The weakness of concrete in tension and its brittleness under various types of loadings has resulted in using different and convenient fibers, including steel and poly propylene, which in addition increasing of ductility and improvement in post-cracking behavior of concrete, have a major role in minimizing shrinkage and thermal cracks. In this study, the effects of high temperatures (200, 300, 400 and 600oC) on compressive strength, splitting strength, flexural strength and energy absorption capacity or toughness of self-compacting concretes containing steel, polypropylene and polyethylene terephthalate (PET) fibers were evaluated. The test results on fresh concrete imply that the increase in fibers make some criteria of self-compacting concrete unachievable. Compared to the unheated non-fiber specimens (SCC2), increasing temperature up to 600oC decreased compressive strength at steel, polypropylene and PET fiber containing specimens 30, 37.5 and 34.5%, respectively. However, residual strengths were 22, 8 and 13% higher than the heated non-fiber specimens. At 600oC, flexural toughness and maximum flexural load were 5 and 1.8 times higher than control specimens. Adding fibers had a positive effect on specimens’ explosive Spalling so that Spalling threshold was shifted to higher temperature levels. The proposed relationships and models at the elevated temperature are compared with experimental results. These results are used to predict more accurate and general compressive and splitting strengths, flexural strength, elasticity modulus, flexural load peak-point and flexural deflection relationships.

Concrete is a useful material in today industry that must be known behavior ,against environmental phenomenon including fire concurrent using this material in various industries. Generally, in concrete two phases being visible, the solid phase includes cement paste with other aggregates and additives, and liquid phase includes water placing in concrete pores. When applying the fire in the concrete segments, in addition to some reactions occur in the solid phase, some changes are seen in the liquid phase and gradually gas phase including vapor in the concrete pores will be built. Usually, evaporation starts in concrete pores water at the 100 °, C temperature and since concrete temperature passes 150 °, C all of the water in pores changes to vapor and flows in the colder side of concrete and accumulate at this portion. When 100 °, C front temperature further progresses in the concrete, evaporation speed increases and flows in the colder side and accumulation zone of water grows until this zone becomes full of vapor and creates a saturated layer in pores that prevents from fluid flowing. After this layer saturated by vapor invasion from the hot side, pore pressure gradually develops and with this event tension stresses at this side of concrete will increase. With continue increasing fire intensity, saturated layer creation speed increases and pore pressure and tension stress increment occur. In the following of this process, if tension stress is becoming bigger than tensile strength, fracturing and loss of material from this layer are caused, i. e. Spalling occurs. This paper present an analytical modeling using ABAQUS software to evaluating concrete fire behavior.  , Modeling and analysis of concrete slab under fire in this study includes some steps. In the first step, heat transfer modeling and analysis of solid part is done. In the following "soils" analysis based on initial heat transfer analysis result is accomplished, that vapor flowing between pores, the saturated layer forming and pore pressure developing occur in this step. Concurrent soils analysis, using USDFLD and UMESHMOTION subroutines that joined to software, pore pressure, and tension stress value are controlled and if Spalling occurs in the concrete slab, spalled layer depth and time of Spalling are determined and saved. One of the most important issues facing in the fire at structures is elevated temperature patterns subject and especially fire curves types. Because of the importance of this issue, some of these fire curves placed in the famous codes.  , One of the most popular fire curves in the structure is the ISO834 fire curve that based on cellulose fire. Although many researchers use the ISO834 fire curve in their research, when a fire occurs in structure with petroleum and hydrocarbons products, elevated temperature speed is higher than ISO834. So the fire curve based on petroleum product in the structure presented, is named hydrocarbon curve. Results show that applying Hydrocarbon fire in the concrete increase pore pressure more than double and accelerate Spalling process in comparison to ISO834 fire and by modifying permeability of concrete from 5×10-17 2-16 m to 5×10 2 m, pore pressure decrease less than one tenth even prevent Spalling phenomenon.

Fire accidents are inevitable and it is one of the significant hazards, which causes loss of life and valuables. The present investigation focused to study the influence of fibers on shear strength of concrete exposed to elevated temperature as per ISO 834. The fibers used in the study were Basalt, Carbon, Glass, Polypropylene and Poly vinyl alcohol. M20, M30, M40 and M50 grades of concrete were used for the investigation. The results revealed that the shear strength is declined with increase in temperature. The shear strength is enhanced by the addition of fiber in the reinforced concrete beams exposed to elevated temperature. Carbon fiber reinforced concrete specimens exhibited better residual shear strength than the other specimens. Addition of carbon fiber and basalt fiber in concrete reduced the micro cracks in the specimens exposed to elevated temperature. Addition of polypropylene fiber and poly vinyl alcohol fiber reduced the Spalling but the crack propagation was not prevented in the specimens exposed to high temperatures.

This paper presents an investigation into the development of stresses in anchorage zone in prestressed post-tensioned concrete beam using the finite element analysis. A finite element computer code on the platform of a supercomputer PARAM 10000 is developed and employed for the present study. A parallel algorithm for matrix inversion method is developed and implemented in the presented finite element code. Concentric and eccentric prestressing forces are applied for prestressing of the beams. Effect of Poisson’s ratio over the bursting tensile force developed in the anchorage zone is studied and an equation to compute the magnitude of bursting tensile force by incorporating the effect of Poisson’s ratio is proposed. Development of Spalling zone is also investigated and it was found that due to eccentric loading, stresses of higher magnitude were developed in this zone.Supercomputer PARAM 10000 is used to carry out present analysis and time reduction has been achieved by using multiple processors of the supercomputer PARAM 10000. At the end the performance of the developed parallel code is studied and presented.

In this paper, a two-dimensional computational model is proposed for predicting the initiation position and propagation path of subsurface crack of spur gear tooth flank. In order to simulate the contact of teeth, an equivalent model of two contacting cylinders is used. The problem is assumed to be under linear elastic fracture mechanic conditions and finite element method is used for numerical study. An initial subsurface crack is considered in the model at different depths. For each position of the initial crack, moving contact loading is applied to the part and value of DKII is obtained for the crack tips. The position of maximum DKII is selected as the location of crack initiation. It is shown that the subsurface crack appears at the maximum shear stress point. The maximum tangential stress criterion is used to determine the crack growth angle. The crack is incrementally propagated until the crack tip reaches the part surface and a cavity is formed on the tooth surface. Analyzing the stress field and stress intensity factors are performed in ABAQUS software. The obtained results for the depth and shape of the spall are in good agreement with the experimental results reported in literature.

Nowadays fire has become one of the large prominent threats to buildings and concrete structures in the world. In this research, an experimental study was performed to examine the Spalling phenomenon and residual mechanical properties of fiber toughened Ultra-High-Performance Concrete (polypropylene (PPF) and steel fibers (SF)). Moreover, the effect of high temperatures, namely, 250 ºC and 500 ºC for 2. 5 hours and 5 hours has been studied for each mix of samples. This research discussed the results of compressive strength, flexural tensile strength, and splitting strength. Weight loss of the specimens and the effect of hybrid fibers incorporation (PPF and SF) behavior Ultra-High-Performance Concrete at high temperature were studied. The study concludes that the residual resistance of UHPC decreases as the temperature increases. Also, increasing the heating time resulted in lowering the residual concrete strength. The addition of the optimum percentage of PPF (0. 8%) results in a remarkable effect on decreasing the risk of Spalling in the UHPFRC. Polypropylene fibers provide channels in the concrete for this reduced pore pressures and the risk of Spalling. Incorporating hybrid fiber seems to enhance the resistance of UHPFRC to explosive Spalling due to the significant increase of permeability in UHPFRC. In addition to that, the steel fibers will increase the ductility of the UHPFRC and render it more able to withstand the high internal pressures which were experimentally confirmed by this work.