Journal of Rehabilitation in Civil Engineering
Volume:5 Issue: 1, Winter - Spring 2017

In this study, the effect of deep excavation on the seismic response of RC moment resisting building systems has been studied. Deep excavation can cause significant changes in the stress and strain levels of soil environment and also changes in the propagation of seismic waves. This leads to permanent displacements in the foundation system. In this study, three RC building systems, i.e. 5, 10, and, 15 stories, were modelled considering the nonlinear behaviour of soil and structural material as well as the soil-structure interaction effect. Nonlinear dynamic responses of buildings were evaluated before and after excavation and also with a rigid base (without soil modelling) under the seven earthquake records. Analysis results indicate an increase in seismic demands and responses in the vicinity of the excavation. So for 15-storey buildings near the excavation, 35% increase in the base shear, 70% increase in maximum drift, 26% increase in the story shear force, and a 30% increase in the maximum story acceleration was observed. As a result, considering the effect of excavation on the seismic response of RC building systems is inevitable.

Asphalt modification/reinforcement has received considerable attention as viable solutions to enhance flexible pavement performance. This is mainly prompted by the unsatisfactory performance of traditional road materials exposed to dramatic increases and changes in traffic patterns. This paper presents the evaluation of fatigue behaviour of nano reinforced Stone Mastic Asphalt mixtures. Fatigue is one of the most important distresses in asphalt pavement structure due to repeated load of heavy traffic services which occur at intermediate temperatures. There are different test methods used throughout the world to measure fatigue resistance for asphalt concrete mixtures. In this study, indirect tensile fatigue test was conducted to estimate fatigue number of asphalt mixture with different contents of nano SiO2 and Nano TiO2. The results indicated that the addition of different percentages of nano particles is capable to improve the shear modulus of modified bitumen. Also, modified SMA mixtures had more resistance against fatigue cracking phenomena.

One of the efficient techniques to improve the behavior of the paved road under traffic loads is implementing the geosynthetic material in the sub-base or the soil under the road. In the past years, many researches have been done about this topic, but the study on the effect of soil/load conditions on the performance of the rehabilitated paved road by geogrid in order to investigate the effective parameters on it is still open. In this paper a series of 2D FEM models using the software PLAXIS-2D are carried out to evaluate the effects of soil/load conditions which includes the effect of the subgrade material and load properties (such as modulus of elasticity, Poisson's ratio, drainage conditions, shear strength and the area of load), in the presence of soil-geogrid-interaction. The results showed that the use of a geogrid reinforcement layer decreases the vertical settlement in a soft subgrade surface, and this indicates that the main mechanism of the geogrid is to restrain soils from lateral displacement through interlocking with the particles. In addition, it is concluded that increasing the Poisson's ratio of the subgrade leads to reducing the vertical settlement and increasing the value of modulus elasticity leads to decrease of the vertical displacement, it is also shown that with increasing un-drained shear strength, vertical deflection has also decreased.

One of feasible and efficient method to retrofit structures is spraying shotcrete which is widely applied around the world. Shotcrete is concrete with fine aggregates which are sprayed through a hose and by air pressure coat at high velocity onto a surface. In current research three masonry schools from different regions of Iran are selected. The retrofitted wall surfaces have been prepared and became flatted and Schmidt hammer and Ultrasonic tests are performed for each point. The results from experimental investigation are compared with each other and some experimental results are compared with theoretically results. To investigate the seismic behavior of structures, one of the schools is chosen and then finite element method is used to do time history analysis regarding four ground motions record. Finally, there was an agreement between experimental and theoretically dynamic modules. In retrofitted conditions the obtained frequencies are more than un-retrofitted condition and dynamic time- history analyses have shown that in retrofitted condition, the displacements will decrease and the seismic performance of structure will increase considerably.

Polymer modified concrete (PMC) consists of Portland cement concrete with a polymer modifier. Its advantages are proper bonding strength to substrate concrete, high tensile and flexural strength and low amount of shrinkage and permeability. Using PMC overlays can be considered as a method for preservation of damaged concrete structures due to their suitable performance and durability. In this research, 24 mix designs of polymer modified concrete as the repair overlay containing two different types of modifier polymers (Styrene butadiene rubber (SBR)-based and Acrylic-based polymers) with different replacement percentages and various amounts of silica fume was considered to investigate the effect of type and amount of polymers and also presence of silica fume. The in-situ strengths are obtained by Pull-off method in different conditions of presence of cores and without cores on cubic samples and without cores on repair overlays. The bonding strength of repair overlays to substrate is also assessed and a formula is presented for prediction of bonding strength and in-situ strength by consideration mechanical properties .In both polymer modifiers, maximum bonding occurred in presence of polymer with 20% of cement weight. SBR-based PMC showed stronger bonding compared to the Acrylic-based PMC.

Load carrying capacity of flat double-layer space structures majorly depend on the structure's imperfections. Imperfections in initial curvature, length, and residual stress of members are all innately random and can affect the load-bearing capacity of the members and consequently that of the structure. The double-layer space trusses are susceptible to progressive collapse due to sudden buckling of compression members. Progressive collapse is a chain of local failures leading to the collapse of either the entire or a part of the structure. In this paper, the effects of the probabilistic distribution of initial curvature and length imperfections on the bearing capacity of flat double layer grid space structures for different member’s length and support conditions have been studied. First, equal to the number of the members of the structure, two sets of random numbers have been generated using the Gamma and Gaussian distributions to account for the initial curvature and the length imperfections, respectively. Thereupon, the amount of the imperfection randomly varies from one member to another. Afterwards, based on the Push Down analysis, the ultimate load bearing capacity of the structure was determined through nonlinear analyzes performed through the OpenSees software and this procedure for certainty was repeated numerous times. Finally, based on the Monte Carlo simulation method, the structure’s reliability diagrams and tables were procured. The acquired results indicate that the behavior of flat double-layer space grids are sensitive to and can be affected by the random distribution of initial imperfections.

In this paper, the initiation and propagation of structural damage in a building due to truck collision to one of its corner columns was investigated. For this purpose, a three dimensional 4-story moment resisting steel frame with intermediate ductility was considered. The structure was designed using ETABS software under standard dead, live, and earthquake loads, and then impact loading was applied on the structure using ABAQUS software. The effect of truck collision with different weights and speeds was simulated conducting three dimensional nonlinear dynamic analyses. The internal stresses and forces created in the directly impacted column as well as other parts of the structure were obtained. Using appropriate plasticity models, the shear failure of steel material was considered. A parametric study was performed in order to investigate the effect of different parameters on the possibility of progressive collapse. To validate the procedure of impact modeling, some available experimental vehicle to column collision tests were simulated. The results revealed that the mass and speed of the impactor had a significant effect on the response of the structure. So that, for high-momentum impactors, the traditional column removal method may yield a good approximation of the behaviour of the structure. However, for low-momentum impactors, a time-history analysis without removing the hit column is needed.