Concrete structures may be exposed to high heat. In such a way that high heat in the vicinity of concrete structures causes damage in concrete. The aim of this study is assessment of effect of electric high heat on the bending capacity, energy absorption, fracture type and crack distribution of circular fiber concrete slab under monotonic loading. The concrete aggregates with a fracture percentage of 45% are from the mines around Tehran and the fibers used in the concrete are of macrosynthetic type. The concrete mixing design was based on the target compressive strength of 45 MPa and the amount of fibers equal to 0.5% of concrete volume. The heating of the concrete samples was done by a 2400-liter device with a power of 90 KW and maximum temperature of 550 degrees Celsius. To perform slab tests, Dartec9600 device was used with monotonic loading at a rate 0.004 mm/s. based on the Experimental studies conducted on the fiber concrete slab, the application of high heat did not cause concrete peeling but it reduced the capacity of the slab by 89.3% and decreased the energy absorption of the slab compared to the control sample. Also, SEM photos have shown the aggressive destruction of macrosynthetic fibers and the creation of cracks under the effect of high heat in fiber concrete.

In recent decades, many terrorist attacks have occurred all over the world, which have left many financial and human damages. As a result of these events, engineers felt the need to design explosion-resistant structures. Among the important structures in transportation systems are bridges. On the other hand, this important structure can be an attractive target for terrorist attacks. Therefore, the analysis and investigation of explosive loading on this structure is very important. Considering the frequency and expansion of the construction of concrete deck bridges in Iran, this research has investigated and numerically analyzed the deck slab of a reinforced concrete bridge. The parameters investigated in this research include deck displacement and deflection, stress, element removal, the amount of deck destruction and how cracks are formed, the change in scale distance and the mass of the explosive. Also, LS-DYNA finite element software has been used for modeling. The results show that on the concrete decks in the bridges, the parameters of the amount and location of the explosion are very important and effective in such a way that it causes extensive damages at the level of the near explosions. Based on the results obtained, with the increase in the weight of the explosive, the displacement and stress values in the structure increase in such a way that after the explosion of 250 kg of explosive in the air, linear cracks were created, while after the explosion of 500 kg of the explosive on On the surface of the concrete bridge deck, there is a spherical punch-like destruction with an approximate diameter of 2.4 meters. Also, by changing the explosive material from 250 kg to 500 kg TNT, the amount of displacement for the center of the bridge deck will increase by 5.5 times, and by changing the explosive material from 500 kg to 700 kg TNT, we will see an increase in the amount of displacement at the edge of the deck by 2.5 times.

The seismic behavior of concrete end diaphragms of bridges has not been studied before and there are no significant design provisions available. According to the American Association of State Highway and Transportation Officials (AASHTO), the end diaphragms being part of the seismic load path have to remain elastic under the prescribed seismic design forces, regardless of the type of bearings used. In this paper, using a three dimensional finite element model and nonlinear time history analyses, the behavior of reinforced concrete end diaphragms in straight single-span slab-girder bridges has been investigated. The results are compared to AASHTO's design provisions. It is concluded that for slab-girder concrete bridges, the concrete diaphragms remain elastic under design earthquake loading. It is also concluded that AASHTO's recommended seismic design force for end diaphragms could be unsafe in most cases.

The reinforced concrete flat slab structures are highly susceptible to punching shear failure. This occurs due to the transferring of shear force and due to the bending moment between the slab and the column. The initial local failure and the following redistribution of load can lead to punching failure of the slab in the adjacent column locations. This issue can collapse an entire building or a huge portion of a structure. Hence, an alternate load path method is necessary for preventing the catastrophic failure of the buildings. Compared to the moment frame buildings, flat slab buildings are more prone to the progressive collapse. Thus, the designing of flat plate structures demands more attention and study. Due to higher construction costs and limitations in the test set up, the researchers have adopted scale down structures for the experimental studies. The progressive collapse behavior of the prototype structures is usually analyzed using both analytical and numerical simulations. This paper discusses the existing researchers on the analytical study, experimental study, and numerical simulations of flat slab structures along with various load resisting mechanisms to mitigate progressive collapse. Further, various strengthening techniques available in the literature for the flat slab structures have been discussed. A parametric study and comparison of different strengthening techniques are also performed in this work.

Due to the large number of fire and the resulting financial and human costs, it is necessary to prevent the roof from collapsing as one of the key members of the building during a fire. Because concrete has an inherent weakness in tensile stress, cracking in the tensile area of slabs is inevitable. On the other hand, in a system of prestressed concrete joist slab system, the tensile area of the concrete is usually completely eliminated or effectively reduced, and the performance of the floor can be expected to improve under fire conditions. The critical temperature was obtained and compared in 9 samples that differed in the amount of prestressing force, strength and concrete cover as well as the span length. The thermal load was applied to the studied samples according to the ISO 834-1 standard protocol. The temperature distribution across the slab was applied uniformly and incrementally and the failure states in the model were predicted and verified with laboratory results. The results showed that the prestressing force has the greatest effect and the span length has the least effect on decreasing or increasing the critical temperature index. Changing the prestressing parameter from zero to 600 and 1120 MPa, increases the critical temperature index by 20 and 43% and changing the beam length parameter from the initial value of 4.5 m to 6 and 7.5 m, decreasing the critical temperature index by 1 and 2%, respectively. Changing the parameter of concrete cover from 20 mm to 10 and 30 mm has caused a decrease and increase of critical temperature index by 11 and 9%, respectively. Also, in all samples, the same failure mode occurred in the middle of the joist in a bending manner.

The use of steel fibre instead of Rebar reinforcement or in combination with them have advantage such as increasing flexibility, energy absorption and control of crack. Laboratory studies have been performed on the performance of slabs with steel fibres, but no specific numerical study has been performed that enters the fibre properties directly into the analysis process. Steel fibre concrete in this study modeled with finite element method and laboratory work with existing fibre-reinforced slab compare and validate. Then, with the development of fibre-reinforced slab track model, relies on the rebound under the bed moving a simulated load. The results show that the presence of fibres in the service load range has little effect on the shear and flexural forces of the slab. In the following, using FIB regulations, the process of designing steel fibre concretes and the possibility of using steel fibres in slab track is examined. The results show that the use of fibres in the slab alone does not have the necessary flexural strength to withstand the incoming loads and the crack width is obtained several times the allowable value of the regulations. As a result, the combination of fibres and reinforcement is used to control cracks and the design graph of the combination of fibres and reinforcement in the slab is obtained. The results show that with the addition of fibres, the amount of reinforcement required is slightly reduced and the crack width is significantly reduced. For example, in the case of axial load of 25 tons, load speed of 120 km / h and hardness of 32, 000 kN/m with fibre volume percentages of 0. 25, 0. 5 and 0. 75 in slab track model, the reinforcement used is reduced by 26, 30 and 35% respectively. as well as crack width used is reduced by 3. 5, 4. 9 and 6. 3% respectively.

This study investigates the response of Reinforced Concrete (RC) voided one-way slabs under four-point bending, focusing on a novel and simple strengthening technique using embedded steel plates. Seven slab specimens were constructed with identical dimensions: 2000 × 600 × 130 mm. One specimen was a solid slab, serving as the control, while the remaining six were voided slabs. Among the voided slabs, one lacked a steel plate, and the other five were strengthened with steel plates of 1-, 2-, and 3-mm thickness. The primary objective of this study was to investigate whether the steel plate could compensate for the loss of strength and mitigate the impact of reducing the slab cross-section. The unstrengthened voided slab demonstrated substantial performance degradation compared to the reference solid slab, with 57% greater deflection at service load and significant reductions in ultimate load, stiffness, ductility, and toughness of about 23. 5%, 25. 4%, 10%, and 35%, respectively. Conversely, slabs strengthened with steel plates demonstrated a notable performance improvement. This was achieved by increasing flexural stiffness and reducing deflection at service load, with reductions ranging from 16% to 32% across the strengthened specimens. The percentage increase in ultimate strength ranged from 24% to 46% compared to the unstrengthened sample. Finally, a Finite Element Analysis (FEA) was performed using ABAQUS to validate the experimental results

One of the main issues in track maintenance-management systems which is required for organizing rail line's repair and maintenance activities, is evaluation of superstructure conditions. Slab tracks superstructure condition in respect of maintenance parameters is a qualitative issue which should be converted to a quantitative parameter in order to maintenance operation decision making and forecasting of rail road future condition in a management system. In this case the track structure condition index and track geometry condition index are used. However, a comprehensive method for evaluation of slab track superstructures isn't presented yet, in spite of significant development of slab track systems in Iran and all around the world. The methodology which is given in this research, is used in development of evaluation models based on mechanical and field inspection. Field researches and inspections of some parts of main slab tracked rail road were done, in order to calibrating the model and its experimental implementation on a test route. track structure condition indexes in our case study track was 95,89 and 88 for fastener, slab track and ordinary rail group respectively, which shows that converting slab track's components quality condition to quantity based on offered methodology and what we expected for, has appropriate result. It shows also that damages categorizing and its intensity limitation in order to determining different kinds of damages is suitable. The track geometrical condition indexes which are used in this research, consider mean parameter in addition to standard deviation. Geometrical index for case study is between 0 and 3.02 in slab track which satisfies sufficient requirements to let the train pass safely.

A reliability-based method was developed for predicting the initiation time and the probability of flexural failure for continuous slab bridges with load-induced cracks exposed to chloride environment resulting from deicing salts. A practical methodology was used for predicting the diffusion coefficient of chloride ingress into the pre-existing load-induced cracks in concrete. The reduction in the cross-sectional area of the reinforcement due to corrosion was included in the model. The proposed methodology accounts for uncertainties in the strength demand, structural capacity, and corrosion models, as well as uncertainties in environmental conditions, material properties, and structural geometry. All probabilistic data on uncertainties were estimated from the information contained in previous experimental and statistical studies.As an application of the proposed model, a three-span continuous slab bridge in Ohio is presented for demonstration of the developed methodology. A comparison of results clearly shows the importance of considering the effects of the load-induced cracks for correct prediction of the initiation of corrosion time and the critical time to maintain structural integrity.