Fundamental Time Period Research Articles

Impact of irregular masonry infill walls on the seismic response of reinforced concrete frame buildings using linear dynamic analysis

This paper aimed to investigate the seismic response of reinforced concrete (RC) frame buildings using linear dynamic analysis. The study focused on the effects of irregular distributions of masonry infill walls both in elevation (soft story at different levels) and in horizontal (plan) distribution on seismic behavior. Seventeen models were analyzed, including infill frame models with soft stories, models with infill panels only in certain bays, and bare frame models. All models were analyzed using the linear response spectrum (RS) dynamic analysis method. Structural design typically focuses on peak response values, and response spectrum analysis examines the structure's behavior and performance through these peak values. The analysis results indicate that masonry infill walls significantly affect the building's fundamental time period, base shear, story shear, and inter-story drift.

Evaluation of Lateral Load Resisting Systems in High-Rise Buildings

The rapid urbanization and the scarcity of residential space in metropolitan areas necessitate the construction of tall structures to meet the growing accommodation demands. This research paper focuses mainly on the structural act of high-rise structures under lateral loads, especially earthquake forces. Three lateral load resisting systems, namely outrigger system, shear wall at core and shear wall at corner are compared and analysed. The study reviews relevant literature, discussing parameters affecting the fundamental time period of structural models and the effectiveness of distributed belt wall systems. The research methodology involves the analysis of a 40-storey regular office building using three different lateral load resisting systems. The results obtained through response spectrum analysis, shows that the outrigger system exhibits efficient structural capability in tall buildings. The maximum lateral displacement is significantly reduced in the outrigger system compared to core shear-wall and corner-shear wall. The study concludes that enhancing lateral load resistance and providing a transition path to perimeter columns subjected to lateral load, as seen in the outrigger-system, proves effective in mitigating the impact of earthquake loads on high-rise buildings.

A comparative analysis of RCC and composite buildings using the new plastic deformation (PD) method

Low computational efficiency and non-linearity behaviour make the simulation of the overall building structure problematic to attain with a single dynamic or static method. Thus, this paper uses a plastic deformation (PD) method based on concrete plasticity theory (CPT) for comparative analysis of multi-storey reinforcement cement concrete (RCC) and composite buildings under common and rare earthquake loads. For this purpose, a 15-storey tall building was selected for analysis using ABAQUS software. At first, a possible building model was created and then plastic deformation analysis was performed using the new PD method under both common and rare earthquakes. After that, a nonlinear time history analysis was conducted, and the results of plastic strain distribution, lateral displacement, peak acceleration, storey stiffness, shear force, storey drift, normalised shear, and top deflection of the RCC and composite buildings were studied deeply. The fundamental time period of the RCC model was found to be 5.2 s while the fundamental time period of the composite model was 6 s. Under common and rare earthquake leads, the peak acceleration of the RCC building was 19% and 22% higher than composite buildings, respectively. Under common and rare seismic loads, the top deflections of the composite building were 33% and 36% higher than those of RCC buildings, respectively. In the case of the RCC building, it was found in this study that higher peak acceleration (PA) of the ground motion led to higher storey top displacement, storey drift, shear force and top deflection under both ground motions. Numerical results suggested that the use of composite structure is more durable than RCC structure. It was also concluded that the PD method could also be effectively used for the analysis of RCC and composite buildings under dynamic loads.

Investigation of Seismic Response of Irregular Steel Buildings: A Case Study of U-Shaped Structures

Tills paper presents a dynamic analysis focusing on the influence of plan shape on tall steel structures. The study specifically investigates the seismic behavior of two 22-story buildings, one with a square plan and the other adopting a U-shaped configuration. Utilizing OpenSEES platform for nonlinear time history analysis, the research sheds light on the impact of plan irregularities on fundamental time periods, displacements, drift ratios, and base shear. Results reveal that the U-shaped building experiences liiglier dynamic response compared to the square shaped reference building, the U-shaped building experiences liiglier time periods across all modes due to increased mass and irregular stiffness distribution in the building's grid. Top story displacements reveal an increase in maximum displacement by 30% compared to the reference structure, showing a non-linear pattern. Inter-story drift ratios had peaks at the 8th and 18th floors showing increments of 43% and 117%. respectively. The time liistoiy response illustrates a liiglier response over time for the U-shaped building, indicating distinct behavioral differences. Base shear time liistoiy revealed liiglier values for the U-shaped building over time, including a 48% increase in maximum base shear compared to the reference building. These findings reveal the significant effect of plan regularity in tall steel building design on the seismic response and the importance of considering it in building design.

Comparative Study Dynamics Analysis of a Multi-story Building with and without a Floating Column

Parking spaces, lobby areas, terrace gardens, and other amenities are highly sought-after in densely populated urban regions. Although floating columns can be useful and an achievable choice, it is important to research their structural performance and cost-effectiveness in the event of substantial ground motion imposed on by an earthquake. A building’s overall dimensions, geometry, and shape all impact how it acts and acts when subjected to seismic loads. For this reason, it is necessary to assess how well floating column buildings perform in seismically vulnerable places in comparison to conventional buildings. In this work, the performance of structures with floating columns for seismic loading is observed using dynamic analytic techniques in accordance with IS 1893 (2005). This study analyses both the floating columns and the conventional building without floating columns. When compared to a regular building, the research reveals that the floating column buildings exhibit a very quick increase in base shear and story displacement. The horizontal displacements experienced by floating column buildings are proportionally larger due to an increase in the fundamental time period. If the lateral displacement exceeds the codespecified maximum limit, damage to structural and non-structural parts may result. Because of the discontinuity in the load distribution path, seismic base shear and overturning moment are also increasing in the case of buildings with floating columns. Additionally, while asymmetrically introducing floating columns, torsional irregularity has been produced but the modal mass participation ratio has decreased. While it is true that the use of floating columns in high-rise structures allows for continuous open floor plans, they are also dangerous and susceptible in seismically active locations

Evaluation of Soil Structure Interaction Effects on Seismic Response of RC Framed Buildings Using Simplified Method

In the current practice for the design of the building structure is done by considering the footing as fixed based. The mid-rise buildings having variation in storey height from 3- to 10-storey were selected for the research. In this research, analysis was done to study into the interaction between the seismic response of RC-framed buildings and the soil-structure for various soil types. To study the linear responses of the structures, the model was developed in FEM software SAP2000. The underneath soil was modelled by using direct method, where the soil is considered as solid element. The considered depth of soil was considered 30 m and the viscous spring dashpot were applied to avoid the reflection of seismic waves in soil medium along the effective horizontal soil boundaries. The seismic response variables such as maximum lateral deflection, inter-storey drift and fundamental time periods have been studied. SSI amplified the lateral deflection, inter-storey drift and time period of structure shifting the performance level from life safety to near collapse level. Fundamental time period of the first mode was increased by 23 % for very soft soil. The maximum lateral deflection of 10-storey building for very soft soil was amplified up to 282 % for Kobe and the performance level was shifted from life safety (1.5 %) to collapse level for all the considered model for soil type D . The performance level of structure was checked against the different soil types on varying storey height and finally a simplified method has been proposed to incorporate the effects of SSI in fixed base structures.

Numerical Studies on Seismic Response of Structural Systems Using a Response-Spectra Based Intensity Measure

This paper proposes a novel intensity measure (IM) based on the geometric mean of acceleration response spectral ordinates to assess the probabilistic performance of structures subjected to seismic loading. Instead of relying solely on the fundamental period, the proposed IM is evaluated across a fixed period range for all structural systems, which allows consideration of higher mode effects and period changes due to nonlinearity. The proposed seismic IM is evaluated using two established indices sufficiency and efficiency. Sufficiency quantifies the independence of an engineering demand parameter at a specific intensity level with ground motion characteristics such as seismic magnitude [Formula: see text] and distance from site to fault plane [Formula: see text]. It is calculated by linear regression analysis, or using gradient-based relative sufficiency measures. On the other hand, efficiency is measured as dispersion across ground motions at a given intensity level for any physical response quantity. It helps to reduce computational demand for failure probability assessment by considering a smaller number of records compared to an inefficient IM for similar confidence levels. The effectiveness of the proposed IM along with 10 other IMs is demonstrated on single degree of freedom systems with various fundamental periods by performing nonlinear time history analysis using a far-field ground motion record set. The study is also extended to five degree of freedom lumped mass stick models, 2D models (4-, 8-, and 12-story archetype steel frames), and 3D reinforced concrete shear wall building model. The results indicate that the proposed IM limits dispersion to within 10% for long-time period structures, and demonstrates improved sufficiency across different structural systems. For example, gradient of the proposed IM with respect to magnitude [Formula: see text] and site-to-source distance [Formula: see text] for a 12-story steel frame is reduced by 42.9% and 94%, respectively, compared to spectral acceleration at fundamental time period. Potential application of this research lies in efficiently conducting seismic reliability assessment and design for structural systems.

Linear and Nonlinear Dynamic Analysis of Reinforced Concrete Building with V Shape Steel Bracing

In this study, the RC-MRCBFs were used with V braced frame. The core objective of this examination is to understand the earthquake behavior of the RC-MRCBFs in steel V braced frames. Response spectrum analysis (RSA) is used to understand the seismic performance of the steel braced and un-braced RC frames. Total 12 steel braced RC frames and 12 un-braced frames for all 4 story, 8story, 12 stories and 16 stories are studied and observed the seismic parameter such as fundamental time period (FTP), top story displacements, inter-story drift, base shear and story stiffness of the structures. After studying the parametric study of the 4 to 16 story buildings with a linear and nonlinear analysis tool it was observed that to get the effective braced frame with expected failure mechanism, ductility, the columns should be designed such that, they resist at least 50% base shear contributions. It is observed that using the steel V bracing in the low rise to mid-rise buildings, improves the seismic behaviors of the structures. The steel bracing reduces the maximum top story displacements, drift and time period of the building and increases the seismic base shear demand, stiffness of the structures. The result shows that as increasing the base shear contribution in the columns, the drift and displacement of the story increases and base shear decreases. Key Words: Response Spectrum Analysis, displacement, Maximum storey drift, Storey shear, Storey stiffness, braced frame, RC buildings.

Seismic Behaviors of RC Buildings in Slopping Ground

This thesis is the study of seismic behavior of RC building in hilly areas i.e. sloping grounds. The study of dynamic response of structure on hilly areas has been done. Almost 13 configuration of structure has been considered for analysis. Six of them are step-back and which consider ground slope. Six are set-back configuration which is like in plain land. Remaining one is plan buildings. Three models are normal step back, setback and plan buildings and remaining are combination of shear wall, steel bracings. Various literature reviews of studies on the seismic behavior of RC building on hilly areas i.e. sloping ground has been studied and presented in this thesis. All considered configuration of building is modeled using ETABS v20.0.0 and IS 1893:2016 and analyzed by using equivalent static analysis and response spectrum methods. Then considered buildings have been compared in terms of base shear, Fundamental time period, top storey displacement, drift and story stiffness. The seismic behavior of building on hilly areas (sloping ground) is found differ from building plain ground. Most of studies lead to conclusion that building on hilly areas (sloping ground) has higher displacement and base shear compared to building on plain land. Also conclude shorter column attracts more forces and cause damage when earthquake occurs. Step back configuration could prove more vulnerable to seismic activities. We also concluded that building with shear wall improves seismic behavior of building by increasing strength and stiffness and also reduce in deflection. Keywords: Hilly areas, step-back configuration, step-back, set- back configuration,

Self-adaptive penalty approach as an alternative technique for lateral load analysis of framed type elevated water tank stagings

Elevated water tanks are vulnerable to lateral loads since heavy mass is concentrated at the top of the slender supporting staging. For the prediction of lateral loads due to earthquakes fundamental time period of tank stagings is essential because it influences the value of the acceleration coefficient from the response spectrum graph. Time period in turn depends on the lateral stiffness of the framed type tank staging. Staging in elevated water tanks is more flexible to lateral loads up to top panel and behaves rigidly above it due to rigid connection of heavy mass which is placed over top of the staging with massive ring girder and monolithic connection of side wall and bottom slab. This rigid behavior will establish kinematic relations among the top nodal points of the staging with container when subjected to lateral loads. The rigid nature of the container and its lateral movement can be stared with the lateral movement of the centre of gravity of the container. Hence, in order to obtain optimum ideal behavior of the staging, centre of gravity of the container connected with top panel top nodal points of the staging with rigid links in the mathematical model. In the current study, Stiffness of the staging is being evaluated by kinematic relations between the centre of gravity point and the top nodal points of the staging using the penalty function approach. Appropriate penalty parameters are identified and have been applied to the elevated water tank staging with different configurations. This approach is much more precise, and it may be employed to design elevated water tank staging.

A shake table investigation on low-cost seismic isolation using unbonded scrap tyre pad isolators

Seismic isolation is an effective strategy to mitigate the effect of earthquake on structures. Conventional seismic isolation is still inaccessible to developing countries as it is expensive. Scrap tyres have been identified to be suitable for use as base isolators. It is also a challenge to recycle, reuse and effectively dispose this rapidly accumulating waste material without harming the environment as it is heavy, thick and made up of multiple materials. In this paper, the effectiveness of using scrap tyre pads for base isolation is investigated. Scrap tyres of size 175/65/R14 are considered in the study. The tread portion of the scrap tyre is cut into pads of definite size and shape and arranged one above the other to form the isolator. The scrap tyre pads which contain both rubber and intervening steel cords make it vertically stiff and laterally flexible which will in turn reduce the cost of the system as they do not require additional materials for enhancing the stiffness properties. The application without steel end plates further reduces the cost and hence suitable as a low-cost seismic protection system for developing countries. In the present study square shaped unbonded scrap tyre pad isolators of three configurations using 4, 6 and 8 layers of scrap tyre pads are considered. Initially, the dynamic horizontal stiffness of different configurations of scrap tyre pad isolators is estimated using a shake table test on a system consisting of a set of rectangular plates supported by 4 isolators at the corners of the base plate. A shake table test is also conducted on a three storied scaled building frame model supported on four isolators at the four corners of the base of the model. All the isolators are found to be effective in shifting the fundamental time period of the frame. Finite element analysis on isolators with 4, 6, 8 and 10 layers are also carried out to determine the effect of vertical pressure on the fundamental frequency and dynamic stiffness of isolator systems.

A comparative study on the response of the L-shaped base isolated multi-storey building to near and far field earthquake ground motion

This study aims to understand the behaviour of a base isolated l-shaped building under far field and near field earthquake ground motion. A ten-storey l-shaped building was considered for the study and modelled using SAP2000, which is finite-element-based software. At first, a non-isolated model was created, and the required data was generated in order to develop an isolated model. After that, a non-linear time history analysis was performed, and the results of storey displacement, torsional irregularity, and base shear have been discussed for the base isolated model and the non-isolated model. The fundamental time period of base isolated l-shaped building was found to be 2.56 s while the base model had fundamental time period of 0.88 s. It was found in this study that higher peak ground acceleration (PGA) and peak ground velocity (PGV) of the ground motion led to higher storey displacement, storey drift, and base shear but a lower torsional irregularity ratio under near field ground motion, while torsional irregularity ratio of base isolated building was found to be increased under far field ground motion.

Effects of fundamental natural time periods on the seismic performance of base isolated multistorey buildings

Effects of fundamental natural time periods on the seismic performance of base isolated multistorey buildings

Comparative Effectiveness of Equivalent Static Analysis & Response Spectrum Analysis in Extreme Seismic Zones

Earthquake is one of the horrible natural disasters. With the considerable developments in the constructional science, the experts have been able to find out the factor forces that cause earthquakes the damage and destructions in different types of buildings, including residential and commercial buildings, caused by earthquake are of high importance and need to be considered. The damage caused by earthquakes in multi-story buildings is usually in the weak points of the building, which is caused by Strength and changes in stiffness. this paper deal with two methods of analyze, linear static analysis (Equivalent Static Analysis) and linear dynamic analysis (Response Spectrum Analysis) on three different height structures(5-Storey, 10-Storey, 15-Storey) with regular plan in two various seismic zones (IV, V) as per IS1893-2016 and compared parameters, max story displacement, max drift ratio, base shear, max axial force in column, max bending moment in column and fundamental time period from the effect of two analysis methods, using ETABS software. After the analysis, these conclusions were made:Effect of equivalent static analysis in both seismic zones IV, V in Max Story Displacement is more than response spectrum analysis, 36% in 15 Storey building, 38% in 10 Storey building and 34% in 5 Storey building. Fundamental Time Period is equal in equivalent static analysis and response spectrum analysis in both seismic zones and with the 5 storey gap between each buildings time period, 9.5% less from 15 storey to 10 storey and 29% less from 10 storey to 5 storey. Effect of equivalent static analysis in both seismic zones at Max Drift Ratio 27%, 33%, 30% in (15,10,5) storeys buildings is more than response spectrum analysis. In general, it can be said that the values coming from the all parameters in equivalent static analysis are to most of the values of response spectrum analysis.

Structural Performance Comparison of Structural Systems Using LIRA and ETABS

This paper investigates a comparison of structural systems of high rise (96m of 30 stories) buildings subjected to gravity load and wind load of speed 90mph. Three structural systems, Moment frame system, Shear wall system, and Tube-in-Tube system of identical base area and loadings are structurally designed, in ETABS and LIRA software. Linear wind response analysis was carried out as per ASCE 7-05. Parameters like fundamental time period, Maximum story displacement, Maximum column axial load and Vertical floor displacement are considered in this study. As per the findings, the maximum story displacement is found to be within the allowable limiting value. Tube-in-Tube system shows a better performance from the other systems for minimizing the story displacement. The modal time period, vertical displacement and Maximum column axial load values are also minimum in Tube -in-tube system.

Masonry infill in structural analysis: effects on seismic performance

In structural analysis, masonry infill is commonly regarded as a non-structural component. However, understanding the true behavior of a structure requires incorporating the effects of masonry infill in seismic evaluations. This paper reviews the effects of masonry infill on seismic performance through analyses including pushover analysis, time history analysis, response spectrum analysis, linear static analysis, and eigenvalue analysis. Ten research papers were reviewed, covering different aspects of masonry infill effects on structures of varying configurations and seismic zones. Results indicate that including masonry infill reduces the fundamental time period of vibration and storey displacement while increasing the base shear compared to bare frame structures. This comprehensive review underscores the importance of considering masonry infill in structural analysis to enhance seismic performance.

Effect of Frequency Content of Earthquake Ground Motions on Structures with Varying Dimension

An earthquake is a catastrophe which is always a topic of concern for structural designers and civil technocrats. Not only it causes physical damage to the structures but also successful to impart psychological disorder in human minds for long-run. In order to mitigate the devastating effects of earthquake on society, it is eminent to study the dynamic characteristics in detailed manner i.e. to examine how the structure responds owing to the seismic characteristics. The various ground motion characteristic includes time-duration and velocity, frequency content and amplitude, displacement, incremental velocity and incremental displacement, peak ground accelerations (PGAs), etc. Out of these, effect of frequency content and maximum amplitude value of earthquake ground motions on the seismic response of structures is often underestimated. This paper investigates the effect of frequency content and maximum amplitude value on the seismic response of structures which is dominant of all characteristics. The study proceeds with recording time-history of acceleration obtained from conventional unidirectional harmonic shake table. Further, FFT (Fast Fourier Transform) analysis of applied time-history is done and the effect of frequency content and the maximum amplitude value of applied time-history on the seismic responses of structures is investigated and studied. For this, structures with varying dimensions (height, length, and width) are modelled and time-history analysis of structural models has been carried out in SAP2000v19. Seismic responses of analysed structures are represented in the form of fundamental natural frequency, storey displacement, and base shear. It is reported that out of many earthquake indices, frequency content and amplitude of earthquake ground motions are the most dominating. It is reported that the resonance phenomena occurs for the less height structure and thus it shows maximum displacement and base shear responses. Also, as height, length, and width of structure increases; displacement, base shear, and fundamental time-period of structure increases.

Seismic performance evaluation of masonry infill R.C. frame considering soil-structure interaction

The structural damage due to recent seismic events in Nepal has led to a dire need for studies considering soil-structure interaction (SSI) as the majority of designers still adopt conventional design principles. These damages may be the result of the conventional fixed base method’s failure to take into account the underlying soil properties. Post $$M_w$$ 7.8 Gorkha earthquake, revised Nepal National Building code NNBC 105:2020 has classified soil types based on the rigidity of the soil. A comparative analysis is carried out using linear-static and nonlinear static (Pushover) analysis considering the fixed and flexible base of a masonry infill RC frame. The seismic performance parameter evaluated for a target inelastic drift of 2% are in terms of their fundamental time period, peak floor displacement, inter-storey drift ratio (IDR), ultimate load carrying capacity and yield mechanism. The consideration of SSI drastically influenced the fundamental time period, peak floor displacement and IDR with decreasing rigidity of soil. The fixed base structure exhibited a higher ultimate load-carrying capacity than the flexible base structure for all soil types. The masonry infill dissipated the seismic energy by the failure of the majority of struts. Furthermore, the post-yield behaviour of all models highlighted that the damage level of RC frame and masonry infill elements were higher for fixed base.

Effect of Different Types of Bracing System and Shear Wall on the Seismic Response of RC Buildings Resting on Sloped Terrain

Several factors have been affecting the urban design areas, leading to the construction of reinforced concrete (RC) buildings. Buildings on sloped terrains have been gaining increased popularity, especially from architectural peers. The vulnerability of constructions to seismic loads on sloped terrains increases due to mass and vertical irregularity, which in turn increases the torsional moments as well as shear forces. To control the effect of the seismic loads, many systems have been implemented, including shear walls and bracing systems. The objective of this work is to evaluate the effects of different strengthening systems and to identify the most suitable one for seismic load resistance. This paper studies the behavior of buildings with different strengthening systems applied to seismic loads using ETABS V18.1 and response spectrum analysis. A parametric study for these buildings has been performed to evaluate the effect of seismic loads on them. A dynamic analysis of the buildings in terms of shear forces, displacement, drift, fundamental time period, base shear, and story stiffness was carried out. The results demonstrated that the use of a combined strengthening system increased the stiffness and stability of the models and the resistance of RC buildings to seismic loads on sloped terrains. Doi: 10.28991/CEJ-2022-08-09-014 Full Text: PDF

Modeling of opening for realistic assessment of infilled RC frame buildings

Openings provided to meet functional requirements are often neglected in analytical assessment of Un-Reinforced Masonry (URM) infilled Reinforced Concrete (RC) frame buildings, mostly due to unavailability of simplified comprehensive model to simulate its effect. Ignoring presence of opening in infills results unrealistic assessment of seismic response for these popular building typologies, as opening reduces the strength and stiffness of the composite frame. Several reduction factor models have been developed over the years to account effect of opening in infills. In the present study efficacy of five such models of opening have been investigated which can be used by design practitioners for simulation of opening with sufficient accuracy in predicting the response of composite frame. Extensive analytical study has been conducted on a set of mid-rise and high-rise Indian infilled RC frame buildings considering various realistic combinations of openings by varying size, shape of doors and windows. The study revealed that increasing opening in infills significantly affects the seismic performance, and consequent fragility thereby reduces lateral strength, stiffness, ductility, while increasing fundamental time period, overall deformation capacity and damage probability.