سال:1393 | دوره: | شماره: |تعداد مقالات:9

This study is devoted to tracing the equilibrium path of structures with severe nonlinear behavior. A new displacement increment is suggested to do the analysis. Moreover, the increment of the load factor is obtained by minimizing the residual displacement. To evaluate the capabilities of the presented method against existing ones, a comparison study is performed. In this process, five benchmark frame and truss problems are solved. Each of the structures is analyzed more than 600 times, and the outcomes are compared with each other. According to the results, the authors' scheme is more competent than the methods of residual load minimization, normal plane, updated normal plane, cylindrical arc length, work control, residual displacement minimization, generalized displacement control and modified normal flow.

This paper presents the behavior of steel fibre concrete post material burned under compression. Experimental program is carried out by making a concrete cylinder specimen in which the parameters being reviewed are the concrete compressive strength and the temperatures. The results of such experiments is that the degradation of steel fibre concrete compressive strength of the specimen average quality control on all concrete is about 10% to 20% when the specimen is burned at a temperature of 300oC, where the degradation increases with the increasing compressive strength of concrete. The degradation of concrete compressive strength on the control specimens is significantly (50%-60%) will occur when the specimen is burned at a temperature of 600oC. When the firing temperature is increased to 900oC the degradation of compressive strength will fall, and the maximum compressive strength loss occurs on high strength concrete that is approximately 75%. The stress-strain models of steel fibre concrete at various temperature levels are developed, and the results of validation show the behavior before and after the peak which are relatively close to the experimental results.

Self-compacting concrete (SCC) due to several economical and technical advantages is increasingly used in construction industry. It can be improved on strength behavior when the fibers are added. Although the workability as a significant factor for this concrete must be maintained. This investigation experimentally evaluated the effects of steel and PET (polyethylene terephthalate) fibers separately on the properties of either fresh or hardened SCC. Fresh properties of concrete have been investigated by slump flow, V-funnel and Lbox tests. Hardended properties were tested for compressive strength, splitting tensile strength, flexural strength, shrinkage and ultrasonic pulse velocity (UPV) tests. The results showed that 30 Kg/m3 Steel and 3 Kg/m3 PET fibers can be considered as suitable contents regarding to fresh and hardened properties of SCC. However, the addition of PET fibers have caused a slight decrease in compressive strength.

The main objective of this paper is to present a new approach for seismic design of RC shear-walls. In order to achieve the desired performance with the minimum possible cost, a formulation is presented which fulfills the constraints of FEMA 365. The robust metaheuristic algorithm PSO and its recently enhanced version, PSOHS, are employed and the results compared. This approach is applied to some practical structural examples to certify the proposed formulation, and to examine whether the PSOHS performs better than PSO in this class of problems. The results illustrate the effectiveness of the PSOHS and its suitability for design of shear-walls.

Roofing systems have been vulnerable to strong wind uplift pressures. Roofing systems are basically evaluated for wind uplift pressures according to standardized test methods. Currently, there is no consensus on the ideal table size to be used in these testing protocols. Table size effect has been recently studies by the authors for the Thermoplastic roofing systems. The objective of this paper is to study the impact of table size on the Modified Bituminous (Mod-Bit) roofing system performance. To achieve this purpose, extensive analytical experiments have been conducted to investigate the performance of Mod-Bit roofing systems subjected to wind uplift pressures. Analytical results compared well with those obtained from experimental work, benchmarking the numerical modeling. This paper presents some of these comparisons and also suggests ideal table sizes and correction factors for various configurations having Mod-Bit membrane.

A study for the load deflection behavior of reinforced beams cast using reactive powder concrete RPC – as an ultra high strength concrete type - was executed experimentally and analytically. The experimental program was carried out to study the effect of cement content, using steel fiber and using two types of reinforcement. Results showed positive effect on cracking and ultimate loads of reactive concrete beams due to increasing of the cement content. The ductility of the reactive concrete beams is increased by using steel fibers. An analytical study was performed using a nonlinear computer program based on finite element technique. A comparison between analytical and experimental results was carried out to evaluate the efficiency and the accuracy of the used nonlinear computer program. The computer program results were practically close enough to the experimental results. The numerical analysis with the chosen finite element method presented a good simulation to the RPC beams.

In the present paper, the behavior of steel plate shear walls (SPSWs) with stiffened full height rectangular openings is studied. A series of single and multi-story SPSWs of various aspect ratios, with different opening features (i.e. length and horizontal location) and without openings is analyzed using the finite element method to investigate the changes in system behavior due to the introduction of openings in terms of strength, stiffness and ductility. Results show that the opening features can have an important impact on the behavior of SPSWs with the openings. The introduction of stiffened openings always reduces the infill plate strength and also the initial stiffness and ductility, while it somewhat increases the frame strength. It is found that the relative reduction in the infill plate strength as well as the relative reduction in the initial stiffness and ductility due to the introduction of the openings can be reasonably assessed based on the relative reduction in the infill plate area.

During January – December 2012 more than 1341 records were recovered from permanent Iran strong motion stations operated by the Road, Housing and Urban Development Research Center. Accelerograms were recovered from ISMN triggered by 634 earthquakes in the magnitude 2.0 to 6.4 ranges. Peak ground acceleration was recorded in Chaykandi1 station about 607 cm/s2 on September 27th, 2012 earthquake.

The present work described the influence of polymer admixture (i.e. polymer latexes) contents on the physical/mechanical properties of latex modified concretes (LMCs). At the first step, the optimum water to cement ratio was determined for a LMC concrete according to the results of compressive strength. Afterwards, six latexes were investigated as admixture for LMCs at 10% of latex content. Their physical and mechanical properties including compressive strength, flexural strength, splitting tensile strength and capillary water absorption was evaluated. Finally, two latexes which were better in LMCs general properties (i.e. Acrylic and Co-polymer Acrylic) were incorporated at 5 and 15% of latex contents to concrete. The result have shown that the increase in the amount of latex content decreased the compressive strength, but the other properties including flexural strength and split tensile strength were improved. Also, an improvement in barrier efficiency for water absorption of LMC concrete with increment of latex content was observed.