Sharif Digital Repository

These days steel frames are among the most widespread structural systems, and apart from this, tendency for using slender members in these frames, shows the need for study of effects of axial force and in other words stability of the structure and its members. When secondary effects due to axial gravity forces which results in lateral displacement of the structure come in action, they will reduce strength significantly; as a consequent ductility demand with raise. If this decreased strength exceeds the existing redundant strength, displacements will increase significantly and cause instability of the structure and its collapse. AISC 360-10 has introduced 3 methods for analyzing stability of... 

Today using cold-formed steel elements as members of light-weight structures is more common especially in low-rise residential and industrial buildings. Due to Thin-walled plates used to make these sections, members of the frame are prone to premature local buckling and they don’t show good ductility under seismic loadings. Beacause of these reasons, using cold-formed steel elements in moment frames has become a big challenge for scientists. Lots of numerical and experimental models have been presented.
In this study, we investigated the behavior of a beam-column moment connection, consists of two back to back channel sections with curved flanges, using a plate passing through the... 

Life-cycle cost analysis (LCCA) is an assessment tool for studying the performance of systems in many fields of engineering. In earthquake engineering LCCA demands the calculation of the cost components that are related to the performance of the structure in multiple earthquake hazard levels. In this work structural performance required for LCC estimation is achieved by performing ET analysis, while Incremental static and dynamic analyses are two procedures that can be traditionally used for estimating the seismic capacity of structural systems. In this method the structure is subjected to an increasing accelerogram which its time represents ascending earthquake intensities corresponding to... 

This paper puts forward an innovative energy dissipation system in steel moment resisting frames, and presents its experimental and numerical studies. In the proposed system, a replaceable beam with a smaller cross-section than that of the main beam is placed at the mid span of the beam designed to act as a shear fuse. This shifts the location of the plastic hinging from the ends of the beam to the middle since the shear fuse yields in shear prior to the flexural yielding of the main beam. This system eliminates the need to comply with the rigorous limitation on the beam span-to-depth ratio that is proposed by seismic design codes to ensure the formation of plastic hinges at the two ends of... 

Shape memory alloys (SMAs) are nowadays promising candidates for seismic engineering appli-cations due to their ability to undergo reversible deformations and to dissipate energy when subjected to cyclic loading. This thesis presents a numerical study of the torsional performance of structures equipped with end-plates connections using SMA as well as high strength steel bolts and identifies the required locations of SMA connections in a number of typical steel mo-ment resisting frames to improve their seismic torsional performance in terms of maximum inter-story drift and residual deformations. In this regard, 6 and 9-story steel structures were considered with eccentricity ratios of 0%,... 

In this work the response modification factor (RMF), behaviour factor, of two-dimensional regular and split-level steel braced frames was worked out and presented. A total number of 840 frames with various number of stories, spans, braced spans and span lengths were studied. Frames were loaded based on ASCE 7-10 and designed in accordance with AISC 360-10. Static nonlinear analysis and Uang method were used for obtaining the RMFs of the studied frames. The effect of split-level irregularity and parameters such as number of stories on the RMF were worked out and are presented in this thesis. Linear regression was used to develop formulae for RMFs of regular and split-level braced frames.... 

Nowadays, proper design and retrofitting of structures against natural and manmade disasters, is among the main concerns of researchers and designers in order to reduce financial and human costs. Extensive research has been carried out on the structures resistance against earthquake up to now. Although, the vast amount of research has resulted various regulations and guidelines, there is still a long way ahead to achieve the desirable results. Due to high sensitivity of the steel to temperature variations, fire exposure is more destructive for steel structures compared with the concrete ones. The performance of an intermediate three-storey steel moment frame with 4 spans was studied in this... 

The preliminary design of building structures is normally based on the equivalent lateral forces provided in seismic design guidelines. The height-wise distribution of these loads is predominantly based on elastic vibration modes. However, as structures exceed their elastic limits in severe earthquakes, these design load patterns may not necessarily lead to efficient distribution of strength within the structures. To address this issue, several alternative load patterns have been proposed for the seismic design of non-linear structures. However, due to the simplifications involved in the development of these design load patterns, their adequacy needs to be assessed for different structural... 

Study of former earthquakes damages reveals that irregular structures are more susceptive to failure than regular ones. Irregular structures are classified into two categories, namely those with irregularity in elevation and the ones with irregularity in plan. Besides, one of the crucial parameters in working out the earthquake’s equivalent static load is response modification coefficient (R). Based on the type of seismic lateral force-resisting system, this parameter can have various values. In this research, using nonlinear static analysis, the response modification coefficient of a great number of 3-D steel frames of 5, 7 and 9 m spans and having 1 to 10 stories with various... 

Following a large earthquake, numerous aftershocks can be triggered due to the complex stress interaction between and within tectonic plates. The aftershocks have the potential to cause severe weakening of mainshock-damaged buildings, threaten life safety, hamper reoccupation and restoration of buildings, and increase financial loss. The probability of aftershocks has not been included in the description of seismic hazard in performance-based earthquake engineering. This study proposes methodologies and a framework to investigate the seismic performance in the lifetime of steel MRF structures subjected to mainshock-aftershock sequences. The case studies correspond to three SAC 2D steel MRF... 

In the conventional design of buildings, seismic loading codes consider the base shear as an earthquake-induced load, and by distributing this base shear along the height of the structure, members are designed to withstand lateral loads (i.e. earthquake force). The most common form of earthquake force distribution is based on the response of the main mode (first mode) of the elastic structure. But this lateral distribution has two major problems. First, it does not take into account the impact of higher modes on the structural response; and second, the entry of the structure to its inelastic domain in severe earthquakes and the difference resulting from this structural behavior change in... 

In this dissertation, a vast number of 2D steel IMFs (Intermediate Moment Frames) with various number of stories and bays, each having one soft storey, of various intensities (ordinary soft storey & extreme soft storey), were studied. The frames were loaded according to ASCE SEI-7-16 and were designed based on AISC-360-10. In order to make a storey softer than others, its height was increased with respect to those of other ones. The dynamic ‘nonlinear spectral analysis,’ and two different static approaches, namely those of ‘ASCE/SEI-7-90’ and ‘ASCE/SEI-7-16,’ were used to study the frames. Comparison of the results obtained from the three aforementioned methods, one dynamic and two static... 

Seismic resistant structural systems or lateral load-bearing systems must enjoy adequate resistance and hardness against lateral forces and displacements in addition to resisting large deformations to absorb and dissipate energy. Since Iran is located in a seismic area and almost all metropolises of Iran are located in the vicinity of faults, it is critically important to pay close attention to development and application of efficient seismic systems in the constructional system of Iran. The HKB (Hat Knee Bracing) system is a lateral load-bearing system, the construction of which is inspired from divergent bracing systems. In other words, as in... 

Abstract
In this research, the effect of irregularity in the plan floor of structures, including geometric and torsional irregularity on the seismic behavior of steel moment frames braced with chevron knee braces (CKBs) has been investigated. To achieve this, three–dimensional 5-, 8-, 12-story steel buildings models with regular and irregular plan floors were built in OpenSees software and subjected to nonlinear static (pushover) and nonlinear incremental dynamic analysis (IDA) under 22 ground motion records. The performance of each model was then examined by calculation of three seismic design parameters: response modification (R), structural over strength (Ω), and structural ductility... 

In the seismic design of steel special moment frames, it is necessary to ensure that columns are generally stronger than beams. This reduces the probability of a weak story failure mechanism of the frame, and ensures the formation of beams' plastic hinges earlier than the columns’. This criterion is known as strong column-weak beam (SCWB) in seismic design codes and is checked by a formula in the form of a ratio of total flexural strengths of columns to beams framing at each joint. It is common practice to ignore the column’s section change at the splice location and to use the flexural strength of the column’s larger section in evaluating this ratio. In this paper, several 20-story steel... 

This research describes a numerical investigation on a lateral load resisting system comprising of a pin-supported rocking concrete wall coupled with steel moment resisting frames (MRF) models with different support conditions. Two 4 and 8-story structural models are considered for case study analyses with hinged, half-clamped, and clamped support conditions. Fluid viscous dampers (FVDs) are added to the combined system to provide supplemental energy dissipation under the rocking action of the wall. This study aims to compare the efficiency of the proposed system on shear force distribution, residual drift reduction, decreasing the absolute accelerations, as well as comparison of the support... 

Civil structures are on the verge of changing which leads energy dissipation capacity to decline. Structural Health Monitoring (SHM) as a process in order to implement a damage detection strategy and assess the condition of structure plays a key role in structural reliability. Earthquake is a recognized factor in variation of structures condition, inasmuch as inelastic behavior of a building subjected to design level earthquakes is plausible. In this study Hilbert Hunag Transformation (HHT) is superseded by Ensemble Empirical Mode decomposition (EEMD) and Hilbert Transform (HT) together. Albeit this method is closely resemble HHT, EEMD brings more appropriate Intrinsic Mode Functions (IMFs).... 

Structural optimization has always been one of the concerns of engineers. Usually, engineers decide to optimize the structure with its weight. Nowadays we know that the best solution in weight optimization is not good for the structural damage and performance of the structure due to risk analysis.In this study, using the genetic algorithm to reduce construction cost, Loss and damaged cost and total cost of the structure by calculating structural damage based on FEMA-P58 guidelines according to two types of connections (rigid or hinge) and their elements (beams and columns) in two types of structures 4 and 8 story has been investigated.At each stage of increment in algorithms, first, the... 

Abstract- Due to vulnerability of metallic structures to fire, to have an advance estimate of the behaviour and performance of the structure during fire, can greatly assist the designers to make preparations and take precautionary measures to prevent excessive damage to the building. The study of the behaviour of a structure at high temperatures can be divided into two parts, that of its members, and that of its joints. The survey of the literature reveals that most of the previous work concentrated on the former, and it seems that there has not been much work on the latter. The objective of this project was to study the behaviour of structural joints at elevated temperatures, in general,... 

Regarding the advantages of steel shear walls compared with other lateral load-bearing systems, the need for having better knowledge on their performance becomes more obvious. While much study, either theoretically or experimentally, have been conducted on these systems in the past, less attention has been paid to their nonlinear behaviour. This has happened where in many practical situations some parts of such systems experience nonlinearity. Therefore, it is necessary to study the nonlinear behaviour of such walls either individually or as part of a framing system. In this project, using Finite Elements Methods (FEM), the behaviour of a number of samples of an innovative steel shear wall,...