Story Levels Research Articles

A quantitative classification criterion for beam-to-column rigid connections in steel braced frames

As the key part of the force-transfer path in a steel frame, a reasonable modeling method of beam-to-column connections in the structural analysis model is crucial. From the designer’s perspective, a rational and accurate classification of beam-to-column connections is an invaluable basis for improving modeling efficiency and design accuracy. Although some investigations led by Eurocode 3 (EC3) have provided a systematic and quantitative approach for classifying beam-to-column connections, it is not sufficiently developed for general steel braced frames. In this paper, based on a modified analytical model of the beam-to-column connection substructure that accounts for the effect of braces, the rotational stiffness demand of the beam-to-column rigid connection is derived from the perspectives of structural lateral stiffness and stability. The quantitative relationship is established between the rotational stiffness demand and the relative stiffness of the braces. The accuracy and reasonability of the proposed analytical model and stiffness demand are verified using finite element models (FEMs) at both the story and structure levels. Particularly, the effect of the non-linear behavior of beam-to-column connections on the structural response under high-intensity earthquakes is further comparatively analyzed in the context of seismic design. The results demonstrate that, a beam-to-column connection can be modeled as a continuous rigid connection in non-linear analysis only if it simultaneously satisfies the following requirements: the rotational stiffness meets the demand proposed in this study, and the bending capacity is designed to be overstrength compared to the beam cross-section.

The Influence of Open-Ground Floors on the Impact of RC Columns Due to Seismic Pounding from Adjacent Lower-Height Structures

The substantial influences of masonry infills used as partition walls on the seismic behavior of multistory reinforced concrete (RC) structures have long been recognized. Thereupon, in this study, considering open-ground floors due to a lack of infills (pilotis configuration), the structural pounding phenomenon between adjoining RC buildings with unequal story levels and unequal total heights is investigated. Emphasis is placed on the impact of the external columns of the higher structure, which suffer from the slabs of adjoining shorter buildings. The developing maximum shear forces of the columns due to the impact are discussed and compared with the available shear strength. Furthermore, it is stressed that the structures are partially in contact, as is the case in most real adjacent structures; therefore, the torsional vibrations brought about due to the pounding phenomenon are examined by performing 3D nonlinear dynamic analyses (asymmetric pounding). In this study, an eight-story RC frame structure that is considered to be fully infilled or has an open-ground floor interacts with shorter buildings with ns stories, where ns = 6, 3, and 1. Two natural seismic excitations are used, with each one applied twice—once in the positive direction and once in the negative direction—to investigate the influence of seismic directionality on the asymmetric pounding effect. Finally, from the results of this study, it is concluded that the open-ground story significantly increases the shear capacity demands of the columns that suffer the impact and the inelastic rotation demands of the structure, whereas these demands further increase as the stories of the adjoining shorter building increase.

Critical Egress Parameters Governing Assisted Evacuation in Hospital Buildings

This paper presents the critical egress parameters that influence emergency evacuation in a typical hospital building. A parametric study of a 20-story hospital building is conducted using a computer model “Pathfinder” to simulate the evacuation efficiency and assess the influencing parameters. The main egress parameters that influence the evacuation efficiency, including the location of stairways, number of stairways, location of the fire, exit width, and number of low-speed occupants are varied. Two scenarios are simulated: one being the regular (practice) evacuation drill and the other is the actual fire drill. The result shows that the location of stairways significantly affects the total evacuation time with the optimal stairway arrangement consisting of one stairway outside the core of the building. Similarly, the story level at which the fire occurs is another key parameter with fires at lower levels being critical to dictating the evacuation time in a hospital building. The total evacuation time when the fire occurs between the third and sixth floor is found to be 170 min which is 36% and 15% higher than fires at the top story levels (15–18th floor) and the intermediate story levels (9–12th floor), respectively.

Asymmetric seismic pounding between multistorey reinforced concrete structures in a city block

Usually within city blocks land ownerships are not equal and exhibit various geometries. Therefore, it is most probable adjacent structures to be partly and in an asymmetric way in contact. Consequently, buildings asymmetrically restrained in lateral displacements during earthquake excitations carry out torsional oscillations. The interaction of an 8-storey reinforced concrete frame building designed according to Eurocodes with an adjoining structure for various parameters is thoroughly investigated. The 8-storey frame is considered with pilotis configuration and fully infilled whereas the other structure is studied for the cases of 6-stories, 3-stories and single storey. Further the two interacting structures form an L-shape plan and are studied for three cases of asymmetric contact, whereas two natural seismic excitations each one applied in two directions (positive – negative). Thereupon, for the thorough study of the problem more than 100 pounding pairs for structures having equal storey levels (floor-to-floor pounding) and 100 pairs for structures having unequal storey levels (floor-to-column or interstorey pounding) have been investigated. The whole study highlights crucial aspects of the issue such as the unfavourable role of pilotis configuration, the significant torsional vibrations induced and the almost inevitable shear failure of columns that suffer an impact by an adjacent building within their deformable height.

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.

Performance evaluation of high-rise reinforced concrete buildings under dynamic loading considering different structural systems

With the growing construction of towering structures owing to modernisation and growth in land use, tackling the height and stiffness concerns are now essential. Several structural systems have been developed to withstand various loading scenarios, including framed systems, shear wall systems, braced framed systems, outrigger systems, and diagrid systems. The present investigation employs E-tabs software to accomplish dynamic analyses on a G + 16 story RCC building with regard to every structural system. The variables studied were base shear values, storey shear force values, maximum displacement values, maximum storey drift values, stiffness of storey levels, and time periods. The major goal was to find the most appropriate system among those examined. This study can add to our knowledge concerning building dynamics and helps to make well-versed assessments about prospective high-rise constructions and the findings can be useful in the design of high-rise structures. After accomplishing the study, it was demonstrated that for numerous response parameters, the diagrid structural system proved to be the most successful in managing lateral forces, functioning similarly to the shear-walled model. The diagrid structural system's efficiency in optimising stability and resistance against dynamic loads demonstrates its potential for improving the safety as well as the performance of these structures. Finally, the diagrid system offers potential as a feasible high-rise building choice, providing an efficient and effective response to the issues faced by urbanization-driven vertical expansion.

Performance-based system reliability analysis for steel moment frames

This study aims to bridge the gap between two major design philosophies in structural design: load and resistance factor design (LRFD) and performance-based design (PBD). While LRFD prioritizes the design of structural members, PBD starts by controlling the system's target parameter. The main area for improvement of LRFD is paying attention to the structure's performance. At the same time, PBD needs to pay attention to the sufficiency of internal members in the presence of local damages. To bring these two attitudes closer together, the study proposes a system-reliability-performance-based design analysis to simultaneously measure the entire structure's safety level associated with the reliability of elements. As a state-of-the-art, new performance-based limit state functions are introduced to measure structural reliability indices corresponding to desired performance levels. Multi-story frames were designed and evaluated based on incremental dynamic analysis. The entire structure was designed and controlled using the linear static analysis method, and static and dynamic nonlinear analyzes were performed to evaluate its behavior. Dynamic analysis of acceleration mapping was also performed to investigate the performance of the structural components. The proposed combined design algorithm aims to develop a new set of performance-based load combinations and provide a strong interlock between LRFD and PBD. The study's results show that the IO level has the lowest performance-based system reliability index, while the CP level has the highest. It was observed that as the number of story levels increases, the performance-based system reliability index decreases due to an upsurge in the possibility of failure patterns. Therefore, the current LRFD practices are unlikely to provide the IO's perfect reliable level for the entire system. The study concludes that the new approach can enhance the safety of structures and prevent catastrophic failure.

Investigating the effectiveness of a CRM system: full scale reverse cyclic tests on a two-storey rubblestone masonry building

The research work aims at investigating the effectiveness of a minimally invasive strengthening technique used to repair a full scale two-storey building, consisting of 350 mm thick two-leaf rubblestone masonry walls, a timber floor, and a timber roof with clay tiles. The strengthening technique consists in applying on the external façade of the building a single layer of a Composite Reinforced Mortar (CRM) System, which consists in a mortar coating containing a Glass Fiber Reinforced Polymer (GFRP) mesh; artificial diatons connecting both wythes of the walls were also applied. The reverse cyclic load was applied to each of the two longitudinal walls of the building by means of a servo-controlled hydraulic jack pinned to a vertical steel beam. This beam allowed splitting the total lateral force into two forces, acting at first story and roof levels; these forces were calculated proportional to the product of the floor mass with the floor level.The first cyclic test was carried out on the Unreinforced Masonry (URM) building up to attaining a damage level quite close to that corresponding to the ultimate limit state of the structure. Then, the building was repaired (RM) with the proposed technique and tested again, up to reaching a near-collapse condition. The experiments proved the effectiveness of the proposed strengthening method showing a resistance increment of 240%, a larger displacement capacity (150%) and a significant increase of the total dissipated energy. The importance of the artificial diatons to prevent the separation of the masonry leaves in strengthened walls was also clearly highlighted.

Probabilistic assessment of SMRFs with infill masonry walls incorporating nonlinear soil-structure interaction

Infill Masonry Walls (IMWs) are used in the perimeter of a building to separate the inner and outer space. IMWs may affect the lateral behavior of buildings, while they are different from those partition walls that separate two inner spaces. This study focused on the seismic vulnerability assessment of Steel Moment-Resisting Frames (SMRFs) assuming different placement of IMWs incorporating nonlinear Soil-Structure Interaction (SSI). The aim is to explore the damage states of IMWs and use their ability for improving the vulnerability of SMRFs. For this purpose, the three, five, seven, and nine story levels (3-Story, 5-Story, 7-Story, and 9-Story) SMRFs were modeled considering four soil types. Incremental Dynamic Analyses (IDAs) were performed to determine the seismic performance limit-state capacities of SMRFs considering the Far-Fault (FF) record subset suggested by FEMA P695. To accurately model the influence of IMWs on the seismic response of SMRFs, a Tcl programming algorithm was developed to intelligently monitor the damage states of IMWs in each floor level. Results of the analysis show that assuming different placement of IMWs can significantly increase the seismic limit-state capacities of SMRFs with and without considering SSI effects. In addition, IMWs can play a crucial role to improve the seismic performances as well as the seismic collapse probability, which may be suggested for retrofitting purposes.

Investigation of the Effects of Different Types of Traditional Timber Load-Bearing Systems Used in Turkey on Building Behaviour

Recently historic timber structures in Turkey are unfortunately not given the value they deserve. Although timber structures are unique symbols of our cultural heritage, they are forgotten for natural and human reasons. On the other hand, when traditional timber structures standing today to repairs and / or reinforcements and restorations are examined, it is seen that timber elements according to the knowledge and skill of construction foreman are constructed with different types of structural systems. This matter reveals that choosing the right timber structural system is very important. This study the effects of their behaviour of traditional timber structural systems of different types widely used in the construction of timber structures in Turkey were comparatively examined. With this purpose, teen different structural system models with the Sta-stell program of the timber-framed (with Çatkı) Safran mansion which is widely used in Turkey were created and the findings were compared with each other by carried out structural analyses. The findings obtained reveal that buttresses are important in meeting, distributing and transferring the loads acting on the structural system, especially earthquake loads, to the foundation and the displacement distributions in the storey levels of the buttressed building models are less. In addition, the findings obtained show that buttresses that increase the lateral rigidity of timber structures increase the performance of the structure in question and reduce the internal forces of the structural elements. Turkey's widely used timber structural systems (in accordance with the Safran mansion architecture, which received the best restored mansion award) were modelled and analysed. The results presented are aimed to design recommendations and better understanding of the behaviour of different timber structural systems in today’s architectural practice.

Benefits of Backstay Effect in Design of Podium Structure for Tall Building as Per IS 16700:2017

In a multi-functional tall building, generally the building has a more extensive plan area and higher lateral resistance at the lower story level than the above story levels. So, the scope of this study is to understand the realistic behaviour of such structures under lateral loads considering the backstay effect as per IS: 16700(2017). The present work focus on the effect of podium structure of single tower structure connected by a common podium at the interface level under seismic load. For this purpose, the simulation model with varying tower height and podium height is created in the ETABs and it is analysed for the equivalent static and response spectrum method. In this study, the effect on the top displacement of the tower connected with podium structure under equivalent static and response spectrum method of analysis is observed. The backstay forces that are developed to resist the lateral overturning actions at the interface when the lateral horizontal forces are transferred from the tower to the podium are studied. The unfavourable effect of podium on the shear force distribution at and above the interface level of the structural wall is observed. The positioning of the tower on the podium structure is found to be the reason for the differential displacement between the structural walls.

Comparative Study on Dynamic Response of Buildings with Floating Columns

High-rise buildings are essential for providing the necessary space for both residence and offices due to the lack of large areas in an urban setting. However, these multi-storey buildings are prone to lateral loads such as earthquake loads due to their large mass. Often, columns of such multi-storey buildings are truncated at some level either due to some obstructions or some architectural restrictions. Such columns that do not directly rest on the foundation are called floating columns. The floating columns are generally considered harmful, especially for buildings constructed in seismically active areas. Their existence creates a discontinuity in the path to transfer the load resulting in an inadequate structure performance. Hence, this study focuses on reducing the risk factor due to seismic effects by strengthening buildings with floating columns using the shear walls, bracings, and masonry infills. A typical building with floating columns located at two different seismic zones was considered for the study. This building was strengthened by considering various approaches such as diagonal bracings, shear walls and infill walls. The equivalent static method is used in the study to carry out the seismic analysis. The results indicate that using any strengthening methods mentioned above can significantly reduce storey displacements. However, providing a shear wall is found to be more effective in reducing the storey displacements in both the directions of earthquake forces when compared with other methods. Though infills and bracings can reduce storey drifts, it was also found that at lower storey levels, there is a considerable increase in the storey drifts when bracings and infill walls are considered. This is mainly attributed to the presence of the open first storey. However, the storey drift values reduce at the higher levels.

Damage detection at storey and element levels of high-rise buildings: a hybrid method

Damage detection at storey and element levels of high-rise buildings: a hybrid method

Seismic response reduction of high rise steel-concrete composite buildings equipped with base isolation system

This study presents the effectiveness of the high-rise multi-storey buildings in reducing the seismic response induced during the earthquake events with the implementation of the Base Isolation system. For this, two base-isolated steel–concrete buildings are considered for the analysis having twelve and fifteen storey levels. The lead rubber bearing isolators are used for providing the base isolation system for these buildings. For the sake of comparison of the seismic responses of composite base-isolated buildings, their fixed base Reinforced Concrete and Composite counterparts are also modelled. The Seismic responses are evaluated by performing the response spectrum method for the highest seismic zone as per Indian Code. The results of the study indicate that that base isolation provided with the lead rubber bearing isolators is effective in reducing the overall seismic responses of the composite buildings in the range of 50% - 60%. The effectiveness of the base isolation is more in the case of 15 storeyed building. The reduction of approximately 50% is found in the storey drift and displacements of the base isolated composite building in comparison to reinforced concrete building.

Seismic demands of structural and non-structural components in self-centering precast concrete wall buildings

Self-centering (SC) precast concrete wall structures have been developed as an earthquake resilient structural system characterized by low structural damage and controllable residual drift. Despite the superior structural performance, harmonizing to seismic performance between structural and non-structural components is expected to be considered for further comprehensive performance assessment. This paper extensively evaluates the seismic demands of structural and non-structural components, especially for those sensitive to accelerations in SC precast concrete wall structures. Factors considered include building heights, earthquake ground motion types and intensities, energy dissipation, as well as base rocking, and impact against the foundation. The seismic demands of SC precast concrete walls are firstly compared with conventional reinforced concrete (RC) walls by nonlinear time history analysis (NTHA) in terms of displacement and acceleration responses. Then, attention is focused on investigating the dominant factors for the seismic demands of acceleration-sensitive non-structural components in SC precast wall structures through floor response spectrum analysis and parametric analyses. The results confirm that the SC precast walls exhibit excellent lateral response, especially with limited residual drifts. However, for the floor acceleration response, which is highly related to the demands of non-structural components, the results show that higher modes have a critical influence on SC precast wall structures. It also indicates that the floor acceleration response of SC precast wall structures is strongly influenced by the location of the story levels but not strongly influenced by the base rocking impact and energy dissipation capability.

Effect of Backstay on Tall Structure with Podium Structure

In a multi-functional tall building, generally the building has a more extensive plan area and higher lateral resistance at the lower story level than the above story levels. So, the scope of this study is to understand the realistic behavior of such structures under lateral loads considering the backstay effect as per IS: 16700(2017). A Sensitivity Analysis was performed as per IS: 16700(2017) provisions by considering the stiffness parameters given in code to understand the changes in the shear force distribution among structural elements when the tower and Podium are modeled together. The changes in the force distribution are compared with the structure without the backstay effect. At the podium-tower interface level, the amount of backstay forces developed is also presented in this paper, along with the impact on backstay forces with changes in the lateral resistances by changing floor diaphragm thickness and by changing the podium area.

Blast Vulnerability of Multi-Storey Masonry Infill Reinforced Concrete Frames

The prototype or experimental study of blast effect on structures is not always possible due to high risk of life and environmental wellbeing. However, advancement in computational science had made it possible to solve such complex and risky problems. Researchers in the past few decades have presented ample computational and numerical studies on blast effect on masonry structure using deterministic approach. The studies have neglected the effect of various uncertainties that may perhaps occur during an actual blast scenario. Therefore, in present study probabilistic Finite Element (FE) analysis was performed on three statistically stable masonry infill RC (Reinforced Concrete) frames having single (G+0), two (G+1) and three (G+2) storey levels respectively to arrive at the blast fragility curves. The probability of failure was computed based on the inelastic tension damage curves developed for the masonry. The effect of scaled distance and different storey levels on blast vulnerability of masonry infill RC frame walls are investigated through these fragility curves. The results indicate a noteworthy effect of scaled distance and storey levels on the blast resistance of the structure. Frame G+0 is found to be comparatively more vulnerable against the blast load effect than other multi-storey frames. The critical value of scaled distance (Z_critical) corresponding to PF 90% in panel P1 was found as 6.67m/kg^1/3, 4.81m/kg^1/3 and 4.66m/kg^1/3 respectively of frames G+0, G+1 and G+2; in panel P2 was found as 4.3m/kg^1/3 and 4.6m/kg^1/3 respectively of frames G+2 and G+3 and; in panel P3 was found as 4.32 m/kg^1/3 of frame G+3. It is also observed that RC frame is negligibly affected with respect to the masonry panel in terms of blast load mitigation.

Comparative seismic RISK assessment of existing RC buildings using seismic vulnerability index approach

The implementation of seismic risk management is becoming increasingly important all over the world, and especially in East-Asia as the structures aging surpass. In this context, three existing reinforced concrete buildings located in Malaysia have been selected for seismic vulnerability assessment. This work aims to apply the Seismic Vulnerability Index (SVI) via a Non-Linear Parametric Analysis (NL-PA) for each of the 3 RC existing buildings having different storey levels and clusters; low-rise (BLR), mid-rise (BMR), and high-rise (BHR). This approach can be achieved by undertaking a NL-PA as an analytical strategy instead of the empirical approach, which relies primarily on physical vulnerability parameters, earthquake-resistant design (ERD), and engineering demand parameters (EDP) by simulating a set of seismic records that can define the fragility features. The assessed SVI values for three different clusters of buildings are obtained for Far-Field (FF) and Near-Field (NF) seismic scenarios. With regards to the non-linear static analysis (NL-SA), the SVI values interact very well with the findings acquired from the NL-DA which are in good compliance with the low-rise building, in contrast for the two mid- and high-rise buildings. According to the obtained probabilistic vulnerability curves, the reference buildings are classified to be in D2 and D3 damage grades with dominancy of D3 level for the mid-rise and high-rise structures.

Experimental and numerical study on the deflection of multi-storey light-frame timber shear walls

This study aims at investigating the deflection behavior of multi-storey shear walls, including the effect of the diaphragm out of plane stiffness. Two-storey half-scale light-frame shear walls were investigated experimentally and numerically. Each level was loaded separately in order to isolate the effect of load transfer and deformation from one level on the other. The study shows that the deflection estimated based on the cumulative effect assumption was reasonably close to that observed in the experimental study, when no consideration for the floor diaphragm’s out of plane stiffness was included. It was observed that the majority of the cumulative effect stems from the rigid body rotation due to deformation in the hold-down devices. Results from a numerical model showed that the assumption of cumulative effects due to rigid body rotation is valid for stacked shear walls when consideration for the floor diaphragm’s out-of-plane stiffness is not included. The design expression showed a slight tendency to over-estimate the deflection especially at higher storey levels. The results of investigating the effect of the diaphragm’s out of plane stiffness showed that a significant reduction in the shear wall deflection. Diaphragm supported on multiple wall panels was found to further reduce the deflection of the shearwalls.

WITHDRAWN: Earth quake analysis of regular and irregular structures for all the soil types in seismic zone V

Abstract There has been a remarkable advancement in the research on design in the scope of engineering in the last couple of decades. There are many studies that contribute to better performance of buildings. Herein, to understand the seismic effects on a building when one of the design parameters is varying while others remaining constant, this study is conducted. The lateral forces at different levels of a structure in seismic zone V in all of the soil types are studied. The seismic loading with a varying soil conditions in the seismic zone is applied on all the structures. Both regularly and irregularly planned buildings are incorporated which are of varying heights (G + 3, G + 6, G + 9, and G + 12). The structure’s response in terms of lateral forces at all storey levels is analyzed varying the parameters. While the pattern observed is similar in regular and irregular cases, the soft soil type had higher storey shear when the storey levels increased.