Energy Dissipation Systems Research Articles

Numerical study of visco-hyperelastic damper with high axial damping rubber subjected to harmonic loading

Structural control prevents structural damage and provides the desirable performance level through the ductility of components and using passive energy dissipation systems. In this paper, the performance of a recently introduced passive control device called Visco-Hyperelastic Damper (VHD) is investigated by ABAQUS FEM software. This device has the properties of both velocity-dependent and displacement-dependent dampers and provides additional energy dissipation for structures. This device consists of a viscoelastic material sandwiched between two metal rings dissipating energy through a combination of the elastic behavior of the viscoelastic material and the plastic deformation of the steel parts. In order to validate the numerical model, after separately testing the steel and rubber parts, their results are used in damper modeling. VHD performs desirably under different levels of excitation such that 82% to 99% of energy dissipation, depending on the type of loading, is observed by this device. The dynamic behavior of VHD can be further improved by modifying variable parameters such as dimensions and type of materials of the device.

Seismic performance of reinforced concrete tall buildings with conventional and non-conventional construction systems

Currently in the city of Lima there is a limited number of high-rise buildings. Therefore, there is not much literature on this type of building in Peru. Peruvian codes focus on medium and low-rise buildings. For this reason, studies are required to analyze and design these tall buildings more appropriately according to the reality of the country. In this article, a pushover modal analysis of 6 types of 35-Story reinforced concrete buildings in the city of Lima will be developed. Three building models with different structural systems and square and rectangular plan are proposed, being the areas of 29m × 29m and 52m × 26m respectively. These structural systems are rigid core and frames with an energy dissipation system (fluid viscous dampers and shear-link-bozzo dissipators SLB) in order to study their behavior against seismic stresses. These buildings were based on the criteria and requirements of the current codes in the country as well as the distribution of the floor plan of buildings commonly used for offices and homes. Natural periods (T) were found to range from 2.6 to 3.3 seconds for rigid core buildings. There is an increase for viscous damping buildings from 4.2 to 5.4 seconds and also for SLB devices to range from 3.7 to 4.6 seconds. In turn, modal static nonlinear analysis was performed to obtain the capacity curves for each type of building, which were compared with the seismic demands according to the design provisions of the Peruvian seismic standard E.030 and an average of design spectra. of acceleration records of severe seismic events in Peru and scaled in a range of 0.2T to 1.5T. The performance points for each building case were determined following the ATC-40 methodologies, finding that tall buildings with a rigid core have approximately twice the stiffness of buildings with SLB dampers, as well as low ductility, unlike buildings with dissipators, that have a high ductility.

Self-centering BRBs with composite tendons in series:Tests and structural analyses

The self-centering system and yielding energy dissipation system are two main parts of self-centering buckling-restrained braces (SC-BRBs), which have important influences on brace performance. To improve the performance of the two parts, an SC-BRB with composite tendons in series (SC-BRB-CTS) is proposed by introducing a self-centering system in series that can improve the deformation capability of the brace, and the yielding energy dissipation system made of low-yield steel LYP160 with a strong energy dissipation capacity is adopted. The performance of the braces is studied by quasi-static tests, and the influence of the self-centering system in series and low-yield steel on the seismic performance of the structure is determined by nonlinear dynamic analyses and fragility analyses. The results show that the deformation capacity of the SC-BRB-CTS is approximately 44% higher than that of a traditional SC-BRB, and the collapse resistance of the structure is improved by avoiding or delaying tendon fracture. The use of LYP160 steel core plates can substantially improve the energy dissipation capacity and post-yielding bearing capacity of the brace, which is beneficial for reducing the seismic response of the structure.

Dynamic Seismic Response of Nonlinear Displacement Dependent Devices versus Testing Required by Codes: Experimental Case Studies

Passive energy dissipation systems are one of the most resilient solutions to mitigate the seismic risk of structures. In case of strong motions, they can confine the eventual damages into easily replaceable anti-seismic devices. The performance characteristics of nonlinear displacement dependent devices (NLD) shall be defined by the force-displacement cyclic behavior, as well as the expected number of cycles related to both the duration of the earthquake and to the fundamental frequency of the structural systems. The aims of this paper are the comparison between the dynamic results of two different experimental campaigns performed on NLDs included in dissipative bracing systems and the assessment of the reliability of quasi-static testing procedures proposed by current seismic codes for type tests and factory production control tests. The number of cycles under the design earthquake of hysteretic dampers were experimentally evaluated through shaking table testing. Two experimental case studies of a two-story steel frame and of a three-story post-tensioned timber frame both with bracing systems including flexural steel dampers, hysteretic dampers (HDs), and U-shaped flexural plates (UFPs) respectively, were analyzed. Controlled-displacement tests of NLDs were performed considering quasi-static loading procedures specified by codes. Shaking table tests were carried out considering almost the same seismic sequence composed by a set of seven natural earthquakes at increasing peak ground acceleration (PGA) levels. More than one hundred inelastic cycles were experimentally recorded from dynamic tests before the failure of devices in both cases. In line with American standards testing requirements, the number of cycles at the design PGA level, estimated from shaking table tests and from non-linear dynamic analyses, shows a decreasing trend with the increase of ductility demand.

Improved seismic behavior and performance of energy-absorbing systems constructed with steel rings

In this study, an innovative energy dissipation system of steel dual-ring dampers (SDRDs) system are provided and investigated using numerical method. The aim of this study are provided the energy absorption system to improve the hysteresis behavior and performance of steel ring dampers (SRD). Hence, two types of SDRDs with different connection details between inner and outer rings are presented. Extensive parametric studies have been performed to evaluate and compare the proposed damper with traditional SRDs. To evaluate the proposed dampers, finite element models were modeled and analyzed under cyclic loading, and finally validated with the results of several experimental specimens. In order to evaluated the results of this study, a comparison are performed between the parameters key the seismic behavior of steel ring and steel dual-ring dampers. The results show that the SDRDs significantly increases the seismic parameters compared to the ring damper. So that in the steel dual-ring dampers yield capacity, ductility and energy dissipated by up to 67.8%, 44.0% and 60.9%, respectively, increase compared to the steel ring damper. Also, the results show that the details of the construction of the internal and external ring connections were a considerable effect on the performance and hysteresis behavior of the SDRDs.

Development and validation of a versatile hysteretic model for pre-compressed self-centering buckling-restrained brace

Due to the preferable self-centering and energy dissipation capabilities, self-centering energy dissipation (SCED) braces have become an emerging structural component in earthquake engineering. In this paper, an innovative self-centering steel buckling-restrained brace (SC-SBRB) consisting of two independent and complementary systems, i.e., a buckling-restrained energy-dissipation system and a pre-compressed disc spring self-centering system, is proposed. The working mechanism and mechanics of the SC-SBRB are investigated under one cycle of cyclic loading. A versatile self-centering hysteretic model (SCHM) is developed based on the working principle of the SC-SBRB to accurately characterize the energy dissipation and self-centering properties of the SC-SBRB under repeated cyclic loading. The SCHM is a path-dependent model that allows for straightforward parameter interpretation of the mechanics of the SC-SBRB. Numerical simulations are conducted on four SC-SBRBs with different self-centering ratios to validate the prediction results obtained from the SCHM. A good agreement between the simulation results and the prediction results confirm the validity of the proposed SCHM. Simulation results also demonstrate that the SC-SBRB can provide a stable and repeatable flag-shaped hysteretic response, as well as substantial energy dissipation and self-centering ability. Additionally, the SCHM is reasonably extended to other SCED braces with similar hysteretic rules. Further validation of the SCHM is performed by comparing the experimental results of the SCED braces with the SCHM results. It is concluded that the proposed SCHM has excellent applicability and can describe the responses of other SCED braces.

Low-Cyclic Loading Tests of Self-Centering Variable Friction (SCVF) Brace

A novel assembled self-centering variable friction (SCVF) brace is proposed which is composed of an energy dissipation system, a self-centering system, and a set of force transmission devices. The hysteretic characteristics and energy dissipation of the SCVF brace with various parameters from low-cyclic loading tests are presented. A finite element model was constructed and tested under simulated examination for comparative analysis. The results indicate that the brace shows an atypical flag-type hysteresis curve. The SCVF brace showed its stable self-centering ability and dissipation energy capacity within the permitted axial deformation under different spring and friction plates. A larger deflection of the friction plate will make the variable friction of this SCVF brace more obvious. A higher friction coefficient will make the energy dissipation capacity of the SCVF brace stronger, but the actual friction coefficient will be lower than the design value after repeated cycles. The results of the fatigue tests showed that the energy dissipation system formed by the ceramic fiber friction blocks and the friction steel plates in the SCVF brace has a certain stability. The finite element simulation results are essentially consistent with the obtained test results, which is conducive to the use of finite element software for calculation and structural analysis in actual engineering design.

Shock responses of nanoporous gold subjected to dynamic loadings: Energy absorption

Using the finite element analysis, we investigate the shock response, deformation behavior and energy–absorbing characteristics of stochastic bicontinuous nanoporous gold computationally, considering the effects of impact speed and relative density of materials. Three deformation modes during shocking, quasi–static compression, transition state and dynamic compression, are observed with the increasing impact speeds and the corresponding internal deformation mechanisms are demonstrated. The shock response under low–speed loading is similar to the R–LHP–L materials model, and it is more inclined to the R–S–H model as the impact speed rises. The peak stress, plateau stress, densification strain, energy, specific energy absorption (per unit volume) are assessed quantitatively. The peak stress shows a monotonous increase with impact speed, due to the enhanced inertial effect. The plateau stress and energy–absorbing efficiency are insensitive to low impact velocity, but significantly enhanced under high–speed loading. Remarkably, the results show that the energy absorption efficiency of nanoporous gold is better than conventional foam materials and nanofluidic energy absorption and dissipation system. The research not only further clarifies the shock responses and associated mechanisms of NPG, but also promotes its industrial application as an energy–absorbing material.

Mechanical response of tensegrity dissipative devices incorporating shape memory alloys

To optimize the seismic performance prescribed by modern structural codes, buildings and infrastructures must provide adequate safety for design level earthquake excitations, with limited levels of damage. This paper deals with the computational modelling of a bracing system with tensegrity architecture, which operates as a lightweight mechanical amplifier of longitudinal displacements in the transverse direction, efficiently limiting the interstory drifts while dissipating energy. The proposed brace is based on a D-bar tensegrity structure with a rhomboidal shape comprising Shape-Memory Alloy (SMA) tendons. The SMA tendons can develop austenitic-martensitic (solid to solid) transformations, which enable them to amplify the signals into wide super elastic hysteresis, while subjected to mechanical cycles, comprising strains up to 6÷8%, with no residual deformations. The enhanced energy dissipation of the proposed SMA-D-bar (SMAD) braces are demonstrated through computational simulations of the response of braced frame to real earthquake events. The efficiency of the intended bracing to minimize the seismic impact of the served structure lays the foundation for the development of novel seismic energy dissipation systems integrating principles of tensegrity with superelasticity.

Advances in Projectile Penetration Mechanism in Soil Media

The penetration to geological shield occurs in many situations at various velocities and scales, for example, meteor-cratering, pile driving, falling of objects from high-rise building construction, and debris/fragments from failed components. The soil media is an efficient energy dissipation system and effective shock protection shield. Impact circumstances are currently getting widespread attention. A lot of research has been done on soil media for impact and penetration. The phenomenon of dynamic penetration in heterogeneous particulate soil medium is very complex and the target soil media under dynamic impact especially under high speed and deep penetration neither behave completely as solid nor as liquid. The topics of recent research interest in the field of penetration to soil media and their significant findings are critically reviewed in the present study. The dedicated review of analytical, empirical, experimental, and computational methods to predict the response of soils media-impacting objects to penetration is presented. The emerging challenges in fundamental research of penetration into soil media are outlined and it is an attempt to formulate the future research directions in the field of soil media penetration.

A new friction-slip connection for moment frames with continuous beams

This paper presents a new configuration for connections in moment frames with continuous beams, which can be used as a friction-slip connection. Some studies on friction-slip connection with this new practice have been performed analytically.In moment frames with continuous beams, two beams are continuously passed next to the column. In current practice for connections in these frames, two vertical connection plates are placed on column flanges; the beams are connecting to these plates via their wings. A new configuration is proposed in this study with the advantage of an in-plane load path. The verification of the new proposed configuration has been done for the welded connection analytically, then some studies have been performed on eight models with friction-slip connection with the new practice. The effects of friction coefficient, design moment, and bolts' pretension load are assessed for two groups of beam sizes. In the new detail, regardless of the size of the beam, the friction joint works as expected. Changing the design moment will change the slip threshold force; as long as the design moment is constant, the change in the pretension load of the bolts or friction coefficient does not change the connection performance. The group slip occurred similar to the theoretical amounts. The amount of energy dissipation for these connections in comparison with corresponding welded connections is considerable; it will increase by increasing the design moment of the connection. So while these friction joints are used as an energy-dissipating system, the structural elements remain elastic.

Practical method of obtaining different levels of seismic energy dissipation using viscous fluid protective system on bridges

In order to achieve an optimal stability performance during transient vibratory actions the damping method is used for the bridge structures. Conventional approach would dictate that a structure must inherently attenuate or dissipate the effects of transient inputs through a combination of strength, flexibility and deformity. The damping level is being at low values at a conventional elastic structure and hence the amount of dissipated energy during transient vibratory actions is also in very low value. In the event of an earthquake, conventional structures usually perform high deformations which when situated beyond their elastic limits can cause the collapse. In such cases most of the dissipated energy amount is absorbed by the structure through localized damage as it fails. The concept of supplemental dampers added to a structure assumes that most of the energy amount input to the structure from a transient vibratory action will be absorbed, not by the structure itself, but rather by supplemental damping elements. Properly implemented, an energy dissipation system can be able to simultaneously reduce both stress and deflection within the structure elements. The fluid viscous protective system concept is presented as an optimum energy dissipation solution for bridge structure types. The operation of these devices is on the hydro-static principle of fluid flow through orifices of a special diameter value. In this paper it is presented an innovative functional and constructive model of fluid viscous device based on a practical design method which allows the controlled operation regime regarding the viscous fluid flow inside the device cylinder being able to provide considerable resistant force levels to relative motions between a bridge structural frames where is mounted and achieving considerable amounts of seismic energy dissipation when an earthquake occurs. For the constructive method of fluid viscous system model is adopted a practical constructive method aiming the direct control on the circulated fluid flow rate so that the device response force should be considerably larger, acting for limiting the relative movement of the structural frames and without introducing additional stiffness to the structural system to which it is attached, due to the elasticity of the working fluid type used. It represents an innovative method because of the special design orifices for fluid flow rate control used which, depending on the specific diameter values, can provide device different response force values and implicitly different dissipated energy amount levels based on the characteristic represented by the resistant force variation law according to the piston stroke.

Comparison Regarding the Effects of Different Baffle Systems as Impacted by Rock Avalanches

Baffle array is generally embedded ahead of the protecting site for reducing rock avalanche’s flow energy. This study explored the arc-shape baffles in comparison with common baffles (cylindrical and square baffles) according to the application of science in practice. The comparing process of three categories of baffles was delved into experimentally, primarily highlighting the disaster reduction effectivity. The comparison of disaster reduction effective between these three categories of baffles is analyzed by three elements, which are deposition, VRR (velocity decrease rate), and U* (dimensionless velocity). Based on the rock avalanche final deposition, the optimal configuration for arc shape, square, and cylindrical baffles satisfy Sr = 4.5 and Sc = 3.5, Sr = 4.5 and Sc = 4.5, and Sr = 4.5 and Sc = 2.5, separately. As suggested from the results, the arc-shape baffle is the optimal case among those three categories of baffle. Shape alteration (cylindrical to arc-shape) can elevate the fragment block degree; the succeeding avalanches can occur around the avalanche deposits, causing kinetic energy to dissipate significantly. Besides, based on the contrast of VRR, U*, and deposition, arc-shape baffle mechanism was reported significantly superior to block. The energy dissipation system of the arc-shape baffle is primarily explained as: (1) the friction of rock fragment will be generated in the movement around the arc surface, thereby causing additional loss of kinetic; (2) a natural cushion is formed when rock fragment accumulated between the arc-shape baffle, being critical to energy dissipation for subsequent rock avalanches.

Cyclic behavior of an energy dissipation system with steel dual-ring dampers (SDRDs)

In this paper, the energy absorption system of a steel dual-ring damper (SDRD) is presented and its cyclic behavior is studied analytically and numerically. The energy dissipation mechanism of the SDRD occurs through the formation of moment plastic hinges in steel rings. The purpose of this study is to provide an analytical relationship for estimating the yield strength, yield displacement, and elastic stiffness of the proposed SDRDs. An analytical relationship is presented for calculating the elastic stiffness of SDRDs using the structural analysis method. Also, using plastic analysis and considering the mechanism of plastic hinge formation, a relation has been obtained for estimating the yield strength and yield displacement of SDRDs. Extensive parametric studies have been carried out using a nonlinear finite element method to examine the accuracy of the obtained analytical relationships. The parametric studies include investigating the influence of thickness parameters as well as the inner and outer ring diameters of SDRDs. Nonlinear static analysis is employed to analyze finite element (FE) models under cyclic loading. Also, validation of the results of the finite element models is performed with experimental specimens. There is a good agreement between the results of yielding capacity, yielding displacement, and elastic stiffness of the analytical relationship and FE models parametric studies. The results of the parametric models and the proposed relationship reveal that with elevation of the steel ring diameter, the energy dissipation has increased. Also, as the diameter to thickness (D/t) ratio increases, ductility and equivalent viscous damping ratio are reduced.

Editorial for “Recent Advances in the Design of Structures with Passive Energy Dissipation Systems”

Civil engineering structures and infrastructures are inherently vulnerable to exceptional loads related to natural disasters, primarily earthquakes, tsunamis, strong winds, and floods [...]

Response of Photosynthetic Performance to Drought Duration and Re-Watering in Maize

The drought tolerance and capacity to recover after drought are important for plant growth and yield. In this study, two maize lines with different drought resistance were used to investigate the effects of different drought durations and subsequent re-watering on photosynthetic capacity, electron transfer and energy distribution, and antioxidative defense mechanisms of maize. Under short drought, maize plants decreased stomatal conductance and photosynthetic electron transport rate, and increased NPQ (Non-photochemical quenching) to dissipate excess excitation energy in time and protect the photosynthetic apparatus. With the increased drought duration, NPQ, antioxidase activity, PItotal (total performance index), ∆I/Io, ψEo (quantum yield for electron transport), φEo (efficiency/probability that an electron moves further than QA−), δRo (efficiency/probability with which an electron from the intersystem electron carriers is transferred to reduce end electron acceptors at the PSI acceptor side) and φRo (the quantum yield for the reduction of the end electron acceptors at the PSI acceptor side) were significantly reduced, while Y(NO) (quantum yield of nonregulated energy dissipation) and MDA (malondialdehyde) began to quickly increase. The photosynthetic rate and capacity of photosynthetic electron transport could not recover to the level of the plants subjected to normal water status after re-watering. These findings indicated that long drought damaged the PSI (photosystem I) and PSII (photosystem II) reaction center and decreased the electron transfer efficiency, and this damage could not be recovered by re-watering. Different drought resistance and recovery levels of photosynthetic performance were achieved by different maize lines. Compared with D340, D1798Z had higher NPQ and antioxidase activity, which was able to maintain functionality for longer in response to progressive drought, and it could also recover at more severe drought after re-watering, which indicated its higher tolerance to drought. It was concluded that the capacity of the energy dissipation and antioxidant enzyme system is crucial to mitigate the effects caused by drought, and the capacity to recover after re-watering was dependent on the severity and persistence of drought, adaptability, and recovery differences of the maize lines. The results provide a profound insight to understand the maize functional traits’ responses to drought stresses and re-watering.

The influence of ATP treatment on energy dissipation system in postharvest longan fruit during senescence

Abstract The harvested longan fruit are prone to senescence, leading to a decline in fruit quality like pericarp browning. There are two energy dissipative proteins involving in fruit senescence: alternative oxidase (AOX) and plant uncoupling mitochondrial protein (PUMP). The purpose of this work was to elucidate the influence of adenosine triphosphate (ATP) treatment on energy dissipation system in postharvest longan fruit during senescence. The results showed that the ATP content in postharvest longan fruit exhibited negative correlations with the expressions of DlAOX1, DlAOX2, DlPUMP3, and DlPUMP5. Moreover, compared to the control longan fruit, the treatment of exogenous ATP prevented the increases in the expressions of DlAOX1, DlAOX2, DlPUMP3, and DlPUMP5, helped maintain higher contents of ATP, ADP and higher level of energy charge, but lower respiration rate, lower cell membrane permeability, and lower pericarp browning index in postharvest longan fruit. These data indicated that the supply of exogenous ATP could reduce the induction of the expressions of DlAOX1, DlAOX2, DlPUMP3 and DlPUMP5, and consequently reduce the energy dissipation and retard the decline of energy level, which lead to the delayed senescence in postharvest longan fruit.

Seismic behavior of highly irregular structures with multiple passive energy dissipation system: Case study of a single‐column elevated station

SummaryThis paper presents a case study of the layout strategy for a multiple passive energy dissipation (MPED) system and its influence on the seismic behavior of highly irregular structures. The investigated structure is a single‐column elevated station in a cantilevered structure form, which is unique and characterized by uneven mass and stiffness distributions in both elevation and plane. To improve seismic resistances of the focused structure, the MPED system composed of multiple types of passive energy dissipation (PED) devices targeting different vulnerabilities is devised. In addition, a high‐fidelity and efficient numerical model is developed to assess the structural seismic performance, by leveraging the secondary development based on proprietary finite‐element analysis package MARC.MSC. The fiber beam–column elements are employed to simulate the composite members under complex loading conditions, and spring elements incorporated with cyclic hardening property are developed to simulate the PED devices. Nonlinear static and time history analysis are conducted for the key substructures and whole structure. The results demonstrate that the MPED system can effectively improve the stiffness, strength, and ductility of the structure and significantly reduce its global responses. A comprehensive evaluation indicates that the MPED system is beneficial for the members directly equipped with PED devices, but the benefits are limited for unprotected members that require special attentions in design to avoid secondary damage. Through this study, valid analysis tools and suggestions are provided for the design of high‐irregular structures with MPED system.

Experimental Campaign of a Low-Cost and Replaceable System for Passive Energy Dissipation in Precast Concrete Structures

This research develops a new low-cost energy dissipation system, capable of being implemented in residential structures in developing countries with high seismic activity, in which the current solutions are not economically viable. These residential structures are entirely made of precast concrete elements (foundations, walls, and slabs). A solution is developed that consists of a new connection between a precast foundation and a structural wall, which is capable of dissipating almost all the seismic energy, and therfore protecting the rest of the building from structural damage. To validate the solution, a testing campaign is carried out, including a first set of “pushover” tests on isolated structural walls, a second set of “pushover” tests on structural frames, and a final set of seismic tests on a real-scale three-storey building. For the first and second set of tests, ductility is analyzed in accordance with ACI 374.2R-13, while for the third one, the dynamic response to a reference earthquake is evaluated. The results reveal that the solution developed shows great ductility and no relevant damage is observed in the rest of the building, except in the low-cost energy dissipation system. Once an earthquake has finished, a precast building implemented with this low-cost energy dissipation system is capable of showing a structural performance level of “immediate occupancy” according to ACI 374.2R-13.

Earthquake Resisting Elements and Techniques in High Rise Buildings

An earthquake resisting elements are the components that are introduced in a structure to improve its seismic resistance and method of application of these elements are said as techniques. Though structures are designed and detailed as per code provision there remains some possibility of damage or failure in strong earthquake. Performance of buildings may be improved using earthquake resistant elements and techniques. An earthquake produces seismic waves on earth surface of earth due to releases of large energy from lithosphere which produces waves in earth surface causing disturbance in structures resulting failure of seismically weak structures. Seismic waves then travels in horizontal and vertical direction. It causes horizontal and vertical ground movement or vibration. These seismic waves cause disturbances in in buildings. The disturbance caused depends on position of building with respect to the center of disturbance called as epicenter. Intensity of these seismic waves is maximum at center and goes on reducing away from epicenter. Generally horizontal waves are of stronger than vertical so buildings are designed to horizontal seismic forces. These valves travel in any direction but from design purpose it is resolved in two orthogonal directions. Few constructional precautions may help to avoid or minimize damage in buildings. Earthquake resistance of building may be improved with proper design and construction of structures. Some earthquake resisting elements like shear wall, moment resisting frame or innovative techniques like base isolation, or energy dissipation system are used in many high rise buildings to avoid or minimize damage and hence loss of lives and properties. Shear walls are RC member generally introduced in a structure during construction in symmetrical manner. Base isolators in the form bearings are placed between sub and super structure to reduce stiffness of structures. Structures are braced with seismic dampers in energy dissipation system. Composites are used by mixing in concrete or as a warp. All these techniques are reviewed herewith with special attention on shear walls.