Partially Replacing Fly Ash with Limestone Powder in the Paste - Influence and Characterization
Paste filling is an important research direction of coalmine "green mining" which can dispose coalmines solid waste and achieve environmental protection. The mechanical properties such as compressive strength, workability, ulti- mate tension value, shear strength and splitting strength of paste, in which the fly ash was partially replaced by limestone powder, was studied. Adiabatic temperature rise, setting time, shear strength, permeability, frost resistance and dry shrinkage of different substitution rate were investigated and the results were compared with traditional paste. The test re- sults showed that the influence of limestone powder on workability, permeability and frost resistance performance of paste was slight, the setting time of paste were shortened, adiabatic temperature rise and mechanics performance of paste were decreased, dry shrinkage value was increased with limestone powder content increasing.
Nonlinear Analysis of Reinforced Concrete Frames by a Combined Method
A more rea listic and hence nonlinear analysis of reinforced concrete structures is becoming i n- creasingly important. A combination of the displacement method, the transfer matrix method, and a cross- section module is suggested which leads to an effective analysis method for reinforced and prestressed con- crete frames. The combined method considers both material and geometrical nonlinearities including large displacements and rotations. The computation of the system is incrementally and iteratively carried out by the displacement method. At element level, an extended transfer matrix method is used. Thus neither displace- ment nor force shape functions are required. Instead, the axial strain and curvature distributions along the element are segmentally approximated by polynomials. The transfer matrix method provides both the element forces and the element stiffness matrix. It is recursively applied to the deformed element, which is discretised into individual segments whose number and lengths depend on the stiffness gradient. The cross section mod- ule is based on cross-sectional integration. It takes into account nonlinear material behaviour including crack- ing, softening and yielding of reinforcement. The combined method is presented for plane frames but can be extended to spatial systems.
Evaluation of Nonlinear Frame Finite-Element Models
In recent years nonlinear dynamic analysis of three-dimensional structural models is used more and more in the assessment of existing structures in zones of high seismic risk and in the development of appropriate retrofit strategies. In this framework beam finite-element models of various degrees of sophistication are used in the description of the hysteretic behavior of structural components under a predominantly uniaxial state of strain and stress. These models are commonly derived with the displacement method of analysis, but recent studies have highlighted the benefits of frame models that are based on force interpolation functions (flexibility approach). These benefits derive from the fact that models with force interpolation functions that reproduce the variation of internal element forces in a strict sense yield the exact solution of the governing equations in the absence of geometric nonlinearity. While the numerical implementation of force-based models at first appears cumbersome, simple examples of nonlinear analysis in this paper offer conclusive proof of the numerical and computational superiority of these models on account of the smaller number of model degrees of freedom for the same degree of accuracy in the global and local response. A numerical implementation that bypasses the iterative nature of the element state determination in recent force-based elements is also introduced, thus further expanding the benefits of flexibility-based nonlinear frame models.