ABSTRACT

Compressive stress-strain model for concrete of FRP confined cylinders
Liu Mingxue Qian Jiaru

(Tsinghua University, Beijing 100084, China)

Abstract: To develop a compressive stress-strain model for fiber reinforced polymer (FRP) confined concrete, the test results of 305 axially loaded FRP confined concrete cylinder (FCC) specimens are analyzed. The analytic results indicate that the fiber characteristic value, the FRP laminate structure and the loading method are the three major factors that influence the compressive stress-strain relationships of concrete of the FCCs. By analyzing the 305 test results and the existing models, an improved compressive stress-strain model for concrete of the FCCs, with the three factors taken into consideration, is proposed. The model includes work hardening and softening. Comparing with the test results, the agreement of the proposed model is better than that of the existing models.
Keywords: fiber characteristic value; FRP laminate structure; loading method; FRP confined concrete cylinder; concrete stress-strain model
E-mail: qianjr@mail.tsinghua.edu.cn

Study of the stress-strain relationship of FRP-confined circular concrete
column with a strain-softening response

Wu Gang1 Wu Zhishen1，2 Lü Zhitao1
（1. Southeast University，Nanjing 210096, China；
2. Ibaraki University, Hitachi 316-8511, Japan）

Abstract: The performances of circular concrete columns confined with FRP of various volumetric ratios and three different types of FRPs, including high strength FRP, high modulus of elasticity FRP and high ductility FRP, were tested. The FRP-confined circular concrete columns may or may not exhibit strain-softening. The maximum stress of FRP-confined concrete mainly depends on the confinement strength or the confinement modulus of FRP, while the axial ultimate strain of FRP-confined concrete is related not only to these two parameters but also to the ultimate tensile strain of FRP. Boundary values of the confinement ratio are suggested for determining the stress-strain curves of FRP-confined circular concrete columns with or without strain-softening. Based on the discussions on the effects of confinement strength and confinement modulus of FRP, the ultimate tensile strain of FRP, the strength and the modulus of elasticity of concrete, two stress-strain models as well as formulations for predicting the peak stress and the corresponding strain, the ultimate stress and the ultimate strain of FRP-confined circular concrete columns with strain-softening are proposed. The formulations and models demonstrate good agreement with experimental results from the present and previous studies.
Keywords: fiber reinforced polymer(FRP) ; circular concrete columns; confinement; softening; stress-strain relationship
E-mail: g.wu@seu.edu.cn

Experimental study on large precast prestressed concrete spatial structures

Xue Weichen1 Chen Yiyi1 Jiang Dongsheng1 Xu Zhuangtao1 Lin Yingru2
(1.Tongji University，Shanghai 200092;
2.Institute of Architectural Design & Research,Shanghai 200041）

Abstract: Monotonic static test and nonlinear finite element analysis are conducted on a 1∶15 scaled model of a large precast prestressed concrete spatial structure in China to investigate the failure mode, failure mechanism, variation of crack propagation, the stress increment of prestressed tendons and steel rebars and the section curvatures. Experimental results indicate that the structure fails when the concrete at roots of radial girders crushes and the structure is basically in the elastic range under the design loads. Cracks initiate at the joints of the precast oblique beams and the circular beams. All 64 precast oblique beams work concertedly under the applied prestressing at the early stage of loading, and work separately at the later stage of loading. The structure finally fails in compressive bending at the roots of the radial girders. The structure behaves with a rather sufficient safety margin and a deformation capacity with a displacement ductility coefficient of about 2.04.
Keywords: precast prestressed concrete; space structure; monotonic static test; nonlinear finite element; failure mechanism; displacement ductility
E-mail: xuewc@mail.tongji.edu.cn

Experimental study on the fatigue elastic modulus of
steel fiber reinforced prestressed concrete slabs

Hou Jie1 Cheng Heming1 Wang Shiyue1 Tian Fang 2
（1.Kunming University of Science and Technology, Kunming 650093, China;
2.Quzhou college, Quzhou 324000, China）

Abstract: The attenuation of elastic modulus of Steel Fiber Reinforced Prestressed Concrete Slabs (SFRPCS) with different steel fiber contents (0%、1%、2%) and under different stress levels (0.80、0.85) is investigated through flexural fatigue experiments. Three types of attenuation curves in the middle of slabs are obtained，and these curves reveal that the elastic modulus attenuation of SFRPCS could be divided into three stages during the fatigue process and the second stage is nearly linear. The elastic modulus is about 59.9 percent of its initial value when the SFRPCS fails．A model for fatigue-life prediction is proposed according to the Miner cumulative damage theory, and a method of micro-damage experiment is provided to predict the fatigue-life. The model predicted fatigue-life is within three times of the experimentally measured fatigue-life.
Keywords: steel fiber reinforced prestressed concrete slab； fatigue； elastic modulus； fatigue-life prediction
E-mail: houjie01107@163.com

Failure mechanism of single-layer latticed cylindrical
shells subjected to strong earthquake

Wang Xiaoke Fan Feng Zhi Xudong Shen Shizhao
(Harbin Institute of Technology, Harbin 150090, China)

Abstract: The characteristics of latticed cylindrical shells are different from those of other latticed shells，which make some particularity on failure mechanism. Based on the structural response analysis method in Abaqus, considering multi-indexes responses from macroscopic and microscopic levels, a large number of parameter analyses for single-layer latticed cylindrical shells have been done, which can be used for exploring the failure mechanism under strong earthquakes. After the analysis of some typical cases the failure modes and some characteristics have been determined. According to a great number of analytical calculated data a practical dynamic failure criteria of single-layer latticed cylindrical shells is given. Under strong earthquakes, the dynamic instability of single-layer latticed cylindrical shells may appear suddenly, and when it happens, the plastic deformation is very limited, the structural stiffness is almost as same as before and the displacements are not considerable. The strength failure of single-layer latticed cylindrical shells may also happen. It seems quite different. The strength failure includes strength failure modeⅠ and strength failure modeⅡ. Strength failure modeⅡ has obvious similar phenomena as those in dynamic instability, while strength failure modeⅠhas not. Using maximum displacement and the ratio of whole-section yield elements (8p) as reference indexes the practical failure criteria can be used for determining the ultimate loads of strength failure modeⅠ and modeⅡ. In this paper the preliminary study on failure mechanism of damaged single-layer latticed cylindrical shells subjected to strong earthquake motion is also studied, a reduced damage coefficient for engineering design is given.
Keywords: single-layer latticed cylindrical shell; strong earthquake; failure mechanism; dynamic instability; strength failure
E-mail: gloria-w@163.com

Theoretical and experimental study on the construction of cable domes

Chen Lianmeng1,2 Dong Shilin2 Yuan Xingfei2
(1.Wenzhou University, Wenzhou 325035,China;
2. Zhejiang University, Hangzhou 310027,China )

Abstract: Based on the geometric topology of the structures composed of cables in tension and struts in compression, a new construction scheme is proposed for adjusting the length of the struts from the outer to the inner hoop. The relationship between the nodal coordinates and the internal forces of the elements of known original length is established, and a method is proposed to find the internal force of the elements and the nodal coordinates of the structures in equilibrium state by controlling the original length with the dynamic relaxation method. A cable dome model with a diameter of 5.0m is formulated to test this theory. The experimental results are mostly consistent with the theoretical ones, which indicate that the proposed form-finding method by controlling the original length with the dynamic relaxation method is accurate and effective and the proposed construction scheme is reasonable.
Keyword: cable-dome; construction scheme; dynamic relaxation method; original length; model experiment
E-mail: wzchenlm@sina.com

A study on the wind-induced buffeting responses of large-span roof structures

Gu Ming Zhou Xuanyi Huang Peng
（Tongji University, Shanghai 200092, China）

Abstract: A systematic method is developed for test and analysis of the non-steady wind pressure distributions in wind tunnel test of wind-induced dynamic responses of large-span roof structures. The parallel tube-manifold system is applied to augment the number of simultaneous measuring points to ensure that the non-steady wind pressures on a large-span roof can be obtained simultaneously from the rigid model wind tunnel test. The wind-induced buffeting responses can be computed by using the mode-superposition method (Complete Quadratic Combination method), to take the modal coupling effects into account, and a corresponding computer code-SWDP is developed. The characteristics of the buffeting responses of the roof structure of the Shanghai South Railway Station are analyzed. The results indicate:(1)the parallel tube-manifold system can effectively extend the number of simultaneous measurement points of wind pressures,(2)the non-steady wind load-based CQC method can be effectively employed for computing the dynamic responses of large roof structures, and (3) the background components usually contribute significantly to the total buffeting responses.
Keywords: large-span roof structure; non-steady wind pressure; parallel tube-manifold system; complete quadratic combination method; dynamic response
E-mail: minggu@mail.tongji.edu.cn

A complex partial quadratic combination (CPQC) method for
seismic responses of non-classically damped linear system

Yu Ruifang Zhou Xiyuan
（Beijing Key Laboratory of Earthquake Engineering and Structural Retrofit,
Beijing University of Technology, Beijing, 100022）

Abstract: For non-classically damped linear systems, when the complex mode superposition method based on seismic response spectrum, i.e. the complex complete quadratic combination (CCQC) formula, is used for seismic response analysis, the amount of calculation is fairly large. Hence, the applicability of the CSRSS (complex square root of the sum of squares) method is provided for studying the variations of the modal displacement, velocity, displacement-velocity correlation coefficients along with the ratios of different frequencies and damping. Based on these analyses, a simplified method, which only considers the contributions from relatively adjacent modes in CCQC method and is named as simplified CCQC or complex partial quadratic combination (CPQC) method, is proposed for reducing computational time. A numerical example is presented to analyze the applicability, computational accuracy and efficiency. The proposed simplified method is useful for classically damped linear systems as well, and may also be named as a partial quadratic combination (PQC) method.
Keywords: mode superposition; non-classical damping; Complex Complete Quadratic Combination (CCQC) Method; Complex Partial Quadratic Combination (CPQC) Method; Partial Quadratic Combination (PQC) Method
E-mail: yuruifang@emails.bjut.edu.cn

An experimental study on double-K fracture parameters of concrete for dam construction with various grading aggregates

Xu Shilang1 Zhou Hougui2 Gao Hongbo1 Zhao Shouyang 2
（1. The State Key Laboratory of Coastal and Offshore Engineering, Dalian University of
Technology, Dalian 116024, China; 2. China Gezhouba Group Corporation, Yichang 443002, China）

Abstract: To further provide sufficient test data for formulating the norm fracture of hydro-engineering concrete in China, as suggested by the committee on norm concrete fracture test, a series of fracture tests were performed on a total of 140 specimens via three-point bending and wedge-splitting, with the maximum dimensions being S×D×B=2200 mm×550 mm×240 mm and 2H×D×B=1200 mm×1200 mm×250 mm respectively. With the arrangement of electric resistance strain gauges, the load vs. strain curves are obtained, and the initial cracking load and maximum load are specified. Double-K fracture parameters are calculated, and discussions on the size effect and geometry effect are also made. The results indicate that it is feasible to measure the initial cracking load by using electric resistance strain gauge and the ratio of the initial cracking load to the unstable fracture load that approximately falls into the range from 0.6 to 0.85. Based on the test results of three-point bending of beams, the double-K fracture parameters are rather size-independent. While for the wedge-splitting specimens, the influence of additional vertical load induced moment on the stress field around the crack tip enables the double-K fracture parameters to exhibit size effect to some extent. However, when eliminating or reducing such influence, wedge-splitting geometry has no obvious size effect on the double-K fracture parameters. The double-K fracture parameters, determined from using the same concrete and depth but different geometries are comparable, indicating that the double-K fracture parameters are independent of size and geometry and can be treated as the fracture parameters to describe fracture initiation and instability for crack propagation in concrete structures.
Keywords: concrete fracture test norm; double-K fracture model; three-point bending beam; wedge-splitting specimen; size effect；geometry effect；initial cracking load
E-mail: slxu@dlut.edu.cn

Experimental study on the tensile performance of steel flber reinforced concrete

Han Rong1 Zhao Shunbo2 Qu Fulai3
(1．Beijing Jiaotong University，Beijing 100044，China；2．North China University of Water Conservancy and Electric Power，Zhengzhou 450011，China；3．Dalian University of Technology，Dalian 116024，China)

Abstract: The effects of steel fiber volumetric ratio, steel fiber slenderness ratio and steel fiber type on the splitting tensile strength, axial tensile strength and axial tensile stress-strain curve of steel fiber reinforced concrete (SFRC) are studied. In axial tensile stress-strain SFRC tests, axial tensile specimens of various cross-sections with embedded end reinforcements are tested in an ordinary universal test machine with a subsidiary rigid frame added. The results indicate that both the splitting tensile strength and the axial tensile strength of SFRC increase with the increasing of the steel fiber volumetric ratio and the steel fiber slenderness ratio. Axial tensile stress-strain curves of SFRC are obtained. The effects of the steel fiber volumetric ratio and the concrete strength on the axial tensile stress-strain curve are studied. A relationship between the axial tensile strength and the splitting tensile strength of SFRC is proposed. An analytical formula for the axial tensile stress-strain relationship of SFRC is proposed.
Keywords: steel fiber reinforced concrete (SFRC)；axial tensile strength；splitting tensile strength；stress-strain full curve
E-mail: hrhanrong@163.com

Design methods and construction techniques for the outer-jacketing structure reconstruction(extension)project of the Suifenhe Qingyun Market

Zheng Wenzhong1 Liu Tie1 Tan Jun1 Xie Hengyan1 Li Zhongmin2
（1. Harbin Institute of Technology, Harbin150090，China;
2. SuiFenHe Trading Co., Ltd., Suifenhe157300, China）

Abstract: In connection with the reconstruction(extension)project of the Suifenhe Qingyun Market, a design approach is proposed, in which similar links are employed to connect the newly-added frame and the original structure only at the roof of the original building, and the new structure and the original structure are connected by links at each floor after settlement of the new structure is complete. Similar connections between the original structure and the outer-jacketing frame columns are formed during construction by using concrete blocks placed between the roof of the original building and the outer-jacketing frame columns and by prestressing the reinforcing tendons between the two outer columns. After the new structure is constructed, steel bars embedded in the two outer columns at the height of the roof of the original building are welded together, and concrete of a certain depth is cast. In this way, the permanent firm connection between the roof of the original structure and the new structure is formed. The post-installed steel bars in the original frame joints are welded with embedded steel bars in the outer columns to work as the connection at each floor. In order to ensure that the original building works as usual during the construction, the design and construction methods of self-supporting concrete floor during construction are presented, the main idea of which is that the steel truss suspended by formwork can bear the construction load of encased steel-truss-concrete composite beam, that the steel box suspended by formwork can support the construction load of encased steel-box-concrete composite beam, and that the channel welded perpendicular to the encased steel box can carry the floor load.
Keywords: reconstruction(extension)project; prestress; encased steel truss-concrete composite frame beam; encased steel box-concrete composite secondary beam
E-mail: zhenwenzhong@hit.edu.cn

Experiments on the torsional behavior of FRP strengthened RC box beams
subjected to combined action with cyclic torque

Li Zhongxian Jing Meng
(Tianjin University, Tianjin 300072, China)

Abstract: Experiments on the torsional behavior of RC box beams strengthened with fiber-reinforced polymer (FRP) laminates are performed under the combined action of bending moment, shear and cyclic torque. Four RC box beams are designed and fabricated, of which, three are strengthened with FRP laminates and one is kept as original for comparison purpose. The tests were run on a self-manufactured torsion test apparatus, and the box beams are synchronously subjected to bending moment, shear and cyclic torque. Take the strengthening scheme and the number of FRP layers as the main parameters, the failure mode, torsion capacity, deformation capacity and hysteresis behavior of the specimens are investigated. According to the change of strains in FRP and reinforcement, the torsional mechanism of the FRP strengthened box beams is discussed. Based on the hysteresis and the torque vs. twist-angle curves, a model is developed for the torsional recovering force of the FRP strengthened box beams, which provides an important reference for theoretical study and engineering application of the FRP torsional reinforcement to RC box beams.
Keywords: reinforced concrete(RC)box beam; torsional behaviour; strengthening; fiber-reinforced polymer (FRP) laminate; combined action; cyclic torque
E-mail: zxli@tju.edu.cn

Study on the seismic response control of self-anchored suspension bridges with MR dampers

Yang Menggang 1，2 Chen Zhengqing 2 Hu Jianhua 3
（1.Central South University, Changsha 410075, China; 2. Hunan University, Changsha 410082, China;3. Hunan Provincial Communications Planning, Survey and Design Institute, Changsha 410008, China）

Abstract: To mitigate the seismic response of self-anchored suspension bridges, based on the earthquake dynamic equation of bridge structure and a mechanical model of magnetic-rheological (MR) damper, a system composed of the bridge structure and the MR damper is established, and a computer program is developed and employed for studying the seismic response control of a single-tower self-anchored suspension bridge with a main span of 350m. The effect of seismic response control via variable current, number and setting position of MR dampers is discussed. The study indicates that MR dampers can effectively reduce the longitudinal seismic response of self-anchored suspension bridges. With increase in the input current and the number of MR dampers between the main tower and the main girder in the longitudinal bridge direction, the longitudinal displacements of the tower top and the main girder decrease, and the internal force response of the structure can effectively be controlled. The best effect of seismic response control would be reached when all MR dampers are placed between the main tower and the main girder in the longitudinal bridge direction.
Keywords: suspension bridge; self-anchored; MR damper; seismic response control
E-mail: mgyang@mail.csu.edu.cn

A study on the design method of seismic restrainers for bridges

Wang Junwen1 Li Jianzhong2 Fan Lichu2
（1. Shijiazhuang Railway Institute, Shijiazhuang 050043, China；2. Tongji University, Shanghai 200092, China）

Abstract: Seismic restrainers are often needed at expansion joints of bridges to prevent the superstructures from falling off during earthquakes. Factors affecting the relative displacement between bridge segments at expansion joints are investigated, and a design procedure for restrainers, based on a linearized model, is developed. This restrainer design procedure not only takes into consideration the dynamic characteristic out-of-phase motion of adjacent bridge segments, but also the effect on the relative displacement due to impact between bridge segments. Inelastic behavior of piers is represented by using the substitute structure method, and the effect of impact on relative displacement is considered by using the relative displacement response spectra with impact effect. Reliability of the proposed restrainer design procedure is validated through parametric studies, and the effect of this restrainer design procedure in limiting relative displacement is assessed by comparing with existing restrainer design procedures. The results of the studies indicate that, comparing with existing restrainer design procedures, the restrainers designed from using proposed procedure are more consistent with those from nonlinear time-history analysis.
Keywords: earthquake; bridge; pounding; restrainer; design procedure; seismic response
E-mail：wjunwen2901@163.com

Test on the lateral bearing behavior of a diaphragm wall in loess area

Meng Fanchao1 Li Tao2 Chen Xiaodong 1 Gong Weiming 2
(1.China Highway Planning and Design Institute Consultants, INC., Beijing100010,China;
2. Southeast University, Nanjing 210096, China)

Abstract: As a new type of foundation, the shaft diaphragm wall is employed for an arched bridge in loess area. To study the lateral bearing behavior, one single diaphragm wall is tested under lateral load. Strain gauges and deflection inclinometer are embedded inside the wall, and pressure cells are embedded at the back side of the wall. Slow sustaining load is applied in the test, the displacement, strain and soil resistance data are collected, and relationship between the lateral load, H, and the displacement, Y, is derived. The bending moment is calculated from the strain by using the calibrated section method and the theoretical method, soil resistance is calculated from the bending moment according to the elastic foundation beam theory, and comparisons with the actual values are conducted. The lateral bearing capacity, internal force and lateral displacement of the single diaphragm wall, the distribution of soil resistance, the relationship between soil resistance and lateral displacement at different depths (q-y curve) and the m-value of the lateral subgrade coefficient are calculated through analyzing the test data.
Keywords: diaphragm wall foundation; single diaphragm wall; lateral load; lateral displacement; bending moment in wall; soil resistance; m-value
E-mail: chenxiaodongsir@vip.sina.com

Experimental study of shaft ventilation modes for road tunnels in case of fire

Yan Zhiguo1 Yang Qixin2 Wang Mingnian3 Zhu Hehua1
（1．Tongji University， Shanghai 200092，China；
2．Southwest Jiaotong University，Chengdu 610031，China）

Abstract: To establish an effective ventilation mode for fire fighting in the Qinling road tunnel, an experiment is carried out to study the temperature distribution and smoke propagation in the ventilation duct and shaft of the tunnel in case of fire.. The model tunnel is 100 m long, has a circular cross-section with an inner diameter of 1.8 m. Two ventilation shafts with a diameter of 1 m are constructed. An oil pool is employed as the source of fire. Three fire loads and three fire locations are employed to simulate different fire scenarios. The results indicate that the temperature distribution and smoke propagation vary significantly with different fire loads, fire locations, ventilation modes and fire stages in the tunnel, the ventilation duct and the shaft. These phenomena suggest that different ventilation modes, in case of fire, should be considered in order to show a consistent effect with the fire locations and fire stages. Based on the results of the experiments, an effective ventilation mode is established for fire fighting in the Qinling tunnel.
Keywords: road tunnel；tunnel fire；experimental study；ventilation mode
E-mail: yanzguo@126.com

Signal-processing-based ITS data compression techniques and applications

Geng Yanbin1 Yu Lei2，3 Wu Xu2 Liu Menghan2 Zhao Hui2 Wu Jiaqing 4
(1. Transport Planning and Research Institute, Ministry of Communications, Beijing 100029, China;2. Beijing Jiaotong University, Beijing 100044, China; 3. Texas Southern University,
Houston TX 77004, U.S.A; 4. Beijing Public Transport Holdings, Ltd., Beijing 100073, China)

Abstract: The rapid development of Intelligent Transportation Systems (ITS) data collection technologies has generated massive ITS data, presenting a critical obstacle to storing, transmitting and disseminating the data within the transportation system. After analyzing the characteristics of ITS data, this paper proposes a highly effective ITS data compression and reconstruction approach with a limited distortion by designing the appropriate feature-distilling threshold and quantizer, based on the Wavelet Transform, Discrete Cosine Transform (DCT), and Quantizing and Coding techniques for signal-processing. The objective of the compression is to minimize the data redundancy, keep the maximum amount of useful information and limit the level of distortion. Test on the traffic flow data of the 3rd ring expressway in Beijing demonstrates that the proposed technique has increased the compression rate by 61.92 percent in comparison with the widely used lossless compression approach (WinZip software), and that only 1.27 percent of the data has shown a larger-than-five-percent error between the reconstructed and the original raw data. This indicates that the proposed technique can significantly improve the effectiveness of compression with a limited distortion.
Keywords: Intelligent Transportation Systems (ITS); data compression; wavelet transform; degree of distortion; quantizing
E-mail: ybgeng@tom.com

Model and algorithm of transportation network design for emission reduction

Zhang Haozhi Gao Ziyou Zhang Bei
(Beijing Jiaotong University, Beijing 100044, China)

Abstract: The total emissions in congested urban transportation networks depend significantly on the emission factor, the road traveling time and the intersection delay. Road capacity enhancement and signal timing adjustment directly affect the emission factor, the road traveling time and the intersection delay, and consequently the total emissions. Therefore, two speed-related emission factors, i.e., the road-traveling emission factor and the intersection-queuing emission factor, are introduced, according to the vehicle traveling condition, and a formula for total-emission calculation, applicable to transportation network design, is proposed. Signal timing and road network design problems are simultaneously optimized to minimize the total emissions by using the bi-level programming approach. The bi-level programming model can determine the optimal road capacity enhancement and the optimal signal circle and signal split with the objective being total emission minimization. Based on the Particle Swarm Optimization (PSO) algorithm, a simple global solution algorithm is designed for the bi-level programming model. An example is presented to verify the proposed model and algorithm.
Keywords: transportation emission; road network design; signal timing; bi-level programming; particle swarm optimization
E-mail: haozhizhang7@126.com

Management performance improvement of agent system for
government invested construction projects

Yan Ling Yin Yilin
（Tianjin University of Technology, Tianjin 300072, China）

Abstract: Government investment projects play important roles in the economy of China. However, the current administration agent system of public projects has resulted in low efficiency in the work performance. As one of the significant reform methods, an agent construction system still has some aspects that need to be improved. Whether the reformation of an agent construction system is more effective and how to improve its performance are the issues discussed in the paper. In the framework of a new paradigm of project governance, the evolution of governance model of public projects is explored, whereas the project ownership arrangement in the context of administration agent system is analyzed. Moreover, the corresponding primary evaluation indexes of governance level are set up together with the agent construction program.. In conclusion, a new paradigm of the project governance theory to improve the management performance of agent construction system is established, including three routes: internal project governance, external project governance and government supervised mechanism.
Keywords: public project; agent construction system; project governance structure; evaluate index of governance level; project performance improvement
E-mail: lingyantj@163.com