to exposure to hydrolysis during the immersion in boiling water for 100 hours. At temperatures above −30°C, there was a large extent of plastic deformation in the vicinity of crack planes while at temperatures below −50°C, the extent of plastic deformation was substantially reduced. This resulted in a change in the major energy dissipation mechanism and led to a decrease of both CNIS and Gc′ values for SGF/TPUR composites. It was suggested that the plastic deformation of TPUR matrix in the immediate vicinity of glass fibers was the primary source of energy dissipation at temperatures above −30°C, while the friction and fiber pull‐out was the main dissipative process below −50°C. Over the whole temperature interval investigated, greater Gc′ values were obtained at higher strain rate of 150 s−1, without any significant change in the fractographic patterns observed on the fracture planes. The CNIS/Gc′ ratio, used to assess suitability of CNIS for comparison of materials, changed with temperature substantially suggesting that the functional dependences of CNIS and Gc′ on temperature differ substantially. Hence, CNIS data do not provide a reliable base for material selection and for design purposes in this case.

Thermal modelling of a porous silicon-based pellistor-type catalytic flammable gas sensor with two supporting beams

A three-dimensional transient thermal mathematical model of a porous silicon based pellistor with two supporting beams was developed. The model was numerically solved using the implicit alternating-direction finite difference method. A computer program written in ANSI C and run on a VAX/VMS computer was utilised to study the influence of the power consumption and the main geometrical dimensions (membrane, beam and heater size) of the pellistor mentioned above on its transient and steady-state thermal behaviour. It was found that considerable improvement in the thermal behaviour of the pellistor could be achieved by reducing the membrane size (length and width). The optimal beam length was determined as 100μm. By comparing the main sources of energy dissipation it was found that energy was lost predominantly through the heat conduction into the supporting beams.

Dissipation of energy in steel frames with PR connections

The major sources of energy dissipation in steel frames with partially restrained (PR) connections are evaluated. Available experimental results are used to verify the mathematical model used in this study. The verified model is then used to quantify the energy dissipation in PR connections due to hysteretic behavior, due to viscous damping and at plastic hinges if they are formed. Observations are made for two load conditions: a sinusoidal load applied at the top of the frame, and a sinusoidal ground acceleration applied at the base of the frame representing a seismic loading condition. This analytical study confirms the general behavior, observed during experimental investigations, that PR connections reduce the overall stiffness of frames, but add a major source of energy dissipation. As the connections become stiffer, the contribution of PR connections in dissipating energy becomes less significant. A connection with a T ratio (representing its stiffness) of at least 0.9 should not be considered as fully restrained as is commonly assumed, since the energy dissipation characteristics are different. The flexibility of PR connections alters the fundamental frequency of the frame. Depending on the situation, it may bring the frame closer to or further from the resonance condition. If the frame approaches the resonance condition, the effect of damping is expected to be very important. However, if the frame moves away from the resonance condition, the energy dissipation at the PR connections is expected to be significant with an increase in the deformation of the frame, particularly for low damping values. For low damping values, the dissipation of energy at plastic hinges is comparable to that due to viscous damping, and increases as the frame approaches failure. For the range of parameters considered in this study, the energy dissipations at the PR connections and at the plastic hinges are of the same order of magnitude. The study quantitatively confirms the general observations made in experimental investigations for steel frames with PR connections; however, proper consideration of the stiffness of PR connections and other dynamic properties is essential in predicting the dynamic behavior.

The plastic energy dissipation in metal matrix composites during cyclic loading

Plastic deformation of materials is a major source of energy dissipation during external loading. In metal matrix composites (MMCs), local plastic strain may arise even if the overall external load is below the yield stress of the matrix because of the difference of elastic modulus between the reinforcement and the matrix. In this paper, the finite element method combined with cell modelling is employed to discuss the energy dissipation of MMCs under cyclic loading for this case. The influence of the elastic modulus, the shape and the volume fraction of reinforcement on the energy dissipation was investigated numerically. The relation between external loading and energy dissipation was clarified. It was found that the energy dissipation became constant after two or three cycles and showed a strong dependence on loading amplitude and the volume fraction as well as the elastic modulus of inclusions. However, the energy dissipated is hardly influenced by the shape of the inclusions.

The Dynamic Response of Wood-Frame Shear Walls with Viscoelastic Dampers

Results are presented of an experimental investigation, the objectives of which were to evaluate and compare the performance of conventional plywood shear walls with walls that include viscoelastic (VE) dampers. Cyclic tests were conducted on conventional walls and walls with VE dampers; five different damper configurations were tested. The walls with the VE dampers showed an increase in the total energy dissipation and an increase in the effective stiffness, relative to the conventional wall, with increases in energy dissipation as high as 59 percent. Tests demonstrated that the sheathing-to-stud and corner dampers can easily be installed within the confines of the wall and can be utilized without impacting the design, construction, or finishing of the shear wall. The results demonstrate that addition of the viscoelastic dampers significantly enhanced the dynamic performance of the walls by increasing the energy dissipation capacity and providing a constant source of energy dissipation.

Crack Deflection and Propagation in Layered Silicon Nitride/Boron Nitride Ceramics

Crack deflection and the subsequent growth of delamination cracks can be a potent source of energy dissipation during the fracture of layered ceramics. In this study, multilayered ceramics that consist of silicon nitride (Si3N4) layers separated by boron nitride/silicon nitride (BN/Si3N4) interphases have been manufactured and tested. Flexural tests reveal that the crack path is dependent on the composition of the interphase between the Si3N4 layers. Experimental measurements of interfacial fracture resistance and frictional sliding resistance show that both quantities increase as the Si3N4 content in the interphase increases. However, contrary to existing theories, high energy‐absorption capacity has not been realized in materials that exhibit crack deflection but also have moderately high interfacial fracture resistance. Significant energy absorption has been measured only in materials with very low interfacial fracture resistance values. A method of predicting the critical value of the interfacial fracture resistance necessary to ensure a high energy‐absorption capacity is presented.

An Inverse Dynamic Model of a Spherical Electrohydraulic Actuator for Use in a Dexterous Mechanical Hand

The purpose of this article is to develop an inverse dynamic model of a two-degree-of-freedom electrohydraulic actuator. The actuator is to be incorporated at the base of each of three fingers of a nine-degree-of-freedom mechanical hand, currently under development. Motion in the proposed actuator is fa cilitated about intersecting pitch and yaw axes, thus creating spherical actuation. The dynamic model incorporates frictional and hydraulic losses, which are commonly overlooked sources of energy dissipation. The model is to be used in the control scheme of the mechanical hand and in the optimal synthesis procedure of the actuator. The latter application, briefly de scribed here, takes into account specified motion and torque requirements, pressure, peak-input force, and size constraints. Particular attention is paid to traditional performance indices, such as mechanical advantage.

On the measurement of concrete fracture energy using three-point bend tests

The RILEM proposal for measuring the fracture energy (GF) of mortar and concrete by means of three-point bend tests on notched beams [1] aroused a vivid discussion on the size dependence of GF. The authors of this note, in 1992, summarized in three papers [2–4] their research on the RILEM proposal, placing special emphasis on several sources of energy dissipation during testing. In particular, it was shown that the dissipated energy at the very end of the test cannot be neglected for small specimens when tests are stopped at a reasonably small rotation.

Supplementary energy dissipators for maximum earthquake protection of tall building structures

AbstractDuctility, or deformation energy, is by far the largest source of energy dissipation of structures, since normal levels of internal damping represent only a small portion of energy dissipation. However, large material deformations such as those required in building components to perform in a ductile manner, are often associated with cracking and degradation of its strength, particularly in concrete structures. The installation of some manufactured devices to critical regions of structural systems, specifically engineered to concentrate on them the largest part of the dissipated energy during an earthquake, increases the structure's overall thoroughness and improves its performance and reliability during major seismic events.Passive dissipation of energy is a promising trend in upgrading and retrofitting existing structures, since codes very seldom deal with detailed procedures to attain safe retrofits, as they strongly depend on the actual condition of the particular structure in each case. It is also sought as a very convenient method to reduce the impact of seismic forces on new structures, especially on tall and medium rise buildings in seismic regions.It is intended that the energy dissipative devices installed in the structure serve as a first defense line against seismic forces, leaving the structure itself and its inelastic reserve of strength, as a second defense line. If structures are designed in accordance to these criteria, the structures only receive part of the seismic forces calculated according to the Code, while the rest is being dissipated through the hysteric ductile behavior of the devices.Importantly, the hysteric cycles of steel plate devices, ADAS (Added Damping And Stiffness) provide substantial amounts of supplemental energy dissipation and internal damping to the structure, which can reduce the spectral acceleration and therefore, the earthquake forces.The 1987 Mexico Building Code1 contains no specific provisions regarding the use of energy dissipative devices of any type, and although it does not specifically admit their use, it does not forbid it either.In order to adopt this novel technique, the professional practitioner has to rely on analytical procedures not required by the Code to find what he believes to be the most appropriate procedure to a rational solution to the problem. It is necessary to identify the objective levels of system strength, stiffness and ductility, and be consistent with the selection of the input design earthquake.Being aware that system ductility is subjectively developed, and its basis comes largely from engineering judgment and intuition, the author encourages to look for a different seismic resistant approach in order not to depend only on ductility to resist earthquake peak demands

Toughening of highly crosslinked epoxy resins by reactive blending with bisphenol A polycarbonate. II. Yield and fracture behavior

AbstractThe yield and fracture behavior of highly crosslinked epoxy resin modified by a reactive blending process carried out in the presence of bisphenol A polycarbonate has been studied. It was found that the fracture toughness of this blend system increases markedly with increasing PC content in the blend. Scanning electron microscopy of the fractured surfaces indicated a crack blunting mechanism as the main source of energy dissipation in the various investigated blend compositions. No evidence of phase separation of the minor component during the curing and postcuring steps was observed. The yield data were correlated with the fracture toughness data to evaluate the extent of crack‐tip blunting. © 1994 John Wiley & Sons, Inc.

Modeling of distributed electromechanical systems using Extended Bond Graphs

The Extended Bond Graph (EBG) method is used to develop a network model for distributed electromechanical systems. The mechanical and magnetoquasistatic fields are written in terms of the defined displacement and momentum states, and Galerkin's method is used to reticulate the distributed systems into discrete power-based representations. Using these EBG descriptions, the energy storage, dissipation and external sources for the distributed systems are reticulated as multiport elements with associated power bonds. The EBG junction structures connecting the power bonds to these multiport elements are established for the mechanical and magnetoquasistatic energy modes by enforcing power balance principles. The coupling effects of the distributed electromechanical systems are also consistently reticulated into a power-based multi-energetic, multiport IC element to connect the two junction structures. The energy stored in this IC element is contributed to simultaneously by the electromechanically-induced distributed forces and currents. The power flows associated with these forces and currents are directed to each energetic domain to satisfy the power balance relations. The overall EBG network reticulation provides a unified way to model nonuniform mechanical and magnetoquasistatic fields in distributed electromechanical systems.

Experiences on the Use of Supplementary Energy Dissipators on Building Structures

Ductility, or deformation energy, is by far the largest source of energy dissipation of structures, since normal levels of internal damping represent only a small portion of energy dissipation. However, large material deformations such as those required in building components to perform in a ductile manner, are often associated with cracking and degradation of its strength, particularly in concrete structures. The installation of some manufactured devices to critical regions of structural systems, specifically engineered to concentrate on them the largest part of the dissipated energy during an earthquake, increases the structure's overall thoroughness and improves its performance and reliability during major seismic events. This paper describes the retrofit of three buildings in Mexico City using damping devices. The size and number of these added elements are a function of the dynamic characteristics of the specific structure, the amount of previous damage, the anticipated earthquake motion imposed to the structure and the design performance level intended.

Measurement of the fracture energy using three-point bend tests: Part 3—influence of cutting theP-δ tail

Available measures of the fracture energyGF obtained with the procedure proposed by RILEM TC-50 provide values that appear to change with sample size, calling into question the possibility of consideringGF as a material parameter. In previous papers several sources of energy dissipation were analysed and it was concluded that, although important, they were not enough to account for the measured size effect. Here, the dissipated energy at the very end of the test is analysed. It is shown that this energy cannot be neglected for small specimens if the tests are interrupted at a reasonably low rotation. When this energy is taken into account, the final values ofGF appear to be almost size-independent. This result supportsGF as a material parameter and provides further confidence in the RILEM proposal. Moreover, it furnishes a physical explanation for the perturbed ligament model previously developed by the authors.

Measurement of the fracture energy using three-point bend tests: Part 2—Influence of bulk energy dissipation

Avialable measures of the fracture energy GF obtained with the procedure proposed by RILEM TC-50 provide values that appear to change with sample size, calling into question whether GF can be considered as a material parameter. In a previous paper, possible sources of energy dissipation from the testing equipment and lateral supports were considered. In this paper new possible sources of energy dissipation in the sample, apart from the fracture crack itself, are considered. Such dissipation will take place inside the bulk of the most stressed regions of the specimen and, if it is not taken into account, higher values of GF will be recorded than that strictly due to surface fracture energy. When this constribution and the possible energy dissipation analysed in previous work are considered, they are not enough to account for the measured size effect. If GF is to be considered a material parameter, the evaluation of the results from the RILEM method should be analysed more carefully. In any case, the dissipated energy reported here represents a non-negligible amount of GF and should be taken into account when performing measurements.

Measurement of the fracture energy using three-point bend tests: Part 1—Influence of experimental procedures

Available measures of the fracture energy GF obtained with the procedure proposed by RILEM TC-50 provide values that appear to change with sample size, calling into question the possibility of considering GF as a material parameter. In this paper some possible sources of experimental errors, when the RILEM proposal is applied, are ascertained, namely the apparent energy dissipation from hysteresis in the testing equipment and energy dissipation in the lateral supports. It is concluded that either some other sources of energy dissipation are operative or that GF cannot be considered a material property.