Residual Drift Demands Research Articles

The role of masonry infills on the interstory drift demand of reinforced concrete frames

Most frame buildings, especially those with shear-type moment resistance frames, are affected by masonry infill panels, which change the mechanical properties of whole systems in a big way. In turn, seismic performance varies depending on the infill panel and frame interactions. In conventional structural design practice, such interaction has been overlooked. This study looks at the range of local displacement demands in shear-type frames with and without infill panels. Generic frames are developed by tuning the story stiffness and mass to produce a reasonable period range between 0.2 and 2.0 s. The masonry infill panels are simulated through equivalent diagonal struts. A Bouc–Wen-based hysteretic model is applied to incorporate the post-yielding hysteresis degradations of both columns and masonry panels. The hysteresis loop control parameter values are also given for incorporating masonry infill properties. The correlation analysis between the strength and stiffness of RC frames and masonry infills is supplied as an instrument for calibrating the hysteretic model. In the collection of records, there are a lot of near-fault ground motions, which puts a lot of seismic demands on the buildings. The modification factors via regression analysis are proposed using over 1254 nonlinear response history analyses. This modification factor is figured out by looking at the difference between the mean drift spectrum for a set of generic frames that are both bare and filled. The nonlinear analysis shows that residual drift demands can be reduced in the case of panel effects that exist for masonry-infilled mid-rise RC shear-type frames.

The importance of hazard-consistency when estimating seismic residual drifts in steel moment frames

Residual drifts are routinely used to assess the post-earthquake safety of buildings. Despite their importance, studies on the probabilistic assessment of residual drifts in multi-storey buildings with Steel Moment Resisting Frames (SMRF) are far less common than those dealing with their transient peak drift counterpart. More seriously, although residual drift prediction models have been developed with a particular broad ground-motion type or soil condition in mind, all models proposed to date remain oblivious to the central issue of hazard consistency. Hence, missing the causal connection between the seismic hazard level and the ground-motion suite used and potentially compromising the meaningfulness of their results. This oversight is expected to introduce a bias in the estimation of residual drifts but its magnitude has not yet been properly evaluated. In this paper, we evaluate and quantify the significance of these effects. To this end, we use the Conditional Scenario Spectra framework, which provides a set of realistic earthquake spectra with assigned rates of occurrences based on their spectral shape and intensity, thus preserving the critical relationship of hazard consistency. Nonlinear Response History Analyses (NRHA) of 24 deteriorating SMRFs under 816 ground-motion records are performed to construct a database of residual drift demands. These NRHA results are used to examine the residual drift trends and to construct benchmark residual drift hazard curves. An extensive feature selection process employing several Machine Learning (ML) algorithms precedes the development of hybrid data-driven predictive models. Finally, we compare our hazard-consistent predictions with currently available models and quantify the massive under- and over-estimations associated with previously proposed non-hazard-consistent assumptions.

Approximate Methods to Estimate Residual Drift Demands in Steel Structures with Viscous Dampers Designed by the DDBD Approach

Approximate Methods to Estimate Residual Drift Demands in Steel Structures with Viscous Dampers Designed by the DDBD Approach

Comparative fire-following-earthquake performance of code-compliant low-rise base-isolated structures

Seismic base isolation is an effective way of protecting structures against seismic loads and is very effective in terms of both collapse mitigation of structures and protection of non-structural elements under severe ground shaking. In this study, the structural demand of base-isolated three- and four-story steel moment-resisting frames is determined in case of a fire event followed by an earthquake, and compared with the results of fixed-base frames, which have similar geometry, load, and seismic hazard for a location in California. Four compartments are selected as possible locations for fire events in each building, and beams and columns in those compartments are exposed to a representative temperature increase in time, which includes a cooling phase as well. Maximum, minimum, and residual axial force, and moment demands on elements of the fire compartments, and drift demand of structural frames on the first and second floor, where the fire is assumed to occur, are determined and compared. Results are given in terms of parameters of three-parameter log-normal distribution, hence fragility curves can be constructed for each response considered in the study. Seismic isolation is effective in reducing both maximum and residual drift demand of the frames, and axial force in the beam element for each compartment considered. Fixed-base frames have 20% more maximum axial load on beams. Beam and column elements in the four-story configuration are under relatively more moments in case of a fire, while the performance of three-story frames depends on the location of the assumed fire.

Post-earthquake fire collapse performance and residual story drift fragility of two-dimensional structural frames

Structural systems have deteriorated seismic performance as they are exposed to thermal effect due to dependency of material properties to temperature. Following an earthquake, once structure has already some residual displacement, fire ignition is very likely to occur. This makes it necessary to evaluate structural response of a building considering the fire event which follows an earthquake to have robust evaluation of structural response. Thus, it is required to model structural systems with consideration of both earthquake and thermal loads to capture multi-hazard behavior. In this study, performance of two-dimensional steel frames in case of fire following an earthquake is evaluated and collapse parameters of frames are calculated. Fragility curves related to collapse and residual story drift demands are given, and comparison of results between earthquake and fire-following-earthquake is illustrated. In addition, collapse probability of frames in fifty years is also given. Results of collapse performance evaluation are adjusted with the consideration of expected seismic hazard on site. Median collapse capacity decreases more than 30% and there is an apparent increase in collapse probability of fire-exposed frames in fifty years, which is more than three times for some frames.

The effects of modeling uncertainties on the residual drift of steel structures under mainshock-aftershock sequences

Uncertainty in parameters that define the behavior of yielding components in structures has been shown to affect the validity of predicted near-collapse behavior. After a large-magnitude seismic event, the effect of uncertainties on predicted seismic demands can be intensified by upcoming aftershocks. On the other hand, cumulated damage through seismic sequences should be quantified by demand parameters that are able to properly present the capacity loss of damaged buildings. Residual drifts, an important measure of inelastic deformations, have a significant role in post-mainshock assessment of structures, and of interest in this study is to quantify changes in the sensitivity of residual drifts to the uncertainty of modeling parameters during sequential seismic events. In addition, the relationship between residual drifts and peak transient drifts is investigated. The study is based on two prototype 3- and 9-story steel moment resisting frames subjected to two levels of mainshock intensities that are followed by aftershocks. 20 as-recorded seismic sequences recorded at far-field accelerographic stations are considered. Sensitivity analysis is performed using the one-at-a-time (OAT) method. It was found that seismic demands are more sensitive to strength modeling parameters and beam ductility modeling parameters, and these sensitivities increase by an average of 20% during aftershocks. As-recorded aftershocks increase residual drift demands up to 19 and 15% at risk-targeted maximum considered earthquake MCER level for the 3- and 9-story frames, respectively, while aftershocks increase the dispersion of peak drift demands considerably.

Residual Drift Estimation for Moment Resisting Frames with Steel Degradation Properties

AbstractInter‐story drifts are the most important engineering demand parameters required for the evaluation of performance of structures subjected to lateral loading. Even though the transient inter‐story drifts are usually used for the assessment and design using the codes of practice, the residual drifts often govern the economic loss in buildings. Therefore, the residual drifts can be critical in the post‐earthquake evaluation of the structures and should be given greater consideration in the process of design of steel moment resisting frames (MRFs). This study examines an improved approach for the estimation of the residual drift demands in steel moment resisting frames subjected to realistic earthquake loading. The advancement is implemented through application of a steel degradation material model in order to capture the stiffness degradation in the inelastic range correctly. Then, this modelling is compared with simplified bilinear steel material model in order to demonstrate the advantages of the deterioration model in performance‐based assessment.

Residual drift spectra for RC bridge columns subjected to near-fault earthquakes

Permanent displacement of a bridge column can be directly measured during the inspection after near-fault earthquakes. However, the engineer needs to estimate the expected residual drift at the design stage to determine if the bridge seismic performance is satisfactory. The most direct method to estimate the residual displacement is nonlinear response history analysis, which is time consuming and cumbersome. Alternatively, an attractive but indirect method is generating estimated residual displacement spectra that depend on displacement ductility demand, column period, site conditions, and earthquake characteristics. Given the period and the expected displacement ductility demand for the column, the residual drift response spectra curves can be utilized to estimate the residual drift demand. Residual drift spectra that are applicable to RC bridge columns in different parts of the United States were developed based on nonlinear response history analyses using a comprehensive collection of recorded and synthetic near-fault ground motions and were linked to one-second spectral acceleration (S1) of the AASHTO maps. It was also found that the residual drift ratio is below one percent when S1 is less than 0.6 g.

Seismic performance evaluation of adjacent buildings with consideration of improved soil conditions

Consideration of soil's response in dynamic analysis is equally important as modeling superstructure to capture all nonlinear behavior in evaluating its seismic performance. This becomes more important if an adjacent building exists nearby, which can alter dynamic response of both structures. Also, soft soil makes effect of interaction between superstructure and soil more pronounced due to low stiffness which can be improved by implementation of some stiffer elements inside the soil. In this study, effects of soil-structure and structure-soil-structure interaction are investigated with consideration of improved soil consideration. Fixed base, soil-structure and adjacent frames with soil and improved soil conditions are modeled, and nonlinear time history analyses are performed. Results are given in terms of maximum story drift and residual drift demand. In addition, fragility curves are obtained performing incremental dynamic analysis and adjusted based on results of seismic hazard analysis on considered site. Collapse probability of frames in fifty years is also shown. The results indicate that stone column improvement reduces demand on superstructure and collapse probability of frames.

Evaluation of approximate methods for estimating residual drift demands in BRBFs

Nowadays, Buckling Restrained Braced Frame (BRBF) system is extensively used for the seismic design of new buildings. This system is composed of Buckling Restrained Braces (BRBs) that do not buckle under compression forces, and have high energy-dissipation capacity. However, low post-yield stiffness of the brace core in BRBs may cause large residual drifts after the occurrence of an earthquake. In this study, four approximate methods for estimating residual drift demands in BRBFs are evaluated. These methods include the FEMA P-58 method, the method proposed in this study, the method proposed by Erochko et al. and the coefficients method introduced by Ruiz-García and Chora, calibrated in this study for BRBFs. To evaluate the estimated residual drifts of BRBFs according to these approximate methods, 2-, 4-, 6-, 8-, 10- and 12-story BRBFs are designed. Nonlinear dynamic analyses are performed on the BRBFs using 78 ground motion records scaled to different ground motion intensity levels. The results show that the proposed method is more accurate than the FEMA P-58 and Erochko et al. methods that are conservative for estimating the median and mean residual drifts of BRBFs, respectively. Moreover, the coefficients method, which estimates the median of maximum residual drifts, is the most accurate method among the four methods considered. However, it does not provide information about the height-wise distribution of residual drifts.

Ground motion selection for the evaluation of residual inter-story drifts in moment-resisting reinforced concrete frame buildings

An evaluation of some structural parameters affecting the amplitude and height-wise distribution of peak and residual drift demands of reinforced concrete frame buildings modeled as 3D complex MDOF systems is presented. In addition, the influence of different ground motion selection methods on the uncertainty in the estimation of both peak and residual drifts is assessed. For this purpose, buildings with different characteristics were subjected to record sets selected: a) randomly, b) considering the magnitude and epicentral distance, and c) to match an objective spectral shape. Results indicate that parameters like the post-yielding stiffness ratio and the structural overstrength importantly affect the magnitude and height-wise distribution of residual drift demands on buildings. The estimation of residual drifts involves a higher level of uncertainty than that of peak drift demands. Selecting records based on a target spectral shape is very effective in reducing the uncertainty on the estimation of both peak and residual inter-story drift demands. Residual drifts may be underestimated if the design/assessment of buildings is conducted by using seismic records that were selected randomly or according to their magnitude and epicentral distance only.

Multi-material core as self-centering mechanism for buildings incorporating BRBs

Conventional buckling restrained braces used in concentrically braced frames are expected to yield in both tension and compression without major degradation of capacity under severe seismic ground motions. One of the weakness points of a standard buckling restrained braced frame is the low post-yield stiffness and thus large residual deformation under moderate to severe ground motions. This phenomenon can be attributed to low post-yield stiffness of core member in a BRB. This paper introduces a multi-core buckling restrained brace. The multi-core term arises from the use of more than one core component with different steel materials, including high-performance steel (HPS-70W) and stainless steel (304L) with high strain hardening properties. Nonlinear dynamic time history analyses were conducted on variety of diagonally braced frames with different heights, in order to compare the seismic performance of regular and multi-core buckling restrained braced frames. The results exhibited that the proposed multi-core buckling restrained braces reduce inter-story and especially residual drift demands in BRBFs. In addition, the results of seismic fragility analysis designated that the probability of exceedance of residual drifts in multi-core buckling restrained braced frames is significantly lower in comparison to standard BRBFs.

Modular tied eccentrically braced frames for improved seismic response of tall buildings

Two alternative braced frame configurations are examined to improve the vertical distribution of seismic storey drifts and inelastic demands in multi-storey steel eccentrically braced frames (EBFs): the tied braced frame (TBF) system and a modular tied-braced frame (M-TBF) system. In TBFs, the concentration of inelastic deformation is prevented by connecting all ductile links over the frame height with vertical tie members. In the M-TBF configuration, the ties are interrupted at one or more locations along the frame height to reduce member forces while achieving the same objective as the TBF. The performance of each bracing system is investigated through nonlinear response history analysis for 8-, 16-, and 24-storey prototype building structures. For the 16-storey building, two M-TBF configurations are examined, two 8-storey modules and four 4-storey modules, to investigate the influence of this parameter. The analysis results show that the TBFs exhibited smaller and more uniform storey drifts and residual drifts at the expense of high axial force demands in the tie members. Soft-storey response could also be mitigated with M-TBFs, but member forces diminished significantly when adopting a modular tied braced frame configuration, which led to a reduction in the required steel tonnage with limited increases in peak and residual drift demands. Performance assessment using incremental dynamic analysis showed that the 16-storey EBF could not pass the FEMA P695 collapse safety criteria whereas all tied braced frames could exhibit satisfactory performance.

Improving the Structural Reliability of Steel Frames Using Posttensioned Connections

In this paper, various moment‐resisting steel frames (MRSFs) are subjected to 30 narrow‐band motions scaled at different ground motion intensity levels in terms of spectral acceleration at first mode of vibration Sa(T1) in order to perform incremental dynamic analysis for peak and residual interstory drift demands. The results are used to compute the structural reliability of the steel frames by means of hazard curves for peak and residual drifts. It is observed that the structures exceed the threshold residual drift of 0.5%, which is perceptible to human occupants, and it could lead to human discomfort according to recent investigations. For this reason, posttensioned connections (PTCs) are incorporated into the steel frames in order to improve the structural reliability. The results suggest that the annual rate of exceedance of peak and residual interstory drift demands are reduced with the use of PTC. Thus, the structural reliability of the steel frames with PTC is superior to that of the MRSFs. In particular, the residual drift demands tend to be smaller when PTCs are incorporated in the steel structures.

Seismic Analysis of Low‐Rise Self‐Centering Prestressed Concrete Frames considering Soil‐Structure Interaction

In this study, the seismic behavior of low‐rise self‐centering (SC) prestressed concrete frames considering soil‐structure interaction (SSI) is presented. For this purpose, a typical 4‐story SC concrete frame, with and without flexible foundations, is analyzed through nonlinear dynamic analysis. Ground motion sets with two hazard levels are selected for analysis. A conventional reinforced concrete (RC) frame is also studied, and the structural demands of the RC and SC frames are compared in terms of peak and residual drifts, base shear, residual settlement, and rotation of foundation. The analysis results show that considering soil‐structure interaction generally increases the peak and residual drift demands and reduces the base shear and connection rotation demands when compared to fixed base conditions. For the cases with and without flexible foundations, the SC frame is found to have comparable peak story drifts with the RC frame and have the inherent potential of significantly reducing the residual drifts. The seismic analysis results of the frames with flexible bases show that the RC and SC frames can experience foundation damage due to excessive residual foundation rotations after the maximum considered earthquake (MCE).

Residual displacement estimation of simple structures considering soil structure interaction

As the residual displacement and/or drift demands are commonly used for seismic assessment of buildings, the estimation of these values play a very critical role through earthquake design philosophy. The residual displacement estimation of fixed base structures has been the topic of numerous researches up to now, but the effect of soil flexibility is almost always omitted. In this study, residual displacement demands are investigated for SDOF systems with period range of 0.1-3.0 s for nearfield and far-field ground motions for both fixed and interacting cases. The elastoplastic model is used to represent nondegrading structures. Based on time history analyses, a new simple yet effective equation is proposed for residual displacement demand of any system whether fixed base or interacting as a function of structural period, lateral strength ratio and spectral displacement.

Numerical Investigation of Seismic Response of Hybrid Buckling Restrained Braced Frames

The Conventional buckling restrained braces used in concentrically braced frames are expected to yield in both tension and compression without major degradation of capacity under severe seismic ground motions. One of the weakness points of a standard buckling restrained braced frame is the low post-yield stiffness and thus large residual deformation under moderate to severe ground motions. This phenomenon can be related to the low post-yield stiffness of the core segment in comparison to its elastic stiffness. This paper investigates the application of stainless steel as the core material in a hybrid buckling restrained brace. The “hybrid” term arises from the use of more than one core component with different steel materials, including high strength high-performance steel and stainless steel (304L) with high strain hardening in the core of buckling restrained brace. Nonlinear dynamic time history analyses were conducted on a variety of diagonally braced frames with different heights, in order to compare the seismic performance of standard (non-hybrid) and hybrid buckling restrained braced frames. The results showed that the proposed hybrid buckling restrained braces reduce the inter-story and specially the residual drift demands in buckling restrained braced frames.

Permanent seismic drifts in steel moment frames

This paper examines residual drift demands in steel moment-resisting frames incorporating the influence of degradation and ground motion frequency content. Detailed assessments are carried out using 54 multi-storey framed buildings, with a wide range of structural characteristics, which are designed according to the provisions of Eurocode 8. In order to identify the influence of cyclic and in-cycle degradation effects, the analysis is carried out with and without degradation modelling. Incremental dynamic analysis is employed in order to achieve various limits of lateral strength demand, using a suite of 56 ground motion records. It is shown that residual drifts are markedly higher in degrading models in comparison with non-degrading models, with the differences being more pronounced in relatively short period ranges, when higher rates of cyclic deterioration are employed, and for comparatively high lateral strength demand levels. The residual drift demand is also shown to increase with the increase in number of stories, and is often concentrated in the lower levels when degrading models are used. Overall, significant residual drift demands are observed in the structural systems considered, with a high likelihood of exceeding a 0.5% residual drift limit in most cases. Based on the results, two simplified prediction relationships are proposed to estimate the permanent drifts of multi-storey steel moment framed systems. The first is concerned with the design stage based on the results of elastic analysis, whilst the second is associated with post-earthquake structural assessment based on actual measurements of residual drifts.

Seismic Performance Assessment of High-Rise Buildings with Different Lateral Load Resisting Systems Under Near-Field Earthquakes with Fling Step

Seismic assessment and design of buildings require the prediction of earthquake characteristics and its effects on buildings. In this paper, the seismic performance of three high-rise buildings with 14, 21 and 28 stories with three lateral load resisting systems, moment-resisting frame (MRF), steel plate shear wall (SPSW) and concentrically braced frame (CBF), under seven near-field earthquake records with fling step is modeled in OpenSees studies utilizing nonlinear dynamic analysis. Results show that, under near-field earthquakes with fling steps, in all buildings with different stories, inter-story drift ratio, residual drift and ductility demand of MRF systems are more than SPSW and CBF systems. Also, mentioned parameters in CBF systems are more than in SPSW systems. Furthermore, energy dissipation in SPSW systems is more than another system in all cases. So, in general, the SPSW lateral load resisting system in high-rise buildings under near-field earthquakes has the best performance.

Ground Motion Intensity Measures for Rocking Building Systems

This paper investigates the effectiveness of various ground motion intensity measures (IMs) in estimating the structural response of two types of rocking systems: (a) a controlled rocking steel braced frame system with self-centering action and (b) a rocking spine system for reinforced concrete infill frames. The IMs are evaluated based on the dispersion in engineering demand parameter (EDP) predictions (efficiency) and the sensitivity of the conditional distributions of EDPs to the distributions of the magnitudes, distances and spectral shape parameter (ε) of ground motion records (sufficiency). The EDPs include maximum transient and residual story drifts and peak floor accelerations. The spectral acceleration averaged over a range of periods (Saavg) is most effective for predicting transient and residual drift demands and peak ground acceleration (PGA) is generally the best predictor of peak floor accelerations. The proximity of the frequency range most affecting an EDP to that best reflected in an IM is found to be a good indicator of the performance of that IM.