An analytical model was developed for the mechanical behavior in joint surface of composite structures, which consist of steel plates and concrete. Steel plates were idealized into shell elements and assumed to behave as the elastoperfectly plastic models. Concrete was idealized into solid elements and assumed to behave as the elastoplastic model in which the hardening and softening behavior of concrete can be estimated due to the 2 parameters model of Drucker-Prager type yield surface. In the joint surface, using Lagrange undecided multiplier method in which the continuity of displacement can be taken into account and the joint elements in which the slip can be taken into account, the modeling of virtual elements was constructed. Due to the comparison between the experimental and analytical results for the mortarfilled steel tubular columns under uniaxial compression, the analytical results show a good agreement with experimental results and it should be noted that the applicability of the proposed model was confirmed.
Exradosed bridges are recently increasing as a suitable bridge type between cable stayed bridges and box girder bridges, and the past tower height of exradosed bridges with three spans have been restricted under 10 to 15 meter. On the other hand, two span bridges supported by both ends have better precondition on stress fluctuation and displacement. It means that parts of tower and girder can be decreased with increasing a tower height. In this study, we analyzed characteristics of the three main parts (tower, girder, cable) and tried to optimize a structural system. As a result, we found that the most suitable tower height is about 25 meter, which is twice of exradosed bridges. This result was confirmed through a design and a construction, and this paper proposes a new optimal structural design.
This research features the bond strength between FRP laminates and concrete. To develop a simple prediction formula for bond strength, the bond stress-slippage model proposed by the authors (Popovics model) is considered. The equivalent bond stress block (EBSB) is newly defined as the area of EBSB has same area of the Popovics model. Bond stress is assumed to a constant value by EBSB, strain and slippage of FRP laminates are given by solving a simple second derivative equation. A new prediction formula is proposed, which covers both cases of the ranges of bond length : one is longer than effective bond length and the other is shorter than that. The predicted values show a very good agreement with experimental results.
The estimation of health for 7 span continuous rigid-frame bridge with prestressed concrete girder, having local damages, was conducted by nondestructive tests and load test. In this bridge, local damages of crack and flake-off, having 1.7 m in width and 0.75 m in height, were observed from the lower flange of middle span to the outside of web. The slack or rapture of PC bar was considered as cause of these damages, and the deterioration of load carrying capacity caused by damages was worried about. Therefore, the actual state of damage was grasped, the cause of damage was investigated, and then the estimation of health of bridge was carried out as a structure. From the results, it was confirmed that the damage had occurred for a coupler to strike into girder concrete at prestressing, then cracks had generated forward the outside of girder concrete, having a thick covering, by cleavability stress. However, it was confirmed as follows : PC bar was not ruptured. There was no difference between healthy span and damaged span in the performance of both dynamic deflection and vibration by using test vehicles, which satisfied with calculated value using the model of the third dimensional elements of alignment. This bridge has sufficient load carrying capacity for the opening.
Mat foundations, composed with foundation slabs and footing beams, are usually cast-in-place concrete constructions and monolithic structures. This paper proposes the mat foundation system, composed with post-cast (cast-in-place) foundations slabs and pre-cast footing beams, that is the new system of mat foundation. Then we have made a series of experiments, to investigate the slip strength of connections between slabs and beams, according 3 types of connection forms. And also we have investigated the strength of beam to beam connection. The results of those experiments are as follows. The connection with beam side cotter between slabs and beams are satisfied with those slip strength and stiffness. And the strength of beam to beam connections are also enough for practical use.
Vapor diffusion tests were carried out using concrete, mortar and cement paste test pieces to obtain water vapor flux associated with internal evaporation took place at wetting front of liquid water infiltrated across the bottom of the test pieces. A two-layer model, composed of dry and saturated region, was proposed to calculate a temperature profile over these two regions and then a relationship between hydraulic conductivity and vapor diffusivity of concrete can be evaluated. The water vapor flux for concrete piece could be estimated based on the water vapor flux for cement paste and volumetric cement content.
This study presents the construction of a new simple analytical model for the bond-slip relation at the intersection nodes of CFRP (Carbon Fiber-renforced Plastic) grids, with consideration of parameters obtained from experimental data. Presented analytical model employs bond linkage elements for FEM analysis which consists of bi-linear springs to express the bond-slip behaviors on lines and intersention nodes of CFRP grids. It is the feature of this model to treat bond-slip of the intersection nodes separately from bond-slip of the lines. The validity of this model is verified by comparison with pull-out test results of CFRP grids embedded in concrete. Furthermore, a normalized bond-slip relation at the intersection nodes of CFRP grids is also presented to neglect the effects of diameters of CFRP grids line and concrete strength. In addition, the development length at the end of CFRP grids line is estimated based on the normalized bond slip relation at the intersection nodes of CFRP grids.
In this paper a macroscopic model for evaluating the maximum strength of framed RC shear walls with an opening is proposed, and its analytical method is shown. Furthermore, the validity of the macroscopic model and its analytical method is investigated by analyzing the maximum strength of fifty-three specimens of the framed shear walls with an opening. From the analysis, it is obtained that the values of mean, standard deviation, and coefficient of variation for the ratios of the observed maximum strengths to the analytical ones are 1.039, 0.131, and 0.126, respectively. This result shows that the macroscopic model and its analytical method are well adequate.