The true behavior of many large complex structures involves interaction between the in-plane and transverse shear loads acting on the reinforced concrete (RC) element. This paper presents a model using a fiber-based finite element formulation to predict the strength of reinforced concrete members subjected to multi-directional shear loads. The shear mechanism along the element is modeled by adopting a Timoshenko beam approach. The nonlinearity of the concrete and steel materials is accounted for at the fiber level through the use of proper constitutive laws. The concrete constitutive law is based on the Softened Membrane Model (SMM), which was modified to account for transverse shear load effects. The modification of the concrete model is derived based on the findings of an extensive experimental program. The validity of the finite element model is established by correlation of analytical results with experimental tests of RC specimens subjected to multi-directional loads and available in the literature. These numerical studies showed that the model can accurately predict the reduction in strength due to the effect of transverse loads.
This paper describes a method for estimating creep deformations of PVA-ECC under high stress levels from short-term tests. To obtain necessary data, a series of accelerated bending and compression creep tests under a sequence of increasing loads were carried out. Of particular interest was to study the evolution of plasticity and damage under varying load levels, and thus allow the rate of plasticity and fracturing as functions of evolving strain and fracture to be determined. Based on these behavioral aspects, predictions of creep of ECC at high stress levels were made. It is found that creep rupture in flexure and compression occurs at nearly the same order of lifetime in a logarithm scale, being the rupture at 90% of flexural strength about one order longer than that under compression. The tensile and compressive strains at rupture, when the load level is decreased from 90% to 75% of the short-term strength, are 1.1-1.4 and 1.6-3.5 times the short-term tensile and compression strain capacities, respectively.
Frost damage mechanism under freezing and thawing cycles is an important issue for service life evaluation of concrete structures in cold regions. In order to simulate the frost damage mechanism, this paper presents a simulation method in meso-scale for coupled mechanical and transfer analysis in which Rigid Body Spring Model (RBSM) is applied. This method can simulate the coupled heat and moisture transfer in mortar, and also the ice formation process based on thermodynamic equilibrium. In addition, a degradation constitutive model is proposed to describe the deformation behavior under several Freezing and Thawing Cycles (FTCs). To evaluate the effectiveness of this method, the simulation results are compared with experimental data of the strain behavior under FTCs and found in satisfactory agreement with the experimental data.
This study focused mainly on prestressed concrete box girder bridges with steel truss web members, also known as Hybrid Truss Bridge (HTB). Previously, French engineers worked to improve the structural efficiency of prestressed concrete box girders by using concrete-steel hybrid subcomponents in an effort to reduce the weight of the superstructure. As a result of these efforts, several HTBs have recently been constructed in Japan and Korea. All of these bridges have unique connection systems between the concrete slabs and web truss members, which dictate the safety as well as the failure behavior of the hybrid girders. Thus, evaluation of both construction and structural safety of the connection systems regarded as an essential step in the design of HTB. In this study, four new connection systems using either hinge devices or T-type perfobonds have been proposed as improvements to the assemblage and to eliminate the need for welding during construction while satisfying load carrying capacity requirements. The static loading tests for six connection specimens in real scale were carried out in order to fully evaluate structural safety of the newly proposed connection systems. Also, a real scale railway bridge specimen with a 20m single span and an embedded hinge connection system was designed and constructed in a structural laboratory to perform for static and dynamic tests. Using this specimen, the possibility of using an embedded hinge connection system in a HTB, both for railway and general roadway usage, was evaluated.