Maximum Inter-story Drift Demands Research Articles

Characteristics and selection of near-fault simulated earthquake ground motions for nonlinear analysis of buildings

Earthquake-induced ground shaking near rupturing faults is highly sensitive to the rupture characteristics, seismic wave propagation patterns and site conditions, and field recordings of near-fault shaking are relatively sparse. These challenges complicate the assessment of the seismic performance of near-fault structures. A common approach to representing near-fault ground motion in engineering analysis is to explicitly consider and select records with strong directivity pulses (pulse records). We use three-dimensional high-resolution physics-based earthquake simulations to test this approach in the context of scenario-based ground motion record selection, and to study the important characteristics of near-fault ground shaking. We highlight the deficiencies associated with classifying near-fault simulated records as “pulse” or “non-pulse,” based on the presence of a single dominating pulse in the velocity time history. We show that this approach is inadequate for characterizing near-fault shaking on soft soils which can be dominated by both forward rupture directivity and basin amplification effects. We conduct ground motion selection experiments for the analysis of near-fault structures with and without explicit classification of the pulse features in the records, and evaluate the bias in the predicted structural demands. We find that the maximum interstory drift demands on building structures imposed by unscaled site-specific simulated ground motion records selected based on relevant spectral shape features are not sensitive to the classification of records as pulse/non-pulse. Therefore, with regard to predicting the maximum interstory drifts in near-fault buildings, we do not find justification for the binary pulse classification of near-fault records.

Nonlinear Behavior of Reinforced Concrete Frames Equipped with and without Steel Plate Shear Wall under Sequence of Real and Artificial Earthquakes

There is a possibility of increasing structural damage in the sequential earthquake compared to the main earthquake according to past earthquakes. This study investigates the effects of seismic sequence on the behavior and increased response of reinforced concrete frames (RCF) with/without steel plate shear walls (SPSW). Four systems of 4, 8, 12, and 24 story, which represent low‐, mid‐, and high‐rise structures, are designed and subjected to nonlinear time history analysis under critical single and consecutive records with real, repetitive, and randomized methods. The seismic scenarios used include sequential recorded critical earthquakes. The analysis showed that the predominant period of the after‐shock significantly influences the post main‐shock response. In RCF with and without SPSW, real seismic sequence increases the ratio of peak maximum interstory drift by an average of 2, 2 times the similar demand in the main shock, and increases the ratio of maximum ductility demand by 1.52 and 1.65 times in the structure, respectively. In an artificial sequence, the ratio of peak maximum interstory drift demand increase is in 100%, 150%, and 200% after‐shocks, In the iteration method, it is equal to 1.2, 2.0, and 2.6 times the main shock in RCF with SPSW and 1.9, 3.2, and 4.8 times the main shock in RCF without SPSW. After‐shocks may change the direction and magnitude of residual displacement in real and artificial seismic sequences. Continuation of the equation to calculate the demand for seismic sequence ductility was extracted.

Influence of shape memory alloy brace design parameters on seismic performance of self‐centering steel frame buildings

This paper investigates the seismic and collapse performance of shape memory alloy (SMA) braced steel frame structures considering the effects of various brace design parameters and ultimate state of SMAs. An SMA-braced steel frame building is designed to have comparable strength and stiffness with a steel-moment resisting frame selected as case study building. Then, the stiffness and ultimate deformation capacity of the SMA braces in the initially designed reference SMA-braced frame are systematically varied. First, the static pushover analysis and incremental dynamic analysis are employed to illustrate the significance of SMA brace failure consideration in seismic performance assessment of steel frames with SMA elements. Then, the influence of SMA brace initial stiffness and ultimate deformation capacity on the seismic and collapse performance of SMA braced frames are studied through pushover analyses, nonlinear response history analyses, and incremental dynamic analysis. The results show that the SMA brace initial stiffness does not affect the interstory drift and floor absolute acceleration response at design and maximum considered earthquake level seismic hazard or collapse capacity of the frame. However, it has considerable influence on post-event functionality of the frame. It is also found that the SMA brace ultimate deformation capacity should be at least 80% of maximum interstory drift demand at maximum considered earthquake level for satisfactory seismic performance, whereas larger values provide higher collapse capacity for the SMA-braced frame.

A simplified procedure to estimate peak drift demands for mid-rise steel and R/C frames under narrow-band motions in terms of the spectral-shape-based intensity measure INp

In this study, a simplified procedure to predict the maximum inter-story drift demands of mid-rise framed buildings in terms of a spectral-shape-based ground motion intensity measure is proposed. For this aim, the maximum inter-story drift of steel and reinforced concrete (R/C) frames with 4, 6, 8 and 10 stories subjected to several narrow-band ground motions is estimated as a function of the spectral acceleration at first mode of vibration of the structure Sa(T1), which is commonly used in earthquake engineering and seismology, and with the recently developed parameter related to the structural response known as INp. It is observed that the spectral-shape-based intensity measure INp is the parameter best related with the structural response of the selected frames under narrow-band motions. Therefore, a new approach is used to propose equations to compute maximum inter-story drift demands and seismic uncertainty of mid-rise frames as a function of INp. The equations can be used for the rapid seismic assessment and to obtain structural fragility curves of the steel and R/C frame models. The fragility curves obtained with the simplified approach are compared to those obtained with traditional procedure to compute structural fragility. It is observed that the proposed equations provide good accuracy to calculate fragility curves of steel and R/C structures under narrow-band earthquake ground motions in terms of the spectral-shape-based intensity measure INp.

Maximum inter-story drift demands of steel frames in terms of the intensity measure INp

In the present work, a new equation to predict the maximum inter-story drift demands of mid-rise steel framed buildings is proposed in terms of a new ground motion intensity measures based on the spectral shape. For this aim, the maxim\um inter-story drift of steel frames with 4, 6, 8 and 10 stories subjected to several narrow-band ground motions is estimated as a function of the spectral acceleration at first mode of vibration SaT1, which is commonly used in earthquake engineering and seismology, and with a new parameter related to the structural response known as INp. It is observed that the spectral-shape-based intensity measure INp is the parameter best related with the structural response of the selected steel frames under narrow-band motions. For this reason, an equation to compute the maximum inter-story drift demand of mid-rise steel frames as a function of INp is proposed. The equation is useful for the rapid seismic assessment.

Effects of pulse-like ground motions parameters on inter-story drift spectra of multi-story buildings

This article attempts to study the effect of various pulse-like ground motion parameters and local site conditions on the linear response of different multi-story buildings with special shear and flexural behaviour. The multi-story buildings are modelled using a combination of a shear and flexural beams with representative lateral stiffness ratios. A total of 61 near-fault pulse-like ground motions are selected for this study. The effects of peak ground velocity (PGV), PGV/PGA, rupture distance, Arias intensity, earthquake magnitude and local site conditions on maximum inter-story drift spectra (MIDS) and distribution of the inter-story drift ratio (IDR) along the height of the multi-story buildings are evaluated. It was observed that both the fundamental period of the structure and the lateral stiffness ratio can significantly change maximum inter-story drift demands in buildings subjected to pulse-like ground motions. The near-fault pulse-like ground motions are more dangerous for multi-story buildings with flexural behaviour than those with shear behaviour. The effects of peak ground velocity (PGV) and Arias intensity (I) on inter-story drift spectra is more obvious than others parameters.

Investigation of Effects of Capacity Spectrum Method on Performance Evaluation of Multi-Story Buildings According to the IRAQI Seismic Code Requirements

The aim of this study is to assess the performance objectives defined in the Iraqi Seismic Code (ISC) in order to make a realistic evaluation related to Performance-Based Seismic Design (PBSD) of multi-story reinforced concrete buildings and also to compare and evaluate structural response demands obtained from nonlinear static analysis procedures according to two versions of the capacity spectrum method (CSM) which are recommended in ATC 40 and ATC 55. Two groups of three-dimensional RC buildings with different heights, designed according to Iraqi Building Code Requirements for Reinforced Concrete (IBC), are investigated. Pushover analyses are carried out to determine the nonlinear behavior of the buildings under three different seismic hazard levels, for two Iraqi seismic zones, of earthquake loads. In order to determine performance levels of the buildings, maximum inter-story drift demands and plasticizing sequence are determined and compared with the related limits using the CSM recommended in ATC 40 and ATC 55. From the results of this research, it can be concluded that RC buildings designed according to the Iraqi codes sufficiently provide the performance objectives stipulated in the ISC. Comparing structural response quantities obtained from the two versions of CSM, effects on performance evaluations of the buildings are investigated comparatively, as well.

Seismic Design of MRF-EBF Dual Systems with Vertical Links: EC8 vs Plastic Design

Despite the fact that Eccentrically Braced Frames with Vertical Links (VL-EBFs), also referred to as inverted Y-scheme, are codified in Eurocode 8, the issues related to their seismic response and design have not been widely investigated, so that design criteria commonly applied for Eccentrically Braced Frames with Horizontal Links (HL-EBFs) are commonly applied. However, the Theory of Plastic Mechanism Control (TPMC) has been recently extended to the case of VL-EBFs. The aims of this article, on one hand, are to provide a further validation of the recently proposed design procedure, based on TPMC, and, on the other hand, are to compare the seismic performance of dual systems composed by a moment-resisting part and VL-EBF part designed by means of TPMC with those occurring when Eurocode 8 design criteria are applied. The validation of the proposed design procedure is carried out by means of Incremental Dynamic Analyses (IDA). The main purpose of such analyses is the check of the fulfilment of the design goal of TPMC, i.e., the development of a pattern of yielding consistent with the collapse mechanism of global type. Such mechanism is universally recognized as the one leading to the highest energy dissipation capacity. In case of MRF-EBF dual systems, it is characterized by the yielding of all the links and all the beams at their ends. Conversely, all the columns and the diagonal braces remain in elastic range. Obviously, exception is made for the base sections of first story columns. In particular, two case studies are analyzed which are characterized by a different number of stories. Each building structure is designed according to both TPMC and Eurocode 8 provisions. The seismic response obtained is investigated by both push-over and IDA analyses. The attention is focused on the pattern of yielding obtained, the maximum interstory drift demand, the link plastic rotation demand and sharing of the seismic base shear between the moment-resisting part and the bracing part of the structural system. The results obtained point out improvement of the seismic response, compared to Eurocode 8 provisions, achieved by means of TPMC.

Estimation of cyclic interstory drift capacity of steel framed structures and future applications for seismic design.

Several studies have been devoted to calibrate damage indices for steel and reinforced concrete members with the purpose of overcoming some of the shortcomings of the parameters currently used during seismic design. Nevertheless, there is a challenge to study and calibrate the use of such indices for the practical structural evaluation of complex structures. In this paper, an energy-based damage model for multidegree-of-freedom (MDOF) steel framed structures that accounts explicitly for the effects of cumulative plastic deformation demands is used to estimate the cyclic drift capacity of steel structures. To achieve this, seismic hazard curves are used to discuss the limitations of the maximum interstory drift demand as a performance parameter to achieve adequate damage control. Then the concept of cyclic drift capacity, which incorporates information of the influence of cumulative plastic deformation demands, is introduced as an alternative for future applications of seismic design of structures subjected to long duration ground motions.

The variability of deformation demand with ground motion intensity

The use of Nonlinear Dynamic Analyses is coupled to the demands produced by earthquakes of different intensities. The uncertainties associated with the demands are highly dependent on the variable adopted as the intensity measure (IM). This generates the need to compare different IMs and in particular the dispersion of the demand measure in relation to each IM. For this purpose correlations between maximum inter-story drift demand of nine reinforced concrete Multiple Degree of Freedom tridimensional structures and a number of widely used ground motion intensity parameters have been investigated. To determine the optimum parameter to be used as the IM, two additional intensity parameters are analyzed, the spectral acceleration corresponding to the cracked and non-linear period of each structure, Sa(Tcrack) and Sa(T∗), respectively. The results showed that these two IMs have the best correlation with the deformation demand and their use produces a lower variability of structural response.

Correlation of Deformation Demands with Ground Motion Intensity

A comprehensive study has been carried out to investigate the correlation between maximum interstory drift demand of frame structures and a number of widely used ground motion intensity parameters. Nonlinear time–history analyses of 16 reinforced concrete frames were performed under a set of 80 ground motion records. The frames were selected to represent features of typical low- to mid-rise reinforced concrete structures. The records contained in the ground motion database were compiled from recorded ground motions with the intention to represent a wide range of seismic forces that impose various degrees of elastic as well as inelastic response of the frames. The maximum interstory drift ratios computed were compared with the ground motion intensity parameters employed and correlations between them were investigated through coefficients of correlation and determination. The results revealed that spectrum intensity parameters, having the strongest correlation, are superior to other parameters such as peak ground velocity, peak ground acceleration, and spectral acceleration.

Seismic risk assessment for the mega-city of Istanbul: Ductility, strength and maximum interstory drift demands

This study investigates the seismic demands due to the catastrophic 1999 M w = 7.4 Kocaeli and the M w = 7.1 Duzce earthquakes. The inelastic response spectra for the Kocaeli and Duzce earthquakes are investigated for systems with known strength and ductility. An analytical fiber element model is developed for a typical reinforced concrete building in Turkey. The interstory drifts are calculated from nonlinear dynamic analysis using 26 recorded strong-motion data from the 1999 Kocaeli and the Duzce earthquakes. In the dynamic analysis, the structural members are modeled by employing distributed plasticity fiber elements and both geometrical as well as material nonlinearities are taken into account. This study shows that the ductility and interstory drift demands due to the Kocaeli and the Duzce earthquakes were very severe (well above the code prescribed values) even for moderately inelastic structures. It is apparent from the results that the forward directivity effect is the most influential factor on the interstory drift demand. Both the distance to the fault rupture and the site conditions affect seismic demands, but the site conditions and the local topography are more influential than the distance from the fault rupture. This study shows that substantial damage should be expected in a future earthquake at all districts of Istanbul, but especially at Avcilar, Cekmece, Fatih, Bakirkoy and the Zeytinburnu districts. It is also shown that base isolation may substantially improve the performance of a structure in the inelastic domain and base isolated structures may be designed for lower minimum lateral strengths and higher strength reduction factors.

Multiobjective optimization for performance‐based seismic design of steel moment frame structures

AbstractThe performance‐based seismic design of steel special moment‐resisting frame (SMRF) structures is formulated as a multiobjective optimization problem, in which conflicting design criteria that respectively reflect the present capital investment and the future seismic risk are treated simultaneously as separate objectives other than stringent constraints. Specifically, the initial construction expenses are accounted for by the steel material weight as well as by the number of different standard steel section types, the latter roughly quantifying the degree of design complexity related additional construction cost; the seismic risk is considered in terms of maximum interstory drift demands at two hazard levels with exceedance probabilities being 50% and 2% in 50 years, respectively. The present formulation allows structural engineers to find an optimized design solution by explicitly striving for a desirable compromise between the initial investment and seismic performance. Member sizing for code‐compliant design of a planar five‐story four‐bay SMRF is presented as an application example using the proposed procedure that is automated by a multiobjective genetic algorithm. Copyright © 2004 John Wiley & Sons, Ltd.