Advanced Materials Research Vols. 163-167

Abstract: In some long-span prestressed concrete box girder bridges, excessive deflections of main girders are often observed. These unacceptable deflections have detrimental influence on the serviceability and safety of the structures. To better understand and estimate short term and long term deflections for prestressed concrete box girder bridges, pier vertical deformation and its effect on deflections of main girders of Jinghe Bridg is investigated in this paper. Piers in Jinghe Bridge are tall and the difference in height between piers up to 22 m. Analysis indicates that although the short term deformations of piers are small, the long term deformations of piers can be 3 times as large as that of short-term ones. The maximum short-term downward deflection of Jinghe Bridge caused by pier deformation for main girders is 7.7 mm and the maximum long-term downward deflection is 33.3 mm. These values are relatively small compared with the span length of the bridge. But when the deflection of the main girder itself is also included, the final total deflection of the main girder may exceed the design code limit.

Abstract: Reciprocal theorem method (RTM) is generalized to solve the problem of bending of thick rectangular plate under concentrated load with four edges fixed and with two opposite edges fixed, the third edge simply supported, and the fourth edge free based on Reissner’s theory. The analytical solutions of the thick plate are given, and the relevant date and diagram are given to guidance engineering application.

Abstract: Using the computer program SAFIR, the behaviors of restrained reinforced concrete (RC) beams with slab exposed to ISO834 standard fire are analyzed. The influences of three parameters (i.e., width of slab, axial restraint stiffness ratio, and rotational restraint stiffness ratio) on the beams’ behaviors in fire are investigated. Simulation results show that: (a) the axial force in the slab is much larger than that in the beam on the whole; (b) after 0.5 hour of heating the axial force in the slab decreases gradually with an increasing of the slab width ranging from 1.0 m to 2.5 m, but the influence of the slab width ranging from 1.0 m to 2.5 m on the axial force in the beam is limited; and (c) the effect of the rotational restraint stiffness ratio on the axial force in the beam/slab is very limited, but the beam’s peak hogging moment increases gradually with an increasing of the rotational restraint stiffness ratio.

Abstract: Externally bonding fiber reinforcement polymer (FRP)laminate to the soffit of reinforced concrete (RC) beam is an effective way to increase its flexural strength. However, there is little investigation on flexural behavior of RC beam by side-bonding FRP laminates.To investigate the difference of flexural behavior between soffit-bonding and side-binding FRP laminates RC beams,a total of 9RC beams were tested, including 8 strengthened beams and 1 control beam. The test results showedthat:1) As fiber reinforced concrete, side-bonding FRP laminates can also effectively increase the first crack strength of RC beams.The first crack load improved significantly; 2) side-bonding FRP laminates is not a good method to improve the flexural behavior of RC beam at the yield stage and the post yield stage. 3) Side-bonding of CFRP laminates is a good way for existing RC beams to control its crack width and deflection.

Abstract: Based on the links among various shear failure modes and the unified model for beam-like shear and symmetrical punching previously proposed, a new approach is presented to allow for the effect of column rectangularity on the shear capacities of members in general shear, which includes punching and beam-like shear as two particular extremes. In succeeded regression analysis, linear metric form is selected out of practical concern, and a lower-bound design equation is finally developed that can not only measure the influence of this variable on members in general shear, but can give a clear physical explanation to the measurement, as is absent in certain codes.

Abstract: Seven beams were tested to investigate the effects of beam depth and longitudinal reinforcement ratio on the shear strength of reinforced concrete beams. To investigate the effects of beam depth on shear strength, beams of five different sizes were tested. Two beams were designed to investigate the shear behaviour of beams with small percentage of longitudinal reinforcement. In addition to an experimental investigation, a survey of data in the literature was performed to gain insight into the influence of beam depth and longitudinal reinforcement ratio. Based on test results and a data analysis, conclusions regarding the influence of beam depth and longitudinal reinforcement ratio on shear strength of reinforced concrete beams are presented herein.

Abstract: Mechanical behaviours of three-tower suspension bridges from perspective of influence line help insight into mechanical behaviour nature, and grasp the differences between two-tower and three-tower suspension bridges in Static and dynamic behaviours. Based on the Taizhou Yangtze River Bridge, three dimensional space finite element models of two-tower, three-tower with floating system and three-tower with elastic cables between mid-tower and the girder were constructed. Through analysis of influence lines characteristics of different key effects and effect envelop under vehicular load, main conclusions are got as follows: Some factors such as deflection-to-span ratio of girder, anti-slipping safety factor between the main cable and saddle of the mid-tower and force in the mid-tower, horizontal displacement at the end of girder, which are not important in two-tower design, become controlling ones in three-tower suspension bridges and effects under vehicular load is the most important. When live load acts on all or part of one main span, the four control factors reach the worst case, but in very low probability. Code restriction on deflection-to-span ratio of girder can be flexible to relax restriction to 1/220, and riding comfort is still guaranteed. Stresses of mid-tower under vehicular load plus dead load are in a state of compressive stress in the majority of operating conditions and fatigue problem is not obvious.

Abstract: The creep deflections in service stage of bridges are discussed with the effect of the variable temperature and humidity on creep. A coefficient of equivalent duration of loading (CEDL) is proposed, which is an indicator of the effect of the variable temperature and humidity. According to the periodicity of the climate and based on the recorded and collected daily average temperature and humidity in five cities in Pearl River delta from 2002 to 2006, the monthly average CEDL and the yearly average CEDL are thus given to study the effect of the variable temperature and humidity on the creep deflection of a five spans single plane cable-stayed bridge. It is demonstrated that the effect of the variable temperature and humidity is notable in the early phase but inapparent in the later phase of the service stage of the bridge.

Abstract: Based on the pseudo-dynamic and pseudo-static under low-cycle test of 10-storey model building without seams and 6-storey model building with seams, the change of dynamic characteristics, the failure mechanism, the deformation feature and ductility of two type structures are discussed. The result of experimental study proves that the capacity of hollow shear wall is well; In elastic stage, the hollow shear wall and common shear wall are similar: high stiffness and little deformation; In elastic-plastic stage, the deformation is increasing, and the slit hollow shear wall are divided into several little walls, the property of energy dissipation of hollow shear wall structure is good. The seismic behavior of the slit and integral hollow shear walls are used in the multi-story and low high-rise building.

Abstract: In the three kinds of constraint ratio (ξ = 0.065, ξ= 0.1025, ξ= 0.205), respectively, by the comparative analysis of 55 prism specimens using CFRP confined concrete(strain ratses are 10^-5/s-1, 10^-4/s-1, 10^-3/s-1 and 10^-2/s-1), the stress-strain curves, strength, strain, elastic modulus and Poisson's ratio were studied at different constraints and different strain rate. The results show that: (1) with the strain rate increased,the inflexion strength and ultimate strength of concrete were improved; (2) with the strain rate increased, the static and dynamic elastic modulus increased slightly; (3) Poisson's ratio increased slightly with the growth strain rate.