Xiu Li Du

Flexural Capacity of Concrete Beams Prestressed with Carbon Fiber Reinforced Polymer (CFRP) Tendons

Fiber reinforced polymer (FRP), particularly those incorporating carbon fiber (CFRP), has high strength, high stiffness-to-weight ratio and high resistance to corrosion, which shows potential for use as prestressing tendons in corrosive environment. However, concrete beams prestressed with FRP tendons have showed brittle flexural failure due to the elastic rupture of FRP tendons. In order to improve the ductility, a combination of bonded and/or unbonded prestressing tendons was used. Nine prestressed concrete beams were tested up to failure to study the effect of bonded and unbonded FRP tendons on their flexural capacity. Three factors were taken into consideration; the bonding condition of CFRP tendons, the location of CFRP tendons and the prestressing ratio. Also an analytical investigation was carried out to extend some flexural capacity calculation equations to this beam type. The results of the experimental showed that under the same condition, the carrying capacity of concrete beam prestressed with bonded FRP tendons was 20% higher than that of internal unbonded prestressed beam, and was 40% higher than that of external unbonded prestressed beam without deviators. By combination of bonded and unbonded FRP tendons, the ductility of prestressed concrete beams can be improved.

Shaking Table Test on Seismic Response of Isolated Bridge

In order to investigate isolation effectiveness on seismic performance of the continuous rigid frame bridge, shaking table test with nine sub-tables on 1/10 scaled reinforced concrete rigid frame bridge specimen was performed. The experimental results demonstrate that isolation devices provide flexibility to transform natural period of the scaled model, and additional it can improve the ability of energy dissipation when lead is used. The initial first frequency is 8.17Hz for plate-type rubber bearing and 9.12Hz for leading rubber bearing. The plate rubber bearing and lead-rubber bearing are quite sensitive to seismic wave frequency. The use of various isolation devices affects response of the bridge model. The results show that the more difference in the isolation devices, the more difference in response. Moreover, isolation effect of lead-rubber bearing show obviously more advantage than the one of plate-type rubber bearing, especially in controlling responses of the bridge during major earthquakes.

Research on Cementitious Capillary Crystalline Waterproofing Coating for Underground Concrete Works

Cementitious capillary crystalline waterproofing coating was developed, whose doping quantity of active substances was primarily determined by using orthogonal tests, the doping quantity of the active substances and the cement-sand ratio were optimized, and the formulation of the waterproofing coating was: 50.45% of silicate cement, 40% of quartz sand, 2.4% of assistants and 7.15% of active chemical substances. Test results showed that all the properties of the developed waterproofing coating conform to standard requirements, the bonding strength of wet substrate reached 1.8 MPa, and 28d seepage resistance reached 1.3 MPa.

The Relationship between the Strength and the Pore Structures of Cement Paste with Mineral Admixtures

This paper presents the effects of mineral admixtures and the water to binder ratio (W/B) on the tensile and compressive strength and micro pore structure of hardened cement pastes. The test results show that: with the water to binder ratio increasing, the tensile and compressive strength of cement paste with different mineral admixtures will decrease, air content and mean pore diameter will decrease and the cement paste with the ground blast furnace slag is the lowest. The artificial neural network based on its nonlinear mapping function can fit the relationship between strength and pore structure more accurate than an empirical formula.

Shear Behavior of CFRP Prestressed Concrete Beams without Stirrups

Five beams were tested up to failure to study the shear behavior of concrete beams prestressed with fiber reinforced polymer (FRP). Different factors were taken into consideration: the type of prestressing tendons and the shear span ratio. The shear failure modes and the influence of different factors on shear behavior were investigated in details. The test results showed that FRP prestressed beams without stirrups had two shear failure modes: diagonal compression failure and shear compression failure; the shear span ratio was the most important factor to determine the failure mode and shear capacity of the prestressed beams. The shear capacity of concrete members prestressed with FRP tendons was lower than that of concrete beams prestressed with steel cables.

Shear Band Analysis of Sand Based on Digital Image Processing Technique

A series of drained tests of ISO medium sand were performed to study the onset and formation of shear band. Using the digital image processing technique, the multifunctional triaxial equipment of GDS was improved. Strain isogram and local stress-strain relation at every sampling time point were recorded based on the improved equipment. The onset of shear band was from inhomogeneity of soil, while the inhomogeneous deformation can be induced by end friction and initial defect. Based on results of global stress-strain and local stress-strain relation, the end friction effect was found to have a strong influence on the radial strain. The macroscopic non-uniform sample was obtained by putting silt clay block into sand sample, evolution of shear band during the loading process showed that the discontinuation of stiffness formed at interface of two materials, with inhomogeneous deformation developing, macroscopic continues shear band fully formed.

Application of Damp Newton Algorithm on FEPG Platform

Damp Newton algorithm based on FEPG system is developed for calculating strain softening problem. The algorithm can solve displacement and yield surface equation simultaneously. Soften modulus is introduced into D-P yield function. The example result shows that, the algorithm with damp factor can be used to solve softening problems. The plastic theory described by finite element weak form has no requirement of continuity, so appropriate outcome can be obtained by first-order element. Descent segment of stress-strain curve and cloud picture of finite shear band are presented.

Process Simulation and Formation Mechanism of Shear Band in Soil

Shape multiformity and formation mechanism of shear band in normal consolidated soil were analyzed based on Modified Cam-Clay model under plane strain condition. The results proved that shear band forms because of impact action caused by strain energy releasing. End restraint and initial defect can induce and control the formation process and shape of shear band. The interaction of different boundary and initial defect settings was analyzed in order to obtain the mechanism and deformation process of shear band.

Testing and Numerical Simulation Research on Shear Band of Soil

The triaxial equipment of GDS with digital image processing technique is used in drained test of sand. The result shows that the end restraint and initial defect have significant effect on mechanical properties of sand sample. End restraint and initial defect of sample both can cause inhomogeneous deformation, then form macroscopic shear band in soil testing and numerical simulation. Shape multiformity and formation mechanism of shear band in normal consolidated soil is analyzed based on Modified Cam-Clay Model under plane strain condition. The result shows that end restraint and initial defect can induce and control the formation and shape of shear band. The impaction of different boundaries and initial defect setting are analyzed.

Experimental Study of CFRP Confined RC Rectangular Hollow Section Bridge Piers

To investigate the seismic performance of FRP strengthened RC hollow section bridge piers under multi-dimensional earthquake excitation, the pseudo-static test was carried out to RC rectangular hollow section as-built and CFRP confined bridge piers under constant axial compression force and bidirectional horizontal repeated load. The failure characteristics, lateral force-deformation curves and ductility of specimens were analyzed. The experimental result shows that CFRP constraining may change the failure mode of hollow section bridge piers, and significantly improve the deformation ductility, plastic deformation, however, it is less contribution to horizontal force of specimens with less wall-thickness.