Maximum Inter-storey Drift Research Articles

Simplified method for seismic vulnerability of plan irregular RC buildings using degree of irregularity

Irregular buildings are more vulnerable to seismic loading, depending on their degree of irregularity. The degree of irregularity in vertically irregular buildings and its correlation to seismic vulnerability (SV) have been quantified in previous studies. However, these studies on plan irregular buildings were focused on only evaluating seismic performance. A simplified method, based on the degree of irregularity, is proposed to identify the SV of plan irregular reinforced concrete (PIRC) buildings. The different types of plan irregularities considered were diaphragm discontinuity, re-entrant corners, non-parallel systems and torsional irregularity. For each type of plan irregularity, numerical models were developed with varying degrees of irregularity. The numerical models were subjected to incremental dynamic analysis and the maximum interstorey drift was recorded to develop fragility curves. The proposed simplified method effectively identified the SV of the PIRC buildings based on their degree of plan irregularity. The method can help to identify the most vulnerable PIRC buildings at the initial stage of large-scale seismic simulations, such as integrated earthquake simulations of urban areas. It can thus be used as a filtering method to select the most vulnerable PIRC buildings that need detailed seismic analyses.

Study on seismic performance of prestressed fabricated reinforced concrete frame structure assembled by steel sleeves

This paper introduces a novel type of prestressed fabricated reinforced concrete frame (PSFRC frame) structure, which utilizes steel sleeves for assembly. The PSFRC frame incorporates prestressed tendons, stiffened steel sleeves, and high-strength bolts, resulting in improved bearing capacity and assembly efficiency. To assess the seismic performance of the PSFRC frame joint, experimental tests were conducted on one reinforced concrete (RC) joint and two PSFRC frame joints under cyclic loading. Hysteresis analysis and elastic-plastic time-history analysis were also performed using a finite element model. The experimental results showed that the PSFRC edge joint reached a peak load of 89.30 kN, while the PSFRC middle joint exhibited a capacity of 169.95 kN, which was 58.87 % higher than that of the cast-in-place specimen XJ (107.87 kN). The hysteresis curves of the PSFRC joints demonstrated significant fullness, with the equivalent damping coefficient of the PSFRC joint being increased by 11.56 % compared to the RC joint. Additionally, a simulation method using ABAQUS software was proposed to investigate the seismic response of the integral structure of the PSFRC frame. Finite element models for both PSFRC and RC frames were established, and their seismic performance was analyzed under cyclic loading and the El Centro seismic wave. Various parameters including peak loading capacity, stiffness degradation, peak acceleration value, inter-storey drift ratio, and concrete damage value were considered. The finite element analysis results revealed that the load-carrying capacity of the PSFRC frame (435.33 kN) was approximately 30 % higher than that of the RC frame (386.48 kN). Furthermore, at the peak acceleration of 600 gal, the maximum inter-storey drift ratio of the first floor for the PSFRC frame was 1/58, which was below the limit value of 1/50. The plastic hinge position at the beam end of the PSFRC frame was further from the core area, aligning with seismic design objectives. This research provides valuable insights into the design of fabricated building structures and methods for analyzing seismic performance.

Experimental and numerical simulation of seismic behavior of reinforced concrete frames infilled with refractory straw blocks

Recent earthquakes have highlighted the vulnerability of infilled reinforced concrete structures due to the insufficient consideration of infill masonry walls' contribution to strength and stiffness. This study presents a novel refractory straw block (RSB) designed to address these challenges and improve the seismic performance of reinforced concrete (RC) frames. Unlike traditional infills, RSB is characterized by low-elastic-modulus, low-density, and high-ductility. Quasi-static tests were performed on three types of frames: unfilled, infilled hollow grouted bricks (HGB), and infilled RSBs. Failure model, stiffness, and load-displacement response of three specimens were investigated and analyzed. The results indicate that RSBs as infill material does not alter the failure mode and constitutive relationship of bare frame, while HGBs leads to shear failure. The peak load for the specimen IF-HGB was 69.3 kN at 1.1 % drift, compared to 38.8 kN at 2.4 % drift for the specimen IF-RSB, and 36.4 kN at 2.0 % drift for the specimen BF. The strengths of specimens IF-HGB and IF-RSB were 1.90 and 1.07 times that of specimen BF, respectively. The stiffness of specimen IF-HGB was 3.7 times that of the other specimens, but its allowable displacement was only 61 % of theirs. Dynamic time-history analyses were also performed on structures with no longitudinal infill (BF), with RSBs (SBF), and with fired bricks (FBF). At the design level of rare events (magnitude 8, PGA 400 gal), severe damage occurred, but collapse was limited. When the PGA increased further, the collapse probability of model FBF rose rapidly, whereas the collapse probabilities of models SBF and BF remained low and similar. Accounting for the confining effect of walls, model FBF showed a higher probability of severe damage than models SBF and BF, particularly under minor earthquakes. The maximum inter-storey drift ratio of the model SBF and FBF were respectively 1.2 times and 1.7 times that of the model BF, which shows that straw blocks as infill can greatly avoid the effect of infill on the seismic behavior of the structure. The study also emphasized the often-overlooked confining effect of masonry on columns, which can lead to unrealistic damage assessments and seismic shear force distributions.

Parametric Analysis of Moment-Resisting Timber Frames Combined with Cross Laminated Timber Walls and Prediction Models Using Nonlinear Regression and Artificial Neural Networks

The light weight and moderate stiffness of multistorey timber buildings make them susceptible to increased lateral displacements and accelerations under service-level wind loading. Therefore, the fulfilment of serviceability requirements is a major challenge. In this study, linear elastic finite element analysis was used to perform a parametric study of moment-resisting timber frames combined with cross laminated timber walls. In the parametric study, various mechanical and geometrical parameters were varied within practical ranges. The results of the parametric study were used to derive simplified analytical expressions and to train artificial neural networks which can be used to estimate fundamental frequency, mode shape, top floor displacement, maximum inter-storey drift, and wind-induced acceleration. The analytical expressions and the artificial neural networks can be used for the preliminary assessment of serviceability performance of moment-resisting timber frames with and without cross laminated timber walls, under service-level wind loading.

Interpretable machine learning models for displacement demand prediction in reinforced concrete buildings under pulse-like earthquakes

This work proposes a novel procedure to guide the development of machine learning models for estimating the seismic demand in existing reinforced concrete (RC) buildings. The proposed approach is organized across two scales. A large-scale (nonparametric) machine learning model is first obtained by means of Gaussian Process Regression (GPR) using all candidate building attributes and intensity measures. SHapley Additive exPlanations (SHAP) values are utilized to facilitate its interpretation and to assist the rational selection of a small subset of intensity measures, which is finally employed to develop a (symbolic) reduced-scale machine learning model by means of Genetic Programming (GP). Simplified models of archetype buildings are adopted to develop machine learning techniques at both scales, in such a way to alleviate the simulation time for preparing large datasets. Refined models representative of actual buildings are instead considered for the unbiased final assessment.The proposed approach is applied to develop predictive machine learning models for the maximum inter-storey drift in bare frames, pilotis frames and frames with infills under pulse-like seismic ground motions. Consequently, the critical examination of the SHAP values revealed the most significant intensity measures and unfolded interesting patterns depending on the occupancy rate of the infills. Moreover, the final assessment demonstrates that this approach allows the management of a non-homogeneous building stock consisting of very diverse structural systems (i.e., spanning from existing buildings designed against gravity loads only to buildings that comply with outdated seismic codes) while providing satisfactory predictions of the seismic demand with minimum computational effort.

Inerter-based tuned mass dampers for response control of multi-degree-of-freedom structures subjected to wind and earthquake excitations

The present work explores the utilization of the tuned mass damper-inerter (TMDI) in controlling the structural response subjected to wind and earthquake excitations. An example of a 25-storey reinforced concrete building is taken up. The equations of motion of the structure-TMDI combined system are established by assuming the building behaves as a shear-building with multiple degrees of freedom. These equations are solved using Newmark’s time integration method. The objective functions are the wind- and earthquake-induced structural response quantities, such as the maximum inter-storey drift ratio (MIDR) and peak floor acceleration (PFA). The prime contribution of this study is the inclusion of statistical measures such as the mean, 85th, and 95th percentiles for these quantities. A genetic algorithm-based multi-objective optimization is performed to estimate the optimum TMDI parameters. Based on the outcomes of this study, it can be recommended that the TMDI be optimized to perform well under the 95th percentile for MIDR and PFA in effectively reducing the peak structural responses. Frequency domain analysis results demonstrate TMDI’s multiple-mode controlling capability. The energy comparison plots of the uncontrolled and controlled structures prove the effectiveness of the optimum TMDI in providing enough damping and ensuring structural stability.

Seismic effect of steel bracing systems in RC frame models

A bracing system is a common type of construction used in multi-storyed buildings for strengthening the structure. This type of technique may be used for retrofitting of existing building. Steel braced frame is used to resist earthquake loads in multistoried buildings. Steel bracing systems are affordable, simple to install, take up less space and may be designed in a variety of ways to achieve the desired strength and stiffness. In this study, three different heights of building model were considered to analyze the effect of bracing systems. For the study, each model is considered to be different bracing system viz. X-bracing, diagonal bracing, inverted V-bracing, eccentric bracing. The bracing is provided for peripheral columns of each model. Using STAAD Pro software, the building models were analyzed for seismic zone IV according to IS 1893: 2002. According to the results, the X type of steel bracing significantly increases structural rigidity and reduces the maximum interstorey drift of the frames. Global and story drifts are used to analyze the building's performance.

Seismic reinforcement analysis and measurement research of reinforced concrete frame structure

In China, there are many reinforced concrete frame buildings that have reached the end of their design life, or have not been designed with seismic requirements in mind and need to be reinforced. In this paper, a reinforced concrete frame structure which needs to be reinforced is taken as an example. Two common reinforcement methods are used to reinforce the reinforced concrete frame structure by adding shear wall and increasing column section. BIM-GSSAP software is used to analyze maximum inter-storey drift angle and the member response under frequent earthquakes, and the whole structure of the weak layer under rare earthquakes is checked. The results show that both methods can significantly improve the seismic performance of buildings. At the same time, combined with the project example, the advantages and disadvantages of the construction process are analyzed, which can provide a useful case reference for this kind of reinforced concrete frame structure projects.

Design and optimization of roof-top fire water tanks as compliant deep tank dampers-inerter for seismic protection of multi-storeyed buildings

Water tanks are installed on the roofs of high-rise buildings for services and to fight fire outbreaks. These tanks are often considered unsuitable for design as tuned liquid dampers (TLDs) and have higher depth ratios than that required in conventional TLDs due to practical constraints in dimensioning the tank as per the tuning requirement. The present work aims at alleviating these hindrances and utilizing deep water storage tanks as effective passive damping devices for the host building. In this paper, a water storage tank for firefighting, situated on the roof of a building, is designed as a compliant deep tank damper inerter (CDTDI) in controlling the response of the host building subjected to seismic excitations. The tank is flexibly connected to the building through spring and damping elements to act as a compliant damper system. Further, the tuning effect, mass, and damping enhancement potential of an inerter element are employed to improve the volumetric efficiency of the compliant damper system. Two example buildings, 10- and 20-storey, are taken up and modeled as multi-degree-of-freedom (MDOF) systems whose masses are lumped at storey levels. The coupled dynamic equations of motion of the CDTDI-MDOF structural system are formed and solved in the time domain using the Newmark-β method. An external excitation-dependent, multi-objective Grey Wolf optimization is performed to estimate the optimum CDTDI parameters by subjecting the buildings to 100 recorded seismic ground excitations. The average values of the peak roof displacement, the maximum inter-storey drift ratio, and the peak floor acceleration are considered objective functions of the optimization. The results reveal the proficiency of the CDTDI in controlling the multiple modes of the structure. Further, the optimally designed CDTDI provides significant damping and stability to the structure, which is evident from the energy plots.

Utilising Artificial Neural Networks for Assessing Seismic Demands of Buckling Restrained Braces Due to Pulse-like Motions

Buckling restrained brace frames (BRBFs) exhibit exceptional lateral stiffness, load-bearing capacity, and energy dissipation properties, rendering them a highly promising choice for regions susceptible to seismic activity. The precise and expeditious prediction of seismic demands on BRBFs is a crucial and challenging task. In this paper, the potential of artificial neural networks (ANNs) to predict the seismic demands of BRBFs is explored. The study presents the characteristics and modelling of prototype BRBFs with different numbers of stories and material properties, utilising the OpenSees software (Version 2.5.0) for numerical simulations. The seismic performance of the BRBFs is evaluated using 91 near-fault pulse-like ground motions, and the maximum inter-storey drift ratio (MIDR) and global drift ratio (GDR) are recorded as a measure of seismic demand. ANNs are then trained to predict the MIDR and GDR of the selected prototypes. The model’s performance is assessed by analysing the residuals and error metrics and then comparing the trend of the results with the real dataset. Feature selection is utilised to decrease the complexity of the problem, with spectral acceleration at the fundamental period (T) of the structure (Sa), peak ground acceleration (PGA), peak ground velocity (PGV), and T being the primary factors impacting seismic demand estimation. The findings demonstrate the effectiveness of the proposed ANN approach in accurately predicting the seismic demands of BRBFs.

Inelastic response spectra for an integrated displacement and energy-based seismic design (DEBD) of structures

The severe socio-economic impact of recent earthquakes has further highlighted the crucial need for a paradigm shift in performance-based design criteria and objectives towards a low-damage design philosophy, in order to reduce losses in terms of human lives, repair/reconstruction costs, and recovery time (deaths, dollars and downtime). Currently, displacement-based parameters are typically adopted to design/assess the seismic performance of the structures, by limiting the maximum displacement or the maximum interstorey drift ratio (IDR) reached by the structure under different earthquake intensities. However and arguably, displacement-based quantities are characterized by inherent weaknesses, since, for instance, they are not cumulated parameters, thus not able to capture directly the effects of multiple cycles, deterioration and damage cumulation. Therefore, in the last decades, energy-based approaches were investigated and developed in order to establish alternative engineering demand parameters for the assessment of post-event damage through a dynamic energy balance. Towards the main goal of developing an integrated Displacement and Energy-Based Design/assessment procedure (DEBD) for actual use in practice, this research work proposes an innovative approach based on the use of inelastic spectra correlating the energy components with the corresponding maximum displacement response parameters of the structure. In practical terms, the proposal is to further integrate and develop the well-known Direct Displacement-Based Design, by directly adopting the hysteretic energy as an additional design parameter. The energy inelastic spectra are developed through an extensive parametric analysis of Single-Degree-of-Freedom (SDoF) systems, with different nonlinear hysteretic models. In such an approach, the maximum seismic energy demand imparted to a structure can be directly predicted and controlled, whilst distinguishing the various components of the energy balance, including the hysteretic one. The effects of near-field and far-field earthquakes are also investigated. Results show that in the first case the seismic demand is concentrated in the peak of a few large cycles that absorb the demand energy induced by the high component in peak ground velocity in the second case the higher equivalent number of plastic cycles tends to become critical for structures with inadequate structural details and prone to suffer by cumulative cycles and overall plastic fatigue mechanisms.

Multi-level performance-based seismic design optimisation of RC frames

Conventional structural optimisation techniques often result in unconventional structural configurations, unrealistic structural elements and ignore actual construction costs. This paper presents an effective performance-based optimisation framework for minimising initial material costs of realistic multi-storey reinforced concrete (RC) frames, while satisfying pre-determined performance targets under multiple seismic hazard levels as well as a set of practical design and construction constraints. A new low computational-cost optimisation method is proposed to directly control specific response parameters at both the element and structural levels (i.e. plastic rotation and inter-storey drift). For the first time, the concept of Uniform Damage Distribution (UDD) is adopted to simplify the complex design optimisation problem of RC buildings with multiple design variables in terms of section sizes and reinforcement ratios. The optimum design solution is achieved by gradually redistributing materials from strong to weak parts of the structure, aiming to fully exploit the material capacity. The efficiency of the proposed optimisation framework is then demonstrated in the optimum designs of 3-, 5-, 10- and 15-storey RC frames under a set of six spectrum-compatible earthquake records. The results indicate that compared to structures designed by current codes, optimum solutions required up to 20 % and 43 % less concrete volume and steel reinforcement weight, respectively. It is also noted that due to more efficient use of materials, optimum structures exhibited considerably lower global damage index (up to 88 %), less maximum inter-storey drift (up to 58 %), and less maximum plastic rotations (up to 78 %). Sensitivity analysis on earthquake record selection shows that using a single earthquake record may not lead to reliable design solutions, in particular for tall buildings, and hence a set of spectrum-compatible records should be used in the optimisation process. This research will lead to more economical and safe design of multi-storey RC structures in seismic regions by developing a practical multi-level optimisation method with low computational costs.

Shaking table test of fully assembled precast concrete shear wall substructure with tooth groove connection and vertical reinforcement lapping in reserved hole

In this paper, an innovative fully assembled precast concrete shear wall structural system with tooth groove connection and vertical reinforcement lapping in reserved hole was proposed, and the constructional requirements and joint assembly process were elaborated in detail. Based on the similarity theory, a 1/2 scaled fully assembled precast shear wall substructure was designed and manufactured. The damage mode, dynamic characteristics, acceleration response, displacement response, seismic action response, inter-storey shear response and strain response of the fully assembled precast concrete shear wall substructure with tooth groove connection and vertical reinforcement lapping in reserved hole under the different earthquake excitations were comprehensively analyzed by shaking table test, and the connection performance and seismic performance of the substructure in high intensity areas were investigated. The research results showed that the cracks at the horizontal joint of the 1st floor were completely penetrated, accompanied by slight concrete spalling, the 1st floor shear wall perpendicular to the input direction of seismic excitation was slightly uplifted, and there was no obvious damage in other parts. Overall, the tooth groove connection and vertical reinforcement lapping in reserved hole was reliable. Besides, the dynamic characteristics and seismic response of the substructure were consistent with the three-stage test phenomena. The acceleration amplification factor, storey displacement, seismic action increased with the increase of the height of the substructure and the excitation of PGA. When the excitation of PGA = 0.638 g, the maximum inter-storey drift was 1/213, which was in line with the plastic limit of 1/120. On the whole, the integrity of the substructure remained good and there was no danger of collapse. Finally, a comprehensive seismic performance evaluation method suitable for fully assembled precast concrete shear wall substructure with tooth groove connection and vertical reinforcement lapping in reserved hole was proposed with inter-storey drift and damage index as quantitative indicators.

Seismic Analysis of Flat Slab Buildings on Hilly Ground

In India, hilly region especially northern part is more seismically active region. Flat Slab systems are widely popular in multi-storey buildings. Flat slab building has more advantages than a regular building like fast construction, free design space, reduced floor to floor height and economical. Flat slab buildings are also being built in high seismicity region. Buildings on hilly ground are vulnerable due to their vertical and horizontal irregularity and they undergo high shear and torsion during the earthquake. Further due to short column and soft storey on uphill side has higher lateral forces that are cause to failure of buildings. In this paper, an attempt has been made to assess the seismic behavior of flat slab resting on hilly slope with soft storey and set back configuration. The methodologies have been adopted are linear dynamic analysis i.e. response spectrum analysis. Building is analyzed and designed by Etabs software. Maximum displacement, maximum inter-storey drift and storey shear are determined as response quantities. It is observed from the study that for flat slab buildings on hill slopes the storey shear is very high in the bottom columns at higher ground level, therefore extra care should be taken to design these columns for earthquake load.

On the choice of ground motion intensity measure and the number of records for cloud analysis-based seismic demand assessment

Cloud analysis has emerged as a popular tool for the seismic demand/fragility assessment of structures. The output of cloud analysis is a seismic demand model which relates an Engineering Demand Parameter (EDP) indicative of structural distress to an Intensity Measure (IM) signifying the severity of ground shaking. IMs commonly used for probabilistic seismic demand assessment are quite heterogenous with respect to their “efficiency”, i.e. their degree of correlation with a specific EDP. This feature has serious implications on the number of ground motion records that must be used to perform cloud analysis on a given structure in order to accurately describe the distribution of the EDP at various IM levels. In the current study, demand models for maximum interstorey drift (?max), based on a wide spectrum of IMs, are developed from the cloud analyses of a five-storey RC bare frame structure using a suite of fifty unscaled natural ground motion records. The method of bootstrap resampling is used to investigate the convergence of the regression coefficients in the demand model with the size of the bootstrap subsamples, each comprising of a limited subset of records drawn from the original suite with repetitions allowed. This procedure helps determine the minimum number of ground motion records necessary for the calibration of demand models without compromising its accuracy in predicting the drift demands. Results from the study indicate a strong correlation between the efficiency of various IMs and the optimal number of records required to produce reliable seismic demand models.

Seismic retrofit of torsionally coupled RC soft-storey building using short yielding core BRBs

This study presents seismic retrofitting of medium-rise torsionally coupled Reinforced-Concrete (RC) non-ductile building with soft ground storey. An irregular RC building with T-shaped plan is considered for the present study. In this sample building the presence of plan irregularity results in the torsional coupling of lateral modes. The location of staircase in the sample building significantly enhances the plan irregularity. Therefore, the contribution of stiffness of the staircase slabs is considered in the overall stiffness of the numerical model. Buckling Restrained Braces (BRBs) with short yielding cores are adopted to improve the seismic performance of the sample building. Short yielding core BRBs are installed in the ground storey to control the seismic lateral response induced by the soft-storey and torsional coupling of lateral modes. Displacement-based design method is adopted for the design of short yielding core BRBs to enhance the stiffness and energy dissipation of the structure so that it can endure the considered earthquake without exceeding the target drift level. Nonlinear dynamic analysis of the sample building is carried out before and after retrofit under bidirectional horizontal ground excitations applied simultaneously. The seismic performance is assessed in terms of maximum inter-storey drift, torsional response, plastic hinge distribution, residual displacement. Maximum axial force distribution of BRBs, maximum ductility and cumulative ductility demand of BRBs are discussed for a critical ground motion record. Analysis of the results reveals that the installation of BRBs decouples the torsionally coupled lateral modes of the sample building; and decreases inter-storey drift, torsional response and residual displacement in the soft ground storey. Thus, the retrofit design considered in this study, enhances the overall structural performance of the sample building reducing the lateral response due to the combined effect of the soft-storey and torsional coupling of lateral modes.

Nonlinear behaviour of FRP-retrofitted RC coupled shear walls

This paper presents a numerical study of the effectiveness of fibre-reinforced polymer (FRP) composites in upgrading the seismic performance of conventional reinforced concrete (RC) coupled shear walls. The study investigates the performance of two RC coupled shear wall buildings with different heights when their coupling beams are retrofitted using FRP U-wraps for increased ductility of the beams. The 10- and 15-storey existing buildings are located in Montreal, Canada, and were designed according to the 1970 National Building Code of Canada (NBCC). The FRP retrofit aims to increase the shear capacity of nominally ductile coupling beams, and hence increase their rotational ductility to the limited ductility, moderate ductility, and ductile levels. Nonlinear incremental dynamic analyses were conducted for existing and FRP-retrofitted buildings when subjected to twelve ground motion records with different frequency contents. The seismic behaviour of the analyzed cases was compared based on the maximum earthquake intensity that can be resisted by the building, maximum interstorey drift ratio, maximum storey shear, maximum coupling moment, maximum energy dissipated, and maximum wall forces. Moreover, the twelve earthquake records were scaled to match the NBCC 2015 design response spectrum of Montreal to determine the optimum retrofit level for the coupling beams of the two buildings in consideration.

Convolutional Neural Network-Based Rapid Post-Earthquake Structural Damage Detection: Case Study.

It is necessary to detect the structural damage condition of essential buildings immediately after an earthquake to identify safe structures, evacuate, or resume crucial activities. For this reason, a CNN methodology proposed to detect the structural damage condition of a building is here improved and validated for two currently instrumented essential buildings (Tahara City Hall and Toyohashi Fire Station). Three-dimensional frames instead of lumped mass models are used for the buildings. Besides this, a methodology to select records is introduced to reduce the variability of the structural responses. The maximum inter-storey drift and absolute acceleration of each storey are used as damage indicators. The accuracy is evaluated by the usability of the building, total damage condition, storey damage condition, and total comparison of the damage indicators. Finally, the maximum accuracy and R2 of the responses are obtained as follows: for the Tahara City Hall building, 90.0% and 0.825, respectively; for the Toyohashi Fire Station building, 100% and 0.909, respectively.

Structural feasibility of braced-damper system with adaptive negative stiffness devices in yielding multi-storey steel frames

This paper investigated the structural feasibility of braced-damper system with adaptive negative stiffness devices (i.e., negative stiffness amplifying damper, NSAD) in yielding multi-storey steel frames (MSFs). The nonlinear analytical model of yielding MSFs with NSADs was established. Seismic responses of a 3-storey typical structure with and without NSAD were evaluated to illustrate the working mechanism of NSAD applied at yielding MSFs. Parametric study concerning the maximum inter-storey drift, residual deformation, and structural acceleration was conducted thoroughly to quantify the effect of NSAD. The rational distribution of NSADs was also discussed respectively for both regular and irregular yielding MSFs. Numerical results showed that the adaptive NSAD is effective in mitigating inter-storey drift, residual deformation, and structural acceleration of yielding MSFs when subjected to multiple intensities of earthquakes. It is recommended that the adaptive NSAD shall be applied at storeys with small drift response, i.e., whose stiffness (previous conclusion on elastic MSFs) and strength (new contribution of this paper on yielding MSFs) are high. In other word, the feature of NSAD that helps reducing non-arranged storey drift is also valid for the plastic scenarios.

High strength steel frames with curved knee braces: Performance-based damage-control design framework

High strength steel frames with curved knee braces (HSSFs-CKBs) are typical seismic resilient structural systems. Previous experimental research showed that an HSSF-CKBs specimen could be readily repaired after an earthquake by replacing damaged curved knee braces (CKBs) which serve as energy dissipating devices, as long as high strength steel components stay essentially elastic to shake down post-earthquake residual deformations. To provide a practical tool for engineers in seismic resilience design, this paper developed a performance-based damage-control design framework for low-to-medium rise HSSFs-CKBs. A multi-storey HSSF-CKBs was first interlinked with an equivalent bilinear single-degree-of-freedom (SDOF) system. Then, the seismic input energy demand of the HSSF-CKBs was determined based on the seismic energy balance of the equivalent SDOF system, which was further distributed to different storeys to design structural components. To facilitate the design, a stepwise design procedure was proposed. A three-storey low-rise HSSF-CKBs and a six-storey medium-rise HSSF-CKBs were designed following the procedure. The seismic response of the designed structures was examined by pushover analyses and nonlinear time-history analyses using numerical models verified by shaking table test data. The analysis results showed that the designed structures exhibited the expected behaviour, and the maximum interstorey drifts were controlled below the design target, which verified the effectiveness of the proposed design framework.