A Nonlinear Macro-model for Numerical Simulation of Perforated Steel Beams

Saeed Erfani,Vahid Akrami 한국강구조학회 2019 International Journal of Steel Structures Vol.19 No.5

Perforated steel beams are being used widely in moment resisting frames. Given the computational expense of detailed numerical simulations, it seems necessary to introduce a simplifi ed macro-model to be used in nonlinear analyses. This paper presents a nonlinear macro-model for numerical simulation of perforated steel I-beams. Results of fi nite element analysis on eighty perforated beams are used to calibrate the parameters of proposed macro-model. Then, results from proposed macromodel are verifi ed against eight experiments gathered from other references and nine FE models analyzed by authors. The comparison shows that, the proposed macro-model has acceptable accuracy and can be utilized for further studies on the perforated steel I-beams.

The beneficial effects of beam web opening in seismic behavior of steel moment frames

Saeed Erfani,Ata Babazadeh Naseri,Vahid Akrami 국제구조공학회 2012 Steel and Composite Structures, An International J Vol.13 No.1

Implementation of openings in beams web has been introduced as an innovative method for improving seismic performance of steel moment frames. In this paper, several steel moment frames have been studied in order to evaluate the effect of openings in beams web. The beam sections with web opening have been modeled as a simplified super-element to be used in designing frames and to determine opening configurations. Finite element models of designed frames were generated and nonlinear static pushover analysis was conducted. The efficient location for openings along the beam length was discovered and the effects of beams with web openings on local and global behavioral characteristics of frames were discussed. Base on the results, seismic performance of steel moment frames was improved by creating openings in beams web, in terms of reduction in stress level of frame sensitive areas such as beam to column connections and panel zones.

An analytical model for shear links in eccentrically braced frames

Saeed Erfani,Amir Ashtari 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.22 No.3

When an eccentrically braced frame (EBF) is subjected to severe earthquakes, the links experience inelastic deformations while beams outside of the link, braces and columns are designed to remain elastic. To perform reliable inelastic analyses of EBFs sufficient analytical model which can accurately predict the inelastic performance of the links is needed. It is said in the literature that available analytical models for shear links generally predict very well the maximum shear forces and deformations from experiments on shear links, but may underestimate the intermediary values. In this study it is shown that available analytical models do not predict very well the maximum shear forces and deformations too. In this study an analytical model which can accurately predict both maximum and intermediary values of shear force and deformation is proposed. The model parameters are established based on test results from several experiments on shear links. Comparison of available test results with the hysteresis curves obtained using the proposed analytical model established the accuracy of the model. The proposed model is recommended to be used to perform inelastic analyses of EBFs.

Evaluation of cyclic fracture in perforated beams using micromechanical fatigue model

Saeed Erfani,Vahid Akrami 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.20 No.4

It is common practice to use Reduced Web Beam Sections (RWBS) in steel moment resisting frames. Perforation of beam web in these members may cause stress and strain concentration around the opening area and facilitate ductile fracture under cyclic loading. This paper presents a numerical study on the cyclic fracture of these structural components. The considered connections are configured as T-shaped assemblies with beams of elongated circular perforations. The failure of specimens under Ultra Low Cycle Fatigue (ULCF) condition is simulated using Cyclic Void Growth Model (CVGM) which is a micromechanics based fracture model. In each model, CVGM fracture index is calculated based on the stress and strain time histories and then models with different opening configurations are compared based on the calculated fracture index. In addition to the global models, sub-models with refined mesh are used to evaluate fracture index around the beam to column weldment. Modeling techniques are validated using data from previous experiments. Results show that as the perforation size increases, opening corners experience greater fracture index. This is while as the opening size increases the maximum observed fracture index at the connection welds decreases. However, the initiation of fracture at connection welds occurs at lower drift angles compared to opening corners. Finally, a probabilistic framework is applied to CVGM in order to account for the uncertainties existing in the prediction of ductile fracture and results are discussed.

Effect of In-Service Strengthening on the Axial Load Carrying Capacity of Steel Box Columns

Saeed Erfani,Mohsen Naseri,Vahid Akrami 한국강구조학회 2017 International Journal of Steel Structures Vol.17 No.1

To avoid any interruption of service and considering economic issues, strengthening of existing columns usually occurs while the member is under service loads. One of the important issues being neglected in the redesign process of retrofitted columns is the effects of significant axial load existing in the columns. This paper presents a numerical study to investigate the behavior and the ultimate bearing capacity of box shaped steel columns reinforced with continuous welded plates while under load. In the first phase of the study, it is intended to evaluate the variation of results with respect to the existing design relations. For this purpose, the ultimate bearing capacity of un-preloaded models is assumed to be in accordance with the selected design code and the corresponding geometric imperfection for each model is defined using several analyses to reach the values obtained with the design code, for further studies. In the second phase, the magnitude of initial imperfection is set to 1/500 of the studied columns. In both phases, the effect of magnitude of existing preload on ultimate bearing capacity is investigated considering two influential parameters, namely the slenderness ratio of the column and the ratio between cross sectional area of the column and reinforcing plates. Results show that by increasing the preload magnitude, the ultimate bearing capacity of reinforced columns with identical reinforcing plates, decreases. This reduction is more notable for the columns with median slenderness ratios. However, as the magnitude of preload increases, the effect of slenderness ratio on the reduction of ultimate bearing capacity becomes more evident. Also, it is found that by using a fixed imperfection ratio of L/500, even for un-preloaded models the ultimate bearing capacity of the strengthened column will be less than the values calculated as per the selected design code. Finally, an empirical relation is proposed to calculate reduction of ultimate bearing capacity for columns affected from various preload level considering different slenderness ratios.

Seismic Performance Evaluation of SSMF with Simple Beam–Column Connections Under the Base Level

Amirhosein Shabani,Saeed Erfani 한국강구조학회 2020 International Journal of Steel Structures Vol.20 No.1

Simple beam–column connections are simpler and cheaper in construction than rigid beam–column connections, moreover, beams under the base level are only carrying gravity loads because of high rigidity of basement walls; therefore, seismic performance of special steel moment frame with basement wall is investigated in two cases in this paper. First, as the normal case of design, rigid beam–column connections are used under the base level, then all of the beam–column connections under the base level are changed to simple connections. The seismic performance of these two types is evaluated by FEMA P695 method. For predicting the collapse capacity of each archetype, adjusted collapse margin ratios are evaluated based on several nonlinear analyses and compared to acceptance criteria. Finally, seismic performance of these two kinds of structures is compared with each other. Despite the structural system’s change in height, seismic performance factors of special steel moment frames are considered for designing whole of the structures. Finally all two types of structures pass the acceptability checks and all the initial assumption are proved.

Effect of local web buckling on the cyclic behavior of reduced web beam sections (RWBS)

Vahid Akrami,Saeed Erfani 국제구조공학회 2015 Steel and Composite Structures, An International J Vol.18 No.3

Application of reduced web beam section (RWBS) as a sacrificial fuse element has become a popular research field in recent years. Weakening of beam web in these connections may cause local web buckling around the opening area which can affect cyclic behavior of connection including: maximum load carrying capacity, strength degradation rate, dissipated energy, rotation capacity, etc. In this research, effect of local web buckling on the cyclic behavior of RWBS connections is investigated using finite element modeling (FEM). For this purpose, a T-shaped moment connection which has been tested under cyclic loading by another author is used as the reference model. Fracture initiation in models is simulated using Cyclic Void Growth Model (CVGM) which is based on micro-void growth and coalescence. Included in the results are: effect of opening corner radii, opening dimensions, beam web thickness and opening reinforcement. Based on the results, local web buckling around the opening area plays a significant role on the cyclic behavior of connection and hence any parameter affecting the local web buckling will affect entire connection behavior.

Employing a fiber-based finite-length plastic hinge model for representing the cyclic and seismic behaviour of hollow steel columns

Mojtaba Farahi,Saeed Erfani 국제구조공학회 2017 Steel and Composite Structures, An International J Vol.23 No.5

Numerical simulations are prevalently used to evaluate the seismic behaviour of structures. The accuracy of the simulation results depends directly on the accuracy of the modelling techniques employed to simulate the behaviour of individual structural members. An empirical modelling technique is employed in this paper to simulate the behaviour of column members under cyclic and seismic loading. Despite the common modelling techniques, this technique is capable of simulating two important aspects of the cyclic and seismic behaviour of columns simultaneously. The proposed fiber-based modelling technique captures explicitly the interaction between the bending moment and the axial force in columns, and the cyclic deterioration of the hysteretic behaviour of these members is implicitly taken into account. The fiber-based model is calibrated based on the cyclic behaviour of square hollow steel sections. The behaviour of several column archetypes is investigated under a dual cyclic loading protocol to develop a benchmark database before the calibration procedure. The dual loading protocol used in this study consists of both axial and lateral loading cycles with varying amplitudes. After the calibration procedure, a regression analysis is conducted to derive an equation for predicting a varying calibrated modelling parameter. Finally, several nonlinear time-history analyses are conducted on a 6-story steel special moment frame in order to investigate how the results of numerical simulations can be affected by employing the intended modelling technique for columns instead of other common modelling techniques.