نشریه مهندسی سازه و ساخت
سال پنجم شماره 2 (پیاپی 17، تابستان 1397)

Nowadays, one of the most popular ways to get a more sustainable cement industry is using additions as cement replacement. However, there are many civil engineering applications in which the use of sustainable cements is not extended yet, such as special foundations, and particularly micro piles, even though the standards do not restrict the cement type to use. These elements are frequently exposed to the sulphates present in soils. The purpose of this research is to study the effects of using pinyon pine ash as a substitution for ordinary Portland cement and reduce its content in the concrete mix design. For this reason, 20 % of pinyon pine ash with respect to cement weight was used and the compressive strength of concrete is obtained from testing cubic and standard cylinder specimens. Considering the results obtained, using pinyon pine ash increase the compressive strength of concrete. On the other hand, more axial micro cracks were occurred in pinyon included specimens and their colour were darker comparing to representative specimens without pinyon pine ash. This study shows that using pinyon pine ash could be an effective and Eco-friendly alternative for ordinary Portland cement in industry and construction and could reduce the dangerous effects of using cement in concrete.

Dynamic time history analysis methods are commonly used to determine the seismic responses of structures. Despite their ability to somewhat precisely estimate seismic demand, nonlinear dynamic methods require extensively complex computations and are sensitive to the nature of earthquake records. Nonlinear static analysis methods also estimate the seismic responses of structures within an error range. The continuum analytical model is an alternative computation method for estimation of the seismic demand of structures. If the seismic behaviour of a structure is modeled based on the interaction between the equivalent flexural and shear cantilevers, it is possible to develop an analytical procedure based on the closed-form equations. In this study, the studied models were prepared using a hybrid and a bundled moment framed tube skeletons as 10-story structures which are symmetric and regular with plan and height. The variations range of seismic responses of the studied structures was calculated using the closed-form model of flexural and shear combined cantilever. Then, these results are compared with the response parameters obtained from linear and nonlinear time history analyses subjected the three components earthquake records contain strong forward directivity effects. Some of the characteristics of near-field records are powerful low-frequency band, pulse-like motions with long periods, rapid release of kinetic vibration energy in a short period, and ratio of peak velocity to peak acceleration. This research results denote the presence of an overestimation on the seismic demand parameters with relative precision.

The behavior of different structures subjected to blast loads is always an important factor to study. Sandwich panels have a wide range of applications in different fields of engineering and the construction of some industrial and military structures. These panels are made of two sheets and an intermediate core. The core has a significant role in reducing the deflection and enhancing energy absorb of structure. In this article, the effect of the shape of the corrugated panel and the type of panel materials is investigated. Hence, the reaction of aluminum and steel sandwich panels subjected to blast loads has been investigated. In the process of analysis, four kinds of profiles, which are: rectangular, trapezoidal, triangular and elliptical, are considered as panel cores. the most deflection was for rectangular profiles and the least deflection was for triangular ones. Those panels which are completely made of aluminum or the panels with steel cores can sustain more strain energy by their back sheets. all the panels that are completely made of aluminum have more damped energy than others. Those panels which have only aluminum sheets or aluminum cores are placed next to whole aluminum panels in order to damped energy level. In the study of the joint effect of the type of materials and the shape of the core panel, the panel with the upper and back of the steel and aluminum core with the triangular shape has the most desirable.

The effect of mass parameters on the natural vibration period of isolated bridges is discussable, especially in case of substructure mass components, because of the disagreement of different researchers about it. This is while some bridge design codes such as AASHTO guide specification, ignores substructure mass in simplified method of analysis. Current paper investigates the effects of substructure mass components on the longitudinal period of base isolated bridges. These components include: pier mass, cap beam mass, pier rotational moments of inertia, and cap beam rotational moments of inertia. In this paper, a three degree of freedom analytical model of isolated bridge in longitudinal direction is presented and the natural vibration period of this model is calculated in four cases. These cases are: (1) exact solution, (2) by ignoring the rotational moments of inertia, (3) by ignoring the cap beam mass, and (4) by ignoring the pier and cap beam mass (AASHTO model). The periods obtained from exact analytical model were compared with those obtained from finite element model and the results showed the good conformity. The results also showed that the substructure rotational moments of inertia isn’t a determinative parameter in the calculation of the first longitudinal period; while the cap beam mass have a significant impact on the longitudinal period of base isolated bridges with tall piers or stiff isolators. The ignorance of cap beam mass caused 8% error in the period of such bridges. The results showed that the simplified method of AASHTO guide specification isn't applicable in some bridges and may cause more than 10% error. By increasing the ratio of isolator stiffness to substructure stiffness, the error of period which is calculated by AASHTO model, increases.

The ability of elastomers to withstand very large strains (of beyond 500%) without breakage or permanent deformation makes them an ideal material for many applications, including, but not limited to, aerospace, medical, and automobile industries, bridge bearings, seismic isolation, and supplemental dampers. It is essential for design purposes to simulate accurately the response behavior of elastomers under various loading conditions. Given the nonlinear stress-strain relationship in an elastomeric material, a hyperelastic model, instead of Hooke's law, must be employed in stress analysis of the material. The literature includes a variety of constitutive hyperelastic models for elastomeric materials. However, choosing a suitable constitutive model that simulates the elastomer stress-strain behavior under different loading conditions is challenging. This paper examines the effectiveness of various hyperelastic models of which the constant model parameters have been evaluated using the results of a standard uniaxial tensile test conducted at different strain values. The model parameters are evaluated through a curve fitting technique performed by MSC-MARC, a commercial finite element software program. A thorough examination of the efficiency and accuracy of various hyperelastic constitutive models at different strain ranges shows that the Neo-Hooken and Arruda-Boyce are suitable models for the range of small deformations, and the Ogden and Yeoh models are suitable for a wide range of deformations.

Using of polymeric fibers for reinforced concrete structures has significantly developed in recent years. Polymeric fibers start their contribution in the behavior of concrete members after cracking. In order to a careful investigation into post-cracking behavior need to apply fracture mechanic concept (growth of cracks) in reinforced concrete members. For this purpose, in this research 14 concrete prisms (100×100×400 mm in dimensions) with 35 mm notch depth (at the center of tensile side) for four-point flexural strength test were fabricated. Fiber composition, geometry and hybridization percent were varied in these samples. Derived outputs illustrated that macro polypropylene (PP) fiber has no significant effect on concrete ductility, whereas it leads to increase the flexural strength. But micro polyester (PET) and PP fibers have more effective performance during forming cracks in concrete members. PET and PP fibers have a more suitable function during concrete cracking and the samples containing these fibers have no significant drop in their bearing while the cracking is started. In addition, samples reinforced with PP and PET fibers indicated that by increase in macro fibers, the flexural strength were increased where as ductility indices decreased. In general, samples reinforced with %60 of PP macro fibers and %40 PET micro fibers have the best performance.