Stiffness Irregularity Research Articles

Analysis of G+20 Horizontally Connected Buildings with and Without Fluid Viscous Dampers

As urban populations continue to grow globally, the demand for new cities and high-rise structures is increasing due to limited land resources and expanding social and commercial activities. To address these challenges, this study investigates the seismic performance of G+20 horizontally connected buildings, focusing on the effects of fluid viscous dampers (FVDs) on structural response. A 3D model of two G+20 buildings, one with and one without FVDs, was developed using ETABS software, and seismic analysis was conducted for a Zone V seismic region in India. The study evaluates key performance parameters, including storey displacement, storey drift, and storey shear, to assess the effectiveness of the dampers. Results showed that adding FVDs significantly reduced overall building displacement, particularly in the X-direction at the top storey, with a reduction of approximately 40%. The Y-direction saw a more modest 5% reduction, attributed to geometric and stiffness irregularities. Additionally, storey drifts in the X-direction were higher than in the Y-direction but were significantly reduced after installing dampers. The findings highlight the importance of FVDs in improving the seismic resilience of horizontally connected high-rise buildings and offer valuable insights for future structural design in earthquake prone areas.

Effect of Vertical Aspect Ratio on Mass, Stiffness and Vertical Geometric Irregular Structures

Occurrence of earthquake will highly damage the structures which are not modelled and designed to resist such loads it may cause sometimes the collapse of structures leads to loss of human lives. The size of the building and slenderness ratio are the important factors for the efficient structural design. The aspect ratio of buildings is considerably effects under seismic loads. It is important to know the influence of aspect ratio on the irregular structures in high seismic zone areas. The research has been performed on the 15 storey building frames of five cases with mass, stiffness and vertical geometric irregularities. Each case comprises of four models having various vertical aspect ratios. The purpose of this study is to investigate the influence of vertical aspect ratio on mass, stiffness and vertical geometric irregular structures and how the structure will vary under seismic loads. The irregularities are incorporated in to the buildings by increasing the loads and column height in particular storeys and by eliminating the columns and beam sections compared to adjacent storeys. Linear dynamic analysis is performed. It is observed that with the decrease of vertical aspect ratio the structural response will increases the response of storey displacement, base shear, storey drift and over turning moment in the cases of mass and stiffness irregular structures. In the case of vertical geometric irregular structures with the decrease of vertical aspect ratio the storey displacement and storey drift values decrease for all the models, the base shear, overturning moment and stiffness increases with the decrease of vertical aspect ratio. Key words: Mass irregularity, Stiffness irregularity, Vertical geometric irregularity, Vertical aspect ratio, Linear dynamic analysis.

The influence of elastic pads deterioration in the fastening system on the dynamic characteristics of the vehicle-turnout system

The deterioration of the elastic pads in the fastening system in high-speed turnout areas increases longitudinal stiffness irregularities along the track, posing potential hazards to wheel-rail impact and train running safety. This paper takes the frog area of No. 18 turnout as an example and constructs a vehicle-turnout rigid-flexible coupling model considering the detailed structure of the fastener elastic pads. By increasing the stiffness of the rubber pad under the tie plate to simulate the deterioration of the elastic pads in the turnout area, the study investigates the effects of deterioration location, degree, and number on the dynamic characteristics of the vehicle-turnout system, providing theoretical guidance for stiffness optimization and maintenance of the turnout area. The results indicate that: 1) the deterioration of the elastic pads significantly affects wheel-rail interaction and safety indicators, while having a minor effect on vehicle running stability; 2) the 95th sleeper (point rail with a top width of 60 mm) is identified as the most critical location for the deterioration of elastic pads; 3) comprehensively considering, the stiffness replacement limit for elastic pads in ballastless turnout areas can be set to twice the design stiffness, which is 50 kN/mm.

A Case Study on the Effect of Multiple Earthquakes on Mid-rise RC Buildings with Mass and Stiffness Irregularity in Height

A Case Study on the Effect of Multiple Earthquakes on Mid-rise RC Buildings with Mass and Stiffness Irregularity in Height

Unsupervised Machine Learning-Driven Assessment of Infill Wall Systems for Structural Performance in Soft Stories

Infill wall systems have been extensively studied as potential solutions to mitigate the adverse effects of stiffness irregularity in soft-storey structures. This research leverages unsupervised machine learning techniques, specifically clustering algorithms, to analyze and compare the mechanical behavior of different columns in a nine-storey unsymmetrical reinforced concrete building subjected to seismic loading. The primary objective is to assess the effectiveness of various infill wall systems, including 5-inch and 10-inch wide brick walls and 5-inch, 7.5-inch, and 10-inch wide concrete walls, in enhancing structural resilience. The study employs a comprehensive data-driven approach, incorporating ETABS modeling, data preprocessing, exploratory data analysis, and clustering to identify patterns and relationships in the structural performance of columns. Key findings indicate that more comprehensive and concrete infill walls significantly reduce displacement values, improving structural stiffness. Cluster analysis reveals that columns connected to multiple infill walls, particularly exterior corner columns, exhibit enhanced structural performance. Specifically, the 10-inch comprehensive concrete infill wall system demonstrated the highest efficacy in mitigating stiffness irregularity. The research further highlights that clustering algorithms, such as K-Means, effectively categorize columns based on their mechanical responses, facilitating a comparative evaluation of infill wall systems. These insights provide valuable recommendations for designing and retrofitting soft-storey structures to enhance seismic resilience.

Method to identify if torsional mode of a building is its first mode

Torsionally flexible buildings (that have torsional mode as fundamental mode) twist during earthquake shaking, and may collapse partially or completely depending upon the direction and level of shaking. The problem is aggravated when the building is torsionally unsymmetrical. Some design codes (like Eurocode, Indian Code) explicitly prohibit the design of such buildings. This paper presents a simple approximate method to identify torsionally flexible RC Moment Frame and RC Structural Wall buildings at the initial proportioning stage itself without carrying out a detailed structural analysis. It is possible to identify whether or not the first mode is torsional mode of a building (i.e., torsionally flexible building) if Natural Period Ratio τ>1 by modelling the building with rigid diaphragm and distribution of mass & stiffness along the height of building, and estimating: (1) radius of gyration of rotational mass rm of each floor plan geometry by lumping the masses of slabs, beams and all vertical elements at each nodes, (2) radius of gyration of twisting stiffness rKθ of all vertical elements using their translational and torsional stiffnesses (considering flexibility of adjoining beams and vertical elements accounting for both flexural and shear deformations), and (iv) τ (=rm/rKθ). The method is validated with 3D Modal Analysis (using τ =Tθ/T, where Tθ is Uncoupled Torsional Natural Period and T Uncoupled Translational Natural Period) of hypothetical buildings using a commercial structural analysis software. Also, parameters are identified that lead to τ>1, and solutions suggested to avoid torsional flexibility in buildings. Further, the method helps identify vertical stiffness irregularity in buildings. Draft provisions are suggested for inclusion in seismic codes. Also, poor performance of multi-storey building (with τ>1) is demonstrated using nonlinear static and nonlinear time history analyses.

Stiffness Irregularity in RC High-rise Building

Stiffness Irregularity in RC High-rise Building

Seismic fragility of vertically irregular gravity column-core tube structure subjected to pulse-like ground motions

The effects of the pulse-like ground motion and structurally vertical irregularity on the seismic fragility of the new gravity column-core tube structural system are investigated. Based on the shaking table test, the finite element parameters are verified. By changing the stiffness ratio of the first story to the second story, the typical vertically irregular gravity column-core tube structure models of 20-, 30- and 40-stories are established. Selecting 10 pulse-like and 10 corresponding non-pulse-like ground motion records, the incremental dynamic analysis and seismic fragility analysis are performed to these structures employing CANNY program. The results show that the maximum inter-story drift ratio (θmax) and the probability of exceeding the limit state (Pf) of each structure under pulse-like cases are significantly greater than those under non-pulse-like cases. From slight damage to approaching collapse state, the difference in seismic fragility curves between pulse-like cases and non-pulse-like cases is gradually amplified. It is suggested that the seismic strength reduction factor of these new type of structures be reduced properly to consider the pulse-like ground motion effect. With the stiffness ratio decreases, θmax and Pf have an increasing trend. However, the increasing quantity is small, which may be due to the effect similar to the isolation in the first story. As a limit value of vertical irregularity in the first story, the stiffness ratio of 1.5 provisioned in the code is conservative. To give consideration to both the safety and the economy, it is recommended to lower the limit value to about 1.2 for the gravity column-core wall structures with stiffness irregularity at the first story.

Seismic assessment of structures with mass and stiffness irregularities under multiple earthquakes

Seismic assessment of structures with mass and stiffness irregularities under multiple earthquakes

Seismic Response of Stiffness Irregularity at Ground Floor with and without Shear Walls

In today's scenario, one of the greatest challenges for structural engineers is designing and constructing seismic-resistant structures. Seismic activity, or earthquakes, poses a significant threat to civil engineering structures, and ensuring that buildings can withstand the forces generated during an earthquake is crucial for public safety and infrastructure resilience. Irregular configurations, whether in the building's floor plan or its elevation, are widely acknowledged as significant contributors to failure during seismic events. These irregularities can lead to uneven distribution of forces and stresses, compromising the building's ability to withstand the seismic forces and potentially resulting in structural failure. Soft storeys, typically located at ground levels for various functional purposes, pose challenges in seismic regions due to their lack of sufficient lateral load-resisting elements resulting in excessive lateral deformation and collapse during intensive earthquakes. Hence, the present study investigated the seismic response of irregular reinforced concrete structures possessing stiffness irregularity at ground floor with and without shear walls. A ten-storey regular frame is modified by incorporating vertical irregularity in elevation by increasing the height of the ground floor. The complete structural analysis and modeling are carried out by using the software ETABS 2020. The Time History method is applied, and the study is focused on seismic zones V in India. The performance of structures are compared based on criteria such as storey displacement, storey drift, storey shear and overturning moment. The results lead to the conclusion that a building structure exhibiting stiffness irregularity is prone to instability which is indicated by higher displacement and drift values. Structures incorporating shear walls have demonstrated greater stability compared to structures without shear wall as they exhibited higher base shear values and experienced a reduction in lateral displacement by more than 40%. The presence of shear walls also has enhanced the stability and strength of the structure, showing a linear response during critical earthquakes.

Experimental Investigate on Seismic Performance of RC Hill-Side Stilted Buildings Affected by Vertical Stiffness Irregularity

ABSTRACT In this study, the ratio of lateral stiffness of the stilted story to that of the second story was proposed as the story stiffness ratio (SSR) to quantify vertical stiffness irregularities of hillside stilted buildings. A quasi-static experiment was conducted on a plane stilted frame with an SSR of 40 in the slope direction. Experimental results were compared with those of a stilted frame with an SSR of 1.01. The results show that SSR is an important factor influencing seismic failure modes of stilted buildings. As SSR decreases, structural ductility and deformation capacity improve, and stiffness degradation decelerates.

Impact of strongback on structure with varying damper and stiffness irregularity arrangements

Structures susceptible to soft story mechanisms are particularly vulnerable to earthquakes because damage concentrated at a single story can lead to premature failure of the structure. The strongback, a stiff vertical spine pinned at the structure's base and running its height, has been proposed as a way to impose a more uniform pattern of floor displacements and prevent soft story mechanisms. However, changes in the impact of strongbacks on the performance of structures remain unclear when considering vertical stiffness irregularities at different positions along the height of a structure and different arrangements of energy dissipation devices in a structure. This study aims to address these gaps through an extensive parametric experimental investigation varying the location of vertical stiffness irregularities and the arrangement of dampers in a small-scale four-story elastic structure with and without a strongback. For this study, each configuration of the structure is loaded with shake table-produced seismic ground motion. The results of this study show that, regardless of which story a stiffness irregularity is located, the strongback significantly reduces the maximum story drift in the structure. Furthermore, with the strongback, the maximum story and roof drift are insensitive to damper position and distribution, whereas, without it, the damper position significantly impacts the structural performance. The strongback's ability to protect against soft story vertical irregularities, regardless of their locations, and the insensitivity of structural performance to damper arrangement when utilizing a strongback, presents promising new options for structural design, architectural design, and remediation efforts.

Impact of asymmetrical corrosion of piers on seismic fragility of ageing irregular concrete bridges

This article investigates the seismic fragility of ageing irregular multi-span reinforced concrete (RC) bridges. Different irregularity sources are considered, including: (i) substructure stiffness irregularity arising from the unequal-height piers, (ii) substructure stiffness irregularity arising from the spatially variable (asymmetrical) corrosion damage of piers and (iii) irregular distribution of effective tributary masses on piers of varying heights. To this end, a three-dimensional nonlinear finite element model is developed for multi-span RC bridges and verified against a large-scale shake table test results of a two-span concrete bridge specimen available in the literature. Nonlinear pushover, incremental dynamic and seismic fragility analyses are performed on three groups of two-span RC bridges with different configurations. Moreover, a time-dependent dimensionless local damage index is employed to evaluate the failure sequence and collapse probability of selected bridge layouts. The analysis results of the three studied irregularity sources show the considerable significance of spatially variable corrosion of bridge piers and substructure irregularity on the failure sequence of piers and seismic fragility of multi-span RC bridges. Furthermore, analysis outcomes show that uneven corrosion of piers triggers an unbalanced distribution of seismic ductility demands and irregular seismic response of equal-height multi-span RC bridges.

SESMIC ANALYSIS OF VERTICALLY REGULAR AND IRREGULAR BUILDING

Earthquake damage results from several key factors, including irregularities in building design, soft stories, inadequate lateral strength, and structural interactions between the building and the ground. Within contemporary urban infrastructure, tall irregular structures play a significant role, representing a prominent feature that significantly impacts a building's response to seismic activity. Irregular structures are characterized by variations in geometry, mass distribution, and stiffness, making them susceptible to earthquake-induced damage. This study focuses on the analytical examination of vertical irregularities, encompassing stiffness irregularities, mass irregularities, and vertical geometry irregularities. The study comprises a total of 10 models, including an 11-story moment- resisting frame (MRF) building, along with additional models derived from the initial one to investigate stiffness, mass, and vertical geometry irregularities. Response spectrum analysis considering the design response spectrum provided by NBC 105:2020 is performed in each model and various responses of building are compared. From the study, it is concluded that there is significant variation in the responses of tall building with introduction of different vertical irregularities. Among the different kinds, the vertical geometry irregularity has comparatively more effect in responses in comparison to mass and stiffness irregularity in a particular storey.

Methodology & Impact of Vertical Irregularities on Seismic Responses in Tall Buildings: A Comparative Analysis

The vulnerability of tall buildings to earthquake damage is influenced by numerous factors, including irregularities in their design and construction. Irregular structures, characterized by variations in geometry, mass distribution, and stiffness, are particularly susceptible to seismic- induced damage. In this study, we conduct an in- depth analytical examination of vertical irregularities, encompassing stiffness, mass, and vertical geometry variations. Ten structural models are considered, including an 11-story moment-resisting frame (MRF) building and its derivative models, to investigate the effects of these irregularities. Response spectrum analysis, based on the design response spectrum from NBC 105:2020, is performed on each model, and the building's responses are compared. Our findings reveal significant variations in the responses of tall buildings when different vertical irregularities are introduced. Notably, vertical geometry irregularities have a more pronounced effect on responses compared to mass and stiffness irregularities in specific storeys. This research provides valuable insights into the seismic behavior of tall buildings and their vulnerability to vertical irregularities.

Experimental Testing of Post‐installed Anchors for Use in Retrofitting of RC Frame with Steel Braces

AbstractThe retrofitting of deficient Reinforced Concrete (RC) frames, particularly those with strength and stiffness irregularities such as Open Ground Story, has been widely researched. Steel braces are a great option for retrofitting these buildings, but the narrow section sizes of existing beams and columns pose a challenge. However, post‐installed chemical anchors can provide an efficient, cost‐effective solution for connecting such structures with steel braces, provided that they are designed properly to account for all possible failure modes. This study investigates the use of post‐installed chemical anchors to connect steel braces with narrow‐beam column subassemblies in existing low‐ to mid‐rise Open Ground Story buildings. The three experiment are considered to test the bracing conditions with elastic and yielding brace. The gusset plate is designed as per Balanced Design Procedure to obtain an economical section with controlled yielding and failure sequence. The forces on gusset plate are computed using the Uniform Force Method, which helps in designing the post‐installed anchor dimension and spacing. A comparison is drawn between the three test from which it is seen that the chemical anchors perform well in all cases and conventional brace shows expected performance.

Design of a multi-story steel building according to the Turkish Building Earthquake Codes: TBEC-2007 vs. TBEC-2018

People have built structures to survive and to meet their shelter needs. While buildings had progressed horizontally at first, the increase in population and shrinkage of spaces over time led the construction industry to build multi-story buildings. In the research, the Turkish Building Earthquake Code 2007 (TBEC-2007) and the Turkish Building Earthquake Code 2018 (TBEC-2018) were extensively examined and an 8-story steel business center building having high ductility levels in both directions and consisting of concentrically braced steel frames was designed according to the two earthquake codes. The Equivalent Static Method was utilized while designing according to the codes. For structural elements’ dimensioning, the Regulation on Design, Calculation, and Construction Principles of Steel Structures principles were followed and the Load and Resistance Factor Design Method was utilized. After performing the analyses of the building according to both earthquake codes, the effects of the code differences on the system periods, earthquake loads, lateral displacements, the story drifts, second-order effects, A1 type torsional irregularities, B2 type stiffness irregularities, and dimensioning of the elements were evaluated in detail. It was observed that in TBEC-2018 compared to TBEC-2007, the structure’s coordinates are determined more specifically while identifying the earthquake load, more sensitive soil options are presented, separate calculations according to building height are performed, and base shear forces are smaller. Moreover, it was deduced that there was no significant variance between the codes in terms of calculations of building importance coefficient, natural vibration period, story drifts, and irregularities.

Study on seismic performance of reinforced concrete stilted building with steel braces in mountainous areas

As one of the wildly used structural forms in the mountainous area, the stilted buildings suffered severe damage under strong earthquakes due to their significant stiffness irregularities. This paper employed the steel braces at the stilted story to reduce stiffness irregularities and improve stilted buildings' seismic performance. Firstly, the effectiveness of setting steel brace to reduce the stiffness irregularities of the stilted story was verified through theoretical analysis. Then a pseudo-static test of a three-story two-span RC stilted frame with steel braces was conducted according to the scale ratio of 1/3. Its seismic performance was analyzed by comparison with a test of an RC frame without steel braces regarding bearing capacity, hysteretic curve, ductility, and energy dissipation capacity. Further, finite element models of stilted prototype buildings were established to investigate the force characteristics of stilted columns for stilted buildings with and without steel braces during earthquakes. Experimental results showed that setting steel braces could change the failure mode of the stilted building, and a more reasonable failure mechanism was achieved. Stilted buildings' ductility and deformation ability was improved by setting steel braces, proving the rationality of the layout form of steel braces in the stilted story. Last, the finite element analysis showed that setting steel braces significantly changed the mechanical characteristic of stilted prototype buildings. The sheer force of the short column at the stilted story decreased significantly while the braces bore most of the shear force.

Analysis of Internal Forces and Structural Dimensions on the Variations of Courtroom Placement of DPRK Building

The construction of state buildings is caused by the increased mobility of needs. One of them is the DPRK building that wants the placement of the plenary session room to be on the 2nd or 3rd floor. This study aims to evaluate the internal style and behavior of the structure that arises due to variations in the placement of the plenary session room so as to produce the most optimal choice of courtroom for the most effective structural dimensions. Structural analysis was carried out using the ETABS program by carrying out 4 variations of courtroom placement, namely Varian 1 (the courtroom is located on the 1st floor), Varian 2 (2nd floor), Varian 3 (3rd floor), and Varian 4 (4th floor). Variant 2 (DED) is a reference sourced from the DED from the planning consultant. The seismic load analysis used is the method of Dynamic Analysis of Response Spectrum Variety. Parameters reviewed are internal forces (axial, normal, and moment) and structural behavior (story displacement, displacement between floors, nominal base shear forces, and vertical irregularities). The calculation analysis refers to the latest standards, namely SNI 1726:2019, SNI 1727:2020, and SNI 2847:2019. The results of this study indicate that the greatest internal force values occur in Variant 4. The level displacement and the displacement between floors increase in the variant with the smaller structural element dimensions. The level displacement of the X and Y axes has increased in Variant 3 and Variant 4, and has decreased in Variant 1. The nominal base shear force value has decreased for Variants 1, 3, and 4 against Variant 2 (DED) because it has smaller structural dimensions. . All modeling variants experienced soft stiffness irregularity type 1A, excessive soft stiffness irregularity type 1B, and heavy (mass) irregularity type 2. Variant 1 was chosen as the variant with the best courtroom placement, because it met the requirements for earthquake design.

Influence of a Soft Story on the Seismic Response of Non-Structural Components

Multi-story, reinforced-concrete (RC) building structures with soft stories are highly vulnerable to damage due to earthquake loads. The soft story causes a significant stiffness irregularity, which has led to numerous buildings collapsing in previous seismic events. In addition to the structural collapse, the failure of non-structural components (NSCs) has also been observed during past earthquakes. In light of this, this study investigates the effect of a soft story and its location on the seismic behavior of a supporting building and NSCs. The soft story is assumed to be located on the bottom (ground), middle, and top-story levels of the considered building models. Story displacements and inter-story drift ratios are evaluated to assess structural behavior. The floor response spectra and the amplification effects of NSC on the floor acceleration responses are studied to understand the behavior of NSCs. The analysis results revealed that the bottom soft story exhibits a considerable vertical stiffness irregularity, and its position substantially affects the floor response spectra. The amplification in the floor acceleration response was found to be greater at the soft-story level. This study reported that middle soft-story buildings exhibit the most remarkable amplification in the component’s acceleration. Finally, peak floor response demands are compared with the code-based formulation, and it is found that the code-based formulation’s linear assumption may lead peak floor response demands to be underestimated or overestimated.