مجله مهندسی زیر ساخت های حمل و نقل
سال چهارم شماره 2 (پیاپی 14، تابستان 1397)

Evaluation of pavement structure is an important part of the pavement management system at the network and project levels, which is usually performed by using falling weight deflectometer (FWD) device. In using the FWD device, strength of the pavement layers is determined by back-calculations method. Using this method is not financially and temporally affordable for management at network level because of complexity and need for accurate initial information, and therefore it is usually used at the project level. Dynamic cone penetrometer (DCP) is another equipment, which is fast and cheap, and is used in evaluation of pavement structure at network level. In this research, 50 km of arterial road of Kermanshah province was tested by using the FWD and DCP devices. Results showed acceptable correlation between penetration index, as DCP output, and the obtained data of FWD device for pavement layers. The PI variation range for different pavement structure situations at network level was presented by analyzing the FWD and DCP outputs. Output results of network analysis using both methods showed acceptable PI criterion validity as simple and cheap criterion for pavement structure evaluation in pavement management at network level.

Tire-derived aggregates mixed with granular soils are amongst the new materials with different characteristics, as compared to the base materials, which are being used more commonly with the increase of waste rubbers and tires. These lightweight materials, having controlled compressibility, could be used in civil engineering infrastructures, road construction, and geotechnical structures. Up to now, limited experimental studies have been performed to present optimum mixing ratio of waste rubber and sand to attain the engineering purposes including the maximum bearing capacity and the most proper compressibility. Nevertheless, determination of a specific mixing ratio and identification of shear strength parameters of sand-rubber mixtures under different stress paths needs further study. In this research, results of triaxial tests, considering constant radial stress (CRS) and constant axial stress (CAS) paths on the sand alone and also mixed with rubber chips and granulated rubber are presented. Results of relative density tests demonstrated that the optimum rubber mixing ratio of 30% in weight acquires the least void ratio when sand is mixed with rubber chips. The sand alone tests resulted in an effective strength envelope which is approximately linear with a friction angle of approximately 36.8° in both stress paths. While, the outcome of the two different loading methods on the sand-rubber mixtures is an approximately bilinear stress envelope. The internal friction angle of sand mixed with rubber chips is greater than that of sand alone by 8.5 and 4 degrees under the CAS and CRS conditions, respectively. This parameter is about 1.5 and 5 degrees less than sand alone for granulated rubber mixed with sand, under the CAS and CRS conditions, respectively.

Resilience assessment can be assumed as an important tool for decision making for disaster managers. Considering the recovery time in the resiliency approach causes this approach to be different from other frameworks of decision-making process in the preparation phase in estimation of losses and time-dependent consequences. The recovery process after distaster occurrence may be modeled by simple recovery functions or complex organizational and social models. The obvious point in using resiliency approach is that it could give the disaster managers a recovery trend of infrastructures after disasters, with respect to important factor of time, to allocate the available resources on the basis of resiliency criterion. Currently, the selection of retrofitting strategies of infrastructures, especially subway stations, is performed by economic and technical approaches according to the state of the art standards. In these analyses, recovery trend of the performance after disasters is usually ignored. In this study, on one hand, the concept of resiliency of infrastructures after disasters, its dimensions and analysis methods are investigated, and on the other hand, some retrofitting methods are proposed for stations and subway tunnels. In the next step, considering the proposed algorithm for attaining the quantitative resiliency, first, the 15-Khordad subway station in Shiraz was modeled and displacements due to 11 earthquakes with different PGAs were analyzed in 10 control points. Then, the discrete and cumulative damage-probabilities were calculated by comparing the calculated displacements with damage-level threshold. The resiliency of the substation under different retrofitting strategies is quantified in the next stage considering calculated damage probabilities and different recovery functions. Finally, the ranking of retrofitting strategies for infrastructures was done based on the resiliency concept. The proposed method can be generalized to other infrastructures.

Two adjacent footings behave often differently from a single footing. Nowadays, with the scarcity of suitable land for construction purposes and population growth in the coastal zone of Caspian Sea, construction without considering the interference of the footings is increasing. This issue has been further complicated due to the unequal and non-simultaneous loading of the adjacent footings. In other words, initially, the light or old footing has been constructed, and then the heavy or new footing will be constructed adjacent to the old footing. This is also true in ports where containers are stacked side by side. In this study, the influence of unreinforced concrete pedestals on improvement of saturated loose sandy soil is investigated through modeling the small-scale 1g tests. The main focus was on the load bearing capacity, settlement and tilt of the light footing nearby the heavy footing, when the pedestals are placed beneath the heavy footing. Results of this study illustrated that with fixed diameter pedestals (D=5 cm), increasing the pedestal length (L) from 15 to 25 cm, as refining factor of the soil underneath the heavy footing, led to 18 and 38 percent decrease in settlement and tilt of the light footing nearby the heavy one, respectively, when the S/B ratio was zero.

Construction of roads and development projects on sandy soils is usually done due to lack of adequate strength to the displacement of subgrade soil or redirecting. Therefore, stabilization and investigation of the factors affecting its strengthening with different materials have always been of interest to the researchers. Studies have shown that the use of polypropylene fibers generally increases the ductility and mechanical strength, such as compressive strength and shear strength, of soils. On the other hand, the initial moisture content plays an important role in stabilizing with emulsion bitumen. Therefore, in this study, the stabilization and improvement of dune sand, using different initial moisture contents, emulsion asphalt binder, and fiber in optimum cement percent were considered. Uniaxial compressive test results showed that addition of fiber increases the bearing capacity by an average of 10%. Increasing the initial moisture content increased the strength performance of the sand subgrade and then decreased in high moisture contents. Also, increasing the percentage of emulsion asphalt binder and fiber had a significant impact on the enhancement of stabilized subgrade ductility.

There are several methods to investigate the behavior of hot mix asphalt (HMA) at low temperatures. One of these methods is the use of principles of linear elastic fracture mechanics (LEFM). In this paper, the LEFM principles is used to investigate the effects of different loading modes and temperatures on the fracture resistance of HMA incorporating carbon fibers at subzero temperatures. Three-point fracture tests were successfully performed on the semi-circular bend (SCB) specimen containing an asymmetric vertical edge crack under different modes of loading including pure mode I (pure tensile), pure mode II (pure shear) and mixed-mode I/II (tensile-shear). Critical stress intensity factors were then computed using the critical load obtained from the fracture experiments and the geometry factors were determined from the finite element analyses. Results revealed that at all loading modes, modified HMA has higher resistance against crack growth than the unmodified HMA, particularly at low temperatures. Also, fracture resistance of tested HMA was improved by 30-43 percent in the pure tensile mode, 13.2-41 percent in the mixed mode (Me=0.5), 10.5-40 percent in the mixed mode (Me=0.2) and 2-12.5 percent in the pure shear mode.

Evaluation of highway bridges is a matter of importance in terms of seismic performance analysis for pre-and post-earthquake planning of a transportation system. Irregular structures have always been in the spotlight of researchers and engineers. In this study, a three-dimensional model of seat-type abutments is generated in a set of irregular bridges with unequal height of piers using OpenSess finite element software. Since altitudinal irregularity leads to different stiffness of individual piers, the distribution of seismic forces will be dissimilar for each pier. On the other hand, the proportion of seismic forces absorbed by the abutments is dependent on strength and stiffness of central piers. In addition to irregularity effects, the influence of two distinct approaches of pier support modeling such as fixed-base and flexible-base (soil-structure-interaction) is taken into account in the analyses. In addition, in order to obtain maximum demand on bridge members with complex behavior, subjected to the ground motion by orthogonal components, nonlinear time-history analysis using multiple earthquake records should be applied in different directions. Therefore, incremental dynamic analysis is performed on each bridge model for a set of seismic records each rotated in seven various directions. By processing the outcomes obtained from analysis of two levels of damage states, it is determined that the irregularity ratio and configuration, soil-structure-interaction, and incident angle of seismic motions are three important factors in evaluation of fragility characteristics of abutment constitutive members. With no exceptions in the investigated models, the fixed-base assumption of central piers produces conservative response of the abutment components in comparison to soil-structure-interaction consideration. However, the effects of ground motion directionality on the fragility characteristics of individual members of abutment vary for different damage states from one model to another.