Tridimensional Long-Term Finite Element Analysis of Reinforced Concrete Structures with Rate-Type Creep Approach

This paper presents a general procedure for a rate-type creep analysis (based on the use of the continuous retardation spectrum) which avoids the need of recalculating the Kelvin chain stiffness elements at each time step. In this procedure are incorporated three different creep constitutive relations, two recommended by national codes such as the ACI (North-American) and EC2 (European) building codes and one by the RILEM research association. The approximate expressions of the different creep functions with the corresponding Dirichlet series are generated using the continuous retardation spectrum approach based on the Post–Widder formula. The proposed rate-type formulation is implemented into a 3D finite element code and applied to study the long-term deflections of a prestressed concrete bridge built in Romania, which crosses a wide artificial channel that connects the Danube river to the port of Constanta in the Black Sea.

Waste Plastic-Modified Bitumen: Rheological Study

Bitumen blends were prepared for road applications by the introduction of 9% of waste Polyethylene by weight (9 wt%). The relaxation stress, relaxation and retardation spectrum and viscosity of bitumen blends were studied at different temperatures and compared to those of the original pure bitumen. These properties were tested using an ARESRheometer (Rheometric Scientific, Co.) equipment. The measurements were performed in the dynamic mode, plate-plate geometry of 8 mm diameter over the temperature range from -10 to 60°C and angular frequency (ω) varied from 10-1 to 102 radian/s. The relaxation stress and viscosity were modified by the addition of waste PE. The results also indicate that the incorporation of the waste PE enhances stability of the bitumen blends.

The Calculation of the Tear Energy of Elastomers from Their Viscoelastic Behavior

The creep behavior and the rate dependence of the tear energy have been determined on nine elastomers with widely varying structures. When compared at their glass temperatures the short-time creep compliances, J(t), were located at the same positions on the time scale. Therefore, the terminal zones of response were widely spaced depending on the breadth of the viscoelastic spectra. The positions of the tear energy curves were similarly positioned on the reciprocal rate scale. An equation is proposed for the calculation of tear energy curves from the viscoelastic retardation spectrum.