Story Stiffness Research Articles

Optimum Location of Soft Storey in Multi-Storeyed Building

The present study is focus on 11-storey reinforced concrete buildings to optimize the location of soft storey under seismic zone-v. The plan of building 40m x 40m is considered. In X- direction and y-direction number of bays is 8 and each bay width is 5m. To observe the non linear behaviour of multi-storeyed building will be studied for various position of soft storey by increasing the storey height. Soft storey is provided at 1st storey, 5th storey and 10th storey. In this first three models is analyzed by increasing height of storey as 4.5m and other three models is analyzed by increasing height of storey as 5.1m and remaining storey height is kept as 3m are compare with regular building by using ETABS software. Comparison is made for the storey displacement, storey stiffness, base shear and formation of hinge patterns. The result remarks the conclusion that base shear carrying capacity of the structure increases as the soft storey is placed at higher levels and is least when the soft storey is at the ground. The seismic performance of structures is very sensitive to stiffness ratio. The lower the stiffness ratio of soft storey displacement of that structure is high.

Stiffness configuration of strongbacks to mitigate inter-story drift concentration in buildings

This paper examines the stiffness configuration of strongbacks to effectively mitigate inter-story drift concentration in buildings. This study first develops a simplified numerical model for simulating buildings with strongbacks. This simplified numerical model is capable of reflecting the various deformation types of the strongbacks and the original buildings, in which the distribution types of story stiffnesses and story masses are not limited. Through this simplified numerical model, a parametric analysis of the ratio of the stiffness of strongbacks to that of original buildings with various building heights and deformation types was conducted. In addition to the stated stiffness ratio, this study further explores the preferred stiffness distribution over the height of the strongbacks. The buildings with uniform distributions of story masses and story stiffnesses over the building heights rather than other specific distributions were considered in the parametric analysis. One nine-story steel moment-resisting frame building and one three-story reinforced concrete (RC) building with infilled RC walls were investigated to verify the effectiveness of the proposed stiffness configuration of strongbacks.

Analog Search of Different Lateral Load Resisting System for High Rise Building

As the rate of growth of population is increasing day by day, the requirement of land is increasing for different purposes. To accommodate this increased population, the height of building is increasing thereby subsequently increasing the importance of lateral load resisting system which provide adequate strength against lateral loading arising due to earthquake and wind. In present study various lateral load resisting system have been introduced which can resist the lateral forces and safely transfer them to soil thereby improving the strength and stiffness of column structures. The lateral load resisting systems that are widely used are conventional beam column system, shear wall system, tube system, outrigger system, tubular system etc. Diagrid structural system is generally adopted in tall buildings due to its structural efficiency and flexibility in planning. Compared to closely space vertical columns in Conventional Beam column system, diagrid structure consists of inclined columns on the exterior surface of building. The concrete diagrids member is used in both precast and cast in-situ type. An exhaustive study has been performed on the performance of 20 storey RCC building with plan size 18 m × 18 m using E-TAB software. All structural members are designed as per IS 456:2000 and all the load combinations of seismic forces are considered as per IS 1893(Part 1): 2002. Finally, Parameter such as storey displacement, storey stiffness and time period are compared and obtained results were presented in both graphically and tabular format

Performance Evaluation of Various Geometries of Shear Wall in Buildings by Equivalent Static Judgment

In the present era, tall buildings are very much prominent, therefore its safety against earthquake forces is of vital importance. Shear wall provides an excellent means of resisting the earthquake forces by resisting the lateral force occurring on the building. To provide desired amount of strength and stiffness shear walls are used in the buildings. However, positioning of shear walls requires due consideration both in symmetrical and unsymmetrical buildings. In symmetrical buildings the center of gravity and the centre of rigidity coincide, so that the placement of shear walls is symmetric along the outer edges or inner edges of building. Therefore, it is necessary to find the most ideal and efficient position of shear wall to minimise the effect of torsion. The work presented in this paper focuses on the performance of various geometries of shear wall namely: Cshaped, L-shaped, I-shaped, Rectangular-shaped. In this study G+6, G+16 and G+25 storeyed building is modelled and analysed for lateral displacement, storey stiffness, storey drift using ETABS-2016 software. The analysis of the building is done by using equivalent static method and the results obtained from this method are plotted graphically.

A combined control strategy using tuned liquid dampers to reduce displacement demands of base-isolated structures: a probabilistic approach

This paper investigates a hybrid structural control system using tuned liquid dampers (TLDs) and lead-rubber bearing (LRB) systems for mitigating earthquake-induced vibrations. Furthermore, a new approach for taking into account the uncertainties associated with the steel shear buildings is proposed. In the proposed approach, the probabilistic distributions of the stiffness and yield properties of stories of a set of reference steel moment frame structures are derived through Monte-Carlo sampling. The approach is applied to steel shear buildings isolated with LRB systems. The base isolation systems are designed for different target base displacements by minimizing a relative performance index using Genetic Algorithm. Thereafter, the base-isolated structures are equipped with TLDs and a combination of the base and TLD properties is sought by which the maximum reduction occurs in the base displacement without compromising the performance of the system. In addition, the effects of TLD properties on the performance of the system are studied through a parametric study. Based on the analyses results, the base displacement can be reduced 23% by average, however, the maximum reduction can go beyond 30%.

The structural identification of the infill walls contribution in the dynamic response of framed buildings

Reinforced concrete (RC) frame buildings containing unreinforced masonry infill walls are commonly used in structural systems around the world. The performance of this type of building can be significantly affected by the presence of infill walls according to their type and distribution in the plane and along the height as revealed by earthquakes. This paper presents data collection, system identification, and finite element modeling of an existing RC framed building designed for gravity loads and containing unreinforced masonry infill walls. Based on a previously carried out ambient vibration test, a three-dimensional finite element model, comprising infill walls and partitions, was successfully updated on the basis of the global modes identified by the in situ test, pointing out the important role of the nonstructural components for this type of building. The influence of the infill walls and partitions on the vibration period was examined, introducing a comparison with simple formulations for the period calculation suggested by codes or available in the literature. The updated model has been further used to assess an approach for an approximate estimation of the story and global stiffness of the building considering the effect of the secondary elements. The dynamic test with the model updating results an efficient procedure for a complete identification of the elastic behavior of the structure.

Structural reliability and performance evaluation of symmetric and asymmetric multi-storey buildings subjected to lateral wind forces

Lately there has been enormous enhancement of buildings architecturally. Most of the buildings are designed and constructed with diverse variations like soft–storey, torsional irregularity, asymmetrical layout of walls, irregularities in plan and elevation and thus overall building configuration. Any such variation result in challenging implications in terms of structural reliability and appropriate design of structural members. Calculation of lateral forces on these structures is an essential process in case of high– rise structures and structural performance of these aesthetically appealing asymmetric irregular shaped buildings especially when subjected to heavy wind forces need to be carefully assessed by structural engineers. The present work intends at performance evaluation by studying structural reliability of symmetrical and asymmetrical regular square, L, C and T–shaped reinforced concrete multi–storey buildings subjected to wind loads. The wind load analysis on these buildings is carried out in line with ASCE 7–10 design code. A comparative evaluation of critical parameters like fundamental period, natural and circular frequency of building, maximum joint displacement, storey drift ratio, inter–storey drift, internal forces in structural members, storey response and storey stiffness determines that difference in shape of a particular storey (or building) influence overall structural performance of building.

Application of a mode shape derivative-based damage index in artificial neural network for structural damage identification in shear frame building

Artificial Neural Networks (ANN) have been proven applicable for updating finite-element (FE) baseline model and structural damage assessment. Most ANN-based damage identification methods use natural frequencies and mode shapes as input layer, limiting their application to quantifying single symmetrical damage in small structures. However, getting higher modal information of a structure is a crucial challenge in practice. As of late, researchers began utilizing mode shape derivatives as input layer in ANN to defeat the challenges for damage assessment in real-life structures. This study, therefore, proposes an ANN-based damage assessment method that employs the change in the first mode shape slope (CFMSS) damage index (DI) as input layer in ANN. For single-damage scenarios, the CFMSS-based DI has been able to detect, locate, and quantify the damage. For multiple-damage scenarios, the DI and corresponding stiffness reduction (SR) are fit as input and output layers, respectively, in ANN to measure the damage severity. Structural damage intensity is indicated as rate of decrease in story stiffness compared to baseline model. The efficiency of the proposed damage identification method is demonstrated through a nine-story numerical shear frame model and an experimental test on a three-story steel shear frame model.

An order statistics approach to multiobjective structural optimization considering robustness and confidence of responses

A design method is proposed for reducing the worst value of representative response of structure under random variation of structural parameters. To reduce the computational cost for finding the worst value, the requirement of ‘worst’ is relaxed to the value corresponding to the specified quantile of the distribution function. The order statistics is used for defining the level of robustness of the approximate worst response value for specified confidence. Obviously, a larger estimate of response is required for ensuring larger robustness with the same confidence. Therefore, a trade-off relation exists between the order of response generated by random parameter values and the robustness in estimation of the worst response. A multiobjective optimization problem is formulated to minimize the representative responses with various order; thus, the solutions with various levels of robustness are simultaneously obtained. A numerical example of a 20-story shear frame is presented for minimizing the maximum interstory drift against seismic motions under constraint on the total amount of damping coefficient, where uncertainty is considered in the story stiffness and the floor mass as well as the damping coefficient that is also the design variable. It is shown that the distribution of additional damping coefficients depends on the level of robustness in estimation of the worst response value.

Seismic structural design methodology for inelastic shear buildings that regulates floor accelerations

A new seismic structural design methodology which is based on optimal control theory is developed for inelastic shear buildings. The methodology is aimed at minimizing the maximum absolute accelerations by changing the floor masses and horizontal story stiffnesses only. The design approach utilizes a modified H∞-synthesis algorithm tailored to structural design variables and uniquely adapted to a closed-loop system of structured controller. This resembles to minimizing the Square Root of the Sum of the Squares (SRSS) of the Magnitude of Absolute Acceleration Gains (MAAGs), while subjected to dynamic equilibrium and structural constraints. The free-parameter of the structured controller (i.e., design variables) are the floor and roof masses and horizontal story stiffnesses. The modified H∞-synthesis algorithm addresses linear systems, but when inelastic shear buildings are concerned the methodology resorts to the two newly developed iterative equivalent linearization procedures. The first procedure, referred to as the inelastic-to-elastic procedure, employs the direct-displacement-based-design (DDBD) approach in calculating the effective story stiffness coefficients of an equivalent linearly-elastic building. The second procedure, referred to as the elastic-to-inelastic procedure, reverses the DDBD approach and transforms the linearly-elastic building (after being upgraded by the modified H∞-synthesis) back into the redesigned inelastic building. A five-story inelastic shear building is analyzed and redesigned in the case-study of this paper. The H∞-synthesis solution is thoroughly examined concerning changing the algorithm variables, and the two DDBD based procedures are tested regarding peak response and modal properties. The redesigned building shows significant improvement in absolute story accelerations. The design methodology developed achieves optimal changes that depend on the assigned side-constraints only in four distinct steps. This in itself is a novel approach to the utilization of H∞ based algorithms.

Seismic Behavior Analysis of Composite Buildings with Respect to RCC Buildings

Steel concrete composite construction has gained wide acceptance worldwide as an alternative to pure steel and pure concrete construction. The use of steel in construction industry is very low in Nepal compared to many developing countries. There is a great potential for increasing the volume of steel in construction, especially in the current development needs. Not using steel as an alternative construction material and not using it where it is economical is a heavy loss for the country. Use of composite material is of particular interest, due to its significant potential in improving the overall performance through rather modest changes in manufacturing and constructional technologies. Steel concrete composite construction means the concrete slab is connected to the composite beam with the help of shear connectors so that they act as a single unit. In the present work, steel concrete composite (both full and half composite) with RCC options are considered for comparative study of seismic behavior of 10 multistoried commercial buildings (4-storied, 5-storied, 6-storied, 7-storied, 8-storied, 9-storied, 10-storied, 12-storied, 16-storied and 20-storied which is situated in earthquake zone V and for earthquake loading, the provisions of IS:1893 (Part1)-2002 is considered. For modeling of composite and RCC structures, SAP2000 software is used. Steel-concrete composite construction system is an efficient, economical and innovative method for seismic resistance of multi storied buildings. Equivalent static method of seismic analysis is used in the analysis of models. Comparison of parameters like time period, axial force, shear force, bending moment, deflection, storey drifts, base shear, storey stiffness is done for full composite (beam-column both composite), half composite (column composite) and RCC structures. The results are compared and found that composite structure is better in several aspects.

Seismic Strength and Stiffness for Recycled Aggregate Concrete‐Filled Steel Tube Frame

To study the seismic strength and stiffness for recycled aggregate concrete‐filled steel tube (RACFST) frame, two‐frame specimens made up of RACFST column and reinforced recycled aggregate concrete (RAC) beam were used for a seismic test under reversed low‐cycle loading. The failure mechanism, hysteresis curve, strength attenuation, and stiffness degradation were determined for the specimens. The design methods for the story shear bearing capacity and stiffness for the single‐layer single‐span RACFST frame were discussed. It is shown that the seismic design requirements including “strong column weak beam” and “strong shear weak bending” can be met. The hysteresis curves are symmetric and the strength attenuation and rigidity degeneration change significantly, then change a little, and then significantly again under the same displacement. It is possible that the methods including elastic bending moment at the column end, plastic hinge at the column end, and plastic hinge at the column bottom can all be applied to the design calculation of the story shear bearing capacity for the single‐layer single‐span RACFST frame. The method adopted in this paper can be used to estimate the original elastic layer stiffness of the RACFST frame.

Degradation evaluation of lateral story stiffness using HLA-based deep learning networks

Hysteresis loop analysis (HLA) has proven an effective indicator of damage detection in civil engineering structural health monitoring (SHM). In this paper, the histogram of stiffness (HOS) features are extracted from segregated half cycles of hysteresis loops reconstructed from measured response. A deep learning network (DLN) is proposed with the use of the HOS to classify the damage index (DI) based on stiffness degradation for damage identification. Training data are obtained using numerical simulations of 30,000 realistic, randomly created hysteresis loops, including a wide range of typical linear and nonlinear structural behaviours. Performance of the trained DLN model is assessed using both 1800 additional simulated 3-story “virtual” buildings and experimental data from a 3-story full-scale real building. Results are compared to the validated HLA method.Validation on simulated virtual building data yields prediction accuracy for 97.2% and 91.6% samples without and with 10% added noise, respectively. The comparison shows a good match of trend and percentage stiffness drop between DLN and HLA identification with the average difference for all cases within 1.1–4.6%, indicating a good accuracy of the proposed DLN prediction model for real structures. The overall results show its potential to provide a rapid, and real-time alarm or other notice on damage states and mitigation to emergency response using DLN and thus without detailed engineering analysis.

Evaluation Method of Story Stiffness and Damping Coefficients Through Structural Response Influenced by SSI Effects

Evaluation Method of Story Stiffness and Damping Coefficients Through Structural Response Influenced by SSI Effects

Influence of mean period of ground motion on inelastic drift demands in CBFs designed to Eurocode 8

The influence of mean ground motion period, Tm, on the inelastic drift response of steel Concentrically Braced Frame (CBF) structures designed to Eurocode 8 is investigated. Incremental dynamic analysis is performed for a set of case study frames with varying structural characteristics at four different seismic intensity levels. From the results of these analyses, regression models for predicting both global and inter-storey drift are developed. It is shown that that both global and inter-storey drift tend to increase nonlinearly as the ratio of fundamental structural period to mean ground motion period, T1/Tm, decreases below unity. The rate of this increase is dependent on the ground motion intensity, represented by the EC8 behaviour factor q. The first mode participation factor, relative storey stiffness and column-to brace stiffness are also shown to influence inter-storey drift response. The values of drift predicted by the developed regression models are compared to values predicted by design codes as well as other predictive models developed in previous studies. It is observed that design codes can under predict drift at lower T1/Tm values.

Advanced two-step integrated optimization of actively controlled nonlinear structure under mainshock–aftershock sequences

In this paper, an attempt is made to examine a new method for designing and applying the active vibration control system to improve building performance under mainshock–aftershock sequences. In this regard, three different structures are considered; 5-, 10-, and 15-story buildings. Seven mainshock–aftershock sequences are selected from the Iranian accelerogram database for analyzing the structures. By implementing an advanced two-step optimization method, buildings equipped with the active vibration control system (linear–quadratic regulator (LQR) algorithm) are designed to withstand all events of mainshock–aftershock sequences. In the first optimization step, a multi-objective optimization with the genetic algorithm is performed and a set of optimal Pareto front results is obtained. In the next step, the life-cycle cost of each optimal design sample of the Pareto front is calculated by considering the cumulative damage and the design sample with the minimum cost is selected as a final optimal property. The results prove that the active vibration control system is capable of reducing structural responses, including acceleration, drift, and residual drift under mainshock–aftershock sequences, and consequently the life-cycle cost of buildings, especially the taller ones. In addition, obtaining the building design variables (story stiffness and yielding force) and active LQR algorithm properties simultaneously leads to a slightly softer final building model than the conventional structure designed by the common building design code. Moreover, it is revealed that, by considering the aftershocks, the building life-cycle cost increases significantly.

Application of Bayesian statistical method in sensitivity-based seismic damage identification of structures: Numerical and experimental validation

Most of the developed sensitivity-based damage detection methods are based on the application of external excitations which could be prohibitive due to infeasible excitation of all structural degrees of freedom. In this regard, identification of damage properties using seismic structural response would be advantageous. In this research, sensitivity-based finite element model updating method is proposed to identify structural damage by earthquake response in the frequency domain and the transfer function of the structure due to ground excitation. The obtained sensitivity equation is solved by linear least square method through defining constraints on the design variables. Since the attainable measured data are restricted by limits on the instrumentations and preciseness of the measurements and due to the fact that only a few of the lower modes of a structure can generally be determined with confidence, a Bayesian statistical method is utilized to enhance the reliability of the predicted damage properties. The proposed technique is applied to a numerical frame model and an experimental six-story steel structure with various scenarios of story stiffness reduction. The results are indicative of the capability of the proposed method for identification of damage location and severity.

Damage Index Distributions in RC Dual Lateral Load-Resistant Multi-Story Buildings Considering SSI Effects Under Bidirectional Earthquakes

Inelastic seismic responses of flexibly supported reinforced concrete (RC) moment-resisting frames representing short-to-tall structures stiffened with ductile RC structural walls were evaluated considering both far-field and near-field ground motions. A dual shear wall-frame resisting system with symmetric reference plan was created by adding shear walls into excitation direction of the three-dimensional frames developed by generic structure algorithm. The current study also aims to take into account soil–structure interaction effects in to damage assessment of multi-story RC buildings in terms of ductility demand, damage index, story shear force and overturning moment, as well as kinetic energy profile over the structure height. In doing so, the developed set of generic frames was considered accounting for different values of story strength, stiffness distribution and number of stories. A realistic modeling of nonlinear ductile behavior of RC elements was developed in combination with the sub-structuring method to consider the foundation flexibility in nonlinear seismic responses. Conducting a parametric study through nonlinear static analyses (pushover) as well as nonlinear response history analyses, the results indicated that the near-field ground motion presents much more damage than the far-field one. Inelastic dynamic responses to near-field records demonstrated that structures with a fundamental period greater than the pulse period respond differently from those that have shorter periods. The results were also presented as charts and tables that provide helpful information for engineering design purposes such as damage assessment of multi-story RC buildings with specific fundamental natural period and base shear strength.

Stiffness Identification of High-Rise Buildings Based on Statistical Model-Updating Approach

A system identification problem is investigated for high-rise buildings to identify the story stiffnesses of a shear-bending model (SB model). In the previously proposed stiffness identification method due to the present authors, the shear and bending stiffnesses of the SB model were identified by means of the subspace and inverse-mode methods. The lowest mode of horizontal displacements and floor rotation angles of the objective building was identified first by using measured data of both horizontal and rotational accelerations via the subspace method. Considering the resolution in the measurement of floor rotation angles in lower stories, floor rotation angles in most stories were predicted from the floor rotation angle at the top floor. However, it was difficult to obtain the bending stiffnesses reliably in the previous method. In this paper, to overcome the difficulty in the stiffness identification method using the SB model, a statistical model-updating approach is proposed where the probability distribution of floor rotation angles in the lowest mode is obtained for the identified SB model, and a conditional probability problem is applied by providing additional measured data on floor rotation angle. The proposed stiffness identification method is useful for the structural health monitoring of high-rise buildings. For investigation of the reliability and accuracy of the proposed stiffness identification method, a 10-story building frame subjected to micro-tremor is examined.

Dynamic performance of a multi-story traditional timber pagoda

This paper presents a study on the dynamic performance of a multi-story traditional timber pagoda. A shaking table test was conducted with a 1:5 scaled pagoda model and various excitation intensities. Both artificial and recorded earthquake waves were considered. Ambient excitation test before seismic excitations and white noise excitation tests during the intervals of increasing seismic excitations were conducted to detect the fundamental frequencies and damping ratios of the model pagoda. Equivalent story stiffness was evaluated from the measured inter-story load-displacement hysteretic curves and a lumped mass model was established to determine the dynamic properties of the pagoda during strong excitations. It was found that the pagoda model survived all the input earthquake excitations (up to 0.44g in PGA) with only minor damages. The model frequencies detected after increasing earthquake excitations decreased only by 16% while the damping ratio increased from 1.24% to more than 10%, indicating a good seismic resilience of the pagoda. It was also found that the detected frequencies highly relied on the intensity of the excitations (up to 59% in difference), possibly due to the transition between static and sliding frictions amongst wood members and the recoverable looseness of the mortise-tenon joints.