Background and Aim: In patients with complete denture, some clinicians have used modelling plastic impression compound (MPIC) along tissue conditioner (TC) materials simultaneously. Little information is available on the composition of these materials and the interaction between them. The purpose of this study was to evaluate the influence of two components of MPIC on the structure and chemical composition of TC.Materials and Methods: In this experimental study, MPIC specimens were provided in 25×2 mm discs. Specimens were randomly divided into three groups and were immersed in ethanol 70%, plasticizer (dibutyl phthalate) and a mixture of them (ethanol 70% and dibutyl phthalate). All of the discs were weighed with a digital balance before and 2, 4, 6 and 24 hours after immersion. Values were analyzed by non parametric Kruskal-Wallis (a= 0.05) and SPSS 16 for Windows (SPSS Inc., Chicago, IL) was used for statistical analysis.Results: Statistical analysis indicated significant differences among all groups (p>.05).Conclusion: Dibutyl phthalate (DBP) had high impact on the solubility of MP, while the mixture of dibutyl phthalate (DBP) and ethanol demonstrated the highest impact.

This paper highlights the importance of selection of a suitable ductile composite, incorporating it into the predefined locations, for better seismic performance. Replacement of normal concrete with ductile composites at plastic hinge locations is an idea, which can be well thought for in the conceptual approach to structural design. A simple experimental investigation was carried out to establish this concept. The ability of the structure to sustain levels of inelastic deformation implicit in ductility values is dependent on the material and detailing used. Concrete, which is inherently brittle and weak in tension, were modified by incorporating polymeric materials like natural rubber latex and steel fibers. This improves ductility, strain at peak load and energy absorption capability. The validity of the scheme is proved by a couple of experiments including the stress- strain characteristics of the material as they play a significant role in ductile response of structural elements. Three point bending tests were conducted on four types reinforced concrete beams with different concrete matrixes at the central region and high strength concrete at other regions. As ductility and damage modeling of structural components plays an important role in achieving the performance objectives, they have been quantified using the experimental data by suitable methods. Damage index evaluation was done using one of the well-known damage models, which takes into account the hysteretic energy dissipation along with ductility. A response factor directly related to the damage index is found out in order to get the major design variable displacement ductility, thus helping the design stage calculations.

An evolutionary structural optimization (ESO) method is used for plastic design of frames. Based on safe theorems some criteria are derived and made an effort to satisfy them during the optimization process. In this regard, equilibrium is checked and yield condition is gradually satisfied during the optimization process. In this method, the amount of used material and the stiffness for each element are improved, simultaneously, to impose upper bound of moment in the element. Frame analysis and optimization algorithm are implemented as PLADOF (plastic design of Frames) computer code. Four examples are presented to illustrate the performance of the algorithm.

The main purpose of this study is to provide a simple and efficient method for calculating the capacity of fillet welds subjected to in-plane eccentric loads. Various methods have been proposed to determine the capacity of fillet welds under such circumstances over time. The existing design methods, such as the conventional elastic method, are very conservative and do not match the test results well due to neglecting of ductility and strain compatibility of the weld group. On the other hand, the instantaneous center of rotation method (IC) considers the above parameters but requires complex calculations. Therefore, in the present study, a method for the design of the fillet welds is introduced which considers the inelastic properties of the welds in a simple manner, while provides a very good prediction of the weld group capacity. The proposed method is much more accurate than the conventional elastic method in the design of fillet welds and is much simpler than the IC method which has limitations in use and complexity in calculations. In this method, considering the ductility for welds, it is assumed that the stress distribution in welds is uniform when the weld reaches its maximum bearable deformation. The performance of the proposed method which is called plastic design Method has been compared and evaluated in comparison with the prequalified IC method. To this end, 8 different configurations of weld groups from the AISC Manual were selected and their capacities were calculated for different amount of load eccentricity. Accordingly, despite the fact that the new method has almost the same computational cost of the elastic design method, it offers more accurate strength predictions of the weld groups. For all considered cases, the ultimate loads obtained from the proposed plastic method are just slightly different from those of the IC method and they are mainly on the safe side. To be more precise, the accuracy of the results calculated by the proposed method is within 90% of those of the IC method. In accordance with the authors’ parametric studies on the factors affecting the results of the plastic design method (e.g., the angle of loading (θ), the weld length (l), the weld throat thickness (d), the secondary parameter (k) and the tensile strength of the welded metal), it was found that the angle of loading has the most profound effect. Therefore, the influence of loading angle on the predicted results was included. Accordingly, three different loading angles (i.e., zero, 45 and 75 degrees) were chosen and the weld groups capacities were calculated in each case. The corresponding results showed that as the loading angle increases, the accuracy of the results decreases and the most accurate predictions are obtained for the case of zero angle loading as compared with those of the IC method. Nevertheless, the predictions are still in an acceptable range for non-zero angles. It is also worth mentioning that irrespective of the loading angle, the new plastic method strength predictions are always far better than those of the conventional elastic design method.

The paper introduces the principles of displacement-based plastic design (DBPD) and its applications to the efficient design of parallel chord steel vierendeel girders under normal nodal forces. A simplifying assumption has been made that the mathematical model is composed of imaginary, pin connected modules that fit within the bays of the prototype. The use of this modeling concept in conjunction with the applications of the uniform strength theory leads to the development of an algorithm that is ideally suited for manual, minimum weight design of steel vierendeel girders under any distribution of vertical nodal forces. The resulting solutions are exact and unique and lend themselves well to DBPD and minimum weight treatment. In DBPD which is akin to performance control, member strengths and stiffnesses are assigned rather than tested. Several generic examples have been provided to illustrate the applications of the proposed design procedures.The numerical results of these examples have been verified through long hand and computer methods of analysis.An extensive proof of the proposed method of approach has been provided in the ‘‘Appendix’’.

This paper presents a Performance-based plastic design (PBPD) methodology for the design of steel concentric braced frames. The design base shear is obtained based on energy–work balance equation using pre-selected target drift and yield mechanism. To achieve the intended yield mechanism and behavior, plastic design is applied to detail the frame members. For validity, three baseline frames (3, 6, 9-story) are designed according to AISC (Seismic Provisions for Structural Steel Buildings, American Institute of Steel Construction, Chicago, 2005) seismic provisions (baseline frames). Then, the frames are redesigned based on the PBPD method. These frames are subjected to extensive nonlinear dynamic time-history analyses. The results show that the PBPD frames meet all the intended performance objectives in terms of yield mechanisms and target drifts, whereas the baseline frames show very poor response due to premature brace fractures leading to unacceptably large drifts and instability.

Coupled steel plate shear walls are an extension of the steel plate shear wall (SPSW) system. Limited research and lack of appropriate methodology to analyze and design such system has led to less understanding of the behavior and conservative design requirements. In this paper the conventional elastic design approach for the system is introduced and Performance-based plastic design (PBPD) method is developed for seismic design of this system. In order to evaluate the design method, 12 samples of 6 and 12-story structures with 30, 45 and 60 percent coupling and different coupling beam length are designed using this methodology. To evaluate the performance of sample structures a nonlinear static analysis is conducted. Steel plates are modeled with nonlinear orthotropic membrane elements. The results showed that the proposed design method, would lead to further insight into the structural behavior, more control over the design and achieve performance targets.