نشریه مهندسی عمران
سال چهل و پنجم شماره 2 (زمستان 1392)

Due to the positive effects of adding lime in fine-grained soils and reinforcing these soils with polypropylene fiber, durability evaluation of stabilized or reinforced soils especially in cold regions where are more exposed to periodical freezing and thawing cycles is still necessary. In this research, 12 different treatments were prepared by using three levels of lime (0, 2 and 4 percent by weight of dry soil) and four levels of polypropylene fiber (0, 0.25, 0.5 and 1 percent by weight of dry soil). Each treatments with three replications has been cured for 28 days and undergoes numerous cycles of freezing and thawing including 0, 1, 4, 7 and 10 cycles, then unconfined compressive strength of the specimens were determined. According to results of various tests, it was found that using 4% lime with 0.5% polypropylene fibre is the most appropriate combination for making strongest and most durable mixture, as unconfined shear strength of test samples do not change after taking numerous cycles of freezing and thawing.

Corrosion of reinforcement has very serious effects on structural behavior of reinforced concrete structures. Because of damages due to corrosion, several methods of reviving of such structures have been developed. Using of FRP sheets is one of them. In this research, the compression and tension behavior of corroded RC elements strengthened with FRP sheet is surveyed through modeling of these elements by the means of COM3 and WCOMD software developed at the University of Tokyo and a written program in FORTRAN code. Fixed smeared crack approach has been used for nonlinear analysis. In this method, the average behavior of materials (including concrete, reinforcing bar and FRP sheets) is applied in the modeling. After attaining the material constitutive laws of corroded RC elements and also repaired ones by FRP sheet, the consequences are verified through a comparison with laboratory test results.

As it mentioned in the literature the key factors in construction projects success are cost, quality and time. The construction supply chain management (which manage both suppliers and subcontractors relationship with the general contractor) is one of the most essential approaches in improvement of these factors in the construction industry. Thus, the construction companies are inevitable to improve their supply chain management. In this research, firstly, the authors represent the conceptual coordination between value engineering and construction supply chain management. Next, the results of their simultaneous implementation in the project management are specified. At last, the steps of executing value engineering in the construction corporations’ organization are represented.

Chemically grouts are usually injected in soils for increasing of strength or reducing of permeability in which suspended grout could not pass through the small voids of soil mass and filteration of grout particle. Chemically grouts are injected easily to voids of soils due to liquidity and non-suspending of them. One of important factors of these grouts is their viscosity in which controls the grouting potential of them, so that increasing of grout viscosity reduces its grouting ability. In this paper the grouting ability of sandy soils with a chemically grout is investigated. For evaluation of the soil grouting potential, samples with 4 cm in diameter and 100 cm in height were constructed and then injected. Sand samples with four different particle size (coarse, medium, fine and silty sand) and three relative densities (loose, medium and dens) were injected by sodium silicate grout with three different viscosities (water to sodium silicate ratio). Tests results showed that, particle size has the greatest effect on the grouting and the other mentioned parameters depend on this factor. Reducing of particle size decreases the grouting potential of soil, so that adding 50 % silt to soil (50 % silt and 50 % sand) impossible to fully grouting of the sample without fracturing the sample.

Among various methods for modification and treatment of saturated loose deposits, Explosive Compaction (EC) can be realized as an effective and common deep soil improvement method. In this paper, 18 different sites from U.S, Canada, India, Nigeria, Poland and etc. have been studied. Explosive Compaction successfully has been performed for modifying of loose saturated soils layers with thicknesses varied from 5 to 40 m in these sites. While EC performance, volume change due to densification ranged about 2% to 10% was observed. Analysis on the compiled database focused for Powder Factor (PF) role in induced settlement due to EC. Moreover, by using nonlinear optimization, a new relation has been proposed for settlement prediction in which PF, depth of Explosive charges and number of explosion phase’s factor have been considered simultaneously. This relation indicates it is required to increase used powder factor by increasing depth of charge to get an enough compaction as well as influence of first and second phases in final settlement is more than further phases.

In a soil mass, a rise in pore water pressure leads to a decrease in the mean effective normal stresses, while the vertical loads due to surcharge may experience small changes. Under such loading, very loose and loose sands may initially experience small volumetric expansion, and then start to contract significantly as failure is approached. These large contractions can lead to the increase in pore water pressure and, consequently, failure of the soil mass under poor drainage conditions. In this paper, an experimental model is used to examine slope instability resulting from rise in water level. It was noticed that the main factor controlling the mode of failure was initial density, but other factors such as method of increase in pore pressure, distribution of pore pressure, and geometry of the test tank also influenced failures.

ACI 440.1R-06 Code overestimates the bond strength of lap-spliced FRP reinforced concrete beams. In this code, the effect of transverse reinforcement along the splice length on bond strength is not taken into account. In this paper, ACI 440.1R-06 equation was modified for calculating the bond strength of spliced bars in specimens without transverse reinforcement along the splice length using reliability analysis and experimental results. Then, 13 beam specimens were manufactured and tested for evaluating the effect of transverse reinforcement on bond strength. Experimental results show that the influence of transverse reinforcement depends on surface geometries of FRP bars. In this study, the bond strength produced by transverse reinforcement is formulated as a function of surface geometries of bars. This equation is obtained by means of experimental results and Monte Carlo simulation. The bond strength calculated by the proposed equations correlates well with the experimental results in comparison with the values predicted by the code provisions.

Due to complex nature of the collapse phenomena, along with its important role in structural performance, collapse assessment has recently gained a great attention in performance based earthquake engineering. Furthermore, uncertain sensitive parameters on seismic collapse performance have intensified the complexity. In this paper, a novel probabilistic approach based on simulating failure modes within IDA framework with application of Bayesian Probability Network (BPN) is proposed to evaluate collapse of structures. Applying pushover analysis, likely Failure Modes (FMs) are recognized first, and then along with sensitive Random Variables (RVs), these FMs are incorporated in BPN. Conditional probability of these FMs related to the incorporated RVs, are calculated within IDA agendum, which directly considers record-to-record uncertainty.
Some of the results investigated in this research are: Comparing mean annual rate of collapse derived from the proposed method with the conventional limit-states considered in IDA approach, detection of structural response in a probabilistic framework and updating through BPN. Totally, it can be claimed that via the newly proposed methodology not only the safety index of structures are calculated in an effective way, but also structural response in the collapse limit state is detected probabilistically.

Significant proportion of national and infrastructure investment devotes to construction activities in nature. These investment must be selected with sufficient confidence to ensure survival and duration of vital interest. In this study after collecting information including slope angle, lithology, fault's length, River's length, Road's length Rainfall, earthquake and vegetation in packed cell map is processed in Geographical Information System( GIS) . finally landslide hazard zonation in Doroud-Andimeshk railway is presented. Zonation map of the area is prepared using Moora-Varson method and is validated using AHP method. Slope angle is obtained from digital elevation map of the area.1/250000 topography map is used to obtain digital elevation map. Lithology map is prepared using 1/100000 geological map. Fault's length, Road's length, river's length and vegetation are obtained from Landsat satellite map. Rainfal and earthquake data are obtained from Meteorology center and Geophysical Institute of Tehran. At the end, the area with high risk of rockfall was introduced.

In order to design retaining walls, first the initial dimensions of the wall should be estimated. In order to choose these dimensions, the designer should use reasonable proportions that were achieved by previous experiences of the designing different retaining walls. These dimensions are introduced based on a ratio of the height of walls. Current reseasrches showed that by changing the conditions such as properties of the backfill materials of the retaining wall, the local seismic conditions, the height of the wall and limitation in choosing the arbitrarily dimensions etc, these estimated dimensions would not be appropriate for an economical design. In this paper, by means of genetic and bees algorithms, economical dimensions of the wall for static, pseudostatic and pseudodynamic loading conditions will be calculated precisely in a such way that stability of the retaining wall against sliding, overturning and bearing capacity are provided. Also from structural consideration point of view, the designed walls could resist appropriately against the applied forces.