Journal of Rehabilitation in Civil Engineering
Volume:3 Issue: 2, Summer - Autumn 2015

Extensive research has been focused on the progressive collapse analysis of buildings and most of them are based on the alternative path method (APM) with sudden removal of one or several columns. However, in this method the damage of adjacent elements of removed columns under blast conditions was ignored and this issue can lead to an incorrect prediction of progressive collapse. Therefore, in this study to evaluate the alternative load path method in predicting the progressive collapse due to blast loading, a 3-D finite element model of a 7 storey steel building simulated and the behavior of structure was studied using the direct applying of blast load method and alternative load path method. For simulating and applying the blast loading and assessment of their direct effects on structures, a blast load equivalent to 1 ton TNT was considered at a distance of 4 meters from the corner of the structure. The pressures of this blast in 4 loading cases are applied to the adjacent structural members and the structural response has been examined. Finally, the exciting forces in adjacent structural members of blast site in each case have been compared. The results show that in assessment of the potential of progressive collapse occurrence by considering the blast loading as the initial reason of failure, the structure response will be different compared with the common methods that have been used for evaluation of progressive collapse occurrence and in those methods the initial reason of progressive collapse was ignored.

The ultra-high strength self-compacting concrete, UHSSCC is the new generation type of concrete with a compressive strength higher than 80MPa. The application of this type of concrete on the serviceability state in CFRP strengthened unbounded post-tensioned indeterminate I-beam is monitored and the results are compared theoretically using different standards. For this aim, full scale I-beam of 9m length was cast, by UHSSCC. During the beam service load test, the stress and strain of materials, and also deflection and crack widths were monitored at different locations using different types of sensors. Based on the experimental measurements and observations, the beam serviceability response was compared theoretically by different methods. As the considerations prepared in the standards do not cover strengthening of such members with unbonded tendons, and also no trace of deflection prediction for such continuous member, one can find in the open literature. It is therefore, this investigation was planned.
A comparison between theoretical and monitored results was performed for serviceability response and it was found that although, the stress of materials are well within the standards limitations for crack widths of wcr0.1 and wcr0.2 of bonded tendon, but the full service load is reached at a higher load, while the flexural crack, experience a width of 0.3mm. It is also apparent that the loads corresponding to the conventional suggested deflection limits will cause to exceed serviceability state of strengthened unbounded beam, and new limitations are introduced for crack widths of 0.1, 0.2 and 0.3mm to predict service deflection of beams.

This study presents the results of an experimental program to investigate the effectiveness of an innovative combined FRP technique using combination of externally bonded (EB) FRP fabrics and near surface mounted (NSM) FRP rods for flexural strengthening of existing reinforced concrete (RC) two-way slabs with low clear cover thickness. Three full-scale RC slabs (1500×1500×120 mm) were tested under monotonic four-point bending. One slab was kept un-strengthened as the control specimen, one slab was strengthened using NSM GFRP rods, and the other one slab was strengthened using combination of EB CFRP fabrics and NSM GFRP rods. The load-deflection responses, strain measurements, and failure modes of the tested slabs were studied and discussed. The behavior of the slab strengthened with this technique was compared to the behavior of the slab strengthened with GFRP rods. The test results confirmed the feasibility and efficacy of this technique in improving the flexural behavior of RC two-way slabs. Strengthened slabs showed an increase in flexural capacity between 250 and 394% over the control specimen. The slab strengthened using this technique showed higher ductility compared to the slab strengthened using GFRP rods. A 3D nonlinear numerical model was also developed using the finite element (FE) method to predict the flexural behavior of the tested slabs. A good agreement between experimental and numerical results was observed.

The main objective of this paper is concentrated on presenting a new two-stage method for damage localization and quantification in the linear-shaped structures. A linear-shaped structure is defined as a structure in which all elements are arranged only in a straight line. At the first stage, by employing Grey System Theory (GST) and diagonal members of the Generalized Flexibility Matrix (GFM), a new damage index is suggested for damage localization using only the first several modes’ data. It is followed by the second stage which is devoted to damage quantification in the damaged elements by proposing an optimization-based procedure to formulate fault prognosis problem as an inverse problem, and it is solved by the Pattern Search Algorithm (PSA) to reach the optimal solution. The applicability of the presented method is demonstrated by studying different damage patterns on three numerical examples of linear-shaped structures. In addition, the stability of the presented method in the presence of random noises is evaluated. The obtained results reveal good and acceptable performance of the proposed method for detecting damage in linear-shaped structures.

Scour in the downstream of hydraulic structures is a phenomenon which usually occurs due to exceed the velocity or shear stress from a critical level. In this research by using the laboratory information which was gathered by Borman- Jouline and De-Agostino, it was tried to get more accurate equations in order to calculate the maximum depth of scour in the downstream of the water level regulation structures. The comparing of these relations with the equations of the other researchers showed that these relations are much more accurate. Artificial neurotic networks (ANNs) with learning algorithm of error back propagation (BP) were used to estimate maximum water scour depth, and the model which has seven neurons in its latent layer was produced as the most appropriate model.Finally by using statistical parameters, the neurotic model was compared with optimized equations. The results of this study showed the more appropriate and higher accuracy of artificial neurotic networks.

Accurate predictions of the amount and the rate of long- term deformation of reinforced soils under an applied load are important key issue in geotechnical engineering, in which the deformation of soil develops with time at a state of constant effective stress. Since geosynthetic is generally considered creep sensitive therefore, evaluation of creep behavior of geosynthetic reinforced soil (GRS) is necessary. In this study, to investigate the effect of reinforcing on the creep behavior of sandy clay soil, experimental tests on soil creep of reinforced sandy clay soil with geotextile yarn in one dimensional consolidation test are conducted and data analysis is explained based on relationship of the change in void ratio (∆e) and coefficient of secondary compression (Cα). Test results indicate that in reinforced water saturated samples with geotextile yarn, with increasing the percent of geotextile yarn creep, deformation decreases and time required for beginning the creep deformation increases.

In recent years application of CFRP sheets in strengthening of concrete circular column has increased numerously. Knowing the exact behavior of concrete cylindrical columns confined with CFRP is of first order importance. ISIS code of Canada, has given relations for strength increase of circular columns confined with CFRP sheets, these relations are defined for a specified range of confinement pressure; and for higher confinement pressures there are no relations describing behavior of the confined specimen. In this paper cylindrical specimens with different concrete strengths and variable number of CFRP layer were used. They were modeled in finite element software.