Key Engineering Materials Vols. 400-402

Abstract: Steel Fiber Reinforced Self-stressing Concrete (SFRSSC) is a new type of fiber reinforced composite material. It has various applications in civil engineering for its well known superior properties such as self-expansive performance and high tensile resistance. However, it is not widely accepted as an effective reinforcement in the rehabilitation of the old bridges at present. The primary goal of this research is to apply SFRSSC to improve the crack resistance in the negative bending moment areas of the old bridges. Firstly, a computer analysis on the internal force of the continuous T-beams with 5 spans is given in this paper. The results show that the expansive action of SFRSSC can effectively decrease the internal force in the negative bending moment area. Meanwhile, based on the experiments of 5 composite concrete inverted T-beams, the crack resistance of the beams reinforced with SFRSSC layers is investigated. The test results obviously indicated that the composite layers enhanced the cracking moments 44.9% more than conventional concrete layers, though its height is only 13.9% of the cross section height. It is concluded that the continuous beams strengthened by SFRSSC has greatly improved the crack resistance in negative bending moment areas compared with the continuous beams strengthened by conventional concrete. According to the existing theoretical models, a procedure how to determine the self-stress is supplied and a formula which evaluating the crack resistance of composite T-beams in negative moment area is deduced in order to supply references to the old bridge rehabilitation design.

Abstract: Experimental research on square and octagonal concrete filled thin-walled steel tube long columns of 6 specimens in axial compression and 8 specimens in eccentric compression is undertaken. The relationship of global buckling bearing capacity of the columns and local buckling of the steel tubes is obtained. The test indicates that local buckling occurs in steel tube of each column before it reaches ultimate capacity, and has little effect on global buckling performance. The ultimate load decreases obviously with the increase of slender ratio and eccentricity. The ductility of columns increases with the increase of steel ratio in composite sections. Composite beam element of ANSYS is adopted in the finite element analysis. The theoretical results are agreed well with test..

Abstract: The purpose of present paper is to study the flexural behaviors of concrete T-beams prestressed with external carbon fiber reinforced polymer(CFRP) tendons. Tests were carried out on 5 beams under four-point load, of which four beams were reinforced with hybrid both external CFRP tendons and internal steel rebars and another one only reinforced with internal steel rebars. Such parameters as the different initial loading states at external CFRP tendon jacking and different jacking stress in tendon were considered in experiment. A program was developed to predict the behaviors of those beams prestressed with externally prestressed tendons and the parametric study was conducted using the program. The predicted results from the program were in good agreement with the test results. Such parameters as jacking stress, elastic modulus of external tendons, configuration of deviators and ratio of span to effective depth of beam were chosen as primary analytical factors for the study on the flexural behaviors of beams prestressed with external tendons. The initial loading state on the beam before tendon jacking has no significant influence on the ultimate loading capacity and deflection.

Abstract: In order to research behaviors of unbonded prestressed concrete beams reinforced with CFRP tendons, static load experiments on 4 partially prestressed simple beams with unbonded CFRP tendons and 9 two spans partially prestressed concrete continuous beams with unbonded CFRP tendons were performed. Based on the experiment results of simple beams, the law of ultimate stress increment in unbonded CFRP tendons in simple beams was obtained. Based on the experiment results of continuous beams, the law of stress increment in unbonded CFRP tendons in continuous beams was obtained at serviceability state and at strength limit state of bending capacity. The calculation formula of length of equivalent plastic hinge for this kind of continuous beam was presented. The calculation formulas of moment modification coefficient with composite reinforcement index for intermediate support as variable and relative plastic rotation for intermediate support as variable were given respectively.

Abstract: The classical Euler-Bernoulli girder theory is not applicable due to shear deformation of corrugated steel web, elastic bending theory considering shear deformation is presented to analyze deflection and mechanical property. Differential equation is derived based on displacement field assumption, internal force equilibrium equations, deformation compatibility condition and relation of deformation and internal force, and solutions are obtained according to boundary and load condition. Simply supported I and box girder bridges with corrugated steel web are analyzed with elastic bending theory considering shear deformation, their predicted results are found in good agreement with those by 3D finite element analysis and test. A limit value of depth-span ratio is suggested for considering influence of shear deformation or not, the simplified formula of deflection in middle span is presented to guide deflection design. Corrugated web accounts for more than 80% of total shear force in the whole span under uniform load while one third apart from bearing under concentrated load in mid-span. The elastic bending theory considering shear deformation makes a reference for designing composite bridge with corrugated steel web.

Abstract: The design and construction of concrete water treatment and storage structures in Australia has catered for the existing markets. The next generation of these structures needs a more sophisticated approach. Engineers who analyse and design water treatment plants, or water and liquid storage structures, as well as other complex reinforced and pre-stressed concrete structures, will find this paper of interest. Advanced water treatment plants and water factories for recycling domestic and industrial waste water have introduced new complexities into concrete tank design. Two recently constructed Australian water purifying plants provide examples of the theoretical and practical challenges of designing and constructing the large and complex process vessels required by modern plants to produce large volumes of high-quality water.

Abstract: This paper concentrates on the fragility analysis method for vertically plan reinforced concrete frame structures. The weakness story inter-story drift ratio is selected as the fragility variable for vertically plan structures. Five states are established to distinguish the structural seismic performance levels, which are expressed with inter-story drift ratio. Then through the nonlinear dynamic analysis and linear regress, the exceeding probability function of seismic response is obtained and a new fragility analysis method is put forward for vertically irregular frame structures. Two kind of unit models, two kind of hysteretic models and forty earthquake records are chosen to established structure-earthquake system samples. Thus one hundred and twenty structure-earthquake system samples are obtained for irregular reinforced concrete frame, which take into account the uncertainty of member materials, structures systems, numerical simulation models and earthquake motions adequately. Then example is presented to demonstrate the applicability and utility of the proposed methodology. Seismic performances of a vertically irregular reinforced concrete frame structure are evaluated in detail. It is concluded that fragility curves are more abrupt in low input earthquake motion intensity and they are influenced much by the structural performance levels.

Abstract: A shaking table model test is conducted for Guangzhou West Tower to study its seismic behavior in State Key Laboratory for Disaster Reduction in Civil Engineering at Tongji University. Guangzhou West Tower adopts a new structure system and the significant characteristic of this system is the non-perpendicular frame arranged around the building, acting both as columns and bracings. Based on the similarity theory and member equivalent principle，a 1/80 scale model of this building is made of polymethyl methacrylate(PMMA). The model’s dynamic characteristics, earthquake-resistant behavior, responses of acceleration and deformation under different wave peak values are investigated, then the seismic responses of the prototype structure are deduced and analyzed. The whiplash effect of the prototype structure is studied, and the weak position of the structure is found out. The experiment results demonstrate that it is feasible to apply this structural type to practical engineering. Finally, some suggestions for the engineering design of the prototype structure are put forward.

Abstract: A performance evaluation method of high-rise buildings is presented, by means of capacity spectra method which allows for higher mode effects. The multi-degree-of-freedom system (MDOF) of each mode is transformed into equivalent single-degree-of-freedom (ESDOF) system, and the ESDOF system is supposed to be elastic perfectly plastic. In elastic range, the equivalent displacement of ESDOF system for each mode is deduced by displacement response spectra based on the natural period, and the structural lateral elastic displacement of each mode could be determined by the corresponding equivalent displacement and mode shape. In inelastic range, according to capacity spectra method, the relationships among demand curve, capacity curve and ductility coefficient are built. The structural performance under moderate or major earthquake is determined by iteration method. The paper illustrates the application of the proposed procedure with an example and attempts to prove its feasibility by nonlinear time-history analysis.

Abstract: Based on the finite element software ETABS, the effect of outriggers on the seismic response of a 50-story steel frame-reinforced concrete core tube structure was analyzed in this paper. Periods of free-vibrations were obtained from mode analysis. Response spectrum on the seismic properties was discussed. Elastic time history method was used to get complete analysis of the structure adopting four seismic waves. Structural horizontal displacement, drift angle, internal force of components and the distribution of internal forces between inner tube and outer frame under earthquake were studied. The rational quantity and locations of outriggers were considered. Further research in elastic time history was presented considering the influence of quantity of outriggers when outriggers were all set in “reasonable locations”. Some suggestions about steel frame-reinforced concrete core tube structures with outriggers in earthquake areas were given.