Comparison of seismic performance of steel frames equipped with diagonal and chevron viscous damper under near and far field earthquakes

A complete comparison of seismic behavior of the application of Diagonal and Chevron Viscous Damper in steel structures is presented in this paper. OpenSees software is used for the numerical modeling of structures. Fifteen numbers of earthquake records are applied to the structures and full nonlinear time history analysis is done. Force-displacement of chevron braces with and without a damper are compared and the results of IDA curves are also presented for different percentiles

Mathematical Modeling of Column-Base Connections under Monotonic Loading

Some considerable damage to steel structures during the Hyogo-ken Nanbu Earthquake occurred. Among them, many exposed-type column bases failed in several consistent patterns, such as brittle base plate fracture, excessive bolt elongation, unexpected early bolt failure, and inferior construction work, etc. The lessons from these phenomena led to the need for improved understanding of column base behavior. Joint behavior must be modeled when analyzing semi-rigid frames, which is associated with a mathematical model of the moment–rotation curve. The most accurate model uses continuous nonlinear functions. This article presents three areas of steel joint research: (1) analysis methods of semi-rigid joints; (2) prediction methods for the mechanical behavior of joints; (3) mathematical representations of the moment–rotation curve. In the current study, a new exponential model to depict the moment–rotation relationship of column base connection is proposed. The proposed nonlinear model represents an approach to the prediction of M–θ curves, taking into account the possible failure modes and the deformation characteristics of the connection elements. The new model has three physical parameters, along with two curve-fitted factors. These physical parameters are generated from dimensional details of the connection, as well as the material properties. The M–θ curves obtained by the model are compared with published connection tests and 3D FEM research. The proposed mathematical model adequately comes close to characterizing M–θ behavior through the full range of loading/rotations. As a result, modeling of column base connections using the proposed mathematical model can give crucial beforehand information, and overcome the disadvantages of time consuming workmanship and cost of experimental studies

Response Modification Factor of Coupled Steel Shear Walls

The present research is concerned with the determination of ductility, over-strength and response modification factors of coupled steel shear wall frames. Three structural models with various numbers of stories, bay width and coupling beam height were analyzed using static pushover and incremental nonlinear dynamic analyses. The ductility, over-strength and response modification factors for the three models are determined. Tentative values of 11.1, 11.6 and 10.6 are suggested for the response modification factor of coupled steel shear wall frames with deep and medium depth coupling beams, and uncoupled steel shear wall frames, respectively in the allowable stress design method

Connections rigidity effect on probability of fracture in steel moment frames

Connections in steel moment frames are idealized in full pinned and full rigid conditions. Because with this assumption, in spite of real behavior of connection, real story drifts are less anticipated and maybe frame is designed without performance of bracing. There are several methods for modeling actual behavior of semi rigid connections. In this method a connection with certain rigidity is modeled by a rotational spring with corresponding stiffness. This stiffness is achieved by certain formula. In other words, each percent of rigidity corresponds to one rotational spring stiffness. In this research in order to evaluate the real behavior of connection in analysis and designing process and fracture probability one frame including four stories and one bay with three types of connection has been modeled and designed in ETABS. Each model has an individual rigidity which is equal to 10, 75 and 90 percent. With respect to maximum drift and different PGA in roof, probabilities of low, medium, high and complete fracture were calculated. For this purpose, with applying different PGA to modeled frames, amounts of drift in the roof are achieved. Then these values are compared with given values in American code. Finally, investigation showed that when rigidity in frame connections increases, the probability of frame fracture decreases. In other words, fully rigid assumption of connection in analysis process leads to decreasing in real probability of fracture in frames which is a noticeable risk in building designing processes

On the effect of the near field records on the steel braced frames equipped with energy dissipating devices

The behavior of braced steel frame structures is of special importance due to its extensive use. Also the application of active and semi-active control systems, regarding to their benefits in obtaining better seismic performance has increased significantly. The majority of the works on steel structures and steel connections has been done under far field records, and the behavior of steel frame structures equipped with yielding dampers under these circumstances has not yet been fully analyzed. The main purpose of this paper is to determine the behavior of structures equipped with yielding dampers, located in near field based on energy concepts. In order to optimize their seismic behavior, the codes and solutions are also presented.The selected system is a braced steel frame system which is equipped with yielding dampers and the analysis is performed using the "Perform 3D V.4" software and the conclusions are drawn upon energy criterion. The effect of PGA variation and height of the frames are also considered in the study .Finally, using the above mentioned results, a proper solution is presented for typical systems in order to increase the energy damping ability and reduce the destructive effects in structures on an earthquake event, so that a great amount of induced energy is damped and destruction of the structure is prevented as much as possible

Seismic Fragility Assessment of Special Truss Moment Frames (STMF) Using the Capacity Spectrum Method

Fragility curves represent the probabilities that structural damages, under various levels of seismic excitation, will exceed the specified damage states by means of earthquake intensity damage relations. Conceptual aspects related to seismic vulnerability, damage and risk evaluation are discussed first, together with a short review of the most widely used possibilities for the seismic evaluation of structures. The capacity spectrum method starting from capacity and fragility curves is then discussed. The determination of capacity curves for buildings using a non-linear structural analysis tools is then explained, together with a simplified expeditious procedure allowing the development of fragility curves. Next, the seismic risk of the special truss moment frame (STMF) systems of Tehran, the capital of Iran, is analysed in this paper using the capacity spectrum method. The seismic hazard of the studied area is described by using the reduced 5%-damped elastic response spectra. Significant damage is obtained for mid-rise and high-rise special truss moment frames with a Vierendeel middle panel, because of the buckling and early fracture of truss web members. Special truss moment frames with an X-diagonal middle segment also show a low seismic capacity leading to significant expected damage

Comparing Hysteretic Energy and inter-story drift in steel frames with V-shaped brace under near and far fault earthquakes

Different researches have shown that during destructive earthquakes, most structures enter non-reactionary range. Hysteretic Energy, which is wasted after the yield within its hysteresis rings, is very influential on generating structural damage of the system, being the most important component in the equation of the energy, inflicted on the structures. Therefore, controlling this amount of energy leads to controlling the structure behavior. The amount of Hysteretic Energy in a structure could be an index of its damage level or its malleability. The current paper carries out a nonlinear dynamic analysis on steel buildings with a V-shaped (Chevron) brace, hence surveying Hysteretic Energy distribution as well as maximum inter-story drift in the stories of these buildings, under the influence of equalized near and far fault records. Results show that the inter-story drift need for equalized near fault records is more than the far fault ones. Also the results show Hysteretic Energy caused by near fault records that are more than the far fault ones. What is more, as the building height rises, the share of building’s higher stories from the Hysteretic Energy increases. Keywords: Inelastic dynamic behavior, Energy concepts, Hysteretic Energy, Equalized near and far records, Nonlinear dynamic analysi

Probability Assessment and Risk Management of Progressive Collapse in Strategic Buildings Facing Blast Loads

Nowadays, as a result of increased terrorist and bomb attacks throughout the globe in the vicinity of strategic buildings, designing these structures against impact loads, particularly the blast-related ones, has been taken into more consideration. The current procedure for designing the structure against an explosion is a design against the local failure of the current elements in the first step and then, in the next step, against local damage as well as tactful thinking to prevent this damage from spreading to other parts of the structure. The present research investigates the impacts of explosives, derived from probable terror–stricken scenarios inside and outside a strategic four-story steel building with a special moment frame system. Then, the resistive capacity of the damaged building (due to blast) has been evaluated against the progressive collapse, and finally, the rate of the collapse risk and the reliability of the structure have been obtained by presenting a probable method. Thus, the vulnerable parts inside and outside the building are identified and safety measures have been determined, so that in case of no safety or excessive collapse risk- access to dangerous parts of the building could be reinforced or limited. Results show that progressive collapse probability and reliability of the building are 57% and 43% respectively