Maximum Base Shear Research Articles

Seismic performance of outrigger\u2013belt truss system considering soil\u2013structure interaction

The focus of this study is to investigate the seismic behavior of outrigger-braced building considering the soil–structure interaction based on finding the best location of outrigger and belt truss system. For this purpose, a central outrigger-braced frame of a steel tall building is considered. A layered soil deposit underlied this frame and the resulting soil–structure system is subjected to seismic excitation. To analyze this system, direct method is employed in OpenSees. Also, elastic and in-elastic analyses are both considered and a comparison is made between current results and the results related to the system with fixed base. The best location of outrigger–belt truss system is determined by considering the maximum roof displacement, base moment and base shear with and without soil–structure interaction. It is shown that considering SSI affects the location of outrigger–belt truss system. Elastic analysis of both systems, namely with fixed base and with soil–structure interaction, showed that locating the belt truss at higher stories caused lower amounts of roof displacement.

Fluid-structure-soil interaction effect on dynamic behaviour of circular water tanks

To investigate the seismic behaviour of concrete tanks on different soil conditions, fluid-structure-soil interaction system is simulated using finite element analysis software ANSYS. The influence of soil properties on tank's dynamic behaviour is studied by performing modal and transient analyses of cylindrical tanks resting on different soil conditions. Considering four different soil properties, comparisons are made on response parameters such as displacement in radial direction at top of tank wall, maximum hoop force, bending moment and base shear. The effect of frequency content of earthquake on seismic behaviour circular concrete tank is investigated by conducting time history analyses of the tanks under three different earthquakes. All the analyses were performed for half fill and full fill condition. Transient analyses show that the soil property, frequency content of earthquake and water fill condition have significant effect on seismic response of the water tanks.

Static and dynamic analysis of guyed steel lattice towers

Guyed steel lattice towers (or guyed masts) are widely used for supporting antennas for telecommunications and broadcasting. This paper presents a numerical study on the static and dynamic response of guyed towers. Three-dimensional nonlinear finite-element models are used to simulate the response. Through performing static pushover analyses and free-vibration (modal) analyses, the effect of different bracing configurations is investigated. In addition, seismic analyses are performed on towers of different heights to study the influence of earthquake excitation time-lag (or the earthquake travel distance between tower anchors) and antenna weight on the seismic response of guyed towers. The results show that the inclusion of time lag in the seismic analysis of guyed towers can influence shear and moment distribution along the height of the mast. Moreover, it is found that the lateral response is insensitive to bracing configurations. The results also show that, depending on the mast height, an increased antenna weight can reduce the tower maximum base shear while other response quantities, such as cables tension force are found to be insensitive to variation in the antenna weight.

Finite element analysis for the seismic performance of steel frame-tube structures with replaceable shear links

In steel frame-tube structures (SFTSs) the application of flexural beam is not suitable for the beam with span-to-depth ratio lower than five because the plastic hinges at beam-ends can not be developed properly. This can lead to lower ductility and energy dissipation capacity of the SFTS. To address this problem, a replaceable shear link, acting as a ductile fuse at the mid length of deep beams, is proposed. SFTS with replaceable shear links (SFTS-RSLs) dissipate seismic energy through shear deformation of the link. In order to evaluate this proposal, buildings were designed to compare the seismic performance of SFTS-RSLs and SFTSs. Several sub-structures were selected from the design buildings and finite element models (FEMs) were established to study their hysteretic behavior. Static pushover and dynamic analyses were undertaken in comparing seismic performance of the FEMs for each building. The results indicated that the SFTS-RSL and SFTS had similar initial lateral stiffness. Compared with SFTS, SFTS-RSL had lower yield strength and maximum strength, but higher ductility and energy dissipation capacity. During earthquakes, SFTS-RSL had lower interstory drift, maximum base shear force and story shear force compared with the SFTS. Placing a shear link at the beam mid-span did not increase shear lag effects for the structure. The SFTS-RSL concentrates plasticity on the shear link. Other structural components remain elastic during seismic loading. It is expected that the SFTS-RSL will be a reliable dual resistant system. It offers the benefit of being able to repair the structure by replacing damaged shear links after earthquakes.

Comparative study on the seismic performance assessment of existing buildings with and without retrofit strategies

A large number of infilled RC frame buildings have undergone moderate to extensive structural damages and even collapsed after the 2015 Gorkha earthquake. The repair and maintenance works are still being carried out in the existing RC buildings, many of them without any consultation with design engineers. Such practices are likely to create a benefit of doubt on the efficiency of the retrofitting works and repair/maintenance works. Therefore, the present study aims to evaluate the seismic performance of the existing non- and pre-engineered buildings, and later employed retrofit measures that are commonly practised in the region. The analytical results revealed that the selected buildings were seismically deficient and are most likely to undergo extensive damage to collapse states, at 0.3 g PGA. It was found that the retrofit measure significantly enhances the stiffness, maximum strength and ductility in the existing buildings. The pushover curves indicated that the steel bracing highly increased the stiffness, strength and ductility capacity in all case study buildings. The steel-braced building was recorded to have increased the maximum base shear capacity by almost ten times for the soft-storey MRT1 building. Similarly, the retrofit measures also eliminated the potential single storey drift concentration recorded in the original building, such that a uniform inter-storey drift profile can be attained throughout. The conditional probability of collapse for the case study buildings, at 0.3 g PGA, ranges from 13.5 to 42% and could be minimized below 4% in the worst case scenario for the shear wall. All the numerical results demonstrated that steel bracing was much more effective in enhancing the seismic performance of the existing buildings.

The effect of composite-elastomer isolation system on the seismic response of liquid-storage tanks: Part I

A typical viable technique to decrease the seismic response of liquid storage tanks is to isolate them at the base. Base-isolation systems are an efficient and feasible solution to reduce the vulnerability of structures in high seismic risk zones. Nevertheless, when liquid storage tanks are under long-period shaking, the base-isolation systems could have different impacts. These kinds of earthquakes can damage the tanks readily. Hence, the seismic behaviour and vibration of cylindrical liquid storage tanks, subjected to earthquakes, is of paramount importance, and it is investigated in this paper. The Finite Element Method is used to evaluate seismic response in addition to the reduction of excessive liquid sloshing in the tank when subjected to the long-period ground motion. The non-linear stress-strain behaviour pertaining to polymers and rubbers is implemented while non-linear contact elements are employed to describe the 3-D surface-to-surface contact. Therefore, Nonlinear Procedures are used to investigate the fluid-structure interactions (FSI) between liquid and the tank wall while there is incompressible liquid. Part I, examines the effect of the flexibility of the isolation system and the tank aspect ratio (height to radius) on the tank wall radial displacements of the tank wall and the liquid sloshing heights. Maximum stress and base shear force for various aspect ratios and different base-isolators, which are subjected to three seismic conditions, will be discussed in Part II. It is shown that the composite-base isolator is much more effective than other isolators due to its high flexibility and strength combined. Moreover, the base isolators may decrease the maximum level pertaining to radial displacement.

Retrofitting of soft storey building by using different bracing system due to earthquake load

In this research, one residential building of soft storey situated at Seremban, Negeri Sembilan is selected. SAP 2000 which is structural analysis software is being used to determine the maximum displacement and base shear of the soft storey. Four different types of model are introduced to do the modeling. Acheh, Indonesia earthquake data is considered for time history analysis. The comparison of these models for different type of bracing system like X bracing type and V bracing type is carried out. Based on this comparative study, it can conclude that model 3 which is V bracing type is the best and effective method of bracing system for soft storey building. From the result obtained, it shown that V bracing has the lowest value for maximum displacement compared other 3 models. In addition, V bracing type also showed the lowest value of base shear. Thus, it proved that V bracing type reduces the maximum displacement and base shear of the soft storey building.

A Comparative Study of Different Positioning of Reinforced Concrete Shear Walls in Soft Storey Building Subjected to Acheh Eartquake Event

The system of shear wall as an additive in retrofitting of soft storey structure has been investigated in previous and present research to improve the strength of structures due to seismic load. The aim of this research is to conduct comparative study on Equivalent Static Analysis (ESA), Response Spectrum Analysis (RSA) and Time History Analysis (THA) of structure between reference sample and shear wall systems was performed in order to determine the strength and stiffness of soft storey structure. The locations and shapes of shear wall system were used as retrofitting method. The retrofitting of soft storey structure was done for fives (5) models consist of one (1) model without shear wall as reference sample and the other four (4) models of different location and shape of shear wall systems. The models were tested by using SAP200 computer software to performed strength of structure. The models had been checking by value of lateral displacement and base shear resistance. Based on the collected data, the additional of shear wall was found to increase the strength and stiffness of soft storey structure. The swastika shape of shear wall and provide at centre experienced the maximum base shear resistance in all X, Y and Z direction and the least displacement compared to other model. Through this study had shown the improvement of strength of soft storey structure by applying shear wall system as an additive strength and stiffness of structure due earthquake event.

Seismic Capacity Assessment of Existing RC Building by Using Pushover Analysis

The infrastructure, existing in Sudan, is mostly not structured or designed to resist seismic forces accordingly. The study investigated the seismic damage of a 5 storey existing reinforced concrete building in Khartoum, Sudan. Three performance levels were considered in the study, which included immediate occupancy, life safety, and collapse prevention. The gravity push was carried out using force control method and lateral push with displacement control, using SAP2000. Pushover analysis produces push curve, consisting of capacity spectrum, demand spectrum, and performance point. It showed the performance level of building components along with maximum base shear carrying capacity. It has been observed that demand curve intersected the capacity curve between the points B and C at the X direction that is life safety level; and between the points B and C at the Y direction that is life safety and collapse prevention level. Therefore, some building elements are needed to be strengthened.

Application of the Artificial Neural Network for Predicting Mainshock-Aftershock Sequences in Seismic Assessment of Reinforced Concrete Structures

ABSTRACT Studies from past earthquakes have shown that aftershocks can increase the vulnerability of structures damaged under mainshocks. However, the main challenge is to take these threats into account during the process of design and retrofit. Using the accelerograms that are compatible with the mainshock and the corresponding aftershocks can lead to a proper evaluation of seismic performance of a structure during the mainshock and aftershock, based on time history analyses. Therefore, it is necessary to simulate the aftershock motions consistent with the predicted mainshock spectrum. This study first investigates the relationship between the frequency content of an aftershock and its corresponding mainshock. It then discusses the development of a method for the generation of artificial aftershocks based on the acceleration response spectrum obtained from the artificial neural networks. To evaluate the effectiveness of the proposed method for the generation of artificial seismic sequences, a large number of time-history analyses have been conducted using both the current (the conventional back-to-back approach) and the proposed methods for three different structures including a column (representing the pier of a bridge), a reinforced concrete (RC) building, and an RC bridge. In these analyses, a wide range of different elements and materials have been employed and different responses, including maximum drift, residual drift, inter-story drift, floor acceleration, column curvature, and base shear, have also been studied. The results revealed that the proposed method produces the appropriate estimation of structural responses, and has a considerably higher efficiency compared to the conventional BTB approach that often introduces considerably large errors in the estimation of responses.

Assessment of proposed lateral load patterns in pushover analysis for base-isolated frames

The effectiveness of two proposed lateral load patterns (LLPs) to estimate the seismic demands of base-isolated building frames by the pushover analysis (POA) is assessed by comparing their estimates with the benchmark responses obtained by the nonlinear time history analysis (NTHA). The proposed LLPs include: (i) pattern derived from the square root of the sum of squares (SRSS) of first three mode shapes of BI frame; and (ii) two variants derived by the modification of the uniform force distribution load pattern. The conventional first mode shape LLP is also used in the POA for the purpose of comparison. A mid-rise (5-storey) and a high-rise (10-storey) base isolated (BI) reinforced concrete building frames are considered as illustrative examples for the analysis. An ensemble of five ground motion time-histories, each of far-field and near-field with forward directivity and fling-step effects are employed for NTHA. Target displacement-based comparison is performed by considering three target displacements, which cater to elastic, elastic to plastic and plastic states on the capacity curve of the building frames. The seismic demands namely, peak storey displacement, maximum inter-storey drift, number of plastic hinges, SRSS of plastic hinge rotations, maximum base shear and maximum isolator displacement are considered for comparison. The study reveals that (i) the errors in estimating the seismic demands by different LLPs depend on the state (elastic or elastic–plastic or plastic) of the building frame in which target displacement is considered; and (ii) the proposed LLP (modified uniform distribution) is found to best estimate the NTHA predictions.

Improving Seismic Behavior of MRFs by U-shaped Hysteretic Damper Along Diagonal Brace

This paper presents seismic assessment of a U-shaped hysteretic damper as an enhancement system, in moment resisting frames. The proposed system is consisted of a damping box at the middle of a diagonal brace. The box includes U-shaped steel plates welded to the side plates. When a transverse load, like earthquake, is exerted to the building, relative displacement between the stories forms and will be transmitted to the braces where energy dissipation will be achieved by adding a displacement-dependent U-shaped damper. For this purpose, the system is applied to a 2D 2-span 3-story frame to which by applying eight different earthquake records, far-field, near-field and mid-field, seismic response are evaluated. The responses are the roof displacement, inter-story drifts, root mean squared of roof displacement and base shear. Result verification is carried out via calibrating characteristics of this damper with an experimental work on a somewhat similar device conducted at the University of Toronto. The results showed that by using this system, the roof maximum displacement decreased 38.9, 40.0 and 37.1% and the maximum base shear decreased 36.5, 28.5 and 39.5% respectively under near-field, mid-field and far-field records, averagely. Similar results were observed in inter-story drifts and roof displacement RMS.

Effect of damped outriggers arrangement on the seismic response of high-rise steel structures

Recently, a novel structural system, which is defined as damped outrigger system, has been proposed to control dynamic vibration of tall buildings. This paper examines seismic performance of tall buildings involving multiple outriggers equipped with viscous dampers. In this respect, a dual structural system (braced moment frame) is selected as a bare structure. In addition, the number and position of outriggers are assumed to be variable along the height of structure. Nonlinear response history analysis (RHA) is performed to evaluate the efficiency of damped-outrigger system under eight scaled ground motions. The results are presented based on the average of all ground motions. The mean inter-story drift ratio and maximum base shear force are compared in order to determine the best arrangement of damped outriggers. Conclusively, based on minimizing base shear force, the optimal location of damped outriggers under dynamic excitation is generally the same as that made for conventional outriggers. According to the inter-story drift ratio parameter, it is recommended to place one of the outriggers at the roof level.

Time history analysis of a steel water tank with pinned and fixed foundations under varying ground perturbations

Earthquake is a natural phenomenon which is caused by sudden release of energy in the Earth's crust that creates seismic waves. Seismic response of an overhead water tank with varying foundation types subjected to five different earthquake accelerograms was simulated using Time History Analysis. Tank responses observed includes the base shear, base moment and displacement at some joints. The maximum base shear obtained was 9.521E+03 kN and 1.093E+04 kN for pinned and fixed foundations respectively. The maximum displacements at three selected joints labelled as joint 12, joint 22 and joint 32 were 3.67E-01m, 4.349E-01 m and 3.67E-01 m for pinned foundation and 8.68E-02m, 1.119E-01 m and 8.68E-01 m when the foundations were fixed. The results revealed that using a fixed foundation increased the base shear but reduced displacements at the selected joints when compared to when a pinned foundation was used.

Effect of near-field earthquake excitation on seismic behavior of knee-braced moment frames

Inelastic behavioral characteristics of knee-braced moment-resisting frames having 3, 8 or, 12 stories were investigated under near-source earthquake excitation using initially pinned frames that were subsequently substituted with rigid knee elements. These frames were designed so that the knee braces would yield and buckle under seismic loading. Inelastic time-history analysis was carried out to assess the structural performance of the buildings by evaluating the maximum axial forces of the columns, vertical displacement of internal beams, roof horizontal displacement, and maximum base shear of columns in the building members using PERFORM-3D software. The nonlinear behavior of the frames was investigated by comparing the results of pinned and rigid knee elements subjected to near-field earthquakes. The results indicate that rigid-to-pinned connections for knee elements can increase the axial forces of columns by nearly 15% for a 3-story building and about 7% for 8- and 12-story buildings. The vertical displacement of the beams was noticeable, especially for the three-story building. The horizontal displacement of the roof and base shear of columns using pinned connections for knee elements were generally greater than for the rigid connections.

Seismic Performance of Base‐Isolated Precast Concrete Shear Wall Structure with AHW Connections

To improve the seismic performance and seismic reliability of precast concrete shear wall (PCSW) structure with improved assembly horizontal wall connections (AHW connections), base isolation technology was proposed to be applied in the PCSW structure. Two 1/4‐scaled structure models using the improved AHW connections were constructed: a lead‐rubber bearing (LRB) base‐isolated PCSW structure model and a base‐fixed PCSW structure model. Shaking table tests were conducted on these two models with three strong ground motions to assess the seismic performance of the structures. It was found that the improved AHW connections in the base‐isolated PCSW structure are useful and effective and that they fulfil the requirements to be met by the connections to withstand an earthquake. In addition, the maximum absolute acceleration and base shear force of the base‐isolated PCSW structure model were less than those of the base‐fixed PCSW structure model, and the isolation effect on the absolute acceleration responses and base shear responses increased with increase in the intensity of ground motions. In a word, the seismic performance and seismic reliability of PCSW structures can be effectively improved using base isolation technology. After this investigation, the seismic responses of the base‐isolated PCSW structure model were numerically simulated using OpenSees software. There was a reasonable agreement between the numerically simulated results and test results; thus, the numerical simulation method and analysis model used for the base‐isolated PCSW structure model were verified.

Effects of vertical component of near-field ground motions on seismic responses of asymmetric structures supported on TCFP bearings

The effects of vertical component of earthquakes on torsional amplification due to mass eccentricity in seismic responses of base-isolated structures subjected to near-field ground motions are studied in this paper. 3-, 6- and 9-story superstructures and aspect ratios of 1, 2 and 3 have been modeled as steel special moment frames mounted on Triple Concave Friction Pendulum (TCFP) bearings considering different period and damping ratios. Three-dimensional linear superstructures resting on nonlinear isolators are subjected to both 2 and 3 component near-field ground motions. Effects of mass eccentricity and vertical component of 25 near-field earthquakes on the seismic responses including maximum isolator displacement and base shear as well as peak superstructure acceleration are studied. The results indicate that the effect of vertical component on the responses of asymmetric structures, especially on the base shear is significant. Therefore, it can be claimed that in the absence of the vertical component, mass eccentricity has a little effect on the base shear increase. Additionally, the impact of this component on acceleration is remarkable so the roof acceleration of a nine-story structure has been increased 1.67 times, compared to the case that the structure is subjected to only horizontal components of earthquakes.

Type-1 and Type-2 Fuzzy Logic Control Algorithms for Semi-Active Seismic Vibration Control of the College Urban Bridge Using MR Dampers

In this study, the application of type-1 and type-2 fuzzy inference system (FIS) in semi-active seismic vibration control of the College Bridge using magnetorheological (MR) dampers is investigated. For this purpose, a detailed 3D finite element model of the bridge fitted with MR dampers is created in OpenSees. The command voltage of MR dampers is determined by employing both types of FISs in Matlab environment and making connection between both software. The results show the higher performance of the type-2 FIS for reducing the undesirable vibrations than that of type-1. This is because of the fact that the type-2 FIS considers interval membership functions for inputs in order to obtain the command voltage of MR dampers. Moreover, type-2 FIS effectively includes the effect of uncertainties and time delay. The results demonstrate that type-2 fuzzy controller is capable of reducing further the maximum displacement, base shear, and moment of the bridge by 24.6, 22.8, and 39.25%, respectively, compared to the type-1 fuzzy controller.

Effect of masonry infill walls with openings on nonlinear response of reinforced concrete frames

Masonry infill walls are unavoidable parts of any building to create a separation between internal space and external environment. In general, there are some prevalent openings in the infill wall due to functional needs, architectural considerations or aesthetic concerns. In current design practice, the strength and stiffness contribution of infill walls is not considered. However, the presence of infill walls may decisively influence the seismic response of structures subjected to earthquake loads and cause a different behavior from that predicted for a bare frame. Furthermore, partial openings in the masonry infill wall are significant parameter affecting the seismic behavior of infilled frames thereby decreasing the lateral stiffness and strength. The possible effects of openings in the infill wall on seismic behavior of RC frames is analytically studied by means of pushover analysis of several bare, partially and fully infilled frames having different bay and story numbers. The stiffness loss due to partial opening is introduced by the stiffness reduction factors which are developed from finite element analysis of frames considering frame-infill interaction. Pushover curves of frames are plotted and the maximum base shear forces, the yield displacement, the yield base shear force coefficient, the displacement demand, interstory drift ratios and the distribution of story shear forces are determined. The comparison of parameters both in terms of seismic demand and capacity indicates that partial openings decisively influences the nonlinear behavior of RC frames and cause a different behavior from that predicted for a bare frame or fully infilled frame.

Semi-active seismic control of an 11-DOF building model with TMD+MR damper using type-1 and -2 fuzzy algorithms

Nowadays, vibration control of structures is considered as a challenging field among scientists and engineers. Structural damage and financial losses due to recent earthquakes in different countries have more than ever before accentuated the importance of controlling earthquake-induced vibrations. In recent years, semi-active control has been introduced as an efficient and reliable type of structural control which provides the reliability of passive control and flexibility of active control systems at the same time. In this study, the performance of a semi-active tuned mass damper (TMD) with adaptive magnetorheological (MR) damper is investigated using type-1 and -2 fuzzy controllers for seismic vibration mitigation of an 11-degree of freedom building model. The TMD is installed on the roof and the MR damper is located on the 11th story. The MR damper has a capacity of producing a 1000 kN control force. The fuzzy system is designed based on the acceleration and velocity of the top floor determining the input voltage needed to produce the control force based on accelerating or decelerating movements of structure. The seismic performance of semi-active type-2 controller, which considers the uncertainties related to input variables, is higher than that of the type-1 fuzzy controller. The type-2 fuzzy controller is capable of reducing further the maximum displacement, acceleration, and base shear of the structure by 11.7, 14, and 11.2%, respectively, compared to the type-1 fuzzy controller.