جستجوی مقالات مرتبط با کلیدواژه « عرشه بتنی » در نشریات گروه « عمران »

One way to diagnose damage in structures is to use their modal strain energy change index. Since occurrence of damage in parts of a structure, in addition to changing the modal strain energy of the damaged parts, also changes the modal strain energy of the healthy parts, in the vicinity of the main damaged elements, false damaged elements will appear, which makes it difficult to identify the main damaged elements. To solve this problem, in the present work a two-step method has been used to determine the location of the damage on the deck of a concrete bridge. In the first step, by finite element modelling and performing the modal analysis, the initial damage index of different parts of the bridge deck is determined based on modal strain energy changes, using a few vibration mode shapes. In the second step, using weight coefficients, the modified damage index for each element is calculated separately, minimizing the number of false damaged elements. The proposed method for calculating weight coefficients is simple and at the same time accurate. The efficiency of this method was investigated in several damage scenarios with an intensity of only 5% in different parts of the deck of bridge. The results showed that, while the initial damage index could not distinguish even 3 damaged elements in the bridge deck from the healthy elements, the modified damage index was able to identify up to 7 damaged elements in different parts of the bridge deck with good accuracy using only 2 mode shapes.

Given that terrorist operations have increased in recent decades, it is therefore necessary to confront the dangers of this phenomenon. The explosions can cause severe damage to buildings and cause the progressive and complete destruction of these structures. Blast stresses are one of the most destructive loads which a structure may experience. Many of the existing structures are vulnerable to loads caused by the blast wave, so their resistance to such loads should be investigated to identify critical points of structures. In the meantime, bridges are considered as the vital available structures for terrorist operations, but with respect to their importance, solutions must be provided to reduce the vulnerability of bridges subjected to explosive loads. This paper investigates the behavior of bridge under blast loads in different weights and distances. Several experiments samples have been modeled and analyzed under blast loads for validating the results at finite element ABAQUS software, and the analyses showed that this software is able to predict the behavior of studied systems under blast loads. In this case, a bridge that has been located in Tehran, Shahid Saniechr('39') Khani bridge, was chosen and investigated by utilizing ABAQUS. This bridge was subjected to blast loading substance, TNT, in different weights of 45.4, 100, and 150 kg and in different distances of 0.5, 1.2, 1.83, 2.54, and 3.83 meters from the center area of the bridge’s slab. Additionally, a new system U-boot named was added to the initial model for investigating its influences under blast loading.  To conclude, firstly, increasing the amount of exploding substance (in a fixed distance from the center of the slab) cause an increase in the slab displacement and subsequently the damage in the slab is being increased. Secondly, increasing the exploding substance from the center of the slab and assuming a fixed weight for it in both first and second cases showed that increase in the amount of distance could lead to decreasing the displacement in slab and subsequently the damages decreases. Finally, adding the U-boot system leads to incredible improvement in the whole model in comparison with the initial one.

The use of prestressed concrete, has begun progress today and on this basis, both experimental and theoretical has strong backing, but this technique is less concerned with steel, and especially when the combination of concrete and steel is used, the lack of instructions becomes more apparent. In this paper, by presenting the proposed increase in load method, the first results of the plastic analysis of a single-span beam were compared with the strain increase method and the experiment and then, the method of analysis of a continuous double beam with combine of stiffness and flexible method, such as a bridge, has been investigated and finally, the variables of cable length, eccentricity of the cable, and the thickness of the slab in terms of performance optimization, are illustrated by the diagram. It has been found that in the combinatorial method analysis , the inversion of smaller matrices is required compared to the stiffness method, and  the results in the optimization section are shown, adding cables will increase the final load bearing in this sample, and a larger eccentricity will cause a larger internal resistance in the beam. Also, although the thickness of the concrete slab strength, increases the final capacity in these specimens, it does not affect the elastic capacity in pre-tension before concrete.