Journal of Rehabilitation in Civil Engineering
Volume:2 Issue: 1, Winter - Spring 2014

The present study was conducted to determine peak ground acceleration (PGA) over bedrock in probabilistic analysis methods for the seismic hazard and uniform hazard spectra at different hazard levels for Esfahan city. A series of statistics containing historical and instrumental seismic data covering from the 8th century A.D. to the now up to a radius of 200 km was employed and seismic sources were modeled up to a radius of 200 km from Esfahan city. For this purpose the method proposed by Kijko (2000) was employed considering uncertainty in magnitude and incomplete earthquake catalogue. Seismic hazard analysis is then carried out for Esfahan city by using SEISRlSK III (Bender and Perkins, 1987) program for 11×13 grid points. Four different attenuation relationships of PGA and SA with logic tree were used to determine the PGA on bedrock. The PGA can be determined for 143 points and the hazard spectra can be specified for 20 points of the city. Covering %2 and %10 probability of exceedance in one life cycle of 50 years are presented. Finally, the uniform hazard spectra was also presented with %10 and %2 of probability of exceedance in one life cycles of 50 years are presented along with New Mark and Hall Spectra.

In this paper a simple model of a three story building with inclined first-story columns has presented. The stories are supposed to be rigid and are connected to axially rigid mass less columns by elasto-plastic rotational springs and linear rotational dampers. The considered model is subjected to horizontal component of fault normal pulse with different magnitudes and the governed nonlinear differential equations of motion have been solved by the forth order Runge-Kutta method. Results indicate that the inclination of the first-story columns stiffens the system. However, the change of the frequency of the first mode is small. The deformation of the first story with inclined columns is such that it forces the building in a pendulum-like motion. So it would be possible to reduce the relative building response. Results indicate that an optimum value of inclination angle of the first-story columns is. Under this condition the first-story drift decreases while upper-story drift increases, respect to the common building. For larger inclination angles the gravity effect leads to increase the first-story drift as well. This solution would be useful in earthquake resistant design of buildings which have architectural limitations at the first story.

The use of unbounded tendons is common in prestressed concrete structures and evaluation of the stress increase in unbonded tendons at ultimate flexural strength of such structure has posed a great challenge over the years. Based on the bending experiment for two-span continuous post-tension beams with unbounded tendons and externally applied CFRP sheets, the monitoring of the stress increment of unbounded tendons is made in the loading process. For these aims, in this paper there are presented results of two continuous un-bonded post-tensioned I-beams were cast with high strength concrete (HSC) and monitored by electrical strain gauges. The beams are made of which are compared with the theory proposed by different codes. The results indicate that the ACI 318-2011 provides better estimates than AASHTO-2010 model whereas this model provides better estimates than BS 8110-97. Comparison of experimental ultimate tendon stress increase of strengthened and non-strengthened beams casted with HSC indicates that increase in tendon stress at an ultimate state in strengthened unbounded post-tensioned beam is lower than non-strengthened unbounded post-tension beam casted with HSC.

Fiber reinforced Polymers (FRP) have widely used for the purposes of enhances strength and ductility of concrete columns. Proper design of such hybrid columns, however, requires a better recognition of the behavior of concrete columns confined with FRP. In this paper, the influence of FRP thickness, concrete compressive strength, and column size on the performance of eccentrically loaded reactive powder concrete (RPC) columns confined with FRP is investigated. In this regard, five different FRP thicknesses, three types of column sizes, and concrete compressive strength values ranging from 140 MPa to 180 MPa are considered. For this purpose, two-dimensional nonlinear finite element analyses are carried out so as to predict the behavior of FRP-confined RPC columns. OpenSees software is employed to analyze the considered columns. To validate finite element model, the numerical predictions are compared with the experimental data. The study, from a numerical point of view, derived some important relevant conclusions regarding the behavior of RPC columns confined with FRP.

The objective of this review to be submitted in two independent parts, for steel frames and for RC frames, is to compare their structural performance with respect to the proposed N2-method, and so also of the consequent convenience of using pushover methodology for the seismic analysis of these structures. A preliminary investigation is presented on a pushover analysis used for the seismic performance of metallic braced frames equipped with diagonal X-bracing and K-bracing systems. Three steel frames are analysed corresponding to 3, 6 and 10 floor regular buildings that were modelled in the MIDAS/Civil finite element software. To obtain the pushover curve a non-linear static methodology is used. For the RC frames three commercial programs (SAP 2000, SeismoStruck and MIDAS/Civil) are used in order to perform a parametric study based on pushover analyses. The equivalent strut method is applied to simulate the influence of the masonry infill panels; to evaluate the influence of these on the capacity curves, several strut width values are considered. The parametric study also addresses the influence of other parameters on the structural behaviour and non-linear capacity curves of the RC frame, namely: length and position of the plastic hinges and different loading patterns (uniform, modal and triangular distributions).

Subgrade soil stabilization is one of the primary and major processes in the construction of any highway; also environmental authorities are concerned about the growing amount of polyethylene (PET) bottles produced by household sectors. This research in order to study effect of adding recycled polyester fiber on soil engineering properties, especially shear strength and California Bearing Ratio (CBR) used clay soil with low liquid limit (CL) and atterberg limits used high liquid limit (CH). Clay soil with recycled polyester fibers are mixed with soil in three different percentages 0.1%, 0.3% & 0.5% (the portion of stabilizer matters to soil net weight). Shear strength, CBR, atterberg limits of stabilizer samples were measured by direct shear test and CBR test and atterberg limits test. Experiments results show this fact that using of recycled polyester leads to increasing shear strength and CBR and reduction, plasticity index. It is remarkable that according to economic problems, the most optimum quantity of recycled polyester fiber to reach to favorite strength is 0.5%.

This paper presents a new model for predicting the compressive strength of steel-confined concrete on circular concrete filled steel tube (CCFST) stub columns under axial loading condition based on Artificial Neural Networks (ANNs) by using a large wide of experimental investigations. The input parameters were selected based on past studies such as outer diameter of column, compressive strength of unconfined concrete, length of column, wall thickness and tensile yield stress of steel tube. After the learning step, the neural network can be extracted the relationships between the input variables and output parameters. The criteria for stopping the training of the networks are Regression values and Mean Square Error. After constructing networks with constant input neurons but with different number of hidden-layer neurons, the best network was selected. The neural network results are compared with the existing models which showed the results are in good agreement with experiments.