نشریه مهندسی عمران فردوسی
سال بیست و نهم شماره 2 (تابستان 1396)

The purpose of footing design is transferring structure load to soil without causing shear failure and extra settlement in soil. Therefore, footing bearing capacity should be considered in various projects. In special case, footings are placed in various positions with respect to slope ground and position of ground slope affects footing bearing capacity. In fact, slope affects failure surface of soil beneath the foundation remarkably and therefore, footing location with respect to slope must be cared to determine exact footing bearing capacity. In present paper, analytical method is presented based on soil stability beneath the footing. Virtual retaining wall method is used in present study and by applying equilibrium between active and passive forces on virtual wall, footing bearing capacity on reinforced and unreinforced soils is determined in various positions with respect to slope ground. Also, varied parameters include soil resistance, footing spacing with respect to slope ground, width and depth of foundation and seismic coefficient. Results indicate, in various depths and widths of foundation, bearing capacity of footing on flat ground is more than top of slope and bearing capacity of footing top of slope is more than down of slope. Also, bearing capacity of footing on slope is minimum. Based on proposed method, footing location with respect to slope affects passive and active force on virtual retaining wall and footing bearing capacity remarkably. Also, the proposed method can determine effect of slope angle and reinforcement on footing bearing capacity. Presented method indicates effective distance from slope crest is almost 4.5B. Finally, the predicted results are compared with those reported from analytical and experimental methods performed by others, indicating an acceptable agreement.

To find the critical slip surface is one of the most important steps in this analysis. The shape of slip surface in many analyses is circular which convenience for calculating is. Optimization methods are one of the methods to find critical slip surface. In this paper is presented a new method to find critical slip surface and minimum factor of safety using DOSS program. DOSS program is written by authors in FORTRAN and can find critical circular slip surface by using grid search and critical line segments slip surface by using optimization method. This program is applicable for homogeneous and non-homogeneous materials with water level. The examples prove the efficiency and precision of the suggested method.

Sluice gates are widely used for water level control and flow measurement in open channels. The sharp edge of sluice gates causes low contraction coefficient (Cc) and limited flow rate capacity. Here, the performance of a new sluice gate which is consisted of a sharp-edged sluice gate and a drum gate (a sluice gate with a cylindrical end) is experimentally evaluated. Since the streamline leaves the gate more smoothly, Cc is considerably increased. i.e., from 0.6 in sharp edged gates reached to 1.0 in cylindrical-edged gates. Moreover for a given upstream depth, this gate was less likely to become submerged compared to an equivalent sharp edged sluice gate. For upstream water depth of gate to opening of gate(H0/W) in range 4-18,tailwater depth to opening of gate( yt/W) increased up to 22 percent for drum diameter of 63, 90, 125 and 200 mm. This feature obviates the need to increase the free board height in the upstream channel and refrains from upstream overflow whenever unexpected downstream tail water rise occurs. Moreover, distinguishing condition curves for these gates were obtained.

Using the Soil Nailing due to its numerous advantages, the traditional approach is to stabilize the excavation walls fitted. Due to the different behavior of marl soils in short and long-term and fundamental role of friction between soil cement grout around the walls were nailed, In this study, tensile strength and creep behavior of soil nails to maintain green marl are discussed. Therefore, the number 6 nails diameter of 11 cm and a length of 4 m in vertical and 2 achieve the same as the horizontal at an angle of 15 degrees to the horizon scale has been constructed and the effect of Drillings Type on the tensile strength and creep behavior were investigated. the results indicates 20 to 25% increasing in tensile strength of nails in vertical mode and 15% increasing in a horizontal mode implemented with non-smooth drill compared to smooth drill.

One of the methods for damage detection is dynamic methods based on the signal, which can be used to detect damage in the structures through signal processing. In this study, wavelet transform is used in order to determine the location and extent of the damage in steel plate shear walls so that the mode shape of modal analysis is decomposed as the input signal by wavelet transform and in the case of damage, it is possible to identify its accurate location. As a result, by using this transform without information of healthy structure, the possible damage scenarios that occur in the structure can be detected through disturbances which are created in the signal or the mode shapes of steel plate shear walls.

A building may need retrofitting, based on change of occupancy, change in design codes or deficiencies in design or performance. One method used early years for seismic retrofitting of reinforced concrete frame is by using steel bracing. In this article, first, the formation of plastic hingesand performance levels provided by RC structures are determined by nonlinear static and dynamic analysis; then, these structures reinforced by steel bracing and re-evaluate for performance levels and contrast with first condition. Structures are selected of two different plans in 10- and 15-story. Moreover, the structures of this study, in addition to being tall, are selected irregular in plans to evaluate the effects of the irregularity in results, too. Results show that using steel bracing promoteperformance level and seismic capacity of structures, significantly.

Fixity of column base connection plays a major role in overall behavior of steel structures. Several parameters influence the real behavior of the column base connections, among them base plate thickness, anchor bolts and stiffeners details can be mentioned. A nonlinear three dimensional finite element method has been utilized for numerical studying of the behavior of the column base connection. Thickness of the base plate and stiffeners and also sizes and numbers of the anchor bolts were changed in a number of models to determine their effects on the nonlinear behavior of the regular column base connection. It was observed that column base connection characteristics such as its moment-rotation behavior, yielding pattern of base plate and anchor bolts and local stress concentration of the connection elements can be significantly affected by changing any detail of the connecting elements. The effects of each parameter on the behavior of column base connection were categorized and presented in this paper.

In this research, the effect of micro monofilament polypropylene fibres with three different lengths and five different amounts of fibre in two cases of non-shred and shred fibres on compressive and flexural strengths of concrete has been investigated and compared. The objective has been to obtain the most favourable length and amount of polypropylene fibres for suitable concrete mechanical properties (compressive and flexural strengths). Obtained results show that for both cases of non-shred and shred fibres, the use of 1.8 kg/m3 of polypropylene fibres with a length of 12 mm has a considerable effect on increasing compressive strength. Use of 2.4 kg/m3 of polypropylene fibres of 24 mm long significantly increases flexural strength. Furthermore use of shred fibres causes the increase of compressive and flexural strengths of concrete compared to non-shred fibres.

In this research, the performance-based seismic design method for eccentrically braced frames has been implemented which combines the advantages of the force based and displacement based design methods “so called” hybrid force-displacement design method (HFD). This method is started by transforming of maximum inter story drift and local ductility into target roof displacement and then for ductility and strength reduction factor, proposes some relations. In this research, hybrid method for eccentrically braced steel frames has been applied. For this purpose, sixty eccentrically braced steel frames with different number of stories, bay widths, number of spans, various bracing dimensions, etc.. have been analyzed using nonlinear static analysis method (Push Over Analysis). Then, the nonlinear multiple-parameter regression model has been utilized for proposing the formulas for strength reduction factor and ductility. Obtained relations are influenced by lateral loading system type, earthquake level, slenderness of braces, intensity of earthquake, number of roofs and bays. The obtained results in compare with force based and direct displacement based methods show the reliable accuracy in roof displacement and base shear that lead to economical design of structures.