Seismic Design Forces Research Articles

SEISMIC CONDITIOT{S IN BAGHDAD REGION ANI) EVALUATION OF SETSMIC DESIGN FORCES

In this paper, a study of the earthquakes that have affected Baghdad region in Iraq is made" The documents collected from different references are analyzed to determine the seismic zone of Baghdad. Evaluation of seismic design forces for equivalent static analysis of earthquakes in Baghdad region is mc"de according to the Iraqi seismic code and the lnternational Building Code (I8C,2000). The studies reached that intensity greater than V on Mercalli Scale has never been recorded on the site at Baghdad. While Seismicity Map of Iraq, proposed by Iraqi Seismic Code, reveals that, Baghdad places in a zone of intensity between (VI-VII) on the Modified Mercalli Scale. Also, the studies reached that magnitude greater than 5.7 on Richter Scale has never been recorded on Baghdad. When calculating the total horizontal seismic design force acting on buildings and structures according to the formula of the Iraqi Seismic Code Requirements for Buildings (1997), the coefficient Z (seismic hazard zoning coefficient) shall be talien as (0.05) for Baghdad region.

Seismic Design Force for Rectangular Water Tank with Flexible Walls

Seismic Design Force for Rectangular Water Tank with Flexible Walls

Fuzzy inference system model for the spectrum site coefficients of the Türkiye Building Earthquake Code (2018)

The response spectra in the seismic design codes guide the seismic design force calculations that are crucial for structural safety and construction costs. In general, they are determined by crisp logic-based numerical classifications of seismic parameters, which primarily affect the shape and values of the spectrum. Crisp logic response spectra generation may have limitations in the accurate determination of relevant parameters. In this paper, a fuzzy inference system (FIS) rule-based model is proposed to address this issue. The proposed model uses spectral acceleration coefficients and shear wave velocity as inputs to generate the site coefficients of the response spectra according to the Türkiye Building Earthquake Code (TBEC 2018). The FIS model spectra generation is compared with the crisp logic model for thirty-five examples, and the model performance is evaluated. The study demonstrates significant differences between the two models in terms of the response spectra' shape and acceleration spectrum intensity values, but the FIS model provides comparatively better accuracy in response spectra generation. The proposed model can be modified and applied to various parameters for generating response spectra in different seismic design codes with the exposition of fuzzy logic rules that show the concerned problem's internal working mechanism.

Fuzzy inference system model for the spectrum characteristic periods of the Türkiye Building Earthquake Code (2007)

Seismic design codes define response spectra with crisp numerical classifications of seismic parameters, which mainly affect the spectrum's shape and determination of seismic design loads. The efficiency of structural safety and construction costs depends on the optimum design and accurately determined seismic forces. As presented in the seismic design codes, several parameters are utilized to calculate the seismic design forces with response spectra. This study proposes a rule-based fuzzy inference system (FIS) model with fuzzy set numbers to determine the relevant parameters. By defining the soil profile thickness and shear wave velocity as inputs, the model generates the spectrum characteristic periods specified in the Türkiye Building Earthquake Code (TBEC 2007). The response spectra of twenty different samples with the FIS and crisp models were generated and compared to assess the model's superiority. Unlike crisp seismic code classifications, the proposed FIS model accounts for imperfections in soil group selection and topmost soil layer thickness, offering a more realistic representation of uncertainties and proving to be an effective tool for addressing linguistic vagueness in seismic response spectra analysis. The comparison between fuzzy and crisp output seismic parameters revealed significant differences in response spectra shape and spectrum intensity values. The FIS model-generated spectra were more conservative in certain building locations, while in others, they provided similar or lower values, suggesting potential cost savings in design. The FIS model demonstrates its efficacy in producing more accurate and robust designs by considering the uncertainties inherent in the problem. Furthermore, this approach has the potential to be extended to study seismic parameters of other design codes, although further research is required to comprehensively explore its capabilities and limitations.

Numerical Modeling of the Section Properties of Cross Laminated Timber

直交集成板(Cross-Laminated Timber)，以下簡稱CLT，質量輕約為鋼筋混凝土重量之0.2倍，具有經濟及自然材料循環再生的特性。CLT板材使用在鋼結構高層建築樓板上因現場組裝便利、迅速，更因為自重輕，可以降低各樓層的重量因而減少設計地震力，使梁柱結構尺寸斷面變小，可提升樓層高度之淨高及增加平面使用之面積。世界各地因為地理環境的不同，各國皆有專屬的特有樹種，以日本為例，將CLT產品性能最佳及經濟化，發展出外層為扁柏內層為杉木之CLT產品。為提供結構設計者一種迅速、可靠的應力分析方式，本次研究以驗證之方式探討CLT案例試驗資料與數值模擬分析結果進行兩者斷面性質比較，藉此結果提出當CLT其集成元具不同斷面組合時，可以運用模擬方式求得彎曲彈性係數E，並在不同支承邊界條件、不同載重形式時，提供精準之斷面應力分析。The light weight of the Laminated of Timber, CLT, is about 0.2 times the weight of the concrete. It is also economical and recyclable from natural materials. CLT panel used in high-raise steel buildings, in addition to the convenience and speed of on-site assembly, CLT flooring panel can reduce the weight of each floor due to its light weight, thereby reducing the design seismic force, making the size and cross-section of the beam-column structure smaller, and increasing the net height of the floor height and the usable area indoor. Nowadays, due to the different geographical environments around the world, each country has its own exclusive tree species. In addition, Japan has developed CLT products with the outer layer of cypress and the inner layer of fir for optimizing the performance and economy of CLT products. In order to provide structural designers with a rapid and reliable stress analysis method, this study discusses the CLT test data and numerical simulation results in a verification way to compare the cross-section properties of these two. The results suggest that when CLT has different integrated component sections, the bending elastic coefficient E can be obtained by simulation, and accurate section stress analysis can be provided under different support boundary conditions and different load forms.

HORIZONTAL ACCELERATION OF FLOOR-MOUNTED NONSTRUCTURAL COMPONENTS UNDER ROCKING MOTION

Floor-mounted nonstructural components (NSCs) that are attached through various types of angles are susceptible to seismic damage as they experience severe rocking motion resulting from their slender geometric configuration. However, current design codes do not reflect such complex dynamic behavior and prescribe design factors based on simplified single-degree-of-freedom (SDOF) models, which might cause an under-estimation of seismic design forces. Therefore, to properly control their seismic damage, the complex rocking dynamic behavior needs to be thoroughly investigated. This paper analyzed the rocking behavior of the floor-mounted NSCs and their effects on the horizontal acceleration response. Floor-mounted NSCs and their mounting attachments were idealized as rigid blocks restrained by linear vertical springs at the corner of the block. The nonlinear equations for the rocking behavior of rigid block were developed, and the analysis was conducted based on the fourth-order Runge-Kutta integration method. First, it is shown that the resonance period of rocking NSCs is mainly affected by the NSC slenderness and the location of the center of gravity of the component. The horizontal acceleration tends to increase as the slenderness and the height of the center of gravity of NSCs increase. Based on the observations, some useful design recommendations were suggested for designing attachments of floor-mounted NSCs.

Fuzzy Inference System (FIS) Model for the Seismic Parameters of Code-Based Earthquake Response Spectra

The response spectra defined in seismic design codes include crisp classifications of seismic parameters, which directly affect the spectra’s shape and greatly alter seismic design loads. The optimum design phase seismic forces have an important role in the efficiency of the construction costs and structural safety. Various parameters are used to calculate the seismic design forces, especially presented in the codes with earthquake design spectra. This study presents a rule-based fuzzy inference model with fuzzy sets to determine these parameters using fuzzy inference system (FIS) modelling, which is the most appropriate approach among the different alternatives because both the input and output variables have numerical and linguistic uncertainties in the earthquake problem. Using the seismic zone factor of the region and shear wave velocity of the soil profile as inputs, the model generates the seismic coefficients and peak ground acceleration values of the response spectra specified in the Uniform Building Code (UBC, 1997). The response spectra in this code can be easily generated with these seismic coefficients after their fuzzification. Response spectra of twenty-five different sample cases with and without the FIS model are generated, which provide comparisons for the model superiority assessment. Significant differences are observed between the crisp logic and the FIS model-generated spectra. It is suggested that the FIS model can be modified and applied to various parameters to generate response spectra in different seismic design codes.

Collapse risk-targeted seismic design of concrete-filled steel tube frame-RC core tube structures

The concrete-filled steel tube (CFST) frame-reinforced concrete (RC) core tube composite structure is a widely-used structural system of high-rise buildings due to its high compressive strength, good plasticity, and convenient construction. The cross-sectional dimensions and bending stiffness of CFST frames are smaller than those of RC frames with the same vertical load-bearing capacity. Since the seismic forces are distributed in proportion to stiffness for components, the assigned seismic forces of CFST frames are smaller, which may result in CFST frames not meeting the minimum load-bearing capacity requirement for the frame part in a dual system. If the CFST frame-core tube structure is designed adopting the dual system seismic design method which is applicable to RC frame-core tube structure, forcefully increasing the design seismic force of the frame, this will significantly increase the amount of material consumed and reduce the available area of the building. In this study, the CFST frame-RC core tube structure is designed according to different seismic design methods and compared through incremental dynamic analysis-based (IDA) fragility analysis. Then, an improved collapse risk-targeted seismic design method is proposed. The study results indicate that the structure designed according to the proposed method can achieve the excellent collapse resistance capacity, low collapse probability, and less material cost, which may provide a reference for seismic design of CFST frame-RC core tube composite structures.

Risk-targeted hazard for seismic design in New Zealand considering individual and societal risk targets

The promotion of risk-targeted hazard as the basis of seismic design internationally has increased over the past decade. Risk-targeted hazard estimates are derived through convolution of hazard curves with representative fragility functions and provide a means to target uniform risk across a region. Using risk targets also enables performance objectives of building codes that are consistent with other life risks and can include societal input into the expected performance of structures. Current design procedures using a uniform-hazard spectrum are unable to provide equal risk across the country due to variation in the shapes of hazard curves in different locations and uncertainty in structural response. In this article a framework is proposed, which can be used with national seismic hazard models, to produce risk-targeted hazard spectra for seismic design. This study extends the risk-targeted hazard framework through full quantification of epistemic uncertainty in seismic hazard and includes multiple risk targets for individual and societal risk at the building and city scales. The article describes a framework that can be used to adjust current seismic design force levels in New Zealand standards to target uniform seismic risk for buildings considering both the performance of individual buildings and the performance of cities.

Risk‐targeted importance factors for prescriptive seismic design of critical buildings

AbstractThe post‐earthquake recovery of a community depends on the ability of important buildings to perform their functions. Lifeline and other critical buildings that meet a predictable enhanced seismic performance increase the community's disaster risk management capacity. In prescriptive force‐based design standards, the seismic design force for these buildings is typically enhanced using an importance factor depending on the risk category. The present paper proposes an innovative framework based on performance‐based seismic design (PBSD) principles using risk‐targeted importance factors suitable for use with prescriptive standards. The framework decouples probabilistic assessments of building typologies to experts, while the structural designers can continue the conventional design approach. The framework explicitly considers probabilistic seismic demand, uncertainty in the performance of the building, and the inter‐building variation within a particular building typology in seismic performance. Six special reinforced concrete (RC) frame buildings conforming to Indian standards are selected to illustrate the framework. Sensitivity studies on parameter selection are used to establish the framework's robustness. An expression for the importance factors is also proposed. The use of the proposed importance factor expression is shown to meet a wide range of risk targets corresponding to different performance levels. The paper also proposes design factors for enhanced performance objectives suitable for the risk‐targeted prescriptive design. Further, the framework is implemented to estimate the seismic risk associated with existing building typology conforming to prevalent design standards. The assembly‐ and critical‐category RC buildings are found to require higher importance factors for achieving enhanced performance objectives than currently prescribed.

Seismic Capacity Estimation for Composite Multi-storeyed RC buildings

Seismic hazard happens to be one of the most devastative natural hazards to be faced by mankind. In view of urbanization and knowledge gained from past natural hazards, several urban cities have seen a transformation in building their habitats. These range from regular, irregular multistoried Reinforced Concrete (RC) buildings to several composite multi storeyed RC buildings due to certain inherent functional benefits (viz., ventilation, parking space, ease of construction etc.,). The existing seismic code regulations provided by BIS (Bureau of Indian Standards) do not specify any approach to arrive at appropriate design seismic forces and capacity for composite multi storeyed buildings. Therefore, it is imminent to assess the structural behaviour of these multistoried composite RC buildings under earthquake forces at the site location to provide a safe and functional configuration. Hence an attempt has been made in this study to analytically compare regular and composite RC building models having similar Plan and Height. The multistoried RC building configurations considered in this study comprises of regular RC building as well as RC building frame coupled with steel joists at certain locations to represent a composite structural system. These models are further analyzed to arrive at inherent nonlinear seismic capacity, ductility and design seismic forces necessary to be considered during design of RC building structure. Hence, a typical hypothetical G+5 regular and composite multistoried buildings were modelled and analysed using the nonlinear static (pushover analysis) approach. The outcomes of these analyses clearly portrays the variation in dynamic characteristics of the building frames represented in terms of its time period, inelastic capacity and response reduction factor (R). Moreover, the present study emphasizes to analytically evaluate the design seismic forces necessary for earthquake resistant design of composite buildings in any urban environment albeit the changes in structural configurations.

Seismic design and parametric study of steel modular frames with distributed seismic resistance

Structures in modular buildings typically have some unique characteristics as compared with conventional structures, e.g., discrete connection of modules through inter-module connections, discontinuous floor diaphragms. The behavior of steel modular structures under earthquake excitations has not been fully understood, and no seismic design method specifically tailored for modular building structures is available. Moreover, although various inter-module connections with different rotational connectivity have been proposed, their suitability for seismic application is questionable. In this paper, the distributed seismic design method, which makes use of the lateral resistance inherent in all modules, was proposed for modular buildings with steel frames. A numerical parametric study was conducted on a 9-story prototype building. The effect of three parameters, i.e., the rotational stiffness of inter-module connections, the seismic design force level, and the height-wise distribution of the design base shear, were studied. The results show that the rotational stiffness of inter-module connections has limited impact on the elastic lateral stiffness and the fundamental period of modular steel frames. However, in the inelastic range, the increase in the rotational stiffness will lead to less plastic drift concentration and better collapse prevention performance. Increasing the seismic design force may not result in enhanced collapse prevention performance, as it is also dependent on the height-wise distribution of the design base shear and if significant higher-mode response is involved in the total response of the structure.

Seismic force distribution in members of confined masonry buildings

Seismic design codes for confined masonry (CM) buildings are few; therefore, in many places these buildings are generally designed and constructed using simplified guidelines or handbooks. For brevity, it is assumed that masonry walls resist all possible loads imparted on CM buildings, while the only role of reinforced concrete (RC) confining members, also known as tie-members, is to provide the confinement and stability (both in-plane as well as out-of-plane) to the masonry walls. Though such an assumption simplifies the design process, it results in missing out on significant material strength that the tie-members can potentially add up to the structural strength. On the other extreme, such a simplification can also result in construction of weaker tie-members, especially the tie-columns, because the seismic design forces are generally not distributed to different members of the CM buildings. In the present study, a methodology was developed to distribute the seismic design forces to different members of CM buildings such that the tie-columns can be formally designed to not only provide confinement and stability to the masonry walls, but also provide reserved strength that may be utilized in case of failure of masonry walls. Empirical and numerical approaches were followed in developing the methodology. The approaches utilized all the available empirical methods for lateral strength estimation of CM walls and results reported in large number of past experimental studies, including three tests carried out by the authors. An extensive parametric finite element study was carried out considering the influence of several important parameters, and a methodology was developed for relative distribution of shear forces in tie-columns and masonry walls of CM walls.

Demands on acceleration-sensitive nonstructural components in special concentrically braced frame and special moment frame buildings

This study investigates demands on acceleration-sensitive nonstructural components (NSCs) in code-compliant Special Concentrically Braced Frame (SCBF) and Special Moment Frame (SMF) structures. Previous studies have highlighted that the assumption of ASCE 7-16 for the ratio of Peak Floor Acceleration (PFA) to Peak Ground Acceleration (PGA) is overly conservative. In most previous studies, the results were based on generic analytical models with non-deteriorating structural behavior or recorded data from instrumented buildings subjected to ground motions that were significantly weaker than the design-level earthquakes. This study evaluates the acceleration demands on NSCs in 11 archetype buildings modeled using advanced techniques. The ground motions used elicit inelastic response in the frames at the level expected by ASCE 7-16 compliant designs. The study examines the effect of the ratio of NSC period to structural period, NSC damping ratio, and NSC vertical location on these demands. Results of this investigation are compared with the provisions of ASCE 7-16 and the recommendations of the recently completed effort by the Applied Technology Council 120 project (ATC-120), which are the basis for the seismic design requirements for nonstructural components in the forthcoming ASCE 7-22 standard. Equations for the PFA/PGA ratio and NSC amplification factor, which account for the dynamic characteristics of the buildings, are developed based on regression analysis of the generated data. Results of the analyses indicate that the formula recommended by ATC-120 for estimating PFA/PGA along the height of the structure, which includes building nonlinearity effects through a constant building ductility reduction factor, overestimates floor accelerations at the top floors but underestimates them in the lower floors of the archetypes considered. At the same time, results show that the NSC seismic design force equation recommended by ATC-120 is conservative for the SCBF archetypes, while it underestimates the NSC force demands in the SMFs.

Analysis & Design of an Earthquake Resistant Multistory Apartment Building in all Seismic Zones to Obtain the Increment in the Required Percentage of Weight of Steel Reinforcement

For designing of an earthquake-resistant structure we follow Indian Seismic design codes are exclusive to a particular country or region. Moreover these seismic codes considered all the criteria such as building typologies, accepted level of seismic risk, local seismology. IS 1893 is an Indian seismic code that provides the seismic zone map and specifies seismic design force. The Bureau of Indian Standard (IS: 1893 (Part-1) 2002) classified India into 4 seismic zones (i.e. Zone II, Zone III, Zone IV & Zone V) and the code allocates 4 levels of seismic intensities as zone factors. But this code does not provide any information regarding how much of required percentage of steel-reinforcement has been increased from zone to zone. The main objective for presenting this project is to obtain the increment in the required percentage of steel-reinforcement for various zones by analyzing a multistory Apartment Building with Stilt + G + 3 Floors as per Indian Standard Codes IS 456 : 2000 and IS 1893 (Part – 1) 2002 using STAAD-Pro Software.

Seismic design force level for precast concrete diaphragms

This paper provides guidance for determining seismic design force level for topped precast concrete diaphragms. This has been a controversial topic ever since ASCE/SEI 7-16, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, introduced a section titled “Alternative Design Provisions for Diaphragms” and mandated its use for precast concrete diaphragms in buildings assigned to seismic design category C, D, E, or F.

Simplified approaches for estimation of required seismic separation distance between adjacent reinforced concrete buildings

This study aims to investigate the determination of seismic separation gap of adjacent low and mid-rise reinforced concrete (RC) buildings with no structural irregularity using nonlinear time history analysis. The low and mid-rise RC buildings were reflected using 3, 4, 5, 6, 7, 8, 9 and 10-story buildings designed per 2018 Turkish Building Earthquake Code (TBEC-2018). Beam and column elements are modeled as nonlinear frame elements with lumped plasticity by defining plastic hinges at both ends of beams and columns. The adjacent three-dimensional (3D) building models are connected to each other by link elements at the floor levels. 1232 nonlinear dynamic (time history) analyses were performed using 56 different building pairs and 11 different earthquake record pairs (22 records) compatible with TBEC-2018 to obtain the required seismic gap distances. The distances necessary to avoid pounding obtained from the analyses were compared with the minimum seismic gap requirements of the current earthquake codes, provisions (Eurocode-8, ASCE 7-16 and TBEC-2018) and several proposed methods (ABS, SRSS and DDC) in the literature. The outcomes indicate that the ASCE 7-16 and EC-8 significantly overestimate the required seismic gap distances for the buildings with similar dynamic characteristics while they provide reasonable estimates for the buildings with significantly different dynamic characteristics. However, the TBEC-2018 requirements are insufficient for the neighboring building period ratios greater than 1.25. Although both the ASCE 7-16 and EC-8 requirements are acceptable for the design of new buildings as being on safe side, they are not useful for the evaluation of existing buildings. Two different simple approaches were proposed to estimate the required seismic gap distances between neighboring buildings. The first approach requires linear static analysis of the buildings subjected to the reduced seismic design forces while the second simplified approach does not need any analysis. The proposed equations in this study are simple and useful for the evaluation of existing low and mid-rise RC buildings with no structural irregularity. Besides, their estimates are acceptable for the design purposes.

The Response Modification Factor for Seismic Design of Integral Abutment Bridges

The response modification factor (R factor) is a crucial parameter for calculating the design seismic forces applied to a bridge structure. This factor considers the nonlinear performance of bridges during strong ground motions. Conventional bridge structures rely on the substructure components to resist earthquake forces. Accordingly, there are R factors available in the design codes based on the type of bridge substructure system. Lateral load resisting system of Integral Abutment Bridges (IABs) in the longitudinal direction is more complex than ordinary bridges. It involves the contributions from soils behind the abutments and soil/structure interaction (SSI) in addition to existing rigid connection between the superstructure and abutments. There is no R factor available in any design code throughout the world for IABs in the longitudinal direction that considers all these parameters. In this research, the Federal Emergency Management Agency publication FEMA P695 methodology has been applied to estimate the R factor for IABs. It is found that 3.5 could be a safe and valid R factor in the longitudinal direction for seismic design of such bridges.

Analytical investigation of a new direct Column-to-Cased shaft connection

In regions of high seismicity, the large seismic design forces sustained by the superstructure must be transferred to the bridge foundations. In these situations, in particular in situations with weak soils, cased shafts, which are concrete filled steel tube (CSFT) components, are used for piles and drilled shafts. Prior research shows that these components have large flexural, axial and shear strengths. Typically, the forces are transferred from the column to the pile through a pile cap. However, direct connections are becoming more common, in particular because they have efficiency in terms of placement and can facilitate accelerated bridge construction. This research studies two different connections: (1) direct embedment of the column reinforcement into the pile and (2) an enhanced connection using a ring at the top of the tube in the pile to enhance mechancial bond and reduce embedment depth. The study was conducted using a high-resolution finite element analysis modeling approach validated using large-scale test results of reinforced concrete (RC) and CFST components and connections. The model included advanced constitutive modeling of the concrete as well as modeling of the bond between the steel tube and concrete fill and the reinforcing steel and the concrete fill. The transfer of forces from the yielding reinforcing bars in the RC pier to the concrete fill and tube of the pile is critical for this connection. Different approaches were investigated to achieve transfer without loss of strength or ductility. A supplemental rib inside the tube ultimately was used to enhance the load transfer with the minimum embedment length. The model was used to conduct a parametric study with the following study parameters: the rib location (lR), tube diameter (D), reinforcing bar diameter, and embedment depth (ld). The results were used to propose initial design recommendations.

Effective stiffness and period-dependent seismic response modification factors for flexure-dominated fully-grouted reinforced masonry rectangular shear walls

The wall effective elastic stiffness, displacement ductility, and seismic force modification factors are important force-based seismic design (FBD) parameters for reinforced masonry (RM) shear walls. The effective stiffness, ke of reinforced masonry shear walls (RMSW) is crucial in computing the natural period and thus the elastic forces, and essential also in computing the displacements corresponding to the design seismic forces. This study analyzes previously reported test results of forty-three flexure-dominated fully-grouted rectangular RMSWs subjected to quasi-static cyclic load to evaluate the FBD parameters adopted by Canadian and American standards. In this study, based on the experimental results of 43 tested walls, a new stiffness reduction factor is proposed considering the effect of axial stress, vertical reinforcement ratio, and horizontal reinforcement ratio. Moreover, the seismic force modification factors are compared to the Canadian and US codes. The results showed that ductility related reduction factors should be dependent on the wall natural frequency and there is a room to relax the current proposed code values. In addition, incremental dynamic analysis was performed using a simplified numerical model to study the effect of dynamic loading on response modification factors and stiffness characteristics of the walls.