Seismic Behavior Of Structures Research Articles

Full 3D modeling of soil structure interaction by using solid finite elements

Numerical studies for considering soil-structure interaction (SSI) are widely used to providing a better understanding of the seismic behavior of structures. The outcomes of these numerical studies are strongly depending on the input parameters. Back to the literature, for modelling different types of soil, there are convenient procedures whereby a single value of the Poisson's ratio is estimated for each type of soil, however a range limitation between (0.10 to 0.40) is possible, and then other required parameters determined utilizing the tables of the international seismic codes and the equations of the literature. In this article, a comprehensive parametric study was carried out with the aim of evaluating influences of the Poisson’s ratio on the seismic behavior of structures, sixteen values of Poisson’s ratios were interpolated between (0.11 to 0.41) in order to examine all possible trails. For achieving this goal a 4 story steel structure was analyzed on four different soil types (soft, stiff, very dense, and rock soils) under the El Centro acceleration record. The results in terms of time history top displacement and base shears have been discussed.

Multi-objective optimum design of nonlinear viscous dampers in steel structures based on life cycle cost

An algorithm for optimum design of nonlinear viscous dampers with the goal of achieving minimum total cost is presented. An appropriate cost model is developed to determine the initial cost of equipping structures with viscous dampers, and the expected costs of the studied structures related to the possible earthquakes over their life time are estimated using life cycle cost analysis (LCCA). The results of this analysis are used in a multi-objective optimization algorithm with the aim of achieving minimum initial and life cycle cost. To evaluate the seismic behavior of structures, the Endurance Time (ET) method is used as a dynamic response-history analysis method which requires much less computational effort in comparison with conventional time history methods. To this end, the optimum arrangement of nonlinear viscous dampers along with their damping exponent (Alpha) for two weak steel moment frames with 4 and 8 stories are acquired using multi-objective genetic algorithm. Results from the proposed method are compared with two classic methods; uniform and stiffness proportional damping methods. With the aim of proposing an optimal Alpha value, a detailed discussion is provided on its effects on the overall performance of studied structures in terms of life cycle cost.

Assessment on the deflection amplification factor of steel buckling-restrained bracing frames

Researchers in the field of earthquake engineering are always looking for new ways to improve the seismic behavior of structures. The buckling-restrained brace (BRB) is one of these exciting innovations that are employed to increase the ductility capacity of traditional steel braced frames. Understanding the nonlinear response of these novel systems in estimating maximum displacements due to an earthquake has been of significant importance for structural designers. Accordingly, this research is carried out to study of deflection amplification factor ( C d) in BRBs, which have recently been presented in seismic design provisions as one of the seismic lateral-resisting systems. To this end, five 3-, 5-, 7-, 10-, and 15-story BRBs are modeled in the software framework of OpenSees. Ground motion simulation is performed by selecting several scaled earthquake records, and the values of elastic and ultimate displacements of structural systems are computed through pushover and nonlinear time-history analyses. The results showed that the deflection amplification factor suggested within famous building codes (such as ASCE-7-16) compared to the obtained values is, in some cases, for certainty; conversely, it is underestimated under some conditions. In fact, the findings indicate that the magnitude of C d in these systems is strongly related to the height of the building.

Using Smart Materials in Enhancing the Seismic Behavior of Structures State-of-the-Art Report

Using Smart Materials in Enhancing the Seismic Behavior of Structures State-of-the-Art Report

Predicting the seismic collapse capacity of adjacent SMRFs retrofitted with fluid viscous dampers in pounding condition

Severe damages of adjacent structures due to structural pounding during earthquakes have emphasized the need to use some seismic retrofit strategy to enhance the structural performance. The purpose of this paper is to study the influence of using linear and nonlinear Fluid Viscous Dampers (FVDs) on the seismic collapse capacities of adjacent structures prone to pounding and proposing modification factors to modify the median collapse capacity of structures considering the effects of pounding. The factors can be used to predict the collapse capacity of structures in pounding condition. A seismic retrofit strategy employs FVDs installed in 3-, 6- and 9-story Special Moment Resisting Frames (SMRFs). The SMRFs were assumed to have different values of separation distance according to the seismic code. To model pounding phenomenon, linear viscoelastic contact elements were used in the OpenSees software. Furthermore, to determine the seismic collapse capacities of each structure, the proposed algorithm was applied to remove the collapsed structure during the incremental dynamic analysis. The results of the analyses illustrate that the existence of FVDs can substantially improve the seismic behavior of structures having a significant influence on the collapse capacities of colliding structures. Moreover, considering the adjacent SMRFs in one or two sides of the main structure can significantly affect the median collapse capacity of the main structure itself. Finally, the proposed modification factors can be successfully used to estimate the effects of pounding on the collapse capacities of adjacent structures.

Increase the effectiveness of AMTMDs and PMTMDs on the seismic behaviour of structures case study: Ten-stories short period concrete building

Controlling the seismic behaviour of structures during an earthquake has become a crucial issue for engineers. For this aim, new seismic devices have developed, such as dampers. In this study, passive multiple tuned mass dampers (PMTMDs) and active multiple tuned mass dampers (AMTMDs) are installed on the different floors of a 10-story reinforced concrete building, and fuzzy logic controller (FLC) is employed to optimize the performance of AMTMDs. Structures are evaluated under different earthquake records using both linear and nonlinear analysis, and the maximum lateral displacement, base shear, load-displacement behaviour of each story, settling time and energy absorption of the structure were measured. Moreover, new models are developed to predict the maximum lateral displacement and base shear of the structures and each floor equipped by PMTMDs and AMTMDs. To show the usefulness of the proposed technique, the obtained results are compared with those previous well-known models. The achieved results indicated that optimizing the dampers’ characteristics leads to increasing the efficiency of dampers and better controlling the seismic behaviour of the buildings. Also, FLC is an effective method to optimize the performance of TMDs. Hence, the maximum displacement of the building is reduced by 90% as a result of optimizing the AMTMDs’ characteristics.

Seismic behavior of a two-level control system with double vertical shear links in series

To improve seismic behavior of structures, a two-level control system is proposed in this paper where by combining two vertical shear panels in series in a chevron bracing configuration, Double-Vertical Shear Panel, D-VSP is introduced. Utilizing two-levels of energy absorption for two different earthquake intensity levels, D-VSP is expected to beneficially change dynamic behavior parameters like strength, stiffness and damping ratio through increasing ductility. To validate research, a VSP is modeled in ABAQUS and related numerical results are compared to those of a previous experimental work. Pushover, quasistatic cyclic and seismic analyses are conducted on two models. The hysteresis curves show symmetric two-level behavior with stable strength and stiffness leading to increase ductility ratio up to 29.4%. Maximum displacement and maximum base shear under seismic loading decrease 5.91 and 11.18% respectively under moderate earthquakes when D-VSP system uses only first fuse, saving second fuse for severe earthquakes. However, in a strong earthquake, both of the shear panels absorb seismic energy and can control vibration better than conventional systems with one level control mechanism. The proposed system using a weaker panel can better control an extensive range of earthquakes as well as the earthquake with foreshocks.

Seismic performance of RC frames strengthened by RC infill walls

This study presents the shake-table tests of a 1/5-scaled RC frame retrofitted with RC infill walls. The intensity of input ground motions increased gradually to comprehensively evaluate the structural seismic behavior. We performed a comparison of the results from the RC frame with masonry walls and that with RC walls. The results showed that the presence of RC infills effectively improved the lateral structural stiffness and loading capacity of the frames and reduced their damage and story drift. RC walls acted as the first seismic line of defense, and their failure was dominated by bending failure and concentrated on the low stories. The displacement ductility of the structure decreased with increasing stiffness of the introducing infills.

Improving seismic behavior using a hybrid control system of friction damper and vertical shear panel in series

In this paper to improve the seismic behavior of structures and decrease structural earthquake damages, a new hybrid control system is proposed consisting of Friction Damper and Vertical Shear Panel (HFD-VSP) in series. The new system benefits of two-level energy dissipation such that in moderate earthquakes friction damper (FD) as the first fuse operates while in strong earthquake both FD and Vertical Shear Panel (VSP) dissipate energy. FD can eliminate the shortcoming of VSP in terms of ductility and low cycle fatigue. FD and VSP are modeled in ABAQUS and related numerical results are compared to those of previous experimental studies for verification purposes. Pushover and cyclic loadings are conducted for two models. The hysteresis curves show symmetric two-level behavior with stable strength and stiffness by increasing the ductility ratio of 87.3%. To study the performance of the HFD-VSP, seismic analysis and incremental dynamic analysis, IDA, are applied to two 5-story buildings with and without hybrid dampers. Maximum drift and maximum roof displacement decrease by 17.4% and 17.1% on average under earthquakes. Average IDA results show that first mode spectral acceleration at HFD-VSP is 1.14 times that of the frame with just VSP. The drift and spectral acceleration of the collapse prevention level increase 33.3% and 28%. The proposed system using FD and VSP performed better than the vertical shear panel against an extensive range of earthquakes as well as the mainshock with strong foreshocks and aftershocks.

Experimental study of the effects of slab openings on seismic behaviour of buildings

Experimentation by producing three-dimensional samples for understanding the seismic behaviour of a structure takes a significant amount of time and these experiments may be highly complicated. Based on literature, the seismic behaviour of structures with slab openings usually was represented by analytical assessments instead of three-dimensional experimental studies. Moreover, the limiting values of slab openings vary greatly between earthquake regulations. This variability has made it important for experimental studies. For this purpose, a total of 5 reinforced concrete carrier system models, with different slab opening ratios, were produced at 1/2 scale. As a result of the study, it was observed that in cases where there were 25% or more openings in the slab, rigid diaphragm behaviour decreased in the structure. It was recommended that for analyses of these types of building systems that the finite element method, based on the assumption of an elastic diaphragm rather than the assumption of a rigid diaphragm, be used.

Investigating the effect of rotational components on the progressive collapse of steel structures

The study of the seismic behavior of structures under strong ground motions has shown that translation components are cause of structural collapses. To prevent the progressive collapse of structures, it is imperative to duly consider the effects of abnormal loads during the design and construction. These loads are of seismic and dynamic nature and have the potential to impose destructive loads on structural members. This study first examines the characteristics of the rotational components of ground motion and a method for reproducing these components. After examining the near-field and far-field translational and rotational components, the study compares the effects of rotational components with and without transitional components on steel structures. The structural parameters are various lateral load resisting system (special moment frame and dual frame) and the height of the structure. Finally, the potential of progressive collapse during the earthquake loading is evaluated. The results shows that the hinge formation pattern is more critical when the structure is subjected to seismic excitation. Moreover rotational components play a more critical role in tall structures. The obtained drift diagrams showed that rotational components had a significant impact on the seismic performance of the modeled structures.

Seismic Analysis and Design of SDOF Elastoplastic Structures with Self-centering Viscous-hysteretic Devices

ABSTRACT A self-centering viscous-hysteretic device (SC-VHD), composed of a viscous damper and ring springs in parallel, which combines velocity-proportional viscous energy dissipation and displacement-proportional hysteretic energy dissipation is studied. To evaluate the seismic behavior of structures with self-centering viscous-hysteretic devices and obtain appropriate parametric combinations between the main structure and the added self-centering viscous-hysteretic devices, a parametric study was conducted on SDOF elastoplastic structures with SC-VHDs. The results show that the SC-VHD can reduce about 30–50% of peak displacement and more than 80% of residual deformation, whilst a small increase in peak acceleration was observed. The reduction of the residual deformation is mainly influenced by the ring springs damping ratio and the ratio of preload to structural yielding strength, while the reduction of the peak displacement is significantly influenced by the viscous damping ratio and the ratio of loading stiffness to structural elastic stiffness. When the SC-VHD was designed with a viscous damping ratio of no less than 5%, a ring springs damping ratio of 15% at most, a ratio of preload to yielding strength of no less than 0.1 and a ratio of loading stiffness to elastic stiffness of no less than 0.1, the 2% peak drift and 0.2% residual drift criteria can be satisfied. Based on the parametric analysis results and an improved equivalent damping model parallel to ASCE 7, a displacement-based design method of SDOF elastoplastic structure was then proposed and evaluated by comparison with nonlinear time-history history analysis results.

Shake table testing of a rocking podium: Results of a blind prediction contest

AbstractRocking motion is sensitive to the boundary and initial conditions of a rocking structure, making experiments nonrepeatable. Thus, the claims that numerical rocking motion models are not only inaccurate but that all rocking structures behave unpredictably. Hence, rocking is not used as a seismic design approach. This paper revisits the issue of rocking motion unpredictability. Seismic behavior of structures is inherently stochastic, because the loading is stochastic. Therefore, the question of interest is not whether models can predict the seismic response to a single ground motion, but if the statistical characteristics of the ensemble of responses to a set of ground motions that define the seismic hazard can be predicted. For this purpose, a rocking podium, which is a three‐dimensional structure comprising an aluminum slab supported by four tubular steel columns, was tested on a shake table excited by two sets of 100 consistently generated ground motions. It was found that the cumulative distribution function (CDF) of the experimentally obtained displacements is statistically stable. Next, a blind prediction contest was organized. The contestants were invited to predict the CDFs of the slab lateral displacement. They were able to predict the slab displacement CDF relatively well. Both finite element and discrete element modeling approaches were used, but no clear pattern emerged as it was found that the performance of either approach depends on the input parameters used and the assumptions made. It was also observed that the contestants who did not use Rayleigh damping in their models produced better predictions.

Effects of Modeling Uncertainties on Fragility Curves of MRFs Considering Accumulation Damage

Incorporating structural modeling uncertainties along with record-to-record variability is of great importance in seismic performance evaluation of structures. It is important to consider these uncertainties in order to accurately estimate the seismic response of structures. On the other hand, structures may be excited by successive earthquakes which can cause accumulative damage in them. Therefore, taking into account the effects of repetitive earthquakes on seismic behavior of structures should be considered as a necessary topic since the seismic design of buildings in most parts of the world is based on the main characteristics of the mainshock. In this study, Latin hypercube sampling was employed to consider the effects of modeling uncertainties in a 4-story steel moment-resisting frame. In this paper, state-dependent fragility which provides a prediction of potential damages during successive earthquakes is plotted for the considered benchmark frame with probabilistic modeling parameters. Moreover, a sensitivity analysis was carried out for different structural modeling input parameters based on the Spearman rank-order correlation. Results showed that the damping ratio has the most impact on estimations.

Assessing the Dynamic Behaviour of Midrise Frame Structures Sitting on Silty Sandy Soil

Background:Midrise 5 to 15 storeys frame structures sitting on soft soils are susceptible to damage induced by seismic events. The level of damage is related to the interaction between the structure, foundation and soil called Soil Structure Interaction (SSI). If the level of ground acceleration is low, the wave gets amplified putting the structure at risk of collapse.Objective and Methods:Concerns about SSI have motivated several researchers to investigate the seismic behaviour of structures rested on cohesive and cohesionless soils. The objective of the work presented in this paper is to evaluate the effects of several parameters on the seismic soil structure interaction behaviour of midrise structures sitting on silty sandy soil. Using ABAQUS, reliable 3D models of 5 to 15 storeys midrise concrete frame structures rested on raft foundation were built. The effects of the structure’s number of storeys, raft size and thickness were explored for different column sizes. Fixed-based structures which capture the model adopted in seismic codes and flexible-based structures were hit at the bottom by El-Centro (1940) and Northridge (1994) earthquakes.Results and Conclusion:The results, presented in terms of storey lateral deflection, inter-storey drift, shear force, foundation rocking and response spectrum showed the important contribution of SSI effects on the behaviour of the midrise structures. The model analyses indicated that column size strongly affects the behaviour of flexible structures. LetNbe the structure number of storeys andCthe column size. The results showed that in terms of storey lateral deflection and levelling shear force, for column sizes C 0.5 X 0.5 m, SSI was detrimental to structures with 10 ≤N≤ 15 and beneficial to structures with 5 ≤N<10. Increasing the column size to C 0.5 X 1 m showed that SSI became detrimental for structures with 10 <N≤ 15 under El-Centro (1940) and for structures with 7≤N≤ 15 under Northridge (1994), and beneficial for structures with 5 ≤N≤ 10 under El-Centro (1940) and for structures with 5 ≤N< 7 under Northridge (1994). The FE results showed that even though base shear increased with raft size, lateral deflections were amplified for C 0.5 X 0.5 m S15 structures and attenuated for C 0.5 X 1 m S15 structures. However, the seismic response of S15 structures was slightly affected by the variation in raft thickness under both column sizes. Finally, the paper includes a discussion and evaluation of the contribution of inertial and kinematic effects, including soil types used on the simulated numerical models’ seismic responses.

Valuation of the Durability of the Concrete Used in the Precast Great Soviet Panel System

The durability of the concrete of the precast Great Soviet Panel system is valued through the resistance to compression, ultrasonic pulse velocity, surface methods, humidity and potential of corrosion. The evaluation is approached, essentially, through experimental and statistical methods, nevertheless, historical-logical and technical methods, such as surveys and interviews, are used in order to gather a bigger amount of information on the resistance to compression of the elements in the original project. While analyzing the results, we can conclude that, in elements in a good technical-constructive state that conform the constructions in exploitation, concrete has an average resistance. However, in elements with the presence of pathological damages, the resistance is low due to the fact that elements show chemical deterioration processes caused by water exposure, which generates the formation of soluble paste compounds, loss of mass, and decrease in mechanical resistance, among other alterations. At the same time, carbonation of concrete is triggered, which, in turn, causes the corrosion of the reinforcing steel. This corrosion leads to the cracking of concrete, delamination of steel, decrease of the concrete-steel adhesion, and other manifestations that affect the durability of concrete. Therefore, the incidence of the durability of concrete should be valued in the structural seismic behavior of constructions.

The seismic behaviour of RC exterior shear walls used for strengthening of intact and damaged frames

Several strengthening techniques such as steel plate bonding, external post-tensioning, steel bracing, or addition of new structural elements have been widely used to improve the seismic behaviour of structures, which suffer from earthquakes. Especially, adding infill walls and shear walls to the structures are preferred because of the added increase in lateral strength and stiffness. Nevertheless, applications of these techniques have some difficulties in terms of labour, cost, usage, and comfort for occupants. Due to these difficulties, the exterior shear wall, instead of an infill wall, is applied to strengthen structures, especially for public buildings like schools, hospitals, etc. In this study, the seismic behaviours of the exterior shear walls used to strengthen intact and damaged frames were investigated experimentally. For this purpose, reinforced concrete shear walls were positioned in parallel to the exterior sides of the damaged and the intact three-dimensional frames. Both frames were tested under cyclic loads. After the investigation, the hysteresis curve, strength envelope, stiffness degradation, and the energy dissipation capacity were obtained to reveal the seismic behaviour of the strengthening exterior shear walls. In addition to these, the differences in behaviours of the shear walls applied to damaged and intact frames were identified.

Fire Evaluation of RC Frames Strengthened with FRPs Using Finite Element Method

Reinforced Concrete (RC) structures may confront with extreme loading conditions. Sometimes, structures are not only under extreme loading such as earthquakes but also, they may be subjected to fire. Therefore, investigation of reinforced concrete structures which are the most common ones is essential. In this study, experimental RC frame is considered to validate in ABAQUS finite element software. RC frame is subjected to both earthquake and fire loading condition to assess the seismic behavior of structure under extreme conditions. FRP techniques is also consider evaluating the seismic behavior such as load capacity, ductility, energy absorption and stiffness. In this regard, two different approaches including reinforcing and wrapping are employed. In this research, the pattern of retrofitting and reinforcing are the novelty of this work. In fact, the effect of using steel bars, BFRP bars and sheets are evaluated. The new method for combination of steel-BFRP bars and different BFRP sheet’s angle as divergence and convergence are investigated. After carrying out the load-displacement diagrams, the seismic parameters of RC frames are compared and the optimized method and model is presented.

Experimental and Analytical Behavior of Square CFDST Column Blind Bolted to Steel Beam Connections

In recent years, steel or composite beam-column connections adopting blind fasteners have drawn increasing praise due to the rapid development of assembled steel structures. However, limited researches have paid attention to the experimental and analytical behavior of concrete filled double-skin steel tube (CFDST) column blind bolted joints. For investigating the structural performance and seismic behavior of this type of connection, cyclic tests on blind bolted joints to square CFDST columns were carried out to explore the effects of column hollow ratio and end plate type. Finite element analytical modelling of the semi-rigid joint was performed considering complex contact interactions and material models. Good agreement between the test and analytical results was observed in terms of the failure modes and the hysteretic behavior. Substantial parametric analyses were conducted on typical CFDST column connections to observe the influence of parameters including strength of steel tube, column hollow ratio and bolt pretension force. Furthermore, certain constructional measures commonly employed in engineering practice were also discussed. It was concluded that the CFDST column blind bolted to the steel beam joint has favorable seismic behavior and is feasible for application in high-intensity earthquake regions.

Design Method and Finite Element Analysis of a New Prefabricated Steel Special-shaped Lattice Column

A new steel special-shaped lattice column (SSLC) was proposed, which can be used in prefabricated steel structure residence. The finite element models of four SSLC with different cross-section (L-shaped, T1-shaped, T2-shaped and X-shaped) were established under cyclic loading by using ABAQUS, in which the strength, lateral resist capacity and hysteretic behavior were analyzed. The results indicate that SSLC has adequate strength, stiffness and safety redundancy. Among the four SSLC, the SSLC with X-shaped has the best structural performance and seismic behavior.