Framed Tube Research Articles

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.

Research on Mechanical Behaviour of High-rise Diagonal Grid Tube Structure and Case study

In order to obtain the mechanical characteristics of high-rise diagonal grid tube structure under horizontal and/or vertical loads, three types of structure model, which were diagonal grid tube structure, diagonal grid–frame tube and framed tube structure, were established by the finite element software Etabs. The laws of internal force distribution, interstory displacement, base shear and shear hysteresis effect, were analysed deeply. The results from three-model showed that compared with the framed tube structure, the diagonal grid tube structure had the larger stiffness and the shorter period. Under the horizontal seismic load, the total shear force of the diagonal grid tube structure improved 20% by that of the conventional framed tube structure, with the interlayer shear force and the interlayer displacement angle distribution keeping basically the same. The inclining column to the diagonal grid structure could enhance the lateral stiffness in its plane effectively, but hardly improve the lateral stiffness out of its plane. Then, the performance under the vertical load was also discussed. Under the action of the vertical load, the shear hysteresis effect appeared, especially for the flange inclined column. Subsequently, the feasibility of the diagonal grid tube in the engineering projects was evaluated. The finite element software ABAQUS was used to analyse the dynamic elastoplastic time history performance of a one-way oblique grid system high-rise building under rare earthquakes. The results showed that the maximum interlayer displacement of the structure was less than the limit of Chinese codes and standards, and the structure could achieve the goal of anti-seismic fortification without collapse under strong earthquakes. There was a conclusion that the diagonal grid tube could be applied as a part of the overall structure for high-rise or super-tall buildings in the zones with seismic design intensity of 7 degree.

Experimental and numerical study regarding a fabricated CFST frame composite wall structure

This paper presents fabricated concrete-filled steel tube (CFST) frame sandwich-insulation composite wall structures, which comprise CFST columns, H-shaped steel beams and a sandwich-insulation composite wall with or without openings. The seismic behaviors of four full-size specimens were investigated under low-cyclic loading, including the failure mode, hysteretic behavior, strength, ductility, strength and stiffness degradation, energy dissipation capacity and strains. The experimental results indicated that the proposed fabricated structures had good seismic behavior. The fabricated composite wall had a significant effect on the bearing capacity of the structures and the stiffness and energy dissipation capacity. The ductility of the fabricated CFST frame sandwich-insulation composite wall structure can meet the requirements of the elastic-plastic inter-story drift limit of seismic design in practical engineering. Although the tested structures had the same opening ratio, the structure with window openings had better seismic performance than the structure with door openings. Furthermore, the equivalent compression strut model was used to calculate the bearing capacity of the proposed structures. The errors between the test and calculation results were within 10%. The equivalent compression strut model can provide useful design guidance for fabricated CFST frame sandwich-insulation composite wall structures.

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.

Experimental study of the lateral performance of a steel stud wall with a semi-rigid connected frame

Recently, a new type of lightweight steel structural system has been developed: a steel stud wall with a semi-rigid connected frame. The lateral resistance of this system was investigated in this study. Eight tests were conducted on seven steel stud walls with steel frames and one with a semi-rigid frame. The specimens were subjected to cyclic loading. The failure process, bearing capacity, stiffness, and energy dissipation capacity of each specimen were compared and analyzed. Test results showed that the steel stud structure significantly improved the lateral bearing capacity and stiffness of the semi-rigid steel frames, resulting in good hysteretic behavior and energy dissipation capacity. Reducing the spacing or increasing the section of vertical steel tubes can improve bearing capacity and stiffness, but only slightly influences the structure’s energy dissipation capacity. An excessive number of welded joints will increase welding residual stress and residual deformation, decreasing the lateral resistance of the structure due to the thinness of the square steel tube. The oriented strand board contributes considerably to the bearing capacity and stiffness of the structure, and is thus an important load-bearing component of the steel stud wall. The energy dissipation performance and ductility of the structure are mainly provided by the square steel tube and semi-rigid steel frame. In addition, the “pinch” phenomenon of the hysteretic curve is mainly caused by the cover board.

A new approach for free vibration analysis of nonuniform tall building structures with axial force effects

SummaryDynamic analysis of beam‐like structures is significantly important in modeling actual cases such as tall buildings and several other related applications as well. This article studies free vibration analysis of tall buildings with nonuniform cross‐section structures. A novel and simple approach is presented to solve natural frequencies of free vibration of cantilevered tall structures with variable flexural rigidity and mass densities. These systems could be replaced by a cantilever Timoshenko beam with varying cross‐sections. The governing partial differential equation for vibration of a nonuniform Timoshenko beam under variable axial loads is transformed with varying coefficients to its weak form of integral equations. Natural frequencies can be determined by requiring the resulting integral equation, which has a nontrivial solution. The presented method in this study has fast convergence. Including high accuracy for the obtained numerical results as well. Numerical examples including framed tube as well as tube‐in‐tube structures are carried out in the study and compared with available results in the literature, and also with the results obtained from finite element analysis in order to show the accuracy of the proposed method in the study. Obtained results indicate that the presented method in this study is powerful enough for the free vibration analysis of tall buildings.

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

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

Energy Partition between Ion and Electron of Collisionless Magnetic Reconnection

Abstract The plasma heating during collisionless magnetic reconnection is investigated using particle-in-cell simulations. We analyze the time evolution of the plasma temperature associated with the motion of the reconnecting flux tube, where the plasma temperature is defined as the second-order moment of the velocity distribution function in the simulation frame/in the center of the flux tube frame, and we show that the plasma heating during magnetic reconnection can be separated into two distinct stages: the nonadiabatic heating stage, in which the magnetic field lines are just reconnecting in the X-type diffusion region, and the adiabatic heating stage, in which the flux tube is shrinking after two flux tubes merge. During the adiabatic heating stage, the plasma temperature T can be approximated by TV γ−1 = const., where γ = 5/3 is the specific heat, and V is the volume of the flux tube. In the nonadiabatic heating stage, we found numerically that the ratio of the increment of the ion temperature to that of the electron temperature can be approximated by , where m i and m e are the ion and electron masses, respectively. We also present a theoretical model based on a magnetic-diffusion-dominated reconnection to explain the simulation result.

Seismic response tests and analytical assessment of blind bolted assembly CFST frames with beam-connected SPSWs

This paper presents a series of experimental and analytical studies to investigate the seismic behavior of blind bolted assembly concrete filled steel tube (CFST) frames with infill steel plate shear walls (SPSWs) connected to beam only. Two specimens of single-bay, two-story blind bolted assembly CFST frames with beam-connected SPSWs were fabricated and tested under lateral cyclic load combined with a constant vertical axial load. The test parameters include the column section type, the beam-SPSW connection type and the SPSW setting. Typical failure modes of the specimens were summarized and discussed. The test results show that the presence of SPSWs can compensate effectively the relatively small lateral stiffness of bare blind bolted CFST frames, and the novel SPSW-frame system exhibited good hysteretic performance, ductility and energy dissipation capacity. Moreover, the moments at the beam ends of a CFST frame with semi-rigid joints under two partial vertical loads resulting from the beam-connected SPSWs are derived. A practical design method for semi-rigid CFST frames with beam-connected SPSWs is summarized for checking the strength of blind bolted end plate joints, steel beams and CFST columns. The accuracy of the design method is also verified by the test results. The study shows that the novel SPSW-frame has good potential for application in earthquake resistant design of steel frame structures.

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.

Damage Detection of Concrete-Filled Square Steel Tube (CFSST) Column Joints under Cyclic Loading Using Piezoceramic Transducers.

Concrete-filled square steel tube column (CFSSTC) joints are the most important parts of concrete-filled steel tube frame structures. It is of great significance to study the damage of CFSSTC joints under the seismic loads. In this paper, embedded piezoceramic transducers are used to monitor the damage of core concrete of CFSSTC joints under cyclic loading and surface-bonded piezoceramic disks are used to monitor the debonding damage of the steel tube and core concrete of two specimens. The damages of the joints under different loading levels and different loading cycles are evaluated by the received signal of the piezoceramic transducers. The experimental results show that the amplitude of the signal attenuates obviously with the appearance of damage in the joints, and the degree of attenuation increases with the development of the damage. The monitoring results from piezoceramic transducers are basically consistent with the hysteresis loops and skeleton curves of the CFSSTC joints during the cyclic loading. The effectiveness of the piezoceramic transducers are verified by the experimental results in structural health monitoring of the CFSSTC joint under cyclic loading.

Seismic Behavior Investigation on Blind Bolted CFST Frames with Precast SCWPs

To explore seismic behavior of blind bolted concrete-filled steel tube (CFST) frames infilled with precast sandwich composite wall panels (SCWPs), a series tests of blind bolted square CFST frames with precast SCWPs under lateral low-cyclic loading were conducted. The influence of the type of wall concrete, wall-to-frame connection and steel brace setting, etc. on the hysteretic curves and failure modes of the type of composite structure was investigated. The seismic behavior of the blind bolted CFST frames with precast SCWPs was evaluated in terms of lateral load–displacement relation curves, strength and stiffness degradation, crack patterns of SCWPs, energy dissipation capacity and ductility. Then, a finite element (FE) analysis modeling using ABAQUS software was developed in considering the nonlinear material properties and complex components interaction. Comparison indicated that the FE analytical results coincided well with the test results. Both the experimental and numerical results indicated that setting the external precast SCWPs could heighten the load carrying capacities and rigidities of the blind bolted CFST frames by using reasonable connectors between frame and SCWPs. These experimental studies and FE analysis would enable improvement in the practical design of the SCWPs in fabricated CFST structure buildings.

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.

The application of Environmental Friendly Technique For Seagrass Transplantation

Many attempts have been made to solve tremendous seagrass losses the marine environment in many area in the world. Artificial transplanting of shoots and spreading of seeds from intact meadows to non-vegetated coastal sediment are the most applied techniques. The study was aimed to apply environmentally seagrass tranplantation techniques in less vegetated area. Frame and small tube made from bamboo were used to do seagrass tranplantation in Jepara Waters. Vegetative shoots (springs) of Enhalus acoroides dan Cymodocea serrulata were collected from a healthy donor bed located nearby the transplantation site, and planted into unvegetated areas. Test transplant survival was assessed every month for three months. The result revealed that the survival rates of transplants were varied with the area. It might have due to difference in sediment characteristics of transplanting sites and transplant technique are discussed.

Optimal stiffness distribution in preliminary design of tubed-system tall buildings

This paper presents an optimal pattern for distributing stiffness along a framed tube structure through an analytic equation, which may be used during the preliminary design stage. Most studies in this field are computationally intensive and time consuming, while a hand-calculation method, as presented here, is a more suitable tool for sensitivity analyses and parametric studies. Approach in development of the analytic model is to minimize the mean compliance (external work) for a given volume of material. A variational statement of the problem is made, and a specified deformation-profile is obtained as the necessary condition for a minimum; enforcing this condition, stiffness is then computed. Due to some near-zero values for stiffness, the problem is modified by considering a lower bound constraint. To deal with this constraint, the design domain is assumed to be divided into two zones of constant stiffness and constant curvature; and the problem is restated in terms of these concepts. It will be shown that this methodology allows for easy computation of stiffness through an analytic and dimensionless equation, valid in any system of units. To show practicality of the proposed method, a tubed-system structure with uniform stiffness distribution is redesigned using the proposed model. Comparative analyses of the results reveal that in addition to simplicity of the proposed method, it provides a rather high degree of accuracy for real-world problems.

A new and simple analytical approach to determining the natural frequencies of framed tube structures

This paper presents a new and simple solution for determining the natural frequencies of framed tube combined with shear-walls and tube-in-tube systems. The novelty of the presented approach is based on the bending moment function approximation instead of the mode shape function approximation. This novelty makes the presented solution very simpler and very shorter in the mathematical calculations process. The shear stiffness, flexural stiffness and mass per unit length of the structure are variable along the height. The effect of the structure weight on its natural frequencies is considered using a variable axial force. The effects of shear lag phenomena has been investigated on the natural frequencies of the structure. The whole structure is modeled by an equivalent non-prismatic shear-flexural cantilever beam under variable axial forces. The governing differential equation of motion is converted into a system of linear algebraic equations and the natural frequencies are calculated by determining a non-trivial solution for the system of equations. The accuracy of the proposed method is verified through several numerical examples and the results are compared with the literature.

Shear-lag effect and its effect on the design of high-rise buildings

For super high-rise buildings, the analysis and selection of suitable structural solutions are very important. The structure has not only to carry the gravity loads (self-weight, live load, etc.), but also to resist lateral loads (wind and earthquake loads). As the buildings become taller, the demand on different structural systems dramatically increases. The article considers the division of the structural systems of tall buildings into two main categories - interior structures for which the major part of the lateral load resisting system is located within the interior of the building, and exterior structures for which the major part of the lateral load resisting system is located at the building perimeter. The basic types of each of the main structural categories are described. In particular, the framed tube structures, which belong to the second main category of exterior structures, seem to be very efficient. That type of structure system allows tall buildings resist the lateral loads. However, those tube systems are affected by shear lag effect - a nonlinear distribution of stresses across the sides of the section, which is commonly found in box girders under lateral loads. Based on a numerical example, some general conclusions for the influence of the shear-lag effect on frequencies, periods, distribution and variation of the magnitude of the internal forces in the structure are presented.

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.

DAMAGE CONTROL FUNCTION AND FAILURE PROBABILITY BASED STRUCTURAL SEISMIC PERFORMANCE MULTI-OBJECTIVE OPTIMIZATION AND ASSESSMENT

To avoid global collapse of high-rise building structures caused by the damage of weak stories, a multi-objective optimization method based on damage control function of story group and failure probability was proposed. Through incremental dynamic analysis, the peak acceleration corresponding to the structural failure probability of 50% was selected as the objective earthquake intensity, and two performance indices:the damage control function of story group and failure probability, were defined and the section dimension of components was used as the variables to conduct the structural optimization analysis. A 30-story reinforced concrete frame-core structure was optimized, and the seismic performance of structure before and after optimization was assessed based on PACT (Performance Assessment Calculation Tool). Results indicate that the inter-story drift angle distribution of the optimized structure is more uniform than that of the original structure, and the damage is gradually decreased from the top to the bottom. The Collapse Margin Ratio (CMR) is increased by 29.8, and the repair cost is reduced for both the frame and core tube. The working coordination between the wall and the frame is strengthened, and the seismic perfomance of the structure after optimization has been significantly improved.

Levonorgestrel-releasing intrauterine system (LNG-IUS 12) for prevention of pregnancy for up to five years

ABSTRACTIntroduction: A new five-year low dose, smaller-framed, levonorgestrel-releasing intrauterine contraceptive system (LNG-IUS 12) has been introduced to complement the currently available systems.Areas Covered: This article will provide an overview of this new intrauterine system – its composition and its mechanisms of action as well as the results of the Phase II and III clinical trials of its efficacy, safety and tolerability.Expert Commentary: This new LNG-IUS 12 provides five-year contraceptive protection a pregnancy rate (less than 1%) in first year of use, which puts it into the top tier with the existing LNG-IUS 20 products; however, the LNG-IUS 12 does not have the high rates of amenorrhea often seen with the higher dose devices. On the other hand, this new IUD shares the smaller frame and narrower insertion tube with the lower dose LNG-IUS 8, but offers longer effective life.