CHINA CIVIL ENGINEERING JOURNAL（Monthly）

Vol.39, No.9　　　　　　Sep. 2006

Cyclic lateral loading test on a sub-structure model of the National Swimming Center

Qian Jiaru¹ 　Hu Xiaobin¹　 Zhao Zuozhou¹　 Fu Xueyi²　 Gu Lei²
（1. Tsinghua University, Beijing100084, China;
2. China Construction(Shenzhen)Design International, Shenzhen 518033, China）

Abstract: To study the seismic behavior of the heavily loaded part of the internal wall of the National Swimming Center, the so called“Water Cube”, an experiment was conducted on a one-third scaled sub-structure model subjected to representative gravity load and cyclic lateral load. Damage of the sub-structure model are in the forms of local buckling and tension fracturing of the base metal of the structural members, and most of the damaged members are at the wall surfaces. Due to the cover plates welded at member ends, the plastic hinges and the damage locations are away from the connections between the members and the joints, thus brittle failure of the weldments is avoided. The nominal yield top drift ratios of the model under push and pull forces are about 1/127 and 1/100, respectively, and the corresponding strength is in the range between 880kN and 746kN, 1.73 and 1.47 times that of the representative gravity load of the model, respectively. The lateral load is 2 times that of the representative gravity load and the top drift ratio is about 1/50, whereas the strength of the model is less than the maximum strength while the lateral displacement may increase further. The sub-structure model exhibits high load-carrying, deformation and energy dissipation capacities.
Keywords: National Swimming Center；sub-structure model；seismic experiment；damage pattern；cover plate
E-mail: qianjr@mail.tsinghua.edu.cn

Experimental study and capacity analysis of double-tapered rectangular steel tubes

Luo Yaozhi¹　 Zhang Bing¹　 Ji Weijie¹　 Dong Shiling¹　 Fu Xueyi²　 Gu Lei²
(1.Space Structures Research Center, Zhejiang University, Hangzhou 310027, China;
2.China Construction (Shenzhen) Design International, Shenzhen 518033, China)

Abstract: Double-tapered rectangular steel tubes are composed of two tapered ends and a prismatic intermediate part. In this article, the formulas for determining the failure location of the double-tapered tubes are derived. Failure pattern, spreading of plastic zone and bearing capacity of double-tapered tubes are investigated under axial-flexural and axial-flexural-torsional loading experiments. Studies on the bearing capacity of members with different geometric parameters are carried out via FE model analyses. Investigations indicate that the bearing capacity of tubes is notably improved with two tapered ends, and the ductility of the whole structure can also be improved when plastic hinges do not occur at the nodal ends.
Keywords: double-tapered；rectangular steel tube；experimental study；bearing capacity；failure position；plastic hinge
E-mail: luoyz@zju.edu.cn

Experimental studies on hysteretic behaviors of steel beam to concrete
filled SHS column connections with stiffening ring

Wang Wenda¹　 Han Linhai²　 You Jingtuan¹
(1. Fuzhou University，Fuzhou 350002，China；2. Tsinghua University，Beijing 100084，China)

Abstract: Eight specimens of steel beam to concrete filled SHS（Square Hollow Section）column connections stiffened by outside rings were experimentally studied on the hysteretic behavior under combined constant axial load and cyclically lateral load. The axial load level of the concrete filled SHS columns and the width of the joint stiffening rings are considered as the experimental parameters of their seismic behavior. The results show that the axial load level of the column has　 an　 obvious effect on both the strength and seismic behavior of the connections.　 With the increase in axial load　 on the columns, the lateral ultimate strength of the connections become lower, and the ductility　 in displacement and the capacity of energy dissipation also decrease. The lateral load（P）versus lateral displacement(Δ) hysteretic curves of all the specimens with different width of outside stiffening rings are of a plump shuttle shape. The curves show no obvious strength deterioration and stiffness degradation. The story drift ductility index μ fluctuates between 3.00 and 7.41, the elastic limit of story drift angle 　θy　 between 2.03［θe］and 5.30［θe］，the elastic-plastic limit of story drift angle　θu between 1.78［θp］and 3.90［θp］, and the equivalent damper coefficient he between 0.3576 and 0.5339. It can be concluded that the tested connections in the study demonstrate good seismic performance.
Keywords: concrete filled SHS column；connections with stiffening ring；seismic behavior；ductility；energy dissipation
E-mail: wangwd@lut.cn

An experimental study on the seismic performance of beam-column joints
in steel frames with the effect of concrete slabs considered

Shi Yongjiu 　Su Di 　Wang Yuanqing
（Tsinghua University, Beijing 100084, China）

Abstract: The effect of concrete slabs on the seismic performance of beam-column joints of steel frames is examined through a series of cyclic loading experiments. Four beam-column joints with floor slabs were tested. The influences of joint details and reinforcement ratios on the load-carrying property, such as rotational stiffness and capacity, energy dissipation capacity, ductility and ultimate failure modes, were thoroughly assessed. From the experimental results, it is found that welding quality is the most important factor for joint ductility. The beam-column joints constructed with proper details and high reinforcement ratios exhibit excellent performance in both bending resistance and energy dissipation under cyclic loads. For those joints with long access holes failed by local buckling, the local stress concentration is reduced while the ductility is improved. Resistance and stiffness of joints increase with the increasing of slab reinforcement. It is found that the unsymmetrical profile of joints due to the existence of concrete slabs should be considered in joint design.
Keywords: joints of frame；composite effect；cyclic loading experiment；seismic performance
E-mail: shiyj@mail.tsinghua.edu.cn

An experimental study on the fatigue life of prestressed concrete
beams under random-amplitude fatigue loading

Feng Xiufeng^1,2 　Song Yupu¹ 　Zhu Meichun³
（1. State Key Lab. of Coastal and Offshore Eng., Dalian Univ. of Technology, Dalian 116024, China;2. Bureau of Land Resources and Housing Administration of Qingdao, Qingdao266002, China;3. Ocean Univ. of China, Qingdao 266071, China）

Abstract: Based on the fatigue loading spectrum of R.C. crane beams, established through a practical survey, a random-amplitude fatigue loading spectrum for conducting tests is obtained through appropriate simplifications. Fatigue tests of prestressed concrete beams under the random-amplitude fatigue loading spectrum are conducted by using MTS fatigue machines. The experimental results suggest that the fatigue lives obtained from the random-amplitude fatigue tests are far lower than those obtained from constant-amplitude fatigue tests with the upper values of fatigue loading assumes the mean value of the loading spectrum.　 Thus it is dangerous to use the experimental results from the latter to estimate the fatigue life of prestressed concrete beams in service. The Miner rule, the relative Miner rule, and the Corten-Dolan cumulative damage rule are applied to calculate the fatigue lives of specimens under random-amplitude fatigue loading. Comparisons between the calculated and the experimental results show that the modified Corten-Dolan cumulative damage rule can accurately predict the fatigue lives of specimens. The relative Miner rule can also provide certain accuracy, whereas the results from the Miner rule are considerably unsafe. It is suggested that the modified Corten-Dolan cumulative damage rule or the relative Miner rule be used in estimating the fatigue life of prestressed concrete beams under random-amplitude fatigue loading.
Keywords: prestressed concrete beam；fatigue life；random-amplitude；life estimation
E-mail: fengxiufeng@163.com

A study on the convective heat transfer coefficient of concrete in wind tunnel experiment

Zhang Jianrong　　 Liu Zhaoqiu
（Tongji University, Shanghai 200092, China）

Abstract: An experimental method is developed for measuring the convective heat transfer coefficient of concrete surface. The test specimen is in the form of a circular tube, heated from inside, and installed longitudinally in a TJ-1 wind tunnel.　 The wind speed varies from 1 m/s to 25 m/s, the heating process is controlled and the test data recorded automatically via a specially developed control system.　 The test results of the three concrete tube specimens agree with each other very well.　 There exist linear correlations between the convective heat transfer coefficient of concrete surface and wind speed, the radiation coefficient of concrete surface and the temperature difference.　 The formulae for calculating the convective heat transfer coefficient, the radiation coefficient, and the total heat transfer coefficient of concrete surface are derived based on analyses of the experimental results.
Keywords: convective heat transfer；concrete；wind speed；temperature
E-mail: zhangjr@mail.tongji.edu.cn

Study on the strength of recycled aggregate concrete based on orthogonal experiment

Li Jun 　Yin Jian 　Zhou Shiqiong 　Li Yijin
（Central South University, Changsha 410075, China）

Abstract: An orthogonal experimental design method involving three factors and three factor levels is adopted for the mix design of recycled aggregate concrete(RAC), and the effect of each factor level on mix proportion of RAC and the difference between each factor levels are analyzed. The influence and mechanism of different experimental factor, which includes water-binder ratio, percentage of recycled aggregate and ultra-fine fly ash (UFA) content, on the strength of RAC is studied and compared with normal concrete. The experimental results indicate that water-binder ratio is the most principal and significant influencing factor on the strength of RAC, regardless of age. Compared with the normal concrete, ratio of the splitting tensile strength to the compression strength of recycled aggregate concrete with fly ash is increased, and the cracking resistance improved.　 An empirical relationship among the strength of RAC, the water-binder ratio, the percentage of recycled aggregate and UFA content is proposed by using multivariate regression analysis.
Keywords: recycled aggregate concrete；mix design；orthogonal experiment；strength；regression model
E-mail: csu25135@163.com

An experimental study on rigid suspendome structures

Chen Zhihua　 Qin Yali Zhao Jianbo　 Guo Yun　 Dou Kailiang　 Li Yang
（Tianjin University, Tianjin 300072, China）

Abstract: State of the art for suspendome research and application is introduced, and the structural performance of suspendome is analyzed. On the basis of half-rigid suspendome, rigid suspendome is proposed according to the two-stage method. The roof of the VIP Hall of Tianjin museum is designed as a rigid suspendome. A loading test plan on the structure is designed and the experimental study is performed under static load. The structural performance, such as deformation and internal force, with loading process are obtained. By comparing the experimental results with theoretical analyses, the rigid suspendome is proved to exhibit a better mechanical performance. The rigid suspendome is compared with a single-layer dome of same geometry, used as the roof of the multi-purpose Hall of the Tianjin museum. The results indicate that the rigid suspendome has a number of advantages, including good structural performance, less steel consumption, convenient construction and low cost.
Keywords: suspendome；rigid suspendome；loading experiment；structural performance；single-layer dome
E-mail: zhchen@tju.edu.cn

A study on the redistribution of internal forces in reinforced
concrete frames under high temperature

Wu Bo　　 He Xiyang
(South China University of Technology, Guangzhou 510640, China)

Abstract: The redistribution of internal forces in reinforced concrete frames under high temperature is primarily studied. For the study, a simplified beam-element-model for reinforced concrete is employed. An analytical procedure for reinforced concrete frames under high temperature is proposed and the procedure is validated by using the test results found in the literature. A three-span one-storey reinforced concrete frame is selected for fire response analysis. Different line-stiffness-ratios of beam to column and different axial load ratios of column are considered in the analysis. The redistribution of internal forces at some key sections in the frame is discussed in the paper. The analysis results indicate: (1) redistribution of internal forces in the frame subjected to high temperature is quite significant; (2) redistribution of the axial force of the beam and the redistribution of the bending moment at the end of the beam are especially significant, and these are the most important causes of the variations of the internal forces in other sections; and (3) with an increase in the line-stiffness-ratio of beam to column and in the axial load ratio, the axial force of the beam increases accordingly.
Keywords: reinforced concrete；frame；high temperature；redistribution of internal force
E-mail: bowu@scut.edu.cn

A simplified model for static analysis of slit RC shear walls

Zhang Yaochun　　 Liu Yonghua　　 Ding Yukun　　 Zhang Wenyuan
（Harbin Institute of Technology, Harbin 150090, China）

Abstract: Slit RC shear walls, which have appropriately large lateral stiffness in elastic state and good ductility in inelastic state, may serve as desirable aseismic structural members. However, there are few applications of slit RC shear walls in China due to lacking an effective model for global structural analysis. A simplified model, i.e., an eccentric cross-bracing model, is proposed to represent the structural actions of the slit RC shear wall in a global analysis. The model is established on the basis of an equivalent lateral stiffness according to the shear force versus lateral deflection curve of the slit RC shear walls. Both section characteristics and material constitutive curve of the simplified model are introduced. Numerical examples involving both the simplified model and a more accurate model, named the equivalent slit panel model, are presented to demonstrate the accuracy of the simplified model. According to the statistical results of the numerical examples, the range of brace eccentricity and the applicability of the simplified model are identified. Numerical results indicate that the simplified model of a slit RC shear wall can be effectively utilized for the global static analysis of frame structures.
Keywords: slit RC shear wall; static analysis; simplified eccentric cross-bracing model; ductility; aseismic behavior
E-mail: jxln753@163.com

A study on the dynamic ultimate capacity of CFST arch bridges

Xu Yan　 Hu Shide
(Tongji University，Shanghai 200092，China)

Abstract: The dynamic stability of concrete filled steel tubular(CFST)arch bridges under earthquakes is studied with respect to the structural ultimate bearing capacity. Based on the finite element software package(ANSYS), a method for using representative responses to study the dynamic ultimate capacity of CFST arch bridges is proposed by application of Incremental Dynamic Analysis in combination with the B-R dynamic criteria. The influence factors, such as earthquake input directions, geometric and material non-linearities, and the initial imperfection modes and magnitudes, are investigated. The results indicate that the bridge is affected the most by lateral earthquake input, that material non-linearity has a more serious effect than geometric non-linearity, and that the initial imperfection reduces the ultimate capacity, and the anti-symmetrical mode might be the worst case. The method is compared with a CFST model arch shaking table test, the result of which indicates that the method proposed is correct and applicable in engineering practice.
Keywords: CFST arch bridge; nonlinear; incremental dynamic analysis; dynamic ultimate capacity
E-mail: helen_xuyan@hotmail.com

A study on the safety assessment method for stay cables of long-span cable-stayed bridges

Zhu Jinsong¹　　 Xiao Rucheng²
（1.Tianjin University, Tianjin 300072, China; 2.Tongji University, Shanghai 200092, China）

Abstract: Stayed cables are primary members for cable-stayed bridges. The safety assessment of stayed cables is a key issue to the safety of the structures.　 Some recently developed models for strength assessment of stayed cables are presented and illustrated.　 These models are based on the Matteo’s ductile-brittle wire model and the Monte Carlo simulation. A linear equation is proposed for simulating the deterioration of the cables，and a safety assessment method for stay cables of long-span cable-stayed bridges is proposed. Application to the Zhao Bao Shan cable-stayed bridge in China is made by taking into account the tensile test results and the empirical data obtained from the design and cable force inspection of the stayed cables. The analysis of the longest cable is illustrated, and the results indicate that the proposed method could be used to assess the safety and residual life of stayed cables in cable-stayed bridges.
Keywords: cable-stayed bridge; cable; assessment; safety factor; Monte Carlo method
E-mail: zhu.jinsong@163.com

Combined numerical simulation method and its application on the
reliability assessment of the Runyang Bridge

Guo Tong　 Li Aiqun　 Miao Changqing　 Fei qingguo
(Southeast University, Nanjing 210096, China)

Abstract: To obtain the reliability of long span bridges under the influence of external random factors and to realize the online condition assessment, numerical simulation and reliability assessment of the Runyang Suspension Bridge is conducted by using the stochastic finite element method (SFEM). The Monte Carlo Importance Sampling method and the Central Composition Response Surface method are combined as the basic tool of numerical simulation. The definition of random factors, the application of the combined method and the assessment criterion based on reliability index are introduced and discussed. The probability sensitivities between random variables are analyzed and the reliability index and the corresponding condition classes are obtained. Examples indicate that the reliability analysis using SFEM can describe the nonlinearity of long span bridges and the combined method can increase the efficiency and accuracy of reliability analysis.
Keywords: reliability; Monte Carlo method; Response Surface method; condition assessment; health monitoring
E-mail: civilcenter@163.com

A mathematical model and the related parameters for EPB shield tunneling

Wang Hongxin^1,2　 Fu Deming²
（1. Tongji University, Shanghai 200092, China;
2. Shanghai Tunnel Engineering Co., Ltd., Shanghai 200082, China）

Abstract: For EPB (Earth Pressure Balance) shield tunneling, one must properly choose driving parameters to maintain face stability and control ground subsidence. Based on the data of a model test, three fundamental equations for EPB shields are derived, from which two general balance equations are developed, to form a mathematical model of EPB shield tunneling. The theoretical relationships between total thrust, in-chamber earth pressure, rotation speed of screw conveyor and advancement rate are established and validated by field data. Empirical relationships between cutter-head torque, cutter-head rotation speed and earth pressure in the chamber are thus obtained.
Keywords: EPB shield; balance equation; model; parameter; relationship
E-mail: tjwanghongxin@sina.com

A simplified method for the analysis of the nonlinear interaction of large scale piled rafts

Sun Xiaoli　　 Yang Min
（Tongji University，Shanghai 200092，China）

Abstract: A simple method is proposed for the analysis of the nonlinear interaction of large piled rafts. The simple method involves applying single pile load test result to the settlement of piled rafts. The raft is modeled as a thin plate and the piles are modeled as interacting nonlinear springs. The Q-S curves from single pile load test can be simulated by a hyperbola function, which can be employed to model the non-linear characteristics of the piles. The interaction between piles is analyzed by using interaction factors, and the‘restraint’action between piles is considered.　 The factors of pile-pile and pile-soil interactions are simulated by using multinomial regressions. The interaction between soil elements can be analyzed by elastic semi-space or finite layer theory. Comparing with the results of the piled raft and the model pile groups, the approximate method can save computing time while gives a　 reasonable results.
Keywords: piled raft；interaction factor；nonlinearity
E-mail: sunxiaoli5428@sina.com

An approach for computing the ventilated foundation of buildings based on controlling the permissible value of permafrost thawing

Xu Xueyan^1,2　 Su Wanxin¹　 Xu Chunhua¹
(1.Harbin Institute of Technology, Harbin 150006, China; 2. State Key laboratory of frozen Soil Engineering, CAREERI, CAS, Lanzhou 730000, China)

Abstract: Based on the heat-transfer theory, a calculation formula is derived for the maximum thawing depth of frozen ground under ventilated foundations. From the design viewpoint in allowing gradual thawing of the foundation soil, both the concept of equivalent floor temperature and the associated temperature coefficient are presented. Through theoretical analysis and numerical simulation, 54 equivalent floor temperatures and the temperature distribution curves with depths are obtained for different inner floor temperatures and spaces between vent-pipes. The calculation method for the equivalent floor temperature factor of ventilated foundations with vent-pipes of a 300mm diameter is obtained by using a compound foundation model and the method of least squares. The design method for areas of ducts that control the permissible value of permafrost thawing is obtained. The reliability and practicability of the calculation method is validated in practical engineering designs.
Keywords: permafrost; ventilated foundation; equivalent floor temperature coefficient; ventilating area
E-mail: xuxueyan_hit@sina.com

Field test on the load transfer and deformation of cement-soil pile group
Ma Hailong

（Zhejiang Sci-Tec University, Hangzhou 310018,China）

Abstract: To obtain the quantitative influence of pile length and replacement ratio on the load transfer and displacement of cement-soil pile groups, strain gauges were mounted on the cement-soil piles and deep settlement instruments buried in the soil, for a total of five 4-pile groups and five 9-pile groups. The axial force along the pile shaft, the skin friction and the soil settlement were measured. It is found that the load critical depth and the friction range increase while the cap breadth increases with the same replacement ratio. The load critical depth changes from 14 to 18 times of the pile diameter while the cap breadth varies from 1.0m to 1.5m. The deformation influence depth is about 1.8 to 2.5 times the cap breadth. The maximum friction occurs at about 6 times of the pile diameter（1.5 m） beneath the cap. Long pile can significantly reduce the settlement. However, the deformation influence depth does not increase when the load-level is equal to or exceeds 70%.
Keywords: cement stabilized soil pile; test in situ; load transfer; load critical depth; load-level
E-mail: ma-hailong@163.com

Application of the Bayesian method on the selection of real estate projects

Wen Haizhen¹　 Jia Shenghua¹　 Yang Zhiwei²
（1. Zhejiang University, Hangzhou 310027,China；
2. The Hong Kong Polytechnic University, Hong Kong, China)

Abstract: Project selection is an important decision-making issue in real estate development. The Bayesian method is applied for project selection under uncertain circumstances, and a Tunxi New Town project in Huangshan City is employed as a case study. Through interview and scoring by expets in the area, two key factors, the progress of the Huihang highway construction and the urban development process of the Tunxi district of Huangshan City, are identified. The Bayesian method is applied to calculating the expected project returns in four circumstances and the Bayesian earnings of 16 decision-making functions. The major conclusions are: for multi-story apartment market, housing demand is mainly local; for villa market, the local demand is smaller, but, with the completion of the Huihang highway, the villa market will be promoted. Empirical analysis also shows that the Bayesian method can effectively facilitate the selection of real estate projects and reduce early-stage risks of project developments.
Keywords: uncertainty；project selection；Bayesian decision
E-mail: wenhaizhen@263.net

Fracture-mechanics analysis of the fatigue life of the
pavement on orthotropic steel bridge decks

Huang Wei¹　　 Lin Guangping¹　　 Qian Zhendong¹　　 Liu Zhenqing²
（1.South-east university, Nanjing 210096, China；
2.Research Institute of Highway, Ministry of Communications, Beijing 100088, China）

Abstract: The stress intensity factor (SIF) for the surface crack of the pavement on orthotropic steel bridge decks is calculated and analyzed. The Paris’formula is employed to forecast the fatigue life of the pavement. A three-dimensional fracture-mechanics finite element model of orthotropic steel bridge deck systems is developed.　 According to the change in the SIF with the change in the loading position of the axle-load, the worst loading position of the axle-load on the cracking pavement of the steel bridge deck is determined, the change in the SIF with the change in the crack depth is analyzed, and the relationship between the SIF and the crack depth is established. The expression of the SIF is substituted into the Paris’formula, and the fatigue life of the pavement is calculated by using an integral of the Paris’formula. The result indicates that fracture mechanics can be employed to forecast the fatigue life of the pavement on orthotropic steel bridge decks.
Keywords: orthotropic steel bridge deck；paving of steel bridge deck；fracture mechanics；stress intensity factor； Paris’formula：fatigue life
Email: lgp215@sohu.com

A study on the sudden changes or double peaks in the dynamic
response of subgrade of high speed railway

Liang　 Bo^1,2　 Sun Changxin³
（1. Key lab. of Structure Engineering, Chongqing Jiaotong University, Chongqing 400074, China;2. Lanzhou Jiaotong University, Lanzhou 730070, China; 3. North China Institute of Water
Conservancy and Hydroelectric Power, Zhengzhou 450008, China）

Abstract: In connection with the development of special high speed passenger railway-lines in China, the dynamic response of railway subgrades is analyzed for train speeds over 200km/h. Using a simulated dynamic load that suitably reflects the vehicle factor and structural factor below the track and using non-linear numerical analyses, the sudden changes or double peaks are identified in the dynamic response of subgrades under high speed conditions. The study found that factors such as the resonant vibration and line irregularity are the major influence factors in various speed ranges. The calculations are compared with test results.
Keywords: high speed railway; subgrade; dynamic response; double peaks
E-mail: liang_laoshi@126.com

Design method for ultra-thin whitetopping (UTW) structures

Li Yuzhi¹　　 Cui Peng²　　 Shao Lageng¹
（1. Changsha University of Science and Technology, Changsha 410076, China;
2. Tongji University, Shanghai 200092, China）

Abstract: In order to investigate the design method for UTW structures on semi-rigid asphalt pavement, a 3-D FE code is employed to calculate the load-induced stresses of a UTW structure. The calculation confirms that the center of the longitudinal joint edge is the design loading position of UTW. Based on an Equivalent Resident Modulus of the top of the base(Et), modulus of existing asphalt layer(Ea) and statistic analysis result, a generalized coefficient of structural strength(Rj) is proposed as, Rj=E t (1/3) ×log(Ea), together with a thickness design chart for Rj<17. It is also validated that the Rj value, if less than 17, is applicable to most asphalt pavements in China that require rehabilitation work. Considering the fatigue and the reliability referencing in the equations of the current cement concrete pavement design specifications, the combined effect of temperature and load on UTW structure for pavement design is calculated and the corresponding design method is validated by a full-scale test. Moreover, the construction method is discussed in the paper to ensure a good interface condition of UTW, and the adaptability of UTW structure is also analyzed. It is pointed out that the adaptability of UTW to heavy-load expressways should be further studied via projects in the field.
Keywords: road engineering; Ultra-thin Whitetopping; general coefficient of structural strength; design method
E-mail: xieshou79@163.com