Framed Tube System Research Articles

An Analytical Study of Flat Slab and Convention Slab with Framed Tube System by Performing Time History Analysis

Abstract: To study seismic demand for regular reinforced concrete frame of flat slab with drop and conventional slab structure by using framed tube structural system by performing time history analysis. The performance of these slabs on 30 storey building will be studied for the analysis, seismic zone (v) will be considered. It is a type of linear dynamic analysis, in which the strength of the structure is tested within the elastic limit of the structure. In this project, high rise building of 30 of area 1296sq.m along with framed tube subjected to earthquake loading are analysed by time history analysis using ETABS software. The dynamic parameters such as base shear, story displacements, and story drift and time period of flat slab building with framed tube is being studied and compared to conventional slab. Keywords: High-rise building, Framed tube, Time history analysis

Study of different tubular systems on the lateral load resistance

Worldwide, high rise construction is recent trend in the building development. Steel has many advantages which includes flexible framing system, assembling, less weight to height ratio, high availability and it doesn’t harm environment. That’s the reason steel has been mostly used material in the high rise buildings. Previously gravity load was considered as an important factor in the construction design. With the demand of high rise buildings now seismic force and lateral force is also gaining more attention. In High rise buildings tubular frames are most commonly used structural system. Among this framed and bundled are most famous tubular frame systems. Precise analysis is required for its design. Tubular systems are used in exterior as well as interior, mainly for resisting seismic force and lateral force. In this research Framed tube system and bundled tube system is analysed for lateral load resistance using ETABS software. For analysis purpose 8 stories steel building was considered. Different factors like lateral displacement at top floor, base shear, storey drift and steel weight were analysed for framed and bundled tubular system.

Study of different tubular systems on the lateral load resistance

Worldwide, high rise construction is recent trend in the building development. Steel has many advantages which includes flexible framing system, assembling, less weight to height ratio, high availability and it doesn’t harm environment. That’s the reason steel has been mostly used material in the high rise buildings. Previously gravity load was considered as an important factor in the construction design. With the demand of high rise buildings now seismic force and lateral force is also gaining more attention. In High rise buildings tubular frames are most commonly used structural system. Among this framed and bundled are most famous tubular frame systems. Precise analysis is required for its design. Tubular systems are used in exterior as well as interior, mainly for resisting seismic force and lateral force. In this research Framed tube system and bundled tube system is analysed for lateral load resistance using ETABS software. For analysis purpose 8 stories steel building was considered. Different factors like lateral displacement at top floor, base shear, storey drift and steel weight were analysed for framed and bundled tubular system.

Investigating the behaviour of steel framed-tube and moment-resisting frame systems exposed to fire

This paper investigates the behaviour of two popular structural systems subjected to overheating and column removal cases, which may follow fire incidents. A typical 15–storey steel building is designed with two types of structural system framed-tube and moment-resisting frame. The nonlinear behaviour of these structures under different fire scenarios is investigated using OpenSees Software. The results indicate that deflection of heated beams is insignificant below 400 °C but after that, degrading mechanical properties of steel material leads to large deflection and runaway of heated beams at temperatures below 600 °C. Also, heating the beams of structures initially induces large axial forces in the beams due to restraints on thermal expansion. Thermal expansion of heated floors induces large horizontal displacement and consequently causes additional bending moments in the exterior column. So columns reach their elastic limit at the early stages of fire. Columns of the framed-tube system reach their elastic limit at lower temperatures (130 °C) but fail at higher temperatures (380 °C) compared to columns of the moment-resisting frame system (210 °C). In addition, the lower storey and interior columns are more vulnerable to progressive collapse and fail at lower temperatures (330 °C) due to carrying more gravity loads. In most fire scenarios, beams and columns of framed-tube systems fail at higher temperatures and perform well in the fire than moment-resisting frame systems. In column removal scenarios, mid-span displacement of the heated beam increases significantly, leading to downward movement of upper stories. Also, column removal in the framed-tube system is more destructive than in the moment-resisting frame system. In general, in both structural systems, column removal scenarios, which may follow fire, induce more damage to the structures than general temperature rise in considered fire scenarios.

An approximate approach for the natural frequencies of tall buildings with trussed-tube system

In this paper, a simple mathematical method, based on a continuous approach, is proposed to determine the natural frequencies and mode shapes of trussed-tube systems in tall buildings. Braces are modelled as transverse springs at specific locations along with the height of the structure. Framed-tube system is idealized as a cantilever beam, representing actual characteristics of the structure. Hamilton’s principle is used in deriving structure’s governing equation of motion. The resulting partial differential equation is then solved by applying the separation of variables method. Applying appropriate boundary conditions, natural frequencies and mode shapes are calculated. Finally, the applicability and accuracy of the solution are investigated through comparison with the results obtained from SAP2000 analysis of the full model. The proposed method is found to be simple and efficient and provides reasonably accurate results in preliminary analysis of tall building structures.

Evaluation of Shear Lag Index in High-Rise RC Buildings Having Exo-skeleton Structural System

Although framed tube system has been found to be the most efficient system for high-rise buildings, they could experience the shear lag effects which will result in nonlinear distribution of axial stress along the flange and the web of the cross-section of the tall building plan. Exoskeleton structure is generally found to be a self-supporting structural system set outside and suitably connected to a primary inner structure, the latter being enhanced or protected. In this article, by studying three types of concrete structures having 20, 30, and 40 stories with elevations of 80, 120, and 160 m, respectively, the effects of change in the location of openings on Exo-Skeleton structures on the shear lag phenomenon are investigated. The shear lag of the compression wing of the structural models, which are perpendicular to the lateral force application, was studied. Among the index related to the shear lag, two indexes of the shear lag index including the axial stress ratio of each element in the axis to the axial stress of the middle element and the axial stress ratio of the corner element to the tensile stress of the middle element derived from the structural analysis under load side effects were studied. It could be concluded that the most effective opening configuration with the greatest reduction in shear lag is proposed for structures with different aspect ratios.

Performance of Tubular Structure under Seismic Excitation

Advancement in the building construction technology and structural analysis the tall structures have been significantly increased due to over growing population and for land mark of country. The tall structures are more prone to lateral load. In this study different forms of tubular structure are used to resist the Earthquake forces. Tubular structures are made based on the idea that building is design to act like a hollow cylinder cantilever perpendicular to the grounds. The aim of this paper is to present the seismic performance of tubular structure with and without central core. The Framed tube system, Tube in tube system, Bundled tube system, Braced tube system and Moment resisting Frame was analyzed to draw the comparison on the basis of base shear, storey drift, time period and storey shear satisfying the structural codes- IS 456-2000, IS 1893(Part 1):2016 in E-TABs software by Response spectrum method.

Static analysis of tall buildings based on Timoshenko beam theory

In this paper, the continuum model, which is known as Kwan model, has been presented for the analysis of tall buildings that have been as an appropriate approximation of the overall behavior of the structure. Tall building was modeled as a cantilever beam and analyzed with the assumption of flexural behavior based on Euler–Bernoulli Beam Theory, then the displacement of floors was calculated. o consider the shear lag effects in the overall displacement of the structure, Timoshenko’s beam model has been considered and related relations were extracted. The lateral displacement formulas obtained and calculated for the framed tube system modeled by Kwan’s method. To verify the results, numerical models were created in software (ETABS) and statically were analyzed for lateral loading. Finally the results were compared with those obtained by computer analysis and the corresponding diagrams were presented. At the end, the shape factor formula has been developed to improve the results of the Timoshenko’s theory.

Reducing static roof displacement and axial forces of columns in tall buildings based on obtaining the best locations for multi-rigid belt truss outrigger systems

In this paper, energy method as a robust method has been used to compute the optimum locations of belt truss and outrigger systems. To achieve this aim, a tall building of constant stiffness along its height, reinforced with a framed tube, shear core and belt truss with outrigger systems has been considered. An equivalent cantilevered beam has been used to model the framed tube system. Here, outrigger–belt truss systems are modeled by rotational springs placed at their spatial position. Utilizing the energy method, belt truss systems are placed at particular positions along the structure’s height, selected so to maximize energy absorption and dissipation. Applicability and accuracy of the proposed method are verified via a numerical example (50-story concrete building) and the results are compared with Stafford Smith’s method. The proposed method demonstrated for several belt truss and outrigger systems a reduction in the values of the roof displacement and axial force in comparison with Stafford Smith’s method. The results show that the structure with two belt–outrigger systems has a better performance in reduction of roof displacement and axial forces (2.3% and 4% reduction, respectively) rather than the one- and three-belt truss systems.

The Effect of Soil around the Basement Walls on the Base Level of Braced Framed Tube System

According to the 2800 standard, the Iranian code of practice for seismic-resistant design of buildings, the base level refers to the level at which it is assumed that the horizontal movement of the ground is transmitted to the structure. In cases that there are reinforced concrete walls being run by an integrative structure in the underground perimeter, and the surrounding ground is dense and compressed, the base level is considered on the top of the basement wall. In tall structures, due to strong forces and moments at the foot of the structure, examining the location of base level and its movement becomes specially important. The aim of this study was to investigate the impact of changing the properties of the soil around the underground perimeter walls on the base level, taking into account the effects of soil-structure interaction systems. In this regard, the soil-structure system was investigated in two-dimensional models and the location of the base level was identified using shear and drift changes. The results indicated that taking into account the level of the upper stories is possible through performing appropriate walls integrated with the structure even without Compacting the soil around the structure.

STRUCTURAL SYSTEMS USED IN VERTICAL CITIES A REVIEW

Smart city mission in India promoted infrastructure development under various parameters like use of smart materials, smart villages, sanitation improvement, sustainable energy and many more. Introducing new vertical cities, iconic structures and use of multi-functional buildings in India is such a step ahead to achieve these parameters into reality. Vertical modern age buildings are already popular worldwide due to its advantages in terms of low consumption of area and multi-functional use. However, these buildings are subjected to intense loading due to wind, earthquake and therefore requires study to withstand safely against these complex forces and to achieve this, structural systems should be given top priority as it plays a vital role. This paper mainly focuses on the review of such structural systems which includes framed tube system, tube in tube system, bundled tube system, diagonalised-rigid system, outrigger system, shear walls, diagrid system which are usually used in high rise buildings, skyscrapers. Further study is done considering case studies of today’s top 5 skyscrapers in the world which are Kingdom tower Jeddah, Burj Khalifa Dubai, Taipei Tower Seoul, Shanghai Tower Shanghai and International Commerce Centre Hong Kong. Concluding remarks are made discussing advantages, disadvantages, comparison and suitability of these structural systems under the Indian context.

Two novel shear fuses in moment resisting frames

Based on the code specifications, in moment-resisting frames the span-to-depth ratio has to be larger than a minimum value to make sure of adequate plastic hinging at beam-ends. This provision poses a restriction on the use of deep beams with short spans, especially for the framed-tube system in tall buildings. In this paper, a new energy dissipation method is introduced for moment-resisting frames by modifying the mid-span of the beam by two different methods, resulting in: (i) Perforated Shear Links (PSLs) and (ii) Slit Shear Links (SSLs). The links dissipate energy through shear yielding of the web, weakened by perforation or slitting, respectively. A thorough study is conducted on the behavior of the proposed shear links through finite element models verified by test results. The rupture propensity of the models is evaluated by calculating and comparing Damage Index (DI) in various link rotations by post-processing the results of the finite element simulations. In this regard, the results show that the proposed systems can be employed in moment resisting frames with short spans to decrease rupture propensity by 43%. The suggested links can also be designed to be replaceable, making them ideal for repair and retrofit purposes which adds to the resiliency of structures and brings about a more sustainable construction.

Effect of Peripheral Wall Openings in Basement and Number of Basement Floors on the Base level of Braced Framed Tube System

For seismic design, the base is defined as the level at which the seismic ground motion is considered to be transferred on to the structure. Although there are many factors affecting the base level, for a typical building without a basement, the base is generally considered near the ground level. This study aims to examine the influence of both, peripheral wall openings in the basement and the number of basement floors, on the base level under near-field earthquakes, taking into account the effect of soil–structure interaction. To this end, five 2D metal-braced frame models with different number of floors and the soil around them were subjected to near-field earthquakes. The basement beams and columns were assumed to be buried within the peripheral basement wall. The results showed that where the opening was greater than 50%, the base level had to be considered one story lower than the ground level, thus, disregarding the effect of openings in high-rise structures could lead to non-conservative results. Moreover, it was concluded that in case the basement beams and columns were buried in the peripheral basement wall so as to provide sufficient stiffness, increasing the number of basement floors from 3 to 6 had little effect on the base level of the studied soil–structure system.

Determination of optimum location for flexible outrigger systems in tall buildings with constant cross section consisting of framed tube, shear core, belt truss and outrigger system using energy method

In this paper, based on maximizing the outrigger-belt truss system’s strain energy, a methodology for determining the optimum location of a flexible outrigger system is presented. Tall building structures with combined systems of framed tube, shear core, belt truss and outrigger system are modeled using continuum approach. In this approach, the framed tube system is modeled as a cantilevered beam with box cross section. The effect of outrigger and shear core systems on framed tube’s response under lateral loading is modeled by a rotational spring placed at the location of belt truss and outrigger system. Optimum location of this spring is obtained when energy absorbed by the spring is maximized. For this purpose, first derivative of the energy equation with respect to spring location as measured from base of the structure, is set to zero. Optimum location for outrigger and belt truss system is calculated for three types of lateral loadings, i.e. uniformly and triangularly distributed loads along structure’s height, and concentrated load at top of the structure. Accuracy of the proposed method is verified through numerical examples. The results show that the proposed method is reasonably accurate. In addition, for different stiffness of shear core and outrigger system, several figures are presented that can be used to determine the optimum location of belt truss and outrigger system.

A continuous–discrete approach for evaluation of natural frequencies and mode shapes of high-rise buildings

In this paper, a continuous–discrete approach based on the concept of lumped mass and equivalent continuous approach is proposed for free vibration analysis of combined system of framed tube, shear core and outrigger-belt truss in high-rise buildings. This system is treated as a continuous system (i.e., discrete beams and columns are replaced with equivalent continuous membranes) and a discrete system (or lumped mass system) at different stages of dynamic analysis. The structure is discretized at each floor of the building as a series of lumped masses placed at the center of shear core. Each mass has two transitional degrees of freedom (lateral and axial( and one rotational. The effect of shear core and outrigger-belt truss on framed tube system is modeled as a rotational spring placed at the location of outrigger-belt truss system along structure’s height. By solving the resulting eigen problem, natural frequencies and mode-shapes are obtained. Numerical examples are presented to show acceptable accuracy of the procedure in estimating the fundamental frequencies and corresponding mode shapes of the combined system as compared to finite element analysis of the complete structure. The simplified proposed method is much faster and should be more suitable for rapid interactive design.

Optimum Location of Outrigger-belt Truss in Tall Buildings Based on Maximization of the Belt Truss Strain Energy

A B S T R A C T In this paper, based on maximizing the outrigger-belt truss system’s strain energy, a methodology for determining the optimum location of an outrigger-belt truss system is presented. Tall building structures with combined systems of framed tube, shear core and outrigger-belt truss system are modeled using continuum approach. In this approach, the framed tube system is modeled as a cantilevered beam with box cross section. The effect of outrigger-belt truss and shear core system on framed tube’s response under lateral loading is modeled by a rotational spring at the outrigger-belt truss location. Optimum location of this spring is obtained when energy absorbed by the spring is maximized. For this purpose, first derivative of the energy equation with respect to spring location as measured from base of the structure, is set to zero. Optimum location for outrigger-belt truss system is calculated for three types of lateral loadings, i.e. uniformly and triangularly distributed loads along structure’s height, and concentrated load at top of the structure. Accuracy of the proposed method is verified through numerical examples. The results show that the proposed method is reasonably accurate.

Performance-based evaluation of tall buildings using advanced intensity measures (case study: 30-story steel structure with framed-tube system)

SUMMARY Performance assessment of high-rise buildings has attracted peculiar attention among engineers. Care should be taken once higher-mode effects are to be incorporated into analyses and designs. Recently, performance-based evaluations have been widely used by designers to meet the required target capacities of engineering projects. A common tool to perform such studies is incremental dynamic analysis (IDA), which has been utilized for first-mode-dominant ordinary structures, whereas taller buildings demand other considerations to be made so that a thorough assessment of the structural response can be achieved. In this paper, performance-based studies have been carried out for a sample 30-story tall building, which takes advantage of tubular frame as lateral-load-resisting system. IDA is performed subsequently to quantify the structural response against a wide-range of seismic loadings. Advanced intensity measures (IMs) are applied to optimize the capacity assessments resulting from multitude of non-linear time-history analyses. Finally, performance-based evaluations have been carried out to provide a thorough assessment of target capacities that are normally advised by widely accepted codes. Results are also compared with regular short buildings where higher-mode effects do not contribute significantly to structural response. Copyright © 2012 John Wiley & Sons, Ltd.

Parametric stress distribution and displacement functions for tall buildings under lateral loads

SUMMARYIn this study, effects of applying higher order axial displacement distribution to solve a continuum model for static analysis of the combined system of framed tube, shear core and outrigger–belt truss system in high‐rise buildings are investigated. Framed tube system is modeled using an orthotropic box beam analogy approach and the interaction between shear core and outrigger–belt truss system on framed tube is modeled with rotating spring placed at outrigger–belt truss location. The axial displacement distributions in web and flange panels along structure's height are proposed to be fifth‐order and fourth‐order polynomials, respectively. Analytic analyses are carried out on the basis of the principle of minimum potential energy. A detailed work is carried out through two numerical examples and the accuracy of proposed approximation functions is compared with previous work and finite element analysis. Results demonstrate that the proposed parametric stress distribution and displacement functions are more accurate than previously proposed functions in comparison with the finite element solution. Copyright © 2012 John Wiley & Sons, Ltd.

Simple Analysis of Framed-Tube Structures with Multiple Internal Tubes

A framed-tube system with multiple internal tubes is analyzed using an orthotropic box beam analogy approach in which each tube is individually modeled by a box beam that accounts for the flexural ...

Correlating dynamic characteristics from field measurements and numerical analysis of a high-rise building

Using the concept of lumped masses and rigid floor slabs, several mathematical models were built using a popular PC-based finite element program to model a tall building with a frame-core wall structural system. These models were analysed to obtain the first nine mode shapes and their natural frequencies which were compared with those from field measurements, using numerical correlation indicators. The comparison shows several factors that can have a significant effect on the analysis results. Firstly, outriggers connecting the outer framed tube system to the inner core walled tube system have a significant effect on fundamental translational mode behaviour. Secondly, detailed modelling of the core considering major and minor openings as well as internal thin walls has the strongest influence on torsional behaviour, whose measurements were shown to be an important aspect of the dynamic behaviour for the structure studied. Fine tuning of an analytical model requires not just considering variation in values of structural parameters but also attention to fine detail. Copyright © 2000 John Wiley & Sons, Ltd.