Braced Steel Structures Research Articles

Investigation on the behaviour and performance of replaceable inverted-Y dissipation device in eccentric braced frame steel structures

Investigation on the behaviour and performance of replaceable inverted-Y dissipation device in eccentric braced frame steel structures

Vibration Modeling and Simulation of Braced and Unbraced Steel Structure

Repeated dynamic loads on multiple stories structure may cause damage in the midst of natural disaster, such as earthquakes and landslides, hence it is necessary to observe how the response occurs. Therefore, this paper studies the performance of two-story steel frame without braces and with inverted V concentric braces. Both frames were given a static and a dynamic load in the form of a sinusoidal load for 2 seconds in the form of forced harmonic vibration. After the dynamic load is turned off, harmonic free vibration applies. Vibration is given to the weakest orthogonal axis on the frame with a frequency of 0,5 Hz; 1,03 Hz; 1.7 Hz. To reduce the deviation between stories that occur due to dynamic loads, bracing is provided as a stiffening element. The test variations are called models 1, 2 and 3 with model 1 unbraced frame and model 2 braced frame with the same load between floors, while model 3 unbraced frame model with weight 2nd floor is 3 times larger than 1st floor. It found that the braced frame has a minimum drift and its drift is enhanced with the increase of load capacity.

Seismic assessment of a dual concentrically braced steel structure under near-fault ground motions

Seismic assessment of a dual concentrically braced steel structure under near-fault ground motions

Seismic torsional effects on multi‐storey steel buildings

AbstractDuring earthquakes, a structure may undergo torsional effects even if it is perfectly symmetrical. One of the causes is that seismic waves do not arrive in‐phase in each point of the infrastructure. Moreover, there are always eccentricities between the mass centre, where the seismic forces are considered to be acting, and the stiffness centre, around which the building rotates, this contributing as well to the occurrence of torsional effects. These eccentricities are generated by asymmetries of the structure itself, position of non‐structural elements, asymmetrically applied loading or other factors. Seismic design codes usually take into account torsional effects by means of an equivalent eccentricity that is added to the actual distance between the centres of mass and stiffness. In ordinary design, to analyse the behaviour of a structure subjected to seismic actions, when establishing the mass of the building, a fraction of the variable loads is considered to be uniformly distributed on each floor. This obviously does not happen in reality. The present paper focuses on estimating the limits of the possible actual variation of internal forces in structural members caused by torsional effects. To this aim, two eccentrically braced steel structures were considered. In each case, the variable loads were redistributed in the plan of the building according to different loading schemes, but keeping their total amount constant, equal to the value corresponding to the uniform arrangement on each floor.

مقایسه کارایی الگوریتم ازدحام ذرات و شبیه سازی تبرید در برازش ارتباط بین شکل پذیری تیر پیوند و شکل پذیری کلی در قاب های مهاربندی واگرا تحت اثر زلزله های دارای جهت پذیری پیشرونده

The most important form of structural ductility, known as global ductility, depends on the base shear force and the displacement of the roof of the structure. If the global ductility of the structure can be calculated by local ductility, the volume of calculations will be significantly reduced. Therefore, it is logical to obtain an acceptable estimate of these two requirements using a simple method during the seismic design process of the building. In this paper, using a database consisting of 12,960 structural frames with 3, 6, 9, 12, 15 and 20 floors, 3 types of column stiffness and 3 degrees of bracing slenderness and using the advantages of Particle Swarm Optimization (PSO) and Simulated Annealing (SA) algorithms present an empirical relationship between global and local ductility. All models have been analyzed under 20 pulse-like near-fault earthquakes considering 4 different performance levels. The results of validation show 81.26% and 69.07% correlation of the proposed relationships from PSO and SA algorithms. Therefore, the coefficients obtained from the particle swarm algorithm were introduced as the final result to apply in the proposed relation the coefficient of behavior of divergently braced steel structures. A comparison of the structural deformation demands resulting from the proposed relationships and an analysis of time history, confirm the existence of an acceptable agreement.

Seismic performance and cost comparative analysis of steel braced frames designed in the framework of EC8

The paper investigates the seismic performance and the cost of case-study buildings embedding different braced steel structures, namely concentrically braced frames, eccentrically braced frames with short or long links, braced frames with buckling restrained braces or double-stage yield buckling restrained braces and dual systems consisting of braced frames with buckling restrained braces and moment-resisting frames with semi-rigid connections. The structures are designed by means of the design prescriptions of Eurocode 8, when available, or according to design procedures proposed by the authors in the framework of the Eurocodes. The seismic response of the structures is determined by incremental nonlinear dynamic analysis considering the effects of the variability of the dynamic properties of the seismic input and the variability of the mechanical properties of steel. The seismic performance is assessed in accordance with Eurocode 8 prescriptions. The results are used to compute the fragility curves of the case-study structures and the mean annual frequency of exceedance of the damage limitation, significant damage and near collapse limit states based on the hazard model proposed in Eurocode 8.

Simulation Analysis on Maximum Height of Semi-Rigid Concentrically Braced Steel Frame

The prefabricated semi-rigid concentrically braced steel frame is a highly-assembled seismic structure. The structure is subject to definite stress and has two seismic precautionary lines. It can be utilized in multi-story and high-rise steel structures. Finite element software is used in this study for response spectrum analysis of a 12-storey semi-rigid concentrically braced steel structure under the conditions of frequent earthquakes to assess the seismic performance of the structure. Dynamic elastic-plastic time history analysis of this structure is also performed under the conditions of rare earthquakes in the case of various seismic precautionary intensities. Critical performance indicators of the structure including plastic hinge development, maximum inter-storey drift angle, and storey shear distribution are also investigated. The results indicate that under earthquakes of various seismic precautionary intensities, the maximum inter-storey drift angles of the prefabricated semi-rigid concentrically braced steel frame structure do satisfy the seismic demands. The brace and the semi-rigid joint steel frame show excellent cooperative work performance. The structure can only be applied in regions with low seismic precautionary intensity.

Application of Conditional Mean Spectrum in the Seismic Assessment of a Braced Frame Steel Structure

Detailed engineering of critical infrastructure and tall buildings require that their response be estimated from nonlinear response history analysis (NLRHA) by subjecting the structure to suites of earthquake accelerograms. Selection of ground motion records due to future earthquake events represents an important step in the robust assessment of structural response. As per the current practice, both site-specific uniform hazard spectrum (UHS) and conditional mean spectrum (CMS) are employed as the target spectra for ground motion record selection. The CMS approach is superior considering that it represents realistic seismic events and also consider the multiple natural periods of the structure. The paper presents the application of conditional mean spectrum in the seismic assessment of an eight-story ordinary braced steel structure built on an example site. The NLRHA was conducted using the ground motions spectrally matched to the CMS at different conditioning periods. It was found that the CMS spectrally matched to larger modal period always result in larger seismic demands. A comparison was also made between seismic demands obtained from UHS & CMS indicating that the structural response parameters are almost the same in both cases except the story shears & drifts which is dominated by UHS in lower floors and by CMS in upper floors.

System level response of braced frame structures under fire exposure scenarios

This paper examines the stability of a braced frame steel structure under realistic fire, loading and restraint scenarios. A set of numerical studies are conducted on a three-dimensional model of a 10-story steel frame building with perimeter V bracing using the finite element software, ABAQUS. The effect of critical parameters such as the location of fire, type of fire exposure and spread of fire from one compartment to another on the stability aspects, as well as fire performance of the structure at the system level is examined. A nonlinear dynamic explicit analysis is carried out to simulate the response beyond stages of a local member failure. At each time step, the calculated stresses, deflections, and axial forces are checked against the failure limit states under strength, deflection, and stability criterion. In addition, following an initial member failure, the progression of the load path towards collapse is monitored. Results from the analysis infer that the likelihood of progressive collapse and global failure time depends significantly on the location and type of fire exposure in a steel framed building. Results also show that the prescriptive fire rating for structural members, as per the current code provisions, may not be conservative under certain severe fire exposure scenarios.

「ブレース材付き鋼フレーム構造の座屈・耐震解析への初期横荷重法 （ILLM） の適用性」への討議・回答

「ブレース材付き鋼フレーム構造の座屈・耐震解析への初期横荷重法 （ILLM） の適用性」への討議・回答

Damage Assessment Using Natural Frequency on Concentric Braced Frame Steel Structures

At present, structural assessment using dynamic characteristics remains to be explored. In this study, a correlation between damage index and natural frequencies of Concentric Braced Frame steel structures has been observed. The study consists of two sections: the first section presents the calculation of the damage indices of structures by means of monotonic and semicyclic pushover analyses using OpenSEES software, while the second section evaluates the structures’ natural frequencies by means of modal analyses using SAP2000 software. Our results show a trend in which with increasing amounts of lateral load, natural frequencies of the structures decrease while the damage indices increase. There is also an apparent ‘jump’ in the damage index values after the lateral loads reach their critical limits. The study results help the understanding of the structural assessment process at the global scale.

ブレース材付き鋼フレーム構造の座屈・耐震解析への初期横荷重法 （ILLM） の適用性

ブレース材付き鋼フレーム構造の座屈・耐震解析への初期横荷重法 （ILLM） の適用性

Determination of the Seismic Performance of Concentrically Braced Steel Structures

Determination of the Seismic Performance of Concentrically Braced Steel Structures

Seismic drift response of seesaw-braced and buckling-restrained braced steel structures: A comparison study

A numerical comparison study of the interstorey and the residual interstorey seismic drifts of steel structures equipped with the seesaw system and buckling-restrained braces is carried out. This investigation involves inelastic time-history seismic analyses of 2-, 5- and 8-storey 3-D steel structures, with specific orientation of columns and configuration of braces, for the design basis earthquake. The effects of soil-structure interaction and seismic incident angle are also considered in these analyses. Comparison of the seismic drift responses experienced by the seesaw-braced and the buckling-restrained braced steel structures, reveals different peak interstorey drift values but in many cases similar drift concentration along the height of the structures. Furthermore, the seesaw-braced steel structures exhibit, in general, larger peak residual drifts than buckling-restrained braced steel structures.

On the seismic behaviour of tension-only concentrically braced steel structures

This paper summarizes the estimated results from three-dimensional non-linear time-history seismic analysis of tension-only concentrically braced steel structures. The braces of these type of steel structures are properly detailed in order to sustain only tension and no compression. In particular, a cheap and easy to fabricate brace detailing allows the brace to slide when in compression and to develop a resisting force when in tension. A comparison between steel structures designed with the proposed tension-only braces and with buckling-restrained braces is performed on the basis of commonly used seismic response and demand indices. It is shown that tension-only and buckling-restrained braced structures may exhibit similar behavior. Nevertheless, column overstress in compression is larger for the tension-only braced structures. Preliminary conclusions regarding the use of the proposed tension-only braces as a seismic force-resisting system for steel structures are drawn.

Evaluating the Behaviour Factor of Concentric X-Braced Steel Structures

The behaviour factor (q-factor) is a factor introduced in Eurocode-8 (EC8) to reduce the seismic elastic forces of structures obtained from an elastic analysis accounting for their ductility and overstrength. Seismic codes, especially the EC8, gives a constant value for q-factor, since change in structural characteristics of building change in behaviour of braced steel structures and that affects on q-factor. In this paper, the q-factor is evaluated for X-braced steel structures using pushover analysis. The effects of brace slenderness ratio and stories number are investigated. The results of this study indicate that the most important parameter that affects the q-factor is the brace slenderness ratio. Furthermore, the EC8 recommends a higher than actual value of q-factor, which is potentially unsafe.

Numerical analysis of braced frame steel structure with buckling

Numerical analysis of braced frame steel structure with buckling

Shake Table Testing of Concentrically Braced Steel Structures With Realistic Connection Details Subjected to Earthquakes

This paper describes an experimental investigation into the seismic response of concentrically braced steel frames (CBFs). Twelve shake table tests were performed on full-scale single storey frames, each containing a pair of identical brace members. The experimental programme examined the behaviour of brace members with four different square and rectangular hollow cross-sections and a range of gusset plate connection details. The aim of the experimental study was to determine the influence of brace and gusset plate properties on CBF response from serviceability to ultimate limit states, including collapse. Consequently, all test frames were subjected to three levels of seismic excitation: (i) low-level excitation to examine elastic frame response, (ii) medium-level excitation to examine brace buckling and yielding effects, and (iii) high-level excitation to induce brace fracture. A detailed set of data on the seismic response of CBFs with realistic brace members and connections were obtained from the tests. The experiments were conducted under representative dynamic response conditions as opposed to the conventional idealised quasi-static loading procedures employed in previous experimental investigations of CBF behaviour. The results faithfully capture the behaviour of brace-gusset plate test specimens with different non-dimensional brace slenderness, brace cross-section slenderness, connection types and gusset plate detailing. The response variables measured in each test included the shaking table and frame accelerations and displacements, brace elongation and axial force, and brace member and gusset plate strains. The experimental observations include elastic frame vibration properties, acceleration and drift demands, ultimate failure modes and ductility capacity. The brace-gusset plate test specimens remained elastic at low-level excitations, brace buckling and yielding occurred in all medium-level excitation tests, while specimens exhibited brace fracture under high-level excitation. Fracture did not occur in the gusset plate connections irrespective of whether these were designed using a conventional design method with a Standard Linear Clearance (SLC), or a balanced design with an Elliptical Clearance (EC). However, the balanced design approach showed more uniform distribution of plastic strains and led to higher brace ductility capacities when compared to the conventional design method. Based on the test results, available methods for predicting the ductility of bracing members are compared and assessed, and a number of considerations for design are highlighted and discussed.

Structural Behaviour of Steel Building with Diagonal and Chevron Braced CBF (Concentrically Braced Frames) by Pushover Analysis

This paper presents diagonal and chevron braced steel structure design with pushover analysis conducted following ATC-40 guidelines. In this study, the lateral load used is increased gradually until plastic hinge and collapse occur. The results are capacity curve, performance point, and the process of plastic hinge until the building collapse. There are five steel structure models designed based on the various types of bracing and bracing configuration. Model 1 is steel structure without bracing, model 2 and 3 are chevron braced steel structure, model 4 and 5 are diagonal braced steel structure. The results of this study indicate that the performance level of five models structure for earthquake in x direction and y direction according to ATC-40 is IO (Immediate Occupancy). Model 4 has the best effectiveness in terms of plastic hinge mechanism compared to other models. In the last step, model 4 is able to reduce plastic hinge 84% from model 1 for earthquake in x direction and 79% from model 1 for earthquake in y direction. Model 3 has the greatest ability to carry the forces of an earthquake compared to other models. It is 185% bigger than model 1 for x direction and 181% bigger than model 1for y direction. Model 3 has the greatest effectiveness in reducing lateral displacements compared to other models in the amount of 65.47% of model 1 for x direction and 72.14% of model 1 for y direction. Model 3 has the greatest effectiveness in reducing storey drift compared to other models in the amount of 73.89% of model 1 for x direction and 80.55% of model 1 for y direction.

Shaking table test for evaluating the seismic response characteristics of concentrically braced steel structure with and without hysteretic dampers

This study represents a summary of a current experimental program in the application of an energy dissipation system for seismic protection of structures. Shaking table test has been carried out for the structures with and without a hysteretic damper device for two types of structures in one direction (CBSS: Concentrically Braced Steel Structure, HDSS: Hysteretic Damper Steel structure). The hysteretic damper device which is proposed in this study has been developed to provide relatively high initial stiffness, stable hysteresis with the limited but controlled yield strength in different stories in order to have equal plastic deformation in high intensity of ground motion, and excellent energy dissipation capabilities. The experimental results and test method have been outlined here. In this experiment, the non-linear dynamic response analysis has been performed with different scaling factor for the two types of idealized three-story concentrically braced steel structures. It has been emphasized that the hysteretic damper can absorb the majority of input energy from earthquakes in order to reduce the displacement and damage to the main steel frame. The mechanical properties of dampers such as yield strength and stiffness are defined to have the equal damage at each story.