Conference

Journal

Journal of Structural and Construction Engineering

Volume

Issue

Pages

Publisher

Iranian Society of Structural Engineering

Description

The frames with Buckling Restrained Braces (BRB’s) are used as a lateral system. The braces often have a limit amount of ductility and dissipated energy in cyclic loading. Therefore, the use of Shape Memory Alloys (SMA’s) in braced frames with regard to the specific properties of these can be an effective improvement in the seismic behaviour of frames. These alloys become known without the need for replacement after an earthquake and the possibility of many deformations and reversal to initial state. Seismic fragility analysis is one of the most important methods in seismic performance-based design that which lead to seismic fragility curves. Fragility curve is a powerful tool for probabilistic vulnerability assessment of structures. In this paper, seismic behavior of frames with BRB’s and the effect of utilizing SMA’s were studied. Then, three 2D-frames with 3, 6 and 9 story were utilized. The OpenSees software used …

Conference

Journal

Civil and Environmental Engineering Reports

Volume

1

Issue

31

Pages

118-138

Publisher

SCIENDO

Description

In this paper, several analytical models are presented for the optimal design of a trapezoidal composite channel cross-section. The objective function is the cost function per unit length of the channel, which includes the excavation and lining costs. To define the system, design variables including channel depth, channel width, side slopes, freeboard, and roughness coefficients were used. The constraints include Manning’s equation, flow velocity, Froude number, and water surface width. The Simultaneous Perturbation Stochastic Approximation (SPSA) algorithm was used to solve the optimization problem. The results are presented in three parts; in the first part, the optimal values of the design variables and the objective function are presented in different discharges. In the second part, the relationship between cost and design variables in different discharges is presented in the form of conceptual and analytical models and mathematical functions. Finally, in the third part, the changes in the design variables and cost function are presented as a graph based on the discharge variations. Results indicate that the cost increases with increasing water depth, left side slope, equivalent roughness coefficient, and freeboard.

Conference

Journal

Civil and Environmental Engineering Reports

Volume

1

Issue

31

Pages

139-160

Publisher

SCIENDO

Description

In the paper, the effects of different percentages of additives (perlite, LECA, pumice) on the mechanical properties of structural lightweight aggregate concrete were tested and evaluated. For the research, 14 mixing designs with different amounts of aggregate, water, and cement were made. Experimental results showed that the specific gravity of lightweight structural concrete made from a mixture of LECA, pumice, and perlite aggregates could be 25-30% lighter than conventional concrete. Lightweight structural concrete with a standard specific gravity can be achieved by using a combination of light LECA with perlite lightweight aggregates (LA) and pumice with perlite in concrete. The results indicated that LECA lightweight aggregates show more effective behavior in the concrete sample. Also, the amount of cement had a direct effect on increasing the strength regardless of the composition of LAs. The amount of cement causes compressive strength to increase. Furthermore, the stability of different experimental models increased from 156 to 345 3kg m while increasing the amount of cement from 300 to 400 3kg m in the mixing designs of LECA and perlite for W/C ratios of 0.3, 0.35, and 0.4. For a fixed amount of cement equal to 300 kg, the compressive strength is reduced by 4% by changing the water to cement ratio from 0.5 to 0.4. The compression ratios of strength for 7 to 28 days obtained in this study for lightweight concrete were between 0.67-0.8. Based on the...

Conference

Journal

Journal of Building Engineering

Volume

44

Issue

Pages

Publisher

Elsevier

Description

Controlled-rocking steel cores (CRSCs) effectively prevent earthquake-induced residual damage while may suffer large lateral displacements. This paper gives a particular emphasis on examining the seismic reliability of CRSCs. Accordingly, extensive nonlinear dynamic analyses are conducted for low- and mid-rise archetypes. A set of random variables (RV), including geometry parameters, material properties, and design details of post-tensioned cables (PTs) and energy dissipations (EDs), are considered for reliability assessment. The vectors of RVs are generated by Monte Carlo simulation for 5, 10, and 15% coefficient of variations. Considering uncertainty associated with RVs, peak displacement responses for CRSCs are determined under 44 far-field ground motions. The probability failure and reliability index are quantified for three performance levels, and sensitivity analysis is performed to measure the significance of RVs. Results indicate that the design procedure is reliable and the safety of CRSCs is provided; however, the probability failure for mid-rise CRSCs is more than low-rise archetypes.

Conference

Journal

The Modares Journal of Civil Engineering

Volume

21

Issue

4

Pages

Tarbiat Modares University

Publisher

Tarbiat Modares University

Description

Buckling-restrained braced (BRB) frames are steadily replacing concentrically braced frames because they can yield without buckling when subjected to both tension and compression loads. Though BRB frames are being widely used in construction industry especially for building structures in high seismicity areas such as Iran, it is shown that at large strains, a considerable amount of permanent deformation is generated at the support connector between the brace and the frame. This drawback can be overcome by providing recentering capabilities to the braced frame system. By applying the concept of a recentering system to the design of BRB frames, we used braced frames that incorporate BRBs with superelastic shape memory alloy (SMA). Also, the use of SMA in the bracing system causes damping and reduction of residual deformation. BRBs are considered as lateral load-bearing systems due to their non …

Conference

Journal

آناليز سازه-زلزله

Volume

18

Issue

2

Pages

47-58

Publisher

دانشگاه آزاد اسلامی واحد مراغه

Description

Historical brick minarets are the main elements of Iranian architecture and exist throughout the country in diverse dimensions and heights. In this research, Gaskar brick minaret with a height of 16.12 meters has been modeled by the finite element software by APDL programming and precise discretization, in order to achieve an accurate damage pattern. Then the demand for the both wind and earthquake loads is determined according to the national building codes and applied to the minaret structure. Macro-modeling has been utilized to model the masonry materials domain. Nonlinear properties are also assigned to masonry materials. The results presented that the minaret is safe against both of the design wind load (90km/h) and the fastest recorded wind in the world (205km/h). If up to 12 times the design wind load is applied to the windshield surface of the minaret, the nonlinear behavior of the building will begin. The minaret is also vulnerable to earthquakes and minor damage has occurred at the bottom of the minaret, indicating that the minaret is at risk of collapse.

Conference

Journal

Sharif Journal of Civil Engineering

Volume

Issue

Pages

Publisher

Sharif University of Technology

Description

The aim of this paper is to reliability analysis of the Pacoima concrete arch dam considering the construction stage. According to the technical literature and codes, the construction stage should be considered in the structural analysis of the concrete arch dams. Structural analysis was done by taking into account the uncertainties in the physical and mechanical properties of the dam body materials and the reservoir water level. Three parameters of normal reservoir water level, the density of dam body materials ,and elasticity modulus of dam body material with coefficients of variation of 5, 10 and 10% with normal distribution function are considered as random variables. Linear elastic behavior assumed for the constitutive law of concrete material in the finite element model. Two load combinations are considered. STG(W) is an unusual static load combination due to dam self-weight which considers the effects of dead load stage construction. STG(W+H) load combination is due to stage construction and hydrostatic reservoir pressure at normal water level. ST(W) and ST(W+H) are the unusual static and usual static load combinations without considering the construction stage. The sensitivity analysis of random variables to the maximum tensile stress of the dam body is investigated, and random parameters with more impact are specified. The results showed that the density of concrete is the most effective parameter in response to maximum tensile stress. Reliability analysis based on the load-resistance model has been utilized. The evaluation of implicit functions of load and resistance has been performed by the finite element method. Monte Carlo method with 20,000 iterations utilized for simulation and the Latin Hypercube method was used for Sampling. The maximum tensile stress in the dam body is considered as a limit state. The values of the probability of failure and reliability index are pf

Conference

Journal

Journal of Building Pathology and Rehabilitation

Volume

6

Issue

1

Pages

Publisher

Springer

Description

Determination of seismic reliability of low-rise moment resisting frame RC buildings has been done using probabilistic analysis in this paper. The effect of the number of stories on the safety level of the structures has also been investigated. Reliability-based analyzes were performed using the Monte Carlo simulation technique. The Latin hypercube technique has also been used to reduce the number of simulation samples and to place the responses in the failure region. Conventional low-rise residential buildings with three bays and 2, 3, and 4 stories have been studied. The considered buildings are regular in plan and height. The site is deemed to be a high relative seismic hazard. The time response analyzed has been done by finite element software. The linear elastic behavior of materials is considered in structural analysis. The horizontal component of the Varzaghan earthquake with the peak ground acceleration of 0.4 g was utilized for seismic loading. The engineering parameter of maximum inter-story drift is assigned as the limit state of the reliability problem. Epistemic uncertainty of geometric parameters, gravitational loads, bare frame own-weight, and mechanical properties of concrete materials are considered. Bay length, story height, beam and column cross-sections dimensions, dead load, live load, modulus of elasticity, the density of concrete, and Poisson ratio are utilized as random variables. The coefficient of variation for live load is considered 40% and for the rest of the random variables is 20%. The results showed that the reliability of the studied buildings is over 90%. Also, with increasing the height of the building, the reliability decreases by about 3.5% per story. Sensitivity analysis results showed that the columns dimension in the lower stories and the frame spans, have notable effects on the inter-story drift. Also, gravitational loads (dead and live loads) and bare-frame own-weight have a minor impact on the inter-story drift.