ABSTRACT

Experimental study on bond-slip behavior between FRP and concrete

Guo Zhanggen¹　 Sun Weimin²　 Cao Shuangyin¹
(1. Nanjing University of technology, Nanjing 210009, China;
2. Southeast University, Nanjing 210096, China)

Abstract: FRP laminates, because of their superior properties, are being successfully used for the strengthening of existing reinforced concrete structures. Critical to strengthening a concrete structure through externally bonded FRP plates is the bond behavior between FRP and concrete. A modified beam test specimen was employed to study the bond behavior and the force transfer of the composite material plates adhered to concrete. The influences of the bond length, and concrete strength on the bond behavior was investigated, the strain development and distribution in GFRP sheet along the bond length was obtained, and the direct shear bond stress distribution and local bond stress versus slippage relationship were analyzed. Based on the test results, three local bond stress-slip constitutive models were proposed. These models matches the experimental results well，and are valuable references for the corresponding codes and engineering applications.
Keywords: FRP；strengthening；bond behavior；slip；constitutive model

E-mail: zhgguo@163.com

Experimental investigation on the fatigue behavior of corroded RC beams

Yi Weijian　Sun Xiaodong
(Hunan University, Changsha 410082, China)

Abstract: The fatigue property RC beams, including its relationship with the rusted main bars, was studied. A control RC beam without steel corrosion and eight RC beams with steel corrosion rates ranging between 4%～12% were tested under fatigue loading. The results of fatigue test showed that the stiffness of the beams performs with three distinctive stages under the fatigue cycle loads, i.e., decline-stabilize-rise stages. There were large amount of spot corrosions resulting from uneven corrosion of the main bars. Generally, the failure of the corroded RC beams occurred at locations with a high stress amplitude and with spot corrosions on the tensile steel bars. With the increase in the corrosion rate for the main bars, the fatigue lifespan of the corroded RC beams is shortened considerably. The fatigue failure of corroded RC beams occurred in the form of brittle fracture of tension steel bars without any precursors. The dynamic testing results showed that the fundamental frequency of corroded RC beams did not decrease monotonously with the cumulated fatigue damage. So the fundamental frequency obtained from the vibration test can not be used to predict the failure of the rusted main bar of the RC beams under fatigue loads. It was also shown that the rusted main bars were converted from the soft steel into hard steel with an increase in the fatigue stress amplitude under the same fatigue cycle loads.
Keywords: steel corrosion; corroded main bar; reinforced concrete beam; fatigue test; fatigue lifespan

E-mail: hunuyi@public.cs.hn.cn

A stability analysis of major diameter thin-walled tube beam-columns

Pan Hanming^1,2　Guo Yanlin¹　Liang Shuo¹
　 Liang Weisheng¹Pei Shengxing² Wang Lewen²
(1. Tsinghua University, Beijing 100084, China；
2.Guangzhou New TV Tower Development CO.,Ltd., Guangzhou 510310, China）

Abstract: For major diameter thin-walled tube beam-columns (MDTTB) with diameter-thickness ratios exceeding 100, there exists no corresponding regulation and reference in the current design standard of steel structures. The influences of initial imperfection, slenderness ratio and unequal end moment on the stability capacity of MDTTB are investigated by using nonlinear finite element analysis. The results indicate that with the increase in diameter-thickness ratio, the stability bearing capacity of MDTTB is clearly reduced. According to the related design standard of steel structures, and on the basis of the numerical analysis results, the formulas for calculation of the stability bearing capacity of MDTTB are presented. Three tests of thin-walled steel tube beam-columns are reported. The deformation and ultimate strength from the tests are found to be in good agreement with the corresponding formula-calculated values, indicating that the proposed method is effective，reliable and convenient for design applications.
Keywords: major diameter thin-walled steel tube; stability bearing capacity of beam-column; initial imperfection; slenderness ratio l

E-mail: chinap@mail.tongji.edu.cn

A study on the shear resistance of aluminum alloy 工 sections

Dong Zhen　Zhang Qilin
(Tongji University, Shanghai 200092, China)

Abstract: The design method for the shear resistance of aluminum alloy 工 sections is presented, taking into consideration of the post-buckling strength of webs and the restraint effect of flanges, and the practical design formulas are proposed. The deflection of aluminum alloy 工 sections under concentrated load is simulated by using the finite element method, and several design theories are discussed. The shear resistance vs. the maximum web displacement curve reflects that the web of aluminum alloy 工 sections is under less shear buckling force, while the entire member has rather high shear resistance. However, the traditional design method is not able to give the real shear resistance of aluminum alloy 工 sections. The analysis shows that the proposed design formulas for the shear resistance of aluminum alloy 工 sections ought to calculate accurately the post-buckling resistance of webs and the shear resistance contribution of flanges. The proposed design formulas are simple and convenient, and the calculation results are consistent with the test data of Hamoodi M J, Burt C A, Evans H R and the calculation results from using Eurocode 9 formulas.
Keywords: aluminum alloy；section；shear resistance；finite element analysis；design study

E-mail: dz_china@126.com

Axial compression test and analysis of circular tube confined HSC stub columns

Zhang Sumei Liu Jiepeng Ma Le Xing Tao
(Harbin Institute of Technology, Harbin 150090, China)

Abstract: A total of 18 circular tube confined high strength concrete (HSC)stub columns were tested under cyclic or monotonic axial compression. The parameters in the study include the compressive strength of concrete (fcu=88.14~94.17 MPa) and diameter-to-thickness ratio of the steel tube (D/t=21.62~43.01). The experimental results indicate that the axial bearing capacity of a steel tube confined concrete stub column is greater than that of a CFT column with equivalent parameters, while difference in ductility is insignificant. The axial bearing capacity of the columns increases as the longitudinal stress of the steel tube decreases. The results of elasto-plastic analysis of the steel tube indicate that the steel yields at the peak load. A design equation is proposed to calculate the axial bearing capacity of circular tube confined concrete columns. The results from the proposed equation for stub columns are consistent with the test results. A modified Mander’s model that is suitable for confined HSC is proposed based on the test results.
Keywords: circular tube confined HSC; cyclic axial compression; diameter-to-thickness ratio; axial load strength

E-mail: smzhang@hit.edu.cn

Fire resistance of reinforced concrete columns of T-shaped cross section

Wu Bo¹　　Xu Yuye²
(1. South China University of Technology, Guangzhou 510640, China;
2. Huaqiao University, Quanzhou 362021, China)

Abstract: Analyses were performed to study the influence of several parameters, such as load ratio, effective length, section dimension, load eccentricity ratio, reinforcement ratio and load angle, on the fire resistance of reinforced concrete columns of T-shaped cross section exposed to the ISO834 standard fire. 5400 hypothetical cases of columns subjected to fire in all sides were selected for fire response analysis. Different load ratios, effective lengths, cross section dimensions, load eccentricity ratios, reinforcement ratios, and load angles were considered in the analyses. Based on the simulation results, a practical method is proposed for calculating the fire resistance of columns of T-shaped cross section subjected to fire in all sides. The simulation results indicate that:(a)reducing the load ratio is an effective measure to improve the fire resistance of columns of T-shaped cross section;(b)the fire resistance of columns of T-shaped cross section decreases linearly with the increase of effective length;(c)the fire resistance of columns of T-shaped cross section decreases significantly with the increase of load eccentricity ratio from 0.0 to 1.0, whereas varies only slightly for a load eccentricity ratio between 1.0 and 2.0; and(d)the influence of load angle on the fire resistance of columns of T-shaped cross section is significant and complex.
Keywords: reinforced concrete column; fire resistance; T-shaped cross section; practical calculation method

E-mail: yuyexu@tom.com

Shaking table test and analysis of core-tube partial suspension structures

Cao Wanlin Lu Zhicheng Zhang Jianwei Chang Wehua Zhao Changjun
(Beijing University of Technology, Beijing 100022)

Abstract: A type of core-tube partial suspension structure is proposed. It take advantage of both the core-tube suspension structure that is good in earthquake resistant performance and the frame core-tube structure that has more lines of seismic resistance, consisting of core-tube suspension with dampers and pure concrete blocks between core tube and suspension floors in the upper four-storey for strong seismic responses and frame core-tube in the bottom four-storey for weak seismic responses .The system can achieve effective control over earthquake responses. A shaking table test of a 1/10 scale model of this type of structure, involving elastic and elasto-plastic stages, is described. A dynamical model is formulated and the dynamic characteristics and earthquake responses of the structure under the El Centro wave are analyzed. The experimental results indicate that the structure performs well under seismic conditions. The elastic and elasto-plastic time-history analyses of the structure are conducted by using SAP2000, and the simulation results agree well with those of the experiment.
Keywords: core tube; partial suspension structure; vibration control; shaking table test

E-mail: wlcao@bjut.edu.cn

Network of energy transfer in frame structures and its preliminary application

Zhang Leiming Liu Xila
(Shanghai Jiaotong University, Shanghai 200030, China)

Abstract: Based on the energy transfer in frame structures under various loading conditions, a network of energy transfer is constructed for structural members and joints. Using the graph theory, the key path of energy transfer in frame structures, namely the most important loading-carrying path, is determined in accordance with the energy transfer in and out of members and joints. By comparing the change of strain energy in the structure with different members removed, the index of member importance is introduced. By tracing the change of the index of member importance due to failure of members, the most important failure mode is determined. A three-story frame collapsed during the Tangshan earthquake is analyzed, illustrating that the presented procedure is effective in determining the index of member importance, the most important load-carrying path as well as the most important failure mode, with full consideration of different loading conditions.
Keywords: Network of energy transfer; importance of member; most important load-carrying path; most important failure mode

E-mail: lmzhang@sjtu.edu.cn

Calculation of the punching shear bearing capacity of
pile caps with ordinary uniform grid reinforcement

Guo Honglei
（Jiang Han University, Wuhan 430056, China）

Abstract: Based on a study on the spatial strut-and-tie bearing mechanism of pile caps, nonlinear finite element analyses are conducted, and combining with a gradual least square method for multiple variables, theoretical formulae are derived for the punching shear bearing capacity of pile caps with ordinary uniform grid reinforcement. Verification study with the published test data of 76 in the literature, including the critical section stress method of the ACI318-05 code, the American CRSI handbook method, the Chinese code JGJ94—94 and GB50007—2002 methods, indicates that the proposed method is suitable for the calculation of the punching shear bearing capacity of pile caps with ordinary uniform grid reinforcement.
Keywords: pile cap;punching shear; spatial strut-and-tie; bearing capacity; calculation

E-mail: ghl5186@yahoo.com.cn

Effects of riverbed scouring depth on the seismic response of bridges on pile foundations

Ye Aijun^1,2　　Zhang Xigang²　　Liu Weian¹
(1.Tongji University, Shanghai 200092, China;
2.China Highway Planning and Design Institute, Beijing 100010, China)

Abstract: Taking a super long-span cable-stayed bridge as the background, a pilot study was carried out to investigate the effect of riverbed scouring depth on the seismic response of a bridge on pile-foundations. A two-particle single-pier model was established to approximately simulate the dynamic behavior of a pier and its high-rise pile cap foundation, the seismic responses corresponding to different scouring depths were calculated, and the dynamic interaction between the pile foundation and the pier was analyzed. The results indicate a significant resonance between the pier and pile foundation because of the large pile-cap mass. Six finite element models corresponding to six riverbed scouring depths of the entire bridge were established, the effects of scouring depth on the seismic response of side piers and towers were analyzed. The conclusion is that the scouring depth has a significant effect on the seismic response of the bridge, and as the scouring depth increases, the seismic response of the bridge does not monotonously decrease, and there possibly is a peak value.
Keywords: Riverbed scouring; bridge on pile foundation; seismic response; resonance

E-mail: yeaijun@mail.tongji.edu.cn

Effect of spatial prestressing for curved box girder bridges

Zhou Xuhong^1,2,3 Dai Peng¹ Di Jin1 Shang Anfan¹
(1.Chang’an University, Xi’an 710064, China; 2.Lanzhou University, Lanzhou 730000, China;
3.Hunan University, Changsha 410082, China)

Abstract: Curved box girder bridge is a complicated spatial structural system. The effect of prestressing may improve the bearing capacity of the members, but may also adversely affect the structure. Using a spatial composite finite element method, combining three-dimensional solid element and bar element, the mechanical analysis of a two-span curved PC continuous box girder bridge is conducted. According to the mechanical characteristics of the bridge, the calculation method for prestress friction loss of the spatial curved prestressed wires is studied. The impact of prestressing radial force on the web plate is analyzed, and the composite finite element method and a simplified method are compared. Two computational models are established to study the influence of prestressing on the bearings, the spatial arrangement between the radial bearings and the approach to promote the performance of the bearings.
Keywords: bridge engineering; curved box girder; prestressed concrete; box girder web; bearing reaction; finite element analysis

E-mail: zxh@lzu.edu.cn

Aerodynamically coupling flutter analysis and flutter mechanism for bridge deck sections

Ding Quanshun Zhu Ledong
(Tongji University, Shanghai 200092, China)

Abstract: A 2DOF coupling flutter analysis is presented based on an uncoupling of torsional and vertical coupled motion equations of system, in which the frequencies and damping ratios of the system vibration characteristics are expressed implicitly as functions of flutter derivatives. It has been noted that the results of the presented method at the critical flutter state is theoretically exact since the critical flutter motion is constant-amplitude and periodically. The comparison of the results with the exact ones by a characteristic analysis of system motion equations is performed so the reliability and applicability of the presented method is proved. Moreover, the mechanism of aerodynamically coupling flutter for a typical bridge deck section is investigated. It is noted that the effect of the coupling flutter derivatives on the frequency of the system modes is small and the aerodynamic damping is mainly made up of the terms of direct flutter derivatives and A*1A*3.
Keywords: bridge deck section; aerodynamic coupling; flutter analysis; flutter mechanism

E-mail: qsding@mail.tongji.edu.cn

Nonlinear model based on damping ratio for clays under seismic loading

Shang Shouping Liu Fangcheng Wang Haidong
(Hunan University, Changsha 410082, China)

Abstract:A dynamic stress-strain model based on the damping ratio of clays is proposed. Importing of the shape coefficient, which represents the soil’s damping ratio, into the hysteretic loop curve function, makes that the theoretical hysteretic stress-strain loop reflect the actual damping characteristics of the soil. The theoretical functions of the hysteretic loops under symmetrical constant amplitude loading are deduced first. Then for the usage of the hysteretic loop model based on damping ratio under seismic loading, the rebuilding of the expanded Masing’s rules is discussed. It is proposed that when the loading or unloading path is on the so-called“small loops”, the loop curve points to the maximum or minimum loading point ever reached in the history. Finally, a cyclic simple shear testing of silt clay is introduced, under both constant amplitude loadings and irregular loadings. The test results indicate that the proposed model can simulate the hysteretic behavior of soils well.
Keywords: nonlinear; constitutive relation; damping ratio; irregular loading; clay; cyclic simple shear test

E-mail: sps@hnu.cn

Coupling analysis of thermal field and stress field for immersed tunnels under fire load

Zhang Mengxi Huang Jin He Xiaoqiang
（Shanghai University，Shanghai 200072, China）

Abstract: The analysis of thermal field and stress field for the immersed tunnel of the Outer-Ring Expressway in Shanghai under fire load was carried out by using the finite element method. Analytical theory and variation of the mechanical behavior of concrete with time were introduced. On the basis of experimental study of tunnel fire, the analytical model along with the boundary conditions was established. The appropriate structural equations were provided. From the results of the finite element analysis, the coupling of thermal field and thermal stress under different temperatures was presented. The analytical results were compared with experimental ones.
Keywords: immersed tunnel; fire load; thermal field; stress field; finite element method; coupling analysis

E-mail: mxzhang@shu.edu.cn

Discussions on predicting the stability of flexible shotcrete and
steel arch frame support for tunnels

Shen Caihua^1，2 Tong Liyuan¹
（1.Southeast University, Nanjing 210096，China；2.Hohai University, Nanjing 210098，China）

Abstract: Since the introduction of the New Austria Tunneling Method (NATM) into China, flexible support composed of anchor, sprayed concrete and steel frame is widely employed in the excavation of large-span road tunnels. Due to lack of a systematic method for forecasting the stability of flexible support, the principles of NATM, however, can not be realistically carried out, resulting in some accidents. In the study of the characteristics of flexible support, a method is proposed for forecasting the stability of the support, based on measurement of strain of the steel arch. With the bending moment and axial and shear forces of the primary support taken into consideration, along with the characteristics of accidents in excavation, the forecasting method evaluates safety by using different ranks, which makes it easier to employ on site. The field testing indicates that this method can reveal the safety and stability levels of surrounding rocks and the primary support.
Keywords: New Austrian Tunneling Method；flexible support；arching-effect；safety evaluation

E-mail: shencaihua@163.com

Studies on capacity of signalized intersections influenced by pedestrian traffic

Chen Xiaoming Shao Chunfu Nie Wei
(Beijing Jiaotong University, Beijing 100044, China)

Abstract: It is a problem of concern to quantify the effect of pedestrian traffic on capacity of signalized intersections. The behaviors of pedestrians and mechanism of pedestrian-vehicle conflict are analyzed in this paper. Pedestrian arrivals in groups are taken into account. Capacity of conflict zone is modeled based on platoon analysis method. The model is calibrated according to field data and lays a foundation for calculating capacity of signalized intersections influenced by pedestrian traffic. Vehicular capacity computed by the proposed model depends much on average conflict times and is generally lower than that by method of Highway Capacity Manual (HCM, 2000). The downtrend of vehicular capacity becomes less and less sharp accompanied by the increase of conflicting pedestrian volume. The proposed model is developed on basis of mechanism of conflict zone, and is more universally applicable. The research provides a theoretical basis for signal timing and traffic management at intersections in mixed traffic condition.
Keywords: signalized intersection; capacity; pedestrian-vehicle conflict; platoon analysis method; pedestrian behavior; gap acceptance

E-mail: chenxm11@163.com

Relationship between fractal dimension and road performance of dense-gradation asphalt mixture

Yang Ruihua Xu Zhihong
(Tongji University, Shanghai 200092,China)

Abstract: The fractal models of grain size distribution, aggregate volume and aggregate pore are deduced from the composition of aggregation by using the theory of fractal geometry. The fractal dimension of aggregate volume is an important parameter with rich information content. There is a strong correlation between the fractal dimension of aggregate volume and the air void of asphalt mixtures. A regression model for the fractal dimension of aggregate volume and air void of AC-16 is derived. The correlations between road performance and the fractal dimension of aggregate volume of AC-16 are obtained from road tests. With the fractal dimension of volume being increased, the high temperature stability performance and anti-skidding performance of asphalt mixtures are weakened, whereas the moisture susceptibility and the low temperature anti-split performance are improved. The road performances of asphalt mixtures with different fractal dimensions of aggregate volume can be estimated accordingly.
Keywords: road engineering; asphalt mixture; dense-gradation; fractal; road performance

E-mail：yangruihua1995@163.com

Calculation method for prediction of highway asphalt pavement rutting under dynamic loading

He Zhaoyi¹　　Lei Ting ¹　　Wang Guoqing² Hou Yanfeng²
(1. Chongqing Jiaotong University, Chongqing 400074, China;
2. Hebei HanChang Highway Construction Branch, Shijiazhuang 050031, China)

Abstract: Based on the coupling of vehicle dynamic loading and the pavement surface unevenness, a calculation method is formulated for prediction of highway asphalt pavement rutting under dynamic loading. A simplified vehicle dynamic loading model is established, and the Burgers model parameters of the asphalt pavement mixture are acquired through creep test in the laboratory with different gradations, temperatures and asphalt aggregate ratios. The method for the rutting equivalent axle loading and the time-series of the vehicle loading are proposed. Through measuring the temperature in the pavement and the dynamic stability of the pavement materials, a new method is established for calculating the representative temperatures in the surface of the highway. Through the different time-series of the repetition and progression in pavement loading, revised parameters of asphalt pavement under dynamic loading are proposed on the basis of the calculation. The prediction of rutting is performed by analysis of the asphalt pavement rutting and loading revised parameters by using the finite element method. The error is 8%～9.5% between the calculation and prediction of asphalt pavement rutting for the test road of the Handan—Cangzhi highway. The agreements between the calculation results and the test data indicate that the rutting prediction method is reasonable and reliable.
Keywords：asphalt pavement; dynamic loading; viscoelastic mode; rutting prediction

E-mail: hzyzwb@cquc.edu.cn