BRJ – Volume 57, Number 2, 2009
Building Research Journal
Volume 57, Number 2, 2009
Pavement subgrade mechanical characterization and potential use of FWD diagnostics . . . 61
Aeroelastic response of spider-web structures . . . 77
Martin Križma, Michal Suchoň, Terezia Nürnbergerová, Martin Moravčík:
Experimental and numerical analysis of deformations of aerated concrete structural elements . . . 93
Alaa M. Rashad, Hosam .el_Din H. Seleem, Khalid M. Yousri:
Compressive strength of concrete mixtures with binary and ternary cement blends . . . 107
Pavement subgrade mechanical characterization and potential use of FWD diagnostics
Mechanistic design or evaluation of pavements requires fundamental material properties and material failure criteria to be formulated as functions of load and environmental effects. The strength or weakness of a pavement structure is based on the performance of the subgrade. (AASHTO Guide, 1986) recommended highway agencies to use a resilient modulus value obtained from a repeated triaxial test for the design of pavements. Resilient modulus as an important material property of the subgrade soils derived from the recoverable strains obtained after application of a series of combination of confining and deviator stresses to the soil specimen. This determination procedure is devised to account for nonlinear behavior of subgrade soils under the traffic loadings. Due to complexity and difficulty of triaxial testing, many correlations have been made between resilient modulus values from repeated triaxial test and measurements obtained from nondestructive field testing methods, such as Cone Penetration Test, Dynamic Cone Penetration Test, Falling Weight Deflectometer (FWD), and Plate Load Test.
The present paper is concerned with subgrade soil material properties in two directions. The first part of the paper describes implementation of the non-linear model of subgrade response proposed in (DesignGuide, 2004) in the classical pavement analysis (based on a linear theory of elastic layered halfspace) through an introduction of the subgrade soil structural number. The results of numerical calculations show close relationship between soil structural number and its (resilient) modulus.
In the second part of the paper, the applicability of the FWD testing for determination of mechanical characteristics of subgrade soil is analyzed. The (pilot) FWD measurements were performed directly on subgrade and the backcalculated subgrade moduli were found to be in basic agreement with values proposed in (Design-Guide, 2004) as typical ones. The series of FWD measurements on subsequently
constructed pavement layers show tendency of increasing values of backcalculated subgrade moduli. These results indicate that it would be expedient to explore a problem of finding optimal test loading and monitoring equipment parameters in order to improve subgrade soil material characterization procedure.
Keywords: subgrade, resilient modulus, soil non-linear model, soil structural number, pavement design, Falling Weight Deflectometer (FWD), subgrade deflections diagnostics
Aeroelastic response of spider-web structures
The analysis of aeroelastic ultimate behaviour of slender spider-web structures (roofs, bridges, walls, shells, etc.) made of laminated wood or carbon fiber composites as load-bearing elements and with glass or plastics as filling members is treated in the present paper. Interactive conditions in resonance and stability ultimate response are considered. Numerical treatment of nonlinear problems appearing is
made using the updated Lagrangian formulation of motion. Each step of the iteration approaches, the solution of linear problem and the feasibility of the adaptive mesh refinement and substructuring for the analysis of ultimate response of spiderweb structures are established. Some numerical results are submitted in order to demonstrate the efficiency of the procedures suggested.
Keywords: aeroelasticity, adaptive mesh refinement, carbon fiber composite, glass, resonance, spider-web structure, stability, ultimate response, updated Lagrangian formulation of motion
Experimental and numerical analysis of deformations of aerated concrete structural elements
Martin Križma, Michal Suchoň, Terezia Nürnbergerová, Martin Moravčík
The results of an extent experimental research of the load bearing capacity and the deformational behaviour of the built-up aerated concrete lintels are presented. The built-up lintels built-in into the vertical structures create a relatively complicated static system which cannot be checked according to the nowadays standards. To verify the reliable application of the lintels, their real conditions in a structure were simulated in the experiments. The experimental results and experimentally determined
material properties were applied in the numerical model. The composition of the numerical model by using the commercial programme is described. The outcomes of the numerical analysis show very good agreement with the experimental values.
Keywords: aerated concrete, deflections, numerical simulation
Compressive strength of concrete mixtures with binary and ternary cement blends
Alaa M. Rashad, Hosam.el_Din H. Seleem, Khalid M. Yousri
A great deal of research has been performed on properties of concrete containing one or more pozzolans or supplementary cementitious materials (SCM). However, use of SCM concrete is sometimes limited due to a lack of understanding about material behaviors and lack of proper specifications for its construction practice. The current research was performed with the aim of studying the evaluation of four types of pozzolans mainly metakaolin (MK), silica fume (SF), fly ash (FA) and ground granulated blast slag (GGBS) in terms of their influence on the concrete properties
in both fresh and hardened state.
Keywords: pozzolana, strength, metakaolin, silica fume, fly ash, blast furnace slag. XRD