Terms Of Interstory Drift Research Articles

Seismic loss assessment of code-compliant moment-resisting RC buildings located on different soil conditions of Mexico City

This research aims to estimate the expected economic losses associated with the repair cost of a set of code-compliant moment-resisting reinforced concrete buildings located on different soil conditions in Mexico City. The loss assessment methodology is based on the second generation of the Performance-Based Earthquake Engineering (PBEE) framework, which quantifies the seismic performance of buildings in terms of metrics such as economic losses, downtime, and casualties, which are more meaningful to owners and stakeholders for the decision-making process. The methodology uses a probabilistic approach that takes into account uncertainties in seismic intensity, structural response, component damage, and consequence prediction. The seismic response of structures was calculated in terms of inter-story drifts and floor accelerations to assess the damage to their structural and non-structural components. In addition, taking into account the seismic hazard of the site, the expected annual losses (EAL) are calculated to provide insight into the seismic performance evaluation of structures with different characteristics in terms of the financial impact in seismic-prone regions like Mexico City.

Post-restoration seismic performance assessment of a historic hypostyle mosque in Anatolia (13th century AD)

Assessment of structural performance under seismic effects is a very important step for restoration process of historic buildings that represent construction techniques and material characteristics of their era. This process consists of three stages namely, on-site examinations, restoration practices, and seismic analysis, and therefore, requires a multidisciplinary approach. Hypostyle structures are mostly timber-framed buildings with masonry walls on two or three facades. This construction method is a combination of Asia (wooden pillar) and Byzantine (masonry walls) techniques. The primary load-bearing system in these buildings is composed of multiple rows of wooden pillars. This paper presents post-restoration seismic assessment of a historic wooden hypostyle mosque complex constructed in 1273. This mosque complex is an important structure representing wooden hypostyle architecture in the Anatolia region of Turkey and is composed of three separate structures namely, a main mosque building, a minaret, and a tomb. Linear performance analysis, displacement-controlled nonlinear analysis, and kinematic limit analysis for failure mechanisms were conducted for the structures after the restoration. The linear performance analysis results indicated that the structures meet shear strength requirements for DD3 and DD2 earthquakes with recurrence periods of 72 and 475 years, respectively. Furthermore, according to the linear and non-linear analyses, the complex was found to satisfy performance limits for both ground motion levels in terms of inter-story drifts.

Nonlinear Inelastic-Degrading Structural Modeling Approach to Assess the Seismic Soil–Structure Interaction Response of Tall Buildings

Oversimplifying structural modeling in the analysis of the seismic performance of tall buildings introduces variability and biases in the computed seismic response. Engineering demand parameters (EDPs) from coupled soil–structure interaction (SSI) systems can only be realistically determined when nonlinear constitutive soil and structural behaviors are adopted in the numerical formulation. Large-magnitude earthquakes mobilize soil and structural demands that are beyond the elastic response of both materials. This paper aims at evaluating the influence of the structural modeling assumptions in the computed soil response due to seismic excitations using a direct fully coupled nonlinear SSI approach. Numerical analyses are conducted on elastic and nonlinear inelastic-degrading tall building models supported on a mat foundation-to-soil continuum domain using a multiple-yield surface plane-strain constitutive model. The models were subjected to multiple ground motion scenarios representative of broadband frequency content. Large discrepancies occur between linear and nonlinear inelastic tall buildings in terms of interstory drifts, peak horizontal accelerations, structural displacements, hysteretic energy, foundation rotation, and soil settlements. The results show how using nonlinear inelastic-degrading structural models of tall buildings largely affect the computed seismic response of the entire SSI system relative to linear elastic structural modeling approaches. More realistic responses are obtained using nonlinear degrading building models including SSI effects, because energy distribution and tradeoff among both the supporting soils and structure vary significantly as the seismic demands induce stresses and strains in the building beyond the onset of structural yielding.

Performance of steel moment-resisting frames in post-earthquake horizontally traveling fire

PurposeThe study investigates the performance of a three-story unprotected steel moment-resisting frame (SMRF) designed for high seismic demand in the fire-only (FO) and post-earthquake uniform and traveling fires (PEF). The primary objective is to investigate the effects of seismic residual deformation on the structure's performance in horizontally traveling fires. The traveling fire methodology, unlike conventional fire models, considers a spatially varying temperature environment.Design/methodology/approachMulti-step finite element simulations were carried out on undamaged and damaged frames to provide insight into the effects of the earthquake-initiated fires on the local and global behavior of SMRF. The earthquake simulations were conducted using nonlinear time history analysis, whereas the structure in the fire was investigated by sequential thermal-structural analysis procedure in ABAQUS. The frame was subjected to a suite of seven ground motions. In total, four horizontal traveling fire sizes were considered along with the Eurocode (EC) parametric fire for a comparison. The deformation history, axial force and moment variation in the critical beams and columns of affected compartments in the fire heating and cooling regimes were examined. The global structural performance in terms of inter-story drifts in FO and PEF scenarios was investigated.FindingsIt was observed that the larger traveling fires (25 and 48%) are more detrimental to the case study frame than the uniform EC parametric fire. Besides, no appreciable difference was observed in time and modes of failure of the structure in FO and PEF scenarios within the study's parameters.Originality/valueThe present study considers improved traveling fire methodology as an alternate design fire for the first time for the PEF performance of SMRF. The analysis results add to the much needed database on structures' performance in a wide range of fire scenarios.

Investigation of the seismic performance of braced low-, mid- and high-rise modular steel building prototypes

For buildings with repeatable units, modular construction provides an alternative to traditional on-site construction. Modular steel buildings (MSBs) are composed of prefabricated volumetric modules that are produced in a controlled environment such as a factory to be transported and assembled on-site to form a larger, permanent building. Although the studies on the dynamic behavior of modular buildings are limited to up to 10-story MSBs, the recently completed 32-story MSB in New York showcased the applicability of this type of construction beyond mid-rise structures. Additionally, in the National Building Code of Canada both the ductility modification factor and the overstrength modification factor are determined based on the type of the seismic force resisting system, regardless of the building height. Previous studies indicated that neglecting the correlation between these design factors and the height of the building could lead to inadequate design as the building height increases. The current paper assesses the seismic design factors and the seismic performances of 6-, 12, and 32-story MSBs by means of pushover analyses and bi-directional nonlinear time history analyses. The seismic performance is evaluated in terms of interstory drift, residual drift, and base shear. Pushover curves indicated that both overstrength and ductility factors decrease as the height of the building increases. Data from the time history analysis revealed that high-rise MSBs tend to exceed collapse prevention limit and develop column plastic hinges under severe ground motions. On the other hand, the residual drift ratio was found to be more pronounced in low- to mid-rise MSBs.

Investigating the effects of seismic isolators on steel asymmetric structures considering soil-structure interaction

Building isolation is a practical and ubiquitous method for reducing inter-story drift and story acceleration. Previously it has been shown that since an isolator can increase the time period and damping, it can decrease the total energy transmitted from the ground to the structure. The main purpose of this study was to investigate the behavior of asymmetric sliding buildings with steel moment frame systems subject to earthquake loading (both horizontal and vertical), while taking into account the effects of soil-structure interaction. A total of 24 three-dimensional structural models, including a single-story structure (40% irregularity), a five-story structure (regularity, 20%, 40% and 60% irregularity) and a ten-story structure (40% irregular) were dynamically analyzed using nonlinear finite element analysis. The results of this study indicated that, in terms of inter-story drift and story accelerations, seismic isolation had a significant impact on the dynamic responses of structures. This effect was more pronounced in single-story structures than in others. Additionally, the results showed that structural irregularities did not affect the dynamic response of the structure, including the displacement and acceleration of the stories. Furthermore, this study showed that when soil is converted from type II to types III and IV, the displacement and slipping speed decreased for all studied structures. Lastly, the results suggested that substructure soil typology had a significant effect on the design parameters of isolators.

The role of viscoelastic damping on retrofitting seismic performance of asymmetric reinforced concrete structures

The primary purpose of this research is to improve the seismic response of a complex asymmetric tall structure using viscoelastic (VE) dampers. Asymmetric structures have detrimental effects on the seismic performance because such structures create abrupt changes in the stiffness or strength that may lead to undesirable stress concentrations at weak locations. Structural control devices are one of the effective ways to reduce seismic impacts, particularly in asymmetric structures. For passive vibration control of structures, VE dampers are considered among the most preferred devices for energy dissipation. Therefore, in this research, VE dampers are implemented at strategic locations in a realistic case study structure to increase the level of distributed damping without occupying significant architectural space and reducing earthquake vibrations in terms of story displacements (drifts) and other design forces. It has been concluded that the seismic response of the considered structure retrofitted with supplemental VE dampers corresponded well in controlling the displacement demands. Moreover, it has been demonstrated that seismic response in terms of interstory drifts was effectively mitigated with supplemental damping when added up to a certain level. Exceeding the supplemental damping from this level did not contribute to additional mitigation of the seismic response of the considered structure. In addition, it was found that the supplemental damping increased the total acceleration of the considered structure at all floor levels, which indicates that for irregular tall structures of this type, VE dampers were only a good retrofitting measure for earthquake induced interstory deformations and their use may not be suitable for acceleration sensitive structures. Overall, the research findings demonstrate how seismic hazards to these types of structures can be reduced by introducing additional damping into the structure.

Development of the Performance-Based Plastic Design Method by Considering the Effects of Aftershocks

ABSTRACT One of the efficient methods for seismic design of structures is Performance-based Plastic Design (PBPD) in which by choosing the desired yield mechanism and the target drift at the beginning of the design, unlike that in conventional design methods, there is no need for a time-consuming process of trial and error to achieve the desired performance. On the other hand, recent earthquakes have shown that aftershocks can increase the damage to a building after the main earthquake and thereby threaten the safety of the inhabitants. However, the seismic hazard of aftershocks is still not explicitly included in the current design codes. In this study, attempts have been made to develop the PBPD method for considering the effects of aftershocks. For this purpose, by performing an incremental dynamic analysis (IDA), the ductility factor μ and the ductility reduction factor Rμ of six PBPD frames (2-, 4-, 6-, 8-, 10-, and 12-story) were calculated under mainshock and mainshock-aftershock sequences. Then, the energy modification factor γ, which is related to the two parameters μ and Rμ, was calculated for both the mainshock and the mainshock-aftershock sequences. An equation is presented in order to calculate the ratio of the energy modification factor of the mainshock-aftershock sequence to the mainshock energy modification factor () according to the design period, and the factor obtained is multiplied by the energy modification factor γ so that the effect of aftershock can be considered for the frame design, and by using this modification, the performance of the frame under the mainshock-aftershock sequence can be improved. The results of the time-history analysis performed on the modified PBPD frames show better performance by the frames designed on the basis of modified PBPD than the frames designed on the basis of the original PBPD method under MS-AS sequences in terms of inter-story drift and rotation of plastic hinges.

Seismic vulnerability and retrofitting scheme for low-to-medium rise reinforced concrete buildings in Nepal

In this paper, seismic capacity assessment is presented for representative low-to-medium rise reinforced concrete (RC) buildings in Nepal. The structural behavior of buildings was studied with different analysis techniques and loading considerations. The non-linear behaviors of nine residential building structures were studied with finite element analysis. Structural performance is presented in terms of strength, stiffness, capacity curves, and inter-story drifts. The building models were analyzed as bare frames, and the drift profiles were compared with some standard drift limits to depict the vulnerability. Buildings noted as vulnerable after the analyses were modified as retrofitted using column jacketing technique, and finite element analyses were carried out again. Comparisons were made in terms of seismic performance of as-built and retrofitted buildings. The sum of observations depicts that column size directly affects the vulnerability of buildings. Moreover, column jacketing significantly ameliorates the seismic performance of low-to-medium rise RC buildings as depicted by the comparison between as-built and retrofitted structures in terms of inter-story drift and fundamental period.

Evaluation of seismic response factors for BRBFs using FEMA P695 methodology

This paper reports the details of a numerical study undertaken to evaluate seismic response factors for steel buckling-restrained braced frames (BRBFs) using the FEMA P695 methodology. In the United States, BRBFs are designed according to Minimum Design Loads for Buildings and Other Structures (ASCE 7) and the Seismic Provisions for Structural Steel Buildings (AISC 341). Twenty-four archetypes were designed according to the U.S. specifications and their behavior was assessed by making use of non-simulated collapse models. The interstory drift, brace axial strain and cumulative brace axial strain demands under collapse level ground motions were determined. The results obtained indicate that the current seismic response factors are adequate in terms of interstory drift and cumulative axial strain demands. On the other hand, large differences between the design level and collapse level axial strains were reported, which can result in undesirable brace behavior. Modified approaches were developed to estimate the axial strains for collapse level ground motions. These include a modification to the deflection amplification factor and a modification to the AISC 341 requirements for expected brace deformations. The archetypes were redesigned using the proposed modifications and reevaluated using the FEMA P695 methodology. The results indicate that the proposed modifications result in axial strain demands that are in close agreement with the calculated demands.

Effects of non-welded multi-rib stiffeners on the performance of steel plate shear walls

This paper presents a numerical investigation of the dynamic performance of steel plate shear walls (SPSWs) stiffened by non-welded multi-rib stiffeners. Multi-rib stiffeners are installed on both sides of the steel plate and connected by threaded bolts through the plate, rather than direct welding as conventionally being done. The influence of constraints between multi-rib stiffeners and steel plate on the performance of SPSWs is first examined by finite element analysis. Afterwards, a numerical model for SPSW structure is developed and validated by the test results. The dynamic performance of SPSW structures with and without non-welded stiffeners is compared in terms of inter-story drift, acceleration response and out-of-plane deformation. Test results indicate that constraints between multi-rib stiffeners and steel plate slightly affect the loading capacity of SPSWs. The loading capacity of the SPSWs with non-welded multi-rib stiffeners is 5.8% lower than that with welded stiffeners. However, buckling of stiffeners can be avoided in the non-welded multi-rib stiffened SPSWs. For the dynamic performance of SPSW structures, use of non-welded multi-rib stiffeners is effective in reducing the inter-story drift, acceleration and out-of-plane deformation of SPSW structures under earthquake attacks, particularly for those subjected to main shocks followed with aftershocks. The use of non-welded stiffeners decreases the maximum inter-story drift and the maximum out-of-plane deformation of SPSW structures by 14.7% and 57.0%, respectively. In addition, non-welded multi-rib stiffeners can uniformly distribute the stiffness of SPSWs along the floors. In general, the proposed non-welded multi-rib stiffeners are effective in enhancing the dynamic performance of SPSWs.

Fractional order PID control design for semi-active control of smart base-isolated structures: A multi-objective cuckoo search approach

Fractional order PID (FOPID) controllers are introduced as a general form of classical PID controllers using fractional calculus. As this controller provides good disturbance rejection and is robust against plant uncertainties it is appropriate for the vibration mitigation in structures. In this paper, an FOPID controller is designed to adjust the contact force of piezoelectric friction dampers for semi-active control of base-isolated structures during far-field and near-field earthquake excitations. A multi-objective cuckoo search algorithm is employed to tune the controller parameters. Considering the resulting Pareto optimal front, the best input for the FOPID controller is selected. For seven pairs of earthquakes and nine performance indices, the performance of the proposed controller is compared with those provided by several well-known control techniques. According to the simulation results, the proposed controller performs better than other controllers in terms of simultaneous reduction of the maximum base displacement and story acceleration for various types of earthquakes. Also, it provides acceptable responses in terms of inter-story drifts, root mean square of base displacements and floor acceleration. In addition, the evaluation of robustness for a stiffness uncertainty of ±10% indicates that the proposed controller gives a robust performance against such modeling errors.

COMPARISON OF DIFFERENT METHODS FOR VISCOUS DAMPER PLACEMENT IN EXISTING FRAME BUILDINGS

The main purpose of this research is to investigate the effects of different vertical distributions of the properties of nonlinear fluid-viscous dampers for the retrofit of existing multi-story reinforced concrete frames. In particular, the different distributions are defined on the basis of the same value of the supplemental damping ratio. Since the viscous dampers are used for the retrofit of existing buildings, they are dimensioned assuming that the structure can exceed the elastic limit, with the only condition to satisfy the prefixed performance limit. In the design phase the different vertical distributions of damper properties are compared in terms of the total sum of the damping coefficients. The effectiveness of the different distributions is then examined by performing time-history analysis of several case studies considering a nonlinear behavior both for the viscous dampers and for the structural members. The results of the nonlinear dynamic analyses are examined in terms of inter-story drifts and dampers forces. The considered case studies are five RC frames characterized by different number of stories (3, 6 and 9 stories) and also by different properties in terms of regularity in elevation. In this way it is also possible to investigate the effect of the vertical distribution of the damper properties for regular and irregular frames.

Bidirectional Pushover Analysis of Irregular Structures

AbstractPushover analysis is one of the most-used nonlinear static procedures for the seismic assessment of structures; therefore, nowadays it is extensively used by practicing engineers for the seismic analysis of virtually every type of building. This paper proposes a bidirectional pushover analysis (BPA) method to overcome the limitations of current pushover methods to assess the seismic response of irregular (both in plan and in elevation) buildings subjected to bidirectional ground motions. The extended N2 method and the proposed BPA method were applied to estimate the nonlinear response of six highly irregular reinforced concrete frame structures designed according to the requirements of Eurocode 8. Results in terms of interstory drifts and floor rotations are compared with those given by nonlinear response history analysis (NRHA). For the latter, a suite of twenty Italian bidirectional seismic ground motions was selected. It was found that results given by the proposed BPA method match those given ...

Evaluation of Egyptian code provisions for seismic design of moment-resisting-frame multi-story buildings

Since the occurrence of the Cairo earthquake on October 1992, the design of structures for earthquakes became a major demand enforced in the Egyptian design codes. The seismic response of building structures can be estimated through utilization of a variety of analysis methods that range from simple equivalent static analysis to complex nonlinear dynamic analysis. The traditional approach is to employ equivalent static analysis methods, while current design practice is moving toward an increased emphasis on the nonlinear analysis method. The Egyptian code provisions for building seismic design adopt the traditional approach of equivalent static load method as the main method for evaluating seismic actions and recommend the response spectrum method for nonsymmetrical buildings. This study aims to evaluate the Egyptian code provisions for the seismic design of moment-resistant frame multi-story building through using nonlinear time history analysis. The analysis procedures are evaluated for their ability to predict deformation demands in terms of inter-story drifts, potential failure mechanisms and story shear force demands. The results of the analysis of the different approaches are used to evaluate the advantages, limitations, and ease of application of each approach for seismic analysis.

Shaking Table and Numerical Seismic Performance Evaluation of a Fluid Viscous-Dissipative Bracing System

A shaking table campaign was carried out on a 2:3-scale, two-story steel frame structure retrofitted by a dissipative bracing system incorporating pressurized fluid viscous spring-dampers. Up to 1.16 g peak ground accelerations were imposed in the most severe of the 33 tests developed. The response was always elastic, with maximum interstory drift ratios limited below 0.62%. The protection technology, in fact, features high dissipative capacities and produced equivalent linear viscous damping coefficients up to 37.5%. A numerical enquiry carried out on the test structure in its original unbraced configuration showed interstory drift reductions from about 80% to about 90% when passing to dissipative braced conditions. A final performance-based analysis developed in terms of interstory drifts and beam and column rotations, in compliance with the criteria formulated in ASCE/SEI 41-06 Standard, emphasized three through five enhancements of building performance in retrofitted conditions for the four earthquake levels examined.

RELIABILITY ANALYSIS OF STEEL BRACED REINFORCED CONCRETE FRAMES WITH SEMI-RIGID CONNECTIONS

This paper presents the reliability analysis of the frame structures with semi-rigid connections. For this purpose, the SEMIFEM finite element program that is capable of dealing with the semi-rigid connections is coded in FORTRAN. Then, this program is connected to the reliability algorithm. The direct coupling method, which is a combination of the reliability method and finite element method, is utilized to determine the reliability indexes and probabilities of failure for the structure. The first order reliability method (FORM) is the one favored in the present reliability analysis. Two sets of steel framed structures are analyzed; each of four and eight stories, consisting of a portal frame and three types of concentrically braced frames. Concrete compression strength limit state in reinforced concrete (RC) columns, steel strength limit state in steel braces and inter-story drift limit state are considered in reliability evaluation. According to the limit states, X braced frames are determined as the safest structures, while the portal frames are regarded as the most unsafe structures. As the connection percentage increases, the safety of the structure increases in terms of inter-story drift and steel strength limit states, but decreases for concrete compression strength limit states.

Comparison of Nonlinear Static Methods for the Seismic Assessment of Plan Irregular Frame Buildings with Non Seismic Details

The use of Nonlinear Static Procedures (NSPs) for the seismic assessment of plan irregular buildings is challenging. The most common pushover-based approaches have led to adequate results in regular buildings, and hence, there is a need to verify the validity of such methods on the assessment of irregular structures. In this article, four commonly used nonlinear static procedures (CSM, N2, MPA, ACSM) are applied on the assessment of two existing five- and eight-story plan-asymmetric buildings in Turkey. The accuracy of the different NSPs is evaluated through comparisons with the results derived from nonlinear dynamic analyses. The results are presented in terms of interstory drifts, normalized top displacements, lateral displacement profiles, chord rotations, base shear, and top displacement ratios. The performance of such procedures in evaluating the damage limitation according to the Eurocode8 is also verified. Special attention is given to the ACSM (Adaptive Capacity Spectrum Method) whose performance in 3D plan irregular buildings has recently been tested. Conclusions about the performance of each NSP are outlined at the end of the article.

Global Interventions for Seismic Upgrading of Substandard RC Buildings

A methodology is developed in this paper for the design and proportioning of interventions for seismic upgrading of substandard reinforced-concrete (RC) buildings. The retrofit approach is presented in the form of a simple design tool that aims toward both demand reduction and enhancement of force and deformation supply through controlled modification of stiffness along the height of the building. This objective is achieved by engineering the translational mode-shape of the structure, so as to optimize the distribution of interstory drift. Results from the proposed approach are summarized in a spectrum format in which demand, expressed in terms of interstory drift, is related to stiffness. Design charts, which relate the characteristics of commonly used global intervention procedures to influence drift demands, are developed to facilitate the retrofit design. The intervention procedures considered in this paper are reinforced-concrete jacketing, the addition of reinforced-concrete walls, and the addition of masonry infills. The proposed methodology is also amenable to adaptation to other strengthening methods, such as the addition of cross-bracing.

EVALUATION OF SEISMIC PERFORMANCE OF MULTISTORY BUILDINGS DESIGNED ACCORDING TO EGYPTIAN CODE

The seismic response of building structures can be estimated by several analysis methods. Each approach incorporates different assumptions and varies in complexity of application. The traditional approach is to employ equivalent static analysis methods while current design practice is moving towards an increased emphasis on nonlinear analysis methods. This study examined the seismic performance of multistory buildings designed according to Egyptian code. Nonlinear time history analysis is used for evaluation of equivalent static and response spectra procedures that recommended by Egyptian codes for seismic design of building structures. In this study, a preliminary seismic response analysis of two buildings was performed using three analysis procedures to evaluate the building seismic performance and the difference in global response predicted by the three methods. Moreover, three analysis procedures are evaluated for their ability to predict deformation demands in terms of inter-story drifts and potential failure mechanisms. Three ground motions of earthquake records are used for seismic demands evaluation of these buildings. The results demonstrated that, for the three analysis methods used in this study, different predictions of seismic response occurred. Furthermore, the results of the analyses are used to evaluate the advantages, limitations, and ease of application of each approach for seismic analysis. Each method is shown to have merits and deficiencies that should be considered when selecting a seismic analysis method for a particular building structure.