Seismic Design Of Structures Research Articles

Impact of ground motion directionality (RotDnn) on the coupled and uncoupled inelastic response of RC circular cantilever columns

Directionality in the representation of earthquake demand for structural seismic design has surfaced as a subject of debate in recent years. Design spectra, as defined in building and bridge codes, account for directionality by considering the peak response in all possible orientations of the motion using the RotDnn measure, where “nn” is the percentile of the peak response. Current seismic hazard maps are based on ground motion models that use the RotD50 spectra (median peak response). However, since 2009, building codes have adopted RotD100 spectra (maximum peak response), raising concern among researchers and engineers. The first objective of this study is to evaluate the impact of design spectra definition, RotD50 or RotD100, on the bidirectional inelastic response of azimuth-independent RC systems. Upcoming updates to seismic hazard maps highlight the need of understanding the implication of this choice in bridge design. While previous research focused on the relationship between RotD50 and RotD100, this work assesses the impact of each definition on the inelastic seismic response of RC circular columns designed following the Direct Displacement-Based Design approach and verified through nonlinear time history analyses (NTHA) using ground motions from shallow crustal active and subduction zone regions. The ratios of NTHA to design displacement confirm that RotD100 spectra should be used to design azimuth-independent RC systems and provide the first known verification of DDBD for bidirectional loading (second objective). These ratios are a function of ductility level, tectonic regime, effective period, and coupling (which is the third objective). Overall results show that RC circular cantilever columns designed to RotD100 spectra show less deviation from the expected design displacement than columns designed to RotD50 spectra. This study presents the first step in resolving the ongoing debate over spectra definition and provides recommendations for displacement demand estimations for response spectra-based design approaches.

Nonlinear Analysis for Investigating Seismic Performance of a Spun Pile-Column of Viaduct Structure

Slab-on-pile SOP viaducts have been constructed on several highways and railways in Indonesia, but there are certain doubts about some practical structural seismic design concepts. Therefore, this study aims to investigate the seismic performance of a single spun pile column for the SOP viaduct using nonlinear analysis. The essential variables used include the effect of top pile reinforced concrete infill treatment, soil-pile structure interaction (SPSI), and different response modification factors (R). Moreover, the single spun pile column was designed as a macro model with a force-based beam-column element having a fiber section in the plastic hinge. The static pushover analysis and quasi-static cyclic were also conducted to determine the displacement limit state and the equal viscous damping, respectively. Furthermore, seven pairs of ground motion excitations were used to investigate seismic performance in line with ASCE 7-10 and ASCE 61-14. The results showed that the implementation of the top-pile reinforced concrete infill treatment slightly reduced seismic response but evoked more severe pile curvature in the embedded zone. In addition, the behavior and seismic performance were slightly better than those without treatment when considering the SPSI. This study recommends the spun pile column for the SOP viaduct with a response modification factor of 1.5 to avoid probable brittle failure occurrence under earthquake load. Doi: 10.28991/CEJ-2023-09-07-02 Full Text: PDF

The effects of selection and scaling procedures of earthquake records on the seismic response dispersion of structures and recommendations toward seismic upgrading of codes

In this study, the effects of selection and scaling procedures of earthquake records on the dispersion of seismic response of structures are examined. This is according to the Standard No. 2800 seismic code and the ASCE code. So that during two case studies, seven earthquakes have been selected and scaled with the spectral acceleration of the seismic Standard No. 2800. Besides, the seismic response of a reinforced concrete (RC) bridge and a 7-story RC building is evaluated against scaled earthquakes. The results of the studies indicate that structures respond differently to earthquake records. However, in order to avoid designers' different decisions and align their views to choose suitable earthquakes and to evolve the selection and scaling methods of earthquake records for the seismic design of structures, in the end, some recommendations are presented. The results show that in selecting earthquakes, it is crucial to consider PGA, magnitude, and a classified range of intensities and durations of strong ground motion. In addition, to select earthquakes, paying attention to the frequency content of accelerograms and the shape of the response spectrum is also of particular importance. Considering the ranges of the scale of accelerograms depending on the importance of the structures is significant. By applying the mentioned recommendations, the methods of selecting and scaling earthquake records will be improved to some extent. In addition, seismic response dispersion will be prevented.

Collapse-based design method for simple seismic design of complex structural systems such as linked column frame system

Seismic design of structures is one of the most complex engineering sciences, in addition, the approaches that are currently used for analysis and design increase this complexity. Therefore, in this paper, a new method of seismic analysis and design of structures is presented, which not only eliminates the behavioral complexities of structures, but also increases accuracy. This method, which is called collapse-based design, is simple yet precise, using which even complex structural systems can be designed simply. For this purpose, linked column frame is considered for design as a new dual structural system that has complex, variable, and unclear seismic behavior. This structural system pursues specific target performance objectives and is designed with the aim of simple and quick repair after an earthquake. Currently, there is a lack of a suitable design method for the LCF system that leads to the design of optimal models with sufficient seismic capacity, hence this system is chosen as the prototype model. In the collapse-based design method, the structure is subjected to a seismic intensity equal to its collapse seismic intensity. The stability of the structure at this seismic intensity means sufficient seismic capacity and the maximum capacity of structural members can be used to maintain the stability. The first LCF model designed using this method is 8.5% lighter than a similar moment resisting frame model. The values of ductility and overstrength of this model are 7.56 and 3, and its maximum interstory drift ratio at the DBE and MCE hazard levels are 2% and 2.8%, respectively. Also, its collapse margin ratio is 2.28. But after the implementation of the target performance objectives, the weight of the model increases to 5% heavier than the similar moment resisting frame model, nevertheless, its seismic capacity decreases slightly. Based on this, it’s found that the implementation of the target performance objectives in the LCF system also causes little destructive effects. And as a final conclusion, the results show that the presented methods and approaches are appropriate for the analysis and design of structures and the comprehensive evaluation of designed models.

Study on Optimal Bracketed Duration Scheme of Seismic Time History Analysis for High-Speed Railway Track-Bridge System

ABSTRACT Seismic duration significantly impacts the structural seismic response. In order to obtain a correct time history analysis result of structural seismic design, determining a reasonable seismic duration scheme is imperative. In this paper, a five-span simply supported beam bridge and China Railway Track System (CRTS) II slab ballastless track system is taken as the research focus. A finite-element model for a high-speed railway track-bridge system was developed. The influence mechanism of starting and end threshold on seismic response was analyzed. Different bracketed duration schemes were put forward, and their applicability was assessed. The optimal bracketed duration scheme of time history analysis for a high-speed railway track-bridge system was determined. The results indicate a response curve deviation between the full duration and partial duration in the starting part due to the inconsistent structural movement trends and a deviation in the end part because of the structure entering a free vibration state in advance. When calculating the seismic peak response, the starting threshold A and end threshold B at both ends should be taken as5% of peak acceleration. When calculating seismic residual response, the starting threshold C at the left end should be taken as 25% of peak acceleration.

Elastoplastic hysteretic behavior and constitutive models of in-service structural steel considering fatigue-induced pre-damages

Fatigue damages are commonly observed in the in-service steel components and progressive deterioration in their mechanical behavior is triggered with increasing service period. Hence the present work aims to investigate the degradation of the mechanical properties of the fatigue-damaged structural steel Q345qD and establish the practical constitutive models. Various fatigue tests before the elastoplastic cyclic loading were conducted to simulate the fatigue-induced pre-damages. The residual mechanical properties of the fatigue-damaged material were investigated and refined versions of the hysteretic constitutive models were proposed. Moreover, the effects of the deterioration in the material properties on the mechanical behavior of the steel components were studied. Experimental results indicate that a prior history of fatigue loading significantly affects the subsequent elastoplastic hysteretic behavior of the in-service material. As the accumulation of the prior fatigue damage, the yield and ultimate strengths of the steel material deteriorate. In particular, the yield plateau disappears when the pre-damage level exceeds 0.5. Both of the strength and ductility of the in-service steel components deteriorate remarkably. This implies that the fatigue damages accumulated in the service history should be included in the seismic design of structures.

EFFECT OF EARTHQUAKE FORCE ON DIFFERENT TYPE OF BRACING IN FRAME STRUCTURE

A Bracing is a system that is provided to minimize the lateral deflection of the structure. The use of braced frames has become more popular in high rise structure and also in seismic design of structure. So, this Study aims to investigate the effect of earthquake on structure with different shapes of bracings. In this project a concrete frame is modeled by using Etabs Software with different type of bracing and effect of these different bracing on earthquake affected structure is studied for different parameter like storey drift and bending moment in column and story displacement. Among these numbers of trials which type of bracing at critical storey is more suitable in seismic areas would be selected for the structure from the observed results.

EFFECT OF EARTHQUAKE FORCE ON DIFFERENT TYPE OF BRACINGIN FRAME STRUCTURE

A Bracing is a system that is provided to minimize the lateral deflection of the structure. The use of braced frames has become more popular in high rise structure and also in seismic design of structure. So, this Study aims to investigate the effect of earthquake on structure with different shapes of bracings. In this project a concrete frame is modeled by using Etabs Software with different type of bracing and effect of these different bracing on earthquake affected structure is studied for different parameter like storey drift and bending moment in column and story displacement. Among these numbers of trials which type of bracing at critical storey is more suitable in seismic areas would be selected for the structure from the observed results.

Feasibility of Timber Pegged Joints for Seismic Design of Structures

This paper investigates the feasibility of employing timber pegged joints in modern seismic-resistant structures or for retrofitting existing structures. The behavior of timber pegged connections has been investigated for about twenty years, but seismic design aspects are not treated in existing standards. In the framework of the force-based design approach, this paper analyzes and defines seismic design aspects and rules for timber pegged connections that are easy-to-use in engineering practice. A large database (more than 350 test results) has been elaborated and the data processed with the purpose of (1) analyzing the effectiveness of the European Yield Model for evaluating the maximum strength of the connection, accounting for the particular embedding behavior due to the presence of timber peg; (2) assessing and defining the capacity design rules to design the dissipative regions (i.e., overstrength factor); and (3) defining the available ductility of the connection with identification of ductility class intervals. The obtained results proved that timber pegged joints have a good potential to be used in seismic-resistant structures. In fact, data processing identified a suitable value for the overstrength factor (useful to project the joint with the capacity design) similar to that used for steel-dowelled connections, and defined a likelihood range of ductility classes. Finally, it is highlighted that the European Yield Model can be a practical tool to calculate connection strength, provided that some modifications are included to consider peg behavior.

Frequency-domain preliminary assessment of coupled site and SSI effects according to the Algerian seismic provisions

PurposeSeveral studies were made on paired site and soil–structure interaction (SSI) effects, but most of them were site specific. This paper aims to investigate the impact of SSI effects in conjunction with local soil condition effects on the seismic response of typical multistory low- to mid-rise–reinforced concrete (RC) buildings resting on Algerian regulatory design sites through a global explicit transfer function (TF).Design/methodology/approachA preliminary quantification of SSI effects associated with site effects is carried out through a frequency-domain solution based on the concept of rock-to-soil surface displacement TF performed for each design site category. It results from the combination of the TFs of structure, foundation and soil and reflects how seismic waves are amplified due to changes in the geological contrast between the rock and overlying soil deposits. As well, response modification factors, denoting displacement ratios of the building responses within the flexible and site-structure conditions with respect to the fixed-base one, are carried out.FindingsIn the context of Algerian seismic regulation, the study provides a clear vision of how and when site or SSI effects are expected to be influential, as opposed to the fixed-base hypothesis still retained by the current regulation. This helps engineers to be aware of the extent of the expected seismic damage.Research limitations/implicationsThe research applies to low- to mid-rise RC buildings within the Algerian seismic regulation, but it may also be expanded to other examples that fall under other seismic regulations.Practical implicationsThe response modification ratio is a quantitative approach to assessing response fluctuations. It draws attention to how the roof level drift varies depending on the condition. These results can be used as numerical parameters in structural seismic design when the structure is comparable because they provide useful information about how the two phenomena interact with the structure.Originality/valueThe study goes beyond particular situations dealing with site specific and offers effective indicators and quantitative evaluation of combined site and SSI effects according to the current national seismic provisions, where no indication about site or SSI effects exists.

Experimental campaign on structural aluminium alloys under monotonic and cyclic loading

In the present paper an extensive experimental campaign is carried out on 5000, 6000 and 7000 aluminium series through monotonic and cyclic tests. The research is part of a collaboration between the Universities of Salerno and Naples “Federico II”involvedfor several decades in the development of the Eurocode recommendation regarding the aluminium alloys for structural purposes. The experimental program is composed of 3 monotonic experiments for each aluminium alloy, 29 low-cycle fatigue tests for 6060, 6082 and 7075 alloys and 10 incremental cyclic tests under different loading cycles for all tested alloys.The main purpose of this campaign is the characterization of such alloys not only in terms of the well-known stress–strain curve while in terms of low cycle fatigue, cyclic hardening, dissipated energy and plastic fracture, to achieve more information about the non linear behaviour which can be exhibited, as an example, under seismic loading. In fact, since now, the largest part of the research has been mainly focused on the behaviour of such materials under a large number of cyclesinelastic range thus neglecting the potential benefits in exploiting the large dissipative capacity of such alloys.Moreover, the collected information could be of fundamental importance in the framework of the revision of the new Eurocode 8 which presents, for the first time, a section devoted to the seismic design of structures made of aluminium alloys. The accurate knowledge of the random material variability and cyclic hardening could be helpful for the setting up of the coefficients to be used for the application of the hierarchy criteria.

The Effect of Soil-Structure Interaction on the Seismic Response of Structures Using Machine Learning, Finite Element Modeling and ASCE 7-16 Methods.

Seismic design of structures taking into account the soil-structure interaction (SSI) methods is considered to be more efficient, cost effective, and safer then fixed-base designs, in most cases. Finite element methods that use direct equations to solve SSI problems are very popular, but the prices of the software are very high, and the analysis time is very long. Even though some low-cost and efficient software are available, the structures are mostly analyzed for the superstructure only, without using the geotechnical properties of the ground and its interaction effects. The reason is that a limited number of researchers have the knowledge of both geotechnical and structural engineering to model accurately the coupled soil-structure system. However, a cost-effective, less time-consuming and easy-to-implement technique is to analyze the structure along with ground properties using machine learning methods. The database techniques using machine learning are robust and provide reliable results. Thus, in this study, machine learning techniques, such as artificial neural networks and support vector machines are used to investigate the effect of soil-structure interactions on the seismic response of structures for different earthquake scenarios. Four frame structures are investigated by varying the soil and seismic properties. In addition, varying sample sizes and different optimization algorithms are used to obtain the best machine learning framework. The input parameters contain both soil and seismic properties, while the outputs consist of three engineering demand parameters. The network is trained using three and five-story buildings and tested on a three-story building with mass irregularity and a four-story building. Furthermore, the proposed method is compared with the dynamic responses obtained using fixed-base and ASCE 7-16 SSI methods. The proposed machine learning method showed better results compared with fixed-base and ASCE 7-16 methods with the nonlinear time history analysis results as a reference.

Stochastic simulation of velocity pulses of near-fault ground motions based on multivariate copula modeling

Due to the featured high-amplitude, long-period pulses in velocity or displacement time–history, the near-fault ground motion may have a stronger destructive effect on engineering structures. Therefore, studying velocity pulses modeling of near-fault ground motions has been an important topic in the earthquake engineering community. However, the variability and probabilistic correlation of pulse model parameters have not received enough attention. To this end, an elegant method for stochastic simulation of velocity pulses of near-fault ground motions is proposed based on the classical Gabor wavelet modeling and probabilistic correlation analysis of associated model parameters by multivariate copula modeling. Especially, an efficient scheme of iteratively determining the optimal copulas pertinent to edges of a complex vine structure is developed, and two parameters relevant to the near-fault ground motion records, i.e., the rupture distance and the strongest pulse orientation, are introduced which provides a physical basis for addressing the dependence structure among variables. For illustrative purposes, the ground accelerograms recorded by near-fault instruments in the 1999 Chi-Chi earthquake are used. It is shown that the multivariate copula modeling enables the efficient representation of probabilistic correlation between model parameters which is consistent with their physical mechanism. The time histories and spectral characteristics of velocity pulses of near-fault ground motions and their stochastic fluctuations with respect to the rupture distance are well simulated. While the empirical linear regression model does not meet the requirements of random vibration analysis and thus cannot guide the safety design of seismic structures.

From “De la pression des terres et des revêtements” to the seismic analysis of retaining structures

In his Essai, Charles-Augustin Coulomb showed that the earth pressure on a retaining wall can be calculated maximising the force obtained by considering equilibrium and strength compatibility. This same approach is still of practical relevance in some design situations and, more importantly, its basic assumptions have paved the road for the numerous successive developments that lead, among other factors, to consideration of the changes in earth pressure induced by seismic forces. A modern approach to the seismic design of structures entails the evaluation of their performance under different shaking intensities, including seismic actions strong enough to activate the system resistance. This paper intends to show that the basic ingredients of the Coulomb’s analysis, that is, equilibrium and strength compatibility, can be used in a rational way not only to predict limit values of the earth pressure, but also to evaluate the performance of retaining structures subjected to moderate and severe seismic actions.

Comparison of seismic structure design in the world

Aseismic performance is one of the important technical indexes of modern buildings, which has been written into the building codes in various countries. Aseismic structure design is to enhance the stability of the building structure, ensure the safety of the building when the earthquake disaster occurs, reduce the loss and casualties. Since ancient times, innovations have been made in the design of seismic structures worldwide, especially in areas with high earthquake incidence. It was found in the previous research that the calculation method and design of seismic structures in American and Chinese building codes are different. Based on the interest of aseismic design, this paper summarizes the traditional and new aseismic structures. This paper first introduces several commonly used aseismic structures, such as multi-storey masonry, frame and seismic wall construction. Then this paper introduces the characteristics and differences of aseismic structure design in different countries from the modern and ancient time dimensions. In the end, Finally, it is concluded that the seismic structures are different due to the differences of geography, culture and climate in various countries. We can learn from the seismic structure analysis of ancient buildings that Aseismic structure design does not have to resist earthquake, but can reduce the damage of earthquake to the building by reducing the seismic force of the building.

Performance Evaluation of RC Frame - Wall Structures Using Incremental Dynamic Analysis

A structure whose resistance to lateral loading is provided by a combination of shear walls and rigid frames, may be categorized as a frame-wall structure. The behaviour of RC structures under the effect of earthquake loading has always been a subject of investigation. Structural seismic design has been undergoing a major revaluation in recent time, with importance shifting from strength to performance. Nonlinear Time-History Analysis (NLTHA) constitutes the accurate way for simulating response of structures subjected to seismic excitation. Incremental Dynamic Analysis (IDA), involves performing nonlinear dynamic analysis of the structure under a set of ground motion records, each scaled monotonically to several intensity levels. In the present paper, RC moment resisting frame-wall structure with 18, 22 and 26 storeys are analysed for seismic zone IV, resting on hard soil and designed as per IS code provisions. Geometrical configuration of the buildings are considered as per IS 16700:2017. Analysis and design of frames are carried out using ETABS-2016. The performance evaluation of above frames is done using NLTHA and IDA using SeismoStruct software for set of 11 recorded ground motions of past Indian earthquake varying in range of magnitude from 5.6 to 7.8. For this parametric study, the performance criteria as per FEMA 356 for the limit states of Immediate Occupancy (IO), Life Safety (LS) and Collapse Prevention (CP) are considered. Results obtained from NLTHA are shown in terms of Interstorey Drift Ratio (IDR) profile. The results of NLTHA showed satisfactory performance when evaluated by a set of recorded ground motions of past Indian earthquakes. Individual and summarized IDA curves for 16%, 50% and 84% IDA of IDR | Sa illustrates that RC Frame-walls crosses the IO performance level and are well below the CP level for all cases which shows acceptable performance.

Probabilistic prediction of ground-motion intensity for regions lacking strong ground-motion records

Probabilistic prediction of ground-motion intensity in regions lacking strong ground-motion records is a vital issue for seismic structural design. Several approaches have been suggested for this purpose, and nearly all of them directly import and adjust the ground-motion prediction equation (GMPE) of ground-motion measures such as the peak ground acceleration (PGA) or spectral acceleration (SA) from data-rich regions. However, as the transmissions of PGA and SA from the source to the site correspond to nonlinear processes, this import and adjustment may lead to an unrealistic evaluation of ground motion. In this study, a novel probabilistic prediction method of ground-motion intensity for such regions is proposed. In contrast to the current approach wherein the GMPE of ground-motion measures such as PGA or SA is directly used, a Fourier amplitude spectral (FAS) model is suggested to express the seismic transmission process from the source to the site. The ground-motion intensities of PGA or SA are obtained from the FAS model using the random vibration theory. The exceedance probability of ground-motion intensity is calculated based on Monte Carlo simulations. As the FAS conforms to the linear system theory and the determination of FAS model does not require too many ground-motion records, the proposed method should be convenient for the probabilistic prediction of ground-motion intensity in regions lacking strong ground-motion records.

Deformation mechanism analysis of steel artificial controllable plastic hinge in prefabricate frame

The concept of structural recoverability has become a vital performance objective in structural seismic design. A novel performance-recoverable beam-column connection device, steel Artificial Controllable Plastic Hinge (ACPH), was proposed to achieve structural function restoration after earthquakes. The bending-shear decoupled prefabricated ACPH is composed of a pin-hinged connection bearing shear force, and two sets of replaceable energy dissipation plates providing flexural resistance. The weakening ratio effect of the energy dissipation plate on the ACPH seismic performance was experimentally explored by three specimens. The results indicated that the ACPH had excellent hysteresis behavior, as well as superior ductility. Moreover, the ACPH yield mode was the compression yield of the energy dissipation plate. The failure mode was the tearing failure in the weakened area of the energy dissipation plate. The pin-hinged connection was barely deformed throughout the working process, which guarantees the ACPH repairability and attains the goal of ACPH damage control. Besides, based on the component method, the deformation model and deformation calculation formula of ACPH were proposed, which considered the deformation effects of the bolt rod, the installation gap, the energy dissipation plate, the end plate of the energy dissipation, and the installation clearance of bolts. The formulas of ultimate moment bearing capacity for the ACPH were put forward based on the thin plate theory.

Dynamic Stress Path under Obliquely Incident P- and SV-Waves

This study derives the expression of dynamic stress components of the soil element in the semi-infinite elastic space under obliquely incident P- and SV-waves, and obtained the corresponding dynamic stress path. The effects of some factors including the incidence angle, Poisson’s ratio, frequency, wave velocity, phase difference, and soil depth on the dynamic stress path are analyzed. It is found that the dynamic stress path in the (σy − σx)/2 − τxy plane is an oblique ellipse, and the above factors have significant effects on that. The maximum dynamic stress level for Poisson’s ratio of 0.3 is about twice that for 0.48. The maximum dynamic stress level for 2.5 Hz is about six times that for 1 Hz. In general, the maximum dynamic stress level is about 40 kPa, no matter how the wave velocity changes. Compared with other phase difference, the dynamic stress level for the phase difference of 60° is largest with a value of 43 kPa. The dynamic stress level becomes greater as the soil depth increases, and the maximum value at 30 m depth is about 40 kPa. The variation trend of the three characteristic parameters with the incident angle exhibits the double-peak or triple-peak curves for different influencing factors. The research findings can provide some guidance for the site seismic dynamic response analysis and structural seismic design.

Common Mistakes and Their Fixes in Earthquake-Resistant Buildings

The primary way to design building structures refers to the stationary loads specified by the governing laws. However, the load pattern does not guarantee the appropriateness of the seismic design. To make matters worse, old or ancient structures are traditionally reinforced for gravitational loads. This study reveals that the traditional reinforcement, in most cases, harms the seismic performance of buildings. The authors introduced the approach of most computer programs for seismic design, along with their limitations. Then, the ancient Roman approach was explained, and the reasons for the survival of many of these ancient structures were exposed thoroughly. After that, classical advices were summarized briefly for good seismic design of structures and reinforcement. Finally, a few classical mistakes were identified in reinforcement design.