فهرست مطالب

Journal of the Structural Engineering and Geotechnics
Volume:12 Issue: 1, Winter and Spring 2022

  • تاریخ انتشار: 1401/11/23
  • تعداد عناوین: 6
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  • Ahmad Shokoohfar *, Peyman Khorshidi Pages 1-5
    Innovative Precast Post-Tensioned Concrete Shear Wall (PPCSW) comprises two columns as boundary elements and a main precast shear wall. Although, there have been some researches about the cyclic behavior of the PPCSWs, the investigation of the effect of openings in this system has been of less interest. The main purpose of this article is to study the effect of a standard opening on the PPCSWs. The numerical models are prepared for three different heights (3,6, and 9 stories) and their cyclic dissipated energy is compared. The concrete damage plasticity model is applied as constitutive material law. The numerical results demonstrate that by increasing the shear wall’s height, the openings become more effective. Therefore, the maximum reduction of dissipated energy belongs to the nine stories shear wall system. And, also the maximum strength reduction due to opening effects is for the nine stories shear wall system. In contrast to the strength and dissipated energy variables, the maximum initial stiffness reduction due to opening effects take place in 3 stories model.
    Keywords: seismic behavior, Concrete Shear wall, Precast, Opening, Cyclic behavior
  • Behtash Javidsharifi, GholamReza Atefatdoost * Pages 7-27

    Existing under-designed structures, which have been built due to the past insufficient constructional knowledge, are an important issue and anticipation of their dynamic responses to seismic events may be a cumbersome task. It is crucial to account for seismic demands of such structures for later retrofitting plans. In this research, three under-designed RC frames with different heights are considered to represent low-, mid- and high-rise structures. By performing non-linear response analyses, maximum seismic demands are calculated subject to five earthquake motions considering soil-structure interaction. The structures are designed for gravity loads and, especially for the high-rise, they lack about 30 percent rebar with respect to requirement for equivalent Special Moment-Resisting Frames. The major factors controlling the results are the input motion and soil conditions. The maximum inter-story drifts differ and critical stories shift upward or downward and may violate code-provided limits when the underlying soil state changes. Judgment can be made about the effects of loose and medium-dense underlying soils on structural responses. The critical sub-soils for low- and high-rise structures are medium-dense and loose sands, respectively. Subject to one single record, when the structure is high-rise, the maximum base shear is bigger with the base of the structure being flexible. For weak low- and mid-rise flexible-base structures, compared to the fixed-base state, the base shear is always smaller. The peak roof acceleration is generally greater than peak ground and bedrock accelerations, with exceptions in low-rise flexible-base structures.

    Keywords: soil-structure interaction, Seismic Demand, RC frame, Structure Height
  • Alireza Yazdankhah, Araliya Mosleh *, Fatemeh Pouran Manjily, Mehran Seyedrazzaghi Pages 29-47
    This research aims to develop seismic fragility curves for small- and medium-sized concrete bridges. Fragility curves were generated as a function of the probability of reaching or exceeding a specific limit state in terms of the peak ground acceleration (PGA) and acceleration spectral intensity (ASI). To this end, a hybrid dataset of the seismic performances of bridges was prepared by combining the results of numerical analyses and neural predictions. Three-dimensional finite-element models for 1032 bridge-earthquake cases were created, considering the nonlinear behavior of critical bridge components. In addition, multilayer perceptron (MLP) neural networks were employed to simulate artificial earthquake-bridge performance scenarios. The yield stress of reinforcing bars (Fy), the bridge height (H) as well as PGA and ASI, were considered as the input vectors of the artificial neural networks (ANN). The results of this study revealed that MLP neural networks are capable of simulating the seismic performances of bridges appropriately. It was also shown that providing a hybrid dataset of numerical results and neural predictions could lead to the fragility curves of higher correlation coefficients. The results also presented that the PGA-based fragility curves had better correlation coefficients comparing to ASI-based ones.
    Keywords: seismic performance, Artificial Neural Network, Concrete bridge, Fragility Curves
  • Sedigheh Gheisari * Pages 49-62
    The Iranian Standard of Seismic Design of Structures No. 2800, IBC 2018, ASCE 7-16 and AISC 341-16 suggest that a response factor, R (also referred to as the R-factor), should be used as a measure to account for some characteristics of the structure such as ductility, degrees of indeterminacy and inherent over-strength capacity. This factor can be applied to buildings of special, ordinary and intermediate Moment Resisting Frame (MRF) systems. This paper presents an investigation of the economic significance of the R-factor on buildings. Previous studies, which focus on construction details of MRF systems, their design criteria and their associated ductility under cyclic loads for domestic manufacturing purposes, are rather limited. The need for such important data became the basis of performance investigation of different moment resisting connections in the present study. A number of 3D regular frames were designed and their regular construction expenses were estimated and compared. Finally, an average of used steel per unit area was derived to provide a measure for quick design inspection of an arbitrary MRF system.
    Keywords: Construction Expenses, Building Codes of Practice, Moment Resisting Frames (MRFs), Economical Comparison, ductility
  • Seyed Hadi Sahlabadi, Meysam Bayat *, Mohsen Mousivand, Mohsen Saadat Pages 63-74
    So far, many studies have been done on the performance of conventional chemical stabilizers such as cement, lime, fly ash or other chemical additives. However, very limited researches were conducted on the mechanical behavior of cement-stabilized soil with fiber inclusion. Fiber-reinforcement of a stabilized soil offers new opportunities to improve ductility and strength characteristics of weak soils. The main objective of this research is considering the effects of curing time, initial moisture content, polypropylene fiber (PPF) or basalt fiber (BF) with or without addition of cement on the Unconfined Compressive Strength (UCS) of the clay soil. Different ratios of PPF or BF and/or cement were added to the soil to identify their influences on the UCS. The study finds that adding cement, PPF or BF to soil causes a remarkable increase in the strength. The strength of the PPF-reinforced specimens was observed significantly more than that of BF-reinforced ones. The strength of specimens increases gradually as the initial moisture content decreases and the cement content or curing time increases. However, the axial strain at failure for cement-stabilized specimens decreased with increasing cement content or curing time. Furthermore, it is concluded that the increase in UCS of combined PPF or BF and cement inclusions is more than the increase caused by each of them, individually.
    Keywords: polypropylene fiber, Basalt fiber, Cement, Unconfined compressive strength, Moisture content
  • Semko Arefpanah *, Alireza Sharafi Pages 75-85
    The upper bound solution of the factor of safety is obtained by optimization calculation. To evaluate the feasibility of the method proposed in this paper, it was compared with the safety factor calculated by the marginal equilibrium method. Were the method to evaluate the stability of the tunnel face in the framework of the upper limit theorem. Consists of two newly defined parameters: one normal stability ratio and the critical stability ratio. Therefore when the initial tunnel is stable or unstable, the relationship between the electric field stability ratio and the critical stability ratio is determined. The stability of the tunnel surface is estimated by the upper limit theorem of the limit analysis together with the strength reduction technique by the safety factor widely used in the slope stability analysis. There are two methods to reach the critical steady state by increasing the tunnel according to the field stabilization factor. One is to calculate external work (increase the external load) and the other internal energy dissipation in a kinematically acceptable velocity field (decrease the internal load). The tunnel bearing capacity relationship is arranged to reach the critical stability ratio of the two external force enhancement methods. In this way, the upper limit solutions of single tunnels, twin tunnels of the same diameter, and twin tunnels of different diameters are analyzed. TAs a result of the comparison, the solutions derived from these two methods agree well with each other, so the method proposed in this paper can be considered effective.
    Keywords: Stability Ratio, Critical State, External Force, Safety Factor, Limit Equilibrium Method