Optimal compensation of differential column shortening in high‐rise buildings

To avoid unexpected damage in structural and nonstructural elements, differential shortening between vertical members resulting from differing stress levels, loading histories, volume‐to‐surface ratios and other factors in a high‐rise building must be properly considered in the design process. While research activity has been reported in the literature on the development of estimation algorithms or prediction procedures for the elastic and inelastic shortenings of vertical members, no algorithms or systematic methods for the compensation of the differential shortenings have been reported. In this paper, a compensation method for the differential column shortening in a high‐rise building is formulated into an optimization problem. A simulated annealing algorithm is used to find optimal solutions. The proposed method is applied to the compensation of the differential shortening of the vertical members in two high‐rise buildings, including one verifying example of a 70‐storey building and a practical example of a 63‐storey building. As demonstrated in the examples, the differential shortenings of the examples are effectively controlled by the optimal compensation method. Copyright © 2003 John Wiley & Sons, Ltd.     

Effect of horizontal members on column shortening of reinforced concrete building structures

An improved analysis method for column shortening of tall buildings has been proposed. The analysis method considers the restraining effects of steel bars and horizontal members. A step‐by‐step method was applied for the exact displacement and internal forces for any elapsed time. The sectional properties of the asymmetrically reinforced and cracked section were also taken into account. Column shortenings of an 80‐story reinforced concrete frame–shear wall building were investigated as numerical examples. The horizontal members reduce the differential shortening between the adjacent vertical members and transfer the axial forces of more shortened vertical members to less shortened members.     

Simplified column shortening analysis of a multi‐storey reinforced concrete frame

An improved column shortening analysis method which can be used at the design stage of a tall building has been proposed. The proposed analysis method considers construction sequences, the restraining effect of horizontal members, as well as creep and shrinkage. The whole analysis period is divided into two phases: before completion and after completion, and correction factors are applied only to the before‐completion phase to consider the gradual nature of construction sequences. Age‐adjusted effective moduli of the horizontal members considering the long‐term behaviour of the members are used for more exact internal forces. Column shortenings of a 70‐storey reinforced concrete frame–shear wall building were investigated as a numerical example. It is shown that the proposed analysis method can be used effectively to evaluate the effects of the differential column shortening to the horizontal members at the design stage. Copyright © 2010 John Wiley & Sons, Ltd.     

Time‐dependent analysis of steel‐reinforced concrete structures

The time‐dependent behavior is a major consideration in the design and construction of tall buildings, especially in concrete and composite structural systems. To make an analysis of long‐term effect of steel‐reinforced concrete structures, the method of using master–slave constraint to deduce substructure element model of composite members was introduced, and the problem of co‐work between steel and concrete was solved. The creep calculation method of combined Age‐adjusted Effective Modulus Method (AEMM) and finite element method was adopted. Steel Reinforced Concrete Construction Modeling (SRCCM), a calculation program based on Visual C++ and ObjectARX, was developed for simulating the construction process of high‐rise composite structures. The use of the method is illustrated through one computation example of Shanghai Center Tower, which is a super high‐rise steel‐reinforced concrete structures. The method provides valuable information about time effects that may be used in designing new structures or in diagnosis existing structures. The results also indicate that the vertical shortening of Shanghai Center Tower between column and core‐tube is significant. Such differential length changes should be compensated during the construction process of high‐rise composite structures. Copyright © 2013 John Wiley & Sons, Ltd.     

Optimum distribution of additional reinforcement to reduce differential column shortening

Differential column shortening should be reduced to mitigate the adverse effects caused by such shortening in a tall building. The axial stiffness of columns with greater shortening than adjacent columns should be increased to reduce the differential column shortening. The axial stiffness of the columns can be effectively increased by utilizing additional reinforcement for them. The optimum distributions of this additional reinforcement to reduce the differential column shortening in a tall building are determined. An optimization problem is formulated to minimize the total amount of reinforcement. Three analysis models, namely a fixed‐section, fixed‐stress and general model, are presented as numerical examples. The contour plots for a two‐variable problem of the three analysis models are presented. The generalized reduced gradient method is applied to obtain the optimum solutions of multi‐variable problems. The differential column shortenings after optimization confirm that the optimization program developed in this study can yield the optimum distributions of additional reinforcement. Copyright © 2015 John Wiley & Sons, Ltd.     

Column shortening of concrete cores and composite columns in a tall building

The effect of column shortening is a major consideration in the design and construction of tall buildings, especially in concrete and composite structural systems. The method presented in the PCA report is the most widely used for the analysis of column shortening, but results can be very different depending on the time function of shrinkage suggested by ACI, CEB‐FIP and PCA. To determine which method is most appropriate, this paper presents predicted and measured shortenings of two reinforced concrete core walls and four steel‐embedded concrete columns in a 69‐storey building. The results show that the measured strains of both core walls and composite columns are more consistent with calculated strains using the shrinkage time functions of CEB‐FIP and PCA rather than of ACI. The results also indicate that further studies are needed on the effect of high steel ratio on the development of column shortening when composite columns of a building have much higher steel ratios than usual. Copyright © 2005 John Wiley & Sons, Ltd.     

A comparison study of conventional construction methods and outrigger damper system for the compensation of differential column shortening in high-rise buildings

The outrigger and belt truss system is commonly used as one of the structural systems to effectively control the excessive drift due to lateral load and minimize the risk of structural and non-structural damage. However, this prominent structural system has a demerit of excessive stressing to structural and nonstructural members during construction due to differential column shortening. In this paper, several potential construction methods managing the outrigger to perimeter column joints experiencing differential column shortening are discussed. These methods include fixed joint without any adjustment, delayed joint, delayed joint with shim plate adjustment, and outrigger damper (or lock-up-device) installed joint. Based on our research through computer analysis, large scale laboratory test, shake table test and real installation of the apparatus to a high-rise project, the building with outrigger damper or lock-up-device system has many advantages in terms of building performance, construction convenience, quality control and cost reduction.     

Approximate analysis of high‐rise frames with flexible connections

An approximate hand method for estimating horizontal deflections in high‐rise steel frames with flexible beam–column connections subjected to horizontal loading is presented. The method is developed from the continuous medium theory for coupled walls which is expressed in non‐dimensional structural parameters. It accounts for bending deformations in all individual members as well as axial deformations in the vertical members and is more accurate for very tall structures. Additional deformations in the beam–column connections contributing to the overall frame deformations are also included in the analysis. This reduction in the frame stiffness requires the non‐dimensional structural parameters to be modified. A closed solution of the differential equation for the cantilevered structure yields a rapid assessment of the influence of different types of connection on the overall behaviour. Results for structures that are uniform with height compare closely with results from stiffness matrix analyses. Copyright © 2000 John Wiley & Sons, Ltd.     

Development of drift design model for high‐rise buildings subjected to lateral and vertical loads

Recent developments of resizing algorithms based on displacement participation factor have had a significant impact on drift design of high‐rise buildings. However, most drift design methods based on resizing algorithms have considered only lateral load and overlooked the effect of the vertical load in the calculation of member displacement participation factors. Therefore, in this paper, the practical drift design method of high‐rise buildings is presented in the form of a resizing algorithm by developing product integral modules required for the calculation of displacement participation factors with the consideration of both lateral and vertical loads. The effect of vertical load on the drift design model based on member displacement participation factors is investigated in detail using the verifying example of a 20‐story building structure. The drift design method in combination with the strength design module is then applied to the drift design of a 60‐story high‐rise building structure. Copyright © 2007 John Wiley & Sons, Ltd.     

Vertical shortening prediction for super‐tall buildings considering enclosure effect and coupling effect

In this paper, the time‐dependent vertical shortening behavior of the super‐tall building is studied considering the enclosure effect and the coupling effect. A combined method to predict the overall strain of the mega section is firstly proposed by combining the B3 model and the fiber modeling approach to consider the enclosure effect of mega steel and validated by a series of in‐house experiments. An iteration method is then proposed based on the construction sequence method to consider the coupling effect of stress and strain in the vertical shortening prediction and illustrated by a super‐tall building project. Finally, the vertical shortening predictions of the super‐tall building project are compared with the field monitoring records. The results show that the strain predictions by the combined method show good agreement with experiments. Without considering the enclosure effect, the overall strain of mega section is overestimated. The coupling effect affects more on the vertical shortening of the mega column than on that of the shear wall and more on the elastic shortening than on the inelastic shortening. Without considering the coupling effect, the elastic shortening is significantly underestimated in the mega column but slightly overestimated in the shear wall. The predictions of vertical shortening in the shear wall show reasonable agreement with the measurements, whereas those in the mega column show large disagreement with the measurements, which enlightens the necessity to improve the prediction method further.     

Integrated multi‐type sensor placement and response reconstruction method for high‐rise buildings under unknown seismic loading

Structural health monitoring system has been implemented on high‐rise buildings to provide real‐time measurement of structural responses for evaluating their serviceability, safety, and sustainability. However, because of the complex structural configuration of a high‐rise building and the limited number of sensors installed in the building, the complete evaluation of structural performance of the building in terms of the information directly recorded by a structural health monitoring system is almost impossible. This is particularly true when seismic‐induced ground motion is unknown. This paper thus proposes an integrated method that enables the optimal placement of multi‐type sensors on a high‐rise building on one hand and the reconstruction of structural responses and excitations using the information from the optimally located sensors on the other hand. The structural responses measured from multi‐type sensors are fused to estimate the full state of the building in the modal coordinates using Kalman filters, from which the structural responses at unmeasured locations and the seismic‐induced ground motion can be reconstructed. The optimal multi‐type sensor placement is simultaneously achieved by minimizing the overall estimation errors of structural responses at the locations of interest to a desired target level. A numerical study using a simplified finite element model of a high‐rise building is performed to illustrate the effectiveness and accuracy of the proposed method. The numerical results show that by using 3 types of sensors (inclinometers, Global Positioning System, and accelerometers), the proposed method offers an effective way to design a multi‐type sensor system, and the multi‐type sensors at their optimal locations can produce sufficient information on the response and excitation reconstruction.     

Outrigger system analysis and design under time‐dependent actions for super‐tall steel buildings

The outrigger system has been widely adopted as an efficient structural lateral‐load resisting system for super‐tall buildings in recent years. Although the outrigger system has many structural advantages, it has a significant defect due to differential shortening, which cannot be neglected. Due to the shrinkage and creep of concrete, as well as the differential settlement of foundation, the shortening of the structural member is an important time‐dependent issue, which leads to additional forces in the outriggers after the lock‐in of the outriggers. As a result, it will increase the size of the structural member cross section in the design. In a real project, engineers can delay the lock‐in time of the outrigger system to release the additional forces caused by the differential shortening during the construction phase. The time‐dependent actions, such as the column shortening and the differential settlement of the foundation, were estimated. A mega frame steel structure was employed to illustrate the analysis and design of the outrigger under the time‐dependent actions. Furthermore, a simple optimal method, considering the structural stability and overall stiffness, was proposed to optimize the construction sequence of the outrigger system.     

Three‐dimensional coupled wind‐induced vibration calculation method for super high‐rise buildings based on high‐frequency force balance technology

High‐frequency force balance test is a major technical means to evaluate the wind effect of super high‐rise buildings. Most super high‐rise buildings have the characteristic that the first two‐order modal frequencies are close, and thus, considerable modal coupling effects (MCEs) may occur under wind load. For a balance model system (BMS), MCEs increase the difficulty of correcting aerodynamic distortion signals. For the wind‐induced vibration analysis of a structural system (PSS), the calculation results of the wind‐induced response and the equivalent static wind load (ESWL) may be significantly affected without considering MCE. Based on the above‐mentioned signal distortion of BMS and the modal coupling problem of PSS, this study proposes a wind‐induced vibration calculation method for the two coupled systems (BMS and PSS). The method uses the second‐order blind identification technique based on complex modal theory and the Bayesian spectral density method considering full aerodynamic characteristics to achieve effective correction of the distortion signal in BMS. In addition, it deduces the calculation method of the wind‐induced response and ESWL considering the three‐dimensional coupled vibration of a super high‐rise building. The wind effect calculation results of a 528‐m super high‐rise building confirm the necessity and effectiveness of the proposed method.     

Vertical deformation analysis of a high‐rise building with high‐position connections

In this paper, a high‐rise frame‐core tube structure with strengthened stories and high‐position connections, a new landmark building in Wuhan, whose height is 238.6 m, is selected as an example. Construction simulation analysis is carried out by the finite element analysis software ETABS to study the vertical deformation and deformation difference of vertical members under the gravity load, taking the influence of construction processes and shrinkage and creep of concrete into consideration. The results show that there is a significant difference between the vertical deformation of the twin‐tower model with connections and that of the single‐tower model. Some engineering countermeasures are put forward to reduce the vertical deformation difference of the twin‐tower connected structure.     

大空间火灾下铝合金构件温升计算方法

性能化抗火设计过程中,火灾下结构构件的温升计算方法对设计结果具有重大影响。为研究大空间火灾下铝合金构件的温升计算方法及火焰辐射对构件温升的影响,对2种常见的铝合金构件截面试件进行了火灾温升试验。试验结果表明,由于火焰辐射的作用,构件温度与周围空气温度较为接近。基于铝合金构件的导热微分方程,提出了一般室内火灾和大空间火灾下铝合金构件的温升计算方法,并与试验结果进行了对比分析。结果表明：计算大空间火灾下铝合金构件温升时,忽略火焰辐射的作用会导致结果偏于不安全;所提出的基于点火源假定的火焰辐射热量计算方法较欧洲规范中的计算方法更为简单准确。此外,火焰辐射下烟气黑度值对构件温升的计算具有较大影响,并根据试验结果拟合了烟气黑度的实用计算式,计算结果与试验拟合结果吻合良好。     

Elastic analysis of asymmetric tall building structures

A simplified elastic hand method for estimating forces in asymmetric multi‐bent structures subjected to horizontal loading is presented. The structures may consist of combinations of coupled walls, rigid frames, braced frames and wall‐frames with shear walls. Results for structures that are uniform in height compare closely with results from stiffness matrix analysis. The method is developed from coupled‐wall deflection theory, which is expressed in nondimensional structural parameters. It accounts for bending deformations in all individual members as well as for axial deformations in the vertical members and is, therefore, more accurate for very tall structures. A closed solution of coupled differential equations for deflection and rotation gives the deflected shape along the height of the building. The proposed method of analysis offers a relatively simple and rapid means of comparing the shear forces and bending moments of different stability systems for a proposed tall building. The derivation of equations for analysis shown in this paper are for unisymmetric stability systems only, but the method is also applicable to general asymmetric structures. Copyright © 2001 John Wiley & Sons, Ltd.     

超高层建筑结构竖向变形估算

本文利用国内外的研究成果,提出在考虑混凝土的弹性压缩、收缩、徐变及温度影响时,如何粗略估计超高层建筑结构各部分的竖向变形差异。     

An estimate on in‐construction differential settlement of super high‐rise frame core–tube buildings

To physically identify the mechanisms behind the development of in‐construction settlement of super high‐rise frame core–tube buildings, a simplified approach is developed by the full understanding about the typical structural layouts, specific construction feature, and load transfer path of those buildings as well as time‐dependent effects. With the reference to several typical structural layouts, a simplified one‐bay multistory model is developed that consists of two overall vertical components and horizontal components representing the exterior columns, core tubes, and beams (or mega trusses), respectively, in those super high‐rise buildings. Based on this model, a simplified approach with a so‐called “global–local” strategy is proposed to account for the difference in the settlement of the corner columns and side columns. The leading construction and final screwing at the rigid connections between beams (or trusses) and exterior columns, which are commonly implemented during the construction of those buildings, are seriously addressed in the simplified approach, as well as strengthened floors and time‐dependent effects. The applicability and accuracy of the proposed approach is demonstrated by a 128‐story 606‐m‐level super high‐rise frame core–tube building. The proposed simplified approach can be helpful for the development of preliminary construction schemes and the control strategy for differential settlement.     

Strengthening of a steel railway bridge and its impact on the dynamic response to passing trains

Two different strengthening methods for a through-girder steel railway bridge are investigated. The studied structure is the Söderström Bridge, located in the city of Stockholm, Sweden. Due to fatigue problems, it is in need of assessment and strengthening. In one of the methods, arches are added under the bridge modifying the structural system and lowering the stress ranges for all structural members. The other method consists of prestressing the floor beams. This increases their stiffness and transforms the mean stress in the lower flanges from tension to compression. A 3D finite element model is created and verified with measurements. The different strengthening methods are tested in the model by dynamic analysis with moving train loads. The strengthening methods show some positive effect concerning the fatigue life. Changes in vertical bridge deck acceleration for high speed traffic are also presented. A comparison between the European code and the Swedish code regarding vertical bridge deck acceleration levels for high speed traffic shows large differences for the bridge.     

高层建筑结构抗震计算方法探讨

详细阐述了高层建筑结构抗震计算方法,并就一些计算方法进行了探讨,通过上述探讨,可为工程设计人员就高层建筑结构的抗震设计积累经验,从而完善高层建筑的结构设计。